The big chill and altitude
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The big chill and altitude
We are recording nightly temperatures of minus 20 with the associated effects on my central heating condensation outlet pipe.
At cruising altitude, on an average day, it's around minus 60.
Question: How do you keep the ice away from forming on the essential functioning parts?
Waste fluid extractors please post in Jet Blast.
At cruising altitude, on an average day, it's around minus 60.
Question: How do you keep the ice away from forming on the essential functioning parts?
Waste fluid extractors please post in Jet Blast.
On the ground, if there is ice or snow on the aircraft then this will be removed before take-off either by brushing or spraying with de-ice fluid. If it is snowing, sleeting, freezing rain, or heavy frost then the aircraft will normally be sprayed with an anti-ice fluid before take-off. This is known as 2 stage de-icing.
In flight ice normally only affects things that are facing into the airflow and only in icing conditions, at -60C it is too cold for ice to attach to the aircraft, so the following applies generally.
Things that stick out into the airflow are usually electrically heated all the time. i.e. Pitot heads, stall angle of attack probes, Water drain masts, outside air temp probes, also static ports.
The intakes of engines can be heated either electrically or using bleed air, but it is normally only switched on when required. (TAT below +8C, SAT above -40C and in visible moisture).
The wings and tail leading edges can be heated by bleed air when required, but on many turbo prop aircraft inflatable boots on the leading edges are used to break ice away.
There is also a system called TKS which I nave seen on HS125 aircraft that uses a de-ice fluid that seeps out through very small holes in the wing leading edge.
Propellors usually use electric heating, although the DH Heron used TKS fluid through small pipes on the blade roots.
This is only a rough guide and there are bound to be many variations.
Hope this helps.
In flight ice normally only affects things that are facing into the airflow and only in icing conditions, at -60C it is too cold for ice to attach to the aircraft, so the following applies generally.
Things that stick out into the airflow are usually electrically heated all the time. i.e. Pitot heads, stall angle of attack probes, Water drain masts, outside air temp probes, also static ports.
The intakes of engines can be heated either electrically or using bleed air, but it is normally only switched on when required. (TAT below +8C, SAT above -40C and in visible moisture).
The wings and tail leading edges can be heated by bleed air when required, but on many turbo prop aircraft inflatable boots on the leading edges are used to break ice away.
There is also a system called TKS which I nave seen on HS125 aircraft that uses a de-ice fluid that seeps out through very small holes in the wing leading edge.
Propellors usually use electric heating, although the DH Heron used TKS fluid through small pipes on the blade roots.
This is only a rough guide and there are bound to be many variations.
Hope this helps.
Join Date: Oct 2005
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Cieloitaliano,
An important difference exists between operations at cruise altitude and the central heating condensation outlet pipe at your house. You have a lot of relative humidity difference, between your home, and the air at 35,000'.
You appear to be asking specifically about condensation, though icing potential still exists in other forms.
Condensation is found on the ground, often in the form of water dripping off the wing around fuel cells (where the fuel is cold from flight), or frost under the wings in the area of the fuel tanks.
Frost sublimates fairly quickly around much of the airframe at cruise, and doesn't really have a chance to form once it's gone, due to lower pressures around the airframe. Icing can occur from various sources. Large supercooled water droplets such as may be found in convective weather can remain liquid and below freezing, and impact with the surfaces of the airplane can break the surface tension on the water droplets, leading to instant freezing. Likewise, freezing rain can cause buildups on the airplane.
Ice protection exists in two basic forms: anti-ice, and de-ice. Anti-ice prevents the buildup from ice, generally by heating the surface that's being protected. De-ice involves various methods, from chemical means, to expanding and contracting surfaces (inflatable rubber "boots"), and also various forms of heating or vibrating surfaces.
Some systems weep a fluid such as isopropyl alcohol over the nose, or wing, or propeller, to help prevent ice formation (and in some cases remove it, though anti-ice systems are never to be counted on for removing ice). Some heat surfaces such as the wing, engine nacelle inlets, windshields, etc. Some, like the boots on some inlets or leading edges, inflate to break up ice.
-60 isn't too cold for ice to attach to the airplane, but it's generally too cold for water to remain in liquid form. Water has been found in liquid form as low as -40 degrees, but much beyond that, and everything is frozen. Once frozen, it doesn't tend to adhere to the airplane.
Airplanes that operate at fast speeds tend to experience a significant change in surface temperature due to ram air effects. Ice that forms at slower speeds often won't at higher speeds. Thin surfaces and airfoils tend to ice more easily than thick ones, and tend to be more easily affected by smaller buildups of ice.
Most of all, we generally try to stay out of icing conditions, where ever possible. When we do have to fly in icing conditions, we minimize our exposure to ice, and avoid severe ice. We tend to turn on ice protection equipment early in most cases (not all; some doesn't function well until it's already iced-up). Sometimes we have operating limitations when ice protection is in use (the airplane I presently fly has minimum engine power settings when nacelle anti-ice is in use, for example, to ensure enough hot air from the engine "bleed" system is available to properly protect the engine nacelles).
Avoiding ice is always better than having to contend with it, whenever possible.
An important difference exists between operations at cruise altitude and the central heating condensation outlet pipe at your house. You have a lot of relative humidity difference, between your home, and the air at 35,000'.
You appear to be asking specifically about condensation, though icing potential still exists in other forms.
Condensation is found on the ground, often in the form of water dripping off the wing around fuel cells (where the fuel is cold from flight), or frost under the wings in the area of the fuel tanks.
Frost sublimates fairly quickly around much of the airframe at cruise, and doesn't really have a chance to form once it's gone, due to lower pressures around the airframe. Icing can occur from various sources. Large supercooled water droplets such as may be found in convective weather can remain liquid and below freezing, and impact with the surfaces of the airplane can break the surface tension on the water droplets, leading to instant freezing. Likewise, freezing rain can cause buildups on the airplane.
Ice protection exists in two basic forms: anti-ice, and de-ice. Anti-ice prevents the buildup from ice, generally by heating the surface that's being protected. De-ice involves various methods, from chemical means, to expanding and contracting surfaces (inflatable rubber "boots"), and also various forms of heating or vibrating surfaces.
Some systems weep a fluid such as isopropyl alcohol over the nose, or wing, or propeller, to help prevent ice formation (and in some cases remove it, though anti-ice systems are never to be counted on for removing ice). Some heat surfaces such as the wing, engine nacelle inlets, windshields, etc. Some, like the boots on some inlets or leading edges, inflate to break up ice.
-60 isn't too cold for ice to attach to the airplane, but it's generally too cold for water to remain in liquid form. Water has been found in liquid form as low as -40 degrees, but much beyond that, and everything is frozen. Once frozen, it doesn't tend to adhere to the airplane.
Airplanes that operate at fast speeds tend to experience a significant change in surface temperature due to ram air effects. Ice that forms at slower speeds often won't at higher speeds. Thin surfaces and airfoils tend to ice more easily than thick ones, and tend to be more easily affected by smaller buildups of ice.
Most of all, we generally try to stay out of icing conditions, where ever possible. When we do have to fly in icing conditions, we minimize our exposure to ice, and avoid severe ice. We tend to turn on ice protection equipment early in most cases (not all; some doesn't function well until it's already iced-up). Sometimes we have operating limitations when ice protection is in use (the airplane I presently fly has minimum engine power settings when nacelle anti-ice is in use, for example, to ensure enough hot air from the engine "bleed" system is available to properly protect the engine nacelles).
Avoiding ice is always better than having to contend with it, whenever possible.
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Dry air at altitude.
At the higher altitudes where most jets cruise the air is extremely dry.
The air you breath in the cabin of your jet transport was extracted from the outside ambient air compressed & filtered before it was pumped into the cabin. You remember from your many flights how dry your skin feels, how quickly bread, served to you, turns stale & hard and how thirsty you feel on long flights at high altitudes. In fact the relative humidity in the cabin of an airliner cruising at high altitudes is dryer (much dryer) than any desert on the surface of the earth.
At high altitudes and low temperatures [you mentioned -60C] most of the water vapor was condensed out of the air long before it reached those very low temperatures. As the air cools its ability to hold water in suspention decreases and the water vapor condenses out in the form of mist, cloud, rain, snow and hail. By the time the temperature reaches -60C most of the water content is gone; the air is dry, exceedingly dry. Without moisture, water vapor, ice is unable to form.
Not that icing is impossible at -60C, it is not very common at all. To encounter ice at -60C other factors need to be present, not cruising in clear air at altitude.
All of the above is a long way of saying.............
Others have done an outstanding job in describing the various means of keeping ice off the jet, I couldn't add anything at all.
The air you breath in the cabin of your jet transport was extracted from the outside ambient air compressed & filtered before it was pumped into the cabin. You remember from your many flights how dry your skin feels, how quickly bread, served to you, turns stale & hard and how thirsty you feel on long flights at high altitudes. In fact the relative humidity in the cabin of an airliner cruising at high altitudes is dryer (much dryer) than any desert on the surface of the earth.
At high altitudes and low temperatures [you mentioned -60C] most of the water vapor was condensed out of the air long before it reached those very low temperatures. As the air cools its ability to hold water in suspention decreases and the water vapor condenses out in the form of mist, cloud, rain, snow and hail. By the time the temperature reaches -60C most of the water content is gone; the air is dry, exceedingly dry. Without moisture, water vapor, ice is unable to form.
Not that icing is impossible at -60C, it is not very common at all. To encounter ice at -60C other factors need to be present, not cruising in clear air at altitude.
All of the above is a long way of saying.............
No moisture, no ice.
Last edited by Northbeach; 30th Nov 2010 at 05:03.
