March 13th, 2010 by , under nnmj.com.
..... take-off? Why is that?You can get icing anytime depending on the weather. You can get hoar frost forming on the aircraft when it sits still. Any ice on the aircraft is not a good thing. I have heard (I have not found it yet though) that if you have ice on the aircraft, and it is buffed smooth it is legal to fly like that. Nacelle anti-ice is going to be turned on any time you're in atmospheric conditions in which ice MAY form. In most cases this is when the temperature is less than 10C (50F) and visible moisture is present (rain, snow, fog with vis less than 1 mile). This prevents ice from forming inside the engine (nacelle anti-ice usually heats other components inside the engine as well - i.e. stator vanes).
Wing anti ice is only turned on when you actually see ice building up on the wings. There's actually a fairly narrow temperature window in which the wing is going to collect ice. You won't pick up ice on the wing every time you're in visible moisture and the temp is below 10C.as you say "on take-off" I think you are referring to the power loss as being most anti-ice comes from engine bleed. Some like the B737 we take-off with pneumatics or packs off or using apu bleed for pneumatics (air con) instead of engine bleed to use it for additional power on take-off.
Modern or fly by wire aircraft through their EIVMU with anti-ice on tells the FADEC to increase power as engine bleed is used for anti-icing, even the ignition is automatically on "continuous"De-ice systems usually cycle, but anti-ice stays on as long as is necessary, although most systems have over temp sensors that will shut it off when it overheats.
Depending on atmospheric conditions near the ground, ice may form easily. Ice may not be forming at the time, but during takeoff, with engine power at full or takeoff power, the pressure drop inside the inlets can cause the temperature to drop as well. Certain surfaces of the inlet can see just enough temperature drop to reach freezing or below. Other surfaces of the aircraft can do the same, hence wing, stab and vertical anti-ice on many airplanes.
It's very similar to the ice that can build up in an aircraft piston engine carburetor. The lower pressure in the venturi can decrease the temperature enough for ice to form. Most carbureted engines have a heating system to prevent that, called, of all things, carburetor heat.
Here's a panel showing wing and engine anti-ice switches:
http://farm3.static.flickr.com/2069/2305...Takeoff performance data is published for engine anti-ice on, and for engine anti-ice off. The wing should be clean for takeoff---this is accomplished, if necessary, by ground de-icing. Once airborne, wing anti-ice can be turned on, if needed. Engine anti-ice might also include the inboard wing and/or the tail, on some jets.As with any system on an aircraft, the de-ice/anti ice systems can be turned on and off, as needed. The De-ice systems usually run a cycle and go off on their own, until needed again, however, any ice on an aircraft is not good. It adds weight and distorts the flow of air over the airframe and wings. This flow is vital to maintain airworthiness, so eliminating ice is vital. No amount of ice is okay. On modern jet aircraft there is a constant flow of heat along the wings and verticals to avoid ice.
Remember, the temperature drops at a rate of 1.98 degrees celcius/centigrade for every 1000 feet of elevation, so what ever the ground temp is (in celcius/centigrade) it will drop as you climb. It does not take much to reach freezing.#If you have any other info about this subject , Please add it free.# |
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