Influence of blade elasticity and thrust on the whirl flutter stability of a propeller-driven aircraft

ifasd2024 Tracking Number 50

Whirl flutter stability is an important certification criterion for propeller-driven aircraft. This stability is so far verified by introducing analytical propeller derivatives in frequency-domain flutter analysis. These derivatives are based on the assumption of rigid blades though [1]. Recent studies on an isolated propeller model with a new method using identified, frequency dependent transfer matrices for the propeller hub loads have shown that including blade elasticity in the analysis increases whirl flutter stability significantly [2]. However, this effect has not been examined on full aircraft level yet. This paper extends the transfer-matrix (TM-) method [3] to enable its application on complex aircraft models. To decouple the specific propeller model used for transfer-matrix generation from the structural model of the airframe, a few adaption procedures for the transfer matrices are introduced. These include eliminating the propeller mass influence from the transfer matrices as well as aligning the propeller orientation with the coordinate system definition of the structural model. Furthermore, an interpolation routine for the transfer matrices is introduced, reducing computational effort. Frequency-domain flutter analyses of a generic twin-turboprop aircraft are performed to demonstrate the introduced adaptions and evaluate the influence of blade elasticity and thrust on whirl flutter stability. The evaluations successfully show that the stabilizing effect due to blade elasticity also occurs on full aircraft level (see Fig. 1). Even though, it is observed that this stabilizing effect has a limit for very soft blades, the results reveal an additional flutter stability margin, that can be exploited for future aircraft designs.