Supersonic Wind - Tunnel Flutter Tests of Two Rectangular Wings

Two rectangular wings of aspect ratio 4 were flutter tested in a supersonic wind tunnel at Mach numbers 1·6 and 2·0 using a technique in which a structural stiffness was varied to give flutter at the Mach number. The results are in reasonable agreement with calculations using theoretical three-dimensional derivatives and arbitrary wing modes, though in general the calculated critical stiffnesses are rather higher than the test values. It is shown theoretically that structural damping has an important effect upon the stiffness required to avoid flutter, and may in some circumstances be destabilising. 1. Introduction.-Over the past few years, the prediction of flutter characteristics at supersonic speeds has become increasingly important in aircraft and missile design. Flutter calculations are normally based on equations which represent the overall balance of forces occurring in the interaction of two or more natural modes of vibration. In the evaluation of the sets of forces involved it is recognised that the aerodynamic forces present the greatest difficulty. The accuracy of theoretical estimates of these forces is limited by the assumptions, and generally aero foil thickness, viscosity and shock waves are ignored. There is evidence! that these are significant, and experimental aerodynamic-force measurements are clearly required. Of more urgent importance, however, is experimental evidence on whether conventional calculations, using such theoretical aerodynamic derivatives as are available, give realistic flutter speeds. This information can most readily be obtained by flutter-testing models in wind tunnels, and a series of tests is described in this report.