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Author Topic: Bungee Launch 36" Gliders  (Read 35590 times)
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Russ Lister
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« Reply #200 on: April 18, 2014, 07:02:39 PM »

Looks great Jim  Smiley
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Dave Andreski
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« Reply #201 on: April 18, 2014, 07:19:05 PM »

It sure does!
Nice one Jim.
Don't lose 'er.
Dave
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« Reply #202 on: April 19, 2014, 08:09:30 AM »

Really nice looking Jim...can't wait to see her at Geneseo...
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« Reply #203 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....
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spearfish99
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« Reply #204 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
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« Reply #205 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...
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spearfish99
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« Reply #206 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.
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« Reply #207 on: June 14, 2014, 04:19:39 PM »

Hi all, is there a formula for the area of the fin on these models?

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Yak 52
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« Reply #208 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.
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« Reply #209 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

I think I'll go with TLAR Wink
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lincoln
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« Reply #210 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.
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« Reply #211 on: June 15, 2014, 08:32:09 PM »

>think I'll go with TLAR  Wink

Hmm ... the  bikini, too .......    Cool
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« Reply #212 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...

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« Reply #213 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 Grin!
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« Reply #214 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.
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« Reply #215 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   :-)
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« Reply #216 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...
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« Reply #217 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. Grin
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« Reply #218 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).
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« Reply #219 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.
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« Reply #220 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
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« Reply #221 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
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« Reply #222 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.  Grin
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« Reply #223 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.
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« Reply #224 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...
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