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Old Apr 23, 2012, 12:06 PM
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Alex Koehn's Avatar
United States, AL, Emelle
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What size motor?

I'm building a profile Sbach 342 out of DTF. I've been out of the small electric world for a loong time and don't know all the sizes and terms and all of the brushless motors. My plane is a 34" wingspan and I expect a 12-17oz AUW. Would a park 400 be what I need for 3d performance? Also what prop would be good?
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Old Apr 23, 2012, 12:44 PM
Lost but making good time
Joined Nov 2008
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Alex,

I've been at this for 4 years and am not an authority on any aspect of this hobby but have begun to use WebOCalc as a tool to point me in the right direction when I'm looking for a combination of prop, motor, Esc and battery for a plane. You can use the program in two ways. You can plug in the AUW of the plane along with its wingspan and wing area and pick a prop 1/4 the wingspan and continue down an let the program pick out combinations for you. You can also plug in the airframe specs, and what ever size motor etc you think you want to use and see if they are feasible or not.

Play around with it...www.webOcalc.com

Regards,

Hankg
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Old Apr 26, 2012, 10:43 AM
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United States, AL, Emelle
Joined Feb 2012
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Ok I think I've decided to go with a 28-30-750 outrunner with a 25a esc and 3s lipo. I used Motocalc to come up with this. Approx. what size prop should I run with this for 3d performance?
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Old Apr 26, 2012, 07:55 PM
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Alex,

Do you still have that Park 400 and if you do, what is the Kv? It's a good motor for that plane you are considering if it's the 920Kv...750 is to low on Kv.

You're looking for a motor between 900-1200 Kv. I ran a Park 400, 920Kv and with a 9x7.5 prop, a 3S -750mah battery and a 16-19 amp Esc you should be able to hover easily...142 watts per pound, 1.5 to 1 thrust to weight.

Regards,

Hankg
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Last edited by hankg; Apr 26, 2012 at 09:50 PM.
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Old Apr 30, 2012, 09:12 AM
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Tucson
Joined Nov 2009
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You can get in the right ball park by matching the watts of the motor to the expected full up weight. You expect your plane to be about a pound. 1 pound x 150 watts = 150 watts. So a 200 watt motor should let you accelerate straight up. (you should not need a 400 watt motor).

Pick a prop that is matched to the motor. Pick a prop bite that will give you enough speed. Pick a battery that will run the motor, and fit on the plane. Pick a speed controller that can handle the amps of the motor.
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Old May 01, 2012, 08:58 AM
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Thanks for the responses guys. I'll see what I can come up with.
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