Ice Protection System
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In
aeronautics Aeronautics is the science or art involved with the study, design, and manufacturing of air flight–capable machines, and the techniques of operating aircraft and rockets within the atmosphere. The British Royal Aeronautical Society identifies ...
, ice protection systems keep atmospheric
moisture Moisture is the presence of a liquid, especially water, often in trace amounts. Small amounts of water may be found, for example, in the air (humidity), in foods, and in some commercial products. Moisture also refers to the amount of water vapo ...
from accumulating on
aircraft An aircraft is a vehicle that is able to fly by gaining support from the air. It counters the force of gravity by using either static lift or by using the dynamic lift of an airfoil, or in a few cases the downward thrust from jet engines ...
surfaces, such as wings,
propellers A propeller (colloquially often called a screw if on a ship or an airscrew if on an aircraft) is a device with a rotating hub and radiating blades that are set at a pitch to form a helical spiral which, when rotated, exerts linear thrust upon ...
, rotor blades, engine intakes, and
environmental control Heating, ventilation, and air conditioning (HVAC) is the use of various technologies to control the temperature, humidity, and purity of the air in an enclosed space. Its goal is to provide thermal comfort and acceptable indoor air quality. HV ...
intakes. Ice buildup can change the shape of
airfoil An airfoil (American English) or aerofoil (British English) is the cross-sectional shape of an object whose motion through a gas is capable of generating significant lift, such as a wing, a sail, or the blades of propeller, rotor, or turbine. ...
s and
flight control surface Aircraft flight control surfaces are aerodynamic devices allowing a pilot to adjust and control the aircraft's flight attitude. Development of an effective set of flight control surfaces was a critical advance in the development of aircraft. Ea ...
s, degrading control and handling characteristics as well as performance. An anti-icing,
de-icing Deicing is the process of removing snow, ice or frost from a surface. Anti-icing is the application of chemicals that not only deice but also remain on a surface and continue to delay the reformation of ice for a certain period of time, or preve ...
, or ice protection system either prevents formation of ice, or enables the aircraft to shed the ice before it becomes dangerous.


Effects of icing

Aircraft icing increases weight and drag, decreases lift, and can decrease thrust. Ice reduces engine power by blocking air intakes. When ice builds up by freezing upon impact or freezing as runoff, it changes the aerodynamics of the surface by modifying the shape and the smoothness of the surface which increases drag, and decreases wing lift or propeller thrust. Both a decrease in lift on the wing due to an altered airfoil shape, and the increase in weight from the ice load will usually result having to fly at a greater
angle of attack In fluid dynamics, angle of attack (AOA, α, or \alpha) is the angle between a reference line on a body (often the chord line of an airfoil) and the vector representing the relative motion between the body and the fluid through which it is m ...
to compensate for lost lift to maintain altitude. This increases fuel consumption and further reduces speed, making a stall more likely to occur, causing the aircraft to lose altitude. Ice accumulates on helicopter rotor blades and
aircraft propeller An aircraft propeller, also called an airscrew,Beaumont, R.A.; ''Aeronautical Engineering'', Odhams, 1942, Chapter 13, "Airscrews". converts rotary motion from an engine or other power source into a swirling slipstream which pushes the propeller ...
s causing weight and aerodynamic imbalances that are amplified due to their rotation. Anti-ice systems installed on
jet engine A jet engine is a type of reaction engine discharging a fast-moving jet of heated gas (usually air) that generates thrust by jet propulsion. While this broad definition can include rocket, Pump-jet, water jet, and hybrid propulsion, the term ...
s or
turboprop A turboprop is a turbine engine that drives an aircraft propeller. A turboprop consists of an intake, reduction gearbox, compressor, combustor, turbine, and a propelling nozzle. Air enters the intake and is compressed by the compressor. Fuel ...
s help prevent airflow problems and avert the risk of serious internal engine damage from ingested ice. These concerns are most acute with turboprops, which more often have sharp turns in the intake path where ice tends to accumulate.


System types


Pneumatic deicing boots

The pneumatic boot is usually made of layers of
rubber Rubber, also called India rubber, latex, Amazonian rubber, ''caucho'', or ''caoutchouc'', as initially produced, consists of polymers of the organic compound isoprene, with minor impurities of other organic compounds. Thailand, Malaysia, and ...
or other
elastomer An elastomer is a polymer with viscoelasticity (i.e. both viscosity and elasticity) and with weak intermolecular forces, generally low Young's modulus and high failure strain compared with other materials. The term, a portmanteau of ''elastic p ...
s, with one or more air chambers between the layers. If multiple chambers are used, they are typically shaped as stripes aligned with the long direction of the boot. It is typically placed on the leading edge of an aircraft's wings and stabilizers. The chambers are rapidly inflated and deflated, either simultaneously, or in a pattern of specific chambers only. The rapid change in shape of the boot is designed to break the adhesive force between the ice and the rubber, and allow the ice to be carried away by the air flowing past the wing. However, the ice must fall away cleanly from the trailing sections of the surface, or it could re-freeze behind the protected area. Re-freezing of ice in this manner was a contributing factor to the crash of
American Eagle Flight 4184 American Eagle Flight 4184, officially operating as Simmons Airlines Flight 4184, was a scheduled domestic passenger flight from Indianapolis, Indiana to Chicago, Illinois, United States. On , 1994, the performing this route flew into severe ...
. Older pneumatic boots were thought to be subject to ice bridging. Slush could be pushed out of reach of the inflatable sections of the boot before hardening. This was resolved by speeding up the inflation/deflation cycle, and by alternating the timing of adjacent cells. Testing and case studies performed in the 1990s have demonstrated that ice bridging is not a significant concern with modern boot designs. Pneumatic boots are appropriate for low and medium speed aircraft, without leading edge lift devices such as
slats Super Low Altitude Test Satellite (SLATS) or Tsubame was a JAXA satellite intended to demonstrate operations in very low Earth orbit (VLEO, below 200 km), using ion engines to counteract aerodynamic drag from the Earth's atmosphere which i ...
, so this system is most commonly found on smaller
turboprop A turboprop is a turbine engine that drives an aircraft propeller. A turboprop consists of an intake, reduction gearbox, compressor, combustor, turbine, and a propelling nozzle. Air enters the intake and is compressed by the compressor. Fuel ...
aircraft such as the
Saab 340 The Saab 340 is a Swedish twin-engine turboprop aircraft designed and initially produced by Saab AB and Fairchild Aircraft. It is designed to seat 30-36 passengers and, as of July 2018, there were 240 operational aircraft used by 34 different o ...
and
Embraer EMB 120 Brasilia The Embraer EMB 120 Brasilia is a twin-turboprop 30-passenger commuter airliner designed and manufactured by the Brazilian aircraft manufacturer Embraer. The EMB 120 began development during 1974. While initially conceived as a modular series ...
. Pneumatic de-Icing boots are sometimes found on other types, especially older aircraft. These are rarely used on modern jet aircraft. It was invented by B.F. Goodrich in 1923.


Fluid deicing

Propeller blade with fluid deicing system - Glycol is sprayed from hub outward to cover blades Sometimes called a weeping wing, running wet, or evaporative system, these systems use a deicing fluid—typically based on
ethylene glycol Ethylene glycol (IUPAC name: ethane-1,2-diol) is an organic compound (a vicinal diol) with the formula . It is mainly used for two purposes, as a raw material in the manufacture of polyester fibers and for antifreeze formulations. It is an odo ...
or
isopropyl alcohol Isopropyl alcohol (IUPAC name propan-2-ol and also called isopropanol or 2-propanol) is a colorless, flammable organic compound with a pungent alcoholic odor. As an isopropyl group linked to a hydroxyl group (chemical formula ) it is the simple ...
to prevent ice forming and to break up accumulated ice on critical surfaces of an aircraft. One or two electrically-driven pumps send the fluid to proportioning units that divide the flow between areas to be protected. A second pump is used for redundancy, especially for aircraft certified for flight into known
icing conditions In aviation, icing conditions are atmospheric conditions that can lead to the formation of water ice on an aircraft. Ice accretion and accumulation can affect the external surfaces of an aircraft – in which case it is referred to as ''airframe ...
, with additional mechanical pumps for the windshield. Fluid is forced through holes in panels on the leading edges of the wings, horizontal stabilizers, fairings, struts, engine inlets, and from a slinger-ring on the propeller and the windshield sprayer. These panels have diameter holes drilled in them, with . The system is self cleaning, and the fluid helps clean the aircraft, before it is blown away by the slipstream. The system was initially used during
World War II World War II or the Second World War, often abbreviated as WWII or WW2, was a world war that lasted from 1939 to 1945. It involved the vast majority of the world's countries—including all of the great powers—forming two opposin ...
by the
British British may refer to: Peoples, culture, and language * British people, nationals or natives of the United Kingdom, British Overseas Territories, and Crown Dependencies. ** Britishness, the British identity and common culture * British English, ...
, having been developed by Tecalemit-Kilfrost-Sheepbridge Stokes (TKS). Advantages of fluid systems are mechanical simplicity and minimal airflow disruption from the minuscule holes; this made the systems popular in older
business jets A business jet, private jet, or bizjet is a jet aircraft designed for transporting small groups of people. Business jets may be adapted for other roles, such as the evacuation of casualties or express parcel deliveries, and some are used by pub ...
. Disadvantages are greater maintenance requirements than pneumatic boots, the weight of potentially unneeded fluid aboard the aircraft, the finite supply of fluid when it is needed, and the unpredictable need to refill the fluid, which complicates en route stops.


Bleed air

Bleed air Bleed air is compressed air taken from the compressor stage of a gas turbine upstream of its fuel-burning sections. Automatic air supply and cabin pressure controller (ASCPCs) valves bleed air from high or low stage engine compressor sections. Low ...
systems are used by most large aircraft with jet engines or turboprops. Hot air is "bled" off one or more engines' compressor sections into tubes routed through wings, tail surfaces, and engine inlets. Spent air is exhausted through holes in the wings' undersides. A disadvantage of these systems is that supplying an adequate amount of bleed air can negatively affect engine performance. Higher-than-normal power settings are often required during cruise or descent, particularly with one or more inoperative engines. More significantly, use of bleed air affects engine temperature limits and often necessitates reduced power settings during climb, which may cause a substantial loss of climb performance with particularly critical consequences if an engine were to fail. This latter concern has resulted in bleed air systems being uncommon in small turbine aircraft, although they have been successfully implemented on some small aircraft such as the
Cessna CitationJet The Cessna CitationJet/CJ/M2 (also known as the Model 525) are a series of light business jets built by Cessna, and are part of the Citation family. Launched in October 1989, the first flight of the Model 525 was on April 29, 1991. Federal Av ...
.


Electro-thermal

Electro-thermal systems use heating coils (much like a low output stove element) buried in the airframe structure to generate heat when a current is applied. The heat can be generated continuously, or intermittently. The
Boeing 787 Dreamliner The Boeing 787 Dreamliner is an American wide-body jet airliner developed and manufactured by Boeing Commercial Airplanes. After dropping its unconventional Sonic Cruiser project, Boeing announced the conventional 7E7 on January 29, 2003, ...
uses electro-thermal ice protection. In this case the heating coils are embedded within the composite wing structure. Boeing claims the system uses half the energy of engine fed bleed-air systems, and reduces drag and noise. Etched foil heating coils can be bonded to the inside of metal aircraft skins to lower power use compared to embedded circuits as they operate at higher power densities. For
general aviation General aviation (GA) is defined by the International Civil Aviation Organization (ICAO) as all civil aviation aircraft operations with the exception of commercial air transport or aerial work, which is defined as specialized aviation services ...
,
ThermaWing The ThermaWing ice protection system uses a flexible, electrically conductive, graphite foil attached to a wing's leading edge. Once activated the foil heats quickly, melting and then shedding any ice. Background In 1998 NASA Glenn initiated ...
uses a flexible, electrically conductive, graphite foil attached to a wing's leading edge. Electric heaters heat the foil which melts ice. One proposal used
carbon nanotube A scanning tunneling microscopy image of a single-walled carbon nanotube Rotating single-walled zigzag carbon nanotube A carbon nanotube (CNT) is a tube made of carbon with diameters typically measured in nanometers. ''Single-wall carbon na ...
s formed into thin filaments which are spun into a 10 micron-thick film. The film is a poor electrical conductor, due to gaps between the nanotubes. Instead, current causes a rapid rise in temperature, heating up twice as fast as
nichrome Nichrome (also known as NiCr, nickel-chromium or chromium-nickel) is a family of alloys of nickel, chromium, and often iron (and possibly other elements) commonly used as resistance wire, heating elements in devices like toasters, electrical kettl ...
, the
heating element A heating element converts electrical energy into heat through the process of Joule heating. Electric current through the element encounters resistance, resulting in heating of the element. Unlike the Peltier effect, this process is independe ...
of choice for in-flight de-icing, while using half the energy at one ten-thousandth the weight. Sufficient material to cover the wings of a 747 weighs and costs roughly 1% of nichrome.
Aerogel Aerogels are a class of synthetic porous ultralight material derived from a gel, in which the liquid component for the gel has been replaced with a gas, without significant collapse of the gel structure. The result is a solid with extremely low ...
heaters have also been suggested, which could be left on continuously at low power.


Electro-mechanical

Electro-mechanical Expulsion Deicing Systems (EMEDS) use a percussive force initiated by
actuators An actuator is a component of a machine that is responsible for moving and controlling a mechanism or system, for example by opening a valve. In simple terms, it is a "mover". An actuator requires a control device (controlled by control signal) an ...
inside the structure which induce a shock wave in the surface to be cleared. Hybrid systems have also been developed that combine the EMEDS with heating elements, where a heater prevents ice accumulation on the leading edge of the airfoil and the EMED system removes accumulations aft of the heated portion of the airfoil.


Passive (icephobic coatings)

Passive systems employ icephobic surfaces. Icephobicity is analogous to hydrophobicity and describes a material property that is resistant to icing. The term is not well defined but generally includes three properties: low adhesion between ice and the surface, prevention of ice formation, and a repellent effect on supercooled droplets. Icephobicity requires special material properties but is not identical to
hydrophobic In chemistry, hydrophobicity is the physical property of a molecule that is seemingly repelled from a mass of water (known as a hydrophobe). In contrast, hydrophiles are attracted to water. Hydrophobic molecules tend to be nonpolar and, th ...
ity. To minimize accretion, researchers are seeking icephobic materials. Candidates include carbon nanotubes and slippery liquid infused porous surfaces (SLIPS) which repel water when it forms into ice.


See also

*
Atmospheric icing Atmospheric icing occurs in the atmosphere when water droplets suspended in air freezing, freeze on objects they come in contact with. It is not the same as freezing rain, which is caused directly by precipitation. Icing conditions can be particul ...
*
Icing conditions In aviation, icing conditions are atmospheric conditions that can lead to the formation of water ice on an aircraft. Ice accretion and accumulation can affect the external surfaces of an aircraft – in which case it is referred to as ''airframe ...
Icing accidents *
Aero Caribbean Flight 883 Aero Caribbean Flight 883 was a domestic scheduled passenger service from Port-au-Prince, Haiti to Havana, Cuba with a stopover in Santiago de Cuba. On 4 November 2010, the ATR 72 operating the route crashed in the central Cuban province of Sanc ...
(2010) * Air Algérie Flight 5017 (2014) *
Air Florida Flight 90 Air Florida Flight 90 was a scheduled U.S. domestic passenger flight operated by Air Florida from Washington National Airport (now Ronald Reagan Washington National Airport) to Fort Lauderdale–Hollywood International Airport, with an intermed ...
(1982) *
Air France Flight 447 Air France Flight 447 (AF447 or AFR447) was a scheduled international passenger flight from Rio de Janeiro, Brazil, to Paris, France. On 1 June 2009, inconsistent airspeed indications led to the pilots inadvertently stalling the Airbus A330 ser ...
(2009) *
Alan Kulwicki plane crash Alan may refer to: People * Alan (surname), an English and Turkish surname * Alan (given name), an English given name **List of people with given name Alan ''Following are people commonly referred to solely by "Alan" or by a homonymous name.'' * ...
(1993) *
Arrow Air Flight 1285 Arrow Air Flight 1285R was an international charter flight carrying U.S. troops from Cairo, Egypt, to their home base in Fort Campbell, Kentucky, via Cologne, West Germany, and Gander, Newfoundland. On the morning of Thursday, 12 December 1985 ...
(1985) *
Colgan Air Flight 3407 Colgan Air Flight 3407 (marketed as Continental Connection Flight 3407 under a codeshare agreement with Continental Airlines), was a scheduled passenger flight from Newark, New Jersey, to Buffalo, New York, which crashed on February 12, 2009. Th ...
(2009) *
Comair Flight 3272 Comair Flight 3272 was a Comair flight from Cincinnati to Detroit on Thursday, January 9, 1997. While on approach for landing, the Embraer EMB 120 Brasilia aircraft crashed nose-down southwest of Detroit Metropolitan Wayne County Airport at ...
(1997) * Loganair Flight 670 (2001) *
Scandinavian Airlines Flight 751 Scandinavian Airlines System Flight 751 was a regularly scheduled Scandinavian Airlines passenger flight from Stockholm, Sweden, to Warsaw, Poland, via Copenhagen, Denmark. On 27 December 1991, a McDonnell Douglas MD-81 operating the flight, r ...
(1991) *
Sol Líneas Aéreas Flight 5428 Sol Líneas Aéreas Flight 5428 was a passenger flight which crashed near Los Menucos, Argentina, on 18 May 2011, killing all 22 people on board. The aircraft involved, a Saab 340, was operating Sol Líneas Aéreas' scheduled domestic service f ...
(2011) *
United Express Flight 2415 United Express Flight 2415 was a regularly scheduled flight in the northwest United States from Seattle to Pasco, Washington, operated using a BAe Jetstream 31. Late on Tuesday, December 26, 1989, Flight 2415 crashed while attempting to land at ...
(1989) *
West Caribbean Airways Flight 708 West Caribbean Airways Flight 708 was a West Caribbean Airways charter flight that crashed in northwest Venezuela in the early hours of Tuesday, 16 August 2005, killing all 160 passengers and crew on board. The plane, a McDonnell Douglas MD-80, ...
(2005)


References


Bibliography

* *


External links


SAE paper on Electro-Thermal Ice Protection
by Strehlow, R. and Moser, R. {{Aircraft components Ice in transportation