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Old May 19, 2002, 01:27 PM
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Victoria, BC, Canada
Joined Apr 2001
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Re: How does prop RPM affect power?

Originally posted by Ninjak2k
What is the effect of RPMs on performance?
The simple answer is that a big slowly moving propeller is more efficient at moving air. So the higher the gear ratio, the more static thrust you get for the same power. What you sacrifice is speed and some mechanical loss in the gearbox.

Indoor flyers can use very tiny motors geared 16:1 and huge props. They can only fly very slowly. They couldn't fly at all with the same motor direct.
If you want top speed for racing you ordinarily use a direct drive motor with a small prop turning very quickly. The choice depends on how you want to fly.

A complicating factor is voltage and current. The direct drive motor might be 10 volts at 20A to get your 200W. The same motor with a gearbox might be 20 volts and 10 amps (for example). The motor will turn much faster and the current will be lower. Both lead to higher electrical efficiency.

So a well chosen geared setup can be more efficient in almost all ways which helps explain why they have become so popular in most planes.

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