Oosa-Amma electric conversion

[Bob Hunt]

A few years back I retrofitted my Gene Schaffer-designed Oosa-Amma (Stunt Machine 1) from glow to electric power. Since the canopy on this model was forward of the wing, it was necessary to make this conversion a “bottom loader.”  The original cowling had to be modified a bit, and that allowed me to cut the forward portion of the cowl and permanently attach it to the fuselage, leaving plenty of space in which to install the battery . The problem was that the ESC would have to be positioned above the battery, putting it in a dead spot for air flow. I couldn’t put it below the battery because then I couldn’t put the battery in. Then it dawned on me that I could position the ESC on a platform that would be screwed to a plate that went across the fuselage just aft of the motor area, and that platform could be made to swing out of the way to allow battery access by removing one of the screws that held it in place. Viola! It worked perfectly and now the ESC gets a lot of air flow straight back from the intake.

The attached photos should clarify all this. I took the photos because Frank McMillan was going to do the same conversion on his Oosa-Amma and wanted to see what I had done.

Note that the battery is installed at an angle when viewed from the side. This allowed even more room for the ESC platform. The center line of the battery was positioned on the center line of the wing, so there were no vertical CG trim issues. The ship flew perfectly level both ways after this conversion, and it flies a whole bunch better than it did with the glow engine.

I‘m using a BadAss 2814-870 motor, a 5S 2,200 mAh battery, a Jeti Spin 44 ESC and a Fiorotti timer system. I’m currently using a BadAss 11 x 5 reverse pitch wood prop and it pulls the plane with authority. I’m on 64 feet (center to center) .012 solid lines and I’m using  Kaz 90 MM handle. All in all an extremely successful conversion!

Later - Bob Hunt

[Paul Taylor]

As always - nice conversion Bob!
Was there any weight savings going electric?

[Donald R Olson]

Thanks Bob, for sharing your solution. This configuration could be adapted to most any design and it would allow for a narrower fuselage than some other battery tray designs.

[M Spencer]

Looking Good . Does the Motor get bolted down from the front ( thru before the spinners on )  ?

Whats your opinion on sticking controls / control stiction , Without the I. C.  to rattle them loose .

[Ken Culbertson]

Note, however that the weight with the engine did not include fuel, so the actual takeoff weight with the electric setup is actually lighter (at least until the fuel burned off with the glow engine....). 

If you weighed using discharged batteries the weight would be more comparable to an empty tank.

Ken

[Lauri Malila]

If you weighed using discharged batteries the weight would be more comparable to am empty tank.

Ken

True, but with a lesser effect; E=mc^2🤗 L

[Paul Taylor]

Hi Paul:

The weight turned out to be essentially a wash. The plane weighed 52 ounces with the engine; a PA 40R Ultra-Lite Merlin (that thing had almost as many nick names as Apollo Creed in Rocky 4...), and it weighs 52 ounces all up with the battery now. The plane has 620 square inches of wing area, so it flies "light." Note, however that the weight with the engine did not include fuel, so the actual takeoff weight with the electric setup is actually lighter (at least until the fuel burned off with the glow engine....). 

Later - Bob

That’s good news. But I should have guessed it. You build so light anyway. 😉