Starlionblue From Hong Kong, joined Feb 2004, 15870 posts, RR: 66 Reply 2, posted (9 years 1 month 2 days ago) and read 5950 times:
That's the APU (Auxiliary Power Unit) exhaust. It's a turbine engine used to provide power on the ground or in emergencies. It also provides bleed air for engine start.
"There are no stupid questions, but there are a lot of inquisitive idiots." - from Citadel by John Ringo
Starlionblue From Hong Kong, joined Feb 2004, 15870 posts, RR: 66 Reply 8, posted (9 years 1 month 1 day 23 hours ago) and read 5717 times:
That's the great thing about this forum, all the stuff you learn!
Some more fun APU facts:
- The engine cores on the BAe-146/Avro-100 started life as APUs, for example on the 767. APUs are just jet engines although in the 40s-50s some planes had piston powered units.
- The APU for the Classic 747 has 1100 Shaft Horsepower. That's about the same as both engines on the Twin Otter combined.
- The 727 originally only had the APU as an option.
- The 727 APU could obviously not go in the tail so it is located in one of the main gear wells. It can only be used on the ground and is prone to set things on fire. Also, it often creates a tongue of flame snaking over the wing on startup. Pretty good if you want to scare the pax
- I'm not entirely sure, but I think the 737NG APU intake is right under the exhaust:
LongHauler From Canada, joined Mar 2004, 4281 posts, RR: 36 Reply 9, posted (9 years 1 month 1 day 20 hours ago) and read 5572 times:
The B737 APU air intake is on the rear right side of the fuselage foreward of the horizontal stabilizer to the rear of the galley service door, even on the 737NG. You can see it in the picture above.
The vanes you see just outboard of the intake assist in high alititude starting by increasing airflow when airborne.
Never gonna grow up, never gonna slow down .... Barefoot Blue Jean Night
Nyskymasters From , joined Dec 1969, posts, RR: Reply 11, posted (9 years 1 month 1 day 19 hours ago) and read 5326 times:
Starlionblue,
With regard to the B737NG, there are what appears to be two exhaust outlets. Actually, the bigger "hole" is the APU exhaust outlet while the smaller one is, believe it or not, is a cooling inlet. Just another APU fun fact.
TriStarEnvy From United States of America, joined Jan 2004, 2265 posts, RR: 4 Reply 12, posted (9 years 1 month 1 day 18 hours ago) and read 5247 times:
Speaking of APU's, there is a really interesting(and very sad) documentary that's on PBS every now and then, about a group of guys who find a lost B-29 that was ditched in a lake. The show documents the planes history, and the back story of the group.
The plane was put down in a fresh water lake, and the corrosion damage was minimal. They spend forever getting it airworthy. As they try and fly it out, the APU breaks loose in the plane, and catches fire. Everybody gets out, okay, but the plane is lost. They show the crew sitting in the snow, and one of them says, something like, "My tools were in there" in such a deadpan way. I swear I just about cried.
If you don't stand for SOMETHING, you'll fall for ANYTHING.
The doors that are open are not the APU doors. They are actually open to allow access to the built-in work stand for the number 2 engine. The hatch on the bottom allows you to get to the stand from below, and the ones on the top allow you to work underneath the engine fan and core cowls. Even more fun are all the hinges to allow you to remove the #2 engine.
BEG2IAH From United States of America, joined Apr 2004, 827 posts, RR: 12 Reply 18, posted (9 years 1 month 1 day 12 hours ago) and read 4731 times:
Guys,
Thanks for the replies. These APU intake and exhaust holes make some of these planes look like real birds, kinda within the lines of what GKirk and JAL777 said.
Lapper, thanks for these pics. I'm really glad I joined A.net. I realized that I might have chosen a wrong profession. But now it's too late to change it.
Ivan
Use of approved electronic devices is now permitted.
Doug_Or From United States of America, joined Mar 2000, 3163 posts, RR: 4 Reply 19, posted (9 years 1 month 1 day 9 hours ago) and read 4640 times:
Stefandotde- Aircraft only need APUs if there is no air on the ground for starting. It is nice for passengers and crew if there is no electricity, though its not a neccisity. IIRC the DC-8 had no APU, and some BAC 1-11 were also build without (though I couldn't find any pics in the database).
IMissPiedmont From United States of America, joined exactly 12 years ago today! , 6203 posts, RR: 43 Reply 20, posted (9 years 1 month 1 day 4 hours ago) and read 4528 times:
Phollingsworth, you just made me cringe remembering that. It's also the entry to where one goes to inspect the horizontal stabilzer. Instant crush if someone activates the hydraulic system. I hated that little door.
Fun though was the very rare hot start on a 727s APU. Flames leaping out of the right wing 6 feet from a window tended to get the passengers attention.
What is it with all the "is there a possibilty airline X will.." threads? The answer it'll is possible.
Musang From United Kingdom, joined Apr 2001, 754 posts, RR: 7 Reply 21, posted (9 years 1 month 21 hours ago) and read 4429 times:
Lapper - in the selection of pics of APU intakes, the 146 intake is on the side of the rear fuselage, behind the aft door. So its not visible in that pic. If the intake at the base of the fin caught your attention, thats the ram air intake to the cabin in case air con packs fail.
Tristarenvy - in that B-29 incident, it was an auxiliary petrol powered generator roped to the floor, that spilled fuel on itself and caught fire. I agree though, an immensely interesting documentary and very sad at the end.
CitationJet From United States of America, joined Mar 2003, 2235 posts, RR: 3 Reply 22, posted (9 years 1 month 15 hours ago) and read 4344 times:
On the 727 APU operation with flames, there are about half a dozen instances of passengers initiating evacuations on the 727 without the cockpit crew knowing it. When the flames shoot out the APU, the passengers yell fire and open the overwing exits and start climbing on the wing, all while the plane is still taxiing. Check the NTSB accident site.
Mr Spaceman From Canada, joined Mar 2001, 2780 posts, RR: 15 Reply 24, posted (9 years 1 month 13 hours ago) and read 4306 times:
Hi guys.
Here's two photos to show the difference between the APU exhaust on a 737NG and an older 737-3 as mentioned by Nyskymasters. The 737-3 only has the one exhaust pipe, and the 737NG has both the exhaust pipe & cooling inlet.
25 Wing: APU is a self contained gas turbine engine that supplies bleed air for engine starting or air conditioning.It also provides electrical power. The uppe
26 Refueler1974: Doesn't every plane have/need an APU? The majority of your commuter aircraft do to some extend, but htere are still some, like the ATR-42 and SAAB 340
27 JBirdAV8r: Doesn't every plane have/need an APU? Allow me to elaborate. The majority of aircraft (mainly of the smaller variety) do not have, nor do they require
28 Musang: Refueller1974 - The ATRs, and I believe also the Saab 340, have no APU in the conventional sense, but can run the right engine with the prop hydraulic
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