Auxiliary power unit

A Honeywell GTCP36 APU mounted in the tail of a business jet
The APU exhaust in the tailcone of an Airbus A380

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 (rather than 50/60 Hz in mains supply), to run the electrical systems of the aircraft; others can produce 28 V DC voltage.[1] APUs can provide power through single or three-phase systems. A jet fuel starter (JFS) is a similar device to an APU but directly linked to the main engine and started by an onboard compressed air bottle.[2]

  1. ^ "400 Hz Electrical Systems". Ask a Rocket Scientist. Aerospaceweb.org.
  2. ^ A Jet Fuel Starter and Expendable Turbojet, ASME Digital Collection, by C Rodgers · 1986