I really want any one to tell me what is the APU on a plane?? Airbus A380-841 - Airbus | Aviation Photo #0867939 | Airliners.net
Regards …
Rafik
It’s an Auxiliary Power Unit. It provides energy for the aircraft while it is on the ground. It is also used to help start the engines.
It’s also loud and obnoxious on most jets, just like dami…
Way too easy!
thx Dar. and Pika, but still i have a question. what is the APU door beside the tail ?? and why are the engines fans turning slowly while on ground ??
The door is the air intake for the APU. The APU is basically a small turbine engine. (on some larger aircraft like the A380 pictured the APU engine is almost as large as some main engines in small aircraft. Some helicopters come to mind.)
The engines spin while on the ground when the wind passes through them. There is very little friction in the engines and they can start windmilling with just a few knots of wind.
I hope you mean I’m LOUDER than most APUs!
No comment…
Maybe he means that, like most APUs, you talk out your, well, never mind… 
thxxxxx very much for da help 
Rafik
The engines spin while on the ground when the wind passes through them. There is very little friction in the engines and they can start windmilling with just a few knots of wind.
do u mean by this that the spin of the engines on ground is not related with the apu ?
just wanna be sure …
Entirely not related at all!
He just meant that even when the APU isn’t running, a small gust of wind can start the inlet turbine spinning. Very noticeable when you’re standing next to a parked, unoccupied aircraft.
You might also hear the fan blades clanking around if you listen hard enough.