Hip Pocket Builders' Forum

Outdoor Free Flight Forum => Towline Gliders => Topic started by: PeeTee on March 20, 2013, 06:13:39 PM



Title: Bungee Launch 36" Gliders
Post by: PeeTee on March 20, 2013, 06:13:39 PM
Jon (Yak52) started a topic on bungee launch aerodynamics. The UK SAM organisations have just agreed the rules for 36" bungee launch gliders for vintage and classic models, and this allows scaling.

Awhile ago I picked up a plan for a quirky French beginners glider, the CB 34, V dihedral, profile wing and twin fins - luvverly :D. It's of mid 40s vintage, 1m span which I reduced to 36". The profile fuselage is easily made, as are the wings and tail. I'm fitting a Tomy timer for DT, and this is how far I've got at present - ready for a comp over Easter......
Sorry about the rotten photos!

Peter


Title: Re: Bungee Launch 36" Gliders
Post by: FreeFlightModeller on March 20, 2013, 06:44:44 PM
Good news that the class has been more widely accepted ... I'll have to start thinking about a model that will suit both the SAM and Peterborough events.

Will be following your progress Peter  :)


Title: Re: Bungee Launch 36" Gliders
Post by: PeeTee on March 20, 2013, 06:54:35 PM
Russ

Thanks. Bungee launch has been around for many years - I watched the Bournemouth club run a bungee launch comp for Skyleada 3 Footers the best part of 10 years ago, but the Peterboro' club has done a good job of publicising it. I'm not averse to trundling across the ground with a towline glider, but what I've seen of bungee launch makes it look fun, and good for smaller (windier) sites.

If you get down to MW over Easter, all things being equal I'll have the model ready ::)

Either way, I look forward to seeing you there.

Cheers

Peter
ps keep up the good work with the scale builds!


Title: Re: Bungee Launch 36" Gliders
Post by: DaddyO on March 21, 2013, 04:32:11 AM
Ahah!

Now I see why you were rummaging through all those glider plans Mon Ami Mate  ;)

Nice choice of model; typical Gallic style with the twin fins. Any trade secrets you are going to give away about hooks? (I understand that they are angled more than normal and possibly further back?

Hopefully will have sorted out some vehicular transport by then so may pop along to MW to see them in action . . .
Toodlepip
Paul


Title: Re: Bungee Launch 36" Gliders
Post by: Yak 52 on March 21, 2013, 07:59:42 AM
Looks good Peter. I've been building a Lulu Baby scaled up to 36".

Jon


Title: Re: Bungee Launch 36" Gliders
Post by: lincoln on March 21, 2013, 06:46:54 PM
That DOES look like a nice project.

If you like CB designs, and you're ambitious, how about a scaled down CB28?:
http://lesgpr.free.fr/construire/cb28/cb28-2.jpg

More CB stuff:
http://clap54b.free.fr/vollibre/musee/musee.htm

More interesting gliders, some even small enough:
http://claudel.dopp.free.fr/Les_planeurs/Aeromodeles_antiques/Planeurs-antiques.htm#x02_dm
http://www.sam78.cz/apr_list/samlist.php?type=1&orderby=rok



Title: Re: Bungee Launch 36" Gliders
Post by: PeeTee on March 21, 2013, 08:09:39 PM
Lincoln, you are a gent indeed to discover such a vast selection of quirky models - many thanks. I understood that the CB 34 was a mid 40s design, not as early as '41, so that's a useful bit of information. I shall spread the word about the websites you kindly identified.

Thanks also to Paul & Jon for kind words. I think I'm running out of time for the first comp over Easter, but I'll give it a go. Tonight I managed to put mylar on the fus and will cover with tissue tomorrow, and perhaps the tailplane as well. The major job is to join the wing panels in such a way that they won't clap hands on the first launch :( I need to make up some suitable dihedral braces, and am starting to wish I'd chosen a model with just tip dihedral.............oh well, style over substance as they say ::)

Peter


Title: Re: Bungee Launch 36" Gliders
Post by: craig h on March 22, 2013, 07:51:02 AM
 Very interesting...may I ask what size rubber will you use for the launch and what length ? Being unable to run for a launch perhaps this is something I may pursue...I have always wanted to try tow line but being unable to run has not allowed me to try..this may be an answer.

   Thanks..Craig h
Any info will be helpful..


Title: Re: Bungee Launch 36" Gliders
Post by: PeeTee on March 22, 2013, 08:13:43 AM
Craig

The models of this size I've seen launched use 1/8" or less. This kind of bungee launch isn't r/c style where the models accelerate quickly, instead the models tend to kite up (hopefully to the top of the line) with the rubber maintaining tension on the monofilament. The overall  line length is 30m (just under 100ft) with 12.5 metres of unstretched rubber, and the rest nylon monofilament. Of course this is the spec for a low key competition class and you can use whatever you want for sport flying. Here's what a seasoned flyer wrote about it in the SAM 1066 Clarion newsletter:

"Bungee launching, or Hi-start as the Americans call it, has many attractions as those who have tried it will affirm. To see a model sailing high and handsome at the top of the launch and then neatly casting itself off into its flight pattern is a great joy.
But remember, this is not catapult launching. In fact, if you use a bungee as a catapult the model in all probability just ping off the line in a couple of seconds. Surprising little power is required to waft a glider aloft in, ideally, a normal glider-towing breeze – hence the specification of 1/8in rubber."

I hope this is of some interest.

Peter


Title: Re: Bungee Launch 36" Gliders
Post by: ctelehany on April 07, 2013, 07:28:49 PM
Lots of good information on this thread.

I just finished building an Oly II with a 100" span.  I'd like to try this bungee launching technique so that a helper is not required for launching.  Would this be feasible?  Does anyone have a suggestion as to bungee and line lengths and diameters?

I'm not into contest performance. I'd just like to get enough altitude for a couple of minutes of gliding per launch.

Thanks.  Any help will be appreciated.


Title: Re: Bungee Launch 36" Gliders
Post by: Pit on April 07, 2013, 08:42:59 PM
The Oly, and other rc gliders NEED a high-start type of bungee (relative high-power).  A lightly built Oly (~4 pounds, max) might get by with a 6-7mm OD surgical tubing and 1mm nylon monofil - usually 15meter and 100meter.  A bit of a breeze is a good thing.  A better bet for rubber is the next size up - 8-10mm.

The Oly doesn't have ailerons so "kiting" on a weak bungee is asking for trouble if it falls off to the side (usually going inverted) with catastrophic results.


Title: Re: Bungee Launch 36" Gliders
Post by: applehoney on April 08, 2013, 10:19:14 AM
>A lightly built Oly (~4 pounds,

Lightly built ???     :o

Interesting how things vary between categories and disciplines.


Title: Re: Bungee Launch 36" Gliders
Post by: jswain on April 08, 2013, 11:06:53 AM
Lots of good information on this thread.I just finished building an Oly II with a 100" span.  I'd like to try this bungee launching technique so that a helper is not required for launching.  Would this be feasible?  Does anyone have a suggestion as to bungee and line lengths and diameters?I'm not into contest performance. I'd just like to get enough altitude for a couple of minutes of gliding per launch.Thanks.  Any help will be appreciated.

here is an all in one solution for your Oly2 => http://www3.towerhobbies.com/cgi-bin/wti0001p?&I=LXYXK4&P=M (http://www3.towerhobbies.com/cgi-bin/wti0001p?&I=LXYXK4&P=M).  If the field length available is less than the specs listed, feel free to cut the tubing and line dimensions in half for a shorter launch site.  I love my Oly2... ;D

john s.


Title: Re: Bungee Launch 36" Gliders
Post by: JohnOSullivan on April 08, 2013, 05:40:26 PM
Seems to have seriously gone off topic.
The thread is for 36" gliders and is one that deserves serious consideration.
The Olly is an RC 100" glider which has little relevance in this thread.


Title: Re: Bungee Launch 36" Gliders
Post by: craig h on April 09, 2013, 10:51:05 AM
Is it my understanding that the design of glider would have to be before the 1940's and wing span of 36".... no weight restrictions..covering used..and can be beefed up for strength?

  Thanks...Craig h

  This would be my first tow or bungee glider


Title: Re: Bungee Launch 36" Gliders
Post by: Pit on April 09, 2013, 12:05:14 PM
It's the UK SAM group that has set up a class.  Their cut-off dates for Classic and Vintage vary from those in the States from what I recall, so best to check with SAM-UK.


Title: Re: Bungee Launch 36" Gliders
Post by: ctelehany on April 09, 2013, 01:00:23 PM
Sorry to have veered off topic, but thanks for the help. I'm going to try JSWAIN's suggestion.



Title: Re: Bungee Launch 36" Gliders
Post by: martynk on April 19, 2013, 11:18:12 AM
Looks interesting. I was a little inspired when I saw the original Peterborough MAC proposal.
What is the technology?. Is there an autorudder?  if so how is it triggered? -  I suppose that DT will be conventional.

Regards

Martyn


Title: Re: Bungee Launch 36" Gliders
Post by: PeeTee on April 19, 2013, 04:24:35 PM
Martyn

Those who have flown off a bungee tell me that an autorudder probably isn't necessary. I've not finished my model so can't validate this. I do believe that a DT is necessary - a modified Tomy will do but needs a start activator when the model casts off from the line.

Peter


Title: Re: Bungee Launch 36" Gliders
Post by: FreeFlightModeller on April 19, 2013, 04:45:13 PM
I used to do a lot of RC flying off bungee (over 35 years ago now  :o) .... it was more forgiving than I expected.
Looking forward to trying it out with a 36" glider  :)


Title: Re: Bungee Launch 36" Gliders
Post by: skyrocket on May 10, 2013, 02:45:55 PM
Hi guys...just finished spraying everything and ready to start installing all the hardware...it's a Corsair that Peetee told me about..I didn't put a auto-rudder on so we'll see how that goes...pics coming up soon...I'm stoked to get it into the air next week at Geneseo's Hobo Meet, or if the weather looks bad for that weekend, sat my local contest field...


Title: Re: Bungee Launch 36" Gliders
Post by: skyrocket on June 25, 2013, 01:27:15 PM
Tested the "Corsair" last week and it flew great. Didn't fit a auto-rudder yet and I'm not sure they need them. I didn't install a flag on the line either but will next time out as it was reluctant to release. BUT IT FLEW GREAT and with a little more trimming it should soar just fine. I decreased  the incidence by adding a 1/16" shim under the trailing edge and made a 1/16" wire tow hook as the aluminum one I cut out and installed didn't work smooth enough. For those of you who think 1/8" rudder isn't enough, you are in for a treat. I used 25 feet of 1/8" plus 75 feet of 50 lb. kite line attached to a 2 foot pole made from 1" dowel with a spike on the ground end and secured with a tent peg and 3 feet of  cord. Simple, easy to install and tons of fun (reminds me of a woman i once knew but that's another story). 


Title: Re: Bungee Launch 36" Gliders
Post by: dputt7 on June 26, 2013, 03:34:22 AM
Pics please  ;D


Title: Re: Bungee Launch 36" Gliders
Post by: skyrocket on June 26, 2013, 03:27:59 PM
Try these...


Title: Re: Bungee Launch 36" Gliders
Post by: craig h on June 26, 2013, 10:51:41 PM
Very nice glider !  Where did you find the plans....do you mind showing how you did your stake set up...looks like a lot of fun!

     Thanks for sharing


Title: Re: Bungee Launch 36" Gliders
Post by: dputt7 on June 27, 2013, 03:54:19 AM
Certainly looks like a flyer, Thanks for the Photos.
Dave


Title: Re: Bungee Launch 36" Gliders
Post by: JEM on June 27, 2013, 04:53:26 AM
There is a 5 page spread on 36" Hi-Start gliders under the heading of "What is Old is New Again", in the latest edition of Aeromodeller magazine, (July/August 2013), for those that are interested.

John.


Title: Re: Bungee Launch 36" Gliders
Post by: skyrocket on June 27, 2013, 09:41:02 AM
Thanx everyone...I took Peter M's advice and built the Corsair...it appeared in the June, 1953 copy of "Aeromodeller"...I copied the plan page and enlarged it so I could use my architech's scale to draw it up at 36" span...it's a simple process really and I do that for most of my models because I rarely use purchased plans...I was a draftsman for 30 years so it comes naturely for me...I'll post the plan for the model as it appeared in the mag when i get a chance to scan it into my computer...I'll also try to post a pic of the stake set up too...I hope we here in the States can generate some interest in this form of gliders because it is pretty neat to see it go up on its own...the one thing I personally don't want to see is high tech gadgetry and materials, just build 'em the old fashioned way and HAVE FUN...there are so many old designs out there that it boogles the mind and it's so tempting to just build 'em all !...and it's a nice break from my first love - rubber models!


Title: Re: Bungee Launch 36" Gliders
Post by: applehoney on June 27, 2013, 09:55:36 AM
Corsair is a very good choice for this type of flying.   Far from the custormary type of A2 - even in the 50's  -  it's a very stable airplane that tows well, has few (if any vices) and centres well in thermals.  Strong, too.


Title: Re: Bungee Launch 36" Gliders
Post by: skyrocket on June 27, 2013, 10:15:11 AM
Attached are some designs worth considering...


Title: Re: Bungee Launch 36" Gliders
Post by: applehoney on June 27, 2013, 02:53:43 PM
> I personally don't want to see is high tech gadgetry and materials, just build 'em the old fashioned way and HAVE FUN.

Good thinking.   I, too, would like to see the idea become popular.     I do have a little 30"glider boxed away that was built for a postal event that never made it to a second year - would be interesting to see how it handled, though I'd build something at 36" if the event got under way


Title: Re: Bungee Launch 36" Gliders
Post by: skyrocket on June 27, 2013, 03:39:38 PM
Now what about rules rules rules ? Try this on for size :
1.  Maximum wing span = 36"
2.  No weight limits.
3.  Pre 1957 kit or plan of a towline or bungee glider using original materials if available. No     carbon fiber, fiberglas or plasic coverings. The object is to build minature versions of known designs using traditional materials and methods.
4.  No auto-surfaces
5.  Bungee to consist of 25 feet of 1/8" rubber and 75 feet of 30 to 50 pound test string.
6.  Launching stake to be 2 to 3 feet high
7.  3 x 2:00 minute maxes, then 1:00 minute increments there after.
...I'm sure this set of rules can be and will be contested but it's just a start to raise interest.


Title: Re: Bungee Launch 36" Gliders
Post by: Ployd on June 27, 2013, 07:53:46 PM
Corsair was very popular in OZ Vintage glider comps a few years back and the interest in 36" span gliders is slowly finding acceptance at fun fly's. I will try and scan a copy of the Cloud Buster plan which was produced in the late 50's by Montgomery Models here in Melbourne (OZ), 30" span so enlarging will be an improvement. I won my first contest as a kid with this model, lost OOS first flight and found later in the day 24 miles away :o DT mandatory!!

Attached is a photo of my Corsair, fullsize version.

Ployd in OZ


Title: Re: Bungee Launch 36" Gliders
Post by: jswain on July 02, 2013, 02:02:37 PM
there is a nice 5 page article on these 36" gliders in the july/august 2013 Aeromodeller magazine.

fyi you don't have to subscribe to get the magazine, i went on ebay ordered it and it arrived a week later, note that Aeromodeller has two 'LL's and not a typo.

plan shown in article is here => http://adhpublishing.com/shop/store/products/3ft-ruler-plan473/ (http://adhpublishing.com/shop/store/products/3ft-ruler-plan473/)

i like the no running part...

js


Title: Re: Bungee Launch 36" Gliders
Post by: skyrocket on July 02, 2013, 06:23:38 PM
Is that plan an old one?...I seem to recall that SAM in the states has a different cut-off date than the European SAM...if that is the case, it's too bad the US can't extend their date to include some of these wonderful designs in ALL disciplines (sic)...I'm jus sayin...


Title: Re: Bungee Launch 36" Gliders
Post by: applehoney on July 02, 2013, 07:20:29 PM
True enough  - US SAM cutoff is 1942, UK  1950  .... Aussie and NZ I believe 1956

In this instance I do not think it relevant as the emerging bungee glider class does not appear to be an Oldtimer/Vintage event.

Will you  be demonstrating the Corsair at Geneseo this month, Dave ?


Title: Re: Bungee Launch 36" Gliders
Post by: skyrocket on July 03, 2013, 08:19:56 AM
Yep...I'm bringing it with me to fly after hours if I can or when the weather suits us...also the Cleveland Models "Barn Swallow" that I haven't flown yet. Working on a Lockheed "Vega" right now just for giggles because I've always have been in love with that plane...I want to build another bungee model too ( an OT of some sort) to mess around with...


Title: Re: Bungee Launch 36" Gliders
Post by: Ployd on July 05, 2013, 03:06:52 AM
As promised, enlarged plan of the Cloudbuster has been added to the plans list (subject to ratification by the admin).

Ployd in OZ


Title: Re: Bungee Launch 36" Gliders
Post by: FreeFlightModeller on July 05, 2013, 06:31:47 PM
Had a great afternoon and evening flying in 36" bungee launched glider at Peterborough, UK  :)

I have pieced together the body and wings of a Merlin with the tail group from a Vic Smeed Poppet due to a broken tail for the Merlin .... pleased that it actually performed better than the original full Merlin!


Title: Re: Bungee Launch 36" Gliders
Post by: Yak 52 on July 06, 2013, 10:39:34 AM
It was looking really good Russ!
Did you compete in the comp?


Title: Re: Bungee Launch 36" Gliders
Post by: FreeFlightModeller on July 06, 2013, 04:53:21 PM
Cheers Jon .... yes, I flew in both the re-run comps (though one had more competitors than the other for reasons that I'm not quite sure about?)
In the 'most popular re-run' I had two decent flights then fell behind on the last flight .... really enjoyed it though. Looking forward to creating a more 'purpose built' model.


Title: Re: Bungee Launch 36" Gliders
Post by: billdennis747 on July 23, 2013, 06:34:58 AM
I have built a Dolphin for Peterborough. Enlarged to 36", better airfoil, extra spar, narrower fuselage.
After years of building scale models, I was quite taken by the fact that, when you've done the wooden bits, it's done. I just realised that when I was a kid I never got round to building these small simple gliders. They would have been a much better choice than the KK Camel.


Title: Re: Bungee Launch 36" Gliders
Post by: Laurence Marks on July 23, 2013, 08:32:01 AM
Very nice Bill... 


Title: Re: Bungee Launch 36" Gliders
Post by: PeeTee on July 23, 2013, 09:24:40 AM
I second that, and note what the question about check tissue related to. I too like the Dolphin and built a couple a long time ago - as well as many of the Skyleada & KK non-flying scale models ::) I seem to recall towing them up using a curtain ring and thread purloined from my mum's sewing box (I don't think she ever forgave me!)

Peter


Title: Re: Bungee Launch 36" Gliders
Post by: outofbalance on July 25, 2013, 10:20:30 AM
Hi Ployd in OZ

Where can I find an online source for Corsair? Is the plan form shown as a 36" WS or have you or your mates changed the design. Is it an OZ design?

Thank you,

outofbalance
Colorado


Title: Re: Bungee Launch 36" Gliders
Post by: applehoney on July 25, 2013, 10:35:49 AM
isismk2  - Dave - can likely assist as he's flying a 36" version of the Corsair.    The design originates in Britain, 1953, a low aspect ratio A/2 of 48" span that won Open Glider at the Nationals there.


Title: Re: Bungee Launch 36" Gliders
Post by: skyrocket on July 25, 2013, 01:05:22 PM
See my June 27 post...an 8 1/2" x 11" thumbnail shows the Corsair...download it and take it to a copy shop...or request from me my drawing and published article from "Model Aircraft" magazine....


Title: Re: Bungee Launch 36" Gliders
Post by: outofbalance on July 25, 2013, 03:53:00 PM
Hi isismk2 and Applehoney,

I had looked at the files earlier but did not realize I could expand the images. I printed off the plan of Corsair, along with the others. Thanks. Now to choose---the bigger problem, so many goodies!

outofbalance
Loveland, CO


Title: Re: Bungee Launch 36" Gliders
Post by: skyrocket on July 25, 2013, 07:40:57 PM
As Peter Michel says,.."for these 36" models, low aspect ratio works best"...and I agree with him after flying my Corsair a dozen times last weekend at Geneseo...sort of like a big HLG...and the Corsair does fly really nice with a long flat glide on the verge of a stall...I'm pleased with it but I would like to build something pre-1946 to maybe entice FAC to include a bungee event.


Title: Re: Bungee Launch 36" Gliders
Post by: applehoney on July 25, 2013, 10:53:09 PM
Pre-45 gliders are kind of limited in design, structure and stability/performance.


Title: Re: Bungee Launch 36" Gliders
Post by: lincoln on July 26, 2013, 01:34:26 AM
I think there ARE some exceptions. Lots of designs out there. Some of them don't even have those FAT, high camber airfoils. I like the ones with real fuselages and lots of stringers, though I suppose that degrades the performance. And I'll admit I haven't checked tail volume, etc. on the following. Still, check out these from 1945 and before:

Asso 1943:
Spar and center section might need work. Airfoil is not horribly thick and aspect ratio is sorta moderate. Would have to be shrunk a foot, though. But it's gorgeous:
http://www.outerzone.co.uk/plan_details.asp?ID=1260

KK Invader 1944:
Aspect ratio maybe a little bit high for this span, but airfoil is not horribly thick or cambered. Slight shrink required.
http://www.outerzone.co.uk/plan_details.asp?ID=418

Stormbird 1944:
Reasonably thin airfoil, aspect ratio is not astronomical. Probably needs a lower spar cap. A bit odd looking to my eyes. Slight shrink required.
http://www.outerzone.co.uk/plan_details.asp?ID=2107

I'm partial to the Stormy Weather, but it misses the cut by a couple of years:
http://www.outerzone.co.uk/plan_details.asp?ID=3783

Trooper:
I think there may have been two versions, at 30 and 36 inches. Not sure which Jasco and Jetco had, nor what year.
http://www.outerzone.co.uk/plan_details.asp?ID=463

There are probably a few more suitable plans here:
http://www.sam78.cz/apr_list/samlist.php?type=1&orderby=rok


Title: Re: Bungee Launch 36" Gliders
Post by: skyrocket on July 26, 2013, 07:48:34 AM
A nice line up of models...I do think we should up the cut off date like we did for 1/2 size Wakefield to include those models from the early 50's to get a little more performance and bang for the buck (pound? kroner? yen?)...and you are right : full body models do look neat and with careful selection of wood, will not be too heavy
because you do need some penetration under windy conditions. It is amazing to me how how much power is in 1/8" rubber @ 25 feet along with 75 feet of 50lb kite string. It goes up nice and steady. I can see a Sinbad the Sailor flying quite nicely and looking great in the air - almost scale like. I haven't looked at scale designs yet but i'm sure there are some (Bowlus?) that will look good. I just want to inject some free flight into FAC to include those flyers who are diehards (ME) and not so much scale flyers. When we lost out free flight field we turned to scale so as to keep flying but the fire still burns bright in me and I'D RATHER EAT WORMS THAN FLY RADIO CONTROL!!!!!!!!!!!


Title: Re: Bungee Launch 36" Gliders
Post by: lincoln on July 26, 2013, 08:31:22 AM
This worm eater flies both.

Do you really need 50 lb test? That's what I use with 3/8 inch dia to launch a 3.4 meter glider. Round shapes are draggy!

I've had some stick time on a Super Sinbad, and it does look pretty in the air.



Title: Re: Bungee Launch 36" Gliders
Post by: applehoney on July 26, 2013, 10:41:49 AM
Though I have no personal interest or involvement in FAC activities this is an event that I would like to see taken up in other areas.  Reports from  Britain indicate it is good for moderately sized sites as performance of these small gliders is sufficient to be interesting without requiring lengthy retrieves - other than when thermal assisted - which benefits aging legs that may not be up to towing larger models any more.

With the span limitation low aspect ratios would certainly be superior to tapered planforms .. another simple design that comes to mind is the Mercury "Gnome"  which could actually be scaled UP from its 32" span.

Are you likely to be demonstrating the idea at Geneseo in a couple weeks time, Dave?   I have a little 30" glider which is useless to me since the purpose for which it was built faded away; might be interesting to try it this way.


Title: Re: Bungee Launch 36" Gliders
Post by: skyrocket on July 26, 2013, 02:07:10 PM
My feeling about R/C is purely personal and I think people should fly whatever they want...R/C is not an easy subject to fly and Free Flight isn't either...do whatever floats your boat...as far as 50lb test is concerned, i was just trying to get away from stretchy line that might give someone an advantage of it zooming off the line but that might be harder than it appears to do...I will fly it at Geneseo next week but I haven't had the time to add a auto-rudder yet and I'm still trying to justify it. The only thing that is critical in keeping it from occilating too much and crashing is controlled by how far back or forward the tow hook is from the center of gravity. One question that interests me is just how big a flag you need to help release the line from the hook. Mine is about 1 1/2" x 12" (actually ripped off a hankerchief and knotted to the line) and works okay but might be a little small....


Title: Re: Bungee Launch 36" Gliders
Post by: lincoln on July 27, 2013, 10:27:09 PM
I think the stretch of most kinds of line will be negligible compared to that of the rubber itself. The thicker the line, the more the models with lots of wing area have an advantage. In the RC soaring world, this has lead to some 4 meter models and nearly universal use of flaps. As a result, CD's use thicker line so these models don't break it, causing more drag, which encourages people to fly larger models to cope with the increased drag....

If my back of the envelope math is correct, then a high start stretched to a total length of 100 feet with 0.030" thick line has drag equal to wing area of something like 90 square inches! (Assuming wing profile drag coefficient of 0.05, induced drag coefficient of 0.05, line drag coefficient of about 1, no headwind, and neglecting the increased drag of the rubber itself. I'd say that's probably accurate plus or minus a factor of 2 for this kind of model and line tension comparable to the weight of the glider. Round cross sections have much higher drag coefficients than streamlined shapes like airfoils. For a full scale sailplane on a winch, this number would be far worse. A 2000 foot, 1/4 inch winch line might cause two or three times as much drag as the entire sailplane. ) I'm guessing that a 50 lb test dacron line might be around 0.03" thick.

Some kinds of RC CAN be pretty easy, but when it is, I get bored.


Title: Re: Bungee Launch 36" Gliders
Post by: skyrocket on July 28, 2013, 06:56:13 AM
you said..." the thicker the line, the more the models with lots of wing areas have an advantage..." and this is what I'm doing with 50lb. line and low A/R which w as taken from the rules set up in England a number of years ago...I've never been a proponent of low A/R models in rubber flying but when you have a span limit, those extra sq inches help...


Title: Re: Bungee Launch 36" Gliders
Post by: lincoln on July 28, 2013, 05:37:21 PM
I think the low aspect ratio models have an advantage even without the line drag issue.


Title: Re: Bungee Launch 36" Gliders
Post by: Yak 52 on July 28, 2013, 07:17:11 PM
This has proved true in the Peterborough comps, it has been won by both the Mercury Gnome and Veron Cirro-sonic with an aspect ratio of 6.


Title: Re: Bungee Launch 36" Gliders
Post by: lincoln on July 31, 2013, 07:58:18 PM
So, is this shaping up to be an old designs only event, or any simple design? Anyone actually having it as a contest event in the USA? If it's any design, I'm pondering some ideas for a very simple one.
---------
I dug up some older designs which might work in the event. All have aspect ratios in the range of 6 or 7. None of the airfoils are completely awful. Each would have to be enlarged.

1932 Hervey, Firefly   
http://www.kurrawong.net/affp/_plans/Aus%20FF%20design0019.pdf
(http://www.outerzone.co.uk/images/thumbs/plans/4326.jpg)

1939 Classy Class C
http://www.outerzone.co.uk/plan_details.asp?ID=2718
(http://www.outerzone.co.uk/images/thumbs/models/2718.jpg)

an now for something completely different:

1943 Hy 5    Not sure this qualifies. The original is only 14 inches and no mention is made in the article of launching methods. Material is cardboard as this is a wartime "austerity" design. Looks kind of swoopy. Airfoil is thin. But can you put a towline on it? Of course, at 3 feet it would need some extra reinforcement.
http://www.outerzone.co.uk/plan_details.asp?ID=4196
(http://www.outerzone.co.uk/images/thumbs/models/4196.jpg)


Title: Re: Bungee Launch 36" Gliders
Post by: lincoln on August 05, 2013, 03:07:01 PM
another interesting possibility, at 900 mm is right span already. AR is moderate at 7:1
http://sam78.cz/apr_list/images/1946%20-%20Kavka.pdf

from this page:
http://sam78.cz/apr_list/samlist.php?type=1&orderby=rok


Title: Re: Bungee Launch 36" Gliders
Post by: lincoln on August 06, 2013, 10:09:58 AM
Another one, a Dutch model called "Spin". Fairly low aspect ratio. Can anyone figure out the year? Looks old:
http://www.flickr.com/photos/[email protected]/8049875906/in/set-72157632899126730/lightbox/


Title: Re: Bungee Launch 36" Gliders
Post by: lincoln on August 06, 2013, 10:37:11 PM
And another simple one from the same site. Signed 1942 and 1943. Aspect ratio less than 7. Very simple. Just wonder if those leading and trailing edges can do a spar's job? Especially if the model is enlarged to 36 inches.
(http://farm9.staticflickr.com/8042/8049867106_04d0d2f5e5_o.jpg)


Title: Re: Bungee Launch 36" Gliders
Post by: skyrocket on August 13, 2013, 08:56:27 AM
I think a cutoff date of 1956 here in the States would work...Nostalgia Bungee Launch Glider?....it has a ring to it...here's a pic from last weekend :


Title: Re: Bungee Launch 36" Gliders
Post by: applehoney on August 13, 2013, 10:20:26 AM
I've witnessed this glider being flown by Isismk2  on two occasions and it's a very practical and appealing way of putting a model into the air.  Certainly something I'll consider for the winter building board if the idea 'takes off'  (pun intended)

Caley Hand now has the class in her WorldWide Postal - up and running now, through to June 30th.  [email protected] for details


Title: Re: Bungee Launch 36" Gliders
Post by: lincoln on August 13, 2013, 07:21:58 PM
I wonder if this weird one flies ok? Seems like it has an awful lot of reflex on those last couple of ribs!
http://www.outerzone.co.uk/plan_details.asp?ID=2006

-----------
1956 would open up  some thin winged possibilities. Somewhere around 1950, I think ff people started to understand about airfoil thickness a bit better.

I thought I'd find more of these, but here are some designs  from 1950 to 1956 with moderate aspect ratios (<9, I think) and not too thick foils:
 
I kind of like the FROG Diana, although I suppose it would do better with more area. I think it's supposed to be from 1950.
http://www.houseoffrog.co.uk/pictures/diana11.jpg
plans are also on House of Frog web site, where you will also find a few other interesting ones.

Not super thin, but not an RAF 32 either, at least for lightweight version:
http://www.outerzone.co.uk/plan_details.asp?ID=3904

Another weird one:
http://www.outerzone.co.uk/plan_files_02/2370/Nord_2.pdf

Different, but not actually weird. (I think it looks good.):
http://www.outerzone.co.uk/plan_details.asp?ID=1963


Title: Re: Bungee Launch 36" Gliders
Post by: applehoney on August 13, 2013, 11:26:22 PM
"Jader" is a very good glider


Title: Re: Bungee Launch 36" Gliders
Post by: skyrocket on August 14, 2013, 07:09:40 PM
Last weekend, during the WNYFFS Empire Meet, I put the Corsair up for 5 or 6 flights. She behaved herself quite well and the last flight was a 2 minute, beautiful one in a 15mph breeze. I did use a spruce main spar and I recommend it. I don't have a weight for the model yet because I'm TOO HAPPY just flying and a change of pace from worrying about rubber/prop combo's. It's amazing how much the model stretches the rubber UP in a breeze, about 20 to 30 feet more. Like Peter Michel says, it's a mystery how it gets itself off the hook and I'm going to forget about it because when it doesn't, it crashes.  I did learn one thing though : Moving the hook back progressivly stops the weaving. Also, positive incidence in the stab works as I was scared to death to try that. Where have I've been all this time? When I get back from vacation in Cornwall, I'll build another. Sinbad appeals to me as does the Tern (UK oldie). So many ships, so much time (I'm retired).


Title: Re: Bungee Launch 36" Gliders
Post by: lincoln on August 14, 2013, 08:05:03 PM
You must have had a long walk. About half a mile, right?


Title: Re: Bungee Launch 36" Gliders
Post by: skyrocket on August 14, 2013, 10:39:49 PM
Yep...most of the flights were a 1/4 mile out and I was flying 3 events per day at the most so a typical day was about 3 1/2 to 4miles. That's okay because we walk 3 miles a day so I was ready for it. The potatoe field was something else. I did have my bike but it crapped out.
The "Corsair" is a good flier and there are several designs similiar to it in "Aeromodeller" and "Model Aircraft". Most are 48" to72" span and low A/R machines.


Title: Re: Bungee Launch 36" Gliders
Post by: lincoln on August 17, 2013, 09:36:47 PM
This sorta scale Hamilcar might be interesting for the 36 inch bungee event if scaled up to 36 inches. Fuse is fat, but it has a lot of wing area and a reasonable airfoil:
http://www.ffscale.co.uk/planpics/skyleada_hamilcar_glider.pdf

A somewhat more accurate Hamilcar that would have to be scaled down to 36 inches. But the airfoil is kind of thick. From 1946:
http://www.hippocketaeronautics.com/hpa_plans/details.php?image_id=4849

Stahl's Navy Troop Glider might also be a candidate, with moderate aspect ratio and a foil only mildly thick:
http://www.theplanpage.com/esp/tglider.htm


Title: Re: Bungee Launch 36" Gliders
Post by: skyrocket on August 17, 2013, 10:32:56 PM
So this raises the question : should this event be SCALE ships or DURATION types?...I vote for Duration...


Title: Re: Bungee Launch 36" Gliders
Post by: applehoney on August 17, 2013, 11:27:38 PM
Quite simply - a 36" bungee glider class.      Period.

Anyone who wishes to build/fly a scale model -  their personal choice.     Same with those who wish to build non-scale types


Title: Re: Bungee Launch 36" Gliders
Post by: lincoln on August 20, 2013, 12:34:17 PM
What about the cutoff date on the designs? Or maybe no cutoff date? Fly anything that meets the span limit?


Title: Re: Bungee Launch 36" Gliders
Post by: lincoln on August 20, 2013, 12:49:31 PM
I don't think I've mentioned the Modelcraft Soaring Glider in this thread. It has a reasonably low aspect ratio, original span about 31 inches. Might be good for 36 inch bungee.
(http://static.rcgroups.net/forums/attachments/6/8/2/8/t5632430-0-thumb-soaringglidermodelcraft31inchessketchof.jpg?d=1363840490)
(http://static.rcgroups.net/forums/attachments/2/0/0/8/3/9/t5633642-107-thumb-Soaring%20Glider_Modelcraft.jpg?d=1363891633)
Larger version here:
http://static.rcgroups.net/forums/attachments/2/0/0/8/3/9/a5633642-207-Soaring%20Glider_Modelcraft.jpg

Original scans here (click on the pictures to get full size):
http://www.rcgroups.com/forums/showpost.php?p=24486296&postcount=11635


Title: Re: Bungee Launch 36" Gliders
Post by: skyrocket on August 21, 2013, 08:22:22 AM
AND it's a real cutey...rules?
!. Any glider up to 36" span or set a date limit to say 1956
2.No weight limit.
3. 25 foot of 1/8" rubber plus 75 feet of 30 to 50 lb string
4. 3 x 2 min. max's then 1 min. increments
5. No auto surfaces other than auto-rudder
....the only things I find that  I can't come to grips with is weight limit and modern materials...you can't penalize a flyer for his/her ability to not build light (or heavy) but I wouldn't want to see this winding up (?) the way FAI did...and where would we be without Epoxy and cyno?...and would a Sinbad fly well against a more modern style glider? 


Title: Re: Bungee Launch 36" Gliders
Post by: PeeTee on August 21, 2013, 09:38:35 AM
Over here in England there are two distinct classes - the Peterboro' club one where anything goes provided the model is 36" span or less and launched from the prescribed bungee, and the SAM1066/35 vintage and classic class.

The SAM rules for vintage are as follows:

Up to 36” Vintage Glider - Hi start (bungee launch)
1.   Any model designed as a glider with wingspan up to and including 36”, from the Vintage period as described above may be flown (A vintage model must be built in accordance with a design that was first flown, published or kitted prior to 1st January 1951, (January 1951 issues of magazines are accepted as published in 1950).
2.   Maximum towline length 30 metres comprising 7.5 metres (unstretched) rubber strip up to 1/8” wide and 22.5 metres of line
3.   Fixed end of line to be held by an assistant (no stakes to be used)
4.   Line to be reeled in immediately after launch to avoid risk of entanglement
5.   Models may be scaled down from original designs that would otherwise be over 36” span.  Construction is to follow the form of the original with wood sizes being scaled to agree with the model’s scale

The Classic rules are identical except that : A classic model must be built in accordance with a design that was first flown, published or kitted after 30th December 1950 and before 1st January 1961 (January 1961 issues of magazines are accepted as published in 1960).

Why not have two classes

1. Anything goes

2. Vintage & Classic

Vintage and Classic models can be flown in 'Anything goes' but not vice versa.

I wouldn't mandate the line breaking strain as it just complicates matters, and I'd also suggest that the SAM rules are adopted for the rubber strip so that thinner rubber can be used if the model characteristics dictate.

That's my sixpennorth, now all I have to do is get my act together and finish my model which has been languishing for a while.

Peter


Title: Re: Bungee Launch 36" Gliders
Post by: applehoney on August 21, 2013, 09:43:03 AM
If a cutoff date is applied that obviates any use of composites, etc, - and the development of modern advanced designs and airfoils -  it keeps the event within the reach and ability of all comers.
A very wide range of suitable models given that scaling of originals is allowed.

CA and epoxy -  present day materials that would not impact flying of these models.

Update:  PeeTee posted while I was pecking away.    It would be advantageous to the postal - and general encouragement - to have it able to attact all builders/flyers so common rules are desirable  ... even if those pesky metres are involved .... so perhaps an 'Open' event to get things rolling might be a positive move ... able to be fine-tuned with split classes, etc. at a future time when results and experience might dictate ?


Title: Re: Bungee Launch 36" Gliders
Post by: PeeTee on August 21, 2013, 10:22:20 AM
I agree with Jim that it should be as 'open' as possible. As for models going down the FAI route, I'd suggest that competitors with a penchant for FAI flying are unlikely to be attracted to 36" Bungee launching, unless of course they are looking for a respite from carbon and Kevlar ;)

Peter


Title: Re: Bungee Launch 36" Gliders
Post by: lincoln on August 21, 2013, 12:18:08 PM
These models are so small, the launch is so weak, and the optimum aspect ratio is so low, that I don't see any significant advantage to using carbon fiber, unless it makes a particular type of construction easier to do or more crash resistant. Of course, I could be wrong.


Title: Re: Bungee Launch 36" Gliders
Post by: skyrocket on August 21, 2013, 12:20:32 PM
I like the 2 class idea...Vintage is really nice...seeing those old designs flying again...Walkin' Shoes anyone?...and I've been thinking about something for "anything Goes" with very simple construction, pod and boom and light...I agree with both Applehoney and PeeTee...


Title: Re: Bungee Launch 36" Gliders
Post by: Pit on August 21, 2013, 04:55:38 PM
I'm nearly done with the templates for a full-sized Walkin' Shoes ;)...

Can I play?


Title: Re: Bungee Launch 36" Gliders
Post by: PeeTee on August 21, 2013, 05:18:57 PM
Quote
I'm nearly done with the templates for a full-sized Walkin' Shoes ...

Can I play?

Only if it miraculously turns out to be 36" span ;D ;)

As for the other replies, we appear to be in violent agreement :o


Title: Re: Bungee Launch 36" Gliders
Post by: lincoln on August 21, 2013, 11:09:46 PM
I should be doing any number of other things, but I've started to build a very simple 36 inch towline glider to be used for bungee launch too. All sheet. The wing is just a sheet with  tilted down trailing edge stock at front and back. (Inspired by Perryman's "Stephanie's Solidiflier", but simpler.) I remember getting good results from Xfoil for this kind of shape at low Reynolds numbers, but I don't recall if I took it this low. (Maybe 30k??). I probably should have used a wider piece of wood, but I used what I had, which was 3 inches wide, and, with the two pieces of trailing edge stock, gives a chord around 4.5 inches.

The wing is glued up. Tomorrow I plan to saw it in half and put in the dihedral joint.

What's a good weight for this kind of glider? I'm thinking it might be 3 oz. or so.


Title: Re: Bungee Launch 36" Gliders
Post by: larry530 on August 22, 2013, 06:41:38 PM
Lincoln, if possible could you post a photo of your all sheet glider, would love to see whats possible. i have built several small bungee launch gliders that use a 12 foot length of 1/16 rubber and about 40 foot of thread to launch up and have been amazed that it worked so well , i look forward to the new 36 inch class and seeing what people build  ;D


Title: Re: Bungee Launch 36" Gliders
Post by: lincoln on August 22, 2013, 07:45:13 PM
When it's done, I'll send a picture. Nothing much to photograph yet. Two pieces of trailing edge stock glued on either side of a sheet of balsa. And it might always turn out to be really lousy.
-------------------
Speaking of all sheet 36 inch gliders, here's one I found online called the Windrush:
http://outerzone.co.uk/plan_details.asp?ID=4347

(http://outerzone.co.uk/images/thumbs/models/4347.jpg)
(http://outerzone.co.uk/images/thumbs/plans/4347.jpg)


another all sheet, anonymous and undated, 30 inch, like a chuck glider but with a hook:
http://www.kurrawong.net/affp/_plans/Aus%20FF%20design0156.pdf

I ran across another interesting glider for this event, if the cutoff date doesn't matter:
http://www.kurrawong.net/affp/_plans/Aus%20FF%20design0059.pdf


Title: Re: Bungee Launch 36" Gliders
Post by: Hepcat on August 22, 2013, 09:04:13 PM
The 'Windrush' was designed by Andy Crisp, one of the top English aeromodellers in many different classes.  As I remember the 'Windrush' was designed for a special Junior competition at the British Nationals. I  don't think it was a success despite its immaculate ancestry.  It probably did not seem an easy build to a lot of Juniors with its Jedelsky wing and certain other features.  More importantly all sheet aeroplanes can be fine if the builder has access to good wood and knows how to select it but, if not, the result is usually a clunker.

John B


Title: Re: Bungee Launch 36" Gliders
Post by: BEAR on August 23, 2013, 12:59:09 PM
Built two wind rush gliders years ago with my two girls we flew them at the NATs had a great old time with them  :)


Title: Re: Bungee Launch 36" Gliders
Post by: lincoln on August 28, 2013, 03:58:56 PM
While I should have been working on my own model, I discovered two interesting designs on the following page:
http://www.rcgroups.com/forums/showpost.php?p=18068825&postcount=3536
Both are 36 inch span, or appear to be, and are from the 1940's.

I don't think the Dolphin is the same Dolphin usually referred to. It's got a 6:1 aspect ratio, a reasonable airfoil, and a slick looking fuselage. You are supposed to carve the lower fuselage out of a big, thick balsa plank, but if that's a problem I think one might be able to carve a form in foam and then make up planks over it. (foam to be removed, of course) Anyway, I think it's a pretty interesting model.

IMHO, the Hooker doesn't look as good, although it's not unattractive. It has a much higher aspect ratio. (Maybe around 9 or 10?) Very thin airfoil which I suspect would perform quite well, perhaps making up for the high AR.  I wonder if it's strong enough? No spar, just the l.e. and t.e.


Title: Re: Bungee Launch 36" Gliders
Post by: FreeFlightModeller on August 28, 2013, 05:09:09 PM
Hoping to get my OD model ready for the 'Peterborough Rules' event at the Peterborough Flying Aces this weekend!

Sorry, no pictures .... am I taking this too seriously  ;)


Title: Re: Bungee Launch 36" Gliders
Post by: lincoln on August 28, 2013, 07:02:45 PM
Did a bit more work on the all sheet 36 inch glider wing. Looks like it will be a bit porky. I'd guess 55 to 60 grams for the wing alone. I'm thinking it could be much less if the middle sheet (but not the l.e. and t.e.) were made from really light balsa. Maybe 2/3 the weight or less. But I wanted to see how it would come out with ordinary weight balsa. Pictures eventually.


Title: Re: Bungee Launch 36" Gliders
Post by: lincoln on September 04, 2013, 01:22:04 PM
I'm a master of procrastination, though I have got a bit more done since the last post.

However, in the midst of my procrastination, I found a very low aspect ratio design that could be shrunk to 36 inches. AR appears to be between 4 and 5From Aeromodeller, AUgust 1949, it's called Dream Bogey. The airfoil is very thin but perhaps with a little too much camber for the low aspect ratio. But you can't have everything, and maybe it's still better than a thick one? I suspect a 36 inch one would fly quite well.

http://www.rcgroups.com/forums/showatt.php?attachmentid=5732894&d=1367028991
http://www.rcgroups.com/forums/showatt.php?attachmentid=5732895&d=1367028991
from this post:
http://www.rcgroups.com/forums/showpost.php?p=24837632&postcount=957


Title: Re: Bungee Launch 36" Gliders
Post by: Pit on September 04, 2013, 02:58:30 PM
While looking thru another thread, I came across the 35 inch "Baby Gull (http://www.outerzone.co.uk/plan_details.asp?ID=2008)" by Gordon J. Rae (1946).  Quite attractive with THREE different tail options, but the wing is fairly narrow :-\, and the build looks fairly intensive.  I downloaded/printed the plan anyway with remote intentions of building it.


Title: Re: Bungee Launch 36" Gliders
Post by: dephela on September 04, 2013, 03:47:44 PM
I just found a plan for the first towline glider I ever built. Jetco's Thermal 36, airfoil is just plane crummy and fuselage should be made lighter but:
http://www.outerzone.co.uk/plan_details.asp?ID=1572 (http://www.outerzone.co.uk/plan_details.asp?ID=1572)


Title: Re: Bungee Launch 36" Gliders
Post by: lincoln on September 04, 2013, 07:20:36 PM
Seems like there's only one rib on the plan, and that looks like a moderately thin flat bottom. Worse than a 3 percent arc or something, but not so bad for such a small chord, I'd think? After all, they could have used an RAF32.


Title: Re: Bungee Launch 36" Gliders
Post by: pampasam on September 05, 2013, 03:15:35 AM
  Here is my input to this topic.
Idea.... Take one Souper 30 P-30 wing and another stab that was available,
 build a fuselage for said surfaces and almost instant Bungee Launch Glider
is the result.  I have posted two pictures that are 3 weeks old.  In its current
configuration it sports a new 36" wing.  It took some tow hook adjustments
to get a good launch, but now I know where to position the hook to suit the
flying conditions.  I still need to optimize the glide somewhat.  When I get a
chance I will provide a new picture with the new wing.  I almost forgot to state
the weight which is 73.25 grams with the new wing.

Luke


Title: Re: Bungee Launch 36" Gliders
Post by: Pit on September 05, 2013, 08:09:52 AM
I just found a plan for the first towline glider I ever built. Jetco's Thermal 36, airfoil is just plane crummy and fuselage should be made lighter but:
http://www.outerzone.co.uk/plan_details.asp?ID=1572 (http://www.outerzone.co.uk/plan_details.asp?ID=1572)
IIRC, it was also my first glider - ca.1956-7.  I thought it flew great - once I was able to get it to climb straight on tow (didn't have the experience adjusting the auto-rudder).

Got caught in one of Monterrey's soouper-boomers on it's third successful tow, never to be seen again.

I think Aerosente (http://www.aerosente.com/) has the kit in their program


Title: Re: Bungee Launch 36" Gliders
Post by: dephela on September 05, 2013, 06:49:47 PM
I think Aerosente (http://www.aerosente.com/) has the kit in their program

No way do I want another one! I had no one to help me tow it into the air, one man tows didn't work. Other than glide nicely down a slope it taught me the basics of repair.
I'm still in repair mode, some things never change!


Title: Re: Bungee Launch 36" Gliders
Post by: lincoln on October 12, 2013, 07:45:24 PM
An interesting and perhaps suitable glider from 1947, the Go Hi Mk VI. 30 inches:
http://www.outerzone.co.uk/plan_files_03/3545/GoHi_MkVI.pdf

corrected from Mk IV to Mk VI


Title: Re: Bungee Launch 36" Gliders
Post by: applehoney on October 12, 2013, 08:26:29 PM
Not a bad little glider for its time  -  reaonable airfoil, areas and moments, hook in a more sensible position than many gliders of the era - and autorudder.   Could be a good bungee proposition


Title: Re: Bungee Launch 36" Gliders
Post by: skyrocket on October 13, 2013, 07:05:17 AM
How about that Hugh O'Donnell lightweight from 1957 that is being kicked around in SAM-35 recently? it appeared in Zaic's 1957-1958 Yearbook and sports a MVA 301 airfoil....I've been changing my thinking on bungee  in that we shouldn't set a design/published date limit but stick to the idea of no auto surfaces and 36" span with the 25ft/75ft bungee...


Title: Re: Bungee Launch 36" Gliders
Post by: applehoney on October 13, 2013, 10:18:23 AM
Agree with your suggestions.      Have tile-printed and assembled a plan for  a 36" version of my own 'Walkin' Shoes' for attention in relatively near future.

For anyone within reach of Geneseo, NY, I expect to have a bungee glider event listed for the Great Grape Gathering in September next.


Title: Re: Bungee Launch 36" Gliders
Post by: skyrocket on October 14, 2013, 08:22:23 AM
I will be at the GGG in Sept and hope we have a good turnout for this event. I'm looking at several models right now to compete with. The Corsair I built behaves quite well on the line and I like it alot but I don;t think I'll have it much longer because as I fly it it gets better and better and I might as well build a backup now incorporating all the things I learned this year. As i mentioned earlier, the O'Donnell Lt. Wt. looks good as does the Yeabsley "Revenge". I really do think low A/R is the way to go and the only question I have is just how small of a stab can you go with low A/R wings when designing your own?


Title: Re: Bungee Launch 36" Gliders
Post by: Yak 52 on October 14, 2013, 10:02:02 AM
how small of a stab can you go with low A/R wings when designing your own?

The effectiveness of the tail (tail volume) is affected by aspect ratio. The formula is

Tail volume = Tail area x tail moment arm / wing area x average wing chord


A low aspect ratio - increasing area and widening the chord does reduce the tail volume. So you might need a bit bigger than what just 'looks right' on other higher aspect models.

A rough calculation based on a 36" span and 6" chord (aspect ratio of 6) suggests that a sensible minimum might be:
- a tail area 25% of wing area
- a minimum tail length (LE to tail LE) of 3 times the chord.

This would give a tail volume of 0.66 which is not over large for this type of model. I did compile a list of tail volumes for gliders (if I can find it.)


Jon


Title: Re: Bungee Launch 36" Gliders
Post by: applehoney on October 14, 2013, 10:22:06 AM
I'm curious as to why one would want to go to the smallest stab consistent with stability, unless weight is a factor ?   We'd have no maximum total surface limitations, surely ?


Title: Re: Bungee Launch 36" Gliders
Post by: Yak 52 on October 14, 2013, 12:12:32 PM
Jim, it's just that a small tails will have less drag. There's a sweet spot somewhere between that and good trimming.

The tail volume of these towliners varies widely. Here is some data I compiled. (The tail volumes are worked out based on the true tail moment arm - CG to stab aero centre)


Model                       Aspect ratio           Vh

JB87 (Nordic A1)         14.75               0.83
Mercury Grebe             8.5                  1.36
Lulu                           10                   1.00
Veron Cirro-sonic          6                    0.75         (2 x winner at PMFC Aces)
Thermic Trooper           7.5                  0.64
May Morning                7.4                  0.83
Mercury Gnome (32")    6.3                  0.85         (another winner at PMFC Aces)
Corsair                        6                    0.94
Walkin' Shoes             8.5ish               1.16


I think I would be aiming for a tail volume (Vh) of 0.8 myself.

BTW the May Morning is an Andy Crisp plan that I haven't seen mentioned yet:
http://www.rcgroups.com/forums/showpost.php?p=20990553&postcount=273


Title: Re: Bungee Launch 36" Gliders
Post by: applehoney on October 14, 2013, 01:25:16 PM
Hmmmm ....   the 'Shoes' close to the bottom of the desirability limit.

Drag of the stab has never before entered my thoughts in close to 70 years of modelling - not that I ever knew what drag was in the early days.

Still not over concerned about it.  WS originated from power model exposure of the time - powerful stab, made even more so by undercamber, and a CG further back than most gliders.  Lightly loaded, floats well ... good enuff for me


Title: Re: Bungee Launch 36" Gliders
Post by: Yak 52 on October 14, 2013, 01:45:28 PM
Well it's a teeny weeny advantage (a little less drag) versus a big old problem (untrimability), so I think you're right  :)

As I said, for my OD model I'll be plumping for around Vh0.8 which should be quite safe yet not overly large.


Lightly loaded, floats well ...good enuff for me

And very pretty  :)




Jon


Title: Re: Bungee Launch 36" Gliders
Post by: applehoney on October 14, 2013, 02:05:25 PM
Sheesh ...    Now I have to live with a 'Shoes' that thinks it has a big butt .......    thanks a lot, fellas   >:(   


Title: Re: Bungee Launch 36" Gliders
Post by: skyrocket on October 14, 2013, 03:51:56 PM
sheesh is right...I'm drawing up a 36" er right now with a
36" x 5" chord wing
18" x 3 1/2" chord stab
and 20" wing LE to stab LE.......so I may have to re-think it before I cut wood and if what you say is true (and I don't doubt your math) maybe it should have a smaller stab...nez pax?


Title: Re: Bungee Launch 36" Gliders
Post by: Yak 52 on October 14, 2013, 04:23:13 PM
That gives you a tail volume of about 1.25 (assuming the CG to tail AC is 18") and an aspect ratio of 7.2

On the big side perhaps but still within bounds...?

I must stress again - I've only watched these 36"ers fly so far (although I have looked into the design side of them quite a bit.) So feel free to ignore  ;D


Title: Re: Bungee Launch 36" Gliders
Post by: skyrocket on October 14, 2013, 04:41:09 PM
So I did some playing around with numbers and came up with 18" x 3" chord stab and 15" between wing TE and stab LE and came
up with about Tv = .9 which is a little better and I get it because the moment arm is a little longer needing a smaller stab and that checks out with the rubber jobs I fly with smaller stabs now...I still don't understand where you find the tail moment arm so I used the wing TE to tail LE dimension instead...any help guys?


Title: Re: Bungee Launch 36" Gliders
Post by: Yak 52 on October 14, 2013, 05:17:40 PM
I would be inclined to keep the tail longish (better damping) and cut the stab area a little?

I've been working on a moment arm 3 times the wing chord.


I still don't understand where you find the tail moment arm

There are a few fudged versions but the most accurate is from the CG (the pivot point around which the model rotates) to the stabilizer's aerodynamic centre (the point at which the force of the stab acts)

The final CG may not be known yet but with these larger tail volumes it's probably going to be something like 50%-60% of the chord.

The stabs' Aerodynamic Centre is at 25% of the stab mean chord.

With no sweep or taper its very simple (it gets awkward when you have to calculate the mean chords on nice curvy wings and stabs)

For the list I gave, I measured the CG to the tail AC. Where the CG was not shown on the plan I assumed it was 50%. As long as you are consistent it doesn't matter if you fudge a bit.


So for your new design the moment arm would be

15" minus 50% of the chord plus 25% of the stab chord
15 - 2.5 + 0.75 = 13.25"

Giving Vh = 0.795


Title: Re: Bungee Launch 36" Gliders
Post by: lincoln on October 14, 2013, 06:06:47 PM
Shouldn't the measure of tail volume be from 25 percent MAC of the wing to 25 percent MAC of the tail? If you do it from the c.g, I should think you'd need to include the contributions of both surfaces?


Title: Re: Bungee Launch 36" Gliders
Post by: Yak 52 on October 14, 2013, 06:42:14 PM
Nope. That's one of the quick fudges (works fine in RC where the CG more like 25% anyway).


Title: Re: Bungee Launch 36" Gliders
Post by: lincoln on October 14, 2013, 10:43:50 PM
Not sure I believe that. What's the tail volume on a tandem wing?

I don't understand how the wing's contribution can be ignored, which is what you're doing if you don't run that additional number and use the c.g. instead of the wing AC. If you included a term accounting for the wing's distance from the c.g. as well, I might have an easier time with it.

Check out page 282 and 283 here: http://faculty.dwc.edu/sadraey/Chapter%206.%20Tail%20Design.pdf

I'll admit right off that you can find it the other way too, in some reputable on line sources.

I checked Raymer's Simplified Aircraft Design for Homebuilders, and he uses leading edge to leading edge!!

I checked Hoerner's Fluid Dynamic Lift, but couldn't  find a Vh defined. Some of his equations use the surface AC to the c.g., though.

I suppose that you can just say that it's called "tail" volume, and so by definition the wing doesn't count, but no one told the air that.

Thinking about it, seems to me the only really valid way to go about it is to find the aircraft's AC and then compute a Vh for the tail, and then another one for the wing, using the distance between each surface's AC and the aircraft's as the pertinent length. This has the further benefit of treating weird configurations, extra wings, etc. fairly. If the c.g. is not on the AC, seems to me that considering the static margin kinda automatically takes that into consideration.

Then there's flying wings, with and without sweep!


Anyway, I suppose that's getting O.T.



Title: Re: Bungee Launch 36" Gliders
Post by: Yak 52 on October 15, 2013, 07:20:29 AM
Lincoln,


Anyway, I suppose that's getting O.T.

Yup! I will reply briefly but perhaps this is worth a thread of it's own?


I think either way is valid. And as long as you pick one and stick to it you will get a reasonable comparison for design purposes.

Martin Simons, Andy Lennon, Don Stackhouse and Darryl Stinton all give tail moment arm as the '25% MAC to tail AC'. But Mark Drela gives it as 'CG to tail AC'.

http://ocw.mit.edu/courses/aeronautics-and-astronautics/16-01-unified-engineering-i-ii-iii-iv-fall-2005-spring-2006/systems-labs-06/spl8.pdf

as does this EEA article:

http://www.eaa62.org/technotes/tail.htm

(This dimension is given as lh in your previous linked article)



I suppose that you can just say that it's called "tail" volume, and so by definition the wing doesn't count, but no one told the air that.

This is the point. It depends what you are looking for. Tail volume is just a simple comparison of the tails effectiveness, not a full examination of the actual forces required for balance/trim (which does require looking at the wing's contribution, pitching coefficients, it's position ahead of the CG etc.) In practice the camber of the wing section (pitching forces) would need to be at least considered.

Tail volume is simply an area and a moment arm or lever. The true physical force acts as a lever at the CG, that's the 'pivot point' or fulcrum for the model in flight.

If you are looking at longitudinal stability calculations you can resolve forces and moments to any theoretical fulcrum mathematically and for convention we use the wings aero center (25% mean chord or MAC) because this is convenient for the pitching coefficients. You could just as easily resolve moments to the CG, it's just convention.

I suppose this is the reason you find '25% MAC to tail AC' in use. But the true physical property is 'CG to tail AC'.


I would argue that for free flight models with large tails and CG's as far back as 80% then the 'CG to tail AC' is more appropriate. You could have a much shorter tail moment arm than would be apparent from 'wing AC to tail AC' and this has implications for reduced tail effectiveness - especially for dynamic stability.



All this has got me doodling 36"ers again anyway :)


Title: Re: Bungee Launch 36" Gliders
Post by: skyrocket on October 15, 2013, 02:47:10 PM
found this in Model Aircraft, June 1953...


Title: Re: Bungee Launch 36" Gliders
Post by: skyrocket on October 15, 2013, 07:35:24 PM
Here's the start of a new 36" bungee glider...


Title: Re: Bungee Launch 36" Gliders
Post by: Yak 52 on October 16, 2013, 06:27:25 AM
This is your OD model? It looks gorgeous  8)


Title: Re: Bungee Launch 36" Gliders
Post by: skyrocket on October 16, 2013, 08:07:20 AM
Yes...OD...there is a A2 from the late 50's - early 60's by someone from Europe who flew a similiar looking model and I remember the nose being made from "sugar pine", or so the Aeromuddler or Model Aircraft said...I'm thinking it might be Nordic...Nuumanuka ?(sic)..but I just dig the old designs evern though these Bungees are the closest I've ever come to flying them...so many models, so little time...but I'm having FUN


Title: Re: Bungee Launch 36" Gliders
Post by: Yak 52 on October 16, 2013, 08:25:21 AM
Well I really hope you scan it - it looks very attractive. I would seriously have a go at building a beta version. Is the dihedral 3 or 4 panels?


Title: Re: Bungee Launch 36" Gliders
Post by: skyrocket on October 16, 2013, 03:56:53 PM
Let me build it first and see what the weights, fits and finish looks like and then I'll put something up. I chose tip dihedral because the Corsair flew so well with it and it simplfies building and I can put some spruce/basswood spars in the middle panel easily. Thanks for the kind words. Actually, I based everything on the Corsair because I like it so much. I also like geodetic construction to keep everything straight right out of the box. It's a confidence thing with me.  If you haven't built a 36" Corsair yet, it is really forgiving on the bungee and has a nice slooooow glide. I decided to build a 5" chord figuring it would hold in the wind better on the bungee. Also, I'll stick with no auto rudder to keep it simple and a fuse D/T. I'll try and find that A2 I was talking about and post a pic of it.


Title: Re: Bungee Launch 36" Gliders
Post by: skyrocket on October 17, 2013, 07:02:14 PM
I located the model I was thinking of when I started to draw this new 36" bungee up...It's by Tahkapaa from 1959...


Title: Re: Bungee Launch 36" Gliders
Post by: Paul_BB on October 19, 2013, 12:38:25 AM
Hi Peter,

Good luck with the building of the CB 34, you are almost finished.  :)

-Paul


Title: Re: Bungee Launch 36" Gliders
Post by: skyrocket on October 19, 2013, 09:57:02 PM
I built the stab for the new 36" and added the platforms for the stab and wing...then cut out the wing ribs...next up is make the forms for the wing tips and laminate the tips...I have to wait till Monday to build the wings because I need LE and TE stock and some spruce for the spars but it is coming along nicely and should be ready for some pics by midweek...


Title: Re: Bungee Launch 36" Gliders
Post by: applehoney on October 20, 2013, 12:50:35 AM
I admire and envy your productivity, Dave !


Title: Re: Bungee Launch 36" Gliders
Post by: skyrocket on October 20, 2013, 07:56:31 AM
Thanks Jim...I enjoy building...in the early years I had to steal time to build because of job/Kids/house and never built stuff properly but now I have the time to build indoors (my FORMER wife banished me to the garage) I can build more accurately under better conditions...


Title: Re: Bungee Launch 36" Gliders
Post by: applehoney on October 20, 2013, 10:09:10 AM
I enjoy building too - but I have little incentive to do so as I have so many airplanes on the racks - more than can possibly be flown on the occasions I can get to Geneseo - so work is sporadic these days


Title: Re: Bungee Launch 36" Gliders
Post by: skyrocket on October 22, 2013, 10:36:51 PM
Here's what she looks like before I start covering the little beast...


Title: Re: Bungee Launch 36" Gliders
Post by: applehoney on October 22, 2013, 10:56:25 PM
Nice slim lines, Dave.

The model ........   


Title: Re: Bungee Launch 36" Gliders
Post by: craig h on October 23, 2013, 02:51:59 PM
Very nice build isismk2...makes me want to build again....what are you going to cover the bones with? Tissue and dope like the ole days!
 I know it will be nice when compete...
  Thanks for sharing...


Title: Re: Bungee Launch 36" Gliders
Post by: Yak 52 on October 23, 2013, 03:11:41 PM
Looks great Dave, what's the weight before covering?

Jon


Title: Re: Bungee Launch 36" Gliders
Post by: skyrocket on October 23, 2013, 04:47:54 PM
Weight before covering was 98.6 grams and I don't know if that's good or bad but seems okay to me. I covered it today and I'll wait a day or 2 for some warmer weather to spray it and to let the glue stick cure a little more. I tighten the tissue with warm water in a spray bottle. I use Acrylic spray instead of dope to finish as it seals the tissue really well and is light weight. I'll have to see what my "Corsair" weighed after covering to get an idea where i'm at. I'm going to try to test it before winter sets in as the temp is getting down into the 40's regularly now.  I'm geting a real itch to build a full size towline now but i have too many models to build for next season as it is.


Title: Re: Bungee Launch 36" Gliders
Post by: FreeFlightModeller on October 23, 2013, 05:33:52 PM
Nice looking model Dave  :)

My 36" glider came in at about 85g complete .... lighter, but definitely not as strong as your model will be.
This raises an issue that I have been thinking about ..... is a heavier bungee model at any disadvantage at all? (within limits)
I have found with bungee launching that there is a sweet spot for a model when launching ... too little stretch and the model does not launch as high as you would expect ... but too much stretch and the model doesn't always successfully release.
A heavier model would allow more stretch to be used I would imagine and therefore more energy potentially put into the launch ... this would perhaps counter the difference in extra weight?
I suppose the best way to test this would be to use one model ballasted up to various weights?
Something for me to try next year though perhaps?


Title: Re: Bungee Launch 36" Gliders
Post by: Yak 52 on October 23, 2013, 05:53:47 PM
Russ, Geoff's Veron Cirrosonic is 170g and it's won the Aces twice :) Loads of wing area though.
http://www.youtube.com/watch?v=yBjbAK50tsw


For the glide: more weight = fly faster = increased sink rate = less dead air duration

but height is king and if the weight gets you higher then who knows?


Title: Re: Bungee Launch 36" Gliders
Post by: FreeFlightModeller on October 23, 2013, 06:06:18 PM
Yes, that's what I was getting at Jon. It's not like a fixed length towline where the maximum height attained is fairly fixed and therefore the potential energy is more constant (though still proportional to the weight?)
I have not extended the bungee to anywhere near full stretch for any flight I have, so there is definitely more potential for exploiting the extra energy available in my case.


Title: Re: Bungee Launch 36" Gliders
Post by: lincoln on October 23, 2013, 06:34:56 PM
If the towhook is adjusted, perhaps it's possible to release while there's still lots of tension on the bungee? Then maybe you can use a lot of tension with a light model. We do this in the RC world, but then it's possible for us to blip the elevator to get the model off the bungee. (We call them hi starts over here on the west side of the Atlantic)


Title: Re: Bungee Launch 36" Gliders
Post by: FreeFlightModeller on October 23, 2013, 06:40:49 PM
I agree Lincoln (I think we have started to use the term 'Hi Start' more over here too of late)
I have done a lot of RC bungee flying and you do have a greater 'choice' of release time with the control that you have.
The problem I have found with making the towline easier to detach is that sometimes it happens too early and then a flight is ruined.
If you are flying in a competition then this can mean that your day is done.


Title: Re: Bungee Launch 36" Gliders
Post by: PeeTee on October 23, 2013, 06:50:35 PM
Chaps

I put this in reply 8 of this topic

"Bungee launching, or Hi-start as the Americans call it, has many attractions as those who have tried it will affirm. To see a model sailing high and handsome at the top of the launch and then neatly casting itself off into its flight pattern is a great joy.
But remember, this is not catapult launching. In fact, if you use a bungee as a catapult the model in all probability just ping off the line in a couple of seconds. Surprising little power is required to waft a glider aloft in, ideally, a normal glider-towing breeze – hence the specification of 1/8in rubber."

This was written by Peter Michel who has been flying bungee launched FF gliders of different sizes for many years - a case of 'less is more' I suspect.

I've watched zoom and bunt launches on R/C soarers launched by 'hi start', and this is normally achieved by progressively adding up elevator to stretch the rubber more, and finally 'pinging' off the top - but it does need elevator and rudder control to get a good transition to a stable glide. Bear in mind that any slight turn on a FF glider will be accentuated by a faster launch, and unlike with a towline, you are not there to get it back on course.

Peter


Title: Re: Bungee Launch 36" Gliders
Post by: carpetbagger on October 23, 2013, 08:59:49 PM
Have you tried bending the tow hook down? Back in my A-1 towline days the hook was near parallel to the fuse, but I have heard bending the hook down 10-20 degrees allows it to release. In A-1 I had a small "flag" attached to the line near the tow ring, soon as the tension eased wind drag on the flag would drag the hook off. Actually I believe the flag was for the contest timer judge, made it easy for them know a release had occurred.


Title: Re: Bungee Launch 36" Gliders
Post by: skyrocket on October 23, 2013, 10:32:39 PM
Yep...the little flag does help...I use it on the "Corsair"...my tow hooks are adjustable and they are just simple 1/16" wire bent  to shape and held on with small wood  screws...yes, weight does decrease flight time but also allows for penetration so we will have to see later what happens...I'm new to gliders so it's all a part of the learning process...my idea right now is to get my feet wet and learn in the process and build something strong enough to handle in the winds that seem to come around when we actually go flying in contests...but I'm totally stoked about these little jobs...


Title: Re: Bungee Launch 36" Gliders
Post by: applehoney on October 28, 2013, 07:46:52 PM
Have been reading through the thread again and though various ideas on rules were bandied about I don't see any firm final declaration to date.

I would suggest that Caley's postal simple rules be adopted...      Any model up to 36" span,   30 metre line of which no more than 25% may be rubber ,   3 flights to 60 second maximum plus 30 second increments on further flights if required.

I think a point made that such small lowkey models are unlikely to attract modern composites, etc. is valid; I see no problem with a fiberglass fuselage boom however.   General performance of all models is not likely to be outstanding so I think the 60 second is reasonable and likely achievable ... everyone likes to 'max out' which is an incentive.

Line length is same as that used in Britain where the event is gathering support steadily.   I had a feeling that the line had to be held by an assistant and reeled in after use, as against a suggestion that it be attached to a stake and so left lying around on the field   - comments ?      With no cutoff dates  it may be possible to attract postal entries from both the Peterborough Club and the SAM groups, all of which models would be elegible.

I've requested that an initial event be included at the 2014 Great Grape Gathering in the hope that models demonstrated may lead to further interest, and hopefully there'll be some support. An event sponsor would be appreciated in this instance.   I've just started work on a reduced 'Walkin'  Shoes' ... not ideal maybe but ..  I'm fond of it!



Title: Re: Bungee Launch 36" Gliders
Post by: D/T on October 29, 2013, 05:36:18 AM
Re Post #142, the British rule for no stake and reeling in the line is specifically at Middle Wallop airfield, which is an active military field, so foreign object debris must be avoided. The stake was the concern.
Regards
D/T


Title: Re: Bungee Launch 36" Gliders
Post by: lincoln on October 29, 2013, 08:53:25 PM
Chaps

snip

I've watched zoom and bunt launches on R/C soarers launched by 'hi start', and this is normally achieved by progressively adding up elevator to stretch the rubber more, and finally 'pinging' off the top - but it does need elevator and rudder control to get a good transition to a stable glide. Bear in mind that any slight turn on a FF glider will be accentuated by a faster launch, and unlike with a towline, you are not there to get it back on course.

Peter

Peter,
Normally, if you put the towhook back far enough, you don't need any up elevator on a hi start launch, at least not before release. You don't usually get a lot of zoom unless the line is too short to suit the rubber and the model, or the rubber is heavier than the model needs. Of course, when the wind blows, the line will be too short automatically unless you add more. But, if everything is exactly right, including having room for enough line, the model will just fly off at the top.

A winch launch is another story, but the right towhook position still means no up elevator required.


Title: Re: Bungee Launch 36" Gliders
Post by: skyrocket on October 30, 2013, 11:31:53 AM
I agree with Lincoln...these babies go up great on 1/8" rubber all by themselves either in a blow or calmer conditions and the farher back the hook, the better the launch provided you have the height. I really do think a auto rudder is helpful even tho I don't use one yet but sooner or later i will try one. Without a auto rudder you pretty much have to set it up straight and then let the natural set up of the model dictate what glide you have. To be honest, I've never built a model that flew straight in glide so that speaks volumes of my pitiful building skills...and yet it works.


Title: Re: Bungee Launch 36" Gliders
Post by: PeeTee on October 30, 2013, 12:08:17 PM
Quote
Normally, if you put the towhook back far enough, you don't need any up elevator on a hi start launch

Lincoln

That is likely the case with sport RC soaring, but when timing I've stood behind competitors and watched them progressively feed in up elevator in order to stretch the bungy to the maximum. I don't believe that a single hook position will accommodate all windspeeds without some elevator adjustment if you are looking for maximum height gain on launch.

Anyway, we seem to be getting a bit off topic  ;) To turn to Isis's point about auto rudders, the same effect could be achieved with an offset towhook, and I seem to recall that our Australian chums provided information on these, either in this topic, or one of the others in Towline Gliders


Title: Re: Bungee Launch 36" Gliders
Post by: skyrocket on October 31, 2013, 11:12:15 PM
Where can I find this article about offset towhooks?...I'd like to try it on my new one.


Title: Re: Bungee Launch 36" Gliders
Post by: Yak 52 on November 06, 2013, 10:48:39 AM
The UK SAM organisations have just agreed the rules for 36" bungee launch gliders for vintage and classic models, and this allows scaling.

Could anyone point me in the direction of the SAM rules please?
Do they require structure to remain the same if scaled down?

Thanks,
Jon


Title: Re: Bungee Launch 36" Gliders
Post by: PeeTee on November 06, 2013, 11:02:01 AM
Jon

In a word - yes!

Here is an extract:  "5.   Models may be scaled down from original designs that would otherwise be over 36” span.  Construction is to follow the form of the original with wood sizes being scaled to agree with the model’s scale"

The complete rules are here: http://www.sam1066.org/     click on the link on the left had side of the page.

Cheers

Peter


Title: Re: Bungee Launch 36" Gliders
Post by: Yak 52 on November 06, 2013, 01:15:49 PM
Thanks Peter, I quite like the look of the 1950 Archangel but it might be a bit fiddly at 36".


Title: Re: Bungee Launch 36" Gliders
Post by: PeeTee on November 06, 2013, 01:59:20 PM
Jon

Unfortunately a lot of the interesting ones have fiddly construction - but I suppose it's a challenge. If you have a look at the November Clarion on the SAM 1066 website, you'll see that some people have been building a 36" Dream Bogey - it certainly looks different and has loads of wing area. Another one to put on the build list ::)

Peter


Title: Re: Bungee Launch 36" Gliders
Post by: Yak 52 on November 06, 2013, 05:07:14 PM
...some people have been building a 36" Dream Bogey...

Wow, that's my kind of airfoil  ;D  presumably with 1/32 sheet ribs  :o

I realised the other day that Geoff's Cirrosonic is 34" span so the 6" chord gives an aspect ratio of 5.66 - ie very low. I've scanned the plan, does anyone know if there are issues with uploading it to the gallery? I recall Phil Smiths family still have a commercial interest...?

On another note, I've started building my OD 36er - the 'Rumball Strip' :)


Title: Re: Bungee Launch 36" Gliders
Post by: FreeFlightModeller on November 06, 2013, 05:16:39 PM
Surely a copyright violation? ...... you've been 'rumballed'!  ;) ;D


Title: Re: Bungee Launch 36" Gliders
Post by: Yak 52 on November 06, 2013, 05:28:29 PM
It was inspired by yours Russ (not meant to be plagiarism)


Title: Re: Bungee Launch 36" Gliders
Post by: PeeTee on November 06, 2013, 05:34:32 PM
Jon

Scaling down the Dream Bogey gives you ribs closer to 1mm, and I'd be inclined to use that (especially with my fat fingers). The foil looks like a thinned Marquardt, perhaps Dave took a typical lightweight rubber airfoil and stretched it ;).

I look forward to seeing the O/D E36 (and to hearing how Russ's performed).

Peter


Title: Re: Bungee Launch 36" Gliders
Post by: FreeFlightModeller on November 06, 2013, 05:39:28 PM
Sorry Jon .... the humour doesn't come over in type again ... I was only having a laugh.
It was just a vehicle to work in the pun  :-[
Dave will be doubly flattered I'm sure ... and I am flattered to think that I could inspire.
What's most important now is that you inspire us with another design  :)


Title: Re: Bungee Launch 36" Gliders
Post by: lincoln on November 06, 2013, 06:00:21 PM
Sorry. Around here bungee and competition (in RC) just don't go together. All the competition flyers I know put the tow hook about as far back as it can go with good control, and so do I. Makes a big difference in launch height. I use the same position for my high start. When you do this, up elevator is not required. Some people put the hook so far back you need down elevator.

I guess a ff glider wouldn't behave with the tow hook set like that, but if it could behave, the launch would be higher.

I've heard of offset tow hooks. In a plan for the 40 inch Sinbad, they have a balsa gadget with a rudder on it that fits on two towhooks on the bottom of the fuselage to correct for the rudder offset on the model. The model releases from the gadget and the gadget comes down with the towline.
Quote
Normally, if you put the towhook back far enough, you don't need any up elevator on a hi start launch

Lincoln

That is likely the case with sport RC soaring, but when timing I've stood behind competitors and watched them progressively feed in up elevator in order to stretch the bungy to the maximum. I don't believe that a single hook position will accommodate all windspeeds without some elevator adjustment if you are looking for maximum height gain on launch.

Anyway, we seem to be getting a bit off topic  ;) To turn to Isis's point about auto rudders, the same effect could be achieved with an offset towhook, and I seem to recall that our Australian chums provided information on these, either in this topic, or one of the others in Towline Gliders


Title: Re: Bungee Launch 36" Gliders
Post by: Yak 52 on November 06, 2013, 06:01:52 PM
No probs Russ.

Dave will be doubly flattered I'm sure ...

I think he may be getting paranoid by now  :)

Thanks Peter - I see now its scaled 0.6.

My OD is pretty boring, just a low aspect strip of ribs hence the name.


Title: Re: Bungee Launch 36" Gliders
Post by: FreeFlightModeller on November 06, 2013, 06:16:47 PM
I doubt that ... look forward to seeing it.


Title: Re: Bungee Launch 36" Gliders
Post by: Garry on November 23, 2013, 12:39:46 PM
It's been quite for a while.

Here is my entry for the event.

Meteorite  by Vic Smeed as posted Outerzone

Garry


Title: Re: Bungee Launch 36" Gliders
Post by: skyrocket on November 23, 2013, 12:54:30 PM
WOW...that is WAY cool...it captures the mood and style to a TEE....can't wait to see how it flies...


Title: Re: Bungee Launch 36" Gliders
Post by: applehoney on November 23, 2013, 01:15:31 PM
Way to go, Garry  !    Nice airplane.

Looks  more practical than my oncoming airframe - wing and stab built, sides cut ....

JM


Title: Re: Bungee Launch 36" Gliders
Post by: applehoney on November 23, 2013, 04:21:56 PM
All I have so far but the fuselage is likely to appear in the next week

Reminded myself ..   still have to put in a gusset at centre


Title: Re: Bungee Launch 36" Gliders
Post by: applehoney on November 30, 2013, 12:30:20 AM
A few minor things to do before covering, not least whether to add an autorudder with some sort of gentle release system.    28 gms as is


Title: Re: Bungee Launch 36" Gliders
Post by: Paul_BB on November 30, 2013, 03:42:06 AM
Nice bones!

-Paul


Title: Re: Bungee Launch 36" Gliders
Post by: Pit on November 30, 2013, 06:14:06 AM
YAOWZAA!  A Minimee " Walkin' Shoes"!  Hope it goes as well as the biggee :)!

Pete


Title: Re: Bungee Launch 36" Gliders
Post by: skyrocket on November 30, 2013, 09:14:42 AM
OH YA Jim...she really looks sweet...glad to see you building again and can't wait to see it in the air!!


Title: Re: Bungee Launch 36" Gliders
Post by: semeraro on November 30, 2013, 10:49:19 AM
Hello,

After reading a couple of articles in aeromodeller recently I have become very interested in this 36 inch bungee glider thing. I have never flown free flight gliders before. I encounter references to "auto rudder" in the literature. What is auto rudder and how do you set it up? I am planning on building the spirit of ziac from the latest aeromodeller issue. Beautiful airplane. Would it be legal for competition?

Best,
Dave Semeraro


Title: Re: Bungee Launch 36" Gliders
Post by: FreeFlightModeller on December 01, 2013, 04:38:14 PM
Looks great Jim  :)

I'm not sure what rules apply to you Dave, so I will let someone else answer your question ... apart from saying that the Spirit of Zaic is a 'new' design as I understand so would not be be allowed in comps that do not allow new designs.
Looks a nice model though .... I liked Steve's contribution to the history of the Aeromodeller.


Title: Re: Bungee Launch 36" Gliders
Post by: applehoney on December 01, 2013, 06:51:12 PM
The Zaic design is quite elegible for the 36" bungee glider event in the WorldWide Postal - and also for that to be held at the Great Grape Gathering at Geneseo in coming September

However I thought this design heavy and far more suited for the R/C option, than for F/F        There are better designs 'out there'


Title: Re: Bungee Launch 36" Gliders
Post by: Pit on December 18, 2013, 09:34:49 AM
I just ran across the Veron "Cirro-Sonic" on Outerzone (http://www.outerzone.co.uk/plan_details.asp?ID=5146).  Cute little buggar with a constant chord wing and a bit of undercamber, but "only" 34 inch span ::).

Adding a set of ears and maybe a bit of a fuselage stretch, it would appear to make a nice F1H (A1).


Title: Re: Bungee Launch 36" Gliders
Post by: carpetbagger on December 18, 2013, 09:44:02 AM
Saw that plan as well. It appears like a quick easy build and could be easily stretched to 36" span.


Title: Re: Bungee Launch 36" Gliders
Post by: Dave Andreski on December 18, 2013, 10:16:14 AM
A few minor things to do before covering, not least whether to add an autorudder with some sort of gentle release system.    28 gms as is

Jim,
Nice work as always. 28 grams?
Dave


Title: Re: Bungee Launch 36" Gliders
Post by: Yak 52 on December 18, 2013, 04:48:07 PM
Looks good Jim, that's very light  :o


Pete, re the Cirrosonic have a look at post #135. Geoff's is stretched to 36" and built with tip panel dihedral instead of the straight V. Some of our chaps think that is better for stability on the bungee.


What is auto rudder and how do you set it up?

Dave, it appears no one answered this for you. Auto rudder is set up so that the rudder is straight while the model is on the towline or hi-start but when the towline drops off it deflects the rudder to make the model circle. The rudder is just a smallish trim tab usually spring loaded with a small rubber band. There are a few different ways to do it, this link will give you the idea:

http://www.theplanpage.com/things/Lulu/Mods.jpg

The other option is to offset the hook and oppose it with fixed rudder.


Title: Re: Bungee Launch 36" Gliders
Post by: FreeFlightModeller on December 18, 2013, 05:35:55 PM
Still looking forward to seeing your new one Jon  :)


Title: Re: Bungee Launch 36" Gliders
Post by: Yak 52 on December 18, 2013, 06:29:52 PM
Rumballing along Russ. Just finished the flying surfaces.


Title: Re: Bungee Launch 36" Gliders
Post by: OZPAF on December 19, 2013, 04:22:09 AM
Not much drag with that fuselage nor weight for that matter ;D  Bit of a problem with the tow hook position perhaps. :D

Merry Christmas
John


Title: Re: Bungee Launch 36" Gliders
Post by: semeraro on December 19, 2013, 03:00:40 PM
Thanks yak52 for the reply on the rudder question. I will check out the information on the link you sent.


Title: Re: Bungee Launch 36" Gliders
Post by: spearfish99 on January 29, 2014, 07:38:38 AM
Hi Guys,

  This is probably going to seem a stupid question but I'll ask it anyway.  As a very ex aeromodeller, having been seduced away from the fold by RC model boats for 40 years, I have become interested again of late. I do fancy trying the new 36" bungee class and am looking at a Gnome or similar that I can get in a kit for a simple  build.

I have been reading various posts etc about the bungee and have been looking around at the materials to make my own, but slightly confused by something I read. Stupid question -   which end does the rubber go?   Do you anchor the rubber to the stake/assistant, attach the line end to the hook on the glider or is the line attached to the stake and the rubber element has the towring on it at the glider end.  From all the pictures I have seen , it is not clear. Does it even matter?  Any guidance would be appreciated

Did say it was a stupid question


Title: Re: Bungee Launch 36" Gliders
Post by: PeeTee on January 29, 2014, 07:57:39 AM
It's normal to have the rubber at the 'fixed' end i.e the stake or helper, with the line hooked on to the model. I'm not sure if it actually matters, but I've not tried it the other way with the rubber at the model end.

By the way, nothing stupid about the question, and welcome to Hip Pocket. Which part of the country are you in?

Cheers

Peter


Title: Re: Bungee Launch 36" Gliders
Post by: spearfish99 on January 29, 2014, 02:11:43 PM
Hi Peter,

  Thanks for the helpful comments.  I live in Northampton.  Thought that since we have several large parks, the 36" bungee gliders might be flyable there, if the Council haven't made it illegal !


  Regards

Ian


Title: Re: Bungee Launch 36" Gliders
Post by: Baz599 on January 31, 2014, 06:03:42 AM
 "if the Council haven't made it illegal"
If they haven't, as soon as you fly there they will! Enjoyment isn't allowed in the UK public places. Or they might charge you to subsidise the shortfall in government funding.


Title: Re: Bungee Launch 36" Gliders
Post by: Yak 52 on January 31, 2014, 06:52:47 AM
Hi Ian, you are not too far away from us: http://peterboroughmfc.org/ where it all started  :)

We fly at Ferry Meadows on Tuesday's and Fridays from 1pmish and there's usually a bungee set up if the weather is suitable. We are also having a 36" series in 5 competitions over the summer. Feel free to pop along.

Jon


Title: Re: Bungee Launch 36" Gliders
Post by: spearfish99 on January 31, 2014, 10:00:18 AM
Hi Jon,

  Thank you for the invitation. Most kind

Regards

Ian


Title: Re: Bungee Launch 36" Gliders
Post by: applehoney on January 31, 2014, 10:09:20 AM
Lots of opportunities to make scores for Caley's  bungee event in the WorldWide Postal.    Keep it in mind ?


Title: Re: Bungee Launch 36" Gliders
Post by: FreeFlightModeller on January 31, 2014, 12:32:40 PM
Spearfish,

I don't know about the Northampton club, but I know in the past that the Oundle club has had access to a large flying field suitable for free flight .... plenty of choices in your area!  :)
Is your name a reference to a certain cabin cruiser?  :)

Jim,
I'll get around to a postal one of these days .... one of the Peterborough dates would be ideal.


Title: Re: Bungee Launch 36" Gliders
Post by: Yak 52 on January 31, 2014, 12:37:52 PM
They lost it last year Russ - they just have a radio field now  :(


Title: Re: Bungee Launch 36" Gliders
Post by: FreeFlightModeller on January 31, 2014, 12:47:18 PM
That's a shame ... never did get to it, but the MHMAC used to get the odd invite when I was a member there.


Title: Re: Bungee Launch 36" Gliders
Post by: spearfish99 on January 31, 2014, 02:46:08 PM
Hi Russ,

   You are right about the username although it is a bit of a private joke!.  Looking at clubs, I think that the Market Harborough club is the nearest to me that expresses any interest in free flight.  There is a small one in Wellingborough that has a field nearish to me, but the info from them is a bit ambivalent.

  While I am retired, my nephew and I have a little business which does work for some local farmers. I am putting some feelers out to see if I can "borrow" a bit of land.  Since I am a member of the BMPRS for using my model boats, I have £5m third party insurance which covers planes as well so I don't have to worry about that.


 Ian
 


Title: Re: Bungee Launch 36" Gliders
Post by: FreeFlightModeller on January 31, 2014, 05:21:56 PM
I was a member of the MHMAC for nearly a decade ..... although there is interest in free flight and they are a great crowd (as all model clubs are!), we were having to resort to flying the free flight comps in the small RC field.
We were allowed to go into the other fields when flying, but I had a bit of a run-in with a gang of heifers that frightened the life out of me! Put me off flying FF in that field and left me with a difficult decision.
On average I see more Peterborough club members over a year than even I was seeing my own club members at the MHMAC, so the decision was made easier. The Peterborough club is fantastic, especially for free flight .... not trying to influence any decision that you might make though  ;)


Title: Re: Bungee Launch 36" Gliders
Post by: spearfish99 on January 31, 2014, 07:06:34 PM
Russ,

  At the moment, I have two issues really. Since I am coming back from an exceptionally long time out of aero modelling, I do need a bit (lot) of guidance, so a club with active free flighters is really a must. Peterborough or MH are both prime candidates for that. With respect to the other clubs around here, they are predominantly RC clubs .

  At the same time, I would like to be able to fly somewhere fairly local so that I can get as much practice in without too much travelling as possible. Think that there is an old saying in there somewhere concerning cake and eating it!

  As well as the 36" glider, I would also like to try something like a Tomboy with a small diesel . That would probably not be a pretty sight! 

 I know where I am with boats but this aeromodelling is all going to seem strange after all this time.  We shall see.


Title: Re: Bungee Launch 36" Gliders
Post by: Yak 52 on February 01, 2014, 06:38:55 AM
Ian,

If you can find somewhere local to pop out for an hour or two when the weather is good then you'll get a lot more flying done. You don't need an enormous field for the 36" class - that's the point of it. Having said that one chap had a 3 mile/25 minute flight with his May Morning recently (fortunately he had his phone number on it)

I don't know if you've picked a plan yet but the May Morning might be suitable. It's in the latest New Clarion here as it happens: http://www.sam1066.org/nc0214.pdf

The Hi Start we use is 7.5m of 1/8” rubber plus 22.5m of line. The field is about 250m long. But the space you need will depend on the wind. The gliders like a bit of wind to get up, it's harder in a calm. But too much wind also makes things tricky and can put a lot of strain on the model. In ideal wind conditions (with no lift) you don't need masses of space.


Jon


Title: Re: Bungee Launch 36" Gliders
Post by: spearfish99 on February 01, 2014, 07:54:53 AM
Hi Jon,

   Thanks for that.  To get back in to the swing of things I have been looking at available kits rather than plans, simply to get a quick start.

   I have been thinking of the West Wings Merlin or Swallow. Also looked at the Mercury Gnome , KK conquest or KK Dolphin. Need to visit the local model shop and see what he has.  Incidentally, the shop is still run by Nick Evans, son of the famous Ted , the Wakefield class king of the late 40's/early 50's.

  Despite the pedigree, like most shops nowadays , it's aero modeller supplies tend to be more of the ARTF foam and plastic  variety. Pity, I do remember when Ted ran it in the early 60's. It was a Mecca to us schoolboys!  While Ted wasn't always the most welcoming host, he knew his stuff and stocked a bit of everything. Happy days.


Title: Re: Bungee Launch 36" Gliders
Post by: JohnOSullivan on February 01, 2014, 01:00:42 PM
The Bungee 36" Glider class is a good thing. Without reading back through nearly 200 posts, I would like to know what the rules are. From the Clarion, it seems that Vintage and Classic eras are recognized. This is fair game, but I wonder if there is a category for later designs.  Andy Crisp's model is a very nice design from 1975 and wonder where this fits into the class. I have a beginner's design, the Squiggle, built originally in Dec. 1971 and used for many years in a school based model building course. Full size PDF plans are available through Outerzone http://outerzone.co.uk/plan_details.asp?ID=3758. Don't know if it fits in ant 36" category.
John O'S


Title: Re: Bungee Launch 36" Gliders
Post by: PeeTee on February 01, 2014, 01:30:40 PM
John

The vintage and classic rules only apply to comps run by SAMs 35 & 1066. The Peterborough club runs competitions where there is no age limitation (for designs that is  ;D) and I'm sure other clubs will follow suit.

Peter

ps did you see JT's Ray Monks model in the latest Clarion - he does like his downthrust ;)


Title: Re: Bungee Launch 36" Gliders
Post by: JohnOSullivan on February 01, 2014, 04:31:27 PM
The Clarion is a first rate publication, which to which I eagerly look forward every month.
Ray Monk's original model used no downthrust which was typical of the UK designs of that time. I have never used downthrust on any of my designs. To my reasoning, downthrust is just a crutch to overcome improper wing and tail incidences.
 I'm surprised that John Thompson is using so much downthrust although given his pedigree, he must have some justification for it and who am I to find fault with it. He is certainly getting altitude. These light altimeters are more important in trimming than power rating or RPM.
We have had a hard winter in Nova Scotia this year with highly fluctuating temperatures from -20 deg to + 12 within 24 hours. Makes iot messy for flying as the snow melts and forms icy crusty surfaces which is rougher than concrete on model landing. I've been flying Multicopter photo machines and some R/C Electric sailplanes, but have not ventured our with my Free Flight models as retrieval is impossible.
I spent today installing my Dan Kennedy Timer on my Cox 09 Executioner with VIT, DT and Flood off.  I'm looking forward to getting it airborne.


Title: Re: Bungee Launch 36" Gliders
Post by: spearfish99 on February 03, 2014, 03:44:02 PM


  Jon,

   Other than the 36" gliders, what other varieties of free flight  fly at Ferry Meadows. i understand that i.c. is a no no there?


  Regards

Ian


Title: Re: Bungee Launch 36" Gliders
Post by: Yak 52 on February 03, 2014, 05:18:15 PM
Ian,

All sorts of free flight - as well as the 36" glider we have summer comps for P20 rubber duration, catapult glider, E20 electric, radio assist 36" glider. Plus about twenty classes at the Flying Aces day in early September. But people fly all sorts including scale.

You'd be very welcome to visit on a Tues or Fri (we have an arrangement with Ferry to fly those days but not outside those hours) No IC there I'm afraid but many members fly diesel up at Barkston Heath and other larger sites.

Jon


Title: Re: Bungee Launch 36" Gliders
Post by: applehoney on April 18, 2014, 06:56:08 PM
Finally got round to covering and completing my mini-Walkin'Shoes after it languishing  since the end of November.

With 'approximate' ballast in the nose it weighs in at 2.1 ounces


Title: Re: Bungee Launch 36" Gliders
Post by: FreeFlightModeller on April 18, 2014, 07:02:39 PM
Looks great Jim  :)


Title: Re: Bungee Launch 36" Gliders
Post by: Dave Andreski on April 18, 2014, 07:19:05 PM
It sure does!
Nice one Jim.
Don't lose 'er.
Dave


Title: Re: Bungee Launch 36" Gliders
Post by: skyrocket on April 19, 2014, 08:09:30 AM
Really nice looking Jim...can't wait to see her at Geneseo...


Title: Re: Bungee Launch 36" Gliders
Post by: skyrocket on June 05, 2014, 06:18:45 PM
At a 2 day trimming session at Geneseo, Jim flew his Mini Walkin Shoes and she(he?) flew beautifully...nice and light with a floaty glide...my Corsair was flying great also but my Retro-Glide wasn't up to par so 2 weeks ago I built a new lighter fuselage and checked it out last weekend...AUW came down from 105 grams to 79 grams and what a difference that made the glide!!!...Jim's Mini-Walkin Shoes will be a force to reckon with and deserving of a article and/or cook-up...these bungee gliders are great performers and here is hoping those who have gotten out of towline or haven't tried it yet should do so...I've been a Rubber Bander all my life but this something special and great fun....


Title: Re: Bungee Launch 36" Gliders
Post by: spearfish99 on June 05, 2014, 07:27:59 PM
Called in to my local model shop today. Having a look around and came across the new Thunder Tiger kit for the old Keil Kraft Conquest. At about the equivalent of $25 I bought one.

Absolutely crisp laser cutting all round and pretty good wood selection promises an easy build. Fits in with the current SAM rules for the 36" bungee class. Can't wait to get building


Title: Re: Bungee Launch 36" Gliders
Post by: skyrocket on June 07, 2014, 04:25:40 PM
Haven't heard of the Conquest but I hope you post some pics of your build...haven't built a kit in ages (20?30?) and glad to see good ones are around...


Title: Re: Bungee Launch 36" Gliders
Post by: spearfish99 on June 07, 2014, 04:50:54 PM
If it loads, this is what it looks like. It is probably longer since I built a plane kit, since I been running r/c boats for the last 35 years.


Title: Re: Bungee Launch 36" Gliders
Post by: Monique on June 14, 2014, 04:19:39 PM
Hi all, is there a formula for the area of the fin on these models?



Title: Re: Bungee Launch 36" Gliders
Post by: Yak 52 on June 14, 2014, 05:10:32 PM
Not a precise one I'm afraid.

There is Vv or Vertical Tail Volume as outlined on page 4 of this pdf:
http://ocw.mit.edu/courses/aeronautics-and-astronautics/16-01-unified-engineering-i-ii-iii-iv-fall-2005-spring-2006/systems-labs-06/spl8.pdf

But the suggested values are for RC gliders. FF gliders with much more spiral stability, plenty of fuselage area ahead of the CG and a ton of dihedral will need bigger fin. I did collate the Vv data for a few towliners, I'll see if I can dig it out. But IIRC it varied widely.

There is also the Centre of Lateral Area theory (CLA) of Charles Grant which may be of interest, I haven't looked at it too closely. It's based on some assumptions but should work with a conventional model.

Is this an OD model?


Spearfish - glad to see your Conquest is moving along.


Title: Re: Bungee Launch 36" Gliders
Post by: Monique on June 14, 2014, 05:24:05 PM
It is Jon, here's a rough sketch: http://s240.photobucket.com/user/Monsts1/media/SkitterBug_zpsdc276b14.jpg.html (http://s240.photobucket.com/user/Monsts1/media/SkitterBug_zpsdc276b14.jpg.html)

I think I'll go with TLAR ;)


Title: Re: Bungee Launch 36" Gliders
Post by: lincoln on June 14, 2014, 08:22:57 PM
RC gliders need more damping and yaw stability than free flight gliders, because they get perturbed by the radio all the time. Also, ff models need spiral stability and it isn't necessarily required for RC models. The latter may not relate to vertical fin size anyway, although that's pretty counterintuitive to me. But I've yet to hear Mark Drela be wrong on a technical issue, so my intuition may be ignorant.

Anyway, note how small the vertical tail is on the very popular Sweepette:
https://volarlibremente.files.wordpress.com/2012/04/sweepette.jpg

Some comments about vertical tail area. Some of them by Mark Drela:
http://www.rcgroups.com/forums/showthread.php?t=731709&page=2
If I understand his comments correctly, once you have enough dihedral and tail arm for spiral stability, you can get away with as large a vertical stab as you like without losing spiral stability. However, Mark does say that a lot of yaw damping may interfere with the transition from coasting upwards to glide, and facilitate the dreaded spiral "death dive". That death dive may have  more to do with marginal pitch stability than with spiral instability.

This may be less important on a towliner that can afford to have the c.g. a bit further forward. I suspect a towliner with auto horizontal stab can have it further forward than one that's completely "locked up". The epitome of a ff glider that needs lots of yaw stability and damping is a discus launch glider, since it usually gets launched a little bit sideways.

Another factor in yaw stability is the moment of inertia of the whole aircraft in yaw. A model with heavy wing tips is likely to need a larger vertical tail. If the fuselage doesn't change, but the span is increased, more vertical tail area may also be required.

Mark says more area up front adds to yaw damping and decreases yaw stability, thus increasing spiral stability.

Regarding the Skitter Bug, it looks like it's a t-tail. This puts a lot more torsional load on the tailboom and the fin. If the tailboom is a bit oversized, that may be ok, though you should still make sure the fin is stiffer and stronger than usual. And keep the horizontal as light and short as possible.
                                                                                                                                                                                                                                                                                                                                                                                                     
Not a precise one I'm afraid.

There is Vv or Vertical Tail Volume as outlined on page 4 of this pdf:
http://ocw.mit.edu/courses/aeronautics-and-astronautics/16-01-unified-engineering-i-ii-iii-iv-fall-2005-spring-2006/systems-labs-06/spl8.pdf

But the suggested values are for RC gliders. FF gliders with much more spiral stability, plenty of fuselage area ahead of the CG and a ton of dihedral will need bigger fin. I did collate the Vv data for a few towliners, I'll see if I can dig it out. But IIRC it varied widely.

There is also the Centre of Lateral Area theory (CLA) of Charles Grant which may be of interest, I haven't looked at it too closely. It's based on some assumptions but should work with a conventional model.

Is this an OD model?


Spearfish - glad to see your Conquest is moving along.


Title: Re: Bungee Launch 36" Gliders
Post by: applehoney on June 15, 2014, 08:32:09 PM
>think I'll go with TLAR  ;)

Hmm ... the  bikini, too .......    8)


Title: Re: Bungee Launch 36" Gliders
Post by: FLYBOY49 on June 16, 2014, 11:47:38 AM
So many models and so little time.

I've had several possible models on the
TO BUILD' list for a long time.

SINBAD
LULU
STORMBIRD
And others.

But, this 36" Bungee launch may have changed my priorities.  It happens alla time.  I have a TO BUILD list hanging on the wall along side of my cabin building bench.  It's a strip of old adding machine paper tape with models listed as I get the inspiration.  But, as my priorities change I may snip the list and retape it with a certain model now on top of the list.  There are lots of pieces of tape on it.

Now that it is summer here in Alaska, my building and flying time are very limited.  Especially with my summer flying fields about 50 to 75 miles away.  BUT! I recently was given permission to use a local farmers rather small field very near my cabin.  In fact, it's right off the end of the full scale runway that I started many years ago, right behind my cabin.  He is planning to mow it 3 or 4 times this summer.  But, that is a maintenance thing, only to keep bad stuff from getting a start.  H will not be harvesting hay there this year.

These 36" bungee launch gliders would be perfect for that location and being simple and fast to build, it's a match made in heaven for me.

So, add Corsair, Walking shoes, and CB36, etc to the list!!!!

Next project is to build a dart board with 'TO BUILD' model names instead of score numbers on it.

Van...

Balsa dust is absorbing,
It absorbs the troubles of the day!   


Title: Re: Bungee Launch 36" Gliders
Post by: Pit on June 18, 2014, 10:44:01 AM
Don't know if this one's been mentioned, a rather homely job with a 35" span it doesn't need any real enlarging.  I just saw it on Outerzone - the "PRINCE":

http://www.outerzone.co.uk/plan_details.asp?ID=4230

It DOES have twin vert. stabs tho ;D!


Title: Re: Bungee Launch 36" Gliders
Post by: RalphS on July 06, 2014, 06:57:24 AM
Our club - well me, as I do the Competition program(me) - decided to add a 36" bungee launch comp to be flown on the same day as a normally poorly supported class.  We tried it last week with mixed results due to some untrimmed models and a 10 - 12 mph wind plus a few rain spots.

The winner was a 30 to 40 year old model built by the fliers daughter for some junior competition. This benefited from previous attempts at trimming and had the best flight of about 75 seconds.  A newer Veron Cirrosonic model had a similar flight time. I flew a model with wing (cut down to 36") and tailplane from a Downbeat A1 (Hepcat design) and my own hurriedly made fuz. AUW 115g.

We hadn't planned the event very well and had no published rules so made it up as we went along.  We went for three flights, 20 secs attempt, 90 secs max.  What do other comps from the UK use?   The nice Mini Satu built by the same person as the Cirrosonic seems to suffer from the narrow chord but looks lovely.

As usual it was a good fun day at Tatton.


Title: Re: Bungee Launch 36" Gliders
Post by: applehoney on July 06, 2014, 09:38:40 AM
A good day ... and good time had by all.

Why not submit all the names/scores to Caley Hand for her postal bungee event?   Or do so after you have all made better times in your next event   :-)


Title: Re: Bungee Launch 36" Gliders
Post by: FLYBOY49 on July 06, 2014, 09:54:57 AM
Looking at the color picture of the PRINCE in a previous posting from OUTERZONE, it appears there is a brace string or wire that runs from each outer end of the stabilizer under the tail post of the fuselage.

I don't think I have seen this on any other model.

Am I seeing things or is it a real necessary thing?

I wouldn't think it necessary on a model with that wide of a fuselage cross section back there.

Van...


Title: Re: Bungee Launch 36" Gliders
Post by: RalphS on July 06, 2014, 11:33:58 AM
A good day ... and good time had by all.

Why not submit all the names/scores to Caley Hand for her postal bungee event?   Or do so after you have all made better times in your next event   :-)

Thanks for the nudge Jim.  Think we will wait till we get them trimmed. ;D


Title: Re: Bungee Launch 36" Gliders
Post by: Pit on July 06, 2014, 11:50:01 AM
Looking at the color picture of the PRINCE in a previous posting from OUTERZONE, it appears there is a brace string or wire that runs from each outer end of the stabilizer under the tail post of the fuselage.

I don't think I have seen this on any other model.

Am I seeing things or is it a real necessary thing?

I wouldn't think it necessary on a model with that wide of a fuselage cross section back there.

Van...
It's the stab TE (optical illusion).


Title: Re: Bungee Launch 36" Gliders
Post by: Yak 52 on July 07, 2014, 03:47:55 AM
It's the stab TE (optical illusion).

Yep. Whoever coloured in that image hadn't looked too closely at the plan - the stab TE is tapered and slightly swept forward.


Title: Re: Bungee Launch 36" Gliders
Post by: Yak 52 on July 07, 2014, 03:56:16 AM
We went for three flights, 20 secs attempt, 90 secs max.  What do other comps from the UK use?

Hi Ralph,

At the PMFC we fly with a 10 second attempt and a 60 second max. Most flights seem to be around 30-40 seconds. It's a small field though.
What bungee are you using?

Jon


Title: Re: Bungee Launch 36" Gliders
Post by: PeeTee on July 07, 2014, 04:42:29 AM
Ralph

Here's an extract from the SAM 1066 rules for vintage bungee launch (classic is the same except for the date) and shows the line & rubber length. As for attempt and max times, the latter is normally set to be appropriate for the field and the windspeed, and what you flew to sounds good to me.

Up to 36” Vintage Glider - Hi start (bungee launch)
1.   Any model designed as a glider with wingspan up to and including 36”, from the Vintage period as described above may be flown
2.   Maximum towline length 30 metres comprising 7.5 metres (unstretched) rubber strip up to 1/8” wide and 22.5 metres of line
3.   Fixed end of line to be held by an assistant (no stakes to be used)
4.   Line to be reeled in immediately after launch to avoid risk of entanglement
5.   Models may be scaled down from original designs that would otherwise be over 36” span.  Construction is to follow the form of the original with wood sizes being scaled to agree with the model’s scale


Peter


Title: Re: Bungee Launch 36" Gliders
Post by: RalphS on July 07, 2014, 04:49:03 AM
At the PMFC we fly with a 10 second attempt and a 60 second max. Most flights seem to be around 30-40 seconds. It's a small field though.
What bungee are you using? Jon

Thanks for info Jon.  Both figures look a bit low for the performance we saw in quite strong wind and untrimmed models.  We do have a bit more space than Ferry Meadows.  We were using 7.5m of 1/8th rubber and 22.5m of light line to get them up.  My bungee used old brown FAI rubber and the line was from a lovely long gone Japanese kite given to me as a 6 year old by a relative who had outgrown kites.  I would guess it is 85 years old.  Never throw anything anything away, you don't know when it will come in handy.  ;D


Title: Re: Bungee Launch 36" Gliders
Post by: RalphS on July 07, 2014, 04:54:32 AM

Ralph
Here's an extract from the SAM 1066 rules for vintage bungee launch (classic is the same except for the date) and shows the line & rubber length. As for attempt and max times, the latter is normally set to be appropriate for the field and the windspeed, and what you flew to sounds good to me.

Up to 36” Vintage Glider - Hi start (bungee launch)
1.   Any model designed as a glider with wingspan up to and including 36”, from the Vintage period as described above may be flown
2.   Maximum towline length 30 metres comprising 7.5 metres (unstretched) rubber strip up to 1/8” wide and 22.5 metres of line
3.   Fixed end of line to be held by an assistant (no stakes to be used)
4.   Line to be reeled in immediately after launch to avoid risk of entanglement
5.   Models may be scaled down from original designs that would otherwise be over 36” span.  Construction is to follow the form of the original with wood sizes being scaled to agree with the model’s scale   Peter

Thanks Peter.  Your post came through as I pressed the "post" button on previous reply.  I had noted that people were using 7.5 + 22.5 lines but I hadn't seen attempt times and maxes.


Title: Re: Bungee Launch 36" Gliders
Post by: skyrocket on July 22, 2014, 10:07:33 PM
Monique...you might have a look at Ron Warring's article in Model Aircraft, June 1953 for design formulas or suggestions....old but useful...the saying goes that Ron could write on anything if money was involved...not nice but i feel he did have alot of winners in his stable and will look the other way this time...


Title: Re: Bungee Launch 36" Gliders
Post by: skyrocket on September 17, 2014, 05:05:19 PM
We had another 36" Bungee contest last weekend at Geneseo, NY, and had about 7-8 flyers. The weather was pretty "IFFY" but the thermals were around. We flew to 3 x 60 sec. maxes with 1 minute increments thereafter. Jim Moseley and I made the maxes and settled down for our 2 minute maxes. I didn't think the air was that good so I didn't light the fuse....BIG mistake... my Retroglide-II went up to the top of the line and transitioned perfectly and started to go up in the elevator!!...my timer and I watched it go into the cloud base at 16 min. 41 sec and OOS...Jim flew next and made 53 sec and I was relieved I didn't have to fly my Corsair backup...he is a tough competitor and his mini Walkin Shoes has a beautiful glide. Highly recommended....so now I shall build another Retroglide-II but I will add a Texas Timer and set it NO MATTER WHAT...during the last 3-4 weeks my flying partner and I have been flying 20" to 30" British kit gliders for giggles on a smaller bungee of 15 feet of 3/32" of rubber and 30 feet of kite string on our Polo field testing site...WHAT FUN !!!...the KK Dolphin really looks pretty up in the air and Howard's Frog Wren has a beautiful glide...maybe there should be two classes : one for models per kit plans prior to 1960 and one for own designs with locked down surfaces ???...any thoughts guys and dolls?


Title: Re: Bungee Launch 36" Gliders
Post by: FreeFlightModeller on September 17, 2014, 07:30:33 PM
Glad to hear of others enjoying flying this class .... it is the best kind of flying I have had in the past year or so.
Good to hear that yours and Jim's models are performing well too.
At the Peterborough comp there were plenty of the classic designs flying .... I still want to try these as well as new designs. I think I prefer it 'all in one', but perhaps with a winner for pre1960 designs too.


Title: Re: Bungee Launch 36" Gliders
Post by: skyrocket on September 19, 2014, 10:38:50 AM
"all in one" works well and we get to see some pretty nifty designs being flown and as long as we keep it locked down surfaces, we won't have any problems...one thing I noticed when flying in a good breeze is that as it approaches the top, the line and rubber stretches even more and you get extra altitude as it pings off...the other thing is I feel that a auto rudder is essential and proper placement of the hook can make a winner out of a previous dog...being a newcomer to glider flying, I'm having a ball!!! and I'm very happy Western New York Free Flight Society added it to their contest calendar...


Title: Re: Bungee Launch 36" Gliders
Post by: applehoney on October 14, 2014, 02:33:50 PM
A photo of my mini Walkin' Shoes going up on the bungee came to me yesterday; no idea yet of whom the photographer was


Title: Re: Bungee Launch 36" Gliders
Post by: PeeTee on October 14, 2014, 02:48:34 PM
Jim

Luvverly - how about a plan for the builders gallery........please!

Peter


Title: Re: Bungee Launch 36" Gliders
Post by: skyrocket on October 14, 2014, 03:26:28 PM
Jim...nice shot of her going up in the elevator !!!...just finished a new RetroGlide so I'll be testing that until the weather clamps down...or am I dreaming about the weather again?...in any case, I'll fly until the fingers get too stiff or the rum doesn't work...did you finish the Walthew?


Title: Re: Bungee Launch 36" Gliders
Post by: FreeFlightModeller on October 14, 2014, 03:42:53 PM
Looks great Jim  :) ... doesn't look mini at all in that shot.

With a pool of young keen retrievers, this class would be so good for those that can't tow or chase a model very well.


Title: Re: Bungee Launch 36" Gliders
Post by: applehoney on October 14, 2014, 03:55:15 PM
>   a plan for the builders gallery.

I don't really have one ....  I just tile-printed off the 88"  (as copied from MA page of long ago ) to 36", taped together the sheets and then pencilled in suitably amended structure for that size.  The sheets are now really confusing!

Walthew, Dave?   No ...   wouldn't take too much now to finish the clunker though but the incentive is lacking. Maybe sometime through the winter.


Title: Re: Bungee Launch 36" Gliders
Post by: OZPAF on October 14, 2014, 08:07:57 PM
What a neat shot of your mini Walkin' Shoes. Nice traditional proportions.
John


Title: Re: Bungee Launch 36" Gliders
Post by: FLYBOY49 on October 14, 2014, 11:01:57 PM
Jim,

Beautiful has been said.  It's true.

Something I notice.  I've been having difficulty getting my bungee tow ring to release from the tow hook as it should.  My flag is very near the tow ring.  I see that you have yours about a yard down the tow line.  Is this better than up close to the ring?

Van...


Title: Re: Bungee Launch 36" Gliders
Post by: applehoney on October 14, 2014, 11:53:07 PM
Not my line, Van - but I really do not see how flag position is likely to make much difference.    I did find that angling the tow hook a little downwards made a positive difference compared to the more usual practice of it being parallel to the bottom of the fuselage.  Broadly speaking, when towing the line is flicked off the hook by releasing some line tension - with bungee the ring slides off the hook as line slackens and the angle helps it do so. 

I think ....   all speculation   ;D


Title: Re: Bungee Launch 36" Gliders
Post by: FLYBOY49 on October 15, 2014, 12:14:50 AM
Thanx, Jim.

I had been thinking that I had too strong of a bungee and too short of a line.  What I've been using is a hi start from long ago, before I knew about the 36" glider class.  It's made up of 'about' 15 or 20 feet of small surgical tubing (May 3/16" O.D.) and again, 'about' 30 or 35 feet of heavy duty fishing line.

If I resist stretching the bungee out more than about an extra 30 feet, it releases just fine.  But, it doesn't have much altitude.

However, If I do stretch it out to about 3 times it relaxed length, the model ( a Cadet) reaches good altitude and refuses to release.  Even with the tow hook rebent downward to about a 30 degree angle from the datum line.

Boy is that thrilling to endure. !!!!  On occasions, it has transitioned into a dive at tremendous speed, heading for Tera firma with the tow line still pulling hard on the tow hook.

All this while the other end is attached to an anchor in or on the ground.

Van...


Title: Re: Bungee Launch 36" Gliders
Post by: billdennis747 on October 15, 2014, 04:57:25 AM
What a neat shot of your mini Walkin' Shoes. Nice traditional proportions.
John
Ditto. That could be the classic glider I've been looking for, although I thought squillions of riblets was the curse of the scale model!


Title: Re: Bungee Launch 36" Gliders
Post by: skyrocket on October 15, 2014, 08:43:38 AM
This is a good discussion going on about the mechanics of bungee. I set ours up per the way the Brits are doing their bungee - 7.5 meters of 1/8" rubber plus 22.5 meters of 30# kite string. I did add a 1" dowel about 2 feet long as an anchor and a eyebolt on top to connect the line and an eyebolt and rope  plus tent peg. I placed the 9" square flag about 12"-15" down from the tow ring and recently added a release pin for auto-rudder. This set up hasn't failed me yet and I haven't had any negative feed back. We all use the same bungee for the contests. Jim is right about angling the tow hook slightly downward, it works great. Release is a function of where the hook is in relation to the CG and a good place to start is about 20 degrees forward of the CG. With my gliders so far, I pace off about 30 strides to start off and about 40 to 45 at the most. Without an auto-rudder you are pretty much stuck with a straight glide to stop the swerve to either side. And lining up with the wind is important too. Hope this helps. Like PeeTee says, they have a mind of their own when they want to release.


Title: Re: Bungee Launch 36" Gliders
Post by: applehoney on October 15, 2014, 09:20:01 AM
> squillions of riblets

Omitted on the 36"    ;D


Title: Re: Bungee Launch 36" Gliders
Post by: FLYBOY49 on March 29, 2015, 12:42:13 PM
 :-\

I recently repaired my CADET glider and also built a new bungee launcher outta 1/8" rubber and halibut fishing line. 25' of rubber and 75' of line, with a bandana as a flag attached in the open position a short way below the tow ring.  It works a treat!!!

I was surprised that that small of a rubber band could tow that model up to altitude.

I flew it on our frozen lake several times and although it is not thermal season here, it got over a minute flights with regularity without stretching the rubber to it's maximum length.

I love that glider so much that I took the plan to a copy shop and had it reduced to a 36" wing span and am making balsa dust inna cabin, frantically trying to assemble it as a possible model for this falls SAM CHAMPS in Nevada.

Van...


Title: Re: Bungee Launch 36" Gliders
Post by: skyrocket on March 29, 2015, 03:24:52 PM
ATTA boy!!!!...that's the stuff we are talking about here...It's amazing how many designs out there lend themselves to bungee. You can fly larger models on the same 1/8" rubber but you have to walk back a lot farther than the typical 30 t0 40 paces we use because of the weight. This spring we will try larger models at the HOBO meet in Geneseo, NY, with a little heavier rubber and A2 size models in hopes that some flyers who can't run anymore will dust off the cobwebs of some great A2 designs they use to fly. The nice thing about bungee is you can fly alone and do it anytime for as long as you want.


Title: Re: Bungee Launch 36" Gliders
Post by: FLYBOY49 on August 27, 2015, 12:39:02 AM
Guys,

I am almost finished with a reduced to 36" W.S. Cadet.  Still needs color, (Colour for the Brits.) and trim.  But, I did fly it at our Alaska Fall Old Timer (SAM) contest.  It flew a treat!!!

I didn't stretch the bungee to the max. Only a few steps backward stretching the bungee a bot for a test flight.  In almost still air (I did notice a bit of lift) I got about 2 minutes with it.

It's covered in light weight Polyspan from Larry Davidson.  3 coats of thinned Gelatin to seal the fabric and a single coat of 50/50 Nitrate dope.

My plan is to finish it and fly it at Eldorado Dry Lake, Boulder City, Nevada  in the U.S. SAM Champs in October.

It and a Tomboy or two may be the only planes I can ship down this year.

Although I do intend to try to build a Frog Wren also.  It's only one of many on my 'TO BUILD' list.  But, life's interruptions seem to slow down my building dreams.

Van...


Title: Re: Bungee Launch 36" Gliders
Post by: skyrocket on August 27, 2015, 12:01:12 PM
Yep...you got the bug. I lost my #3 RetroGlide at Geneseo when I put a 2 min fuse on it and it went deep into the corn so I built #IV last week. Still waiting to test glide it but it LOOKS promising. On bungee gliders less than 30" span, we use 3/32" rubber  of reduced length along with a reduced kite string. It works well on small fields but still gives good flights long enough to work out the trimming. With 1/8" rubber, 30 to 40 paces is the norm. I did try a full size glider on 3/16" rubber and found I had to step a little further back with a glider weighing 10-11 oz. Of the 3 sizes of models, I like the 36" bungee the best. BTW, you don't have to fly old designs in bungee in this country although they look great in the air.


Title: Re: Bungee Launch 36" Gliders
Post by: FLYBOY49 on August 27, 2015, 12:36:08 PM
This CADET glider is an old timer design that I thank Jim Mossley (APPLEHONEY) for.  The original that I built as best I could from foreign wording was made from wood I harvested from behind my shop here in Willow, Alaska.  Spruce, Birch and Poplar.  very few pieces of balsa in it.  I covered the original with full strength Polyspan and finished it with Nitrate dope.  It took forever to build since I had to sorta kiln dry the wood strips with trouble trying to keep it from wrapping up like pretzel sticks.  But, it flys a treat!

I had a copy shop reduce it to a 36" W.S. for me.  It took several attempts since the kid running the copy shop wasn't the sharpest pencil in the drawer.  And I paid for all the attempts to make it far and get the copy size I wanted.  It was all worth the effort.  BTW:  the reduced one is almost all balsa. But, with hard wood longerons and spars. It does take a bit of lead in the nose to balance it.  And I did make a home designed D.T. hinge for the tail outta soldering lugs and aluminum tubing.  Crude.  But, it works fine.  Gotta figure out how to rig a timer release to it before I take it to Nevada.

Next time I'm going to use full strength Poly Span on the Fuselage.  The light weight stuff dents and punctures too easily.  I am, however sold on using the Gelatin to fill the fabric before doping.  Apply it thinned a bunch and it adds almost no weight.  Then it takes a minimum of dope to finish it.

Thanx, Jim.

Van...


Title: Re: Bungee Launch 36" Gliders
Post by: applehoney on August 27, 2015, 02:18:18 PM
Very welcome, Van


Title: Re: Bungee Launch 36" Gliders
Post by: FLYBOY49 on December 03, 2015, 10:12:55 PM
I have been delinquent in not telling of my luck at the SAM CHAMPS.

I won 3rd place in the Old Timer F/F glider contest with my CADET glider that I built outta mostly hard wood collected out behind my shop last year. It is that glider that I built from Jim Moseley's plan that was written in some foreign language.  Guys on SAMTalk helped me decipher the words I needed and I could measure the sticks on  the drawing myself.

Anyway, I managed to anchor down 3rd place with it at the CHAMPS.  WHOOPEE!

I scaled it down to a 36" wing span and took that reduced size model along, also. But, I didn't do so well with that one.  I had stronger competition in that category. Still came in at 4th place, I think. Not inna money, tho.

I did get 2nd in Twin Pusher.  WOW! For me that's a real shot in the arm.  I also got the 'last to be issued' certificate of induction in the 'NUTWORTHY TWIN PUSHER SOCIETY'. Grant Carson is retiring from that life long role.

Thanx again, Jim.

Van...


Title: Re: Bungee Launch 36" Gliders
Post by: skyrocket on December 04, 2015, 11:03:44 AM
I think this bungee stuff is getting a hold here. The 30" Lulu does fly better with the auto-rudder attached. I haven't tried it on a 1/8" rubber bungee yet, just the 3/32"" rubber set-up at 15 ft. rubber/30 ft. kite string...just right for a small field. I'm building a Keil Kraft 30" Cadet right now. A nice old design so far. I had thought of the 30" Sinbad but there was just too much wood in it...speaking of twin pushers, I do have a 20" job I put together using an old Embryo wing and it is a lot of fun flying it on 2- 1/8" motors and they are very strange trimming out. Also, carving a left hand prop was strange but fun. I was lucky in finding a good all metal old egg beater in a antique store. Not with pressed steel gears but real gears. I wrapped and soldered the hooks on the shafts and it works nice. The manufacturer was "Daisey" and it looks to be late 40's to early 50's. I'll be taking a 36" bungee glider (RetroGlide-IV) and an unlimited size glider down to Palm Bay the 27th. to fly in the KOI meet on a bungee.


Title: Re: Bungee Launch 36" Gliders
Post by: skyrocket on December 25, 2015, 01:23:20 PM
Both the KK Cadet and the Mini-Lulu fly great on the bungee...do add auto-rudders to these little beauties...they go straight up to the top of the line and ping off nicely when you angle the hook downwards a little...and add plenty of lightness...the KK Cadet has a lot of potential at only 30" span...I got the KK Cadet off Outerzone.com and the LULU from a old Aero Modeller...


Title: Re: Bungee Launch 36" Gliders
Post by: FLYBOY49 on December 27, 2015, 01:22:13 PM
My Christmas break build.
 
My build time is fractured into small bits of time each day.  So, for this build I kinda kept track of the approximate time it took each day to build this Bob Holman short kit on Jim O'Reilly plan. I didn't  include the little time it took to gather some sticks from my stash in another building.
 
Wings: A couple half hour sessions, which included gluing together the Stabilizer.
 
Fuselage: A bit longer since it took a bunch of fiddling and jigging.  Approximately  3 hours total.
 
All total, the fastest and easiest build ever!
 
For some reason I am unable to shrink the pic's to a sendable size.
 
Van...


Title: Re: Bungee Launch 36" Gliders
Post by: PeeTee on December 27, 2015, 01:32:42 PM
Van

If you download this software: http://shrink-pic.en.softonic.com/  it automatically reduces the file size of the photos to suit e-mailing or posting photos here. I've used it for years with nary a problem, and as I said, it does it automatically.

Cheers

Peter

ps the Wren is coming along nicely, I saw your photos on FFML


Title: Re: Bungee Launch 36" Gliders
Post by: FLYBOY49 on December 27, 2015, 07:45:01 PM
Here's another go at posting FROG WREN pic's

Van...


Title: Re: Bungee Launch 36" Gliders
Post by: FLYBOY49 on December 27, 2015, 07:48:45 PM
Again, more progress.
Van...


Title: Re: Bungee Launch 36" Gliders
Post by: FLYBOY49 on December 27, 2015, 07:59:59 PM
In that last batch of pic's I included a building tip that I thought I might share.

Before I start pinning parts to the plan for the fuselage, I use my old fashioned draftsman compass (divider to some) to measure and mark all the fiddly uprights and cross pieces directly from the plan.  Then, with them laying 2 at each station, I pin down the longerons and start gluing 'em in.

It makes 'em all exactly the same length, saves time, and makes building a l-o-t faster as well as more accurate.  It also helps if you take a minute to sand the ends to the correct angle right after you cut 'em to length.  This pic shows the uprights.  I do the same thing when attaching the 2 sides together. (Not shown in the pic's, tho.

The lead in the pencil end in mine is #2 and it works O.K.   But, if I still had some HB it would work even better when marking the balsa.  Haven't seen a supply of HB for some time.

Van...


Title: Re: Bungee Launch 36" Gliders
Post by: BigR on December 30, 2015, 05:55:34 PM
Hi All,

I'm making a 36 inch Lulu scaled up from the "50th Anniversary" 30 inch Lulu Baby for the Haggard Bowden contest in Feb. at Perris. Rules say 25 feet of 1/8 inch rubber. Is this one strand 25 feet long or a 25 foot long loop of 50 feet of rubber? Approximately 10 feet per gram, so 2.5 grams or 5 grams of rubber? What do you use for the other 75 foot "string" and as a connector at the tow hook end? I assume a key ring or some such.

As you can see, I'm not a glider guy. Do know enough to use a hardwood spar though, since I folded the wing on a Sinbad at Mile Square with a "zoom" launch.

John in Kalifornia


Title: Re: Bungee Launch 36" Gliders
Post by: FLYBOY49 on December 30, 2015, 08:11:16 PM
John,

It's 25 feet, not doubled, of 1/8th inch flat rubber and 75 feet of any light string.  I use fishing line.  Some use kite string or similar.  These little guys launch so sedately it is beautiful to watch.  No threat of folding a wing, tho.  But, I have successfully launched larger gliders on that same bungee.  It surprised me how well this launcher works.

On mine is a 1/2" split ring to attach  it to the tow hook with a small flag a short distance below the ring.  I am using a piece of a hanky.  My neighbor uses a few pieces (Maybe 4 or 5) of surveyors tape about a foot long.  These help pull the ring off the tow hook.

It also helps to angle the tow hook down from the belly of the plane a few degrees.

Van...


Title: Re: Bungee Launch 36" Gliders
Post by: skyrocket on January 24, 2016, 09:39:58 AM
yes, that is the bungee set up we use for 36" bungee gliders...I've used it for A1's as well...I fly the Baby Lulu on a 3/32" rubber bungee set up on our small field and it is just right...I also fly a KK Cadet on this smaller set up and a auto-rudder to get a straight up tow....I have been using a 3/16" rubber set up on A2 size gliders and a total length of 160 feet. No problems yet. All set ups are with single strands of rubber and kite string. The thing I like about bungee is you can fly independently and get in a lot of flights without wearing your legs out and trim the models in a very short time. An adjustable tow hook is helpful too to make allowance's for wind strength on different days. I've been using fuse D/T but it is time to start thinking about a timer.


Title: Re: Bungee Launch 36" Gliders
Post by: BigR on January 24, 2016, 06:32:45 PM
I made up the towline with the suggested rubber and used braided fishing line. When I got out to the field I found the the tow reel, an old orange and white FAI sullpy item, had become disassembled. What a mess!

The Lulu had a nasty stall which I corrected with lots of nose weight. I think I'll recheck the CG and incidence settings. Next time I'll be more prepared.

John


Title: Re: Bungee Launch 36" Gliders
Post by: skyrocket on January 25, 2016, 11:26:12 AM
I keep the line/rubber on a large kite reel and tangles do occur all the time...I put the line/flag/tow ring on first and that makes the rubber first so I can attach the rubber to the post and then walk out the set up out...by doing this I can drop off the reel at the post and pick up the glider and fly...with the 1/8" rubber set up, I pace off 20 to 30 steps and start flying...the more wind the less paces...try to keep the auto rudder as simple as possible...Baby Lulu came out at 29.4 grams new and I modified the airfoil with a slight under-camber...


Title: Re: Bungee Launch 36" Gliders
Post by: dohrmc on July 18, 2016, 06:54:01 PM
I just flew my first Hi Start flights this weekend with a Retro RC Gnome glider. It is a nice little glider. Based on the instructions in the kit, I used 50' of 1/16" rubber, and 100' of line. I was amazed to see that 1/16" rubber works perfectly well, and hauls the model all the way up to the top of the line.
This event will become a standby in our club, as we have many glider fliers who are getting too old to go tearing around with a towline.
The Retro RC kit is laser cut, and makes a fine glider.


Title: Re: Bungee Launch 36" Gliders
Post by: skyrocket on August 25, 2016, 10:11:36 PM
I'm building a 36" Lulu right now from the 30" Aeromodeller plan I enlarged...seems to be going together nicely...the 30" Lulu is a nice small field flyer so I don't see any trouble coming soon...will build the wing tomorrow and start covering it next week...waiting for the tracker I ordered last week and will try to fit it in Lulu and retro-fit the transmitter to various other models because I've finally reached the point of getting tired of loosing good flying models in the soy beans and corn at Geneseo...it's not a question of money but one of feeling not good enough to warrant one...it's frustrating as hell being close to finding a model when the soy beans just suck it up even when you have a good line on it...does anyone know which of the button timers is the best for small models because I'd like to replace using fuse?...is a button timer the same as a Silly Putty timer or should I try a Tomy style timer?


Title: Re: Bungee Launch 36" Gliders
Post by: Graeme H on August 26, 2016, 08:03:12 AM
Was out flying with my 2 small gliders the other day, a Frog Wren and a Dizzy


Title: Re: Bungee Launch 36" Gliders
Post by: calgoddard on August 26, 2016, 10:25:45 AM
This is in response to Reply #260.

Try the larger Munson badge timer.  It is available in longer and shorter durations.  You can buy them from Starlink Flitetech and Volare Products.

As I understand it the old timers that used Silly Putty were hand made and have mostly been replaced by the Muson badge timers. These are viscous damper mechanisms with a rotating arm.  The arm is rotated manually to an angular position to set the desired DT trigger time.

Where I live fuse timers are not legal due to the fire danger that they allegedly pose.  So we use viscous damper mechanisms because they are inexpensive, and lightweight. I actually prefer TOMY timers for this application, but they are a little heavier (3 - 4 grams) and require some tweaking. They are more accurate and reliable.

The best timer, in my experience, is the BBT electronic timer from Starlink Flitetech.  It weighs about 3 - 4 grams including its battery and is programmable in 5 second increments up to 5 minutes. It is extremely reliable and highly accurate. I think it sells for less than $50.

I am a slow builder.  When I get a model completed and trimmed so that it is flying well I cannot bear to lose it.  For bigger models, like OTR and coupe, I install both an electronic timer and an RF tracker.  They can easily carry the extra 6 - 8 grams and still be competitive.

For smaller models, like an Embryo or a Jimmie Allen Skokie, I use a viscous timer button and put up with its relative inaccuracy.  I had my Skokie DT early at a contest recently when it was still gliding well 50 feet above the ground. That flight ended up being 98 seconds and the early triggering of the DT probably cost me a max.    

A friend of mine just built a 30 inch wing span LULU glider. I can't wait to see how it flies.

PS - Nice looking models Graeme H.

    


Title: Re: Bungee Launch 36" Gliders
Post by: skyrocket on August 26, 2016, 12:55:53 PM
Almost have the 36" Lulu wing built...I will try the Munson timer from Volare...thanks...the 30" Lulu does fly really nice...I'm using 1/32" geodetic ribs in 36" version to cut down warps & weight but the rest is per plan...my buddy flies a Frog Wren on bungee...good looking model...we use 3/32" rubber on the smaller models and suits our small test field...back to it!


Title: Re: Bungee Launch 36" Gliders
Post by: applehoney on August 26, 2016, 02:12:08 PM
Occurred to me that I never, as far as I remember, documented the 36" version of the 'Walthew A/2"  that I built two winters ago, spurred by  the fact it had reasonable wing area for its size and the thick flat-bottom airfoil did not deter me.  Such worked beyond my expectations on my old 'Night Owl' beginners glider.

However initial enthusiasm waned as it became apparent that the Walthew was more in the running for the ugliest clumsiest design award.  At Geneseo - May 2015 - it did show a shortlived promise of flying ability but fell out of an off-field tree and destroyed the fuselage back to the wing.  Though I still have the pristine flying surfaces I just can't imagine building another fuselage for the thing!


Title: Re: Bungee Launch 36" Gliders
Post by: Yak 52 on August 26, 2016, 03:09:50 PM
Was out flying with my 2 small gliders the other day, a Frog Wren and a Dizzy

Looks nice Graeme! Welcome to the forum. How were you launching them?

Jon


Title: Re: Bungee Launch 36" Gliders
Post by: Graeme H on August 26, 2016, 03:56:43 PM
Just off a bungee, 25' of rubber and 75' of listing line


Title: Re: Bungee Launch 36" Gliders
Post by: skyrocket on August 31, 2016, 10:24:44 AM
Just finished the 36" Lulu and it came out at 44 grams and I'm pleased with the build...didn't tissue the fuselage, just 3 coats of Ace Hardware's spray Lacquer and tissued the wing, stab and fins with 2 coats of lacquer on each...I still used a fuse but will have to buy some of those button timers for these small models...pics later after flight testing some time this week...


Title: Re: Bungee Launch 36" Gliders
Post by: Pete Fardell on September 03, 2017, 07:21:05 PM
I think a 3 ft bungee glider might be a good way for me to get into a bit of gentle non-scale competition in a low key way. I might try and build one for next summer. There are also one or two opportunities (eg. Oxford Scalefest) to fly scale gliders in FF competition. I was wondering if it's possible to make an uncomplicated scale glider which is also at least vaguely able to compete with non-scale designs so that I can build a 'two birds with one stone' model. Is this a daft idea? If not, which real gliders most closely resemble good hi-start designs?


Title: Re: Bungee Launch 36" Gliders
Post by: FLYBOY49 on September 03, 2017, 08:44:54 PM
I have just finished building another Frog Wren.  Lost the original one day after completion when my cabin burned to the ground.  Lost my entire building area, all tools and many  models.

But, I almost finished building another place to live and have accumulated most of the necessary building tools and supplies.  The 1st Wren took about 3 days to build.  This one has taken several months.

This one has a Tatone D/T timer. It's tissue over Mylar.  Built from a Bob Holman short kit with Jim O'Reilly plans.  They make building a model a dream come true.

Hand gliding in my small lawn is good.  I'll try bungee launch this coming weekend at Point McKenzie where we hold the Alaska SAM annual contest.  It's a one mile square farmers field that we get to play in after his 2nd cutting of hey.  The farmer keeps a mowed lawn runway in the center for us and we have permanent pit tables set up.

I'll also be taking along a restored Jetco Thermic 'C' that I built many years ago and a couple rubber models that have been hanging on my shop back wall for many years. If I get enough time to putter with it I'll include a Tomboy with a Pfeffer diesel.  I still have one each, F/F and R/C that have been to Boulder City, Nevada and back. (SAM CHAMPS, ya know. I'm scheduled to do that again this October.  So, gotta get crackin' to get stuff ready.

BTW: Jim,  I like the looks of that glider you said was UGLY! (Walthew A/2)  It looks good to me and I would consider making one this winter  if I had the plans or knew where to get 'em.

Van...


Title: Re: Bungee Launch 36" Gliders
Post by: applehoney on September 04, 2017, 12:34:49 AM
Van - sorry ...didn't keep the tileprint plan of  the Walthew.

Contact Derekk Scott   www.model-plans.co.uk     He'll provide you with a plan at nominal cost and likely print to 36" span for you, too.
 


Title: Re: Bungee Launch 36" Gliders
Post by: Yak 52 on September 04, 2017, 04:22:56 AM
I think a 3 ft bungee glider might be a good way for me to get into a bit of gentle non-scale competition in a low key way. I might try and build one for next summer. There are also one or two opportunities (eg. Oxford Scalefest) to fly scale gliders in FF competition. I was wondering if it's possible to make an uncomplicated scale glider which is also at least vaguely able to compete with non-scale designs so that I can build a 'two birds with one stone' model. Is this a daft idea? If not, which real gliders most closely resemble good hi-start designs?

Pete,

There is a scale glider prize in the Peterborough Flying Aces 36" bungee launch competition - held last weekend (but I was on holiday unfortunately). Monique won this a few years back with a Slingsby Kirby Prefect enlarged to 36". There's a thread on here if I recall.

Anything with low aspect ratio and plenty of dihedral effect would be a good starting point. The dihedral makes all the difference in windy conditions and low aspect ratio maximises launch height.

Jon


Title: Re: Bungee Launch 36" Gliders
Post by: Pete Fardell on September 04, 2017, 04:38:02 AM
Thanks, Jon; yes, it was noticing the scale prize mentioned on the Peterborough results last night that made me think of the idea. Good to know it's a goer. High aspect ratio and dihedral noted, I shall start scheming! I might just do a Prefect like Monique's.

EDIT: I've just noticed you said LOW aspect ratio, not high. Do you mean low compared to other gliders, or just low? Presumably it still needs longish wings?


Title: Re: Bungee Launch 36" Gliders
Post by: Yak 52 on September 04, 2017, 04:45:13 AM
Low aspect  ;) another benefit is it gives a lower wing loading.

It's a pain for scale because high aspect ratio is one of the thing that makes a good full size glider  :-\ but older vintage gliders tend to be lower aspect so that's no bad thing  :)


Title: Re: Bungee Launch 36" Gliders
Post by: Pete Fardell on September 04, 2017, 04:47:38 AM
Thanks, Jon. I think your correction and my edit crossed in the ether. That's nice and clear though.


Title: Re: Bungee Launch 36" Gliders
Post by: Yak 52 on September 04, 2017, 05:12:26 AM
Pete sorry, just saw your edit - both too quick  ;D

More span is always good because the more air you can 'reach' and use to make lift with, the better. The bungee class has a maximum span of 36" so it makes sense to build a model with 35.99" wings  8)

If the span is fixed at 36" then aspect ratio only changes the wing area. Lower aspect = more area.

The Prefect aspect ratio is about 12. Some of the most successful non scale models have an aspect ratio of about 6 so they have twice the wing area. Including the Veron Cirrosonic (https://outerzone.co.uk/plan_details.asp?ID=5146) and Mercury Gnome (https://outerzone.co.uk/plan_details.asp?ID=4478) and Corsair (https://outerzone.co.uk/plan_details.asp?ID=5735) when built at 36".

The low aspect ratio also gives a greater chord and so higher Reynolds number, which is a big factor in the drag and therefore sink rate.

There's obviously more to it but generally when span is limited low aspect is better.


On a related but OT subject it's worth noting that with some FF glider classes like Nordic A1 or F1A the span is not limited by the rules but wing area is. In that case high aspect ratio is better. You are accepting the penalty of lower chord/Reynolds number but maximising span.


Title: Re: Bungee Launch 36" Gliders
Post by: skyrocket on September 04, 2017, 09:27:33 AM
Rich Weber was flying a low aspect ratio Primary at the FAC non-nats this summer and it flew rather nicely...more importantly, I think, is a good moment arm for directional stability as they tend to wander a bit on the line going up...


Title: Re: Bungee Launch 36" Gliders
Post by: Monz on September 04, 2017, 10:47:46 AM
I think a 3 ft bungee glider might be a good way for me to get into a bit of gentle non-scale competition in a low key way. I might try and build one for next summer. There are also one or two opportunities (eg. Oxford Scalefest) to fly scale gliders in FF competition. I was wondering if it's possible to make an uncomplicated scale glider which is also at least vaguely able to compete with non-scale designs so that I can build a 'two birds with one stone' model. Is this a daft idea? If not, which real gliders most closely resemble good hi-start designs?

Pete,

There is a scale glider prize in the Peterborough Flying Aces 36" bungee launch competition - held last weekend (but I was on holiday unfortunately). Monique won this a few years back with a Slingsby Kirby Prefect enlarged to 36". There's a thread on here if I recall.

Anything with low aspect ratio and plenty of dihedral effect would be a good starting point. The dihedral makes all the difference in windy conditions and low aspect ratio maximises launch height.

Jon

I didn't win the glider comp, The Prefect was awarded model of the day or something like that.

Pete, if you're going to build one, it won't compete with the purpose built non scale gliders, so you're going to have to build two gliders now ;)


Title: Re: Bungee Launch 36" Gliders
Post by: Pete Fardell on September 04, 2017, 11:24:47 AM
Well I'll see. At least they're quick to build.


Title: Re: Bungee Launch 36" Gliders
Post by: FreeFlightModeller on September 04, 2017, 01:08:41 PM
Jon,
Shouldn't we be dialling in induced drag here too?
This is one thing that goes against low aspect ratio and is a factor to be considered I think?

I do agree that high aspect ratio wings would give some problems at 36" span though.

I opted for 9:1 with my design .... it got a 1st on the first outing at Peterborough ...
A 2nd on the second outing ....
and was trodden on the third time out!
The point I am trying to make (I think) is that you will struggle to find an efficient scale glider with an aspect ratio of 6:1,
but success can be had with something of a higher aspect ratio?
Add to this, Monique's glider flew very well and looked great in the air!


Title: Re: Bungee Launch 36" Gliders
Post by: Yak 52 on September 04, 2017, 03:01:45 PM
Jon,
Shouldn't we be dialling in induced drag here too?
This is one thing that goes against low aspect ratio and is a factor to be considered I think?

Russ, this is only the case when wing area is fixed and span is flexible. If the wing area is fixed, you can only increase aspect ratio by increasing span (which is beneficial as I said above.)

Sorry to get techy :) but the following attempts to answer the query (forgive me if it's incomprehensible - it's complex and I'm shattered :)):

It's important not to confuse the formula for the total induced drag:
(https://wikimedia.org/api/rest_v1/media/math/render/svg/8d8aa7e10ac52ad91c0d3b7dcd126bde0f948fe6)

with the formula for induced drag coefficient:
(https://wikimedia.org/api/rest_v1/media/math/render/svg/07f2238fdcc33d849103f2522a1fb020954faad1)

It's easy to see the last bit of the second formula and assume that high AR means less drag. This is the case when area is fixed and high AR means you get more span. However, where span and weight remain fixed, actual induced drag remains constant. So in a fixed span class with no area limit, low aspect ratio has no downside unless it comes with more weight.

[Mathsy bit: the first formula for Di essentially shows that you can improve induced drag by reducing weight (L in the formula) or increasing ρ (rho = air density), V (speed) or b (span). We assume speed and air density to be constant for the sake of comparison and span is fixed by the rules so all we can do to reduce induced drag is reduce weight. You can also see in the Di formula that there is no mention of area or AR.]

Its a common misconception (that I've also fallen for in the past) based on the the induced drag coefficient that low aspect ratio is bad for drag. But where the span is fixed and area is flexible it's not so :) especially in FF with no need to fly fast (as RC gliders do) in fact low aspect, large area and maximum chord is better for all round drag reduction and improved sink rate - as long as the weight doesn't creep up too. You can see this low AR optimisation in the fixed span classes such as E36 and P30.

At model scales the dominant form of drag is actually profile drag from the airfoil (actually a much higher proportion than suggested by the classical theory that minimum drag occurs where profile and induced drag are equal.) And profile drag is the one that is so badly affected by low Reynolds number ie small chords. So high aspect ratio in a fixed span class comes with a considerable profile drag penalty.

As with all things a balance is needed and I would think 5-6 is a sensible lower limit for aspect ratio. Higher aspect will still work fine and obviously good air and good trimming is a major factor but the optimum for launch height and sink rate performance will be hard to find in a scale model, lovely as they are :)


Title: Re: Bungee Launch 36" Gliders
Post by: faif2d on September 04, 2017, 03:51:40 PM
I am going from memory here but I seem to remember some data that showed sails aspect ratios as 9-1 being the best compromise to weight vs length.  Of course carbon and all sorts of new materials do away with that study from long ago.


Title: Re: Bungee Launch 36" Gliders
Post by: FreeFlightModeller on September 04, 2017, 07:21:19 PM
Quote
Russ, this is only the case when wing area is fixed and span is flexible. If the wing area is fixed, you can only increase aspect ratio by increasing span (which is beneficial as I said above.)
Jon,
I'm no expert ... and do not intend to be!

I think the discussion could get a bit cyclic (... and I'm tired too!), but I'm still not sure why the fixed span limit necessarily leads to low aspect ratio for peak efficiency?
I suppose my 'point of reference' is an A1 glider with a not massively different span still going the high aspect ratio route (I know the area rule applies).
I can imagine a 'mini me' 36" version of an A1 adopting a slightly lower aspect ratio ... but to go as far as 6:1? The 36" class has no minimum weight also ... something else in favour of a higher aspect ratio being viable?
As I say, no expert ... just an observer of the evolution of other classes.



Title: Re: Bungee Launch 36" Gliders
Post by: Yak 52 on September 05, 2017, 05:07:21 AM
I suppose my 'point of reference' is an A1 glider with a not massively different span still going the high aspect ratio route (I know the area rule applies).

The three lower aspect plans I linked to, Cirro-sonic, Corsair and Gnome have all been consistent winners in the hands of Geoff Stubbs, John Ashmole and Dave Rumball. Ian M tried a high aspect OD at one point but gave up on it in the end. He ended up with a very light P30 style wing.

This is not to say a higher aspect model can't work - the Rumball's Yard obviously did well :) But the theory and practice do point towards low aspect being optimal.


... just an observer of the evolution of other classes.

I agree it feels counter intuitive because high aspect ratio is associated with success in so many other disciplines. But the high aspect ratio is good for
- area limit with no span limit (A1, F1A)
- penetration (radio gliders, full size sailplanes)
neither of which are needed in a span limited FF class.

What is needed is a good high launch and a low sink rate (plus stability, etc)

Low aspect maximises launch height on a bungee, where a large wing area can convert the pull force to height better (high max CL - think of it like a payload competition.)

A low sink rate is achieved by
- low span loading for minimising induced drag
- low wing loading
- low profile drag from good airfoils (thin with plenty of camber)
- a reasonably large chord for higher Reynolds numbers

You are right about there being no weight limit. Obviously a low aspect ratio model will have more structure and be harder to build light. So for span loading higher aspect may permit a lower all up weight. But this has to be balanced against the wing loading and Reynolds number problem with shorter chords.

That said, Geoff's Cirrosonic is quite heavy (about 160g IIRC) and still won the Flying Aces a few times.


Please forgive me for getting too deep into theory, just trying to explain the direction my own research for the class has taken - my own 36 incher is still on the board and needs covering! It has an aspect ratio of 6  ;D but I need to turn theory into practice  ::)


Jon


Title: Re: Bungee Launch 36" Gliders
Post by: Pete Fardell on September 05, 2017, 06:40:04 AM
Don't apologise, Jon; I'm enjoying the theory this time because I can just about follow it. Very nicely explained!
With no experience of bungee gliders I shall probably just use someone else's design for my first go, but you've both given me good pointers on the sort of thing to choose.

Incidentally, my indoor Lilienthal glider goes up very easily on a running tow (never properly tried it on a bungee). Is its very low aspect ratio a factor in that? Can't say it's sink rate is overly impressive though!


Title: Re: Bungee Launch 36" Gliders
Post by: FreeFlightModeller on September 05, 2017, 07:00:53 AM
I look forward to seeing your theory put into practice Jon  :) (no sarcasm intended .... I do want to see it)

Please remember, I just thought other factors should be considered .. I'm not running up against what you are saying.
At the end of the day, a good launch is perhaps paramount.

I've been unable to enter for the last couple of years ... the numbers were rrelatively low in the glider comp this year.
If at least the three of us enter next year, then hopefully numbers will pick up again.


Title: Re: Bungee Launch 36" Gliders
Post by: Yak 52 on September 05, 2017, 08:52:23 AM
No probs Russ, I must stress that it's only my current understanding of the problem, so I welcome any further ideas, corrections etc.

The model will get finished eventually (I've got Moley gently pushing me now too  8)) the problem is that the airfoil I gave it could be better (my limited understanding at the time of designing) so it may need another wing.

One thing not mentioned is the tail surfaces - high aspect ratio needs less tail area and so there is a little less drag. It's definitely a balance of lot's of factors and matching the model weight to the bungee power is critical to the launch height. And of course something that releases high and trims nicely will do well even if on paper the sink rate is 'worse'.

Perhaps the Rumball's Yard needs a rebuild?  ;)

Thanks Pete, yes I think the low A of the Lilienthal glider helps with the good climb out. If you imagine making a high aspect model of the same span and weight that's what you'd want to compare it with.

The sink rate will be affected by parasite drag from scale struttery and bracing wires - another complication for a scale model. And perhaps the Lilienthal glider airfoil has a little too much camber IIRC. I do think a 36" Primary glider might do ok if it was built light enough?


Title: Re: Bungee Launch 36" Gliders
Post by: Pete Fardell on September 05, 2017, 11:01:41 AM
Thanks Pete, yes I think the low A of the Lilienthal glider helps with the good climb out. If you imagine making a high aspect model of the same span and weight that's what you'd want to compare it with.

The sink rate will be affected by parasite drag from scale struttery and bracing wires - another complication for a scale model. And perhaps the Lilienthal glider airfoil has a little too much camber IIRC. I do think a 36" Primary glider might do ok if it was built light enough?

You see the trouble is you've now got me thinking about building a 3ft span, bungee launched outdoor Lilienthal! Wouldn't it look great against a blue sky? That's my whole trouble- I can't ever seem to get going on sensible stuff, purposefully built to fly well, without getting side-tracked by another foolhardy scale project! ;D

(Btw, although my indoor Lilienthal has a couple of posts in the wing, it doesn't actually have any rigging. I left it off to reduce drag, but granted it does have a very cambered and unorthodox aerofoil.)


Title: Re: Bungee Launch 36" Gliders
Post by: Hepcat on September 05, 2017, 11:11:40 AM
Jon has covered the tech. stuff very well as usual so I have just a couple of graphs to contribute.  I did a paper on drag in the 2003 Free Flight Forum and at one point in the paper got around to discussing limited span classes and in particular the P30 class.   am sorry that you probably can't read any small stuff, the original paper wasn't printed all that well and my copy won't have improved things but I will try to explain.  I assumed a P30 with aspect ratio ranging from 4 to 12. A base weight is entered for the highest Aspect ratio and then an incrementof weight added per inch of chord. A base zero lift drag is entered and can be incremented and the induced drag is calculated as usual for AR.  The spreadsheet at the top of the page calculates the speed, L/D and sinking speed and calculates glide time from an assumed height of 120 feet.

The results are plotted in the graph at bottom left.  The top line is with no extra weight or drag added and the lower lines as more weight and drag are added.  As the weight increases the high aspect ratio flight time gets nearer to the low aspect ratio time.  The left hand graph is with a lift coefficient of 0.8, the graph on the right assumes a lift coefficient of 1 but even if a higher Cl could be achieved  the low AR would still be best unless the increase in weight due to low AR was considerable.

Another point, not relevant to gliders but it is to a P30 is that the power required for level flight is drag x velocity.  With a low AR, large area wing the velocity will be less and probably less power required to climb.

The 0riginal paper is seven pages.  It is probably clear enough to read if anyone would like a copy and the spreadsheet pictured in Figure 4 is useable I think.

John       PLEASE SEE A LATER POST FOR THE ATTACHMENT



Title: Re: Bungee Launch 36" Gliders
Post by: Hepcat on September 05, 2017, 11:27:38 AM
My last post got messed up and would not load the pic I wanted.  K hope I have it correct now.
John


Title: Re: Bungee Launch 36" Gliders
Post by: Yak 52 on September 06, 2017, 05:44:20 AM
Thanks John, that makes sense.Your results also seem to suggest that low aspect ratio is better as long as weight remains reasonable.

Just for my own interest I did a little analysis in XFLR5 of an A=9 and an A=6 model with full tails. Both were given the same tail volume (Vh0.76) and the same tail moment (3 x chord)

The wing with an aspect ratio of 9 has a 4" chord, the A=6 has a 6" chord.

I gave the A=9 model a weight of 80g (similar to Russ's Rumball's Yard) and the A=6 model a weight of 120g (quite an increase really.)

I tried the models with two of my own modified airfoils
- 'Polymilder' which is a thin section and particularly good at low Reynolds numbers
- A modified BE50 which is a 9% undercambered foil and more realistic for light structures

As seen in the graph below, the low aspect model had a better sink rate in all cases. When using the better lower Re foil, the gap was narrower, showing that careful attention to low Re airfoils is needed with a higher aspect ratio. But with the thicker airfoil, the gap between the models was rather more, meaning that with more practical construction the 6" chord had a big Re number advantage.

The sink rates shown don't include fuselage drag so are not realistic but even so there is a difference of about 20 seconds from 120' if put in terms of John's results.

So XFoil analysis upholds the case for low A, more obviously than I expected.

Also the lighter the model, the slower and so the lower the Re number. So perhaps weight is less of an issue for that reason also.


Jon


Title: Re: Bungee Launch 36" Gliders
Post by: FreeFlightModeller on September 06, 2017, 06:50:56 AM
Ah, but yours DTs into the top of the Ferry Meadows trees whereas  mine flys into the lower branches and lives for the next flight! ;-)


Title: Re: Bungee Launch 36" Gliders
Post by: Yak 52 on September 06, 2017, 06:57:40 AM
Too right Russ  ;D it's all about the flying in the end!


Title: Re: Bungee Launch 36" Gliders
Post by: FreeFlightModeller on September 06, 2017, 07:11:10 AM
On a more serious note ... can I provoke you into further calculations?!

Have you calculated the spectrum of input energy available from the bungee?
Also, with the heavier models needing more bungee extension ... does the consequent drag of the higher acceleration 'sap' this energy significantly.
Also (!) Does 'kiting' compensate for this?

The reason I ask is because my model seems to climb very well on the line ... usually a good launch includes  the model sinking a little before it will release. I have observed a greater sink rate compensated by a high launch height with my model when compared to other successful models.
Oooh, so many parameters, so many variables!


Title: Re: Bungee Launch 36" Gliders
Post by: Yak 52 on September 06, 2017, 09:39:14 AM
Russ,

I don't have any calculations for rubber energy I'm afraid - sad to say I used to leave that sort of thing to Ian M who would no doubt have had a spreadsheet for it  :)

From my more recent experience with RC bungee and F3-RES, I would say that the key is to match the weight to the force of the bungee. The heavier models do really seem to suffer from lower launches and need more wind. The lighter the model, the higher it can get off available energy. The 36" hi-start is of the low power/long stretch variety so kiting is always going to be the best strategy and the key will be getting the model to release under line tension. My RC glider gets 80m height off a 60m total line and pings off under considerable tension - easier with RC of course.


Jon


Title: Re: Bungee Launch 36" Gliders
Post by: FreeFlightModeller on September 06, 2017, 10:45:29 AM
No worries Jon .... it does interest me though.
In particular,  I wonder what the 'intersection point' of the data provided by John and yourself, and the maximum weight for a full height launch is ... if indeed there is one. Clumsy explanation,  but I hope you know what I mean?!


Title: Re: Bungee Launch 36" Gliders
Post by: OZPAF on September 06, 2017, 06:47:28 PM
The question of fixed span and optimum AR is an interesting discussion and Jon has covered it well. a point that Hepcat John indicated with his graphs is the effect of wing loading - or more accurately weight.

As the AR is lowered and thus the area increased then it's possible that the wing loading will reduce (even with a slight increase in weight) and the lowered flying speed and thus Reynold's numbers effect on the airfoil may then offset the gains in sinking speed.

Jon's graph high lights this as the best sinking speed is achieved with the lower AR at the higher weight of 120 gms with the best airfoil.

At the weights and sizes chosen - this would indicate that Reynold's number effect/airfoil is most important.
thus the optimum may not be the slowest model but a combination of speed, chord and airfoil.

There is another aspect of low AR which is not really relative to bungee launched gliders and that is that the actual nose pitching moment from the airfoil increases with chord. Now for a slow flying FF model at high CL that may not be a problem(it would increase the trim loads slightly) but it was most definitely when tried on 2M gliders with AR's as low as 4.5. Huge tail volumes to control the pitching moment were required when penetrating and thus were not a success due to the increased drag and extra weight.

John


Title: Re: Bungee Launch 36" Gliders
Post by: Yak 52 on September 07, 2017, 06:12:56 AM
As the AR is lowered and thus the area increased then it's possible that the wing loading will reduce (even with a slight increase in weight) and the lowered flying speed and thus Reynold's numbers effect on the airfoil may then offset the gains in sinking speed.

John, yes the XFLR5 results bear this out. The attached graph shows that reducing weight of the A9 glider doesn't help the sink rate much.

Russ, I'm not too clear on how John arrived at his results (spreadsheet is hard to read for me) and in particular if he adjusted for Reynolds number effects. If not then the differences would be even more exaggerated. XFLR5 is very good for comparison in that it models actual planforms and airfoils very accurately. It just excludes fuselages so isn't a 'real world scenario' for calculating actual sink rate.

It just struck me that since the bungee is free flight rubber (7.5m of 1/8") that John (Hepcat) may be able to use the energy density from torque calculations to give an idea of the pull force and max stretch? I'm guessing the pull force would be around 800g-1kg? I will try to remember to measure it at the next Ferry session.

I think that a max weight figure would be a bit meaningless because it would depend on the wing area of each model and because wind is such a significant variable. However there is some merit in comparing the model weight to the pull force. With RC bungees the launch begins to suffer when you start getting to pull force less than 5 x model weight. For F3-RES most models are around 1/10 the pull and my Skidoo when up very well at around 1/15th.

With the 36" there is no limit on stretch in the rules so there's an argument for stretching something like 90% of what is possible. As in motor winding, the last 10% to max stretch bumps up the pull force but actually it's the force of the long consistent pull from 90% on that matters.

There's no doubt that lighter launches higher, but this does mean finding a way to get the model off a stretched bungee at the apex of the climb.

Another factor not yet mentioned is that stiffer structures launch higher as wing bending and torsion waste some energy in the climb. So weight is not the only thing to consider. Somewhere there is a balance between launch height and sink rate.

I've also been looking into 5 panel wings with tapered planforms. There does seem to be an improvement in sink rate in XFLR5.


Title: Re: Bungee Launch 36" Gliders
Post by: Yak 52 on September 07, 2017, 06:28:58 AM
On another subject, I'm also keen to work out what the best dihedral is for 36" bungee launch. Anyone want to give details of successful models?

If you can provide the basic geometry I can work out the EDA.


Title: Re: Bungee Launch 36" Gliders
Post by: USch on September 07, 2017, 02:14:08 PM
I am following very closely this topic, trying to apply the lesson to E-36 which has the same span limit but a somewhat different speed envelope.

Jon, can you give us the 5 wing cords for your Ellipse 36 wing other than the root cord of 6,75"? And the length of the single panels.

I would like to play/use with XFLR5, but did not have the courage to open it till today  :(  How about a tutorial on a new topic???

Urs


Title: Re: Bungee Launch 36" Gliders
Post by: Hepcat on September 07, 2017, 05:30:04 PM
Response to #298.

Jon,
I was interested in your reference to EDA.  I did a lot of work on it at one time so, just keeping things simple for the moment, do you treat an even chord wing with square tips as an even chord wing with square tips or do you assume an elliptical lift distribution from tip to tip?
Hepcat John.


Title: Re: Bungee Launch 36" Gliders
Post by: Yak 52 on September 08, 2017, 06:38:32 AM
I am following very closely this topic, trying to apply the lesson to E-36 which has the same span limit but a somewhat different speed envelope.

Jon, can you give us the 5 wing cords for your Ellipse 36 wing other than the root cord of 6,75"? And the length of the single panels.

I would like to play/use with XFLR5, but did not have the courage to open it till today  :(  How about a tutorial on a new topic???

Urs

Urs,

Attached is a first attempt at a 5 panel wing at A=6. This is not yet optimised in XFLR5 in any way but it does 'perform' better that the A=6 constant chord wing on sink rate. It's drawn in metric but chords are essentially 7" root, 6" mid and 4" tip. Rib centres at 47mm (near enough 1 and 7/8".)

When you mention the different envelope for E36 are you talking about a faster climb? In that case I think there would be potential benefit in a more elliptical planform.

Happy to attempt an XFLR5 thread if theres some interest... must admit I'm just learning it myself too though!


Response to #298.

Jon,
I was interested in your reference to EDA.  I did a lot of work on it at one time so, just keeping things simple for the moment, do you treat an even chord wing with square tips as an even chord wing with square tips or do you assume an elliptical lift distribution from tip to tip?
Hepcat John.

John, I did a bit of research on the methods a few years ago but these days I just use one of two calculators:

Martin Brungard's found here: http://www.charlesriverrc.org/articles_modeldesign.htm

And the one in Curtis Suter's 'Sailplane Calc' here: http://tailwindgliders.com/Files.html

They come up with slightly different answers. If I recall correctly the Brungard one takes account of panel areas but the Suter file assumes an elliptical lift distribution.


Jon


Title: Re: Bungee Launch 36" Gliders
Post by: USch on September 08, 2017, 01:51:08 PM
When you mention the different envelope for E36 are you talking about a faster climb?

Jon, exactly. The best E36 go to 180m height in 10 seconds, not my ones (yet). Assuming a spiral climb gives about 240-250m to travel, so actual climb speed would be around the 25m/sec mark.

Urs


Title: Re: Bungee Launch 36" Gliders
Post by: Haoyang Wang on December 12, 2017, 03:00:15 AM
How strong should the tow hook mounting point be, to keep the tow hook from being ripped off the glider? A piece of balsa? Reinforced with fiberglass cloth? A piece of basswood? Plywood?

Most plans only have the tow hook position marked out, but not the specifics of the mount.

Thanks!


Title: Re: Bungee Launch 36" Gliders
Post by: FLYBOY49 on December 12, 2017, 09:31:26 AM
My FROG WREN has the hook inserted in just regular balsa.  Seems to work O.K.

However, it does penetrate the keel piece and wrap over the top of it.

Remember that the bungee is only a 1/8th" piece of rubber. Not much strain to it.

It goes up so stately that I love it.

Gotta build some more designs soon.  Like a LU LU, Gnome, etc.  Kinda wish i could include a WALKING SHOES like Jim has.  Maybe some day. But, 1st I'm building a THERMIC 'C by JASCO. I already have the JETCO model of the 'C'. I'm kinda stuck on building just LASER CUT models except for this one model 'C' which is taking forever.

Might sideline it to get started on something faster to build.

A while back I got a DRIFTY kit for a much smaller glider and had it enlarged to 36" W.S.  Have it framed up, ready to cover.  GottA 'GET 'ER DONE'.

 Van...


Title: Re: Bungee Launch 36" Gliders
Post by: Pete Fardell on May 21, 2018, 12:37:37 PM
Just reviving this thread because I'm thinking of building a glider so I can participate in the occasional bungee launch/hi-start event. Haven't done this before at all, so have been looking around for something simple. I came across the FROG Petrel, which is in the plans gallery and looks pretty and straightforward. Anyone made one? It's only 33" span so I also wondered about enlarging it to the 36" max for these bungee glider comps.


Title: Re: Bungee Launch 36" Gliders
Post by: PeeTee on May 21, 2018, 03:26:04 PM
Pete

Looks OK to me. I would probably enlarge it to 36".


Peter


Title: Re: Bungee Launch 36" Gliders
Post by: FreeFlightModeller on May 21, 2018, 04:25:24 PM
Whatever you build, it's a very enjoyable event Pete  :)
SAM35 'legal' gives access to the most events .... I would  guess the Petrel qualifies?


Title: Re: Bungee Launch 36" Gliders
Post by: Pete Fardell on May 21, 2018, 05:22:10 PM
Thanks chaps! I shall do this then (once my Fokker's finished) and enlarge it to 36". Some more glider newbie questions...
Do I need to incorporate an auto rudder and/or DT, or are they generally unecessary in this event? 

The tip dihedral looks quite extreme to me. Am I better to reduce it a bit?

Russ, will changes in size or messing with dihedral etc. make it SAM35 illegal?

 (Screen shot of the Petrel plan attached to save anyone finding it.)


Title: Re: Bungee Launch 36" Gliders
Post by: billdennis747 on May 21, 2018, 05:29:24 PM
Thanks chaps! I shall do this then (once my Fokker's finished) and enlarge it to 36". Some more glider newbie questions...
Do I need to incorporate an auto rudder and/or DT, or are they generally unecessary in this event? 
Definitely A/R and a Tomy DT which you can start when you let it go
I always enjoy my Dolphin - you get a different view of the model


Title: Re: Bungee Launch 36" Gliders
Post by: OZPAF on May 21, 2018, 06:45:50 PM
Quote
The tip dihedral looks quite extreme to me. Am I better to reduce it a bit?
My recommendation would be to leave it as it is Pete. It has a flat centre section so it will need it.

I would also recommend using 1.5mm dia. screw in cup hooks (straighten to a normal hook ) and screw them into a piece of ply(1.5mm should be enough) along the bottom instead of binding wire hooks to the fuse. This makes it very easy to adjust the position for the best tow by just having  series of drilled holes.

It's a nice looking glider and should go well at 36"WS.

John


Title: Re: Bungee Launch 36" Gliders
Post by: Pete Fardell on May 21, 2018, 07:19:03 PM
Thanks, Bill. I'll have to look properly at all the AR and Tomy DT stuff that I normally skip over! John, thanks too- I'll leave the dihedral alone then. I need to check the rules to see if the the 36" limit is measured as if the wing was flat. (I'm guessing 'yes'.) I like your moveable screw-in hook idea too.


Title: Re: Bungee Launch 36" Gliders
Post by: FreeFlightModeller on May 21, 2018, 07:36:10 PM
Pete,
Couldn't see the rules on the SAM35 website but the SAM1066 has a combined rules document linked on the left hand column.
http://sam1066.org/ (http://sam1066.org/)

Scaling is allowed.


Title: Re: Bungee Launch 36" Gliders
Post by: Pete Fardell on May 22, 2018, 03:46:35 AM
Cheers Russ. Turns out it's a little too late to be 'classic'. 1964 according to the wonderful 'House of Frog' website  http://www.houseoffrog.co.uk where I found the attached pic. It's a year older than me in fact, which means I'm not 'classic' yet either I suppose.

No matter, I shall press on with it regardless...


Title: Re: Bungee Launch 36" Gliders
Post by: FreeFlightModeller on May 22, 2018, 07:07:36 AM
I really like the look of it too, Pete ... look forward to seeing it.



Title: Re: Bungee Launch 36" Gliders
Post by: Pete Fardell on May 22, 2018, 11:41:43 AM
Although I have been mulling over what you said, Russ, about SAM35 legal models having the most opportunities.
If I do build this one though, which events over the summer have an anything goes 36" hi-start comp, preferably events with a bit of scale FF going on too. Peterborough Flying Aces, yes. I think Dreaming Spires too?


Title: Re: Bungee Launch 36" Gliders
Post by: PeeTee on May 22, 2018, 12:53:05 PM
I would go for any old 36" glider myself! The contest at Port Meadow is for any 36" span glider and the Peterborough ones are likewise - go for it!

Peter


Title: Re: Bungee Launch 36" Gliders
Post by: billdennis747 on May 22, 2018, 01:52:44 PM
The Buckminster FF gala Sept 2nd has 36" and scale


Title: Re: Bungee Launch 36" Gliders
Post by: Pete Fardell on May 22, 2018, 01:59:29 PM
Excellent- that's three times I can fly it then, and all at things I was planning on being at anyway. Better crack on with it!


Title: Re: Bungee Launch 36" Gliders
Post by: Pete Fardell on May 22, 2018, 02:28:35 PM
...things I was planning on being at anyway.
EDIT: Actually, the Sept event at Buckminster is welcome news to me. Don't think it's on the BMFA website yet.


Title: Re: Bungee Launch 36" Gliders
Post by: Hepcat on May 22, 2018, 07:04:26 PM
I thought that for the last 100 years or so if rules were being set for FF competition, duration models that it had usually been found that a top limit on the total surface area and a minimum structure weight has been the way to go. After all the years of experience I am surprised that a new class should have a major rule that the wingspan shall be a yard long.

I speak as someone who enjoys 'bunjee' launching and probably did it before anyone else who is reading this. Does anyone else remember? In the war years we could not buy rubber strip but round about the end of the war some model shops got hold of some bits of 'bunjee' cord about half an inch diameter and perhaps 12 inches long.  I got one of these and with care it could be taken apart and inside were lots of strands of 1/32" square rubber. I tied enough together to make a decent 'hi-start'.
   


Title: Re: Bungee Launch 36" Gliders
Post by: OZPAF on May 22, 2018, 07:36:56 PM
I would definitely agree John that this gives those who wish to design new models more scope, however I believe this class is well established now and possibly originated as a fun event with Peterborough MFC.

That's an interesting bit of history - lots of time, patience and careful knot tying. I was not quite up to modelling activities at that time - still crawling, not walking let alone model building :)

John


Title: Re: Bungee Launch 36" Gliders
Post by: D/T on May 23, 2018, 05:56:00 AM
Quote
I am surprised that a new class should have a major rule that the wingspan shall be a yard long

John
E36 and P30 are pretty popular, as well!
Don


Title: Re: Bungee Launch 36" Gliders
Post by: Yak 52 on May 25, 2018, 04:59:00 AM
Bit late to the party on this one - been away on a weeks climbing/sea kayaking/surfing in Cornwall :)

Don't reduce the dihedral Pete - you need all you can get. It gives you the best chance of getting up the line to the top rather than veering off and diving in  :-\

I would suggest you do use a D/T. You just need one good flight without... ::) the maxes tend to be low anyway and when you're flying in a small field on a windy day a d/t is really handy.

Autorudder does make life a lot easier. Getting a straight climb and enough turn in the glide is a challenge. You could try an offset hook though?

John's idea of cup hooks is a good one but I would say you can go much smaller than 1.5mm if necessary, the pull force of the bungee (1/8" rubber) is very low. Another simple idea is to bend a piano wire 'paperclip' and attach it with two screws for and aft. You can then slide the hook forward or back to suit. The attached pic shows the idea although its a bit bent!

The span limit on the class tends to favour models with low aspect ratio, in other words large wing area.


Title: Re: Bungee Launch 36" Gliders
Post by: Pete Fardell on May 25, 2018, 11:03:57 AM
Thanks for all that, Jon. Whilst looking for a subject, I did remember you recommending a low aspect ratio in previous discussions, so was avoiding anything with very skinny wings. With that in mind, before settling (probably) on the Frog Petrel, I was wondering about this 'Doofa' too. It's not as pretty, and the undercambered ribs and pointy tips make it slightly more complicated for my first effort in this field, but the write up with the plan in Aeromodeller sounds quite encouraging. One for next time maybe?


Title: Re: Bungee Launch 36" Gliders
Post by: FLYBOY49 on May 25, 2018, 12:21:30 PM
My 1st choice for this event was a FROG WREN.  Bob Holman has laser cut short kits for it.

I've built 2 of 'em and tehy fly a treat.

Laser cut kits are also the fastest way to build and the parts are so much better cut than I can do from scratch.

Jim O'Reilly makes the plans and both he and Bob Holman can supply both plans and short kits.

I'm currently attempting to build 2 more Thermic 'C's which are 36" W.S.
I found plans for a very rare JASCO 1944 model that is different than the popular 1946 model.  It's on my bench now, ready to cover.
Next up will be the JASCO 1946 model.
Then a 'V' tail model a shown on the 1946 kit box.

And I already have a JETCO model built many years ago.

That'l give me 4 models of the THERMIC 'C' to take to the SAM CHAMPS in October 2019 at Boulder City.

BTW: I sent a copy of the rare JASCO 1944 model to Roland Friestad, the editor of SAM SPEAKS and R/C MICRO WORLD.

He is planning to include that plan in the up coming issue of R/C M.W.

Van...
Balsa dust is absorbing,
It absorbs the troubles of the day.


Title: Re: Bungee Launch 36" Gliders
Post by: JohnOSullivan on May 25, 2018, 05:07:44 PM
I have a 36" free flight called the Squiggle. Plans are available for download at Outerzone.

https://outerzone.co.uk/plan_details.asp?ID=3758


Title: Re: Bungee Launch 36" Gliders
Post by: Pete Fardell on May 30, 2018, 08:03:03 AM
Thanks for the responses.
Before I enlarge the Frog Petrel plan, a quick question...
The rules on the Peterborough MFC website say that the 36" is measured tip to tip, and NOT flat span. Is this the case generally for these histart 36" span contests?


Title: Re: Bungee Launch 36" Gliders
Post by: billdennis747 on May 30, 2018, 08:29:55 AM
I don't know Pete but I would think Dreaming Spires will also use Peterborough rules. Are there any others?


Title: Re: Bungee Launch 36" Gliders
Post by: Pete Fardell on May 30, 2018, 09:11:32 AM
There's the Buckminster event in Sept, but I think that'll be run by John Ashmole or another Peterborough chap anyway won't it? In fact, I daresay the Peterborough rules ARE the rules as far as the UK's concerned, so shall proceed accordingy unless I hear otherwise.


Title: Re: Bungee Launch 36" Gliders
Post by: PeeTee on May 30, 2018, 09:49:47 AM
I agree Pete, the Peterborough rules are as good as any!


Title: Re: Bungee Launch 36" Gliders
Post by: RalphS on May 30, 2018, 11:08:33 AM

Hi Pete - didn't see you at the windy nats.
 
The rules on the Peterborough MFC website say that the 36" is measured tip to tip, and NOT flat span.

Isn't that the same?  Just people writing rules for their clubmates rather than for the FAI or having to subject themselves to interogation by the likes of JOD. 

Probably a similar reason for 36" span rather than some metric dimension plus area plus weight restrictions.  Mainly with the idea of using the simple 1940/50's designs they built as lads.

Ralph

Ralph


Title: Re: Bungee Launch 36" Gliders
Post by: Pete Fardell on May 30, 2018, 11:49:34 AM
Hi Ralph. Sorry to miss you. I was probably too busy breaking my models!

With a design like the Petrel, with considerable tip dihedral, I think I'll gain a few square inches of wing area if I measure the 36 inches as a gap the finished model can pass through, rather than as if the the wing was still flattened out on the board. However my aim is certainly not to extract every last advantage from the rules, but to simply end up with a model which is definitely eligible for these fun comps. So if there's any doubt at all I'll play safe and just enlarge the wing plan to 36".



Title: Re: Bungee Launch 36" Gliders
Post by: FLYBOY49 on May 30, 2018, 12:20:55 PM
NOTE TO 36" glider fans.

I recently discovered that there are 4 different Thermic 'C' designs.

3 by JASCO and one by JETCO.

I am currently building one that has a 1944 date on the bottom of the plan.

It differs from the more popular 1946 plan.

Then there are a couple different pictures of a 'V' tailed one.  One on the 1946 kit box and another reference on the 1944 plan.

Finally the JETCO one is a whole redesign with sparless wing and tail feathers that use trailing edge stock for both leading and trailing edges.

I'm gonna try to build all 4 models for the 2019 SAM Champs in Boulder City.

Side note: I discovered that the pod notches in the printed wood of the 1944 model suck muddy pond water!  So if'n ya try building one of them, plan ahead and put the notches in after gluing the bulkheads to the keel sheet.

Van...
Balsa dust is absorbing,
It absorbs the troubles of the day.


Title: Re: Bungee Launch 36" Gliders
Post by: TheLurker on May 30, 2018, 01:05:42 PM
Ahem.  The Parish Idiot has a question....

I've got about 5 yards of 1/4" flight rubber (that I found in a newsagents1) cluttering up my spares box.  Am I right in thinking that it'd be far too beefy for launching a 36" span model of about 80g-85g and that with a patched up wing?   If it is too beefy would I get away with 3/16"?


1 - One of those frozen in time2 places that you only ever stumble over when you're on holiday.
2 - Late 1967 I think.


Title: Re: Bungee Launch 36" Gliders
Post by: cvasecuk on May 30, 2018, 01:38:46 PM
I would recommend 1/8". The rules state:- Hi Start 7.5m of 1/8” rubber Plus 22.5m of line
Ron


Title: Re: Bungee Launch 36" Gliders
Post by: TheLurker on May 30, 2018, 02:00:39 PM
Evening Ron,

I should have made it clear that this isn't for any sort of competition, it's just for general mucking about and my main concern is to not overstress the patched up wing.  I take it you'd go for 1/8" for general mucking about?

Lurk.


Title: Re: Bungee Launch 36" Gliders
Post by: billdennis747 on May 30, 2018, 02:21:48 PM

I should have made it clear that this isn't for any sort of competition, it's just for general mucking about and my main concern is to not overstress the patched up wing.  I take it you'd go for 1/8" for general mucking about?
1/8" works well. The first thing I learned is that it isn't a catapult - the model more or less kites up into wind


Title: Re: Bungee Launch 36" Gliders
Post by: Yak 52 on May 30, 2018, 02:40:41 PM
Pete, yes, it's projected span after the dihedral has been built in.


Lurker,

You'll find that if you use a short powerful bungee you may get a disappointingly quick release and possible loop off the line. The long steady pull of a long low stretch bungee gives a nice 'kiting' climb. Add some wind into the equation and the forces get fairly stiff on wing spars etc. (That said a more powerful bungee gives more climb when there is no wind.)

Have a play around but more power doesn't mean more height. You just want a long steady pull that is matched to the glider weight. At your stated weight 1/8" rubber is plenty.

The real trick is getting the model to fly off the line at full height and still under tension  :)


(You could use your 1/4" rubber for catapult gliders though - 2g of rubber in a loop.)

Jon


Title: Re: Bungee Launch 36" Gliders
Post by: FLYBOY49 on June 17, 2018, 11:13:16 AM
Happy Fathers day to all.


Yesterday I picked up a small older Olds van at an impound auction for $25.00.  It has a rather nice set of tires on it and the whole thing seems very clean.  No damage at all, other than some bottled trash left inside.  Just might make a good model wagon.


Spent some time yesterday and will again today make balsa dust.  Got a 'V' tailed Thermic 'C' almost finished. 1944 version.  I already have the 1944 conventional tail model completed and the Jetco version.  So, that still leaves the 1946 versions to build. (Both conventional and 'V' tailed.) That'll give me 5 Thermic 'C's to take to the SAM Champs in 2019.


Van...


Title: Re: Bungee Launch 36" Gliders
Post by: Pete Fardell on June 17, 2018, 01:01:14 PM
I've started my FROG Petrel after printing out the plan slightly enlarged to 36 inches span.
Sides are made as are formers F3 and F4, all built over the plan. I'm slightly confused about the other formers though as unlike F3 and F4 these are not shown except as black lines on the side and top views. Are these formers meant to be built up like F3 and F4 (in which case why aren't they also drawn?) or are they perhaps simple sheet balsa rectangles cut to size using the dimensions on the side and plan views?

The instructions (attached) don't really help, unless I'm just missing something.


Title: Re: Bungee Launch 36" Gliders
Post by: Indoorflyer on June 17, 2018, 01:50:24 PM
They were probably just rectangular bulkheads on the printwood, with notched corners. F1 by itself holds the spacing of the fuselage sides, just behind the noseblock.  F2,5,6,and 7 would appear to butt up against the stripwood verticals of the sides, and the corresponding cross members. (according to the instructions, the formers go in first, then the stripwood crossmembers follow)
In Fig 1, it looks like the part labeled S1 should be S2.  There probably should be a gap between S2 and the vertical just behind it, so that former F2 can be "captured".   The plan also infers that there are 2 "S1", the bottom one is glued in place, the upper one is the "lid" to the ballast box.

That should be a pretty model, it certainly has nice lines.


Title: Re: Bungee Launch 36" Gliders
Post by: Pete Fardell on June 17, 2018, 02:05:42 PM
Thanks, I.F.- that all makes sense. I'll proceed accordingly...

(I'm so used to making rubber models, and so UNused to building gliders, that my first assumption was that the formers would have to have a hole in the middle. Presumably for the ... er ... nonexistant motor to pass through. I know. ::))


Title: Re: Bungee Launch 36" Gliders
Post by: FreeFlightModeller on June 17, 2018, 07:20:27 PM
I can't really see at the size the plan is shown, Pete .... but doesn't the isometric drawing of the nose assembly show solid formers to form a weight box?

EDIT: I realise now that you are referring to the rearward formers?


Title: Re: Bungee Launch 36" Gliders
Post by: OZPAF on June 17, 2018, 08:02:09 PM
My reading of the plans is that F1,F2 are as IF mentions to hold the nose shape and form a weight box and are solid. However F5,F6 are as indicated by the small isometric sketch near them, meant to be built up similar to F1,F2.

With no drawing for them, I don't think it would be best to install them before joining the sides. I would suggest adding the vertical legs of the formers to the inside of the fuselage uprights - before joining, but leave the horizontal crosspieces of the formers until after joining the sides as normal. The horizontal sections of F5,F6 could then be added - similar to F1,F2, over long and then trimmed back. This approach would help to avoid distorting the curve of the fuse in plan. F7 could be handled the same way.

Hope that helps.

However I must admit to wondering why formers were needed where F5,F6 are anyway. I would be inclined to leave them out!

John


Title: Re: Bungee Launch 36" Gliders
Post by: Pete Fardell on June 19, 2018, 05:09:08 AM
Many thanks for the responses. I've decided to just make the formers from doubled up (cross grained) sheet, but F5 and F6 will be there only to keep things square and will be knocked out once the cross pieces are in.



Title: Re: Bungee Launch 36" Gliders
Post by: Pete Fardell on June 21, 2018, 04:30:18 PM
The Oxford deadline has kept things moving along on the Petrel. Hopefully I'll be ready to cover it at the weekend, still giving me a few days to mess about with DTs and such.


Title: Re: Bungee Launch 36" Gliders
Post by: OZPAF on June 21, 2018, 08:25:26 PM
It almost looks like it needs a rubber motor :) In this age it is unusual to see a full fuselage and cabin on a glider but it just shows how attractive some of these designs were.

John


Title: Re: Bungee Launch 36" Gliders
Post by: FLYBOY49 on June 22, 2018, 12:55:36 AM
Looks great, Pete.

Are those landing gear in the background or training wheels, eh?

Van...
Still working on my 1944 'V' tail Thermic 'C'.  Almost ready to cover the pod.  Tail feathers are covered. Using one wing for both the 'V' tail and the conventional tail.


Title: Re: Bungee Launch 36" Gliders
Post by: Pete Fardell on June 23, 2018, 07:39:40 AM
Thanks, Flyboy.

Everything ready for covering now, so here are a couple of final uncovered shots. Weighs 27g at the moment, although I've no idea what that means (but if only it were a 3ft span rubber scale model I'd be getting quite excited!)
Really enjoying this glider lark so far.


Title: Re: Bungee Launch 36" Gliders
Post by: LASTWOODSMAN on June 23, 2018, 03:28:13 PM
Hi Pete - you guys are getting me hooked on the FROG GLIDERS,  and I am really enjoying gliders in general.

   LIST OF FROG GLIDERS in increasing size and numerical order of the pics.

1     20"     Junior  (Sailplane )
2     25"     Wren  ( twin rudder)
3     27"     Slingsby Skylark  -  my favorite
4     30"     Vespa
5     33"     Petrel
6     36"     Diana

LASTWOODSMAN
Richard



Title: Re: Bungee Launch 36" Gliders
Post by: FLYBOY49 on June 23, 2018, 07:07:43 PM
I've built 2 Wrens.  The 1st one went up in smoke when my cabin burned down a couple years ago.  But, I have another one hanging in my building room.

Both have been to Boulder City for a SAM CHAMPS contest.

I also have another laser cut kit and plans from Bob Holman and Jim O'Reilly.  So, I can build a 3rd one soon.

Van...


Title: Re: Bungee Launch 36" Gliders
Post by: OZPAF on June 24, 2018, 08:15:05 AM
The Diana looks clean and well proportioned to my eyes anyway.

John


Title: Re: Bungee Launch 36" Gliders
Post by: Pete Fardell on June 24, 2018, 09:36:58 AM
Thanks for posting the FROG collection like that, Richard. They all look nice but for me the Petrel is still the prettiest, mainly due to the slender fus. and tip dihedral I think.
Anyway, I have now covered mine using whatever was handy in my tissue box. Co-incidentally it matches the flowers in our garden quite well! The yellow is the stuff which came with my recent Eindecker kit, so I'm glad I saved it for this instead.

The plan says to acetate the top and triangular side bays just in front of the wing to make a window. I'm not sure about this though. It's not a scale model and I think it might look smarter just to leave that area tissue covered. What do people think?



Title: Re: Bungee Launch 36" Gliders
Post by: PeeTee on June 24, 2018, 09:51:48 AM
Hello Pete, I'd leave it as it is, it looks pretty good to me!


Title: Re: Bungee Launch 36" Gliders
Post by: Indoorflyer on June 24, 2018, 10:28:19 AM
I agree with you and PeeTee.  Glazing would be superfluous.
Nice pics indeed.


Title: Re: Bungee Launch 36" Gliders
Post by: FLYBOY49 on June 24, 2018, 10:38:50 AM
I, too like it as is.   Great job!

But, if'n anybody gives you a convincing argument about having windowz, just overlay this tissue with black or blue tissue and maybe add a paper cutout of a pilots head.

Or, another way is to carefully add 'em with a magic marker.

Van...


Title: Re: Bungee Launch 36" Gliders
Post by: Crabby on June 24, 2018, 10:44:35 AM
Don't do it Pete, remember, the trick is knowing when to stop don't "gild the lilly"


Title: Re: Bungee Launch 36" Gliders
Post by: LASTWOODSMAN on June 24, 2018, 11:57:48 AM
Hi Pete - beautiful pics, excellent 36" PETREL Glider !    8)    I also agree - it looks perfect as is.    :o :o

LASTWOODSMAN
Richard


Title: Re: Bungee Launch 36" Gliders
Post by: applehoney on June 24, 2018, 01:46:53 PM
Agreed - leave it 'as is'

Nice lawn ......


Title: Re: Bungee Launch 36" Gliders
Post by: TheLurker on June 24, 2018, 02:18:38 PM
Quote from: applehoney
Agreed - leave it 'as is'
Nice lawn ......
+1 on both counts. I'm very jealous of Pete's test glide area.
If real life doesn't get in the way I hope to see the Petrel for real at Port Meadow next weekend.


Title: Re: Bungee Launch 36" Gliders
Post by: OZPAF on June 24, 2018, 07:55:23 PM
Definitely leave it as it is Pete. Nice effort. Now set up the DT and go fly it :)

John


Title: Re: Bungee Launch 36" Gliders
Post by: Pete Fardell on July 01, 2018, 06:25:51 PM
Thanks to all who suggested bungee/high-start launching post wing rebuild for the Swallow; works a treat.   Had a very pleasant morning at the Oxford Club's FF rally on Port Meadow today and, after some modifications to the hook suggested by David H. who was up from Chichester, got three (by my lights) very good bungee launched flights out it, a couple in the 30s+ region and one somewhere around about a minute in some really rather awkward wind conditions. 

Also nice to meet Pete Fardell who was there with his Petrel.

Very good to meet you too, Lurks! And big thanks for your help today. That 30 second flight you timed for me was easily my best of the day. Even so, I still sneaked third by default (and this nice little trophy!) largely thanks to you electing not to hand in your own superior times- so thanks for that too! I also learned a lot from from Dave Etherton who helped me mess with it some more after lunch. I think my problems getting it to come off the line were largely due to the rubber band which held the AR line not coming off the tow hook and so keeping the tow ring on there too. He said I should really use a metal ring after the rubber band for the AR line so that it slips off the tow hook metal to metal, so that's what I'll do next time. There were other useful little tips he gave me too, probably obvious to all you non-newbies in the glider game, such as waiting for the wind to pick up before releasing. The exact opposite of scale flying!


Title: Re: Bungee Launch 36" Gliders
Post by: LASTWOODSMAN on July 01, 2018, 09:07:41 PM
Congrats on that nice little trophy Pete !   :D

LASTWOODSMAN
Richard


Title: Re: Bungee Launch 36" Gliders
Post by: PeeTee on July 02, 2018, 06:37:43 AM
Hi Pete
I watched your flights after lunch and I'm inclined to agree with Dave. He flies at Beaulieu,usually gliders, and his advice is good!

Peter


Title: Re: Bungee Launch 36" Gliders
Post by: Pete Fardell on July 02, 2018, 07:22:36 AM
Thanks Peter- I was very glad of his help and advice, and shall proceed accordingly. Hopefully I'll soon have the pleasure of walking miles in the hot sun to fetch my model and maybe even not finding it for hours!  ;D


Title: Re: Bungee Launch 36" Gliders
Post by: skycafe on July 02, 2018, 10:04:01 AM
...I'll soon have the pleasure of walking miles in the hot sun to fetch my model and maybe even not finding it for hours!  ;D

By golly, it is the definition of free flight!


Title: Re: Bungee Launch 36" Gliders
Post by: TheLurker on July 02, 2018, 01:51:34 PM
Quote from: TheLurker
... after some modifications to the hook suggested by David H. who was up from Chichester...
...thanks for your help today.

...I also learned a lot from from Dave Etherton...
Having received a great deal of help from others I'm pleased I was able to offer even a little help.  And it was Dave E who very kindly helped me out as well not Dave H.  Blame my poor heat-addled brain for that mistake.

Quote from: Pete Fardell
...I still sneaked third by default...
No, no, noo.  That place was achieved fair and square.   I didn't nominate any of my flights for timing so that trophy is rightfully yours. I also meant to say yesterday before I shot off the flights that I saw your Petrel make were beautifully stable and it looks even better IRL than it does in its publicity stills upthread.

Quote from: Pete Fardell
I'll soon have the pleasure of walking miles in the hot sun...
Keeps you fit. :)

Many thanks to the Oxford bods for running the event.  I had a great time.


Title: Re: Bungee Launch 36" Gliders
Post by: OZPAF on July 02, 2018, 08:52:07 PM
Good one Peter - now you can go and get fit!

John


Title: Re: Bungee Launch 36" Gliders
Post by: Indoorflyer on July 05, 2018, 12:28:22 AM
I think it worked!   Top secret photo of Pete F practicing for the next level of bungee launch gliders!  (from San Diego Air and Space Museum, no known copyright restrictions)     It's very easy to spend way too much time browsing the SDASM online photo albums...

HERE (https://www.flickr.com/photos/sdasmarchives/16055693016/in/album-72157649474580500/)


Title: Re: Bungee Launch 36" Gliders
Post by: Pete Fardell on July 05, 2018, 01:50:22 AM
You know how it is- you're only trying to fix a loose strut, but suddenly get CA all over your fingers...


Title: Re: Bungee Launch 36" Gliders
Post by: Indoorflyer on July 05, 2018, 02:23:21 AM
 :D


Title: Re: Bungee Launch 36" Gliders
Post by: TheLurker on July 08, 2018, 06:29:14 AM
Anyone got any suggestions, explanations or even cures for "sideways" tows?

Most of the time the Swallow tracks straight and level and lets go of the tow cleanly into a level flight, but sometimes it'll veer, always port, with a distinct bank and come off the line at a nasty nose down angle into a horrible stally, tight turning, flight from which it never really recovers.  These flights are horrid to watch and nearly always end in a harder (nose first) landing than I'd like.   Next flight out will be fine.  Puzzled and concerned by this.   It's not a problem on long grass, but the Lurker Industries Aerodrome has been mowed and is now doing a passable imitation of concrete at the moment.

Launches are into wind and, because I'm on a small field, I wait for light breeze to calm before letting go; I don't want it going too far down-range. 

I assume the problem is trimming issues with the model because the wind direction today was reasonably steady, certainly no wild backing or veering into a side-wind and I still got a handful of bad launches.


Title: Re: Bungee Launch 36" Gliders
Post by: OZPAF on July 08, 2018, 06:56:00 AM
It may possibly be the result of a towhook a little too far aft - ie too close to the CG and a slight cross wind launch.

John


Title: Re: Bungee Launch 36" Gliders
Post by: TheLurker on July 18, 2018, 02:01:14 PM
Quote from: OZPAF
It may possibly be the result of a towhook a little too far aft - ie too close to the CG and a slight cross wind launch.
Thanks for that thought.  I'll have a fiddle with it sometime this weekend.

While I'm here I'll canvas opinion on another design, the Walthew MK II, that I'm currently building.  The wing doesn't have a spar.  If the Dec '49 Aero Modeller article and the 1952 "ABC" are to be believed it flies very well without.  Except... the original AM article mentions in passing that the wing quite often warps (banana along the axis) on tissue shrinking and doping, but it (this made me smile) flies even better if this bend is symmetrical.  I have never yet had a symmetrical warp on anything I've built.  Asymmetric warps without number? Yes. Symmetrical? Hah! 

This made me wonder whether or not it would be worth dropping in a 3/32" spar on the centre section of the wing, it's a tip dihedral and the ribs are only about 1/4" deep at their deepest, to prevent this.

I'm also considering sheeting the centre panel of the wing because I have a sneaking suspicion that Eze-Doped tissue won't stand up to the elastic bands.

Opinions?


Title: Re: Bungee Launch 36" Gliders
Post by: glidermaster on July 18, 2018, 07:21:39 PM
Spar-less wings were quite common, and are certainly prone to the warping trouble your describe - i.e. the dihedral/polyhedral tends to increase. Back then I believe they were better off for dope like substances generally, and could possibly control shrinkage a little more adeptly than we can by using banana oil or low shrink dope. Some stub spars, gussets and/or sheeting in the middle bays would certainly be a wise modification, assuming you are not fanatically following the plan.
When I was young my Dad gave me some old rubber and Jetex models that were of the spar-less wing type, and my memory is that they used harder material than we might choose today, for the leading and trailing edges.


John


Title: Re: Bungee Launch 36" Gliders
Post by: TheLurker on July 19, 2018, 12:35:43 PM
Thanks for those thoughts John.

...assuming you are not fanatically following the plan.

I had hoped to build it according to the plan as published, but there's no point being dogmatic about it if the result is unflyable; that'd just be a waste of wood, time and tissue.  So it looks like it's going to be the world's first Walthew MK IIa.  After all we must never let it be said that The Lurker Industries Aviation Company isn't at the cutting edge, even if the design is 70 years old. :)


Title: Re: Bungee Launch 36" Gliders
Post by: TheLurker on July 21, 2018, 04:08:46 PM
As discussed one part finished Walthew MKIIA wing.  

I'm going to try cutting the spar at R4/R13, so that the centre section spar'll extend to R5/R12, and the panels R4/5 and R12/13 will be spar-less.

If you're even vaguely interested; wing build images starting here (https://www.flickr.com/photos/[email protected]/43541664701/in/album-72157698412359154/)

Haven't had a chance to muck around with the tow hook on the Swallow yet, too busy sitting in a pub garden today.


Title: Re: Bungee Launch 36" Gliders
Post by: LASTWOODSMAN on July 21, 2018, 05:51:06 PM
Nice pics of your model Lurker.   :)   Looks like you have a nice and neat building area    8)  - what type of building board do you use and what are the dimensions ?

LASTWOODSMAN
Richard


Title: Re: Bungee Launch 36" Gliders
Post by: OZPAF on July 21, 2018, 08:46:51 PM
Like your little notes as well Lurk. Shouldn't they have the Lurker Industries Logo on them? :) Something like a hat with wings? :)
It looks like you are running the spar from tip to tip but you mention in your post that you will be leaving 2 panels spar less? I would leave it as you have shown - that is a delicate wing!
Clean work - Lurker Industries must employ more sweepers than actually builders :)

John


Title: Re: Bungee Launch 36" Gliders
Post by: TheLurker on July 22, 2018, 04:12:48 AM
Quote from: OZPAF
I would leave it as you have shown - that is a delicate wing!
Aye, it is delicate and I think I'd advise fitting a spar to this wing regardless of potental warping issues, ditto not butt-jointing the ribs to the L.E & T.E.

Unfortunately it can't be left as is.  The wing has to be cut outboard of Rs 5/12 to set the dihedral, see the sketch.   I built it as it is so that I'd get a good alignment on the spar.

I haven't worked out a neat way of covering the gap over panels R4/5 & R12/13.  There's no a lot of wood to play with in the ribs and I fear that taking any more out of them would weaken them a bit too much.  Had the ribs been meatier I'd have moved the spars on the outboard sections forward/back by the width of the spar, doubled the spar slot width on Rs 4/12 and overlapped the central spar and outboard spars at Rs 4/12.   As it is I'm hoping that the fairly beefy ply dihedral braces on the L.E. & T.E. that extend into panels R4/5 & R12/13 will counteract any tendency to increase in dihedral caused by tissue tension.  We'll shall see.

Quote from: LASTWOODSMAN

... a nice and neat building area

Quote from: OZPAF

....employ more sweepers than actual builders.

Neat work space? Oh that's dreadfully easy.  Work on the dining room table and set it up and tear it down at the beginning and end of each session.  Rules, tools etc. packed into a couple of boxes.   On the other hand my study, which is where I do paid work, is a little *ahem* cluttered.  It doubles, quintuples?, as my office, library, wood store, cycling kit store and hangar.

Quote from: LASTWOODSMAN

...what type of building board..

The building board is 36" x 20".  Half inch cork over 3/4" pine.  Pine from my local DIY warehouse.  Cork from Cantrill, details here. (http://www.hippocketaeronautics.com/hpa_forum/index.php?topic=22277.msg227769#msg227769)


Title: Re: Bungee Launch 36" Gliders
Post by: OZPAF on July 22, 2018, 08:39:15 PM
Quote
As it is I'm hoping that the fairly beefy ply dihedral braces on the L.E. & T.E. that extend into panels R4/5 & R12/13 will counteract any tendency to increase in dihedral caused by tissue tension.  We'll shall see.

I don't think I would trust the braces at the LE and TE to do that. There may be a stress riser at the inboard end of the tip panel spar as well. How about leaving the tip panel spar continuing to the dihedral break rib and adding gussets between the spar and the dihedral rib on the tip and centre panel joins, much he same as the centre spar carry through on the KK ELF. Together with the braces this should be reasonable, without much extra weight.

Anyway happy building.

John


Title: Re: Bungee Launch 36" Gliders
Post by: TheLurker on July 23, 2018, 04:14:02 AM
Quote from: OZPAF
How about leaving the tip panel spar continuing to the dihedral break rib...
Hmmm.  That sounds like a much better idea.  I shall nick it and pass it off as my own.  :)

I can see it being a bit of a fiddle to cut the spar without breaking it and losing too much wood at the cut, but got to be worth a try.   If it comes to it I can resort to one of the bodges I'd considered, but discounted on grounds of weight and general ugliness, of putting in a short "stand-alone" spar supported by gussets either end or a strip of 1/16" x 1/8" as an "I" beam.


Title: Re: Bungee Launch 36" Gliders
Post by: OZPAF on July 23, 2018, 05:47:52 AM
Glad it helps, Lurk. You shouldn't have much trouble getting the spar length correct. Bevel the LE and TE to suit the dihedral angle before adding the tip spar. Then bevel it separately using a gauge and add it to the wing.

Again I had to do something similar on my still unfinished KK Elf - apologies Andrew D, who sent me a clean accurate plan.

Happy building.

John
 


Title: Re: Bungee Launch 36" Gliders
Post by: TheLurker on July 24, 2018, 12:55:12 PM
Well that went better than I had any right to expect.  Tip dihedral set.  Now for the really difficult bit, getting a decent L.E. profile. :)

If you're considering building a Walthew MKIIA wing, i.e. with a spar, I'd suggest that the wing is built in three parts*.  The central section and the two outer sections. This will require 18 ribs rather than 16.  Set the dihedral on the inmost ribs of the outer sections and glue the sections together at the rib faces.  This will mean you don't need the ply dihedral braces, but you may want to add bracing gussets at L.E. and T.E.  A 3 section wing will be very much quicker to build than the approach I've used.

For those morbidly fascinated by people doing things the hard way the dihedral set up for this build begins here. (https://www.flickr.com/photos/[email protected]/43567007042/in/album-72157698412359154/)

After I've got the build out of the way I'll draw up a 3 section wing plan and stick it in the gallery together with any notes of archaeological  interest uncovered on this "dig".

*ABL.  You were right.  It would have been easier.


Title: Re: Bungee Launch 36" Gliders
Post by: applehoney on July 24, 2018, 02:25:35 PM
>Set the dihedral on the inmost ribs of the outer sections and glue the sections together at the rib faces

May I suggest you set the end ribs of the center section, and the inner end ribs of the tip panels, at 50% apiece of the overall dihedral angle?   I've built many glider and gas models wings in this manner with no in-flight failures.  In the event of an unfortunate impact with terra firma a broken-off tip is usually a clean separation without spar, LE and TE damage


Title: Re: Bungee Launch 36" Gliders
Post by: OZPAF on July 24, 2018, 08:45:45 PM
I'm glad it worked for you. It's all very old hat but I only realised how it well it works when building the ELF.

AH raises a good point from his long experience but perhaps the gussets may help in your case as you only have a sliced rib of very shallow depth for this model.

I would prefer taking AH's approach with double ribs butt jointed together in future builds for the easier repair.

John


Title: Re: Bungee Launch 36" Gliders
Post by: TheLurker on July 25, 2018, 02:25:16 AM
AH > ...at 50% apiece of the overall dihedral angle...
A good idea, if you're a better builder than me. I have enough trouble getting one piece of wood sanded to the right angle never mind two. :)

OZPAF > ...double ribs butt jointed together...
That's what I thought I'd described, or were you querying the suggestion of gussets with butt-jointed ribs?  Note to self: Mustt lern to rite betterer inglish. :)



Title: Re: Bungee Launch 36" Gliders
Post by: OZPAF on July 25, 2018, 05:03:16 AM
My apologies - I just didn't read your description of the MK 11A wing! Nothing wong wit wot yu rote!

However as doing this relies on the area of the butted ribs to transfer the load it may nor be strong enough for this model.

Quote
Insert Quote

AH > ...at 50% apiece of the overall dihedral angle...
A good idea, if you're a better builder than me. I have enough trouble getting one piece of wood sanded to the right angle never mind two. Smiley

Use a dihedral gauges to guide your sanding block and it will be ok.

John


Title: Re: Bungee Launch 36" Gliders
Post by: TheLurker on July 25, 2018, 03:37:49 PM
OZPAF > However as doing this relies on the area of the butted ribs to transfer the load it may nor be strong enough for this model.

Aye, a possibility, but as I wasn't able to get near my building board today I scratched out plan for the B (3 section) wing as outlined above anyway, rather than the A "cut and shut with a spar" variant that I've built.  It's especially for those reckless souls who fancy their chances with a completely untested "design".   Paging Mr. Fardell, paging Mr. Fardell. Will Mr. Fardell please go to the green courtesy telephone by the elephant trap. :) 

The B construction variant'll turn up in the gallery in due course.



Title: Re: Bungee Launch 36" Gliders
Post by: TheLurker on August 28, 2018, 04:21:47 PM
Well, the Walthew MK II (A) flies.  Lovely and calm this evening so grabbed an hour this evening to see how it'd go off a bungee. The first couple of launches were low power affairs.  There's quite a bit of room for improvement; current endurance is no better than 15s and I need to undo some of my trim *ahem* improvements that I made and tinker with the forward hook because on higher power launches it's hanging on to the hook and losing some height as a result.


Second, short stretch, launch :  linky (https://www.flickr.com/photos/[email protected]/44329323831/in/album-72157698412359154/)
Hanging on to the hook:  linky (https://www.flickr.com/photos/[email protected]/43424398635/in/album-72157698412359154/)


Title: Re: Bungee Launch 36" Gliders
Post by: billdennis747 on August 29, 2018, 02:14:40 AM
Just bend the hook down till it comes off easily


Title: Re: Bungee Launch 36" Gliders
Post by: TheLurker on August 29, 2018, 02:23:43 PM
Quote from: billdennis747
Just bend the hook down till it comes off easily
That's the plan, such as it is, but the parish idiot didn't take any pliers with him last night did he?  Really, what kind of an unthinking clot, knowing minor tow-hook fettling is likely to be necessary, doesn't take a couple or pairs of pliers with him for the first launches?  That last Q. was rhetorical, in case it's not obvious. :)


Title: Re: Bungee Launch 36" Gliders
Post by: billdennis747 on August 29, 2018, 02:39:04 PM
Quote from: billdennis747
Just bend the hook down till it comes off easily
That's the plan, such as it is, but the parish idiot didn't take any pliers with him last night did he?  Really, what kind of an unthinking clot, knowing minor tow-hook fettling is likely to be necessary, doesn't take a couple or pairs of pliers with him for the first launches?  That last Q. was rhetorical, in case it's not obvious. :)
Well nor did I but fingers and brute force work too, unless the hook is 14swg!


Title: Re: Bungee Launch 36" Gliders
Post by: Indoorflyer on August 29, 2018, 03:12:28 PM
Always use precision tools around aeroplanes large and small. An automobile door jamb and a tire changing iron will provide the necessary bending forces required...


Title: Re: Bungee Launch 36" Gliders
Post by: Pete Fardell on September 10, 2018, 06:36:52 AM
I'm really enjoying following your adventures with the Walthew, Lurks.

I made some pleasing progress with my Frog Petrel at Peterborough yesterday. To start with it was sometimes going up well, but then either not coming off the line or else coming off but flying poorly. Eventually though, some slight change to nose weight and a shim (actually a grass stalk) under the tailplane suddenly sorted it out. What really helped too was that after getting fed up with messing with fiddly bits of thread, and suspecting the wind was lifting the tail from the fuselage, I simply abandoned the AR and DT and just made sure the tail was banded down properly and the rudder fixed straight. It then got very high on the line which was very exciting for me to watch (in a completely different way to watching a rubber scale model's flight).
Anyway, best flight was 26 seconds which is hardly world beating I know, but it looked pretty good in the air and with its other two contest flights that was enough for second place on the very blustery day. The event was won by one C Costa from Portugal, who was here as a guest of Júlio Isidro (long time regular Peterborough vistor and TV star). From what was said at the prize giving I understand Mr Costa, now in his eighties, is some kind of freeflight champion so I was very honoured to be beaten by him!

I not only got one of Russ's nice certificates but, after the prizes proper had finished, Hi-Start instigator Dave Rumball sidled up in the manner of Private Walker and quietly handed me this framed AM cover poster to encourage me further in Hi-Start and, he said, just because he'd really enjoyed watching the Petrel's flights. What a gent!


Title: Re: Bungee Launch 36" Gliders
Post by: TheLurker on September 10, 2018, 01:52:43 PM
Quote from: Pete Fardell
...the Walthew...
[JoeWalker]
Psst, wanna plan?  Cheap.  No rubbish; honest.
[/JoeWalker]

Quote from: Pete Fardell
...best flight was 26 seconds...
Sounds like a very respectable time to me given how windy it was yesterday.  Seeing how blustery it was here yesterday I'm surprised that anyone got any flying in at all.

Quote from: Pete Fardell
...handed me this framed AM cover poster...
I'm rather jealous of that. :)


Title: Re: Bungee Launch 36" Gliders
Post by: LASTWOODSMAN on September 10, 2018, 10:22:37 PM
 Congratulations Pete !    8)
     Regarding Pete's nice framed AM cover poster prize,  in reply  #395 above, for 2nd place in the Bungee Launch 36"  glider category - are there any old time glider modeller experts who would be able to identify the two gliders on the cover, what size they were, were they kitted, and what plans ?   Those look like two perfect "old time" gliders, that I would like to build one thereof, this winter.  Thanks for any help.

LASTWOODSMAN
Richard


Title: Re: Bungee Launch 36" Gliders
Post by: applehoney on September 11, 2018, 09:40:35 AM
Just a generic painting, Richard.