Mark Scarborough's electric P-40

By Mark Scarborough

The airframe is a Brodak P-40 ARC with 7/8" dihedral added to ge the leadouts into the correct position with respect to the vertical CG.

The motor is an AXI 28-26-10. It spins an APC 12x6 electric prop (closer to effective pitch of 7 in reality) at 9200 rpm launch setting.

I use a Castle Creations 45 amp Phoenix speed controller with a Ztron version 4 timer. 

The speed controller is operating in the Govenor mode. It monitors the prop rpm and adds or subtracts voltage to vary the amperage going to the motor to keep the propellor speed constant.

The timer has an adjustable "needle valve" that lets me vary the rpm plus or minus 500 from the programmed stetting to adapt to current conditions.

My battery packs are 4s 4270Mah EVO. I have four packs, two charging systems. It takes approximately one hour to recharge a pack after a flight. I am draining on average 3200 Mah from the batteries per flight. This allows long life for the batteries because they are not getting stressed.

Line length, I am using .018" lines that are 61' eye to eye and my lap times are 5.5 to 5.1.

All up weight is 57 oz except when I fly it with the eagle tree data recorder which adds about 1.5 oz. It is knowingly overweight but flies quite well despite that fact. Power delivery is smooth and consistent and more than adequate for my beast despite its portly nature. The power system weighs almost exactly 20 oz.

I am very impressed and am in process of designing a dedicated airframe to take advantage of some of the electric system's attributes. It should weigh significantly less and fly better though I really can't complain about the way this one flies at all. Pat's wing design will really haul the mail. Right now I am experimenting with another motor, and trying to come up with a combination that will allow me to swing a flatter pitch prop.

I believe that there are performance gains, mostly in braking action, on the downhill side of maneuvers with a flatter pitch setup. The data recorder allows me to monitor actual in flight performance at a rate of 10 samples a second to see what is happening in the maneuvers.

It's actually really interesting to see the results of experiments with factual information instead of relying on my own judgment from the handle.

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This page was upated Oct. 27, 2008