Here's the key thing: Glider structures are bound more by stiffness than by strength. True, pre-pregs can be much stronger than more conventional laminates. However, they allow only a rather modest premium in stiffness.

Think of it like this: Suppose you have a magical material to make wing spars out of that just as stiff as what we use now, but is is twice as strong. Then you use half as much. The result is that you'd have twice the wing deflection per unit g. Your new wing at 2.5g looks like your old one at 5g. And 4g looks like 8g.

That might work out OK, and it would have a pretty soft ride, but the aero effects can be unpredictable, and it gets pretty hard to make control surfaces that work smoothly while following the curvature of a g-bent wing.

Furthermore (and probably much more importantly), stiffness is much more important than strength when mitigating elasticity. So you'd end up using way more of your magic material than dictated by strength just to get the stiffness up where you need it to have Vne with a usable margin against flutter..

And, as others have already touched on, extra mass often results in a structure that is more resistant to handling, assembly, and operational damage. And gliders aren't much fun unless they are operational.

The full sermon on these topics runs around an hour. If you want the whole thing, come to our 21-27 January 2017 Akaflieg:

https://www.facebook.com/events/335703193452266/

Thanks, Bob K.
https://www.facebook.com/pages/HP-24...t/200931354951