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Old Nov 26, 2012, 02:42 PM
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CHSNative's Avatar
United States, NC, Davidson
Joined Feb 2012
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Piper J3 Conversion and Questions

I am starting a nitro to electric conversion of my Piper J3 Cub. I am not sure exactly what version this one is or who made it as I received it from a friend. I am not exactly sure where to start though. I have weighed it and it weighs in right at 7 pounds. I have seen online that for these type of planes that I should calculate 90watts per pound. So that gives me 630. But not sure where to go from here - Hobbyking has sooooo many choices for motors I am lost.
I already have a couple of 2200mah, 11.1v LiPos so I am hoping I can re-use them here too.

Any suggestions for a setup?
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Old Nov 27, 2012, 10:56 AM
jrb
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Edina, MN, USA
Joined Oct 1999
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What size?? -- engine & wing span?

I've done 80" (1/5) & 106" (1/4)
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Old Nov 28, 2012, 08:30 AM
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JoseLG's Avatar
Jerez Frontera (Spain)
Joined Nov 2004
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If the N-numbers are correct this must be The Great Planes 40 Cub (Kit).

3S is feasible, but if you use a 4S battery, 60Amp/ESC and 700/800 kv motor with 13x6" prop you won`t go wrong.

Cheers.
José L.
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Old Nov 28, 2012, 02:35 PM
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Waverly, Nebr.
Joined Apr 2009
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Hey there CHSNative,

I was given a Cub J-3 this past weekend and it is most likely to be my next conversion. While I am not sure as to what I have as far as manufacturer, I agree with JoseLG that you have a Great Planes J-3. His power recommendations look good also.

I am converting a Sig LT-40 and am using a Emax 3526/05 710Kv 950 watt motor, 60 amp esc, and 4S 42mah 35C battery. My largest prop that I currently have is a 12 x 6. I hope to have this system fully tested (maidened) this up coming weekend. I will base my future conversions on the Sig's performance, maybe a 5S battery is in the future works.
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Last edited by beerbrewer; Dec 03, 2012 at 03:28 PM. Reason: typo
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Old Dec 03, 2012, 02:59 PM
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United States, NC, Davidson
Joined Feb 2012
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So I did some research and asking around and here is what I came up with:
Power Up 60 Sport Outrunner Motor
Hifei 80Amp ESC with Switchmode BEC
APC 13 x 6.5E Prop OR 13 x 6 DFDL Wooden Electric Prop
22.2v 4200mah 35C DBY-Power Lipo Battery.

Thoughts?

Also, I am not sure how I am going to mount the motor- do you think I will need to bolt straight to the firewall, or will I need to build it out a bit to push the motor forward?
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Old Dec 03, 2012, 03:53 PM
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beerbrewer's Avatar
Waverly, Nebr.
Joined Apr 2009
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An electric motor is shorter than a slimer engine, so yes you will have to redo the firewall someway to move the motor forward so the prop clears the cowling.

This is what I did for my Sig Lt-40 conversion. I moved the firewall out 2 inches using 3/8 basswood and Gorilla Glue. I bolted it in using the old blind or t-nuts for the mount and steering. It worked out great.

I could be all wet or misinformed, but your power setup might be on the extreme side. What wattage do you think you will get?
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Old Dec 09, 2012, 11:40 AM
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Joined Oct 2000
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You need to measure the wingspan to help identify the model. At 7 pounds it should probably have a low KV-rated brushless outrunner equivalent to a .40 size glow engine and running on 4 or 5 cell lipo packs and 50-60 amp speed control. You will probably be using four standard sized servos so you will need to use a speed control with built-in "switch mode" BEC rated for 5 amps, an add-on 5amp switch mode BEC or a 4 cell NiMh flight battery to power receiver and servos. You will need a power supply and charger for the lipo packs. You will probably need to provide a battery compartment and hatch for motor battery packs.
If you build in an operating side door and window, you can mount battery pack inside with velcro and velcro straps. In order to avoid tail-heaviness, and need to add more dead weight to the nose, you may need to locate battery pack etc., as far foreward as possible.

You may get some ideas from my Sig 1/6 scale Cub conversion on the Scale Electric Plane forum:

http://www.rcgroups.com/forums/showthread.php?t=1754853
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Old Dec 13, 2012, 08:18 PM
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http://www.rcgroups.com/forums/showt...r#post21334959





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