Book Description

This report describes a wind tunnel test of the McDonnell Douglas Helicopter Systems (MDHS) Active Flap Model Rotor at the NASA Langley 14- by 22-Foot Subsonic Tunnel. The test demonstrated that BVI noise reductions and vibration reductions were possible with the use of an active flap. Aerodynamic results supported the acoustic data trends, showing a reduction in the strength of the tip vortex with the deflection of the flap. Acoustic results showed that the flap deployment, depending on the peak deflection angle and azimuthal shift in its deployment schedule, can produce BVI noise reductions as much as 6 dB on the advancing and retreating sides. The noise reduction was accompanied by an increase in low frequency harmonic noise and high frequency broadband noise. A brief assessment of the effect of the flap on vibration showed that significant reductions were possible. The greatest vibration reductions (as much as 76%) were found in the four per rev pitching moment at the hub. Performance improvement cam results were inconclusive, as the improvements were predicted to be smaller than the resolution of the rotor balance. Dawson, Seth and Hassan, Ahmed and Straub, Friedrich and Tadghighi, Hormoz Langley Research Center BLADE-VORTEX INTERACTION; WIND TUNNEL TESTS; NOISE REDUCTION; AIRCRAFT CONTROL; FLAPS (CONTROL SURFACES); HELICOPTERS; AEROACOUSTICS; PRESSURE DISTRIBUTION; ACTIVE CONTROL; INTERACTIONAL AERODYNAMICS; VIBRATION EFFECTS; PITCHING MOMENTS; ROTOR DYNAMICS; SURFACE PROPERTIES; ROTOR BLADES; PRESSURE MEASUREMENT; NOISE SPECTRA; ACOUSTIC PROPERTIES; BLADE SLAP NOISE; DEFLECTION; FREQUENCIES; SUBSONIC SPEED; WING TIP VORTICES...