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ragflyer

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Joined
Apr 17, 2007
Messages
361
...maybe you should change your name to wantodesign :)...while it can definitely be done its a lot more involved than just adding some carbon bid to the spar web. Almost anything can be engineered, but the question is what is the trade off. I don't want to dissuade you (its experimental aviation after all) but you have some design work to do upfront or you can build as you say and test fly and tweak in the old tradition of the pioneers with some very obvious risk to limb and life. Its been done many times and I believe the UL rules still permit you to do that. Your choice!

A few points:

1. the wing as designed handles some twist (about cm = -0.1) due to the camber in the airfoil. Only symmetrical airfoils induce no twist. Adding ailerons increases this about 3 fold.

2. The wing twisting as designed is reacted by the leading edge wing connection which in turn is reacted by the D nose- 0.8mm nose ply and the back of the shear web which for most part is foam. All these components need to be checked to see if they will take the additional torques. Adding (very stiff) carbon bid to the spar web is only one part of the load chain.

3. Carbon bid is about 10,000 to 30,000 times stiffer than foam and 10 to 30 times stiffer than wood. This means it will take all the shear load in the spar rather than the foam and will need to transfer it to the wood caps. If you wrap it around the spar caps then it will see significant bending stress (Billski has posted this out many times). It may be fine but you will need to do check.
 

wanttobuild

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Joined
Jun 13, 2015
Messages
817
Location
kuttawa, ky
Ragflyer, thanks for that helpful information.

I have confidence in the spar, I don't want to change the way its loaded, although I would like to see the caps attached to the web with some mechanical bond in addition to resin bond, but it has a large bonding surface.
So it is good to go for Ailerons with Carbon skins.
OBTW, Toray has got some amazingly thin carbon uni, .0004!, No Crimp. Now that is stiffness without weight!
 

wanttobuild

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Jun 13, 2015
Messages
817
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kuttawa, ky
btw it would be great if you can post the calculations from the FB site... I for one stay away from FB
Complete analysis, but I can't post here on HBA. Maybe Matthew would be so inclined, I would like for you to see it.
I can download and email if u have an address
 
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Protech Racing

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Joined
Jul 10, 2020
Messages
435
You can’t mix spar material. The stiffest will take all of the load and if insufficient, will fail.
The Pup has many flying . It flies well. I would try it per plans first and go from there.
I am using spar mounted spoilerons on my plane but have not flown it yet . It should produce minimal twist on my foam wing.
 

wanttobuild

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Jun 13, 2015
Messages
817
Location
kuttawa, ky
Carbon wing skins on the outer panel bonded top and bottom to the caps will provide plenty of support for 7ft. long 25% differential ailerons.
The pilot reports I have read say it is crosswind challenged. Ailerons are the only logical choice to try and stay on course.
I have learned alot in this thread.
 

wanttobuild

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Jun 13, 2015
Messages
817
Location
kuttawa, ky
one question comes to mind, about the location chord wise of Junker style ailerons.
Why can't Junker style ailerons be located underneath the spar, @ 25%?
 

Groundhog Gravy

Active Member
Joined
Apr 20, 2019
Messages
31
If the goal is to be able to handle crosswinds, this seems like the hard way to go about it. Would a HiMax be a suitable substitute? It's a bit more complicated, sure, but not more complicated than doing what you're talking about.

Side note: I have not heard good things about the Polini 202cc's reliability.
 

Protech Racing

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Jul 10, 2020
Messages
435
Monster adverse yaw . So much so that it was no fun to fly . You would need to eliminate almost all down travel .
 
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