Aircraft Icing Flashcards
What two things do you need for ice to form?
Visible moisture AND temps below zero
What is airframe ice and what are the three main types?
Airframe ice forms when supercooled water droplets strike an airframe when the airframe’s temp is less than 0°C
Rime
Clear Ice
Mixed Ice
Supercooled water droplets tend to favour locations with ____ condensation nuclei levels and ____ currents
Reduced, verticle
What is the difference between rime and clear ice?
Rime is like tiny granules collecting like a sand pile on the leading edge of the wing. Has air pockets between granuals so it lighter
Clear ice is larger droplets that creat a smooth, clear, ‘casing/cap’ on the leading edge of the wing. Because the droplets are bigger, they have a second to spread out before they freez in layers, making this ice much heavier than rime. Eventurally can form a ‘horn’ that juts up into the airflow over the wing
More info on rime ice (must know)
- Formed by instantaneous freezing of small supercooled water droplets (on the skin of the AC that is below 0°)
- Rough and opaque like the inside of a freezer that needs defrosting
- Forms in layer-type clouds like stratus
- Brittle and not very adhesive
- Results in light to moderate levels of icing
More info on clear ice (must know)
- Most dangerous type of ice, heavier, harder to get rid of)
- Formed by large supercooled water droplets
- Looks smooth and transparent
- Lagre and severe accumulations result in horns (picture)
What situations can lead to clear ice formation?
- Freezing rain or drizzle
- Cumuliform clouds with strong vertical currents
- Worse near the tops of these cumuliform clouds
- Lenticulars can also produce severe clear ice
What is mixed ice?
A mixture of clear and rime ice
What are the factors that have an effect on the rate of ice accumulation?
- Airfoil shape (the thinner airfoils collect more than thicker air foils)
- Airfoil speed (the faster the wing is traveling through the air)
- Droplet size
Why do thinner air foils collect more ice than thicker ones?
Has to do with the ‘pressure waves’ the leading edge of the airfoil sends out into the air ahead of it (shoving it out of the way). The droplets heading towards a thicker air foil have bigger pressure waves, slowing them a bit and flinging them aside more, so they hit less directly or sometimes even miss.
On a thinner airfoil, the pressure waves are tiny and therefor the dropplets just smack right into the wing at full speed.
Where might you start seeing ice accumulate before your wings and why?
Antennas and horizontal stabilizers.
Because ice will collect on the thinnest surfaces first.
Supercooled water droplets can exist in temps down to ____ without becoming a solid
-40°C
What are the four severities of ice accumulation?
- Trace: Ice becomes perceptible, not hazardous if 1 hour or less
- Light: Rate of accumulation may create a problem if the flight is over 1 hour)
- Moderate: Rate of accumulation is fast enough that even short encounters are dangerous. De-icing equipment is required to clear it and a diversion may be necessary
- Severe: Rate of accumulation is faster than de-icing can deal with it. Immediate diversion is necessary
What color is icing on the GFA?
One the Icing and Turbulence chart icing is in blue
On the clouds and weather chart, icing is in red
What to do if you encounter icing?
- Make the immediate decision to go back (best idea), descend (second best), or climb (might be a bad idea, or not possible, depending on the circumstances)
- Activate de-icing equipment
Why might climbing not be a good idea to escape icing conditions you may encounter?
- You might not be able to climb at all if you gathered enough ice (not enough thrust to overcome the weight of the ice or the changed shape in the airfoil). So you better know exactly where the top of cloud is and know you can get above it otherwise you might be fucked.
What are the dangers of icing?
- Poor aerodynamics
- Increase in drag and weight
- Decrease in thrust and lift
- Decrease in the power availible due to intake blockage
- Engine failure due to carb ice or blocking of air intake
- Engine FOD damage likely in turbine engines
Effects of icing on a wing
- Stall happens at a lower angle of attack and at a higher speed. Therefore the wings can stall well before you get any warning from the stall horn
- Decreasing trim effectiveness
- Less lift from horizontal stabilizer means more elevator control is required, and may run out
- Wing flap damage when trying to extend or retract them
What is an important thing to remember when you encounter icing and decide to leave?
A lot of airplanes recommend not making any turns with more than 5 degrees angle of bank
In what type of cloud does clear ice tend to form?
In cumuliform clouds. Try to avoid them no matter the season or temperatures
Worst icing in these clouds is between 0°C and -10°C
In what type of cloud does rime ice tend to form?
Stratiform clouds. Accumulation will be greatest between -10°C and -20°C
Anti and de-icing equipment is most effective at removing rime ice
What is the difference between de-icing and anti-icing?
De-icing: Gets rid of ice after it forms
Anti-icing: helps prevent ice from forming in the first place
When does frost form on wings and what effect does it have?
Frost wil form when the temp of the aircraft is below the dew point of the surrounding air and below freezing
Frost that is like medium to coase sandpaper will:
* decrease wing lift by 30%
* increase drag by 40%
What is cold soaked fuel?
At high altitudes where its very cold, fuel tanks in the wings can retain that cold temp when you descend into warmer air.
You will get patches of ice above and below the fuel tank where the warm moist air comes into contact with the still freezing metal over the fuel tanks.
