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Testing Engine Performance
Following many requests from modellers for a statement of realistic usable engine performance
in a low noise configuration, we built an engine thrust test stand to investigate the real flight capability of model aircraft engines. It was decided that thrust would be the most useful parameter
with which to judge the suitability of an engine to power a specific model because it was the actual propulsion force generated by a combination of engine, silencer, fuel and propeller. Noise, is
the common criteria that has to be met to retain many current flying fields. Therefore, performance figures, such as 2.5HP @ 12,000rpm are totally misleading when having to prop down to achieve an
82dB noise limit. At the engine speeds listed opposite, the prop tip speed is the region of 315-350 mph. During the development of our Engine Vibration Eliminators, we noted that when, after
fitting a functional silencer and mounting the engine on a set of our EVEs, all we could hear was a really noisy prop. Prior to fitting the EVEs, the prop noise was combined with, and to some extent
masked by, airframe resonance to produce an unacceptable overall noise level. During the test, two different 18x8 wood props produced different results. The second prop ran 100 rpm less, whilst
developing the same thrust as the first make, but was appreciably quieter. It is not just about max revs!
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