What comes out of the...ass?

[Mr. Bones]

hello guys,

i've been thinking about this for a long time...but now i want an answer: what comes out of the ass of a plane?

it looks like smoke, but is there an engine situated there? i guess not...

to make myself clear, i added a photo bellow...and i'd like to know what's the use of the part in the blue circle? thanx  ;)

[OTTOL]

I like the graphic title! It's like one of those "FREE SEX and BEER" ads, you just can't pass it up!

That's the exhaust for the APU ( auxiliary power unit). It's a small(usually single stage, centrifugal flow), turbine. It has accessory drives for a hydraulic pump, and generator(for DC power). It doesn't provide any thrust, although the idea has come up before(I Think on the B777). This allows the aircraft to "power up" systems, without running the main engines, or hooking up a GPU(ground power unit). The unit remains on until after takeoff(usually shut down after ascending through 18,000') as a backup for any potential system failures. It's usually turned back ON, after clearing the runway, following landing.

[Harrier]

i noticed you said smoke and scenes as your questions already been answered i just thought id say on aerobatic jets (hawks etc.) that its diesel that forms the multi coloured smoke but i dont know i thats where it actually comes from?

[Mr. Bones]

thanks! that's just what i wanted to know!  ;)

[Felix/FFDS]

i noticed you said smoke and scenes as your questions already been answered i just thought id say on aerobatic jets (hawks etc.) that its diesel that forms the multi coloured smoke but i dont know i thats where it actually comes from?

Small holding tanks....  press Shift-I and it's enabled..