Piper Cub J3 1/4 scale conversion

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02-12-2014, 12:31 PM

Wrldctzn

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Piper Cub J3 1/4 scale conversion

I am considering starting on a SIG US Piper Cub J3 1/4 scale but all the specs call for glow engine. I'd rather do it electric. Any recommendations on conversion, motor, BSC and batteries? Weight should be in the 7.5kg range with 2.8m wingspan.

i would use a separate battery for radio and servos anyway so the LiPo would be only for the propulsion.

thanks for any contribution

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03-26-2014, 08:26 AM

aeajr

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EVERYTHING YOU WANTED TO KNOW ABOUT ELECTRIC POWERED FLIGHT
http://www.rcuniverse.com/forum/m_7100376/tm.htm

This e-book will help you.

Also, using a motor selection resource can be helpful too. The Electrifly system works well. I have had good experience with the Rimfire motors.
http://www.electrifly.com/powersyste...tem-index.html

7.5 kg = 16.5 pounds.

Normally when going from fuel to electric we target 100 watts/pound. If you are flying a Cub in a more or less scale manner then as low as 75 watts/pound is fine. A full size cub flies on about 60 watts/pound. If you are looking for lots of power then shoot for 150 watts/pound.

So a 16.5 pound plane (all up flying weight) would call for a 1650 watt motor.

Here is one example from the calculator

Motor Recommendations

[TABLE]
[TR]
[TH][/TH]
[TH]Best Combination
[/TH]
[TH][/TH]
[/TR]
[TR]
[TD="align: right"]Performance
[/TD]
[TD]Sport
[/TD]
[TD][/TD]
[/TR]
[TR]
[TD="align: right"]Motor
[/TD]
[TD]63-62-250 / GPMG4795
[/TD]
[TD][/TD]
[/TR]
[TR]
[TD="align: right"]Gear Ratio
[/TD]
[TD]N/A
[/TD]
[TD][/TD]
[/TR]
[TR]
[TD="align: right"]Gear Drive
[/TD]
[TD]Not Required
[/TD]
[TD][/TD]
[/TR]
[TR]
[TD="align: right"]Propeller
[/TD]
[TD]18x6 in., Wide
[/TD]
[TD][/TD]
[/TR]
[TR]
[TD="align: right"]Battery
[/TD]
[TD]3200 mAh, 37.0v
[/TD]
[TD][/TD]
[/TR]
[TR]
[TD="align: right"]ESC
[/TD]
[TD]SS-100 / GPMM1870
[/TD]
[TD][/TD]
[/TR]
[TR]
[TD="align: right"]ESC Motor Adapter
[/TD]
[TD]Not Required
[/TD]
[TD][/TD]
[/TR]
[TR]
[TD="align: right"]Motor Mount
[/TD]
[TD]X-Large / GPMP1265
[/TD]
[TD][/TD]
[/TR]
[TR]
[TD="align: right"]Current Draw
[/TD]
[TD]40 amps
[/TD]
[TD][/TD]
[/TR]
[TR]
[TD="align: right"]Approximate Speed
[/TD]
[TD]43 mph
[/TD]
[TD][/TD]
[/TR]
[TR]
[TD="align: right"]Approximate Thrust
[/TD]
[TD]181 oz.
[/TD]
[TD][/TD]
[/TR]
[TR]
[TD="align: right"]Weight of Power System
[/TD]
[TD]53.06 oz.
[/TD]
[TD][/TD]
[/TR]
[TR]
[TD="align: right"]Approximate Flight Time at Full Throttle
[/TD]
[TD]4.6 minutes
[/TD]
[TD][/TD]
[/TR]
[TR]
[TD="align: right"]Watts per Pound
[/TD]
[TD]89.7
[/TD]
[TD][/TD]
[/TR]
[/TABLE]

Flight times can be increased by reducing the throttle, using a larger capacity pack or by using two battery packs connected in parallel. Please note that the weight of the motor mount is not included in the system weight. The weight of the different mounts can be found on the ElectriFly web site.

This is configured for a 10S battery pack.

Last edited by aeajr; 03-26-2014 at 08:29 AM.