Prediction of Rotor Instability at High Forward Speeds. Volume Ii. Classical Flutter

摘要

An analytical study was made of the effects of high forward speed on the flutter characteristics of helicopter rotor blades. Linearized equations of motion were used to represent the dynamics of the rotor blades. The aerodynamic forces were obtained by using a fixed azimuth approach with fixed-wing two-dimensional compressible flow aerodynamic coefficients. Flutter speeds and flutter frequencies were calculated for two model helicopter blades for which experimental data were available. One blade was tested in hover at high tip Mach numbers; the other, at high advance ratios with low tip Mach numbers. Agreement between theoretical and experimental data was qualitative. A parametric study was made of the effect on flutter speed of varying blade chordwise elastic axis and center-of-gravity position, torsional and flatwise bending stiffness, and blade mass ratio and feathering mass moment of inertia. The extended normal mode transient analysis was used to perform blade response calculations corresponding to blade configurations and flight conditions for which classicial flutter was calculated. (Author)