AIRCRAFT CHEMICAL ANTI-ICING

Chemical Anti-icing

Certain surfaces and components of an aircraft may be coated with either isopropyl alcohol, or a mixture of ethylene glycol and alcohol. Either of these chemicals lowers the freezing point of the water at the surface of the aircraft, and at the same time makes the surface slick to prevent ice from getting a good grip on the surface.

Chemical anti-icing is normally done to the carburettors, the propellers, and to the windshield from a tank of anti-icing fluid carried in the aircraft. Ground chemical anti-icing is done by spraying all of the surfaces with ethylene glycol before the aircraft takes off, and will be discussed later in this chapter. Rubber de-icer boots are often sprayed with a silicon spray that gives the rubber an extremely smooth surface so the ice cannot adhere to it.

Propeller anti-icing, shown in Figure 5.7, uses isopropyl alcohol which is sprayed onto the leading edges of the propeller blades, preventing icing. The alcohol is stored in a tank from which it is pumped to the propeller when needed. The pump is driven by an electric motor which is controlled by a rheostat. By controlling the pumps speed through the rheostat, the pilot can control the amount of alcohol flowing to the propeller. Each propeller has a slinger ring that uses centrifugal force to dis­tribute the alcohol to the blade nozzles. The length of time this system can be used is limited by the amount of alcohol the tank can carry.