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# Is there a specific twist to airplane (rc) propellers?If so, can I make one at home? Answered

I am working on creating an rc plane but cannot figure out how to find the correct propeller size. Is there a company that sells these?

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I know this is old now but other people maybe interested in the same question.
Previous answers are good but I feel they didn't really answer the question about the shape of propellers.

To keep the prop efficient, no part of the prop should pull any more or less than any other. The tip of each blade travels through a greater volume of air each revolution than the middle does. Therefore the tip requires a shallower angle to achieve the same thrust as the middle. Generally the pitch should gradually decrease from root to tip.

The exception to this is the base of the blade. The base is usually stalled by the fuselage being in the way of the air flow. The angle here is usually less than the middle since directing a large volume of air at the fuselage will waste energy.

Has anyone ever thought of how a helicopters' main rotor can change its pitch to allow for both hovering and forward flight?  I'm posing this question since you're dealing the same principles of pitch and speed, since the propellers on your full-size airplanes like the Piper Cubs have variable pitch for "feathering" in the event of total engine failure and the pilot wants to prevent any further damage to the propeller and the engine.

This is how I understand it: Model airplane propellers are generally designed to have a fixed pitch from the center to the tip. Propellers are curved because the propeller travels faster toward the end of the propeller than in the center (speed = radius * rotational velocity). To "screw" the same distance forward the end of the propeller must have a lower slope than the inside because it travels further, the inside must have a greater slope because it travels less far.

Deciding what pitch you want is a whole other deal.
When you load the engine more it slows down. You load the engine more when you have a higher pitch or larger diameter prop. Higher pitch props are good for high speed, lower pitch props are good for low speed. I explain that in this video, which I just put up yesterday: http://vimeo.com/3085121
I'm working on a page that explains this better right now at http://www.crazybuilders.com
It should be up in a couple of days.

In the end, it is really a shame, but the data really isn't available to do the science before getting the propeller, at least with RC propellers. It is usually best to go with the engine manufacturer's recommendations on prop size.

Propellers are designed to maximize the power of the motor/engine. Depends on the size of the motor/engine as to what propeller you will be able to use. Gas (2-stroke/cycle, 4-stroke/cycle), Diesel, and electric all have different requirements. Check with a knowlegeable/reputable hobb store in your area, or an R/C Flying club in your area. They are waaaaaay too hard to build properly.