WIND TUNNEL INVESTIGATION OF SEMIRIGID FULL-SCALE ROTORS OPERATING AT HIGH ADVANCE RATIOS
Final technical rept.
BELL HELICOPTER TEXTRON INC FORT WORTH TX
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A UH-1B 44-foot-diameter rotor having reduced-thickness tips was evaluated in a range of Mach numbers up to 0.94 and advance ratios of up to 0. 52. Additionally, UH-1D rotor blades reduced in diameter to 34 feet were tested at advance ratios of up to 1.1. Calculated performance is compared with the experimental results obtained to establish the validity of the theoretical technique at high advance ratios. In general, it was found that quasi-static, two-dimensional techniques were adequate up to an advance ratio of about 0.5. Above this advance ratio, theoretical techniques break down, especially with respect to calculating rotor propulsive force or drag. Theory-experiment comparison with the 44-foot-diameter rotor, operated at high Mach numbers, showed that Mach number effects are predictable to an advance ratio of at least 0.45. The 34-foot-diameter rotor became increasingly sensitive to control input with advance ratio. At an advance ratio of 1.1, this rotor system displayed a long transient response to a control input before obtaining its steady-state orientation, and at the largest values of collective pitch, the flapping would not completely stabilize.