Aircraft ice protection Systems
-Nagaraja Bhagav (19AE60R15)
icing on aircraft in flight is extremely dangerous and pilot’s action to it can mean life or death. Throughout aviation history,
icing has caused a significant number of accidents. Icing can take place anywhere on the aircraft surface and there are some
areas which are sensitive to ice formation. As altitude increases, the atmospheric temperature decreases and it goes to
negative. Water freezes at 00 C. Water at negative temperature in clouds will be in supercooled unstable liquid form. It
freezes immediately whenever sticks on hard surface. The formation of ice can occur in many ways and in many conditions.
Types of ice:
1. Rime ice
forms at lower temperature. If water droplets of supercooled clouds are very small, it freezes before another hit and form
the tiny pellets frozen together in spongy mass. It will be in milky white appearance. It is not cohesive and can be flaked
off easily.
2.Clear ice
When a flying aircraft strikes water droplet the leading edge of its structures become covered by a film of water. If cooled
sufficiently this film freezes from inside out forming a clear dense cohesive glaze of clear ice, the most dangerous structural
ice. Its form is a rounded blunt shape on the leading edge and may spread over upper and lower surfaces drastically
disrupting the flow of air and causing a considerable loss of efficiency.
3. Mixed ice
This is the combination of rime and clear ice. An irregular conglomerate forming a rough blunt mass which can build up
to serious proportions.
Effects of ice build up
➢ Reduces overall aerodynamic efficiency
➢ Reduces lift and increases drag
➢ Stall speed is higher than normal
➢ Greater fuel consumption
➢ Reduced maneuverability
➢ Causes damage to external equipment
De-icing:
De-icing is the removal of snow or ice from the surface of the aircraft. There are various methods for removal of ice.
1. Fluid de-icing
It is one or two step process depending on the weather conditions. When there is no more current precipitation or falling
snow, pilots request a type 1 de-icing. Type 1 stands for the type of the fluid used. It is a low viscosity fluid applied at
temperature of 500-800 C and it quickly melts ice. If it is snowing then a type 4 de-icing is applied along with type 1. Type
4 fluid is a pseudoplastic, it is a thick and goopy fluid that prevents the snow from sticking to the wing. When the aircraft
takes of the fluid is designed to shear off at 100 knots.
2. TKS de-icing system
It uses a glycol-based fluid to cover the critical surfaces of an aircraft. The fluid is kept in a reservoir tank and is then
pumped forward to the leading edge and exit through small holes, so melting the ice. It can also be used to de-ice some
propeller blades and windshield.
3. Boots
It is a mechanical system which uses pneumatically inflated boots. It is switched on when there is an ice build-up of between
0.5 and 1.5 centimetres depending on aircraft type. The tubes in the boot sections are inflated with air from aircrafts
compressed air system. The inflation weakens the bond between ice and boot surfaces causing the ice to break away. The
inflation and deflation cycle are repeated during the period the system is in operation.
4. Electro-impulse Deicing
It is an acceleration-based de-icer. An electromagnetic coil is placed behind the skin that induces a strong eddy current in
the metal skin when supplied with AC current. So strong opposing forces are developed between coil and skin. This results
in rapid acceleration that breaks ice in efficient manner.
Anti-icing
It is the method of prevention of ice formation on the surface. The different methods are
1. hot wing anti icing system
Air is rammed through the ducts in the leading edge of each wing and empennage. Combustion heaters or heat exchangers
heat the ram air and circulate through the leading edge of each outer wing panel and stabilizers. In flight air flows
continuously through the system at all times even when the heaters are off.
2. Bleed air anti-icing
Hot air is ducted via the engine bleed valve from the compressor stage within the engine. The air then runs through a pre-
cooler to reduce its temperature to 200 0 C and this cooled air then distributed via bleed ducts to anti-icing system. This
maintains a constant leading-edge temperature and prevents ice formation.
3. Electric heaters
In this method small wires or other conductive material is embedded in the skin. When it is supplied with electric current
it provides sufficient heat to prevent icing. Automatic heaters are used to prevent surface from overheating. This is used in
pitot probes, windscreens, propellers, icing detection devices and other sensors.
Ice detection systems
1.Smiths icing detector
This device has 4 holes at its leading edge and two holes at trailing edge. Air enters through front holes more quickly than
that exits through rear hole. This develops pressure on the diaphragm which keeps the circuit open. Once ice is built up the
airflow get blocked and pressure drops. This closes the circuit and gives warning light.
2. Napier icing detector
A serrated shaft is continuously driven by electric motor. Shaft rotates adjacent to the fixed knife edge cutter and the
clearance is very less. Under normal condition little torque is sufficient to drive the shaft. With ice build up it resists the
motion and greater torque is required. This will be sensed and it gives ice warning light.
3. Rosemount icing detector
It consists a short cylindrical probe mounted on a vibrator housing which vibrates the probe. When ice is formed on probe
the added mass reduces vibrations. When the frequency falls below predetermined level an ice warning is given. This
device is usually fitted on the outer surface of fuselage.
References
1. An overview of the De-icing and Anti icing technologies with prospects for the future -Zdobyslaw Goraj, Warsaw
University of Technology
2. Episode 35 Ice Formation on Aircraft, Anti-Icing and De-icing Systems For Aircraft Surfaces
3. Aircraft ice detectors and related technologies, FAA technical centre
4. https://www.youtube.com/watch?v=mUqSj9FLF0A
