Oodi

I'd like to build an electric trainer from Coroplast. The idea is to utilize a .15 or .20 design with standard radio gear. What would be a good universal motor and speed controller to experiment with? For power I am thinking 2100mAh NiMH pack.

Matt Kirsch

My Feedback: (21)

That's the thing about electrics. There's no "universal" solution that will work everywhere a particular engine size will work. Well, there are, but they're overweight and overkill in most cases. Less is more when you're talking about electrics.

For a .25-size trainer, there are several possibilities:

Kyosho Endoplasma, 4.6:1 gear ratio, 12x8 prop, 10 cells.
AXi 2820/10, 12x8 prop, 10 cells.
Jeti 30/3, 11x6 prop, 10 cells.

These will all power fairly slow flying airplanes up to 5 pounds.

Oodi

Here is what I have in mind, 36" wingspan with 8" chord for 288 sq in wing area. I hope to be able to keep the weight at about 2 to 3 pounds which should be achievable. The numbers are based on scaling down the dimensions of a plane I build for a .20 and reducing weight where I put too much material in. I really meant inexpensive, a plain vanilla brushed motor. Would a speed 400 be suitable, direct drive or geared?

Matt Kirsch

My Feedback: (21)

The power systems I mentioned above weigh close to 2lbs in and of themselves, so I guess I stepped in a big pile of dog poo on this one I assumed you were building a .25-size plane, not a scaled down version OF a .25-size plane.

Even running at its highest power level, a Speed 400 is only good for about 24 ounces, 1.5 pounds, and then only if you've got plenty of wing area. That 2 to 3 pound range is kinda hairy with cheap can motors. A geared Speed 480 on 10 cells will give you 75 Watts per pound on a 2 pound plane, kind of sedate flying... When you jump up to Speed 500, you get a huge increase in weight because you have to run much heavier batteries. A Speed 480 with 3:1 gearbox and 10x7 prop and ten KAN1050 cells only weighs about 13 ounces. A Speed 500 with 3:1 gearbox, 12x8 prop, and ten KAN1800 cells is almost 20 ounces. The heavier batteries are necessary to facilitate the higher current draw of the Speed 500.

If you can build your plane and come in at 1 pound, 12 ounces, up to 2 pounds, for the airframe and radio... Just don't sacrifice wing area to save weight. The more wing area, the better, even if it does increase the weight.

Couple of things about building light SPADs: Use 2mil for the wings, like the HOR. Build your own "gutter pipe" out of 4mil. Much lighter than real PVC gutter pipe.