R.E. Donham

All propeller 1P aerodynamic excitations and their resulting loads are regressive in the rotating system and therefore 0P i.e. steady in the stationary axes (the advancing transport speed of the propeller shaft converts these 1P regressive loads into stationary loads). The 1P and whirl flutter aerodynamic moments (primary energy source) are dynamically amplified principally by the response of the first blade-bending (coupled flap/inplane) mode. Both the modal frequency and the blade aerodynamic damping in the rotating system are the dominant factors in the magnitude of this dynamic response. Relationships between a rotating and stationary system are important when evaluating stationary axes steady and oscillating loads. All propeller whirl flutter instabilities observed too date in the stationary axes, both experimental and analytical results, were low frequency motions well below 1P. Therefore, they are regressive frequencies and motions in the rotating system. The propeller first bladebending (coupled flap/inplane) mode nominally occurs between 1.5P and 2.7P (Campbell diagrams are proprietary data) with percent of critical damping less than æ= .04. When aerodynamically excited at 1P (stationary axes inflow angle of attack) the support loads experience between 1.7 to 1.15 times the stationary axis rigid propeller aerodynamic moment due to blade flap bending dynamic amplification. The dynamic amplification of the stationary axis propeller normal force, beyond the scope of this paper, is small requiring determination of the first inplane bending dynamic response. The 1P rotating forces result in steady loads (0P), therefore, a static aeroelastic solution can determine the aircraft loads for the coupled flexible propeller (bending), with flexible supports that can account for gyroscopic moments, Section 4. These studies show that use of stationary rigid blade aerodynamic coefficients to determine the 1P loads and whirl flutter stability boundaries is appropriate providing the aerodynamic moment terms are multiplied by the appropriate propeller blade bending dynamic amplification factors that are phase shifted. A time history method is presented where single or multiple propeller blade bending modes can be used to determine dynamic amplification and phase based on disc averaged aerodynamics or by using disc azimuth sectors, which can include the effects of sector modal damping changes, spanwise variations of inflow angle, aerodynamic effects such as Mach number, stall, et.al. No assumption is made in this analysis that any of the sectors are stable.

International Forum on Aeroelasticity and Structural Dynamics, 2005, München

Conference Paper

englisch

21,0 x 29,7 cm, 16 Seiten

DGLR-Bericht, 2005, 2005-04, International Forum on Aeroelasticity and Structural Dynamics 2005; S.1-16; 2005; Deutsche Gesellschaft für Luft- und Raumfahrt - Lilienthal-Oberth e.V., Bonn

NA

in getr. Zählung;

propeller blades, structural dynamic analysis, flutter

Bibliothek

2005