Ice protection system

Ice protection systems are designed to keep atmospheric ice from accumulating on aircraft surfaces (particularly leading edges), such as wings, propellers, rotor blades, engine intakes, and environmental control intakes. If ice is allowed to build up to a significant thickness it can change the shape of airfoils and flight control surfaces, degrading the performance, control or handling characteristics of the aircraft. An ice protection system either prevents formation of ice, or enables the aircraft to shed the ice before it can grow to a dangerous thickness. Ice protection systems are designed to keep atmospheric ice from accumulating on aircraft surfaces (particularly leading edges), such as wings, propellers, rotor blades, engine intakes, and environmental control intakes. If ice is allowed to build up to a significant thickness it can change the shape of airfoils and flight control surfaces, degrading the performance, control or handling characteristics of the aircraft. An ice protection system either prevents formation of ice, or enables the aircraft to shed the ice before it can grow to a dangerous thickness. The pneumatic boot is usually made of layers of rubber, 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 relative wind flowing past the aircraft. However, the ice must be carried 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. Certain older designs of pneumatic boot were subject to a phenomenon known as ice bridging. If the ice had not accumulated to a sufficient thickness and fragility, malleable ice could be pushed into a shape out of reach of the inflatable sections of the boot. This problem is mostly solved in modern designs by increasing the speed of inflation/deflation action, and by alternating the timing of inflating/deflating adjacent chambers. The pneumatic boot is most appropriate for low and medium speed aircraft, especially those without leading edge lift devices such as slats. Therefore, this system is most commonly found on turbo propeller aircraft such as the Saab 340, Embraer EMB 120 Brasilia, and British Aerospace Jetstream 41. Pneumatic De-Icing boots are sometimes found on larger piston prop aircraft, smaller turbojets such as the Cessna Citation V, and some older turbojets. This device is rarely used on modern turbojet aircraft. This device was invented by the Goodrich Corporation (previously known as B.F. Goodrich) in 1923. Electro-thermal systems use resistive circuits buried in the airframe structure to generate heat when a current is applied. The heat can be generated continuously to protect the aircraft from icing (anti-ice mode), or intermittently to shed ice as it accretes on key surfaces (de-ice). De-ice operation is generally preferred due to the lower power consumption, as the system only needs to melt the contact layer of ice for the wind-shear to shed the remainder. The Boeing 787 Dreamliner is an example of a commercial airframe to use electro-thermal ice protection. In this case the resistive heating circuit is embedded inside the glass and carbon composite wing structure. Boeing claims the system uses half the energy of traditional bleed-air systems (as provided by the engines), and that drag and noise are also reduced. For metallic aircraft skin structures, etched foil resistive heating circuits have been bonded to the inside surface of skins. This approach holds the potential of enabling a lower overall power requirement than the embedded circuit approach due to its ability to operate at significantly higher power densities. The Thermawing is an electrical ice protection system for general aviation. ThermaWing uses a flexible, electrically conductive, graphite foil attached to a wing's leading edge. Electric heaters heat the foil and melt the ice.