Present-day trends toward flight at high speeds and high altitudes have led to increasing interest in the flutter speed at low densities and high Mach numbers. An experimental investigation has consequently been made to determine some of the effects of these parameters on flutter speed.

Results of four thin unswept flutter airfoils attached to two freely falling bodies are reported. Two airfoils fluttered at a Mach number of 0.85, a third airfoil fluttered at a Mach number of 1.03, and a fourth fluttered at a Mach number of 1.07. Results of calculations of flutter speed using incompressible and compressible air-force coefficients, including Mach number of 1.0, are presented.