Aircraft Icing 飞机积冰
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• Liquid Water Content (LWC) (More water relates to more icing) • Air Temperature (Temperature influences how fast the droplets freeze) • Effective Droplet Diameter (larger droplets take longer to freeze and will roll back on wings)
Aircraft Icing
US-China Aviation Cooperation Program (ACP) Embry-Riddle Training Frederick Mosher
D. C. Pearson, 2002
Part I: Icing Impacts on Aircraft Performance
Implies that wing tips and tail surfaces will first be affected by icing. Also implies that small drone aircraft will be susceptible to icing.
Icing Effects Various Wing Shapes Differently
(Cessna, Beech, EMB) (P-3)
(Piper, Spitfire)
(ATR-42/72)
(Twin Otter)
Different study with other airfoils. Wide variability among airfoils for susceptibility to icing. Twin Otter (DH-6 and C130 least susceptible)
Icing in Cloud Conditions
PPI is Percent Power Increase required to maintain speed. PPI is an indication of effect of icing on aircraft performance.
LWC=Liquid Water Content MVD=Mean droplet diameter T=Air temperature t=time of exposure (5 min) V=aircraft velocity (90m/sec)
5 Minute Exposure Time
15 Minute Exposure Time
30 Minutes Exposure Time
45 Minute Exposure Time
Note the “horns”
Effect of Exposure Time to Icing
Large drizzle size drops (clear icing)
Time of Exposure to Icing
• The pilot has some control of the time spent in icing conditions. • The build up of ice is not linear. • Twice the time in icing conditions means more than twice the ice problem.
(stability and control)
Rime Icing
• Small droplets with trapped air.
Clear Icing
• Larger droplets with little trapped air.
Mixed Icing
• Mixed drop size distribution.
• What factors affect the buildup of ice on aircraft? • How does the buildup of ice affect the plane’s performance? • What can you do to minimize the impact of icing on your airplane?
Icing Accumulation Program Developed by NASA-Lewis Cases run by Don McCann (AWC Forecaster)
Airfoil is Cessna wing. Program calculates coefficient of lift and drag
Deicing Turned Off
Note freezing rain size drops
Uniform coating of ice. Airfoil shape not change much.
Deicing Turned On
While deicing got rid of the ice on the leading edge, the roll back caused lumps of ice to form on the wing top, drastically increasing drag.
Low liquid water
Increasing LWC in cloud
Increasiect of LWC on Icing Intensity
More liquid water: more icing, but results are temperature dependent. More performance degradation in -10 to -20 C range.
Aerodynamic Factors Affecting Ice Accumulation
• Air Speed (faster speed impacts more droplets) • Angle of attack (where on wings ice accumulates) • Airfoil shape (variable icing effects) • Airfoil size (smaller wings ice more) • Time spent in icing conditions (ice builds up with exposure time)
Slow Airplane
Note negative PPI. Icing actually improved performance slightly by changing wind shape.
Faster Airplane
Fast Airplane Gets More Icing
Effect of Aircraft Speed
Part II: Meteorological Conditions Necessary for Icing
Zero Angle of Attack
8 Degree Angle of Attack
Effect of Angle of Attack
Small Wing-Major Icing
Larger Wing-Less Impact
Very Large Wing-Little Effect
Effect of Wing Size on Icing
Icing Type Frequency of Occruance
Big Jets Icing
Medium Size Aircraft Icing
Note most icing pilot reports come from windshield ice rather than wing ice.
Small Airplane Icing
Note that pilot used deicing equipment for leading edge
Research Aircraft Icing
Note the buildup of ice as “horns”
Meteorological Factors Affecting Ice Accumulation
Small cloud size droplets (rime icing)
Deicing Equipment to Get Rid of Ice on Wings – Why Worry about Icing?
Will work well for rime ice on leading edge of wing. However large drops will roll back on wing beyond deicing boots.
“Conventional wisdom” says larger droplet cause more severe icing (clear icing worse than rime).
Simulation does not show this. All icing types can cause performance degradation
Icing Simulation
• After Roselawn crash NASA-Lewis (now NASAGlenn Research Center) developed software to simulate the effects of icing on aircraft. • Icing increases parasitic drag and decreases lift, resulting in degradation of aircraft performance.
The ice builds up rapidly with time. Minimize the time of exposure to icing by changing altitudes or turning around.
Note log scale; i.e. icing severity is not linear with time.
Ice lump
Summary Part I
• • • • • • LWC – More water – more icing Temperature –10 to –15C worst range Droplet diameter – little effect Plane speed – slower speed - less icing Wing angle of attack – worse near 0 deg Wind size – little wings – more icing
Effect of Temperature on Icing Intensity
•
Worst performance degradation near -10 to -15 C temperature range for a typical cloud LWC.
Effect of Droplet Diameter on Icing
Summary Part I(cont)
• Exposure time most critical factor in icing • If caught in an icing situation, get out as soon as possible. Change altitude or turn around. • Monitor your wings when the deicing is turned on. Roll back of droplets past the deicing can cause lumps to build up with large increases in drag.
Aircraft Icing
US-China Aviation Cooperation Program (ACP) Embry-Riddle Training Frederick Mosher
D. C. Pearson, 2002
Part I: Icing Impacts on Aircraft Performance
Implies that wing tips and tail surfaces will first be affected by icing. Also implies that small drone aircraft will be susceptible to icing.
Icing Effects Various Wing Shapes Differently
(Cessna, Beech, EMB) (P-3)
(Piper, Spitfire)
(ATR-42/72)
(Twin Otter)
Different study with other airfoils. Wide variability among airfoils for susceptibility to icing. Twin Otter (DH-6 and C130 least susceptible)
Icing in Cloud Conditions
PPI is Percent Power Increase required to maintain speed. PPI is an indication of effect of icing on aircraft performance.
LWC=Liquid Water Content MVD=Mean droplet diameter T=Air temperature t=time of exposure (5 min) V=aircraft velocity (90m/sec)
5 Minute Exposure Time
15 Minute Exposure Time
30 Minutes Exposure Time
45 Minute Exposure Time
Note the “horns”
Effect of Exposure Time to Icing
Large drizzle size drops (clear icing)
Time of Exposure to Icing
• The pilot has some control of the time spent in icing conditions. • The build up of ice is not linear. • Twice the time in icing conditions means more than twice the ice problem.
(stability and control)
Rime Icing
• Small droplets with trapped air.
Clear Icing
• Larger droplets with little trapped air.
Mixed Icing
• Mixed drop size distribution.
• What factors affect the buildup of ice on aircraft? • How does the buildup of ice affect the plane’s performance? • What can you do to minimize the impact of icing on your airplane?
Icing Accumulation Program Developed by NASA-Lewis Cases run by Don McCann (AWC Forecaster)
Airfoil is Cessna wing. Program calculates coefficient of lift and drag
Deicing Turned Off
Note freezing rain size drops
Uniform coating of ice. Airfoil shape not change much.
Deicing Turned On
While deicing got rid of the ice on the leading edge, the roll back caused lumps of ice to form on the wing top, drastically increasing drag.
Low liquid water
Increasing LWC in cloud
Increasiect of LWC on Icing Intensity
More liquid water: more icing, but results are temperature dependent. More performance degradation in -10 to -20 C range.
Aerodynamic Factors Affecting Ice Accumulation
• Air Speed (faster speed impacts more droplets) • Angle of attack (where on wings ice accumulates) • Airfoil shape (variable icing effects) • Airfoil size (smaller wings ice more) • Time spent in icing conditions (ice builds up with exposure time)
Slow Airplane
Note negative PPI. Icing actually improved performance slightly by changing wind shape.
Faster Airplane
Fast Airplane Gets More Icing
Effect of Aircraft Speed
Part II: Meteorological Conditions Necessary for Icing
Zero Angle of Attack
8 Degree Angle of Attack
Effect of Angle of Attack
Small Wing-Major Icing
Larger Wing-Less Impact
Very Large Wing-Little Effect
Effect of Wing Size on Icing
Icing Type Frequency of Occruance
Big Jets Icing
Medium Size Aircraft Icing
Note most icing pilot reports come from windshield ice rather than wing ice.
Small Airplane Icing
Note that pilot used deicing equipment for leading edge
Research Aircraft Icing
Note the buildup of ice as “horns”
Meteorological Factors Affecting Ice Accumulation
Small cloud size droplets (rime icing)
Deicing Equipment to Get Rid of Ice on Wings – Why Worry about Icing?
Will work well for rime ice on leading edge of wing. However large drops will roll back on wing beyond deicing boots.
“Conventional wisdom” says larger droplet cause more severe icing (clear icing worse than rime).
Simulation does not show this. All icing types can cause performance degradation
Icing Simulation
• After Roselawn crash NASA-Lewis (now NASAGlenn Research Center) developed software to simulate the effects of icing on aircraft. • Icing increases parasitic drag and decreases lift, resulting in degradation of aircraft performance.
The ice builds up rapidly with time. Minimize the time of exposure to icing by changing altitudes or turning around.
Note log scale; i.e. icing severity is not linear with time.
Ice lump
Summary Part I
• • • • • • LWC – More water – more icing Temperature –10 to –15C worst range Droplet diameter – little effect Plane speed – slower speed - less icing Wing angle of attack – worse near 0 deg Wind size – little wings – more icing
Effect of Temperature on Icing Intensity
•
Worst performance degradation near -10 to -15 C temperature range for a typical cloud LWC.
Effect of Droplet Diameter on Icing
Summary Part I(cont)
• Exposure time most critical factor in icing • If caught in an icing situation, get out as soon as possible. Change altitude or turn around. • Monitor your wings when the deicing is turned on. Roll back of droplets past the deicing can cause lumps to build up with large increases in drag.