Acoustics of Ultralight Aeroplanes.

Abstract

Stringent noise limits have been imposed on ultralight aeroplanes in the Federal Republic of Germany. The "Committee on Aviation Environmental Protection" (CAEP) of the "International Civil Aviation Organization" (ICAO) intends to formulate internationally binding noise regulations for ultralight aeroplanes. In view of these developments an experimental and theoretical research program was initiated to investigate specifically the noise sources and noise characteristics of ultralight aeroplanes. The objective of this study was to evaluate the technical feasibility of meeting existing or proposed noise limits - especially in comparison with the noise limits for "light propeller-driven aeroplanes" (ANNEX 16/Chapter 6) and to further establish the minimum noise radiation from various types of ultralight aeroplanes within operational limitations. Flyover and ground static noise measurements on tractor- and pusher-propeller driven ultralight aeroplanes and wind tunnel noise measurements on isolated full-scale ultralight-aeroplane propellers were conducted. Engine noise was studied seperately providing information on the relationship of engine rotational speed and exhaust noise. In an overall sense the study showed that only tractor propeller driven ultralight aeroplanes have a chance to comply with the current stringent (German) noise limits; they must be of clean aerodynamic design, be equipped with thoroughly muffled engines and their operational propeller blade tip Mach number must be limited to values well below 0.5.