BMatthews has it nailed.

The models can go very fast indeed. I recently saw a 2-meter Opus sailplane clocked at 232MPH with a radar gun. A few moments later the wing exploded. Seriously.

What is needed is a very low camber, very thin airfoil. What is also needed is a VERY strong wing. Not only does the spar (or spars) need to be very strong, but the skin must also be very stiff. Full carbon skins are almost a prerequisite.

The problem is that the models simply are not strong enough and something starts to flutter somewhere... and then you have carbon confetti. The thinner the airfoil, the stronger the wing needs to be to maintain bending and torsional stiffness. Most sailplanes, even those "made for DS," are not up to the task, IMHO.

-David