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Old Sep 28, 2015, 03:23 PM
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Sig 1/5th J-3 Cub conversion

My kit is several years old and originally setup with a Saito .62a for power. It's 7lbs, 84.5" wingspan, and 947 sq in Wing area. Converting to electric and have a couple questions.

Any issues with this setup?

GP Rimfire .46 (42-60-800)
APC 11x5 electric prop
eFlite 80 ESC
6s 45C 4000 mAh battery

Currently there is only a small hole in the firewall where the fuel lines passed through. Should I drill out a couple more holes for air flow? Will I need a rear air vent hole?
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Old Sep 29, 2015, 05:32 AM
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My 1/5 scale Cub (DB Sport & Scale, not Sig) weighs in at 6 lbs 11 oz and flies beautifully on 560 watts, so your Rimfire motor should be plenty. Only thing I can think of is maybe you want a slightly lower Kv, or reduce the cell count, so that you can run a larger diameter prop.

My model started out with an OS90FS, which was too much for it. My electric setup uses an AXI4120/14 motor and a Hobbywing 60A ESC. It started out on a 14-cell NiMh pack and a 14x7 prop, but now runs on 3S LiPo and a 16x10 prop.

Mine has no extra air holes, but doesn't seem to heat up at all, probably due to the sedate way I fly it.
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Old Sep 29, 2015, 06:44 AM
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Quote:
Originally Posted by Razer8811 View Post
My kit is several years old and originally setup with a Saito .62a for power. It's 7lbs, 84.5" wingspan, and 947 sq in Wing area. Converting to electric and have a couple questions.

Any issues with this setup?

GP Rimfire .46 (42-60-800)
APC 11x5 electric prop
eFlite 80 ESC
6s 45C 4000 mAh battery

Currently there is only a small hole in the firewall where the fuel lines passed through. Should I drill out a couple more holes for air flow? Will I need a rear air vent hole?
The Kv of that motor is way too high to run 6S with anything bigger than a 8-9" prop.

IMO, your 6S 4000 power source is about ideal, but you need to find a significantly lower Kv motor - The Kv will be determined by the prop size you want to run.
For 13" props Kv around 450 would work well. The Rimfire 55 with Kv=480 is the same size and weight as the 46 and you could run 13x6.5 for about 700W. If a heavier motor suits, then the Eflite Power 60B, Kv=470 is a good 13-14" prop choice
For 14-15" props, then Kv around 400 will work well
On a similar size but heavier Pawnee with 6S I use a Hacker A40-12L, Kv=410 with 15x6 for about 900W.
While you could use the Rimfire .46 on 4S with a 12" prop, to me running larger props more slowly makes more sense for a Cub, so I'd suggest sticking with 6S and choosing Kv that suits the largest diameter prop you can comfortably run.
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Old Sep 29, 2015, 07:26 AM
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Great input, thank you! Since I have one lying around, what about the FMS 4250-Kv580 on 4s 3600? Basically the FMS Warbird power system.

Otherwise, I know the LHS has a Eflite Power 52 which is 590 kv.

I know those are higher kv but both can swing larger props and I have a few 4s batts lying around.
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Old Oct 01, 2015, 07:07 PM
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Setup the Eflite Power 46 which is 670kv, 65a ESC, 14x7 prop, and a 4S 3600mAh 40C battery. Resulted in 620 Watts / 40 Amps.

I figured 525 Watts for Cub-like flying (7lbs @ 75W). Tomorrow hope to try a 13x8 prop. I do have a 4000mAh 40c 4s available too but that shouldn't matter too much.
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Old Oct 01, 2015, 08:17 PM
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Looks to me that between the Power 46 @13" or the FMS 4250 @14" you've got the 4S space well covered.
Imo if all your components can handle it, there's no hard imperative to prop down, as you can use throttle management to control energy use. And the larger higher pitch props are more efficient across the power range.
Gotta admit I was very glad recently of the reserve power in my Eflite Supercub25 when I messed up a touch and go and basically skull dragged the poor thing out of some horrible attitudes close to ground and trees.
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Old Oct 05, 2015, 11:32 AM
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I bought a Cobra 4120/16 from Lucien and plan to use it with a 5S pack or maybe even 4S to keep the prop down to 14" (approximately scale) for My 1/5 Cub. I chose the larger motor for CG and also find they are more efficient .
I have a large Scorpion I was gonna use but decided to try a Cobra as I want to use the Scorpion for the Astro Hog when I get around to building it.
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Old Oct 05, 2015, 07:32 PM
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Quote:
Originally Posted by jollyroger View Post
I bought a Cobra 4120/16 from Lucien and plan to use it with a 5S pack or maybe even 4S to keep the prop down to 14" (approximately scale) for My 1/5 Cub. I chose the larger motor for CG and also find they are more efficient .
I have a large Scorpion I was gonna use but decided to try a Cobra as I want to use the Scorpion for the Astro Hog when I get around to building it.
I'm getting 680 Watts with a Xoar 14x7E wood prop on 4S 4000mAh batts and the Power 46.

I did have to put a few ounces of lead in the cowl for CG.
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Old Oct 06, 2015, 06:36 AM
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680 watts should be fine.
I calculated the actual wattage output of a Continental 65 against the weight of a J3 Cub and came out at around 50W/Lb.
Explains why one does not horse a J3 off the runway.
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Old Oct 07, 2015, 05:51 PM
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I have one of these planes on glow and I'm thinking about switching to electric. How are you guys getting the battery in and out of your plane? Pictures would help.
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Old Oct 08, 2015, 06:08 AM
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A sliding battery tray would be the way to go. I'm going to look at Horizon Hobby web site to see if one from an AFR would work. The problem is my cub is built so access to the fuel tank area is limited.
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Old Oct 08, 2015, 09:40 AM
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That is one of the hold-ups to finishing mine. I plan to add an interior cockpit with both seats, quadrants and pilot so that's going to make things a bit of a challenge.
However, I need to get the airframe all together and then see where the battery pack needs to be placed for proper CG and go from there.
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Old Oct 08, 2015, 09:47 AM
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I have a Carbon Z morgan mill tray for a TF Spitfire kit build I'm doing but this wont fit in the completed plane. If I was building a new kit it might work.

http://www.morganmill.com/RC/Carbon_Z_Cub_Parts.html
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Old Oct 08, 2015, 10:54 AM
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Here's my solution. It's a long battery box that goes back through the firewall, but not too far into the cockpit (depends on your battery shape), and is accessed through a hinged hatch in the front of the cowl. You could use a sliding battery tray in the same location, but I don't see any real advantage. Mine's not a Sig Cub, but since they're scale models the layout should be roughly the same. My ESC is attached to the outside of the battery box, and is accessible when the cowl is removed. I have a battery isolator plug on the side of the cowl so I don't have to access the battery with the prop live.
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Old Oct 08, 2015, 10:59 AM
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abenn, thanks for the pics. That looks like a very easy way to access the battery pack. It looks like you are using a velcro strap to contain the pack and keep it from sliding forward.
That is one idea I've been kicking around. Another is a hatch through the top of the cowl into an area behind the firewall.
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