Whirl Flutter Stability Analysis Using Propeller Transfer Matrices

Abstract

Whirl flutter is an aeroelastic instability that requires accurate prediction during propeller aircraft design. However, current flutter analysis methods in the frequency domain only include simplified propeller transfer functions. This work proposes a new method to represent the propeller using identified transfer matrices between hub displacements and loads. To obtain the transfer matrices, a time-domain simulation model of the isolated propeller is subjected to forced-motion perturbations at the hub, and the time response of the propeller hub loads is measured. After transforming both into the frequency domain, the resulting linear transfer functions for the isolated propeller can be used in a frequency-domain flutter analysis. The transfer matrices include all simulation features of the time-domain model, such as blade elasticity and unsteady propeller aerodynamics. The new method is verified using coupled time-domain simulations. The influence of blade elasticity and more accurate aerodynamic modeling on the flutter stability of two aeroelastic systems is explored. Blade elasticity is shown to have a strongly stabilizing effect on the whirl flutter stability of the simplified pylon model and a generic propeller aircraft. More sophisticated aerodynamic modeling, including 3D potential theory, also stabilizes the system, though minorly.