How big an electric motor for Miss Texas - RC Groups
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Oct 27, 2017, 01:30 PM
DC3 Crazy
Discussion

How big an electric motor for Miss Texas


Hi all,

SInce I'm new to electric, I was wondering what size motor/esc/etc. for a plane that was originally balsa build, with an 84" wing span. Actually, the picture below shows the plane I'm considering building for electric power. Any suggestions if I should modify material/construction techniques or any sound advice on such a build ?

Thanks.
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Oct 27, 2017, 06:37 PM
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scirocco's Avatar
You should do fine with a 6S 5000mAh battery and 60A or larger ESC, even up to 10-12lb, and still be able to fly nice sport aerobatics.

If you can fit a 16" prop, then motors weighing close to 400g and with Kv close to 400 rpm/V like the Eflite Power 60A or Turnigy G60-400 or Scorpion 4035-380 or Cobra C4130/16 will handle more than enough power for flying weight up to about 12lb.

If prop size is limited to 15", then look for motors with Kv about 450 rpm/V

If prop size is limited to 14", then similar motor weight is still needed, but Kv needs to be closer to 500rpm/V eg the Power 60B, Turnigy G60-500.

The best bet is to leave motor and battery choice until after the airframe is built. You can plan for motor and battery installation of course, but for example, if it needs more weight in the nose than a 400g motor and a 750-800g battery, then you could opt for a significantly heavier motor, which may drive you to a different battery solution.

Also, once built, you'll know how large a prop you can use. For a slow flying model like this, you'll want to go close to the maximum diameter you can comfortably use considering ground clearance and then choose motor and battery to suit the prop , not vice versa, There is basically always a suitable motor and battery combination for a given prop - but the reverse is not always true, so work from the prop first.
Oct 30, 2017, 12:50 PM
Registered User
Outerzone has the plan and article to download, the plane flew with a HP61 on a 12x6 or 13x5 prop.

Peter Chin suggests in an old review of a HP61

Typical prop revolutions recorded towards the end of this period included 11,200 on a Power Prop 12x6, 11,400 on a Rev-Up 11x7-1/2, 11,700 on a Rev-Up 11x7 and 12,200 on a Top-Flite "Super-M" 11x7.

So these are the parameters to aim for, a motor that can drive a 12x6 at about 11,500 rpm.
Nov 01, 2017, 09:43 PM
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basicguy's Avatar
My 82" cub flies with a 400 gram motor. Weight is 7.5 pounds. Pick a motor that will balance the plane with the battery pack on the CG. Don't worry about overpowering it Electric motors have low end power. A good place to start is about 10% of the total weight.
Nov 02, 2017, 08:24 AM
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Doug Bartley's Avatar
I've flown several planes in this size using either a Scorpion 4025-440 (4025-12) on 6S/5000mah/30c batteries with an 80 - 85A Esc <either a Turnigy Plush or a TZ85a . I'd rec a 16/10 2 blade or a 15/8/3 blade. Either one will produce approx 1400 watts in power, more than enough to fly this bird well.
A Suppo 4130-6 (430kv) is another good motor for this bird with a slightly smaller prop, 15/8 2 blade or 14/9/3blade, same battery and esc. fwiw Doug B


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