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Prop Question


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Morning all

I looking at ordering a spare wooden prop for my polini thor motor. I already have a helix carbon fiber prop.

Q: Could somebody explain to me why it is important to get a prop with the correct pitch on the prop, also what has gear ratio got to do with it.

I am new(ish) to paramotoring and I am not good with the techie side. I have asked a few people but seem to be getting hazey answers.

Any information would be greatly appreciated

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I will try to answer in simple english, I am sure someone will come along with a more technical answer.

To start with lets make sure we know what pitch is. As I understand it if the pitch is 48 inches it means that for one revolution of the propellor it will have traveled 48 inches forward.

The amount of power required by the engine will increase as the pitch goes up for a given engine RPM.

So there are two problems as I see it.

1. If the pitch is decreased then the RPM of the engine increases, and you must not over rev the engine.

2. If the pitch is increased then the max power of the engine cannot be obtained ( as specified by the engine manafacturer)

So in short it is a balancing act between getting the max power from the engine to give the best possible pitch without over reving the engine.

The Recuction ratio will also have an effect as to how many revolutions of the prop are obtained relative to the RPM of the engine. I think the larger reduction ratio the more power but with a retuction in prop RPM and again there is a balancing act.

I wait to be corrected.


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  • 4 weeks later...

Pitch is not everything, don’t think that if you buy a different prop with the same pitch that it will be perfect for your motor. Other factors such as length, width and profile come into effect. You should buy a prop that was designed and tested for your motor and reduction, and don’t worry too much about the pitch.

Paul D

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