• You'll need about 11 watts per ounce of airplane weight.  So for a 20 ounce airplane, that's 220 watts.  So look at motors that are rated for no less than 220 watts peak power
• For this sized airplane you want to spin the prop between 10000 and 12000 RPM (that drops to about 9000 for a "full sized" stunter)
• For this sized airplane you probably want a 3-cell pack (bigger airplanes = more cells).  This isn't a general rule -- you could probably make this work with two cells, or with four, if you size your motor and ESC right
• A 3-cell pack is an 11.1 volt pack (there's 3.7 volts per cell, and it adds up -- 3.7V/cell * 3 cells = 11.1V)
• You want to spin 12000 RPM at the end of the flight and at full current -- this means you can only count on 8.3V or so (that's 75% of full voltage -- (11.1V)(0.75) = 8.3-ish volts)
• The motor speed is the motor Kv times voltage.  So you want to find Kv from Kv = (target speed) / (voltage).  In our case that's (12000 RPM) / (8.3V) = 1450 RPM/volt
• Now you know enough to go motor shopping -- woo hoo!  Look for motors that can handle 220W peak, and have a Kv of 1450 or better
• If you just can't find a suitable motor, go back to the step where we decided on the number of cells, and try it again with four

• power equals current times voltage.  We can turn that around: current equals power divided by voltage.  So when we're asking for 220 watts from the motor, we need a current of (220W) / (11.1V) = 19.8-ish amps -- call it 20A (more cells means higher voltage, which means less current for the same power -- this is why bigger planes have more cells)
• So you know that you need a 20A ESC that can handle three cells
• If you are using a KR timer, or if you don't care about a "perfect" run, then almost any ESC will work (there's some really cheapo ones that the KR timer doesn't like)
• If you are using a Hubin timer then you need to get an ESC that has a governor mode (the KR timer has a governor -- the Hubin timer depends on the ESC)
• Go select an ESC

• You're going to use about 0.6 or 0.7 watt-hours per flight if you do a full six minutes.
• Watt-hours can be calculated like power: watt-hours = amp-hours * volts.  You can turn that around: amp-hours = (watt-hours)/(volts)
• You have a 20 ounce plane, so you need about 14 watt-hours.  You have an 11.1V battery, so that works out to (14W-h)/(11.1V) = 1.26 amp-hours, or 1260 mA-h (1 amp = 1000 mA, so 1 amp-hour = 1000 mA-hour)
• You only want to discharge the battery by 75%, so you need more than 1260 mA-h: (1260mA-h) / (0.75) = 1680 mA-h
• So you need a 3-cell pack with better than 1680 mA-h capacity.  1800 would be plenty.  You could probably squeak by with 1600, because the Acromaster will probably fly the whole pattern in less than six minutes
• You want at least a 20C discharge rate, and mo is betta
• Go buy a 20C or better 3-cell pack with more than 1680mA-h of capacity

Thanks Tim, why didn't you say this sooner    This made a lot of sense to me.  Even a plumb dumber can do that figure-n. One thing I didn't get is where you came up with 10k-12k RPM's for the smaller Akromaster. Really though, thanks for the equations