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Difference Between Anti-icing And De-icing  
User currently offlineArzouni From UK - England, joined Aug 2012, 7 posts, RR: 0
Posted (2 years 3 months 3 weeks 5 days 21 hours ago) and read 13079 times:

1-what is The principles and types of anti-icing and de-icing systems in use on modern military/commercial aircraft ?

7 replies: All unread, jump to last
 
User currently offlineTb727 From United States of America, joined Jun 2005, 1629 posts, RR: 9
Reply 1, posted (2 years 3 months 3 weeks 5 days 19 hours ago) and read 13036 times:

Anti-icing prevents ice from forming and de-icing does just that, it get's ice that has formed off the plane. On the jets I have flown, and it may be true of most others, there are no de-icing systems, it is all anti-icing. You have the windshield heat, pitot heat(what's to eat haha), the stall vane heat(which is automatic for us)as well engine anti-ice and wing anti-ice.

On the 727 it is fairly rare to have to use wing anti-ice and the tail isn't even covered by any heating system. I've been told the design and sweep of the wing makes it difficult for ice to form unless it is bad icing. Care has to be taken because if any ice does build up on the wing, it can shed and go through the engines if you turn the wing heat on too late so we are always watching for signs of wing ice to start. The engine, S-duct and wing anti-ice are sourced off the engine bleed and all the others are electric heating elements. Icing can be expected in visible moisture below +10C so we turn it on prior to entering clouds in those conditions.



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User currently offlineJetlagged From United Kingdom, joined Jan 2005, 2572 posts, RR: 25
Reply 2, posted (2 years 3 months 3 weeks 2 days 18 hours ago) and read 12656 times:

The two main principles used in aircraft systems are either to add heat to melt any ice or to change the surface shape to cause ice to break off. The latter, which is a de-icing system tends to be used on aircraft which fly in icing conditions most of the time (propeller driven and/or unpressurised aircraft). It's usually done by fitting inflatable rubber "boots" on aerofoil leading edges. Pneumatic pressure is cyclically applied to the boots in icing conditions. This causes them to inflate and deflate, dislodging any ice on the leading edge.

Jet aircraft tend to use thermal anti-ice because they fly quickly through the weather and cruise above it so don't suffer from the same continuous exposure to icing. They also have hot bleed air readily available, and rubber boots would tend to spoil the high speed aerodynamics. Thermal anti-ice is usually either electrically heated or by using hot bleed air from the engines. Probe heat is always electrical for practical reasons, same applies to window heat. Thermal A/I can also be used as de-ice of course. In fact, the wing A/I on the 737NG is basically a de-icing system, it's not primarily intended for use to prevent ice forming.

As well as aerofoils, the engine inlets and propeller leading edges are usually protected in the same way.

There are also chemical de-icing systems, which operate by changing the freezing point of water, rather like a windscreen de-icer spray for a car. These kind of systems are much less common on aircraft these days because of polution issues and greenhouse gas effects. They are widely used for de-icing aircraft while on the ground though.



The glass isn't half empty, or half full, it's twice as big as it needs to be.
User currently offlineViscount724 From Switzerland, joined Oct 2006, 25852 posts, RR: 22
Reply 3, posted (2 years 3 months 3 weeks 2 days 13 hours ago) and read 12609 times:

Quoting Tb727 (Reply 1):
Care has to be taken because if any ice does build up on the wing, it can shed and go through the engines if you turn the wing heat on too late so we are always watching for signs of wing ice to start.

At least 3 727s had the #3 engine separate due to ice ingestion, although they were all due to ice from leaking lavatory drains, not from ice on the wings. NW 727-200 in 1990 below.


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Related news items:
http://www.nytimes.com/1990/01/05/us...nds-after-an-engine-drops-off.html
http://www.flightglobal.com/FlightPD...s=0&scrollbar=0&page=1&view=FitH,0

An SAS MD-80 crashed soon after takeoff from ARN in 1991 when both engines failed due to wing ice ingestion. Blamed on inadequate deicing before departure. Luckily no fatalities.
http://aviation-safety.net/database/record.php?id=19911227-0


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Photo © Ola Carlsson
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Photo © Ola Carlsson



User currently offlineElpinDAB From United States of America, joined Apr 2005, 485 posts, RR: 4
Reply 4, posted (2 years 3 months 3 weeks 2 days 6 hours ago) and read 12521 times:

Quoting Tb727 (Reply 1):
I've been told the design and sweep of the wing makes it difficult for ice to form unless it is bad icing.

No ice protection on the jet that I fly either, and I have seen considerable ice build-up on the horizontal stab during the post-flight. I observed no significant adverse handling characteristics with ice accumulation on the tail. I am always cautious in icing since flying turboprops in severe icing conditions in the Great Lakes region, but I find it interesting that on a turboprop, tail icing can be fatal, while in a jet, this seems to be irrelevant. (Ice on a supercritical airfoil or in the engines, is, however a major concern.) I have read that tail design must meet be able to withstand a certain amount of ice accretion with no adverse handling characteristics, otherwise ice protection must be integrated into the design. Can anybody verify or correct this?

Quoting Jetlagged (Reply 2):
Jet aircraft tend to use thermal anti-ice because they fly quickly through the weather and cruise above it so don't suffer from the same continuous exposure to icing. They also have hot bleed air readily available, and rubber boots would tend to spoil the high speed aerodynamics

True, jets tend to climb through icing more quickly, while turboprops are stuck in the weather longer. But, I don't think this would explain the logic behind systems selection during the design of an aircraft. And yes, rubber boots would spoil high speed aerodynamics. Jets have utilized boots though, such as the G200, Dornier 328Jet, and certain Citations, to name a few. Typically at altitudes where the airfoil is transonic, icing isn't as much of an issue.

But, I am not impressed with pneumatic de-icing boots. They are old technology, dating back to the 1940's or so. I always thought that they were used since too much bleed air would be robbed from the engines for effective use of a "hot wing" system for a turbo-prop. Even pneumatic boots rob alot of bleed air from a turboprop, necessitating lower power settings for climb and cruise. Ironic since you need the extra power during periods of ice accumulation more, but instead need to reduce power. Often, I have needed to descend to lower altitudes during moderate and greater icing above 10,000ft or so because the aircraft didn't have the power to climb above, with the robbed power for engine anti-ice and wing de-icing boots, combined with performance hits from ice accumulation. I have held onto ice accumulated on the wings during climbout all the way through landing, post-fight, and the next flight's de-icing spray-down, even while cruising above the clouds with direct noon sunlight (although cold temps). Boots aren't always effective.

Jet wing anti-ice also robs the engine of thrust when you most need it, but I have never once seen ice build on the wings during proper usage. Only unheated surfaces see ice build-ups, such as winglets, nose, and tail. Operational limitations for jet anti-ice usage typically dictate usage before even a fraction of a millimeter of ice begins to build on critical surfaces, but this video shows a trace amount of ice being shed from a jet wing moments after wing anti-ice is selected on. http://www.youtube.com/watch?v=Rczi0TJ05YA
Only during abnormal situations would the system be used in the de-icing capacity shown in the video, but this illustrates the effectiveness of the system.

I would much rather have a "hot wing" over a wing with a boot. As far as I know, no jet with "hot wings" has ever crashed as a result of ice accumulation except for improper anti-ice usage and those aircraft that took off with contaminated wings, such as the Challenger at Montrose, the Air Florida aircraft at DCA, etc.


User currently offlinetdscanuck From Canada, joined Jan 2006, 12709 posts, RR: 80
Reply 5, posted (2 years 3 months 3 weeks 1 day 17 hours ago) and read 12379 times:

Quoting ElpinDAB (Reply 4):
I have read that tail design must meet be able to withstand a certain amount of ice accretion with no adverse handling characteristics, otherwise ice protection must be integrated into the design. Can anybody verify or correct this?

Yes, you have to do ice accumulation testing as part of certification testing. It used to be done by trying to find natural icing (annoyingly inconsistent), flying behind a KC-135 dumping water (expensive but effective), and today it's usually done with synthetic ice shapes. You use an icing tunnel to figure out what shape ice will build up in, then build that in plastic and stick it to the airplane.

Tom.


User currently offlinetb727 From United States of America, joined Jun 2005, 1629 posts, RR: 9
Reply 6, posted (2 years 3 months 3 weeks 1 day 15 hours ago) and read 12339 times:

Quoting Viscount724 (Reply 3):
At least 3 727s had the #3 engine separate due to ice ingestion, although they were all due to ice from leaking lavatory drains, not from ice on the wings. NW 727-200 in 1990 below.

Check essential!

Luckily we only have 2 that have lavs still but I still look for leaks when we get out the the plane.



Too lazy to work, too scared to steal!
User currently offlineHAWK21M From India, joined Jan 2001, 31702 posts, RR: 56
Reply 7, posted (2 years 3 months 3 weeks 22 hours ago) and read 12215 times:

Anti-Icing:- Preventing Ice from forming.
De-Icing:- Removal of ice after it has formed.

Anti-Icing uses pneumatic/electric methods of heating the areas concerned.

De-Icing can use Deicer boots that vary the surface area to break away formed ice.



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