Propeller De-Icer System; Description And Principles Of Operation - Piper APACHE PA-23-235 Service Manual

PIPER AZTEC SERVICE MANUAL
14-20. PROPELLER DE-ICER SYSTEM.
14-21. DESCRIPTION AND PRINCIPLES OF OPERATION.
(Refer to Figure 14-6 or
14-7.) This section provides service and maintenance procedures for the B. F. Goodrich Elec-
trical Propeller De-Icing System. Each Propeller De-Icing System consists of an electrically-
heated De-lcer (9) bonded to each propeller blade. a slip ring assembly (8) with a brush block
assembly (7) to transfer electrical power to the rotating De-lcers, a timer (1), an ammeter (5),
and a control switch (3) together with wiring harnesses to complete the circuit.
To conserve electrical power, current is cycled to the De-lcer heaters at timed intervals
rather than continuously. Each De-lcer has two separate heaters, one for the outer half and
one for the inner half. By heating all outer or inner heaters on only one propeller at a time,
rotational balance is held during de-icing. Current is drawn from the airplane electrical
system through the switch, ammeter and timer. The timer successively delivers current via the
slip ring and brush block arrangement to the outer heaters on the right propeller, the inner
heaters on the same propeller, the outer heaters on the left propeller and the inner heaters on
the left propeller. The timer energizes each of these four phases in turn for about 30 seconds
and then repeats the cycle as long as the control switch is on. The cycling sequence given is vital
so that outboard heaters on each propeller operate before the inboard heaters. Refer to Figures
14-8 through 14-11 which represent a typical. not a particular. system. Correct circuit diagrams
for each system are shown in Figures 14-18 and 14-19. The use of heat at the ice adhesion sur-
face reduces the grip of the ice which is then removed by the centrifugal effect of rotation and
the blast of the airstream. Note that a minimum thickness or weight of ice must build-up
before centrifugal force becomes important. The system may be used continuously in flight if
needed.
NOTE
Heating may begin at any phase in the cycle depending on the
timer position when the switch was turned off from previous
use.
ACCESSORIES AND UTILITIES
Reissued: 2/18/81
515