Reduced In-Plane, Low Frequency Helicopter Noise of an Active Flap RotorResults from a recent joint DARPA/Boeing/NASA/Army wind tunnel test demonstrated the ability to reduce in-plane, low frequency noise of the full-scale Boeing-SMART rotor using active flaps. Test data reported in this paper illustrated that acoustic energy in the first six blade-passing harmonics could be reduced by up to 6 decibels at a moderate airspeed, level flight condition corresponding to advance ratio of 0.30. Reduced noise levels were attributed to selective active flap schedules that modified in-plane blade airloads on the advancing side of the rotor, in a manner, which generated counteracting acoustic pulses that partially offset the negative pressure peaks associated with in-plane, steady thickness noise. These favorable reduced-noise operating states are a strong function of the active flap actuation amplitude, frequency and phase. The associated noise reductions resulted in reduced aural detection distance by up to 18%, but incurred significant vibratory load penalties due to increased hub shear forces. Small reductions in rotor lift-to-drag ratios, of no more than 3%, were also measured
Document ID
20090036794
Acquisition Source
Ames Research Center
Document Type
Conference Paper
Authors
Sim, Ben W. (Army Aviation Systems Command Moffett Field, CA, United States)
Janakiram, Ram D. (Boeing Co. Mesa, AZ, United States)
Barbely, Natasha L. (NASA Ames Research Center Moffett Field, CA, United States)
Solis, Eduardo (Monterey Technologies, Inc. Monterey, CA, United States)