Bungee launch on foam board wing.

[Motobiman]

Hiya.
Newbie to foamboard wings here, but I used to fly a lot until health and age intruded.
I have been building a few models from the range.
Has anyone tried a bungee launch on a model with the ‘standard’ folded foamboard wing structure?
AndyC UK

 

[Hai-Lee]

I have been doing so for many years now.
See:- https://forum.flitetest.com/index.php?threads/the-best-20-i-invested.53587/

have fun!

 

[Motobiman]

Heh thanks.
Can you enlarge on the towhook position please?
Is it 60 percent FORWARD of the distance between the nose and CoG?
My experience is with carbon fibre spars and very strong wings where the idea is to get to altitude as quick as possible so the rate of climb is very steep and the forces on the wing very big.

 

[Piotrsko]

Rule of thumb: the closer to the actual CG the hook is placed, the higher it will climb. The faster it climbs, the more you will break the wings. A good starting place is the hook should be a 2 thumbs width or three forward of the cg point. @Hai-Lee suggests also only 5 times the weight of the plane is a good starting point for the pull force of the bungee. Ie: if your plane weighs 2lbs you should have < 10 pounds of pull from the launch system. A low launch is preferred to broken wings. Btdtmo , baby steps.

Edit: resist adding up elevator during climb, that breaks wings too.

 

[Motobiman]

Thanks for the input.
My experience of bungee launch is limited.
The club announced evening comp and I built a modified Finger Vee and Bird of Tme.
The Finger Vee with carbon spars and alloy/ply composite joiner was fine on the club bungee, climbing pretty much vertically on the rig that was quite a lot stronger than the one I made up for practice.
The BoT built to plan with spruce spars failed on the first launch, hence my question and concern.
The foamboard models are so quick to build I guess I can afford the time to experiment a bit.

 

[Hai-Lee]

you should know that the launcher does not provide a glider "high start" as it is more like a catapult to get the plane off of the ground and at flying speed, (as on a carrier catapult system).

The model must not have the motor running until after the towline has fallen clear of the plane or it may tangle the launcher cable and convert the launcher into an arrester cable.

finally you can build asmall launch ramp for the launcher but it works just as well without one.

have fun!

 

[Motobiman]

Thanks.
I am thinking gliders specifically and foamboard winged at that.
So I guess a low powered hi-start is what I am after.
Maybe 4mm or even less will do it,
The models generally weight about 350grs so very little power needed to get them away.

 

[Jackson T]

I high started my sister's stock simple soarer with either 4 or 5mm surgical tubing and 50m fishing line. I launched it pretty hard and got the full high start length of altitude, but folded the wings on about the 10th launch. I guess if you take it back a notch and accept less altitude it should handle it (at least for more than 10 launches). I'm sorry to hear about you Bird of Time, they look like a nice glider. Do you remember how big the spar caps were and the spacing between them?

 

[Motobiman]

I high started my sister's stock simple soarer with either 4 or 5mm surgical tubing and 50m fishing line. I launched it pretty hard and got the full high start length of altitude, but folded the wings on about the 10th launch. I guess if you take it back a notch and accept less altitude it should handle it (at least for more than 10 launches). I'm sorry to hear about you Bird of Time, they look like a nice glider. Do you remember how big the spar caps were and the spacing between them?

Thanks for the info.
So its not too onerous to put ply or CF spars into the foamboard wings, even as a retro mod, but let’s face it making a new wing is only half an hours work anyway.
I was thinking 4mm so your experience is valuable.

The Bird of Time was from a short kit so the wing was stock design.
I narrowed the fuselage for SD100 servos and lightened the tail a bit as I HATE lead in the nose.
It was built as a lightweight thermal for a club competition so on reflection (hindsight being the exact science) probably needed CF spars for hi-start.

The Finger Vee with MH32 section instead of Clark Y, a narrowed fuselage to minimise drag and with SD100’s (my favourite servo for small stuff) and tail surfaces built up from carefully selected balsa was an awesome flyer.
One of the best traditional balsa glider designs I built.

I’ll dig an image out.

 

[Motobiman]

Old design, still works well.

 

[Piotrsko]

Bird of time was notorious for having weak as noodle wings back in the '80s. You could box the spars with balsa and a plywood joiner front and aft, but imho the spars are just too small for the wing. I believe arrow shafts fit nicely. The notable things were the shape of the wing and that it dwelled after launch and it was cheap for a big wing plane.

 

[Motobiman]

Bird of time was notorious for having weak as noodle wings back in the '80s. You could box the spars with balsa and a plywood joiner front and aft, but imho the spars are just too small for the wing. I believe arrow shafts fit nicely. The notable things were the shape of the wing and that it dwelled after launch and it was cheap for a big wing plane.

Now he tells me. 🤪
It flew nicely off a towline and often found lift when no one else was.

 

[chrisvdv]

See this thread from @CarolineTyler

Bungee catapult ... where do I put this build thread???

 

[Motobiman]

Thanks but would a foamboard wing withstand the stresses of a catapult launch?

 

[chrisvdv]

@Motobiman that's why i send you the thread, @CarolineTyler is from the UK and the thread describe her build as she fly mainly foam board planes.
https://forum.flitetest.com/index.p...do-i-put-this-build-thread.58502/#post-472823

 

[CarolineTyler]

I don't actually build/fly many foamboard planes currently. I have progressed to EDF jets and iNav FPV planes.
This is some of my current models...

 

[Motobiman]

@Motobiman that's why i send you the thread, @CarolineTyler is from the UK and the thread describe her build as she fly mainly foam board planes.
https://forum.flitetest.com/index.p...do-i-put-this-build-thread.58502/#post-472823

Yep I saw that thanks and read it.
Maybe I should clarify.
I reckon gliders use bungee/hi-start whereas that post is about bungee/catapult.

 

[skymaster]

I don't actually build/fly many foamboard planes currently. I have progressed to EDF jets and iNav FPV planes.
This is some of my current models...
View attachment 208938

I don't actually build/fly many foamboard planes currently. I have progressed to EDF jets and iNav FPV planes.
This is some of my current models...
View attachment 208938

wow nice set of birds. are they scratch builds?

 

[CarolineTyler]

wow nice set of birds. are they scratch builds?

Mainly not, I tend to buy the base kits which require full assembly and choose my own electronics to fit as I find the RTF and ARTF tend to put in the lowest workable quality parts.
None of my planes are flying stock

 

[danskis]

Some random thoughts. For a true glider high start you may be able to just reinforce only the center section of the wing. For warbirds I've simply glued bbq skewers to the foam spars. It seems to help a lot. Depending on how thick your airfoil is (assuming you have dihedral in the middle of the wing) you can get the skewers to go full length. Alternatively, I've been using 1/32 plywood a lot. You can cut it with a scissors. This could work as reinforcement glued to both sides of the foam spar.