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. [1] 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.
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. [2]
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. [4] Testing and case studies performed in the 1990s have demonstrated that ice bridging is not a significant concern with modern boot designs. [5]
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. They were invented by B.F. Goodrich in 1923.
Sometimes called a weeping wing, [6] 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. [7] 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 1⁄400 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. [8] [9] The system was initially used during World War II by the British, having been developed by Tecalemit-Kilfrost-Sheepbridge Stokes (TKS). [9]
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. [10]
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. [11] [12]
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. [13]
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. [14]
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. [15] 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.
Small wires or other conductive materials can be embedded in the windscreen to heat the windscreen. Pilots can turn on the electric heater to provide sufficient heat to prevent the formation of ice on the windscreen. However, windscreen electric heaters may only be used in flight, as they can overheat the windscreen. They can also cause compass deviation errors by as much as 40°. [16]
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. [17]
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. [18] [19] 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. [20]
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. [21] Icephobicity requires special material properties but is not identical to hydrophobicity. [22]
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. [23]
The Fokker F28 Fellowship is a twin-engined, short-range jet airliner designed and built by Dutch aircraft manufacturer Fokker.
Blown flaps, blown wing 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.
The General Electric GEnx is an advanced dual rotor, axial flow, high-bypass turbofan jet engine in production by GE Aerospace for the Boeing 747-8 and 787. The GEnx succeeded the CF6 in GE's product line.
Bleed air in aerospace engineering 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 (ASCPC) valves bleed air from low or high stage engine compressor sections; low stage air is used during high power setting operation, and high stage air is used 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".
De-icing is the process of removing snow, ice or frost from a surface. Anti-icing is the application of chemicals that not only de-ice 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.
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.
Air Ontario Flight 1363 was a scheduled Air Ontario passenger flight which crashed near Dryden, Ontario, Canada, 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 a buildup of ice and snow on the wings.
In aeronautics, icing is the formation of water ice on an aircraft. Icing has resulted in numerous fatal accidents in aviation history. 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.
Atmospheric icing occurs in the atmosphere when water droplets suspended in air freeze on objects they come in contact with. It is not the same as freezing rain, which is caused directly by precipitation.
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 which could severely affect the aircraft's performance.
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, killing all 68 people on board in the high-speed impact.
The Cessna Citation II models are light corporate jets built by Cessna as part of the Citation family. Stretched from the Citation I, the Model 550 was announced in September 1976, first flew on January 31, 1977, and was certified in March 1978. The II/SP is a single pilot version, the improved S/II first flew on February 14, 1984 and the Citation Bravo, a stretched S/II with new avionics and more powerful P&WC PW530A turbofans, first flew on April 25, 1995. The United States Navy adopted a version of the S/II as the T-47A. Production ceased in 2006 after 1,184 of all variants were delivered.
In ground deicing of aircraft, aircraft de-icing fluid (ADF), aircraft de-icer and anti-icer fluid (ADAF) or aircraft anti-icing fluid (AAF) are commonly used for both commercial and general aviation. Environmental concerns include increased salinity of groundwater where de-icing fluids are discharged into soil, and toxicity to humans and other mammals.
The Cessna CitationJet/CJ/M2 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 Aviation Administration (FAA) certification was awarded on October 16, 1992, and the first aircraft was delivered on March 30, 1993. The CJ series are powered by two Williams FJ44 engines; the design uses the Citation II's forward fuselage with a new carry-through section wing and a T-tail. The original CitationJet model has been updated into the CJ1/CJ1+/M2 variants; additionally, the CJ1 was stretched into the CJ2/CJ2+ which was built between 2000 and 2016. The design was then further developed into the CJ3/CJ3+, built from December 2004 to present, and finally into the CJ4 which has been built since 2010. By June 2017, 2,000 of all variants had been delivered.
Aircraft systems are those required to operate an aircraft efficiently and safely. Their complexity varies with the type of aircraft.
The 22 January 1971 Surgut Aeroflot Antonov An-12 crash occurred when an Aeroflot Antonov An-12B, registered CCCP-11000, flying from Omsk Tsentralny Airport, in the Soviet Union's (RSFSR) on 22 January 1971, 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.
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.
American Eagle is a brand name for the regional branch of American Airlines, under which six individual regional airlines operate short- and medium-haul feeder flights. Three of these airlines, Envoy Air, Piedmont Airlines, and PSA Airlines, are wholly owned subsidiaries of the American Airlines Group. American Eagle's largest hub is Charlotte Douglas International's Concourse E, which operates over 340 flights per day, making it the largest regional jet operation in the world.
In aviation, ground deicing of aircraft is the process of removing surface frost, ice or frozen contaminants on aircraft surfaces before an aircraft takes off. This prevents even a small amount of surface frost or ice on aircraft surfaces from severely impacting flight performance. Frozen contaminants on surfaces can also break off in flight, damaging engines or control surfaces.
Rocky Mountain Airways Flight 217, referred to in the media as the "Miracle on Buffalo Pass", was a scheduled domestic passenger flight from Steamboat Springs, Colorado to Denver that crashed on Buffalo Pass. The aircraft, a de Havilland Canada DHC-6 Twin Otter 300, impacted terrain on a gentle slope and was partially buried in snow. All of the 22 passengers and crew survived the impact, but a female passenger died before rescue could arrive, and the captain died of his injuries 3 days after the accident. The investigation determined that the accident was caused by the formation of ice on the wings combined with downdrafts associated with a mountain wave led to the aircraft's loss of control and impact with terrain.