Wing Anti-Ice - What does it do?

[John H Watson]

There seems to be a misconception regarding the function of Wing Anti-Ice. It's really only for protecting part of the wing leading edges and provides little or no de-icing for the rest of the wings or the leading edge flaps.

If you look at this photo, the very front metal section of the leading edge is the part where the de-icing is taking place (i.e. forward of the stowed leading edge flaps).

http://www.iinet.net.au/~b744er@ozemail.com.au/LeadingEdge1a.jpg


Here's a graphic

http://www.iinet.net.au/~b744er@ozemail.com.au/WAIDuct.GIF

Apart from a few slots (vents) shown at the bottom of heated area, there are no other exit points for the heated air. The slots (vents) are to ensure that the air is evenly distributed along the inside the leading edge.

The part shown on the graphic in orange is a perforated metal tube running along a section of the leading edge (into which engine bleed air is fed). The part shown in yellow is the heated area of the leading edge.

Note that hot air exiting the leading edge through the vents would provide very little heating outside of the aircraft (A few psi vented though these slots vs the freezing airflow hitting the leading edge would provide negligible effect on underside of the wing).

There may be a small amount of heat radiated backwards into the cavity where the leading edges are folded, but really small compared with the heat generated by the very large pneumatic manifold in that area.

When the LE flaps are extended, part of the LE flaps swings upward and stops the airflow hitting the leading edge.

http://www.iinet.net.au/~b744er@ozemail.com.au/LEFlap.jpg

There is a danger in this. If the WAI operates during this time, the leading edge could overheat (through lack of cooling airflow over them). On some 747-400's, the WAI is disabled electrically during this time.

Rgds
JHW

[Britjet]

Hi John

I assume that you are referring to my cold weather operations video.
Of course you are correct - my reference to the "de-icer' instead of "anti-ice" is that it is not intended to be operated continually, and as you say - it can't protect the whole wing - but it doesn't need to of course because the wing doesn't collect ice in flight to any significant extent. (The 707 had no wing ice protection at all)

On my previous company it was "culture" to operate it manually for two minutes and then turn it off. I don't know if the "auto" system has a timer or just operates any time the ice detector is on.

It is actually highly unusual for the wing-anti ice to be needed.

Regards

Peter

[John H Watson]

I assume that you are referring to my cold weather operations video.

Not specifically, Peter, but your video did remind me of previous debates on the subject on PPRuNe and elsewhere  I had the opportunity to look at the leading edge close-up (a few years ago) and noted that the heated section had no vents into the cavity where the LE flaps are stowed. If it did, it would probably present a fire hazard. Some 747-400 types even have overheat detectors in this area (i.e. part of a wing/strut overheat system, not related to the dedicated anti-ice overheat systems).

I don't know if the "auto" system has a timer or just operates any time the ice detector is on.

The auto system appears to continually activate the anti-ice systems whenever ice is detected (beyond set ice accumulation limits). There is a 7 second timer in the circuits, but I believe this is only for the protection of leading edges during CMC Ground Tests. Auto-ignition on some systems (and engine/airframe combinations) however, may have time limits (in response to anti-ice activation)

I discovered not long ago that the detectors are still powered on the ground (c/o scorched fingertips  :mrgreen: ). However, they don't output any logic to the anti-ice system (as you mentioned) without an in-air signal.

Rgds
JHW

[Hardy Heinlin]

... previous debates on the subject on PPRuNe and elsewhere

Are these debates about whether the entire wing or just the leading edge is heated? Or about whether it is a de-ice or anti-ice system?

Shouldn't every pilot know that any anti- or de-ice system is always installed in the leading edge only? (Because that's the place where icing occurs.)

If it's just about the defintion of de- and anti-, i.e. ice removal versus ice prevention, then I think this debate will never end because it's a matter of lingual interpretation, and because, in a way, there is a mix of both principles: When the anti-ice starts, the wing may already have a few microscopic ice crystals here and there; getting rid of them can be interpreted as "de-icing" because they were here before the hot air was here :-)


Cheers,

|-|ardy

[Britjet]

No debate from me, Hardy - life is much too short! Thanks for the interesting technical points, John. As you say, there appear to be different designs of the same thing on the aircraft. How strange!

Peter

[John H Watson]

Are these debates about whether the entire wing or just the leading edge is heated? Or about whether it is a de-ice or anti-ice system?

The issue was not about de- or anti-. It was just relating to whether or not that the LE flaps are (or are not) not affected, or that air is vented inside the wing.

Rgds
JHW