Summer 2006 Issue

Airborne Radio

Electric Power Systems

By Del Schier,* K1UHF

These days, electric airplanes are “where it’s at.” Technology in the form of lithium batteries and brushless motors makes electric power as good as wet-fuel power. Little glow plug and ignition engines work great, but they are a hassle and messy. Electric power is clean and easy.

RC airplanes have been flown with electric motors for many years, but until recently they used DC brush motors with nickel-cadmium batteries. While this older technology still works well and is inexpensive, lithium polymer batteries with three phase AC brushless motors offer a big improvement, especially in the power to weight department. Higher power to weight ratio gives higher performance and flight times.

Deciding on the best power system for an airplane can be complicated unless you purchase an airplane with a power system that a dealer or manufacturer correctly recommended. The advice of the supplier is a good starting point, but you still need to have an understanding of what your choices are.

A power system isn’t just the battery and motor. It is also the speed control and propeller, and yes, the propeller may be the most important part. All of the pieces are highly interdependent, and the entire package must match the airplane.

Motors

DC brush motors are inexpensive, $10 or less, as they are made in quantity for cordless drills and screwdrivers. You will also find tiny pager motors or cordless toothbrush motors in smaller airplanes. Mass-produced brush motors are called “can” motors, as they have stamped steel can housings. They usually have bronze bushings or sometimes ball bearings, and they use ferrite magnets.

A 600-size cordless drill brush motor.
 

58 amps at 36 volts AXI outrunner, 600 grams.

A Medusa Research Afterburner inrunner
brushless motor.

A small AXI brand outrunner motor, 9 grams.

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