Auxiliary power unit
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An auxiliary power unit (APU) is a device on a vehicle that provides energy for functions other than propulsion. They are commonly found on large aircraft and naval ships as well as some large land vehicles. Aircraft APUs generally produce 115 V AC voltage at 400 Hz, to run the electrical systems of the aircraft; others can produce 28 V DC voltage. APUs can provide power through single or three-phase systems.
A Honeywell GTCP36 APU mounted in the tail of a business jet
The APU exhaust in the tailcone of an Airbus A380
The intake diverter of the Jumo 004, with pullcord starter handle for Riedel APU and its sparkplug access ports
The Riedel 2-stroke engine used as the pioneering example of an APU, to turn over the central shaft of both World War II-era German BMW 003 and Junkers Jumo 004 jet engines (pullcord starter variant shown).
BMW 003
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The BMW 003 is an early axial turbojet engine produced by BMW AG in Germany during World War II. The 003 and the Junkers Jumo 004 were the only German turbojet engines to reach production during World War II.
Preserved BMW 003 with Riedel flat-twin mechanical APU fitted