A new and highly successful method of collecting far‐field acoustic data radiated by helicopters in forward flight has been developed, utilizing a quiet aircraft flying in formation ahead of the subject helicopter. The lead aircraft, flown as an acoustic probe, was equipped with
tape‐recording equipment and an external microphone. Spatial orientation of the helicopter with respect to the monitoring aircraft was achieved through visual flight reference. Far‐field acoustic data defining the impulsive noise radiation characteristics of the UH‐1H
helicopter during high‐speed flight and partial ‐power descents have been gathered with this technique. Three distinct types of impulsive waveforms have been identified and correlated with helicopter steady operating conditions.
Ames Directorate, U.S. Army Air Mobility R&D Laboratory, Moffett Field, Calif.
Publication date: October 1, 1976
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