Inherent Overheating Protection of D-C Aircraft Motors

Inherent overheating protection is undoubtedly one of the major developments in the fractional-horsepower-motor field in the last decade. Thermal protection is now advocated by some for aircraft motors, and many thermally protected motors are now in aircraft service. In this paper are reported the results of a number of laboratory tests taken on a typical aircraft motor. Tests were taken on a 1/15-horsepower 7,500-rpm d-c motor; loads ranged from locked rotor to the minimum running load sufficient to trip the thermostat. Ambient temperatures ranged from -58 to +78 degrees centigrade. Locked-rotor and running-overload temperature tests were also taken at a density altitude of 42,000 feet. Temperatures of the winding, frame, brush holders, and bearings were measured carefully under all conditions mentioned. Satisfactory protection, without out premature tripping, was invariably achieved.