what is an Auxiliary Power Unit (APU)?

 what is an Auxiliary Power Unit (APU)?

The auxiliary power unit or APU as it's miles normally acknowledged, is a small gasoline turbine engine, suited to aircraft and can offer electric powered strength from shaft pushed mills.

Pneumatic duct stress for aircon and engine starting functions.

Hydraulic strain (In a few aircraft).

example of an Auxiliary energy Unit or APU

An Auxiliary strength Unit (APU) is an automated engine, which typically runs at a governed velocity of a hundred%. a few APUs have an idle facility that lets in the engine to run at eighty five% when no loads are implemented. As it is an automated engine the gas system need to manage the engine throughout the start and going for walks phases of operation. The engine may be shut down if a critical manipulate feature is lost or a critical malfunction such as low oil pressure takes place.

APU’s are specially used on the ground while their important engines aren't running and floor carts (electrical and pneumatic) are not available. On maximum cutting-edge aircraft the APU can also be used in the air to offer air-conditioning in the course of take off and touchdown levels, or to back up the main engines in case of a generator or air system failure.

despite the fact that the APU is normally rated to run at the max cruise altitude of the aircraft it's far suited for, its capacity to take load diminishes with altitude. as the major load on any APU is the air load it may be typical that the APU’s capacity to offer sufficient air for the plane is confined to 15-20,000 feet.

Above this height the APU will handiest offer electric strength, this will also be constrained to much less than the max cruise height. most APU’s supply shaft priority because of this that if air and electric powered mills are on the turbines are given precedence. most aircraft use regular frequency turbines, and their APU’s which run at a steady a hundred% do now not therefore require a regular pace power unit to keep a regular output. If the air hundreds come to be to excessive the APU will reach its max EGT and the manage system will back off the gasoline to save you harm, this would bring the APU generator off frequency and take the generator ‘off line’. instead the air load is reduced to maintain a constant APU velocity.