Aircraft De-Icing Equipment: Pneumatic, Chemical, and Bleed Air
There are a few types of aircraft de-icing equipment that modern aircraft might utilize in the event of ice forming on the airframe. Because of the various factors that affect an airplane in flight, a pilot has to make a few considerations when using said equipment. The practicality of any aircraft de-icing system depends on the density of the ice in question, and how removal will affect the aerodynamic characteristics of the airfoil. Let’s consider the advantages and disadvantages of three main types of aircraft de-icing systems—pneumatic de-icing boots, chemical de-icing, and bleed air heating.
Pneumatic de-icing boots are commonly used for ice removal on smaller propeller-driven aircraft. They are thick panels of inflatable rubber that are often found on the leading edges of an aircraft wing, horizontal stabilizer, and vertical stabilizer. They are powered by bleeding air from the engine compressors, so as long as the engine is running, these devices have a constant power source. Their structure is made up of a series of air bladders that inflate under a larger rubber boot. This multi-bladder system ensures that much of the ice will be removed across a range of the leading edge.
Though these devices have been used for the last century, they have a few disadvantages. When using this system, it is critical that the pilot only engages them when ice first starts to form. Densely formed ice poses a higher risk of breaking off into the engine or damaging various airframe components. The inflated compartments also protrude slightly from the wing, affecting the airfoil, and potentially the stall speed of an aircraft.
Glycol based fluid, also known as TKS fluid, is used in both commercial and general aviation. For commercial aircraft, an airport de-icing facility will usually spray the aircraft with de-icing fluid before take-off. This removes built up ice from the airframe and is one of the most commonly used de-icing methods by commercial aircraft. The most notable disadvantage of this system is the cost of fluid. Price per gallon of de-icing fluid can run up to twenty dollars per gallon. As a result, for a commercial airliner, de-icing can cost in the ballpark of 10,000 USD per aircraft.
Weeping wing systems are used predominantly in smaller, propeller-driven aircraft. Fluid released from leading edges of the aircraft remove existing ice and create a layer of fluid to help prevent further buildup. Despite their smaller size, de-icing fluid for a smaller airplane will still cost you around 2,000 USD on average.
Lastly, bleed air heating is the most prevalent de-icing method in commercial aircraft. Heated air from the engine turbines is directed to leading edge surfaces on the aircraft. When it is engaged soon enough, the heated airflow can prevent ice from forming around engine openings, on wing leading edges, and other critical parts of the aircraft.
The redundancy of this system, as most other systems entail as well, relies on the vigilance of the pilot and avionics. If the system is engaged after a thick layer of ice has built up, the ice can break off upon removal and harm the fuselage or enter an engine.
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