Review of Propeller-rotor Whirl Flutter

Book excerpt: A summary is made of the state of the art of propeller-whirl flutter -- a precession-type instability that can occur on a flexibly mounted aircraft engine-propeller combination. This report reviews the literature relating to this problem from the time it first became of concern on conventional turboprop and V/STOL aircraft. Included in the survey are a description of the basic mechanism of whirl flutter, a summary of generalized trend studies on idealized systems, the status of methods for predicting propeller aerodynamic coefficients, the effects of flapping hinged blades and twisted flexible blades on whirl flutter, and some approaches for including propeller whirl modes as a part of the flutter evaluation for complete aircraft. Also, brief consideration is given to the response of flexibly mounted propeller-nacelle systems to random atmospheric turbulence. Whirl flutter of conventional propeller-nacelle systems is now a reasonably well understood phenomenon and amenable to analysis. For propeller-rotor systems with flapping blades, however, comparisons between experiment and theory suggest the need for further refinements in the mathematical model.