Governor requirements for aircraft alternator drives

RECENTLY much engineering thought has been directed toward the use of a-c power systems in very large aircraft.^1,2 To permit operation at substantially constant frequency, when generators are driven by accessory drive shafts of main aircraft engines, variable-ratio transmissions have been designed. The ratio of such a transmission may be varied by means of a governor which maintains generator speed within a narrow range while the aircraft engine speed varies over a wide range. The engine speed range in typical cases may be three to one or greater. The frequency of a typical a-c system as now designed for large military aircraft must be held within about five per cent of normal, except during unusual transient conditions, when somewhat greater variations are permissible. When alternators are to be operated in parallel, differences in engine speeds should not be permitted to cause loss of synchronism of the generators.