1/3 Scale Cub--Motor Size?

[gallfer]

Was given a Balsa USA 1/3 scale Cub partially built. Would like to go with brushless for power. Having a problem deciding which mfg and size motor is best. Anybody out there with ideas? Thanks!

[Sabrejock]

The 1/3 J-3's I've seen were marginal on an 18-8 turning 7krpm, but fine on a 20-10 at the same rpm [bigger engine]. You could reverse compute those numbers using a calc program to come up with watts. Go from there. Tex.

[jrb]

Have you seen this thread: http://www.rcgroups.com/forums/showthread.php?t=985069 ?

[gallfer]

Yes Thanks, I have. Was hoping for other motor manufacturers. Himax, Axi, Hacker etc.

[twest]

Yes Thanks, I have. Was hoping for other motor manufacturers. Himax, Axi, Hacker etc.

Pretty simple, really. Take the KV of the motor referenced in the other thread, and pick the motor brand of your choice with a similar kv. Then use a 'calc program to fine tune the winding of your choice motor.

[AmpAce]

For scale-like J-3 flight you shouldn't need more than 50 watts/pound. Assuming you can build it light, the Cub shouldn't weigh over about 30 pounds. A power system giving 1500 watts should fly it fine.

As Sabrejock indicated, pick a motor with a low enough KV to turn a scale sized prop, (22 to 24 inch range). On a Cub, you don't need a lot of prop pitch. I would start with an 8 inch pitch and see how it flies. A 6 inch pitch may even prove better for getting off the ground quicker or emergency cilmb-outs, etc.

When you get the power system, you can see what static rpm the prop will turn, and figure your theoretical airspeed from that. You shouldn't need more than 30 mph for the Cub.

This is all just kind of theoretical. You should try several props and see which ones you tend to like best.

Another great thing about e-power, is that if you want more power, just add more battery voltage, as long as the motor and esc will handle it. On a big plane like this, where a little more nose weight may help with the CG anyway, I would deliberately oversize the motor a little bit, to give some room for increasing power later, if needed.

AmpAce

[jrb]

FYI:

My 1/5 80" older H9 ARF: ~9#, A123-5S2P, 400Kv, 15x8, 27amps -- 3SL40-6-18.

1/4 103" H9 ARF: ~16#, A123-10S2P, 230Kv, 17x10, 36amps -- 3SL40-14-32.

These are older 40amp Kontronik ESCs

Both via skis during the winter!

[cooper998]

A Hacker A60-16L would spin a 20x10 prop with ease on 10 cells, I have one sltaed to go in a 1/4 scale Taylorcraft to be use for aerotowing.
I have also used an AXI 5330-18 spinning a 19x12 prop on a Sig Rascal but pulled more amps thean the Hacker does on the same cells.
1/3 scale Cub is built plenty strong for gas engine use and will weight in the 30lb range, this could be lightened extensively and fly great on something like a 5320 series AXI and 8 cells.

cooper998

[gallfer]

Greg Covey at RCU used a Axi 5345 on a clipped wing 1/3 Cub ARF in a review and said it had enough power for very good aerobatics. Thanks to all! Gino