TRAMAN is representative of several systems
Q3. How much greater is the capacity of the
primary pump than the secondary pump?
designed for Navy aircraft. Look at figure 5-9.
Here, you see that the electrical portion of the
circuit serves only to turn the system on or off.
The guide vanes of a turbine-powered engine
Q4. Why is the fuel control schedule 20 percent
direct the flow of inlet air into the compressor
richer than nominal engine requirements?
section. At this point, the air is coldest and most
subject to icing. The biggest problem caused by
ice forming here is blockage of inlet air, causing
air starvation and thus engine failure. Also, there
is a possibility that chunks of ice can be inducted
Q5. What unit minimizes the amount of fuel
into the engine. Therefore, turn on the anti-icing
dropping into the combustion liners during
engine shutdown?
system at the first indication of any icing condition
or before entering an icing condition. Normally,
icing doesn't occur in supersonic flight because
friction of the aircraft passing through the air
POWER PLANT ANTI-ICING AND
creates enough heat to prevent ice formation.
DEICING SYSTEMS
The anti-icing valve is a solenoid-operated
bleed valve. With no electrical input to the
Learning Objective: Recognize operating
solenoid, the bleed valve closes, and there is no
principles and characteristics of aircraft
anti-icing airflow through the valve. When the
power plant anti-icing and deicing systems.
engine is operating with the valve solenoid de-
energized, the main poppet will remain in the
Naval aircraft deicing lets you fly in any type
closed position. When the solenoid energizes, the
of weather. When there is enough moisture in the
solenoid valve unseats and permits air pressure
within the main poppet to escape through the
air and you encounter freezing temperatures, you
must protect the power plant against ice buildup.
overboard vent.
With pressure decreasing in the poppet valve
There are two electrical systems that do this--
body, inlet pressure on the main poppet valve face
the anti-icing and deicing systems. Anti-icing
overcomes spring tension and raises the valve
systems prevent ice from forming and deicing
systems remove ice that has already accumulated.
from its seat. This permits high-pressure air to
Many types of anti-icing systems are used
discharge through the outlet of the valve to the
today. All systems use heated air from the engine
anti-icing manifold on the engine. The regulating
piston and spring valve assembly control discharge
to perform the anti-icing function. The use of
air from the anti-icing valve to a preset pressure.
heated air causes engine power loss; so use
anti-icing only when necessary. In some aircraft,
PROPELLER DEICING SYSTEMS
a reversible electric motor opens and closes an air
valve to supply the needed air. In other aircraft,
an electrical solenoid positions a pneumatic valve
One method of preventing excessive accumu-
to allow regulated heated air into the engine
lation of ice on the propeller blades of turboprop
anti-ice system.
or reciprocating engines is using electric heaters.
Where the mission of the aircraft dictates that
Figure 5-10 is a simplified schematic diagram of
it fly routinely in adverse weather conditions, a
a system for a two-engine aircraft.
fail-safe anti-ice system is used. Fail safe means
The propeller deicing system consists of a
three-position, t w o - s p e e d selector switch
the solenoid-actuated air valve electrically actuates
closed. If the switch is turned on, or if electrical
(propeller deicer switch) and an indicator light,
a two-speed timer, and two propeller deicer relays
power fails, the valve is spring loaded to the open
(one for each propeller). Also, included (for each
position. Some systems anti-ice the complete inlet
propeller) are the brush pad bracket assembly,
duct; while in other systems, only the guide vanes
slip-ring assembly, the aft portion of the propeller
are anti-iced.
assembly, and a neoprene rubber heating element
GUIDE VANE ANTI-ICING SYSTEM
and connector for each blade. Abrasion strips
protect the blade heaters. The deicing system
operates at either a slow cycle of 40-75 seconds
There are a variety of engine anti-icing
on, 120-225 seconds off; or a fast cycle of 17-22
systems in use today. The system covered in this
