why do frosting do not happen for flying aeroplane at 30,000 ft where temperature is about -30 deg C?

Question

Aeroplanes usually fly at high altitudes where surounding atmospheric temperature is in the range of minus 30 degree Centigrade. Why do ice do not form on body, wings of the plane at such temperatures?

Answer 1

At such heights density of air is so low that it cannot hold much moisture, even oxygen becomes rare.

Answer 2

Well some answers are more or less correct but some are wrong and all miss the point. Most commerical planes fly at 35000 to 40000 feet where it can easily be minus 50 C but there is no reason for whatever moisture is there to condense on the plane's surface. To say it is ice which bounces off is plain stupid. Unless your flying through cloud or contrail, moisture is there as vapour and there would need to be a mass transfer force to encourage its condensation onto any surface. Actually the plane's skin will be at a temperature above that of the air for two reasons. The plane itself is heated inside and despite all insulating factors the skin will be "warmer" than the surrounding air and losing heat plus there is some frictional heating due to airspeed. Concorde actually stretched due to the friction heating at its high speed and they reckon it was this constant annealing during every high speed flight which meant that Concorde's skin metal remained in better than expected metalurgical condition.

Where you can suffer icing on planes is at lower altitudes during climb out and if you fly through warmer (than minus 50C) supersaturated air like in thunderclouds.

Answer 3

A couple of reasons.

First, at 30,000 ft, there isn't much moisture in the atmosphere, (which is why it is usually clear at high altitudes). Cold air cannot hold as much moisture as warm air.

Second, the visible moisture that is up there is in the form of ice crystals that simply bounce off the aircraft.

Thunderstorms can carry more moisture up to this altitude, but jets will avoid these.

Frost and ice will typically form as the jet descends to warmer, moister air. The metal of the jet is still cold from high altitudes and causes the moisture to condense and stick to the airframe.

Airframe heating (due to friction) only happens at lower altitudes and high speeds since there is not enough air up at high altitudes to do this.

Answer 4

Icing DOES occur at ALL altitudes where moisture is present!! EVEN at 40,000 ft.!! That is why ALL aircraft that are certificated to fly at those altitudes have Ice protection for all leading edges, engine intakes, and windshields Though when at altitude this problem only occurs when you fly through clouds. (thus exposing your craft to moisture) Clouds do top at as much as 65,000 ft at times. Though rare.

Answer 5

It takes quite a thunderstorm to lift moisture up that high. then lightning up and down drafts pilots fly around the big storms. Winter is a different story moisture freezes instantly in middle altitutes.

Answer 6

the leading edge of airplanes have means for deicing the wings. also you fly at altitudes where water vapor is not as dense.

Answer 7

friction