Aircraft Icing - Weather S/LMK_Icing_Show.pdf · –The aircraft‟s skin remains cold for a time....
Transcript of Aircraft Icing - Weather S/LMK_Icing_Show.pdf · –The aircraft‟s skin remains cold for a time....
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Aircraft Icing
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• Affects of icing
• Causes
• Ice formation
• Types of icing
• Icing and cloud types
• Freezing precipitation
• Sources of Information
Items in This Discussion
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• Liquid water content (LWC)
• Temperature
• Droplet size
• Cloud type
• Airfoil geometry
• Airspeed
• Duration of exposure
Icing Factors
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Ice Formation
• Ice forms first on the shortest radius of
curvature
Shortest Radius
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Cumulative Affects of Icing
Decreases Lift
Increases Weight
IncreasesDrag
DecreasesThrust
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Types of Icing
• Clear
• Mixed
• Induction (Carburetor)
• Rime
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Occurrence of Icing
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• NOT caused by ICE in clouds.
• Is caused by “Super-cooled” liquid water
droplets
– Strike the leading edge of an airfoil
– Freeze on impact
The Cause of Icing
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• Begin with water in liquid form (>32 F)
• Water is cooled rapidly, usually by “lifting”
• Super cooled water drops may also form via
– condensation
– lack of activated ice nuclei
• There does NOT have to be a warm layer for super cooled water to form.
• Climb to warm layer may not be possible
“Super-Cooled Water” Formation
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Liquid Water Content (LWC)
• Amount of
available water
• Varies from
cloud to cloud
• Varies within
same cloud
Useful only in Stratiform Clouds
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Temperature
• Most icing tends to occur at temperatures
between 0° and -20°C
– More than 50% of those occur between -8 and -12° C
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Temperature
• „Cold Soaked‟ Aircraft can be a cause
– Sustained flight in below freezing air
– Descends to warm air, but…
– The aircraft‟s skin remains cold for a time.
•The aircraft must be in cloud
(visible water droplets) for icing
to occur
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Water Droplet Size
• Icing patterns change with droplet size. But...
• In relation to icing hazards
– Droplet size not as important as
– LWC and
– Temperature
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Rime Icing
• Is opaque
• Easily seen
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Rime Icing
Small drops
Leading
edge of
Wing
Trapped air
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Rime Icing
• Tends to form at
leading edge of airfoil
• More easily for de-icing
equipment to remove
Rime
Clear
•Compare with “horns” of
Clear icing
Gray is region where air is stagnant
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Clouds and Droplet Size
• Cumulus - Large drops
• Stratus - Small drops
• High clouds - Ice crystals
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Icing Vs. Cloud Type: Stratiform
Small Cloud Droplets
• Rime/Mixed most common
• Usually confined to layer 3,000-4,000‟ thick
• Max values occur in upper part of cloud
• Large horizontal extent
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Icing Vs. Cloud Type: Cumuliform
Large Cloud Droplets
• Icing found in “updraft” portion of cloud
• Heavy rime most frequently in cloud tops
• Clear icing most likely in building Cu
• Rime often found in fully developed TS
• Relatively small horizontal extent
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Icing Vs. Cloud Type
• Previous statements „generally‟ true…
• BUT research has found…
– Mixed-phase clouds of all types may harbor
sufficient amounts of Super- Cooled water.
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Occurrence of Icing
• Aircraft type and speed affect icing
occurrence
Wheee ! Brrrrrrr !
Same route & altitude
No Ice Loads of ice
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Freezing Rain
• Heavy icing in short time
• Warm air/moisture over-running Cold air
• Begins as rain,
– Then falls through Cold air
– Becomes „Super Cooled Water‟
– Freezes on impact
• Best maneuver may be to gain altitude
– Check with a weather briefer first!
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Freezing Rain
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Information Sources
• Pilot Weather Briefings
• Internet
– aviationweather.gov
– AOPA
– DUATS
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Expanded version of this presentation
• Narrated, web based slide show
• Will be posted on the Indianapolis web site
• Email me to be notified when it‟s posted.
• http://weather.gov/ind
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The
End
ThankYou