Acoustic directivity measurements of the CH-46E, CH-53E, and AH-1A helicopters

Abstract

Presented in this paper are the results from acoustical measurements made of the CH-46E, CH-53E, and AH-1 helicopters. Results from the test will be used to form a database of sound hemispheres that is currently under development for the rotorcraft noise model. A unique feature of the test was the use of two cranes having a tip height of 180 ft, that suspended two vertical arrays of microphones. Positioned between the two cranes was a third array of microphones located on the ground which completed the shape of a U. The helicopters flew through the center of the array with the plane of the rotor approximately inline with the cranes tips. Carried on board the helicopters was a tracking system which was time synchronized with the acoustic recording equipment. The acoustic data and the tracking data are combined in a computer program that depropagates the sound field to a sound hemisphere which preserves the directivity and frequencies of the acoustic field. A sound hemisphere is constructed for each pass through the acoustic array.