In a modern civil aircraft, an important consideration is accretion of airborne material, such as ice particles and/or foreign bodies such as insects, on a leading edge of airfoils of the aircraft. Such accretion of airborne material is undesirable since it is detrimental to the aerodynamic performance of the airfoils and thus detrimental to the performance of the aircraft.
Conventionally, aircraft are provided with thermal anti-icing systems for reducing accretion of ice on the leading edge of airfoils. Thermal anti-icing systems typically draw hot bleed air from the compressor stages of the aircraft engines and distribute the bleed air inside the internal structure of the airfoils. A control system including various temperature sensors, modulated flow valves, and control electronics is used to ensure that the temperature of the airfoil skin is sufficiently hot to melt the ice accretion while remaining under a threshold temperature to prevent overheating and damaging the structure of the airfoil.
Thermal anti-icing systems suffer from multiple drawbacks, including:                Aircraft performance loss due to bleed air extraction. Bleed air extraction from aircraft engines can cause a loss of net thrust of approximately 10% for a dual engine regime of operation and 20% for a single engine regime of operation. This translates into a payload penalty of approximately 5000 to 7000 lbs. for a typical 70-passenger regional jet.        Proximity of heat source to wing fuel tank. The proximity of a heat source to the fuel tank located in the wing of an aircraft represents an inherent safety concern and a significant design challenge. Effort must be spent to assess the impact of control system failures, such as failure of a temperature sensor, on overheating considerations in order to ensure that the airfoil structure and the fuel tank remain unaffected.        Risk of ice runback. Under certain conditions, the melted ice may run back on the top and bottom surfaces of the wing and refreeze thereon in the form of protrusions. Such protrusions are detrimental to the aerodynamic performance of the wing.        Design complexity. The design of thermal anti-icing systems involves a complex mix of aerodynamics, thermodynamics, and control system theories which requires sophisticated tools and highly qualified personnel. The performance of the systems is also highly affected by installation variability.        Foreign bodies contamination. Thermal anti-icing systems have a tendency to cook foreign bodies such as insects that may already be present on the leading edge of airfoils when the system is activated. Such cooking of foreign bodies renders more difficult cleaning of the airfoils and, over time, deteriorates the finish of the airfoil skin surface.        
Pneumatic or electro-expulsive deicing systems are other conventional systems provided on aircraft for reducing accretion of ice on the leading edge of airfoils. Pneumatic deicing systems typically include a number of inflatable bladders, commonly referred to as boots, located on the leading edge of airfoils that break the ice accreting on the leading edge when the ice thickness is sufficiently large. Electro-expulsive deicing systems use repulsive forces from a magnetic field to deform the leading edge skin and to break an ice layer thereon.
Pneumatic or electro-expulsive deicing systems suffer from multiple drawbacks, including:                Minimum ice accumulation requirement. A minimum thickness of accumulated ice on the leading edge is required in order for these deicing systems to function properly. This causes lift penalties.        Leading edge surface distortion. Pneumatic boots are made of a rubber-type material and usually introduce some leading edge surface distortion when they are inflated. Such leading edge surface distortion is detrimental to the aerodynamic performance of the aircraft, especially in the case of high speed, high performance aircraft.        Coverage area. Due to the difficulty for electro-expulsive systems to deform a large portion of the airfoil surface or to limitations on the number and size of pneumatic boots, the area of the airfoil surface that can be kept free of ice is typically smaller than that achieved using thermal anti-icing systems.        Maximum speed of operation. The performance of pneumatic deicing systems reduces as the external pressure on the boots increases, i.e. as the airspeed increases.        Maintenance and repair. The boots of pneumatic deicing systems frequently crack and need to be repaired. Typically, the boots are not easily removable and replaceable and thus repair of the boots usually consists in applying patches on the boot. The patches increase the potential of ice adhering to the boot.        
Existing thermal anti-icing systems and pneumatic and electro-expulsive deicing systems thus suffer from various drawbacks that introduce multiple aircraft performance penalties. Furthermore, such systems are typically not designed to effectively inhibit accretion of foreign bodies such as insects on the leading edge of the airfoils. Accumulation of foreign bodies on the leading edge of the airfoils can have a significant impact on the aerodynamic performance of the airfoil.
Accordingly, there is a need in the industry for an apparatus for inhibiting accretion of airborne material on an airfoil leading edge that alleviates at least in part the problems associated with existing systems.