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Some thoughts on using auto engines in aircraft:
The aircraft does not care how much horsepower or torque the engine makes, only how much thrust the propeller provides.
The propeller will not perform well if the tips are going supersonic, so RPM is going to be limited. You can attach a gear machanism to reduce the prop RPM. Remember to add the weight of the PSRU to the engine when making power/weight and weight/balance calculations.
The aircraft cares quite a lot how much the powerplant weighs, it influences the proportions of the aircraft (balance) and the structural requirements, and finally the overall weight of the whole thing. Which is why there are so few flying diesels.
There are two things auto engine manufactures can be depended on to lie about, how much their engine weighs, and how much power it makes.
The engine must be capable of running WFO for extended times, say more than 10 minutes at a time under full load.. This usually means that the CR is going to be limited to keep the engine from overheating.
I recently read on one of the F1 forums that Ferrari says that their engine has to run WFO for 24 seconds as a time at Spa. They seem to think this is a long time flat out.
So keep in mind that your conversion will be compression limited and RPM limited, and must still have a good enough P/W to be useful as intended, say 10:1...
Yes I do know that Pietenpols can fly with model A engines. I just don't care..
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