| Revision as of 17:38, 20 September 2008 editMadScot (talk | contribs)Extended confirmed users762 edits Added NASA external link← Previous edit | Revision as of 18:00, 20 September 2008 edit undoMadScot (talk | contribs)Extended confirmed users762 edits →Icing prevention and removal: rewrite, added ground deicing plus other changesNext edit → | ||
| Line 14: | Line 14: | ||
| Several methods exist to reduce the dangers of icing. The first, and simplest, is to avoid icing conditions altogether, but for many flights this is not practical. | Several methods exist to reduce the dangers of icing. The first, and simplest, is to avoid icing conditions altogether, but for many flights this is not practical. | ||
| If ice (or other contaminants) are present on an aircraft prior to takeoff, this must be removed from critical surfaces. Removal can take many forms: | |||
| If icing is expected, ] can be applied to the aircraft before flight to prevent ice from forming, or from sticking to the surface if it does form. ]s are often deiced before departure, and the deicing fluid prevents ice buildup for a short time after. | |||
| * Mechanical means, which may be as simple as using a broom or brush to remove snow | |||
| * Application of ] or even hot water to remove ice, snow, etc. | |||
| * Use of infrared heating to melt and remove contaminants | |||
| All of these methods remove existing contamination, but provide no practical protection in icing conditions. If icing conditions exist, or are expected before takeoff, then anti-icing fluids are used. These are thicker than deicing fluids and resist the effects of snow and rain for some time. They are intended to shear off the aircraft during takeoff and provide no inflight protection. | |||
| To protect an aircraft against icing in-flight, various forms of anti-icing or deicing are used: | |||
| Another common approach is to route engine "bleed air" along the leading edges of wings and tailplanes, which can keep the surface ] above freezing point. This is accomplished on a turbine powered aircraft by running ducts out of the side of compressor section into ducting in the wings' leading edge. If the aircraft is turbocharged piston powered, bleed air can be scavenged from the turbocharger. A ] has hundreds of small holes in the leading edges and releases ] on demand to clear the entire wing of ice. Older aircraft and ]s are often equipped with pneumatic ]s | |||
| * One common approach is to route engine "bleed air" into ducting along the leading edges of wings and tailplanes. The air heats the leading edge of the surface and this melts or evaporates icie on contact. On a turbine powered aircraft air is extracted from the compressor section of the engine. If the aircraft is turbocharged piston powered, bleed air can be scavenged from the turbocharger. | |||
| * Some aircraft and ]s are equipped with pneumatic ]s which disperse ice build-up on the surface. These systems require less engine bleed air but are usually less effective than a heated surface. | |||
| * A few aircraft use a ] system which has hundreds of small holes in the leading edges and releases anti-icing fluid on demand to prevent the buildup of ice. | |||
| * Electrical heating is also used to protect aircraft and components against icing. The heating may be applied continuously (usually on small, critical, components, such as ] sensors and angle of attack vanes) or intermittently, giving an effect similar to the use of ]s. | |||
| In all these cases usually only critical aircraft surfaces and components are protected. In particular only the leading edge of a wing is usually protected. | |||
| ] is applied to carbureted engines to prevent and clear icing. ]s are not susceptible to carburetor icing but can suffer from blocked inlets. In these engines an alternate air source is often available. | ] is applied to carbureted engines to prevent and clear icing. ]s are not susceptible to carburetor icing but can suffer from blocked inlets. In these engines an alternate air source is often available. | ||
| Note there is a difference between deicing and anti-icing. | Note there is a difference between deicing and anti-icing. Deicing refers to the removal of ice from the airframe; anti-icing refers to the prevention of ice accumulating on the airframe. | ||
| ==See also== | ==See also== | ||
Revision as of 18:00, 20 September 2008
 | This article does not cite any sources. Please help improve this article by adding citations to reliable sources. Unsourced material may be challenged and removed. Find sources: "Icing" aeronautics – news · newspapers · books · scholar · JSTOR (December 2007) (Learn how and when to remove this message) |
In aviation, icing conditions are those atmospheric conditions that can lead to the formation of water ice on the surfaces of an aircraft, or within the engine as carburetor icing. Inlet icing is another engine-related danger, often occurring in jet aircraft. These icing phenomena do not necessarily occur together. Many aircraft are not certified for flight into known icing—icing conditions which are certain to exist based on pilot reports, observations, and forecasts.
Ice forms when air containing water vapour is cooled below the freezing point of water, which becomes higher with decreasing pressure; ice is likely to form wherever there is reduced pressure, including wings and empennage (where it is known as structural icing), carburetors, pitot tubes, and engine inlets. Ice gradually builds as long as icing conditions exist and if left unchecked results in dangerous conditions. Ice adds to an aircraft's weight and disrupts airflow, increasing the stall speed. In engines, carburetor ice and inlet ice can lead to reduced power or complete engine failure.
Types of structural ice
- Glaze ice is often clear and smooth. Supercooled water droplets, or freezing rain, strike a surface but do not freeze instantly. Often "horns" or protrusions are formed and project into the airflow.
- Rime ice is rough and opaque, formed by supercooled drops rapidly freezing on impact. Forming mostly along an airfoil's stagnation point, it generally conforms to the shape of the airfoil.
- Mixed ice is a combination of clear and rime ice.
- Runback ice is the result of water freezing on unprotected surfaces. Often forming behind deicing boots or heated leading edges, it was a factor in the crash of American Eagle Flight 4184.
Icing prevention and removal
Several methods exist to reduce the dangers of icing. The first, and simplest, is to avoid icing conditions altogether, but for many flights this is not practical.
If ice (or other contaminants) are present on an aircraft prior to takeoff, this must be removed from critical surfaces. Removal can take many forms:
- Mechanical means, which may be as simple as using a broom or brush to remove snow
- Application of deicing fluid or even hot water to remove ice, snow, etc.
- Use of infrared heating to melt and remove contaminants
All of these methods remove existing contamination, but provide no practical protection in icing conditions. If icing conditions exist, or are expected before takeoff, then anti-icing fluids are used. These are thicker than deicing fluids and resist the effects of snow and rain for some time. They are intended to shear off the aircraft during takeoff and provide no inflight protection.
To protect an aircraft against icing in-flight, various forms of anti-icing or deicing are used:
- One common approach is to route engine "bleed air" into ducting along the leading edges of wings and tailplanes. The air heats the leading edge of the surface and this melts or evaporates icie on contact. On a turbine powered aircraft air is extracted from the compressor section of the engine. If the aircraft is turbocharged piston powered, bleed air can be scavenged from the turbocharger.
- Some aircraft and propellers are equipped with pneumatic deicing boots which disperse ice build-up on the surface. These systems require less engine bleed air but are usually less effective than a heated surface.
- A few aircraft use a weeping wing system which has hundreds of small holes in the leading edges and releases anti-icing fluid on demand to prevent the buildup of ice.
- Electrical heating is also used to protect aircraft and components against icing. The heating may be applied continuously (usually on small, critical, components, such as pitot static sensors and angle of attack vanes) or intermittently, giving an effect similar to the use of deicing boots.
In all these cases usually only critical aircraft surfaces and components are protected. In particular only the leading edge of a wing is usually protected.
Carburetor heat is applied to carbureted engines to prevent and clear icing. Fuel-injected engines are not susceptible to carburetor icing but can suffer from blocked inlets. In these engines an alternate air source is often available.
Note there is a difference between deicing and anti-icing. Deicing refers to the removal of ice from the airframe; anti-icing refers to the prevention of ice accumulating on the airframe.