A THEORETICAL ANALYSIS OF ELASTIC VIBRATIONS OF FIXED-ENDED AND HINGED HELICOPTER BLADES IN HOVERING AND VERTICAL FLIGHT

摘要

A theoretical analysis is given of the frequency and damping characteristics of the free modes of Titrations of balanced fixed—ended and hinged elastic helicopter rotor blades in hovering and vertical flight. Torsional vibrations, tending vibrations in flapping and in lagging, and coupling between the flapping and lagging motions are considered. Explicit methods and formulas for the calculation of natural frequencies and logarithmic decrements of the principal modes are developed, from which general conclusions are rigorously drawn. Flutter of helicopter blades, which may occur when the blades are unbalanced, is briefly considered on the basis of quasi—stationary flow, and simple criterions are derived for the stability of the coupled torsional and flapping vibrations in such cases.