Ice protection - HOT AIR SYSTEM

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HOT AIR SYSTEM

Fig. 13-4 Electrical ice protection.

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 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.