Electric power for airplanes

Electric-power loads are increasing rapidly on airplanes and auxiliary-engine-driven generators offer dependable power sources independent of main engines. Minimum weight for the required capacity is essential in the design of generators, motors, and control. The a-c 110-volt 400-cycle three-phase system has been developed for large airplanes with heavy motor loads. Alternators rating 12.5 kva at 75 per cent power factor and two-pole motors running at 22,500 rpm full-load speed are available. Control apparatus builds up the alternator, establishes accurate voltage regulation, and provides direct current for excitation and battery charging. The 24-volt system is applied on airplanes using d-c power which have relatively light motor loads. Generators rate 5 kw and are designed for speeds ranging from 3,200 to 6,000 rpm to conform to prime-mover requirements. Motors have been built which run at 7,500 rpm. The control effectively regulates the voltage, handles battery charging, and provides for starting the power plant.