The art of temperature management
Airplane engines and power systems have needed cooling since the beginning of powered flight, and our electric-powered RC planes are no different. Electric motors generate heat through wire resistance and other types of losses. A battery’s internal resistance, while small, can generate damaging heat as the battery supplies current to the power system. Speed controls generate heat as they switch power thousands of times per second to the motor’s windings. Choosing appropriate power-system components can minimize the amount of heat generated in the system but not completely eliminate it. Cooling airflow, through properly located cowl and fuselage vents and baffles, along with good component location can help manage the heat and keep temperatures below the damage point.
The electric-power system you install in a model is the first decision you make that has an impact on how much cooling the model will need. A marginal motor, speed control, or battery that has to operate near its specified limits will generate more heat than a component that’s comfortably within its limits. Doing the math or plugging the numbers into an electric-power calculator will allow you to make a good choice. I’ve had success using speed controls that are 25 percent or so over the expected current for a given system. They’re not a lot bigger or a lot more expensive, and they tend to run cooler because they’re not stressed by the load. My 30cc Spitfire, for example, draws about 75 amps and has a 120-amp speed control installed. The propeller is an inch smaller than the motor’s maximum size, and the entire power system runs cool enough so that I didn’t need to put any vent holes in that beautiful sleek cowl.
Read the article from the May issue of Electric Flight, Click here.