Critical Flutter Speed of Sailplanes Calculated for High Altitude: Examples of computation

Abstract

Flutter means the vibration of an aircraft or glider in flight caused by elastic, mass and aerodynamic forces.  Flutter calculations determine the minimum flight speed at which un-damped vibrations may occur.  The results presented here were obtained using the flutter calculation program founded by IPPT PAN in Warsaw.  The program determines the aerodynamic forces from Theodorsen’s in-stationary aerodynamic theory. The calculations showed that critical flutter speed decreases as altitude increases.  There are also some kinds of flutter which are possible only at high altitudes.  The possibility of changing the regulations should be considered for well documented cases.  Because of the possibility of new instability areas at altitudes exceeding the test flight altitude, the flutter analysis should be extended up to the estimated operational ceiling of the sailplanes before test flights are started.  A wider flutter analysis would involve slightly higher cost of calculations.