ChickenStick Rick

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Can anyone help me brush up on my prop basics? How does the pitch of a particular prop affect the engine rpm's, how the engine pulls, what give higher top end rpm etc? Someone please give me a quick lesson.

Thanks
Rick

Forgues Research

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Rick,
The finer pitch the more RPM for a given diameter. Now change the propeller for a smaller diameter with more pitch at the same RPM as the other prop, and you will get more speed but less pull
So for 3D flying, you don't want to much pitch but more diameter to get the most thrust as you can.
Remember you can go straight up with a 15 lbs ship on a .60 glo engine. (helicopter) Big diameter very little pitch.
Now take a ducted fan on a .60 glo engine, very little thrust, but once it gets going you can get a lot of speed.

Hope this helps

RSands

I'll just add that prop loading factor (PLF) is easy to calculate. This is a number that gives a relative weighting as to how a certain size prop will effect the motor. If two props have the same PLF, the motor will turn them at the same RPM, irregradless of pitch/diameter (there will be some varation in RPM between manufacturers though, due to airfoil selection, accuracy of manufacturing.etc). To determine a props PLF, take the diamater to the 4th power, then multply the result times the pitch, ie a 10x6 would be 10 x 10 x 10 x 10 x 6, or 60000.

If you motor isn't turning enough RPM's you'd want to use a lower PLF, if it's running too fast, you'd want a higher PLF. For more thrust with less speed, use a larger diameter, and for more speed with less thrust, use a higher pitch.