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777 With 3 Contrails  
User currently offlineCtrl_alt_del From Ireland, joined Feb 2001, 71 posts, RR: 0
Posted (5 years 8 months 2 weeks 5 days 7 hours ago) and read 5456 times:

http://www.flugzeugbilder.de/show.php?id=806977

Anyone know what the third contrail is? Air outlet valve?

18 replies: All unread, jump to last
 
User currently offlineKeesje From , joined Dec 1969, posts, RR:
Reply 1, posted (5 years 8 months 2 weeks 5 days 6 hours ago) and read 5441 times:

APU



User currently offlineOly720man From United Kingdom, joined May 2004, 6741 posts, RR: 11
Reply 2, posted (5 years 8 months 2 weeks 5 days 6 hours ago) and read 5436 times:

Would the APU be on during cruise?

It looks like something is venting from the bottom of the fuselage aft of the wing root fairing. There's a stream of condensation anyway.



wheat and dairy can screw up your brain
User currently offlineCTRL_ALT_DEL From Ireland, joined Feb 2001, 71 posts, RR: 0
Reply 3, posted (5 years 8 months 2 weeks 5 days 6 hours ago) and read 5436 times:

Hi Keesje,
Maybe my eyes are deceiving me but I don't think it's coming from the APU.
It appears to be well forward of the APU on the underside of the fuselage.
The APU is most likely off in this phase of flight.


User currently offlineTupolevTu154 From Germany, joined Aug 2004, 2185 posts, RR: 28
Reply 4, posted (5 years 8 months 2 weeks 5 days 6 hours ago) and read 5424 times:

I'm no mechanic/engineer but that's not from the APU. It wouldn't be operational at that stage of flight. And as Oly720man said, there's definitely something being vented from the aft fuselage, possibly from the galley sinks.


Atheists - Winning since 33 A.D.
User currently offlineHT From Germany, joined May 2005, 6525 posts, RR: 23
Reply 5, posted (5 years 8 months 2 weeks 5 days 5 hours ago) and read 5412 times:



Quoting TupolevTu154 (Reply 4):
And as Oly720man said, there's definitely something being vented from the aft fuselage, possibly from the galley sinks.

Is this still common on modern airliners?
Is it only the fluids from the toilets that go into the waste water tank ?

At which location of the a/c does the consumed fraction of cabin air gets blown off / released ?
Would it contain enough moisture to form visible condensation ?
-HT



Carpe diem ! Life is too short to waste your time ! Keep in mind, that today is the first day of the rest of your life !
User currently offlineLarSPL From Netherlands, joined Apr 2002, 473 posts, RR: 0
Reply 6, posted (5 years 8 months 2 weeks 5 days 5 hours ago) and read 5400 times:

the APU is usually not on, but certain operations/procedures could require the apu to be on. for example; if an engine generator is u/s it could be required.

however, in this case it looks like water from the galley or toilet sink.



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User currently offlinePihero From France, joined Jan 2005, 4462 posts, RR: 76
Reply 7, posted (5 years 8 months 2 weeks 5 days 4 hours ago) and read 5391 times:
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Quoting Oly720man (Reply 2):
It looks like something is venting from the bottom of the fuselage aft of the wing root fairing. There's a stream of condensation anyway.

Spot on.
It's a water drain mast.



Contrail designer
User currently offlineFlyASAGuy2005 From United States of America, joined Sep 2007, 7004 posts, RR: 11
Reply 8, posted (5 years 8 months 2 weeks 5 days 3 hours ago) and read 5348 times:

You can tell it's not the APU. The trail is coming from well under the fuselage.


What gets measured gets done.
User currently offlineTristarSteve From Sweden, joined Nov 2005, 4010 posts, RR: 34
Reply 9, posted (5 years 8 months 2 weeks 5 days 3 hours ago) and read 5342 times:



Quoting LarSPL (Reply 6):
the APU is usually not on, but certain operations/procedures could require the apu to be on. for example; if an engine generator is u/s it could be required.

The B777 has two generators on each engine. The APU is not required for a generator failure.

Quoting Pihero (Reply 7):
It's a water drain mast.

Agreed. On the B777 there is a water drain valve in the line to each drain mast. It builds up a head of pressure then opens and releases a lot of water in one go.

Quoting HT (Reply 5):
Is this still common on modern airliners?
Is it only the fluids from the toilets that go into the waste water tank ?

The B787 is the first airliner to direct grey water into the waste tank. It has no drain masts.


User currently offlineCTRL_ALT_DEL From Ireland, joined Feb 2001, 71 posts, RR: 0
Reply 10, posted (5 years 8 months 2 weeks 5 days 2 hours ago) and read 5333 times:

Interesting.
How many kgs/lbs of water typically does a 777 carry/release on a trans-Atlantic flight?
Does the use of drain masts significantly reduce fuel consumption?


User currently offlineTristarSteve From Sweden, joined Nov 2005, 4010 posts, RR: 34
Reply 11, posted (5 years 8 months 2 weeks 5 days 2 hours ago) and read 5323 times:



Quoting CTRL_ALT_DEL (Reply 10):
How many kgs/lbs of water typically does a 777 carry/release on a trans-Atlantic flight?

About 800kg on a daylight flight. Less on a night flight (the pax are asleep!)


User currently offlineTranspac787 From United States of America, joined Jul 2007, 3208 posts, RR: 13
Reply 12, posted (5 years 8 months 2 weeks 4 days 14 hours ago) and read 5075 times:

I'm no A&P by any means, but I do know that in some cases, a 777 *will* run the APU in flight. This past October I flew DME-ORD on an AA 777, and we were briefly delayed departing DME to get some additional fuel. In flight the captain came back and talked with my briefly (having hung out with the crew on the 2-day layover) and I asked him why we needed the additional fuel and he said because we would be running the APU the entire flight given some ETOPS restriction of some sort.

I have ~no~ idea what the restriction was - if there was an engine generator INOP or what - but I do know for a fact we ran the APU the entire flight from DME to ORD.


User currently offlineSoon7x7 From , joined Dec 1969, posts, RR:
Reply 13, posted (5 years 8 months 2 weeks 4 days 13 hours ago) and read 5044 times:

I've often wondered what is eminating from the belly area of the aircraft. I live under the JFK approach from Europe and always notice the "third stream" venting off the tail cone even though I'm aware it is originating from the belly area...thought it was those last minute rushes to the lavatory which would not bode well as when I witness this I am usually at my sailboat and this discharge occurs over the waters I play in.  frown 

User currently offlineTdscanuck From Canada, joined Jan 2006, 12709 posts, RR: 80
Reply 14, posted (5 years 8 months 2 weeks 4 days 12 hours ago) and read 5016 times:



Quoting Oly720man (Reply 2):
Would the APU be on during cruise?



Quoting TupolevTu154 (Reply 4):
I'm no mechanic/engineer but that's not from the APU. It wouldn't be operational at that stage of flight.



Quoting TristarSteve (Reply 9):
The B777 has two generators on each engine. The APU is not required for a generator failure.

If everything is normal, it's not required for system functions, but it certainly can be on and may have to be on in certain dispatch or ETOPS conditions.

Quoting HT (Reply 5):
Is this still common on modern airliners?
Is it only the fluids from the toilets that go into the waste water tank ?

TristarSteve is right, to the best of my knowledge. Only the 787 keeps its grey water on board. All other modern airliners drop grey water out a mast, whilbe black water (toilets) is held.

Quoting HT (Reply 5):
At which location of the a/c does the consumed fraction of cabin air gets blown off / released ?
Would it contain enough moisture to form visible condensation ?

It goes out at the outflow valves...the location varies by aircraft type. Cabin air is pretty dry, so I suspect it doesn't cause condensation under most conditions, even with the large temperature drop. Even if it does cause condensation, the mass flow is hugely smaller than the engines so it might not be visible from far away.

Quoting CTRL_ALT_DEL (Reply 10):
Does the use of drain masts significantly reduce fuel consumption?

That's a very interesting systems design problem. You save fuel by losing the extra weight, but you burn more by dragging the drain mast through the air. I suspect the optimum solution depends a lot on both your aerodynamics, your size, and your mission profile.

Tom.


User currently offlinePikachu From Bhutan, joined Feb 2002, 89 posts, RR: 0
Reply 15, posted (5 years 8 months 2 weeks 4 days 10 hours ago) and read 4978 times:

"The B777 has two generators on each engine. The APU is not required for a generator failure."

You may wish to double check your QRH about what to do with the APU when you lose a generator...


User currently offlineAirbusA370 From Germany, joined Dec 2008, 253 posts, RR: 0
Reply 16, posted (5 years 8 months 2 weeks 4 days 4 hours ago) and read 4883 times:



Quoting TristarSteve (Reply 9):
The B787 is the first airliner to direct grey water into the waste tank. It has no drain masts.

The A380 does that also, AFAIK.

This happens when you put your excessive coffee in the sink and not in the toilet:

http://www.flickr.com/photos/30247109@N00/2111278667/


User currently offlineGF777 From Bahrain, joined Jan 2009, 41 posts, RR: 0
Reply 17, posted (5 years 8 months 4 days 20 hours ago) and read 3882 times:



Quoting Ctrl_alt_del (Thread starter):
Anyone know what the third contrail is? Air outlet valve?

This is the grey water system aft drain location.

Quoting Oly720man (Reply 2):
It looks like something is venting from the bottom of the fuselage aft of the wing root fairing. There's a stream of condensation anyway.

This could be the Hydraulic air driven pumps which we have two of them in the 777 (left aft body fairing) and they operate as demand pumps if they needed.

Quoting TristarSteve (Reply 9):
The B777 has two generators on each engine. The APU is not required for a generator failure.

True, the B777 has two generators in each engine, but one is buck up and can provide only 20 kVA for the essential loads (unlike the main generator which supply 120 kVA and the APU generator 120 kVA), so in case of one generator failure or engine failure the APU will be needed the whole flight. (the APU in B777 can provide electrical power at any altitude and pneumatic power up to 22,000 feet)


User currently offlineDragon6172 From United States of America, joined Jul 2007, 1203 posts, RR: 0
Reply 18, posted (5 years 8 months 4 days 14 hours ago) and read 3767 times:

In the words of Cousin Eddie...."Sh@#$er was full!!"

Have you all checked yours?



Phrogs Phorever
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