M11 Ice Protection

Wing Icing

• Supercooled water droplets in the air hit the leading edge and immediately fom glaze ice which is clear.
• This only occurs at temperatures 0 - -10 degrees Celsius
• Glaze ice builds up past the leading edge onto the upper surface.
• Rime Ice builds up when temperarues are <-10 and will only form on the leading edge in a double horn formation
• Both these formations of ice will cause an increase of weight and drag but a decrease in lift.
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Engine Icing

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• Should ice build up it will negatively affect the engine in 2 ways: it will disturb the air flow which decreases the efficiency of the engine and ice may also form chunks which may damage fan blades or inlet valves.
• It is usually prevented via thermal methods.

Anti-Icing & De-icing

• There are many techniques to anti icing and deicing aircraft, in order to prevent the formation of ice and to break down ice once it has formed.
• The technique used depends on the type of aircraft and the conditions it is subjected to.
• It is important to establish the difference between what anti icing and de icing is.
• When on ground the systems that are part of the aircraft are not used, therefore other methods are used such as spraying the aircraft with chemicals.

De-icing Techniques - Rubber Boots

• Pneumatic de-icing is used on both GA aircraft and turboprop commuter type aircraft.
• This is often via the use of inflatable rubber boots which are driven by the pneumatic system.
• The boots are alternately inflated and deflated in cycles where the boot will be inflated for 6-8 seconds at a time.
• All ice that has formed on the surface of the boots will be broken and hopefully will separate from the surface when the boot is inflated.
• They are most often found on the wing and will inflate and deflate at certain times not to cause any disturbances to the airflow.
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Rubber Boots Cont.

• The air which will inflate these rubber boots may come from a dedicated engine driven air pump and the suction side of said pump will be the force that deflates the boots.
• Boots are deflated this way to ensure that there is a flat surface and is not disturbing the airflow
• Should they be installed on a turbine aircraft, engine bleed air may be used instead.
• The rubber boots may also contain conductive neoprene to provide resistance to deterioration

Electric De-ice Boots

• These type of boots are rubber heated mats that lie on the wings.
• Controlled by a sequence timer that is initiated by ice detection probes
• Upon heating, the ice will melt
• The mats will operate in pairs to avoid aerodynamic imbalance
• This system is inoperative whilst on ground.

Propeller De-ice

• The propeller is one of the structures most susceptible to the formation of ice and so will need adequate de-icing.
• There are 2 main ways the propeller is de-iced, either using an electro thermal propeller device (electrically heated boot) and using a chemical which is a glycol-based heated fluid.
• Electro thermal propeller device uses a slip ring and brush assembly on the spinner bulkhead and current is sent from the brushes in order to heat the boot.
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Propeller Chemical De-ice

• This method is mainly used by single engine GA aircraft
• A glycol based fluid is supplied to the propeller from and electriacally driven pump and passed through a micro-filter
• The fluid is supplied to the propeller to break down the ice and the centrifugal force will assist in removing all the ice.
• It may be a stand-alone system or could be a part of a chemical wing and stabiliser de-icing system such as the weeping system.

Thermal Anti-ice System

• There are two thermal anti-ice systems on jet aircraft, which are the wing and the engine systems.
• The wing system uses hot air from the pneumatic system
• One or two valves called the wing anti-ice valves to connect the pneumatic system to the anti-ice ducts.
• The engine anti-ice system is effectively the same (has an engine anti-ice valve) and may also use air directly from the engine.
• Hot air travels the valves and ducts and sprays through to the surface which will therefore heat the surface to prevent the build up of ice.
• When the air is not needed, it will leave the area via openings in the lower part of the structure.
• If the leading edge has a slat a telescopic duct must be in place to supply the hot air to the slat upon extension.
• The wing anti ice systems operate only in flight, when the aircraft lands the wing anti-ice valves will automatically close however it is important when carrying out maintenance procedures to be cautious as the system will still remain hot.

Electrical Anti-ice Systems

• All electrical anti-ice systems have a heating element (metal wire), power supply and a temperature/power control circuit.
• The heating element is heated via an electrical current and the amount of heat is proportional to the amount of power in the circuit.
• Many systems on the aircraft use heat as a form of protection against ice, such as the wings, drain mast and the probe systems.
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Drain Mast Heat System

• Prevents freezing of the waste water outlets on the lower part of the fuselage
• This system is switched on automatically when electrical power is on.
• You can find all types of power and temperature control circuits within this system, some of these are identical to the circuits used for heat and water pipes.
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Probe Heat System

• Used on 4 different types of probes on the aircraft:
• The temperature probe (Rosemount Probe) which measures air temperature,
• The pitot tube which measure the dynamic air pressure
• The static ports measure the static air pressure
• The angle of attack/alpha sensors.
• Is switched on automatically when an engine is started (may also be done manually)
• This system has no temperature control circuits
• Should there be a failure in the probe heating, the pilot unreliable information from the probes.
• Therefore a message will appear on the central warning system, should the current be too low.

Chemical Anti-ice System

• This method is used to anti ice the leading edges of wings, stabilisers, windshields and propellers
• The weeping wing system contains formed titanium panels that are laser drilled with over 800 tiny holes per square inch, these are mated with stainless steel rear panels and bonded to the wing and stabiliser leading edges.
• The wing and stabiliser systems are often called the weeping wing system, where as its name suggests an anti freeze solution is pumped from a reservoir through a mesh screen which is embedded in leading edges of the wings and stabilisers.
• It is activated by a switch in the cockpit
• In flight, airflow helps the solution flow over the wing and tail surfaces to prevent the formation on ice.
• The solution the freezing point of the water that hits the surface of the aircraft and allows it to run off the aircraft without freezing.
• The system is designed to be used for anti-icing but can also be used for de-icing, by chemically breaking down any formation of ice already present.

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