ORIGINAL: edpare
I am new to electric power and don't know how to choose an electric power system that would exactly match the performance of a nitro engine such as, say, an O.S. .46 AX ABN.
A small bit of math is all you need.
745watts = 1HP
The OS .46 AX is rated to produce about 1.7HP, realistically it probably produces about 1.5 HP
1.5 x 745 = 1117.5 watts
Now choose a voltage to get you there.
1117.5 / 18.5v = 60A
So to get that level of performance you'll want to use a motor capable of 60A 18.5v or put another way 1118 watts or better.
According to ThrustHP a 12x6 prop spinning at 12000 RPM produces about 1.56 HP.
12000 RPM / 18.5v = 650KV
A 20C 3000mAh 18.5v battery pack can just keep up with all of this, but you'll be driving it very hard.
A 20C-25c 4000mAh 18.5v battery pack will fair much better and a 20C 5000mAh 18.5v pack will give you good long flight times.
So there you have all the motor, ESC and battery specs you need!
It really is that simple, just not often clearly spelled out.