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Author Topic: Bungee Launch 36" Gliders  (Read 34422 times)
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skyrocket
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« Reply #125 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...
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applehoney
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« Reply #126 on: October 20, 2013, 12:50:35 AM »

I admire and envy your productivity, Dave !
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skyrocket
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« Reply #127 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...
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applehoney
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« Reply #128 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
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skyrocket
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« Reply #129 on: October 22, 2013, 10:36:51 PM »

Here's what she looks like before I start covering the little beast...
Attached files Thumbnail(s):
Re: Bungee Launch 36" Gliders
Re: Bungee Launch 36" Gliders
Re: Bungee Launch 36" Gliders
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applehoney
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« Reply #130 on: October 22, 2013, 10:56:25 PM »

Nice slim lines, Dave.

The model ........   
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craig h
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« Reply #131 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...
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Yak 52
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« Reply #132 on: October 23, 2013, 03:11:41 PM »

Looks great Dave, what's the weight before covering?

Jon
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skyrocket
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« Reply #133 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.
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FreeFlightModeller
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« Reply #134 on: October 23, 2013, 05:33:52 PM »

Nice looking model Dave  Smiley

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?
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Yak 52
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« Reply #135 on: October 23, 2013, 05:53:47 PM »

Russ, Geoff's Veron Cirrosonic is 170g and it's won the Aces twice Smiley 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?
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« Reply #136 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.
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lincoln
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« Reply #137 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)
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« Reply #138 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.
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PeeTee
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« Reply #139 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
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carpetbagger
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« Reply #140 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.
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skyrocket
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« Reply #141 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...
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applehoney
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« Reply #142 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!

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« Reply #143 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
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lincoln
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« Reply #144 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.
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skyrocket
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« Reply #145 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.
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PeeTee
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« Reply #146 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  Wink 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
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skyrocket
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« Reply #147 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.
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Yak 52
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« Reply #148 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
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« Reply #149 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
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