U. Arnold

This paper investigates one important source for instability of stopped rotors during the decelerating and accelerating process. Flapping stability is usually lost at advance ratios above two, due to strong parameter excitation through periodic aerodynamic forces. Reducing the angular velocity of a hingeless rotor, on the other hand, increases the nondimensional flapping natural frequency that has a stabilizing effect. The differential equation of motion is set up for the common rigid blade approximation, considering spring restrained hinges with arbitrary hinge offset. Reverse flow, which will be shown to be decisive for the stability boundaries, is included analytically in a straightforward way. The effect of the parameter excitation is discussed by means of MATHIEU- and HILL-type differential equations. Simple stability criteria derived from STRUTI"s stability diagram will be compared with the computed eigenvalues using FLOQUET theory. The effect of the forcing function i.e. the amplitude amplification of the inhomogeneous equation will be shown to be even more important than stability. Simulation results are presented in order to discuss the possibility of suppressing divergent flap oscillations by applying high rotor deceleration and acceleration rates.

17th European Rotorcraft Forum 1991, Berlin

Conference Paper

englisch

21,0 x 29,7 cm, 16 Seiten

DGLR-Bericht, 1991, 1991-08, 17th European Rotorcraft Forum Proceedings; S.419-434; 1991; Deutsche Gesellschaft für Luft- und Raumfahrt - Lilienthal-Oberth e.V., Bonn

NA

helicopters, rotors

Bestellbar

1991