Special Propeller Considerations for Rotary Engine?

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GESchwarz

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Oct 23, 2007
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Ventura County, California, USofA.
Is there anything particular about the rotary engine that should influence the type of propeller used?...

or is the prop designed for max performance at a specific flight phase, regardless of a particular engine's power curve?
 

orion

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Mar 2, 2003
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Western Washington
Fixed pitch props are designed for the ability to achieve best performance at a particular speed with a particular engine, or more specifically on the latter, with a particular torque curve and rpm. Virtually all standard fixed pitch props we have today were designed to operate with conventional aircraft engines.

When installing an auto engine, we generally use the reduction drive to match the operational rpms to those that we normally see with aircraft engines, and then we match the prop to the airframe, the torque and the anticipated speed. With aluminum props, if the auto engine does not work at an optimal level, the prop can be re-twisted in order to get a load distribution that works better with the combination of variables.

And of course with a wooden prop, you can carve something that matches you needs. However as a rule of thumb, the wooden props don't tend to be as efficient as the aluminum ones.

Constant speed prop blades can also be physically re-twisted to better match the operational characteristics however that's less the case generally since the variable pitch of the constant speed mechanism can take care of much of that.
 

Dana

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There's nothing special about a prop for a rotary engine, in that any propeller is optimized for the chosen flight condition(s). The specific parameters (rpm, torque, etc.) for a rotary engine will be different from a piston engine, so the actual prop design will be different but the concept is the same. Of course as Orion pointed out, the reduction drive used on auto engine conversions gives you more flexibility in choosing the optimum rpm than you'd have with a traditional direct drive aircraft engine.

A fixed pitch prop may be optimized for a specific flight condition (climb, cruise, etc.), or it may be a compromise to give better overall performance at the expense of maximum performance in one area.

-Dana

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