silverfox
Posts: 1029
Joined: Thu Mar 15, 2001 8:39 am

'Clouds' In Intake On Take Off

Mon Sep 16, 2002 5:26 am

When i flew a BA 747 i was in the rear facing seat. On the take off run, as the engines spooled up the intakes had a 'cloud' form inside them. it remained for about 10-15 secs (i will check on the video) before disappearing.
What caused this? is it a normal phenomenom, or just the weather conditions at the time?
I havent checked any other intakes as i am normally behind or adjacent to them.
Any ideas etc?
 
BA
Posts: 10133
Joined: Fri May 19, 2000 11:06 am

RE: 'Clouds' In Intake On Take Off

Mon Sep 16, 2002 5:30 am

It's vapor being sucked inside the engine.

It has to do with the weather conditions like you said. The air must have had a lot of moisture. Otherwise known, it was very humid.

It's perfectly normal and nothing to worry about.

Regards
"Generosity is giving more than you can, and pride is taking less than you need." - Khalil Gibran
 
silverfox
Posts: 1029
Joined: Thu Mar 15, 2001 8:39 am

RE: 'Clouds' In Intake On Take Off

Mon Sep 16, 2002 5:33 am

Not worried at all. just fascinated by it. I thought it might have something to do with weather conditions, just needed a confirm. very spectacular in my opinion.
Now we are going to get all the 'neds' looking backwards on takeoff!!
 
OPNLguy
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RE: 'Clouds' In Intake On Take Off

Mon Sep 16, 2002 5:37 am

No biggie, just very humid air. You can also sometimes see it along the leading edges, the wing root, and vapor trails off the wingtips...


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Photo © Gregg Stansbery



Some non-experienced travelers freak out a bit, as they think it's "smoke"....
ALL views, opinions expressed are mine ONLY and are NOT representative of those shared by Southwest Airlines Co.
 
LZ-TLT
Posts: 427
Joined: Mon Apr 23, 2001 10:34 am

RE: 'Clouds' In Intake On Take Off

Mon Sep 16, 2002 5:42 am

A common phenomenon when taking off in high humidity and/or low air temperatures.

As air is sucked into the jet intakes or passes the wing's leading edge, it has a high velocity relatively to the aircraft's parts(ie, engine intake, wing and so on). Since the high velocity produces high dynamic pressure(in means of elementary fluid mechanic), but the sum of the dynamic, static and hydrostatic pressure for a given fluid remains always constant(Bernoulli's equation) and the hydrostatic pressure of the atmosphere depends only on weight, the increase of dynamic pressure is compensated by a drop in static pressure. Lower static pressure means, the condensation threshold for dissolved water vapour sinks, so the water vapours in the air condensate and form this fascinating fog. The same happens over the wing's leading edge.

There are a lot of photos here at a.net where you can see the same thing. A breathtaking sight indeed.
 
OPNLguy
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RE: 'Clouds' In Intake On Take Off

Mon Sep 16, 2002 5:55 am

Forgot to add this one earlier...


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Photo © Matsushita Masashi - aozora karugamotai -

ALL views, opinions expressed are mine ONLY and are NOT representative of those shared by Southwest Airlines Co.
 
BA
Posts: 10133
Joined: Fri May 19, 2000 11:06 am

RE: 'Clouds' In Intake On Take Off

Mon Sep 16, 2002 9:36 am

Quite fascinating what water can do.  Smile

Humid air and planes make a good combination.  Big grin

Regards
"Generosity is giving more than you can, and pride is taking less than you need." - Khalil Gibran
 
silverfox
Posts: 1029
Joined: Thu Mar 15, 2001 8:39 am

RE: 'Clouds' In Intake On Take Off

Tue Sep 17, 2002 7:34 am

Thanks for all the info, i knew about the vortex etc, but as i said it was the first time i had seen it on engines..still get a kick on the video watching it.
Thanks again
 
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PW100
Posts: 2728
Joined: Mon Jan 28, 2002 9:17 pm

RE: 'Clouds' In Intake On Take Off

Wed Sep 18, 2002 2:41 am

LZ-TLT

Very comprehensive explanation indeed! Just one remark... it's valid only for subsonic flow. At supersonic flow it doesn't work no more. Nature's reaction to supersonic flow is the shockwave.

PW100
Immigration officer: "What's the purpose of your visit to the USA?" Spotter: "Shooting airliners with my Canon!"

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