Module 11.12 Ice and rain protection Flashcards
What are the conditions for ice formation?
- Supercooled water droplets
- Below freezing aircraft skin
What are the 3 types of ice?
- Rime ice
- Clear ice
- Mixed ice
What is clear ice caused by?
Large water droplets
- Looks smooth
What is rime ice caused by?
Small water droplets
- Rough surface
What is the problem with mixed ice?
Rapid formation
What areas should have ice protection?
- Leading edges of wings, stabs and engines
- Props and spinners
- Air data probes
- Flight deck windows
- Water and waste system lines and drains
- Antennae
What are the types of ice detectors?
- Visual
- Hot rod
- Accretion or pressure
- Rotary ice
- Vibrating ice
What are the two methods of visual detection?
- Wing inspection lights
- Visual ice indicators
How does a hot rod detector work?
In icing conditions ice will form. Pilot can then see the formation from his window, the pilot will then switch on the heating element to reset it.
There is also a light for night ops
What is the angle of the hot rod detector?
30°
How does the pressure operated ice detector work?
Leading edge of the probe has 4 holes and trailing edge has 2. under normal conditions there will be a pressure build up.
Under icing conditions there will be negative pressure created, this will trigger a warning in the cockpit
What occurs after ice formation has occurred and warnings have been issued?
The heating element will automatically turn on
What does the rotary ice detector consist of?
- Single phase AC motor to spin a rotor
- Knife edge placed less than 0.002” from the rotor
What occurs when ice forms on the rotary detector?
Ice forms and the torque will increase due to the knife edge having to shear this off. The motor will then rotate slightly in its housing. This movement is detected and issues a warning
Why doesn’t a rotary detector have a heater?
As the knife edge shears of the ice and resets it
What happens to the resonating frequency when ice forms on the vibrating probe ice detector?
It decreases
What does the element ice sensing unit/Sangamo Weston ice detector detect?
It detects icing conditions and not formation
What are the 3 main components of the element ice sensing unit?
- Moisture detector controller
- Moisture sensing heads
- Thermal switch
What occurs when ice forms on the probe of a beta particle ice detection probe?
The geiger mueller readings go down, then the heater will be actuated
What is the difference between anti-ice and de-ice?
- Anti-ice is to stop the formation
- De-ice is to remove formation
How may a surface be anti-iced?
- Keep it dry
- Heat it enough to evaporate water or prevent freezing
Where is the thermal pneumatic anti-icing?
Generally leading edges of aerofoils
How does the warm air get to the leading edge?
Ducts (piccolo tubes) with holes to direct hot air to leading edge
What is done to ensure the slat LE doesn’t have ice build up?
The Wing Anti-Ice (WAI) moves air from the leading edge to the slat via a telescopic pipe
What is shown on the WAI indication system?
- Wing manifold pressure
- Valve
- Air pressure
- Air flow
When would the Engine Anti-Ice (EAI) system be turned on automatically?
Before the WAI
The bleed air is directed to the LE like WAI, where is this heated channeled out?
Through outboard vents
What does the electrical windshield anti-ice do?
Removes ice formation and improves the impact resistance
What are wings with chemical anti-ice systems also called?
Wet wings or TKS system (Brand name)
What concept does TKS use?
Freezing point depressant concept
I.e. it makes the freezing point lower
What is the drawback to TKS?
Limited use as only a finite amount of fluid can be stored on board the aircraft
How do de-icer boots work?
They are rubberised section of LE’s and after ice formation the boots are inflated which removes the ice
What is the purpose of the suction in de-icer boots?
To keep a flat LE surface
How are the boots operated?
Manually via a switch
What are electric de-ice boots?
They have electric heating elements on the LE instead of rubber inflatable channels
How may windshields be de-iced?
- Chemically, de-icer sprayed on via nozzle
How is rain repellent applied?
Sprayed on with the wipers on, only in really wet conditions
Liquid used is banned
when should rain repellent never be applied?
Dry conditions
What does a hydrophobic coating do?
Allows water to bead and run off
What are the challenges wipers face?
- Slipstream reduces effectivity
- Oscillation speed may be too slow to keep up with the downpour
Removal via pneumatic rain removal systems has two purposes, what are they?
The heated air:
- Breaks water into small particles to be blown away
- Heats windshield, stops freezing
What are the 3 types of rain removal?
- Chemical
- Pneumatic
- Coating
How are probes anti-iced?
Using heating elements
When would the heating elements around a water tank and drains be turned on?
When a temperature of below freezing is detected
How are windshield wipers actuated?
Electrically via a motor
