getting to grips with COLD WEATHER OPERATIONS 寒冷天气运行(23)

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● Wing leading edges:
Such large aircraft as the Airbuses are significantly more icing resistant than smaller aircraft. This is due to the size and thickness of their wing. It was found that thick wings collect less ice than thin ones. That’s why it was determined unnecessary to de-ice the full wingspan, to reach the iced wing performance shown on figure A2.
The de-iced part is heated so as to be evaporative, which means that the heat flux is so high as to melt the ice when it is accreting and the remaining water evaporates. Then, the heated part of the leading edge remains clean under icing conditions.
But that heat flux has a drawback. As it must keep the leading edges at highly positive temperature in flight, it needs to be computed so as to:
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 First, compensate for outside air cooling (called forced convection),

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 Second, melt the possible ice (compensate for the change of phase from ice to water).

The addition of both represents a high demand on the energy supply. That is the reason why it is inhibited on ground. In the absence of a rapid cooling due to airspeed, heat flux would damage the slats by overheating.
It should be noted that the tailplane and the fin also have leading edges that can pick up ice, but they are not de-iced. This is because it has been proven they both have large margins relative to their maximum needed efficiency. Tailplane maximum efficiency is needed in forward CG maneuvering and fin maximum efficiency is needed in single engine operation. Both are demonstrated to meet the certification targets with ice shapes.
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● Engine intake leading edges
These are the most carefully de-iced, because the engine fan should be best protected. Hot air is bled from the engine compressor and heats the whole of the nacelle leading edge.
The standard procedures call for greater use of the nacelle anti-ice (NAI) than of the wing anti-ice system (WAI). This is due to a special feature of air intakes. In certain flight conditions, the temperature may drop by several degrees inside the intake (.sucking. effect). Therefore, inside icing may occur at slightly positive outside air temperatures, whilst the wing itself wouldn’t. The NAI is never inhibited, because the air is forced through at all speeds by the engine.
A3.1.2 Electrical heating
Electrical heating is typically used where small amounts of ice are encountered or on
small surfaces like turboprop air intake. This method can be found on probes protruding
into the airflow.
On Airbus aircraft sensors, static ports, pitot tubes, TAT and Angle of Attack (AoA) probes,
flight compartment windows and waste-water drain masts are electrically anti-iced.
For these items, the same problem of overheating exists as for the wing leading edge. It
is solved automatically by air/ground logic, so that the pilot does not need to be
concerned.

Electrical heating can also be found on turboprop aircraft to heat the inner part of the
　
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