Will the GWS 4-blade prop be OK for this setup ? - RC Groups
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Nov 09, 2004, 11:53 AM
Styrofoam Bird

Will the GWS 4-blade prop be OK for this setup ?

I am going to build another P-51, and was wondering if the 4-blade prop will be ok with this setup I have... ie: Will I burn up the engine or anything ?

(I believe the GWS 4-blade prop measurements are 254mm x 203mm or 10in x 7.9in)

Himax 2025-4200
Cobri 20
Tanic 3s 1550

Though I have been flying for a while now, I still don't know the "rules" regarding prop size, and have always gone with what was recommended by the manufacturer.

Any advice will be greatly appreciated.

Thanks, Brian
Last edited by Warbird Brian; Nov 09, 2004 at 01:17 PM.
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Nov 09, 2004, 01:25 PM
Registered User
Using a 6.6:1 gearbox, Motocalc estimates 15.5A so you should be within the 10-12C rating. Static thrust is estimated at 893g so you'll be well overpowered!
Nov 09, 2004, 01:32 PM
Styrofoam Bird
Thank you Steve.

Is Motocalc something I can buy and download ? I'd like to figure out these things for myself if I could

Thanks again, Brian
Nov 10, 2004, 04:06 AM
Registered User
Brian, try MotoCalc. I'm a newcomer to electric flight, about 8 months now, and found it a pretty steep learning curve. After other recommendations I got MotoCalc which enables you to run various scenarios through to try to pick a motor/propellor/speed controller/battery setup. Its certainly no replacement for experience, speaking to some long term electric flyers they can quote a prop for a given motor/battery combination without ever actually having measured volts/amps.

I've also bought an electric flight meter which reads motor volts and amps up to 100A which can confirm setups. I used MotoCalc to find a better setup for a Mosquito I have. I was using direct drive 480BB motors with 6x4 props which was pulling over 30A but thrust was disappointing. I ran scenarios through and added 3.33:1 gearboxes plus 10x8 Graupner Cam folding props. For a 2Kg model it now flys well with a lower current. I've used it to predict thrust & current draw for an HVP Beaufighter I've just finished. MotoCalc got the current draw & prop rpm spot on.

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