Experimental Study of a High Advance Ratio Lift-Compounded Slowed Rotor in Rearward Shaft Tilt

Abstract:
The aeromechanics of a full-wing lift-compounded slowed-rotor rotorcraft were investigated experimentally at the Glenn L. Martin Wind Tunnel, characterizing the effects of rotor shaft tilt, wing configuration, and advance ratio on performance, blade structural loads, and hub vibratory loads. Measurements were obtained across advance ratios up to μ=0.7, three shaft tilt angles (-4°, 0°, and 4°), and three wing configurations, including an asymmetric wing arrangement. The results were used to validate the University of Maryland Advanced Rotorcraft Code (UMARC) coupled rotor-wing analysis. Rearward shaft tilt and increased wing lift sharing improved lift-to-drag ratio, reduced blade structural loads, and decreased hub vibratory loads due to the rotor being placed in a descent state and being partially unloaded. Rearward shaft tilt alone yielded a 5% improvement in lift-to-drag ratio and a 32% reduction in steady rotor flap bending moment relative to the forward tilt configuration at an advance ratio of 0.5 and 4° symmetric wing incidence. A peak combined rotor and wing lift-to-drag ratio of 9.6 was achieved at an advance ratio of 0.7 at rearward shaft tilt and with an asymmetric wing incidence configuration, demonstrating the potential of lift compounding for efficient high-speed edgewise rotorcraft flight.

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