FLUID (LIQUID) ICE PROTECTION SYSTEMS:
Liquid ice protection systems can be used as either anti-ice or de-ice systems. The system is designed to project a film or fluid over the surface of the blade which when mixed with water will reduce its freezing point. If ice is already present the fluid will penetrate below the ice layer and reduce its surface tension sufficiently to enable it to be thrown off by centrifugal force.
The fluid is stored in a tank and passes via a filter to an electric supply pump. The pump is controlled by a switch on the instrument panel. In some installations the speed of the pump and thus the quantity of fluid supplied to the propeller can be varied by the use of a rheostat. The output fluid from the pump goes through pipelines which terminate at the rear of the propeller hub. Attached to the propeller hub is a 'U' shaped channel called a slinger ring and from points around the slinger ring delivery nozzles are arranged to apply the fluid along the leading edge root section of each blade. Centrifugal force will then disperse the fluid along the blades' leading edge and the airflow over the blades will allow a film of fluid to be deposited on the face and camber sides of the blades.
The airflow around the blade root however is fairly disturbed and does not always disperse the fluid where it is more required, that is where ice build up is greatest. Propellers with this type of ice protection system usually have boots or feed shoes installed along their leading edges. An overshoe consists of a strip of rubber or plastic material set into the leading edge of the blade, from the delivery nozzle at the root end along the blade's length. The shoe extends about 2/3rds of the length of the blade, and has several open parallel channels in which the fluid can flow under the influence of centrifugal force. The overflow of the channels along the length of the overshoe will evenly disperse the fluid over the blade.