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BSFC vs gas mileage, 2 stroke vs 4 stroke
I've been under the impression that 4 stroke engines get better gas
mileage in aircraft due to their higher BSFC numbers. But I've recently realized that since the 4 stroke engines are so much heavier than a same horse powered 2 stroke you end up having to design a larger aircraft (and engine) to carry the original intended payload plus the additional weight of the engine. So in the end, a purpose built 2 stroke airplane will be smaller, lighter may even get better gas mileage. Unfortunetly, most designs that use 2 stroke engines are high drag ultra lights so going distances isn't really what they do, but it would seem to me there is some potential for a low weight, low drag, in the neighborhood of 500lb empty, 2 seat aircraft designed for one or two 2-stroke power plants. The Pulsar XP seems close because I've seen some with Rotax 582's. The aicraft that attempt to exploit these engines in this way always look like the wings are too small compared to the proportions we're all used to seeing on C172 and other similar formula aircraft. Examples are the cri-cri, BD-5, AR-5 http://www.ar-5.com/sportav93.html |
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