Propeller-Nacelle Whirl Flutter

Abstract

An analytical investigation is made of a heretofore unimportant flutter phenomenon that may occur in a propeller-nacellewing combination—a flutter condition which involves propeller and nacelle precession, and which has been of major concern recently. One of the objects of the investigation is to isolate and show the influence of those parameters which appear to be most strongly linked with this whirl-type instability. Considered, for example, are various combinations of pitch and yaw stiffnesses of the nacelle, structural damping, and propeller speed. To understand the behavior of the system better, the motion due to various initial disturbances is also studied for both subcritical and supercritical conditions. The results presented are derived by digital and analog means, the analog setup being used primarily for the motion studies. Part of the study is devoted to a further examination of the propeller aerodynamics. Finally, a comparison is made of analytically determined critical conditions with results obtained in some wind-tunnel tests.