Best Motor/prop/battery for high altitude - RC Groups
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Jul 10, 2002, 06:41 PM
WickedFunRC's Avatar

Best Motor/prop/battery for high altitude

Hi, I am new to electric planes and have not had much success as of so far. I have a couple of planes that are roughly 26 oz and have a wing area of about 275 sq inch. I have tried a Graupner speed 400 race motor with an 8 cell pack with both 5 X 5 and 4.5 X 4 props and they barely fly. Anyone have suggestions on what would make these planes scream? What is a super hot combination? Should I go brushless? Should I gear it? Should I go to a 10 cell pack? Should I quite asking so many questions?
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Jul 11, 2002, 04:43 AM
(aka Cliff Lawson)
Wright Flyer's Avatar

Have a search for "MotoCalc" and/or "Electricalc". These are two programs where you get to put in all the numbers about a plane (wing area, weight, motor, cells, etc.) and then they let you "try" different props and use mathematics to predict what it will fly like. Both are remarkably accurate. In the case of MotoCalc you can download a trial version that works for 30 days to see if you like it before parting with your cash.


The relevant web sites are:




Jul 11, 2002, 10:18 AM
WickedFunRC's Avatar
OK I downloaded motocalc, wow what a great tool!

Theres alot of factors involed in choosing the right combination for these electrics isn't there -- not quite as easy as gas planes(but not as loud and sloppy either).

Thanks for your help
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Jul 11, 2002, 11:38 AM
Registered User
RPatrick's Avatar
Hi Khen, and welcome to Ezone!

When thinking about your motor setup, the one of the first decisions is to determine whether your plane will fly best with either gearing or direct drive. Sleek low drag planes like direct drive with small props, while planes with thicker profiles need larger props for more thrust and are geared (most of the time, depending on the motor). Once you know this you'll be able to better utilize the prediction programs.

What is a super hot combination?
A brushless motor with 10 cells !!!

Jul 11, 2002, 05:59 PM
Registered User

This works on my 26oz plane

On a 26 oz AUW plane I have, which is a flattened aileron T52 wing and a scratchbuilt fuse, I have had great success with the following power combo.

S400 6V
APC 9.5 x 6.5N Prop (intended for .40 gas pylon racers)
2.9:1 Gearbox
8cell 600AE or RS 1600Nimh

Duration is 6 minutes with AE and 10+ minutes (I always land waaaayyy before the cutoff occurs with this pack) with the RS Nimh. This combo is cheap and gives good thrust and top end.

The funny thing is that in experimenting with these setups the crucial factor after you get in the ballpark with motocalc is trying many differrent props. I collect them almost everytime I go to the hobby store. It seems that every AUW, motor, Battery, Gearbox combo has its own prop sweetspot, and it really just takes flying alot of them to know which one that is. I hope this info helps.
Jul 12, 2002, 01:32 AM
WickedFunRC's Avatar
Thanks! all your help is appreciated. I am slowly starting to figure this stuff out.
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