曝光台 注意防骗
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ground operation in freezing fog. Protection against
ice formation may be required since icing of these
regions can considerably restrict the airflow through
the engine, causing a loss in performance and
possible malfunction of the engine. Additionally,
damage may result from ice breaking away and
being ingested into the engine or hitting the acoustic
material lining the intake duct.
2. An ice protection system must effectively prevent
ice formation within the operational requirements of
the particular aircraft. The system must be reliable,
easy to maintain, present no excessive weight
penalty and cause no serious loss in engine
performance when in operation.
3. Analyses are carried out to determine whether
ice protection is required and, if so, the heat input
required to limit ice build up to acceptable levels. Fig.
13-1 illustrates the areas of a turbo-fan engine
typically considered for ice protection.
4. There are two basic systems of ice protection;
turbo-jet engines generally use a hot air supply (fig.
13-2), and turbo-propeller engines use electrical
power or a combination of electrical power and hot
147
Ice protection
148
Fig. 13-1 Areas typically considered for ice protection.
Fig. 13-2 Hot air ice protection.
air. Protection may be supplemented by the
circulation of hot oil around the air intake as shown in
fig. 13-3. The hot air system is generally used to
prevent the formation of ice and is known as an antiicing
system. The electrical power system is used to
break up ice that has formed on surfaces and is
known as a de-icing system.
HOT AIR SYSTEM
5. The hot air system provides surface heating of
the engine and/or powerplant where ice is likely to
form. The protection of rotor blades is rarely
necessary, because any ice accretions are dispersed
by centrifugal action. If stators are fitted upstream of
the first rotating compressor stage these may require
protection. If the nose cone rotates it may not need
anti-icing if its shape, construction and rotational
characteristics are such that likely icing is
acceptable.
6. The hot air for the anti-icing system is usually
taken from the high pressure compressor stages. It is
ducted through pressure regulating valves, to the
parts requiring anti-icing. Spent air from the nose
cowl anti-icing system may be exhausted into the
compressor intake or vented overboard.
7. If the nose cone is anti-iced its hot air supply may
be independent or integral with that of the nose cowl
and compressor stators. For an independent system,
the nose cone is usually anti-iced by a continuous
Ice protection
149
Fig. 13-3 Combination of hot air, oil and electrical ice protection.
unregulated supply of hot air via internal ducting from
the compressor.
8. The pressure regulating valves are electrically
actuated by manual selection, or automatically by
signals from the aircraft ice detection system. The
valves prevent excessive pressures being developed
in the system, and act also as an economy device at
the higher engine speeds by limiting the air offtake
from the compressor, thus preventing an excessive
loss in performance. The main valve may be
manually locked in a pre-selected position prior to
take-off in the event of a valve malfunction, prior to
replacement.
ELECTRICAL SYSTEM
9. The electrical system of ice protection is
generally used for turbo-propeller engine installations,
as this form of protection is necessary for the
propellers. The surfaces that require electrical
heating are the air intake cowling of the engine, the
propeller blades and spinner and, when applicable,
the oil cooler air intake cowling.
10. Electrical heating pads are bonded to the outer
skin of the cowlings. They consist of strip conductors
sandwiched between layers of neoprene, or glass
cloth impregnated with epoxy resin. To protect the
pads against rain erosion, they are coated with a
special, polyurethane-based paint. When the deicing
system is operating, some of the areas are continuously
heated to prevent an ice cap forming on the
leading edges and also to limit the size of the ice that
forms on the areas that are intermittently heated (fig.
13-4).
11. Electrical power is supplied by a generator and,
to keep the size and weight of the generator to a
minimum, the de-icing electrical loads are cycled
between the engine, propeller and, sometimes, the
airframe.
12. When the ice protection system is in operation,
the continuously heated areas prevent any ice
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