Electric Conversion Step 1
Electric motors for Glow people
Electric motors provide a clean and reliable power source for models. Selecting a motor is not much different than selecting an engine when you look at the fundamental requirements. The basic principles that make an aircraft fly should be used to select a power plant for the performance desired.
Method 1
Our first method is the simplest. There are many aircraft designed for glow engines. We can approximate the required power based on engine displacement. A survey of available engines resulted in the chart below in terms of watt per cubic inch displacement (W/ci)
Sport 2 Cycle 1250W/ci
BB 2 Cycle 1500W/ci
Multiply the displacement of the recommended engine by the W/ci rating to find the amount of power required of the electric motor system.
For example; a .40 plain bearing engine will make .40ci x 1250W/ci = 500W of power.
|
OS Engines |
Practical RPM |
Output (hp @rpm) |
Watt equivalent |
Prop |
| 10LA | 2,500 - 18,000 | 0.2 @ 17,000 | 125 Watts | 7x5 |
| 15LA | 2,500 - 18,000 | 0.4 @ 17,000 | 187 Watts | 8x5 |
| 25LA | 2,000 - 16,000 | 0.6 @ 15,000 | 312 Watts | 9x6 |
| 40LA | 2,000 - 16,000 | 1.0 @ 15,000 | 500 Watts | 10x6 |
| 46LA | 2,000 - 16,000 | 1.2 @ 15,000 | 575 Watts | 11x6 |
| 65LA | 2,000 - 16,000 | 1.7 @ 16,000 | 812 Watts | 12x6 |
Method 2
To customize the motor size the power loading is the first parameter to consider. Power to weight ratio for electric models is generally quoted in watts per pound (W/Lb). This is a basic performance gauge. More power available per pound gives better results. Power loading holds true for models all the way up to full scale. Some examples are listed below. 1 Horsepower (HP) = 746 Watts (W)
Piper Cub 65HP 1220Lb 40W/Lb
B-17 4800HP 65000Lb 55W/Lb
Pitts Special 260HP 1626Lb 120W/Lb
Spitfire IV 1440HP 5000Lb 215W/Lb
The chart shows that high performance requires a high power loading. The Cub flies sedately at 40W/Lb and so will a model with this power loading. Follow the chart below for model aircraft.
Mild ROG Performance 50W/Lb
Mild Aerobatics / Sport 75W/Lb
Aggressive Aerobatics 100W/Lb
3D or High speed 125-150W/Lb
All Out Competition 300+W/Lb
As an example
consider that many .40 size trainer models weigh 6Lb, at 500 watts the power loading works out to 83W/Lb.Once the required power is known we can look for a motor. Look at the motor specifications of your favorite supplier for the power rating in watts. Choosing a motor with a power rating equal to the requirement is safe, but it would be better to choose a motor capable of more than is required.