What is the tail exhaust port on a boeing 747?

Question

Whenever I'm at the airport and I see the 747s lined up for boarding, there is often a very hot looking exhaust coming from a port at the very rear of the tail. What is this? is there a conventional generator in the tail? or is it an additional turbine? does it operate during flight, or is it just a backup?

Answer 1

Calnickel's nearly there. There are several on a 747.



APU's typically swing about 1100 horse each, and are basically just small turboshaft engines running generators.



Bleed air from the compressors is used through the cooling packs for air conditioning, it's also used for heating in cold climates. Electrical power from the starter generator of the APU(S) is used to maintain cabin electrical functions and start engines.



APU's can serve as back up generators in the event that one of the main engine's starter/generator fails. A failure of the S/G doesn't mean the engine fails, it just means that the engine isn't producing electricity.



I've seen APU's in aircraft as small as the Lear 45. Never seen one on anything smaller.



Go to almost any airport in North America in December and you'll find line guys warming themselves in the exhaust from the APU of a Canadair Challenger, which is ducted downward.

Answer 2

RE:

What is the tail exhaust port on a boeing 747?

Whenever I'm at the airport and I see the 747s lined up for boarding, there is often a very hot looking exhaust coming from a port at the very rear of the tail. What is this? is there a conventional generator in the tail? or is it an additional turbine? does it operate during flight, or is it...

Answer 3

Boeing 747 Apu

Answer 4

It is from the APU (auxilliary power unit), a small gas turbine engine that runs two generators for electrical power on the ground. It also supplies high volumes of low pressure air for the air conditioning packs and the air starters on the engines while the plane is parked.



It uses far less fuel than a regular jet engine and is simpler and easier to maintain.

Answer 5

What you are seeing is the exhaust from the Auxilliary Power Unit which is a small turbine engine that drives a generator to supply electrical power to the aircraft, particularly while it is on the ground.

Answer 6

what you are seeing is exhaust from the apu (auxiliary power unit) its a gas turbine engine that is designed to provide pneumatic(air) and electrical power while the plane is on the ground.. if it is flight certified it can be started in the air at about 20,000 ft..(6069 meters).. its also used to start the main engines .

Answer 7

This is from the APU, auxcillary power unit, which is a small turbine driving a power units to provide power while on the ground.

Answer 8

There is an onboard generator (power system) to keep basic systems running while its parked to get the plane ready for the next flight. Thats the exhaust for that generator!!