Whirl flutter analysis using linearized propeller transfer matrices

Abstract

Whirl flutter as an aeroelastic instability can occur for aircraft configurations with propellers mounted on an elastic support. It has to be mitigated in the design process, and its prediction needs to be included in the frequency-domain flutter analysis process of such aircraft. But, as these processes often rely on the classical method developed by Houbolt and Reed and revolve around linear aerodynamic derivatives for the propeller, they are not always compatible with advanced frequency-domain representations of the propeller such as the Transfer-Matrix method. This paper provides a linearization procedure to derive propeller aerodynamic derivatives similar to those from the classical method from frequency-dependent transfer matrices. These linearized derivatives are compatible with legacy workflows and allow an increase in the fidelity of propeller aerodynamics in existing frequency-domain flutter workflows. This paper also compares the impact of different propeller aerodynamic modeling on the whirl flutter stability of a generic, twin-engine turboprop aircraft. Results show the linearized workflow's effectiveness and indicate a stabilizing effect when including more modeling features like unsteady aerodynamics and local induced velocities.