Full-Scale Higher Harmonic Control Research to Reduce Hub Loads and Noise

摘要

Open loop higher harmonic control (HHC) has been researched in the 40- by 80-Foot Wind Tunnel of the National Full-Scale Aerodynamics Complex at NASA Ames. This test involved the modern, 5-bladed, moderate thrust Sikorsky Bearingless Main Rotor. The present HHC effort involved obtaining reductions in dynamic hub loads (1P, 5P) and separately, reductions in noise due to blade vortex interaction (BVI). A study was also made of the effect of 2P control on rotor performance. During dynamics testing, the maximum airspeed was 160 knots with the thrust kept constant at 14,000 lbs, with IP and 5P control being exercised separately. The full-scale BVI experiments were conducted at 12,000 lbs thrust and at 60 and 80 knots, with 5P control. In both hub loads and noise experiments, testing was conducted with all three modes of control: collective, lateral, and longitudinal. The amplitude and phase in each of these modes were varied to determine their optimum values. It was found that in general, in cruise, the 5P inplane shears were reduced substantially by 5P lateral control. A substantial reduction in the 1P normal force was achieved with 1P collective control. Regarding acoustics testing, at the BVI flight condition (descent, 60 and 80 knots), a reduction in BVI-related noise up to 5 dB was consistently obtained; this was achieved by the application of lateral control.