NickB
Topic Author
Posts: 2
Joined: Tue Apr 20, 2004 4:08 am

De-Icing Question

Tue Apr 20, 2004 4:17 am

I've watched commercial jets being de-iced on the ground, and understand what this does.

What happens when these aircraft take-off and fly into icing conditions?

- Do they have expanding boots like smaller planes to knock off the ice? (How effective is this if there are leading edge slats?)

- Do they duct some of the exhaust gasses around to warm the wing? (Ditto)

- Is kinetic heating enough at jet-speeds to stop the formation of ice?

- Do they carry their own supply of de-icing fluid to excrete?

- Any all/of the above, or some other.

//ick
 
PhilSquares
Posts: 3371
Joined: Sun Mar 28, 2004 6:06 pm

RE: De-Icing Question

Tue Apr 20, 2004 4:36 am

I guess I'm not too sure quite what you're asking. But, I will try to answer what I think is your question.

When a/c are deiced on the ground there are several types of deicing fluid that can be used. Generally Type IV provides the best "holdover" time. Holdover time is basically the length of time the a/c can sit in the conditions before it has to be deiced again. There are charts in the a/c that you can refer to that will determine holdover time. It is based on temp and type of precipitation.

As far as taking off in icing conditions, this is all for the 747-400. It is nothing really too special. There is engine anti icing which would be on, that takes bleed air and heats the cowling to prevent the formation of ice. On the -400 there is also wing heat for deicing of the wing leading. However with flaps out of the up position, the bleed air used for the wing heat is vented overboard. Once the flaps are retracted, you have wing heat available. However, the way the wing on the -400 is designed build up on the leading edge almost never occurs. You will find on the classic and the -400 the application of wing heat almost never occurs.

Hope that helps.
Fly fast, live slow
 
VC-10
Posts: 3546
Joined: Tue Oct 26, 1999 11:34 am

RE: De-Icing Question

Tue Apr 20, 2004 5:45 am

However with flaps out of the up position, the bleed air used for the wing heat is vented overboard.

The air isn't vented overboard. If the anti-ice valves are closed the air just stays in the main pneumatic duct. When the LE are retracted the anti-ice valves are 'armed'.
 
doug_or
Posts: 3172
Joined: Sat Mar 18, 2000 9:55 am

That First Flying Job...

Tue Apr 20, 2004 5:50 am

while commercial aircraft do not carry deicing fluid for the flying surfaces, some GA aircraft have been experimenting with the weeping wing concept, whereby a fluid is leaked on the wing.
When in doubt, one B pump off
 
AUAE
Posts: 292
Joined: Fri Apr 09, 2004 4:41 am

RE: De-Icing Question

Tue Apr 20, 2004 5:56 am

Most big commercial jets (ie B737-B777) use bleed air ducted along the wing and stabilizer (Ver and Horz) leading edges to combat ice during flight. Most can operate this sys with the leading edge clean or deployed. Smaller aircraft (ie RJs and props) usually employ bladders or electric heating blankets.

For clarification, bleed air is compressed air bled from the compressor section of an engine, not exhaust gases.

I am not aware of any commercial or other aircraft that excrete deicing fluid. Someone correct me if I am wrong, but I think there are a lot of negatives to a sys like that.

Friction warming probably does help at cruise speed, but at cruise altitudes icing should not be a problem.
Air transport is just a glorified bus operation. -Michael O'Leary, Ryanair's chief executive
 
PhilSquares
Posts: 3371
Joined: Sun Mar 28, 2004 6:06 pm

RE: De-Icing Question

Tue Apr 20, 2004 6:46 am

VC-10,

Not to quibble, but according to my AOM Vol II, it indicates the valves are open with the flaps up, nothing about when the flaps are out of the up position. But looking elsewhere, it would indicate that the EICAS indicates the valve being open regardless of the flap position and the correct epr/n1 correction is made to the thrust ref.

Not a real big deal, in either case when the flaps are out of the up position there is no wing heat.
Fly fast, live slow
 
L-188
Posts: 29881
Joined: Wed Jul 07, 1999 11:27 am

RE: De-Icing Question

Tue Apr 20, 2004 6:47 am

Do they have expanding boots like smaller planes to knock off the ice? (How effective is this if there are leading edge slats?)

- Do they duct some of the exhaust gasses around to warm the wing? (Ditto)

- Is kinetic heating enough at jet-speeds to stop the formation of ice?

- Do they carry their own supply of de-icing fluid to excrete?

- Any all/of the above, or some other.




Some airplanes use boots, some use bleed air, and there are a few aircraft that excrete fluid...aka the TKS system.

Kinetic heating isn't enough unless maybe if you are talking Concorde, but at normal flight levels the air is so cold that it can't hold an moisture, no moisture, no ice.

OBAMA-WORST PRESIDENT EVER....Even SKOORB would be better.
 
aviopic
Posts: 2423
Joined: Sat Mar 13, 2004 7:52 pm

RE: De-Icing Question

Tue Apr 20, 2004 6:52 am

Don't know the exact data but icing can only be a problem up to a certain height, above that the air is very cold and there very dry as well.
Guess every body knows freeze dried food !
There are many different anti icing systems: electric, bleed air and pneumatic to name a few.
As far as I know only used during take off and climb, decent and landing all if required by the circumstances of course.
The truth lives in one’s mind, it doesn’t really exist
 
NickB
Topic Author
Posts: 2
Joined: Tue Apr 20, 2004 4:08 am

RE: De-Icing Question

Tue Apr 20, 2004 8:31 am

Thanks for all the responses. Yes, I appreciate at altitude that this is not a concern, I was just interested in the varying technologies used.

//ick
 
VC-10
Posts: 3546
Joined: Tue Oct 26, 1999 11:34 am

RE: De-Icing Question

Wed Apr 21, 2004 1:39 am

Philsquares

Looking at the my AOM Vol 1 & MM it looks like there has been a change in operation.

The AOM shows that if selected AUTO and the ice detectors sense an ice build up the valves open when the a/c is in flight with the LE's up

When selected to ON the valves open as soon as the a/c becomes airborne.
The AOM shows a revision bar by the 'ON' info.
 
PhilSquares
Posts: 3371
Joined: Sun Mar 28, 2004 6:06 pm

RE: De-Icing Question

Wed Apr 21, 2004 2:29 am

VC-10,

Just checked my Vol II. Don't have that at all. In fact, our a/c are only the on/off switch. I was in the sim yesterday and it appears as though the FMS takes the bleed correction off based on the switch position. So, I really don't know if the valve is closed or if it is dumped overboard. Either way, the end result is the same, no wing heat with the flaps out of the up position.

I suppose we're both right!!

Cheers, back to the UK on Sunday for 10 days....  Wink/being sarcastic
Fly fast, live slow

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