The Unitron GFC-37M Ground Power Unit (GPU) supplies power to a parked or hangared aircraft. A reliable GPU unit is a crucial piece of equipment for any hangar. In a small footprint, a GPU delivers specified power through the use of a standard electrical system, battery, fuel, and a small engine. This Unitron GPU includes lightweight 400 Hz and 28 VDC mobile converters for aircraft ground power applications and the lightest weight-to-power rating ratio on the market.
The purpose of an aircraft Auxiliary Power Unit (APU) is to provide energy for purposes other than propulsion - most often to operate a generator for electrical power. Although small piston-engine APUs were first used in aircraft on a limited basis during World War I, it was in World War II that they came to be used extensively on large aircraft.