Electrical ice protection systems:
Electrical ice protection systems are used on most turbo-props. Resistance wire heater elements are embedded in rubber and cemented from the root to about 2/3rds of the blade's length along the leading edge. The rubber is usually protected by a wire gauze to withstand light stone damage and erosion. Often the aerodynamic spinner and engine intake lip are also protected from ice formation using this method.
This type of ice protection system works on the cyclic principle. The current is fed to the propeller blades, spinner, and the engine intake lip by an automatic time switch. Part of the intake lip is continuously heated. This method ensures that the areas that have de-iced do not turn to water and then flow backwards to freeze again on the unheated trailing edge. The cyclic method also conserves electrical power so a smaller alternator can be installed.
The cyclic timers have two speeds to use under differing ambient temperature conditions.
Fast is used at temperatures from -6°C to +10°C when icing conditions are prevalent, e.g. in rain or clouds.
Slow is used at temperatures of -6°C and below.
The operation of the cyclic de-icing system is usually indicated by flashing lights (usually green or blue) or an ammeter showing the current consumed by the elements. Some aircraft have a phase test switch which enables the operator to check the current drawn from each phase of the a.c. supply. A typical control and test panel is shown in fig.