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As far as I can tell, aviation piston engine power output is typically measured in HP (horsepower).

Automotive engine power output is typically measured by running the host vehicle on a rolling road, or dyno or dynamometer. This directly produces a torque curve, which may be integrated with respect to RPM to provide a power curve.

Obviously it wouldn't make much sense to put a piston-engined aircraft on such a device. Instead, how is horsepower measured for aviation piston engines?

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    $\begingroup$ You can put engines on a dyno hooked up to the shaft directly. $\endgroup$ Commented Oct 26, 2015 at 23:38

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Like anything else a Dynamometer is used except the engine is bolted directly to it (most likely on a test bench). In a car a rolling road is simply a way to couple the tires to the dyno without having to have any custom fittings. For what its worth cars lose a bit of horse power in the transmission/drive shaft/differential so shaft horse power and wheel horsepower are not always the same. However in a plane the prop is bolted more or less to the end of the crank (with the exception of some planes with stepper gear boxes). In any case shaft horsepower on a plane engine is more or less whats available at the prop.

Here is a lycoming engine on a dyno

enter image description here

(source)

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    $\begingroup$ Also, long before the first engine is installed in a car on the assembly line, various pre-production examples are run on a dyno in exactly the same fashion. $\endgroup$
    – FreeMan
    Commented Oct 27, 2015 at 14:38
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How is horsepower measured for aviation piston engines?

One idea is to use a "shaft power meter".

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  • $\begingroup$ Measuring it is one thing, but you actually have to absorb the power output somehow. And spinning a big propeller in a small room is not the best way of doing this. $\endgroup$ Commented Oct 27, 2015 at 22:34

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