flyingbronco05
Posts: 3484
Joined: Fri May 10, 2002 11:43 am

Icing/De-Icing

Hey all-
I searched the forums and found nothing on this topic. This topic is for mostly pilots and people with great knowledge of icing systems. The topic is "icing/de-icing" and my question is this: I know that pilots can turn on the anti ice switch or something like that in the cockpit in flight. But why can't they just flip that switch on the ground instead of getting de-iced by those sprayer guys (sorry again, i dont know what they are called). Thanks again to all.

Flyingbronco05

JETPILOT
Posts: 3094
Joined: Tue May 18, 1999 6:40 am

RE: Icing/De-Icing

Planes do not have de-ice systems.

Leading edge wing heat, engine TAI (thermal anti ice), windshield heat, etc are all anti ice systems. They prevent ice build up.

The upper surfaces of the wing and stabilizers and fusealge aren't heated as they have no contact with precip inflight.

The anti ice systems are designed for inflight use only.

JET

EssentialPowr
Posts: 1646
Joined: Wed Sep 06, 2000 10:30 pm

RE: Icing/De-Icing

Inflight use only b/c these systems must be capable of being VERY hot to prevent ice from accumulating in the worst of conditions; maybe -20C outside air temp in freezing rain, for example. That heat must be sufficient along then entire span of the wing.

Total heat is given by the eqn:

Q = M C (delta T) where
Q = "total" heat
M = mass of aluminum alloy anti-iced in leading edge
C = specific heat for aluminum alloy in the wing
delta T = change in temp required (as a guess, -20C to + 100C = 120C)

Suffice it to say it requires a gob of heat to do this; in some cases the heat required is sufficient to MELT to aluminum unless sufficient airflow is moving over the wings (ie a/c in flight).

Windows are heated for anti ice and to enhance bird strike protection, as warm windows are less brittle than cold ones, and are typically controlled by a thermostat -not a big deal.

Cheers-

POSITIVE RATE
Posts: 2121
Joined: Sun Sep 16, 2001 11:31 am

RE: Icing/De-Icing

SOME planes do have de-ice systems. These are in the form of expandable rubber "boots" on the leading edge of the wing. When ice has built up to a certain amount the pilot activates them and they expand which in turn removes the ice from the leading edge of the wing. Most of the smaller turboprop a/c have this system- e.g F-27/F-50/SF340 etc. Turboprops also have heated elements on the prop blades to prevent ice build-up on them which would result in a power loss.

L-188
Posts: 29881
Joined: Wed Jul 07, 1999 11:27 am

RE: Icing/De-Icing

Flight Ice systems are by nature designed to be used when the aircraft is in motion, As in flying forward through the air.
OBAMA-WORST PRESIDENT EVER....Even SKOORB would be better.

Guest

RE: Icing/De-Icing

Like Positive Rate said, some planes do have de-ice systems and it's not just turboprops either. The problem with anti-ice systems is what EssentialPower said, they need heat and lots of it. The heat typically comes from an engine bleed air source. Anytime you take that much heat from an engine you also take away a significant amount of power.

For anti-ice systems to be effective you must turn them on prior to entering icing conditions, otherwise they will just melt the ice and the water will flow back to places that are protected and refreeze - not a good thing. Also, chunks of ice can come off and go through the engines (B727, DC9, MD-80, Lear, Citation, etc. Anything with rear mounted engines.)

On the Lears that I've flown, turning on the wing heat had a significant effect on the climb capability of the aircraft, something in the range of 50% if I remember correctly. The Astras and Galaxy that I fly have the "old fashioned" boots on the leading edges. When I first trained in the aircraft, I was very sceptical - boots on a modern jet airplane, you've got to be kidding? In the real world, they're actually pretty nice. You only use them when you need them, and they don't extract a performance penality when you do. I've got nearly 4,000 hours in Astras and Galaxys and they work extremely well, I think. I say that because I can count on one hand the actual number of times that I've ever had to use them in self defense, all of the other times were for amusement purposes only.

Jetguy

Guest

RE: Icing/De-Icing

Oops, here's another addition to my personal list of Things I Should Have Said:

For anti-ice systems to be effective you must turn them on prior to entering icing conditions, otherwise they will just melt the ice and the water will flow back to places that are protected and refreeze - not a good thing. Let's make that, "the water will flow back to places that are NOT protected and refreeze."

Jetguy

FLY 8
Posts: 330
Joined: Sat Dec 02, 2000 5:48 am

RE: Icing/De-Icing

Jetpilot, since when don´t have a De-Ice system?
What about Turbo prop airplanes with boots on it. This is a De ice system.

Anti Ice: To prevent ice build up.

De-Ice: you let build up ice on it and then you remove it by boots or liquid (some small airplanes have that)
yes i can handle that alone. - - -famous last words

JETPILOT
Posts: 3094
Joined: Tue May 18, 1999 6:40 am

RE: Icing/De-Icing

Sorry... I was thinking in terms of large airliners.

Boy am I an idiot....

JET

747Teach
Posts: 176
Joined: Wed Nov 29, 2000 3:05 am

RE: Icing/De-Icing

Flyingbronco05: The 747-200 Maintenance Manual, Chapter 30, Ice and Rain Protection, in the Description and Operation, says the following: "Wing Thermal Anti-Ice prevents formation of ice on the leading edge of the wing. The TAI system receives regulated hot air from the bleed air manifold." This regulated bleed air is about 45 psi at 350 degrees F. In flight, when the TAI system is turned on, a valve opens and allows this air to enter the ducting, which then distributes the air to the inside of the leading edge cavity. This air will always be flowing into the cavity as long as the valve is open. If the system is turned on while the aircraft is on the ground, overheat protection will close the anti-ice valves if the temperature in the cavity goes above 200 degrees F.
Chapter 30 says this about the windshields: "The flight compartment windows are electrically heated to provide anti-icing to No. 1 Lt and Rt windows, and defogging for No. 2 and 3 Lt and Rt window. Heat applied to the windows also increases their impact resistance." In flight, the No. 1 windows are maintained at about 85 to 100 degrees F, and on the ground at about 58 to 73 degrees F with the system on. (Note: Some manufacturer's windows have slightly different heat ranges).
So, to give your question a general answer, it's the leading edges of wings, windshields, and sometimes (on some airplanes), nacelles, and vertical and horizontal stabilizers that are the areas of concern, particularily during flight. Those "sprayer guys" are getting rid of ice and snow accumulation over almost all of the airplane because, simply, most of the plane is not heated on the outside, and has no other method to get rid of the ice and snow. Regards,

flyingbronco05
Posts: 3484
Joined: Fri May 10, 2002 11:43 am

RE: Icing/De-Icing

Thanks for all the help. Now i understand it.

bio15
Posts: 1048
Joined: Fri Mar 23, 2001 8:10 am

RE: Icing/De-Icing

How exactly does de 'boot' mechanism for de-icing work? And doesn't anti-icing heat the wing surface? I thought ice buildup on the wing surface was the dangerous thing.
-bio

FlightTest
Posts: 35
Joined: Wed Apr 24, 2002 4:01 am

RE: Icing/De-Icing

The boot is just a rubber boot theat covers the leading edge. It inflates from bleed air just enough to expand it and break away the ice.

shaun3000
Posts: 439
Joined: Thu Mar 14, 2002 4:10 pm

RE: Icing/De-Icing

Anti-ice just heats the leading edge of the wing (or propellor)*

Ice build-up on the leading edge is worse than on the wing surface. Someone else can explain why this is, I am not too sure, myself.

*some planes have a liquid de/anti-ice. The ones I am aware of are smaller, single or twin props. The liquid is alcohol, and it is only on the leading edges of the prop blades on ONE of the engines (if it's a twin)

POSITIVE RATE
Posts: 2121
Joined: Sun Sep 16, 2001 11:31 am

RE: Icing/De-Icing

ice build up on any part of the wing is not good and will result in a decrease in lift/increase in drag. I would say the reason why build up on the leading edge is worse because this is where most of the lift is created on a wing and if there is ice build-up then the camber of the wing will be change and airflow disrupted. Airplanes fitted with leading edge slats/flaps are not are susceptible as ones without. A good example is the F-28 which has no leading edge slats an as a result any ice contamination on the wing will result in a dramatic lift penalty(AKA Air Ontario F-28 crash in 1989). Other a/c with slats aren't as susceptible to this problem.

bio15
Posts: 1048
Joined: Fri Mar 23, 2001 8:10 am

RE: Icing/De-Icing

Again there's my confusion: Why is the most lift generated at the leading edge? Lift is supposed to be generated mostly along the wing surface, where the pressure difference exists, and that's where more thorough de-icing should take place. I just don't see how leading edge icing is more dangerous than wing surface icing. Excuse me if it is really simple and I'm just not getting the obvious, but could someone please expand a bit more on this?
-bio

L-188
Posts: 29881
Joined: Wed Jul 07, 1999 11:27 am

RE: Icing/De-Icing

When I was working on big airplanes we where allowed up to 3/8's of an inch of ice buildup on the bottom surface of the wings before deicing became a concern.

These are the area's where the wing would frost up due to cold soaked fuel.
OBAMA-WORST PRESIDENT EVER....Even SKOORB would be better.

JETPILOT
Posts: 3094
Joined: Tue May 18, 1999 6:40 am

RE: Icing/De-Icing

Bio 15.... your asking questions that are phillisophical in nature and don't really have anything to do with the operation of the aircraft.

Wing surfaces, for whatever reason don't ice in flght. That's just the way it is. Hence no wing surface anti-ice capability. It's not needed.

Leading edge surfaces do have direct contact with visible moisture in flight hence leading edge TAI.

JET

atlamt
Posts: 245
Joined: Thu Sep 13, 2001 12:15 am

RE: Icing/De-Icing

Bio15

Let me try to explain why leading edge icing is so bad.

First the air flowing over a wing has a viscosity which makes it stick to the surface of the wing. The smooth flow over the wing is what causes the drop in pressure on top of the wing which is lift. Now if you have a buildup of ice on the leading edge the airflow over the leading edge becomes very turbulent. The airflow is no longer able to flow smoothly over the wing and you lose lift. As more ice builds up the wing become less and less able to create lift.

Icing is a problem in all stages of flight but during takeoff and landing it is most dangerous because the aircraft is operating so close to stall speed.

I hope this helps.

ATLAMT
Fwd to MCO and Placard

FlightTest
Posts: 35
Joined: Wed Apr 24, 2002 4:01 am

RE: Icing/De-Icing

The fluid type of wing anti/deice systems is called weeping wings. The leading edge is a stainless steel mesh that secretes TKS fluid. TKS fluid is a alcohol/glycol solution. I deal with this system quite a bit on the Hawker bizjets. It is also my understanding that some bizjets have this type of system of deicing the radomes too.

srbmod
Posts: 15446
Joined: Tue Mar 20, 2001 1:32 pm

RE: Icing/De-Icing

The funny thing I've found about the deicing fluid is on the health hazards section. It said if ingested to drink a small quantity of liquor (preferrably whiskey). When I was a ramper, my gate always threatened to drink some just so we could get some liquor. By the way, it has a sweet taste.

FlightTest
Posts: 35
Joined: Wed Apr 24, 2002 4:01 am

RE: Icing/De-Icing

Never drank any, but it sucks getting it in your eyes.

bio15
Posts: 1048
Joined: Fri Mar 23, 2001 8:10 am

RE: Icing/De-Icing

Yes ATLAMT I got the idea thank you.

Bio 15.... your asking questions that are phillisophical in nature and don't really have anything to do with the operation of the aircraft.
Wing surfaces, for whatever reason don't ice in flght

I am aware this does not involve aspects of the operation of the aircraft, but still the question is pertinent in this post. Someone beside you may know why surface icing doesn't occur, leave it to them.
-bio

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