How Do You Pick the Right Electric Motor for Your Size Application?
Stan Janczar would like to know how to properly size electric motors for different size planes. The question raises some interesting theories and I will keep it simple by starting with some basics.
Let’s start with something familiar like glow - powered airplanes. We know that most .40 size planes weigh about 5 pounds and the average .40 engine has almost one horsepower. This ratio of five to one puts you in the sport category. Going up in size to a motor that has 1.5 horsepower will put you in the 3.33 pounds per Hp range and will allow aggressive climb and maneuvering capability.
One of the worst things you can do
to an airplane, is under power it!
So, what is the common denominator between engines and motors? The answer would be; One horsepower equals 746 watts giving us a basis for calculation. A simpler rule of thumb would be to allow 100 watts per pound of airplane. If you are trying to select a motor and the wattage output is not listed, simply multiply Motor Volts X Peak Amps to get Watts.Since an electric motor has full torque available at zero RPM, most electric motors will outperform a comparable glow engine and if you follow the 100 watts per pound theory, you will not be underpowered!
Once you have selected a motor, follow the manufacturers recommendation for Electronic Speed Controls and Prop sizing.
Next month, we will attempt to untangle the further mysteries of RPM Per Volt and Motor/Gearbox/Prop Combinations.
