Possibilities of High Altitude Flutter During Wave Flights.

Normally, flutter is not a concern for type-certificated sailplanes if they are operated within their approved limits. However, in high altitude flight a transgression of these limits can happen. This paper is intended to inform pilots about the conditions and consequences of flutter. The basic flutter mechanisms with torsion and contro. surface rotation are explained, emphasizing the significance of the various wing axes and the importance of mass balance and the coupling of modes. The flutter investigation, usually based on a ground vibration test, results in damping diagrams showing crititcal speeds and corresponding margins of safety. Various instability regions in an altitude/ speed diagram are discussed, and the mean value between a TAS and EAS limit is proposed as V NE above the approved altitude, if no other information is available. For high-altitude soaring, recommendations are given to pilots for flight preparation and performance