Aeroelastic response characteristics of rotor blades

K.S. Nagaraja* Boeing Commercia l Airplane Co. Seat t le , Washington G. Alvin Pierce** Georgia Insti tute of Technology Atlanta , Georgia The objective of this paper is t o demonstra te and evaluate an in tegra ted procedure for t h e combined analytical and experimental determinat ion of aeroelas t ic response character is t ics for rotor blades. For pract ica l reasons t h e scope of this e f fo r t has been l imi ted t o flapwise bending and torsion of two e las t ic blade models, although t h e methods used can be readily extended t o t r e a t t h e flap-lag-torsional dynamics of f ull-scale rotor blades. This procedure initially consists of establishing a s e t of s t ructura l dynamic pa ramete r s for t h e two blades. These pa ramete r s include mass distribution, e las t ic st iffness, natura l frequencies, mode shapes, generalized masses, and s t ructura l damping. Most of t hese pa ramete r s were obtained by both analytical and experimental techniques for verification. The t ransfer matr ix method was used fo r obtaining analytical natural frequencies and mode shapes. The model blades were then dynamically exci ted in a s t a t i c thrus t chamber a t various rotational velocit ies and pitch angles. The exci ta t ion consisted of a simple harmonic displacement of t h e ro tor hub in t h e axial direction, while t h e aeroelas t ic response was measured by bending and torsional s t ra in gage bridges mounted along t h e span. These results a r e corre la ted with predic ted response d a t a obtained f rom a modal analysis which utilized t h e s t ructura l dynamic parameters described above and a s t r ip theory representa t ion of Jones and Rao's unsteady aerodynamic technique.