smokingwreckage

I've received a Dynaflite Piece-o-Cake kit as a gift. This is a 2-3 channel motor glider designed for .049 1/2A engines. It has a 72-inch span and will weigh 24-28 ounces if set up for glow power.

For sentimental reasons (I had one set up for free flight back when we found thermals by looking for teradactyls) I'm building the kit, my first electric model aircraft. I've scrounged the following parts for electrical power:

Himax Gear Motor HA2025-4200 with 6.6:1 gear drive;
Castle Creations Phoenix-25 brushless, sensorless speed control;
4 pieces 3000mAh lithium-polymer 9C continuous, 12C intermittant cells;

or

26 pieces 800 mAh lithium polymer 6.35 continuous (C figure may be higher but that's all I've tested them to because that's all I needed for the application for which the cells are now being used) cells;
APC LP 12038SF 12x3.8SF Slo Flyer composite propeller;

Hitec Electron 6 micro receiver;
Hitec HS-55 servos.

Here are my questions:
Is the power system a good replacement for a .049 glow engine?

The instructions for the plane call for standard servos. Several RC modelers with more experience than me have told me the micro servos will be okay because electric is gentler and a 2-meter floating motorglider has very low control forces. True or false?

The 3000 mAh 3-cell 9C battery will handle 27 amps of continuous output, which is more than the motor requires (30000 mAh x 9C =27,000 mAh - 27 A). Is that how the math is done?

Will a 2S2P arrangement for the 3000 mAh cells provide sufficient power for the plane to have reasonable vertical performance and extend the flight times?

Would I be better off using the 800mAh cells in a 3S3P or 3S4P arrangement?

Thanks for your help.

Time Pilot

The Himaxx 2025 is rated for 175Watts. With electric planes, a general guide is to compare the weight of the plane by how many watts the motor system can provide as watts is the amount of work being produced.

I think "Sport" performance is somewhere around 50 watts per pound, which is likely where you'll end up with, likely more.

I'm not too sure about your batteries, what are they exactly, 3 cell lipos?

If they are 3 cell Lipos (11.1V), I'd bet you could go up to a 12 x 6.

If no one else pipes in on the servo question, the smallest servo I'd go for in that plane would be a something like a Hitec HS-81. In slow flight, I would be confident the HS55's could handle it, but I'd be concerned that if I built up too much speed (like in a dive) the HS55's might not.

smokingwreckage

Thanks for the response.

The batteries aren't batteries, yet. Just individual cells. I have to assemble the cells into batteries. I have 4 of the 3000 mAh cells and 26 of the 800 mAh cells. I'm free to assembly them in any configuration.

I'll go with the HS-81 servos. They'll definately handle the loads better than the Hs-55 servos, and they only cost $3 more for the pair.

I'm not sure what constitutes "sport" performance. The Piece-o-Cake's wing loading should be somewhere around 6-7 oz/ ft^2, and with a double dihedral wing and no ailerons I don't think snap rolls and inverted are in its flight envelope.

Time Pilot

I've not seen a definition for sport performance either, but from my experience, I would guess it would be like a glow powered trainer with the recommended engine.

If you want to play with an electric motor calculator, you might want to try this one:

http://brantuas.com/ezcalc/dma1.asp

They are not 100%, but they give you an idea of what to expect. Plug in your numbers and see what you get.

You may also want to have a go at RCGroups.com. They've got a larger eflight contigent over there and there may be someone who can speak of their conversion.

smokingwreckage

Thanks. I'll give the link a try.