Experimental determination of piston engine share in the light propeller aircraft power plant total noise

Аuthors

Moshkov P. A.^1*, Samokhin V. F.^2**

1. Yakovlev Corporation Regional Aircraft Branch, 26, Leninskaya Sloboda str., Moscow, 115280, Russia
2. Central Aerohydrodynamic Institute named after N.E. Zhukovsky (TsAGI), 1, Zhukovsky str., Zhukovsky, Moscow Region, 140180, Russia

*e-mail: moshkov89@bk.ru, p_moshkov@ssj.irkut.com
**e-mail: samohin_vf@mail.ru

Abstract

The article presents the results of experimental determination of the of the piston engine share in the total power plants noise of the light propeller aircrafts An-2 and Yak-18T, MAI-223M and MAI-890U, performed under static conditions at the local aerodrome. The article provides a brief overview of the mechanisms of noise generation by the aircraft piston engines. The power plant emission band consists of harmonic and broadband components. Its sources are piston engines and propellers.

Based on measurements at several points of the acoustic far-field narrowband spectra we separated harmonic components emitted by the propeller from those emitted by the engine. Separation of the high-frequency component of the engine broadband noise against the background of the propeller whirligig noise appeared to beimpossible. The possible source of the dominant radiation is the turbulent wake behind the rotating blades. The important share of piston engine harmonic emission of the total emission power of engine-propeller power plant is experimentally revealed, and under lower engine operating modes An-2 and Yak-18T (at Mach circumferential propeller velocities less than 0.7) in particular.

The paper presents the factors affecting the piston engine share in the total propeller power plant noise. It also studied the effect of nosing engine on acoustic power level of the engine fundamental tone. It was found that the nosing of the engine could be considered as one of the waysof the afield noise reduction of ultralight aircraft MAI-890U.

We obtained acoustic emission patternsof piston engines typical for light aircraft. Aircraft ASh-62IR and ROTAX-912ULSengines emissioncharacteristic maximums correspond to the azimuth angles of 0° in the forward hemisphere and of 135-150° in the rear hemisphere. M-14P engine emissionis relatively even over the space in the direction angles of 60-120°. Typical minimum levels of engine noise observed on the axis of the crankshaft, i.e. in the direction of 0° in the forward hemisphere and 180° in the rear hemisphere. One can use these emission patterns in the future for the noise prediction models of aircraft piston engines.

Keywords:

aviation piston engine noise, engine-propeller power plant noise, afield aircraft noise

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