Rotation-Frequency-Driven Extension-Torsion Coupled Self-Twisting Rotor Blades

摘要

This paper describes the effects of a composite coupled blade spar on the performance of a slowed-rotation-frequency helicopter rotor in high-speed edgewise flight. Antisymmetric composite coupling in the spar of a UH-60A-like rotor can provide a significant efficiency increase when rotation frequency is reduced. Comprehensive analysis was performed using a full three-dimensional finite element analysis-based aeroelastic computational structural dynamics solver with the inclusion of a free-wake aerodynamics model. This was validated using existing UH-60A test data for high advance ratios. The current study shows that a composite blade can achieve a maximum increase in the lift-to-drag ratio of 1.3 (20% improvement) at 85% of the nominal rotation frequency (NR) of 27rad/s. This efficiency gain is achieved through a combination of delayed stall drag along the retreating side of the rotor and reduced negative lift along the advancing side. A further reduction to 65NR showed a maximum efficiency improvement of 15% and was attributed only to the alleviation of negative lift. A hygrothermally stable layup was shown to perform as well as a nominal coupled layup at 85NR and marginally better at 65NR. Close study of the strains in the rotor showed that these rotors would be within the realm of practical manufacturability as axial strains fell within IM7/8552's allowable tensile strain of 6000 microstrain.