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What Is Hole In The Tail For?  
User currently onlineBEG2IAH From United States of America, joined Apr 2004, 950 posts, RR: 18
Posted (10 years 4 months 1 day 1 hour ago) and read 8279 times:
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Hello guys!

I have one probably simple question, but it keeps bothering me for a while. What is this big hole below the tail? It looks like mouth or whatever. Big grin


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Photo © Mitrovic Uros



When engines are turned off some kind of exhaust keeps getting out of it with a nice smell of kerosene. Is it some sort of power generator's exhaust?

Thanks,
Ivan



FAA killed the purpose of my old signature: Use of approved electronic devices is now permitted.
29 replies: All unread, showing first 25:
 
User currently offlineSQ452 From United States of America, joined Apr 2004, 1111 posts, RR: 0
Reply 1, posted (10 years 4 months 1 day 1 hour ago) and read 8211 times:

I think thats all its for is just exhaust, though not 100% sure on this. I thought when i was young it was a 3rd engine but i think its just exhaust,

someone out there know 100% what it is????



SIN > CVG > BOS
User currently offlineStarlionblue From Greenland, joined Feb 2004, 17014 posts, RR: 67
Reply 2, posted (10 years 4 months 1 day 1 hour ago) and read 8213 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."
User currently offlineJe89_w From United States of America, joined Mar 2002, 2360 posts, RR: 9
Reply 3, posted (10 years 4 months 1 day 1 hour ago) and read 8176 times:
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As Starlionblue said, the APU provides power for the aircraft. It's what makes the noise when planes are parked at the terminal.

User currently offlinePlanespotting From United States of America, joined Apr 2004, 3526 posts, RR: 5
Reply 4, posted (10 years 4 months 1 day 1 hour ago) and read 8166 times:

Yep i concur thats an APU alrite


Do you like movies about gladiators?
User currently onlineBEG2IAH From United States of America, joined Apr 2004, 950 posts, RR: 18
Reply 5, posted (10 years 4 months 1 day 1 hour ago) and read 8163 times:
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Starlionblue, thanks for the reply.

Ivan



FAA killed the purpose of my old signature: Use of approved electronic devices is now permitted.
User currently offlineStarlionblue From Greenland, joined Feb 2004, 17014 posts, RR: 67
Reply 6, posted (10 years 4 months 1 day 1 hour ago) and read 8129 times:

No problem.

BTW here is an APU intake on the 757 (the hatch that has opened next to the fin)


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Photo © Søren Geertsen




"There are no stupid questions, but there are a lot of inquisitive idiots."
User currently onlineBEG2IAH From United States of America, joined Apr 2004, 950 posts, RR: 18
Reply 7, posted (10 years 4 months 1 day 1 hour ago) and read 8094 times:
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Starlionblue,

I've never seen this. I guess you can learn something every day.

I started figuring out the plane from the back.  Smile Who knows how many other dumb questions I'll have once I get to the wings...

Thanks,
Ivan



FAA killed the purpose of my old signature: Use of approved electronic devices is now permitted.
User currently offlineStarlionblue From Greenland, joined Feb 2004, 17014 posts, RR: 67
Reply 8, posted (10 years 4 months 1 day ago) and read 7976 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  Big grin
- I'm not entirely sure, but I think the 737NG APU intake is right under the exhaust:
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Photo © Islam Chen





"There are no stupid questions, but there are a lot of inquisitive idiots."
User currently offlineLongHauler From Canada, joined Mar 2004, 4923 posts, RR: 43
Reply 9, posted (10 years 4 months 21 hours ago) and read 7831 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
User currently offlineGKirk From UK - Scotland, joined Jun 2000, 24923 posts, RR: 56
Reply 10, posted (10 years 4 months 20 hours ago) and read 7713 times:

Geez, Id hate to be behind that if it farted  Big grin


When you hear the noise of the Tartan Army Boys, we'll be coming down the road!
User currently offlineNyskymasters From , joined Dec 1969, posts, RR:
Reply 11, posted (10 years 4 months 19 hours ago) and read 7585 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.


User currently offlineTriStarEnvy From United States of America, joined Jan 2004, 2265 posts, RR: 3
Reply 12, posted (10 years 4 months 19 hours ago) and read 7506 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.
User currently offlineStefandotde From , joined Dec 1969, posts, RR:
Reply 13, posted (10 years 4 months 18 hours ago) and read 7392 times:

Doesn't every plane have/need an APU?

User currently offlineLapper From United Kingdom, joined Mar 2002, 1564 posts, RR: 7
Reply 14, posted (10 years 4 months 18 hours ago) and read 7327 times:

Some examples of APU inlets and exhausts for you, BEG2IAH:

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Photo © Harri Koskinen
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Photo © Freight-Dawg



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Photo © F van Moos
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Photo © 737doctor



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Photo © Jeff Miller
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Photo © Marc-André Veillard



Welcome to the boards!


User currently offlineJAL777 From , joined Dec 1969, posts, RR:
Reply 15, posted (10 years 4 months 18 hours ago) and read 7285 times:

That's where little airplanes come from.

User currently offlineStarrion From United States of America, joined Jul 2003, 1126 posts, RR: 2
Reply 16, posted (10 years 4 months 14 hours ago) and read 7113 times:

"That's where little airplanes come from. "


Don't have a Cessna man!



Knowledge Replaces Fear
User currently offlinePhollingsworth From United Kingdom, joined Mar 2004, 825 posts, RR: 5
Reply 17, posted (10 years 4 months 14 hours ago) and read 7027 times:

Actually in this picture:


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Photo © F van Moos



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.

Have a fun day

Pete


User currently onlineBEG2IAH From United States of America, joined Apr 2004, 950 posts, RR: 18
Reply 18, posted (10 years 4 months 13 hours ago) and read 6990 times:
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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.  Smile

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



FAA killed the purpose of my old signature: Use of approved electronic devices is now permitted.
User currently offlineDoug_Or From United States of America, joined Mar 2000, 3402 posts, RR: 3
Reply 19, posted (10 years 4 months 10 hours ago) and read 6899 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).


When in doubt, one B pump off
User currently offlineIMissPiedmont From United States of America, joined May 2001, 6287 posts, RR: 34
Reply 20, posted (10 years 4 months 5 hours ago) and read 6787 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.



Damn, this website is getting worse daily.
User currently offlineMusang From United Kingdom, joined Apr 2001, 864 posts, RR: 7
Reply 21, posted (10 years 3 months 4 weeks 1 day 21 hours ago) and read 6688 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.

Regards - Musang


User currently offlineCitationJet From United States of America, joined Mar 2003, 2431 posts, RR: 3
Reply 22, posted (10 years 3 months 4 weeks 1 day 15 hours ago) and read 6603 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.


Boeing Flown: 701,702,703;717;720;721,722;731,732,733,734,735,737,738,739;741,742,743,744,747SP;752,753;762,763;772,773.
User currently offlineAloges From Germany, joined Jan 2006, 8702 posts, RR: 43
Reply 23, posted (10 years 3 months 4 weeks 1 day 14 hours ago) and read 6589 times:

"Check the NTSB accident site."

Done! Big grin Here's what I've found, it's indeed interesting:

http://www.ntsb.gov/ntsb/brief.asp?ev_id=20001213X25234&key=1
http://www.ntsb.gov/ntsb/brief.asp?ev_id=20001212X24351&key=1



Walk together, talk together all ye peoples of the earth. Then, and only then, shall ye have peace.
User currently offlineMr Spaceman From Canada, joined Mar 2001, 2787 posts, RR: 9
Reply 24, posted (10 years 3 months 4 weeks 1 day 13 hours ago) and read 6565 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.


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Photo © Stefan Stromwall
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Photo © Patrick Lutz




Chris  Smile




"Just a minute while I re-invent myself"
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
29 Post contains links and images Starlionblue : Thx to those who clarified the difference between the upper and lower holes on the 737NG. Here is a 737 APU intake: View Large View MediumPhoto ©
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