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RUDAS
29th Sep 2003, 21:52
I noticed an odd looking thing a while back, when standing above the wing of a 744 that had just come in from a 1hr30 min sector. It had a fair layer of visible icing on the upper wing surface,but only betwee the two engines. in other words the wing inboard and outboard of the area between the engines was free of ice.

What could have caused this? something to do with the way the anti-ice system is positioned?

LEM
30th Sep 2003, 16:52
Probably that's due to cold soaked fuel.

Some 744 driver will explain that to you.

Cheers ;)

BuzzBox
4th Oct 2003, 20:22
Er, not so Notso Fantastic, I think you'll find the 747 doesn't actually have leading edge slats! As I recall, the wing anti-ice IS there to protect the leading edge - hot air is ported into the leading edge area via a 'spray tube' inside the leading edge of each wing. As a result it becomes ineffective when the leading edge flaps are extended, because the hot air simply gets dumped overboard. As you said though, it is rarely used and any icing on the inboard part of the wing is likely to be caused by condensation freezing on the wing surface because of cold fuel in the tank.

QAVION
5th Oct 2003, 14:56
"As I recall, the wing anti-ice IS there to protect the leading edge - hot air is ported into the leading edge area via a 'spray tube' inside the leading edge of each wing. As a result it becomes ineffective when the leading edge flaps are extended, because the hot air simply gets dumped overboard. "


Notso, guys.....
The air is normally dumped overboard anyway. There is no connection between the cavity into which the hot bleed air is fed for anti-icing and the cavity where the LE Flaps are stowed.

More on the subject...

http://www.pprune.org/forums/showthread.php?s=&threadid=77557

As far as I can see, the very limited number of slots in the underside of the LE (which vents the WTAI air after it has circulated in very front part of the leading edge) would have little or no effect on the LE Flaps.

http://members.ozemail.com.au/~b744er/WAIDucting.gif

http://members.ozemail.com.au/~b744er/LeadingEdge1a.jpg

http://members.ozemail.com.au/~b744er/WingLE.gif

Hope this helps.

Cheers.
Q.

Notso Fantastic
6th Oct 2003, 17:28
Buzzbox- you are quite right- typing in a hurry on a meter connection in Bangkok, I let my p's and q's slip! The 747 does, of course have, flaps , not slats , I'm sure the Trident people will be only too happy to point out the difference and how slats is better! To be honest, all I know is de-icing don't work with LE Flaps extended- I've never really investigated why or how it works, but I do know the air is dumped. On a Classic we did once have a LE flap freeze up which caused a 3000' go-around at LHR, but apart from that it doesn't get used more than a couple of times a year- it seems it's very rare to get ice forming on the leading edge (which you can only just see anyway), but then I don't go to Chicago in the winter!