Wind Tunnel Evaluation of Aeroelastically Conformable Rotors

Abstract : The concept of controlling blade dynamic twist to reduce rotor system loads and to improve aerodynamic efficiency was investigated through wind tunnel testing and analysis. Blade design features which promote favorable dynamic twist were selected based on aeroelastic analysis. Two four-bladed 9-ft diameter 1/6 scale model rotors which permitted parametric investigation of blade torsional stiffness, tip sweep, and camber were fabricated and subjected to forward flight testing in the Langley Research Center Transonic Dynamics Wind Tunnel. The azimuthal variation of dynamic twist was determined based on measured twisting moments. Results showed that relative to a conventional stiffness blade, 20 to 40 percent reductions in vibratory flatwise and torsional moments and 10-percent reductions in power were achieved at an advance ratio of 0.3 by configurations which produced noseup elastic twist on the advancing blade. Four/rev hub vibration was also reduced by blades which reduced advancing blade total twist. The important trends shown by the test results were adequately predicted by a blade aeroelastic response analysis although magnitudes of blade loads were generally unpredicted.