Ice protection system

Last updated
Supercooled large droplet (SLD) ice on a NASA Twin Otter research aircraft Icing on a plane.jpg
Supercooled large droplet (SLD) ice on a NASA Twin Otter research aircraft

In aeronautics, ice protection systems keep atmospheric moisture from accumulating on aircraft surfaces, such as wings, propellers, rotor blades, engine intakes, and environmental control intakes. Ice buildup can change the shape of airfoils and flight control surfaces, degrading control and handling characteristics as well as performance. An anti-icing, de-icing, or ice protection system either prevents formation of ice, or enables the aircraft to shed the ice before it becomes dangerous.

Contents

Effects of icing

Ice accumulation on a rotor blade in a wind tunnel Icing on a rotor.jpg
Ice accumulation on a rotor blade in a wind tunnel

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 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 propellers causing weight and aerodynamic imbalances that are amplified due to their rotation.

Anti-ice systems installed on jet engines or turboprops 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. [1]

System types

Pneumatic deicing boots

Section of pneumatic boot on an aircraft wing Pneumatic deice boot detail.JPG
Section of pneumatic boot on an aircraft wing

The pneumatic boot is usually made of layers of rubber or other elastomers, 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.

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. [2] Testing and case studies performed in the 1990s have demonstrated that ice bridging is not a significant concern with modern boot designs. [3]

Pneumatic boots are appropriate for low and medium speed aircraft, without leading edge lift devices such as slats, so this system is most commonly found on smaller turboprop aircraft such as the Saab 340 and Embraer EMB 120 Brasilia. 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 Propeller blade with TKS deice boot.JPG
Propeller blade with fluid deicing system - Glycol is sprayed from hub outward to cover blades

Sometimes called a weeping wing, [4] running wet, or evaporative system, these systems use a deicing fluid—typically based on ethylene glycol or isopropyl alcohol to prevent ice forming and to break up accumulated ice on critical surfaces of an aircraft. [5] 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, 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 1400 inch (0.064 mm) diameter holes drilled in them, with 800 holes per square inch (120/cm2). The system is self cleaning, and the fluid helps clean the aircraft, before it is blown away by the slipstream. [6] [7] The system was initially used during World War II by the British, having been developed by Tecalemit-Kilfrost-Sheepbridge Stokes (TKS). [8]

Advantages of fluid systems are mechanical simplicity and minimal airflow disruption from the minuscule holes; this made the systems popular in older business jets. 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. [9]

Bleed air

Bleed air 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. [10] [11]

Electro-thermal

Detail of propeller with electro-thermal deicing system Propeller with electric deice detail.JPG
Detail of propeller with electro-thermal deicing system

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. [12]

The Boeing 787 Dreamliner 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. [13]

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. [14] For general aviation, ThermaWing 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 nanotubes 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, the heating element 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 80 g (2.8 oz) and costs roughly 1% of nichrome. Aerogel heaters have also been suggested, which could be left on continuously at low power. [15]

Electro-mechanical

Electro-mechanical Expulsion Deicing Systems (EMEDS) use a percussive force initiated by actuators inside the structure which induce a shock wave in the surface to be cleared. [16] [17] 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. [18]

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. [19] Icephobicity requires special material properties but is not identical to hydrophobicity. [20]

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. [21]

See also

Icing accidents

Related Research Articles

<span class="mw-page-title-main">Fokker F28 Fellowship</span> Short range jet airliner produced 1967-1987

The Fokker F28 Fellowship is a twin-engined, short-range jet airliner designed and built by Dutch aircraft manufacturer Fokker.

<span class="mw-page-title-main">Air Florida Flight 90</span> January 1982 airliner crash near Washington, D.C., US

Air Florida Flight 90 was a scheduled U.S. domestic passenger flight operated by Air Florida from Washington National Airport to Fort Lauderdale–Hollywood International Airport, with an intermediate stopover at Tampa International Airport. On January 13, 1982, the Boeing 737-222 registered as N62AF crashed into the 14th Street Bridge over the Potomac River.

<span class="mw-page-title-main">Blown flap</span>

Blown flaps, or jet flaps, are powered aerodynamic high-lift devices used on the wings of certain aircraft to improve their low-speed flight characteristics. They use air blown through nozzles to shape the airflow over the rear edge of the wing, directing the flow downward to increase the lift coefficient. There are a variety of methods to achieve this airflow, most of which use jet exhaust or high-pressure air bled off of a jet engine's compressor and then redirected to follow the line of trailing-edge flaps.

<span class="mw-page-title-main">General Electric GEnx</span> Turbofan jet engine

The General Electric GEnx is an advanced dual rotor, axial flow, high-bypass turbofan jet engine in production by GE Aviation for the Boeing 787 and 747-8. The GEnx is intended to succeed the CF6 in GE's product line.

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 stage air is used during high power setting operation, and high during descent and other low power setting operations. Bleed air from that system can be utilized for internal cooling of the engine, cross-starting another engine, engine and airframe anti-icing, cabin pressurization, pneumatic actuators, air-driven motors, pressurizing the hydraulic reservoir, and waste and water storage tanks. Some engine maintenance manuals refer to such systems as "customer bleed air". Bleed air is valuable in an aircraft for two properties: high temperature and high pressure.

<span class="mw-page-title-main">Airplane</span> Powered, flying vehicle with wings

An airplane or aeroplane is a fixed-wing aircraft that is propelled forward by thrust from a jet engine, propeller, or rocket engine. Airplanes come in a variety of sizes, shapes, and wing configurations. The broad spectrum of uses for airplanes includes recreation, transportation of goods and people, military, and research. Worldwide, commercial aviation transports more than four billion passengers annually on airliners and transports more than 200 billion tonne-kilometers of cargo annually, which is less than 1% of the world's cargo movement. Most airplanes are flown by a pilot on board the aircraft, but some are designed to be remotely or computer-controlled such as drones.

<span class="mw-page-title-main">Deicing</span> Process of removing ice, snow, or frost from a surface

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 prevent adhesion of ice to make mechanical removal easier.

Air Ontario Inc. was a regional Canadian airline headquartered in Sarnia then London, Ontario. In 2002, Air Ontario became Air Canada Jazz.

<span class="mw-page-title-main">USAir Flight 405</span> March 1992 plane crash in New York, US

USAir Flight 405 was a regularly scheduled domestic passenger flight between LaGuardia Airport in Queens, New York City, New York, and Cleveland, Ohio. On March 22, 1992, a USAir Fokker F28, registration N485US, flying the route, crashed in poor weather in a partially inverted position in Flushing Bay, shortly after liftoff from LaGuardia. The undercarriage lifted off from the runway, but the airplane failed to gain lift, flying only several meters above the ground. The aircraft then veered off the runway and hit several obstructions before coming to rest in Flushing Bay, just beyond the end of the runway. Of the 51 people on board, 27 were killed, including the captain and a member of the cabin crew.

<span class="mw-page-title-main">Air Ontario Flight 1363</span> March 1989 plane crash in Ontario, Canada

Air Ontario Flight 1363 was a scheduled Air Ontario passenger flight which crashed near Dryden, Ontario, on 10 March 1989 shortly after takeoff from Dryden Regional Airport. The aircraft was a Fokker F28-1000 Fellowship twin jet. It crashed after only 49 seconds because it was not able to attain sufficient altitude to clear the trees beyond the end of the runway, due to ice and snow on the wings.

<span class="mw-page-title-main">Let L-410 Turbolet</span> Twin-engine short-range transport aircraft

The Let L-410 Turbolet is a twin-engine short-range transport aircraft, manufactured by the Czech aircraft manufacturer Let Kunovice, often used as an airliner. The aircraft is capable of landing on short and unpaved runways and operating under extreme conditions from −50 °C (−58 °F) to +50 °C (122 °F). By 2016, 1,200 L-410s had been built, and over 350 are in service in more than 50 countries.

<span class="mw-page-title-main">Icing conditions</span> Atmospheric conditions that can lead to the formation of ice on aircraft surfaces

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 – or the engine, resulting in carburetor icing, air inlet icing or more generically engine icing. These phenomena may possibly but do not necessarily occur together. Both airframe and engine icing have resulted in numerous fatal accidents in aviation history.

<span class="mw-page-title-main">Deicing boot</span> Ice protection system installed on aircraft

A deicing boot is a type of ice protection system installed on aircraft surfaces to permit a mechanical deicing in flight. Such boots are generally installed on the leading edges of wings and control surfaces as these areas are most likely to accumulate ice and any contamination could severely affect the aircraft's performance.

<span class="mw-page-title-main">American Eagle Flight 4184</span> 1994 plane crash in Indiana, US

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 October 31, 1994, the ATR 72 performing this route flew into severe icing conditions, lost control and crashed into a field. All 68 people aboard were killed in the high-speed impact.

Ground deicing of aircraft is commonly performed in both commercial and general aviation. The fluids used in this operation are called deicing or anti-icing fluids. The initials ADF, ADAF or AAF are commonly used.

<span class="mw-page-title-main">Belavia Flight 1834</span> 2008 aviation accident

Belavia Flight 1834 was a scheduled international passenger flight from Yerevan, Armenia, to Minsk, Belarus, operated by Belavia. On the morning of February 14, 2008, the Bombardier Canadair Regional Jet carrying 18 passengers and three crew crashed and burst into flames shortly after take off from Zvartnots International Airport near Yerevan, the capital of Armenia.

<span class="mw-page-title-main">Aircraft systems</span> Overview article of aircraft systems

Aircraft systems are those required to operate an aircraft efficiently and safely. Their complexity varies with the type of aircraft.

<span class="mw-page-title-main">1971 January 22 Surgut Aeroflot Antonov An-12 crash</span> Aviation accident in the Soviet Union

The 1971 January 22 Surgut Aeroflot Antonov An-12 crash occurred on 22 January 1971, when an Aeroflot Antonov An-12B, registered CCCP-11000, flying from Omsk Tsentralny Airport, in the Soviet Union's (RSFSR), crashed 15 km (9.3 mi) short of the runway on approach to Surgut International Airport, Surgut, RSFSR. An investigation found the aircraft's ice protection system was ineffective because the engine bleed air valves were closed during the flight; ice therefore built up on the aircraft causing it to go out of control.

<span class="mw-page-title-main">Clean Sky</span>

The Clean Sky Joint Undertaking (CSJU) is a public-private partnership between the European Commission and the European aeronautics industry that coordinates and funds research activities to deliver significantly quieter and more environmentally friendly aircraft. The CSJU manages the Clean Sky Programme (CS) and the Clean Sky 2 Programme (CS2), making it Europe's foremost aeronautical research body.

<span class="mw-page-title-main">Ground deicing of aircraft</span> Ground deicing of aircraft

A very small amount of surface frost or ice on aircraft surfaces can severely impact flight performance. Frozen contaminants on surfaces can also break off in flight, damaging engines or control surfaces. As such it is very important to remove such contaminants before an aircraft takes off. This process is called "ground deicing".

References

  1. Federal Aviation Administration 2015, p. 16–17.
  2. "FAA Information for Operators 09005" (PDF).
  3. Federal Aviation Administration 2015, p. 20.
  4. Szurovy 1999, p. 31.
  5. Federal Aviation Administration 2015, p. 22.
  6. E. McMann, Michael. "TKS Ice Protection: Flying year-round becomes a possibility with the TKS Ice Protection system". Plane & Pilot Magazine. Werner Publishing Corporation. Retrieved 17 October 2014.
  7. "flight april | april iith | fluid system | 1946 | 0710 | Flight Archive". Flightglobal.com. Retrieved 2013-12-11.
  8. "De-Icing for To-day".
  9. Szurovy 1999, pp. 31–32.
  10. Federal Aviation Administration 2015, p. 21.
  11. Szurovy 1999, p. 58.
  12. Sloan, Jeff. "787 integrates new composite wing deicing system". www.compositesworld.com.
  13. "AERO - 787 No-Bleed Systems". www.boeing.com.
  14. http://papers.sae.org/2009-01-3165/ | Capitalizing on the Increased Flexibility that Comes from High Power Density Electrothermal Deicing
  15. "De-icing aeroplanes: Sooty skies". The Economist. 2013-07-26. Retrieved 2013-12-11.
  16. "How They Work: Ice Protection Systems". Aviation Week. 2010.
  17. "Electro- mechanical Deicing". Air & Space Magazine. 2004.
  18. "Deicing and Anti-Icing Unite". NASA STI. 2002. Archived from the original on 2003-04-05.
  19. Hejazi, Vahid; Sobolev, Konstantin; Nosonovsky, Michael (2013-07-12). "From superhydrophobicity to icephobicity: forces and interaction analysis". Scientific Reports. 3 (1): 2194. Bibcode:2013NatSR...3E2194H. doi: 10.1038/srep02194 . ISSN   2045-2322. PMC   3709168 . PMID   23846773.
  20. Jung, Stefan; Dorrestijn, Marko; Raps, Dominik; Das, Arindam; Megaridis, Constantine M.; Poulikakos, Dimos (2011-02-14). "Are Superhydrophobic Surfaces Best for Icephobicity?". Langmuir. 27 (6): 3059–3066. doi: 10.1021/la104762g . ISSN   0743-7463. PMID   21319778.
  21. Kim, Philseok; Wong, Tak-Sing; Alvarenga, Jack; Kreder, Michael J.; Adorno-Martinez, Wilmer E.; Aizenberg, Joanna (28 August 2012). "Liquid-Infused Nanostructured Surfaces with Extreme Anti-Ice and Anti-Frost Performance". ACS Nano. 6 (8): 6569–6577. doi:10.1021/nn302310q. PMID   22680067 via ACS Publications.

Bibliography