Ice protection system


Ice protection system

Ice protection systems are designed to keep atmospheric ice from accumulating on aircraft flight surfaces while in flight. The effects of ice accretion on an aircraft can cause the shape of airfoils and flight control surfaces to change, which can ultimately lead to a complete loss of control and/or insufficient lift to keep the aircraft airborne.

Contents

Types of ice protection systems

  • Pneumatic deicing boots
  • Thermal
    • Electrical heating elements
    • ThermaWing
    • Turbine engine bleed air
  • Electro-mechanical
    • Weeping Wing
    • Electro-Mechanical Expulsion Deicing System (EMEDS)
    • Hybrid Electro-Mechanical Expulsion Deicing System
  • Passive (cover system mainly used in the telecoms and offshore domains)
    • Anti icing cover

The pneumatic boot is a rubber device attached to a wing's leading edge, invented by the Goodrich Corporation (previously known as B.F. Goodrich) in 1923. Portions of the boot are alternately inflated and deflated to break ice off the boot, de-icing the wing. Rubber boots are used on jets and propeller driven aircraft.

The Thermawing, manufactured by Kelly Aerospace Thermal Systems, is an electrical ice protection system. ThermaWing uses a flexible, electrically conductive, graphite foil attached to a wing's leading edge. Electric heaters are usually flexible enough to use as anti-icers or de-icers. Once activated an exact concentration of heat melts the bond between ice and protected surface. Ice no longer sticks to the surface due to aerodynamic forces. As an anti-icer, the heater keeps the surface warm so that ice does not form.

A bleed air system is used by most larger jet aircraft to keep flight surfaces above the freezing temperature required for ice to accumulate (called anti-icing). The hot air is "bled" off the jet engine into tubes routed through wings, tail surfaces, and engine inlets.

Electro-mechanical Expulsion Deicing Systems (EMEDS) use a mechanical force to knock the ice off the flight surface. Typically, actuators are installed underneath the skin of the structure. The actuator is moved to induce a shock wave in the protected surface to dislodge the ice. Cox and Company, Inc. of Plainview, NY developed a light weight, low power system called EMEDS that is the first ice protection technology to receive FAA certification in 50 years, and is currently in-service on multiple commercial aircraft (FAA Part 23 and Part 25)[1] [2] [3] and military aircraft.[4] Innovative Dynamics in Ithaca, NY has developed a system that's light weight and low power using actuators called EIDI.

Hybrid Electro-Mechanical Expulsion Deicing Systems combine an EMEDS de-icer with an electrical heating element anti-icer. The heater prevents ice accumulation on the leading edge of the airfoil and the actuators of the EMED system remove ice that accumulates aft of the heated portion of the airfoil.[5] Cox and Company, Inc. of Plainview, NY has developed multiple versions of Hybrid EMED systems referred to as Thermo-Mechanical Expulsion Deicing System (TMEDS).

A weeping wing system, also known as a TKS system, uses a liquid based on ethylene glycol to coat the surface and prevent ice from accumulating. The leading edges of the wings, horizontal and vertical stabilizer are made of porous, laser-drilled titanium panels, through which the fluid is pumped during flight in icing conditions. A "slinger ring" may be used to distribute fluid on propellers, and a spray bar can be used to apply fluid to the windshield. This system is commonly used on small-to-medium-sized propeller-driven aircraft, and a number of business jet aircraft. It also has some applications in military use.

The Passive systems are a new conceptual non-thermal anti-icing and pollution solution based on textile. This innovative textile has the properties characterized by a high level of water resistance which has a natural self-cleaning effect to repel water, thereby eliminating the build of ice, with a high resistance to UV radiation and harsh climatic conditions and has a durable protective function.

Airframe icing

Ice accumulates on the leading edges of wings, tailplanes, and vertical stabilizers as an aircraft flies through a cloud containing super-cooled water droplets. Super-cooled water is water that is below freezing, but still a liquid. Normally, this water would turn to ice at 32°F (0°C), but there are no "contaminants" (ice nucleus) on which the drops can freeze. When the airplane flies through the super-cooled water droplets, the plane becomes the droplet nucleus, allowing the water to freeze on the surface. This process is known as accretion.

Droplets of supercooled water often exist in stratiform and cumulus clouds.

A popular misconception is that aircraft icing events result from the weight of accreted ice on the airframe. This is not the case. Rather, airframe icing causes problems by modifying the airflow over flight surfaces upon which the ice accretes. When ice accretes on aerodynamic lift surfaces, such as the wing and tailplane, the modification of airflow changes the aerodynamics of the surfaces by modifying both their shape and their surface roughness, typically increasing their drag and decreasing their lift.[6] The particular effect of icing on the aerodynamics of a lift surface is a complicated function of the ice shape and location as well as of the amount of ice.[7] These characteristics in turn depend in a complicated fashion on atmospheric conditions such as the amount, temperature, and droplet size of water in the air.[8] The composite effect of this aerodynamic deterioration over all lift surfaces is a degradation of aircraft flight dynamics. In severe atmospheric conditions, dangerous levels of icing can be obtained in as little as five minutes.[9] Small to moderate amounts of icing generally cause a reduction in aircraft performance in terms of climb rates, range, endurance, and maximum speed and acceleration. Icing effects of this type are known as performance events. As icing increases, separation of air flow from the flight surfaces can cause loss of pilot control and even wildly unstable behaviour. These more severe icing events, known as handling events, are often precipitated by a change in the aircraft configuration or an aircraft maneuver effected by a pilot unaware of the flight-dynamics degradation. This was the case with American Eagle Flight 4184, where the aircraft experienced an uncontrolled roll of 120 degrees in five seconds after the pilot initiated a flap retraction.[10] Another icing event that led to a major crash was the Aero Caribbean Flight 883 that experienced icing conditions at 20,000 feet height after a crew request of course change. They lost control of the aircraft after they initiated a roll to change the aircraft's direction. This loss of control can be defined as a handling event. Handling events generally can be classified into either tailplane stall, where the aircraft pitches forward, or asymmetric wing effects causing a roll upset (or roll snatch) as in the American Eagle Flight 4184 accident.[11]

Rotary-surface icing

Ice can also accumulate on helicopter rotor blades and aircraft propellers. The accretion causes weight and aerodynamic imbalances that are amplified due to the rapid rotation of the propeller or rotor.

Engine-inlet icing

Ice accreting on the leading edge (lip) of engine inlets causes flow problems and can lead to ice ingestion. In turbofan engines, laminar airflow is required at the face of the fan. Because of this, most engine ice protection systems are anti-ice systems (prevent build up).

See also

References

  1. ^ "Low Power Ice Protection Systems - Cox & Company, Inc.". Cox & Company, Inc.. 2001. http://www.coxandco.com/aerospace/lowpower_ice_protection.html. 
  2. ^ "How They Work: Ice Protection Systems". Aviation Week. 2010. http://www.aviationweek.com/aw/generic/story_channel.jsp?channel=bca&id=news/coldops1010p08.xml&headline=null&next=20. 
  3. ^ "Electro- mechanical Deicing". Air & Space Magazine. 2004. http://www.airspacemag.com/how-things-work/deicing.html. 
  4. ^ "CUTAWAY: P-8A Poseidon - A Boeing with boost of bravado". Flight International. 2010. http://www.flightglobal.com/articles/2010/04/26/340955/cutaway-p-8a-poseidon-a-boeing-with-boost-of-bravado.html. 
  5. ^ "Deicing and Anti-Icing Unite". NASA STI. 2002. http://www.sti.nasa.gov/tto/spinoff2002/ps_1.html. 
  6. ^ Lee, Sam; Michael B. Bragg (1999). "Experimental Investigation of Simulated Large-Droplet Ice Shapes on Airfoil Aerodynamics". Journal of Aircraft 36 (5): 844–850. doi:10.2514/2.2518. 
  7. ^ Lee, Sam; Michael B. Bragg (2003). "Investigation of Factors Affecting Iced-Airfoil Aerodynamics". Journal of Aircraft 40 (3): 499–508. doi:10.2514/2.3123. 
  8. ^ Olsen, W; R. Shaw, J. Newton (1984). Ice Shapes and the Resulting Drag Increase for a NACA 0012 Airfoil. NASA Technical Report 83556. 
  9. ^ Reehorst, Andrew L.; J. Chung, Mark Potapczukn, Y. Cho (2000). "Study of Icing Effects on Performance and Controllability of an Accident Aircraft". Journal of Aircraft 37 (2): 253–259. doi:10.2514/2.2588. 
  10. ^ ASN Aircraft accident description Aérospatiale/Aeritalia ATR-72-212 N401AM - Roselawn, IN
  11. ^ Melody, James W. (May 2004). Inflight Characterization of Aircraft Icing. PhD dissertation. University of Illinois. 

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