Thud 105 glider VNE is often limited by wing or control surface flutter, which is a true airspeed limit if i remember my basic bearodynamics. Some gliders can increase their VNE by mass balancing some control surfaces and is done on gliders that are likely to cruise at high speed in wave. I'm not sure when a critical mach number might become relevant, but these guys have taken all those aerodynamic challenges and designed a glider capable of 90, 000' a truly amazing achievement compounded by finding the suitable meteorology and the pilot skill to bring it all together. I understand the really high flight will involve soaring making use of the polar vortex, way beyond this bears limited understanding
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Last edited by bad bear; 10th Sep 2017 at 19:07.