Moulded Supra wing layout

[POF]

I already got myself a moulded Supra from Vladimir. I’m thinking about getting one more for backup but I’m not sure what layout I need.

I guess that a Fiberglas wing is too soft while I often fly in windy conditions. The Supra I fly today is a carbon wing. I didn't have any troubles with that until now but it seems a bit soft in an f3j start and on the winch. Maybe it's not a problem…

Usually carbon wings are stiff and will not give much of a warning before breaking. Isn’t this true?

I noticed that the Supra comes with a Kevlar wing at the same price of a carbon wing, but I'm not really sure what to expect from Kevlar. Could anyone comment on that please?

My carbon Supra is about 1980g and that is ok, but I would like my Supra #2 not to weigh more than this.

[POF]

When seeing how many that has been able to answer my questions, it seems like I have to ask in more general terms. :o

Is it true that kevlar is softer than carbon if used as skin?
Is kevlar stronger and therefore lighter than carbon?
I have never heard about a kevlar main spar (except when wrapping). Is this because carbon is stiffer than kevlar?
Does anyone have a link to somewhere where kevlar ad carbon is compared?

I hope someone is able to help me on this. I have noticed that kevlar is often used in vacuum bagged wings.

[Kiesling]

Kevlar has a very low compressive strength and does not make a good spar cap material. I would go so far to say it would be disasterous if used in a spar cap.

Kevlar's specific stiffness is higher than glass, but not higher than carbon fiber. The tensile strength is generally comperable to carbon, but its specific tensile strength is generally higher (depends on the carbon fiber).

So in cases where absolute torsional stiffness is not required and compression failure is not a problem, such as in an F3J wing, Kevlar is a good choice for a wing skin. My Kevlar Supra was about 2 ounces lighter than the carbon versions, but 2 ounces heavier than the glass versions. This has to do with the weight Kevlar used in the skins. The Kevlar skinned Supra was plenty stiff in torsion for hard F3J tows. I would have preffered it to be stiffer in bending - but this is more a function of the amount of carbon in the spar than the material used for the skin.

Hope this helps.

Tom

[POF]

Thanks Tom. Good input.

So if I want a light stiff wing a kevlar/carbon (mix) would be a good choice?

[Kiesling]

I used a 60 gram/m^2 carbon/Kevlar hybrid cloth on my bagged Supras. The main reason I chose this material is that it was sufficiently stiff for the entire wing. Therefore I did not need to deal with the added complication of adding extra layers of material to the skin in various places such as the control surfaces. One could also use 60 gram/m^2 carbon. It is more expensive, but will yield a wing that is stiffer in torsion. I did not use this material because of availabilty and cost.

Going to an all Kevlar skin is the lightest solution with appropriate stiffness. It requires the use of lighter cloth (1.7 oz/yard^2 and 1 oz/yard^2) and using appropriate doublers in the center panel and carbon doublers on the control surfaces.