What size prop should I use? - RC Groups
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Sep 17, 2001, 11:17 AM
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What size prop should I use?


I built a new foamie out of 1/4 inch blue foam. It looks like the Tumblewatt from Modelair Tech and is about the same size. I am running a speed 300 with a 2.77/1 gearbox. I tried a 7 inch prop but couldn't get the plane to gain any altitude. It flew but would only stay about 3 or 4 feet off the ground. Ready to fly weight is 12 ounces with a 5 cell 600 Mah nicad. I tried out an 8 cell 720 Mah NIMH on the bench but the motor got hot quickly. The prop seems to be spinning fast enough to pull the plane around but it isn't quite doing the job.

My question- can someone suggest what the best prop would be for this plane? It seems as if that's my problem. Any other ideas to remedy this situation gratefully acccepted. Thanks.
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Sep 17, 2001, 12:10 PM
AMA 697691 / FAA 13675
Hi Ernie,

For a geared Speed 280 or 300, you should be able to use 7-cells of NiCd or 8-cells of NiMH. You just don't need to use full power after the ship is airborn.

Limit static bench testing to 10-15seconds runs in duration.

For your geared system, you mention a 7" prop but not the pitch?

Try using an APC 9x4.5 or 10x4.7 prop on your 2.77:1 geared system.

Good luck!
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