Radial Engine Noise Reduction

[Jon Robb]

I am putting together a component list for my 1:3.5 Tomahawk Wilga and currently looking at engine options. I fly from a noise sensitive site, adhering to the 82dB limit. My engine choices are 180-5 Moki / UMS 180-5 or 160-7 UMS. Has anyone got real world data on dB produced by any of these engines. Can anything realistically be done to achieve the 82dB apart from prop selection? The nature of the plane and flying style means I won’t be flying at the upper end of the rev range.

One other option would be electric power as I have a few motor options, however flight time will be around 8 minutes.

[IAN TURNEY-WHITE]

Jon , I don't have any experience with radial engines but have several large petrol engines , the 82 dB(A) limit seems to suit glow engines better than petrol engines , an effectively silenced large petrol engine with its slower revving engine has a deeper tone but looses the irritating high pitched note of a glow engine . My experience is that a petrol engine which has say a noise output higher than 82 dB(A) will often sound less annoying and intrusive than a 82dB(A) glow engine.
My two thirds SF33 motor glider has a King 190cc flat twin petrol engine and Krumscheid cannister silencers and a Menz 34" by 10"
prop , additionally the silencers are internally mounted .The lowest dB(A) at full throttle was about 86.
This combination appeared quiet and well silenced and was not intrusive or annoying
A change to a touch bigger prop lost about 500 rpm (down to about 4900rpm) and reducing the ATV throtle limit on the TX brought the sound level down some more , the difficulty then , was that if I throttle back the motor (half throttle) in the air , I was unable to detect/hear if the engine was still running .
We have within the LMA , several large models powered by large radials and the sound they produce is fabulous , very scale like .
A sound that is enjoyable to listen to and a large part of owning /operating one of these engines.
Possibly you could achieve acceptable sound levels with a silencer that has a volume of say 10 times the engines capacity and limiting the rpm,s ,maybe experimenting with different props , I think that this combination will not be annoying to neighbours .