Aircraft ELECTRO THERMAL PROPELLER DEICING

 ELECTRO THERMAL Propeller Deicing

Many of the modern propellers installed on both reciprocating and turboprop engines are deiced with an electro thermal deicer system. Rubber boots with heater wires embedded in the rubber are bonded to the leading edges of the propeller blades, and electrical current is passed through these wires to heat the rubber and melt any ice that has formed, so centrifugal force and wind can carry the ice away.

The boots in some installations are made in two sections on each blade. Current flows for about a half minute through the outboard section of all blades and then for the same time through the heaters on the inboard section of all of the blades. The time the current flows have been proven by flight tests to be sufficient to allow ice to form over the inactive section and long enough to loosen the ice from the section that is receiving the current.

The complete propeller deicer system, shown in Figure 6.7, consists of the following components:

1.         Electrically heated deicers bonded to the propeller blades.

2.         Slip-ring and brush block assemblies that carry the current to the rotating propeller.

3.         Timer to control the heating time and sequence of the deicing cycle.

4.         An ammeter to indicate the operation of the system.

5.         All of the wiring, switches and circuit breakers necessary to conduct electrical power from the aircraft electrical system into the deicer sys­tem.

The slip-ring assembly is mounted on the propeller either through a specially adapted starter gear, or attached to the spinner bulkhead or the crankshaft flange. The brush block is mounted on the engine so the three brushes will ride squarely on the slip rings. The timer controls the sequence of current to each of the deicers. The sequence of heating is important, to provide the best loosening of the ice so it can be carried away by the centrifugal force. It is also important that the same portion of each blade be heated at the same time, to prevent an out-of-balance condition.