Accession Number : ADA304104

Title :   Directionality of Helicopter Noise and Its Exploitation.

Descriptive Note : Final technical rept.

Corporate Author : FLOW SOLUTIONS LTD BRISTOL (UNITED KINGDOM)

Personal Author(s) : Lowson, Martin V.

PDF Url : ADA304104

Report Date : JAN 1996

Pagination or Media Count : 32

Abstract : The work during the present contract has shown that helicopter BVI noise will have local region of focused propagation in which the decay rate is less than inverse square. This finding has significant consequences for helicopter detection. Instantaneous maximums in helicopter noise during flyby are frequently observed. These have normally been ascribed to non-uniform aerodynamic effects at the rotor. The present model shows that such peaks are a result of th detailed geometry and kinematics of the blade vortex interaction, and a fundamental feature the associated acoustic propagation. The model gives both a prediction of where the peaks will occur at any flight condition, and of the region of the rotor disc where the most acoustically important interactions are caused. The model also allows a search for flight conditions under which noise from Rotor BVI will be minimized. The work has been summarized in a report presented to the European Rotorcraft forum, and a paper to be published in the Journal of Sound and Vibration. An extended version of the paper to be presented in the Journal of Sound Vibration, with the key diagrams in color, is attached.

Descriptors :   *HELICOPTERS, *AIRCRAFT NOISE, KINEMATICS, VIBRATION, SYMPOSIA, DETECTION, INTERACTIONS, VORTICES, HELICOPTER ROTORS, FLIGHT, SOUND TRANSMISSION, ROTARY WING AIRCRAFT, GREAT BRITAIN, DIAGRAMS, DIRECTIONAL.

Subject Categories : Helicopters
      Acoustics

Distribution Statement : APPROVED FOR PUBLIC RELEASE