16 Questions
What is the primary purpose of an overheat control unit in conjunction with an 'override' thermistor and flame-stat?
Final overheat protection system
Where is the entry point for the heated air in the thermal anti-icing system?
At the stagnation point of the leading edge
How does the system work in principle?
By maintaining the temperature of the skin above that at which ice occurs
What is the purpose of the corrugations in the thermal anti-icing system?
To allow hot air to flow back chord-wise to the main aerofoil section
What is the difference between anti-icing and de-icing systems?
Anti-icing systems use a continuous supply of heated air, while de-icing systems use a cyclic supply
What is the purpose of wing and fuselage cross over ducts in the hot air bleed system?
To ensure a supply to all surfaces in the event of an engine shut down in flight
What is the purpose of the hot air bleed system?
To prevent the shedding of ice accretions into the engine intakes
What is the source of hot gas in an EXHAUST GAS HEATING SYSTEM?
All of the above
At what temperature do the anti-icing shut off valves on each engine open to supply air to the leading edge ducting?
200ºC
What is the purpose of the electrically actuated flaps in the EXHAUST GAS HEATING SYSTEM?
To partially divert exhaust gases to flow between the tubes of the heat exchanger
What happens when the temperature sensor fails to control the temperature of the leading edge?
The overhead sensor controls the temperature by regulation of the hot air valve
What is the purpose of the temperature sensors in the leading edge?
To monitor the temperature rise and control the cold air valve
What is the purpose of the interlock between the gas flap actuator and the hot air valve actuator?
To ensure the hot air valve is fully open before the gas flap opens
What happens if the gas flap fails in the open position?
The hot air valve closes and the spill valve opens to direct the hot air overboard
What is the advantage of grading the distribution of air along the wing leading edges on aircraft with engines mounted on the rear fuselage?
To prevent the shedding of ice accretions into the engine intakes
What type of temperature control is provided in the EXHAUST GAS HEATING SYSTEM?
Automatic temperature control with a standby 'manual' facility
Study Notes
Thermal De-icing/Anti-icing Systems
- Thermal de-icing/anti-icing systems in aerofoils use heated air ducted span-wise along the inside of the leading edge to prevent ice formation.
- The heated air enters the leading edge at the stagnation point, where maximum temperature is required, and flows back chord-wise through corrugations to exhaust points.
Exhaust Gas Heating System
- Ambient air is drawn into an intake on the engine nacelle and passes through a heat exchanger, where it is heated by diverted exhaust gases from the jet pipe.
- The heated air is then ducted to the leading edges, passing through an electrically operated hot air valve.
- The system has an emergency manual override facility to prevent overheating of the heat exchanger in case of failure.
Temperature Control
- Temperature control is automatic, with a standby manual facility.
- A control unit, with normal control and overheat thermistors, provides automatic control and overheat protection.
- An overheat control unit, with an override thermistor and flame-stat, provides a final overheat protection system.
Hot Air Bleed System
- In this system, air is bled from a late stage of the gas turbine engine compressor and distributed to aerofoil leading edges.
- The system can be used for anti-icing or de-icing purposes on wing and tail leading edges, and for ice protection of engine intakes.
- The system maintains the skin temperature above that at which ice occurs or raises the skin temperature to melt the ice after it has formed.
System Operation
- Anti-icing shut-off valves open to supply air to the leading edge ducting at temperatures of about 200ºC.
- Wing and fuselage cross-over ducts ensure a supply to all surfaces in the event of an engine shut down in flight.
- Temperature sensors monitor the temperature rise and control the skin temperature by regulating the hot air valve and cold air valve.
Learn about thermal de-icing and anti-icing systems in aerofoils, including exhaust gas heating systems used to prevent ice formation in aircraft.
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