The medium-voltage d.c. system in aircraft and its application in the Princess Class flying boats

The medium-voltage d.c. power system for aircraft is defined and its introduction described. The sources of mechanical power available are suitable for different methods of generating electrical power, but the choice of a d.c. system is supported by desirable motor characteristics, a proved range of contactors and circuit-breakers and suitable light-weight batteries. The ease of maintenance of the system, its simplicity and associated reliability in service are a considerable advantage to the economic utilization of an aircraft, whilst the safety of the system is ensured by comprehensive protective equipment. The `Princess¿ electrical installation illustrates the successful use of a d.c. system and demonstrates the reliability of the many items of d.c. apparatus. The success of any major electrical system in aircraft is attributed to thorough testing in the design stage before the aircraft installation is attempted, which is considered an essential prerequisite to reliable operation in service.