malfunctioning modulator valves. You can detect
of high- and low-expansion material that is locked to a
the portion of the leading edge that has the
sliding piston. In addition, the piston contains an
over-temperature by placing the rotary selector switch,
override spring and ball-type metering valve.
located on the ice control protection panel (fig. 5-5), to
Airflow from the leading edge flows over the core
the different sensor positions: INBD (inboard), CTR
and causes the materials to expand or contract. As
(center), and OUTBD (outboard). The temperature at
temperature rises, the core pulls the piston and metering
the selected sensor is then read at the indicator adjacent
ball from the seated position. This allows pressure from
to the rotary switch. An excessive temperature reading
the modulating valve diaphragm to vent. Increasing
on the indicator denotes a malfunction within the area
temperature causes more air to be bled from the
being tested.
diaphragm chamber. Because of spring action, the
modulating valve moves toward the closed position.
OPERATION
This restricts flow through the modulator valve and
drops the skin temperature. The thermostats in the
The P-3 aircraft wing anti-icing system prevents ice
outboard leading edge plenum areas are set at 145F.
formation on wing leading edges during icing
The wing inboard and center section thermostats are set
conditions. This is a hot wing type system utilizing hot
at 120F.
compressed air from the engines. Engine bleed air,
ducted from two ports at the 14th stage of each engine
Leading Edge Skin Temperature Indicator and
compressor, is orifice regulated. The supply is
Overheat Circuit Caution Light Circuit
maintained at essentially a fixed percentage of engine
airflow for all flights speeds and attitudes. The air from
The temperatures of the wing leading edge sections
both ports, after passing through the two 14th stage duct
are displayed on the LEAD EDGE TEMP indicator on
check valves, is ducted through a single universal
the engine bleed air control panel. Six sensors are used
flexible joint to the bleed air shut-off valve aft of the
in the system, one in each leading edge section. These
14th stage firewall (fig. 5-6).
sensors form part of the circuitry of the airfoil
The bleed air section of the ice protection panel in
temperature sensors amplifier. When the temperature at
figure 5-5 shows a basic diagram of the wing anti-ice
one or more of the sensors exceeds 230F, a relay
system. An engine number labels each engine. Directly
energizes, providing a ground for the LE HOT caution
below each engine block (in the diagram) is an OPEN
light circuit, causing the light to come on. Whenever a
light that illuminates when the bleed air valve is open 2
leading edge skin overheat condition is detected, the
degrees or more. The cross-ship manifold from the
location can be determined by setting WING
bleed air valves goes to each modulating valve and the
LEADING EDGE SKIN TEMP BOMB BAY TEMP
fuselage shutoff valves. The fuselage bleed air shutoff
rotary switch to each position while observing the
valves are normally in the CLOSE position during
indicator. Since there is always a possibility of more
normal anti-icing operation. The bleed air pressure
than one section overheating, all six-wing leading edge
gauge reads cross-ship manifold pressure when one or
sections should be checked. The airfoil temperature
both switches are opened.
sensor amplifier is at the forward load center and is
powered through the AIRFOIL IND & OVHT
A leak test switch is mounted on the upper
WARNING circuit breaker.
right-hand side of the panel. This switch is used to
determine if the leakage of the system is acceptable.
The circuit receives power from the AIRFOIL
IND & OVHT WARNING circuit breaker. The
Three modulating valve control switches are
caution light is energized through the indicator lights
located on the left side of the wing and empennage ice
power system and the indicator light control. The
panel. The OUTBD switch controls the outboard
indicator circuit does not disturb the caution function
modulating valve on the left and right wing, the CTR
of the system.
switch controls the two center modulating valves, and
the INBD switch controls the two inboard modulating
High temperature within the leading edge is
valves.
generally caused by bleed air leakage or
5-6
