I am setting up a Cobra 2826/10 on my Sakitumi-E.  Looking at the Cobra web sight they list max continuous power at 660W.

I started out with an APC 11 x 5.5 EP.  KR timer set at 9200 rpm.  Static amp draw was 19A. Recharge from a 4 minute flight was 1183 mah on a 2800 mah pack.

Next I tried a APC 12 x 6 EP cut down to a 11 x 6 EP. RPM still set at 9200 rpm.  Static amp draw was 25 amps and recharge from a 4 minute flight was 1595 mah on a 2800 mah pack.

Tonight on my work bench I tried a APC 12 x 6 EP without cutting it down. Static amp draw was 30 amps at 15 volts.  So input power was 450W, well below the max 660W rating of the 2826 cobra.

Looking at Cobra's prop chart they say that the 12 x 6 EP amp draw will be 47 amps @ 14.8 volts yielding 695W.  They also state RPMs will be 9,720.  This would be in excess of the 660W max power allowed.

I guess my question is does all this sound reasonable.  Should reducing the RPM from 9720 to 9200 drop the amp draw from 47 amps to 30 amps.  If so it appears OK to use the APC 12 x 6 EP.  If lap times are to fast I can drop the RPM.

By the way I have the time set at 4 minutes because, right now, I am trying to learn the beginner's stunt pattern and 4 minutes is plenty.

I use an APC 13 x 5.5EP cut down to 12 inches.
Shouldn't run your flight prop on the ground for 4 minutes.  It could overload your system.

True.  I never run on the ground more than 30 to 60 seconds. 

John
Motor Amp draw depends on the load you put on the motor. Load comes from RPM and the prop you use. More RPM load goes up less RPM load goes down (with it so the battery consumption as you already noticed from your test).

Props load the motor in two ways.
1: Mechanical load that comes from the mass of the prop ( kind of like a baseball bat: imagine each prop blade separate like a baseball bat you try swing, the heavier the bat the harder it is to swing). So a light prop will load the motor less than a heavier prop. Long story short use the lightest prop you can find that can handle the Rpm you are shooting for.
2: Aerodynamic load (drag from the aerodynamic forces that come from the blade moving through the air) Less pitch will load less than a higher pitch props. If you have two props with same pitch the prop with better airfoil and lift distribution will load the motor less than the crude prop.

What do you need in stunt is acceleration out of a corner (here a Low pitch high RPM is King) and lap time to maintain the speed so it stays on the lines. For Power conservation you want a high pitch and low diameter for thrust you. I would try any prop in the 4-6pitch and vary the Rpm (9600 for 6 pitch to 10500 for a 4 pitch) to achieve the lap time you are shooting for (perhaps in the 5.1-5.3s) and check the power consumption.

And here I go saying just about the same thing Denis said.

Don't forget to try the Xoar wood props.
So far, for their light weight/reasonable cost, they seem about the best value to me, and have worked well for both glow and e power.

R,
Target