Chapter 4 - Aircraft Icing Protection Systems Flashcards
What areas of the aircraft are sensitive to ice formation?
Aerofoil surfaces Engine intakes Engine internal surfaces Rotor blades and propellers Windscreens Control hinges and linkages Instrumentation probes and vanes Weapons and weapon carriers
What effects can icing have on aircraft performance?
Thrust decreases (engine not performing as efficiently)
Lift decreases (change in shape of the wing)
Drag increases (ice build up disrupts the airflow across the wing, body and tail)
Weight increases
What are the two categories of Ice Protection systems?
Active
Passive
How do active ice protection systems work?
Either:
Increase the temp of local areas to above freezing point
or
Chemically reduce the freezing point of precipitation impinging upon the aircraft
How do passive ice protection systems work?
Harness the momentum of the main airstream to separate out precipitation and divert it away.
What are the categories of Active ice protection systems?
Anti-icing
De-icing
What methods are used to alert crews to the risk of ice forming on an aircraft?
Met forecasts
External visible checks
Ice accretion probes - Positioned to be visible from the cockpit
Flood lights
Alerts and automatic systems
Why don’t aircraft always fly with ice protection systems turned on?
The systems require a considerable amount of power.
What are the different types of Ice Detection Devices?
Visual ice detector
Differential static pressure ice detector
Frequency monitor ice detector
Explain how a Visual ice detector works?
Illuminated ice accretion probe viewable from cockpit.
Visual detector - painted matte black to give best visual background to detect ice formation
System can be de-iced in order to observe the rate of ice build up.
Explain how a Differential static pressure ice detector works?
Detector monitors pressure differential between a series of holes on the leading and trailing edges of the diff static detector.
Cockpit alert activated when holes on the leading edge become blocked.
Explain how a Frequency monitor ice detector works?
Utilises changes in resonant frequency of a probe which occurs when ice forms on it.
Probe vibrated at its clean resonant frequency, any mass of ice will reduce the resonant frequency and the detector senses and significant changes, activates an alarm in the cockpit.
What is used for the majority of airframe structure anti-icing and de-icing systems?
Hot air bled from the engines
Must be cooled first and pressure must be reduced.
How does hot air enter the wings?
Piccolo Tube
Note - Learn diagram in manual (web, plenum, etc)
What components of the engine is Thermal (hot air) anti-icing used to protect?
The inlet guide vanes
First stage compressor stator blades
Nose cone
Nose cowling
Structural support members within the intake
Where is electrical heating most useful for anti-icing?
When complex control arrangements are needed or small areas need to be heated.
Normally used for turbo-prop blades.
What is used to de-ice helicopter blades and FW props?
Heating mats (thermal - electrical)
Explain how pneumatic de-icing boots work.
Layers of rubber with one or more air chambers between the layers.
Placed on the leading edge of an aircraft’s wings and stabilisers.
Chambers rapidly inflated and deflated, rapid change in shape breaks the adhesive force between the ice and the rubber, allowing the ice to be carried away by the relative wind flowing past the aircraft.
Caution - Ice must be carried away cleanly from the trailing sections, or it could re-freeze behind the protected area.
How are windscreens protected from icing?
They are heated - thin film on gold used for the heating element and is deposited directly onto the glass.
Both de-ice and de-mist the windscreens.
How are windscreens protected from rain during low speed flight.
High-speed windscreen wipers
What is Holdover Time (HOT)?
The period of time for which de-icing fluids are effective. Timer starts the moment the first drop is applied.
Aircraft needs to get airborne in this time. If it does not it needs to taxi back and the de-icing process must be repeated.
Note - De-icing pastes/gels applied by the groundcrew melt any present ice + prevents reformation for the duration of the HOT.
Where is hot air taken from for de-icing/anti-icing?
From the compressor in the engine
What is the relationship between engine anti-icing and airframe anti-icing?
Independent of each other?
How is an aircraft prepared for flight in icy/snowy conditions?
Ice, snow and slush deposits are first removed by the ground crew.
After physically removing the majority of deposits, chemical fluid de-icing is used to complete the task?
Apart from heated windscreens, how else can we protect the windscreens from ice?
Hot air to de-ice and de-mist?
Wipers?
Note - Check this is correct
