ROTOR BLADE STABILITY IN TURBULENT FLOWS .2.

As a sequel to Part I, this paper is directed toward the effect of turbulence in the atmosphere on the rotor blade stability during a forward flight. Two types of motion are considered: uncoupled flapping, and coupled flapping and torsion. Assuming that the turbulence velocities which appear as parametric excitations can be approximated by white noise processes, the method of the Markov process is applied in the formulation of the problem. The results are presented as stability boundaries for the first- and second-order stochastic moments corresponding to different spectral levels of the excitations. The stability boundaries for the nonturbulence case, previously obtained from deterministic analyses, are also included for comparison. It is shown that the uncoupled flapping motion remains quite stable under the turbulence intensities and operating conditions, which may be reasonably expected in the service life of a helicopter, but the stability region for the coupled flapping and torsional motion is significantly reduced due to normal turbulence. © 1979 American Institute of Aeronautics and Astronautics, Inc., All rights reserved.