Transcript CHAPTER 10 ICING

CHAPTER 10 ICING
ICING
• Aircraft accidents generally occur after a series
of events place a pilot in a box from which he
cannot escape. Having knowledge of icing and
how it affects your aircraft may prevent the last
side of the box from closing. Ice is a Cumulative
hazard
HOMEWORK
• READ CHAPTER 10
• Thursday AOPA’S Weather Wise: Precipitation
and Icing is due
• Many additional free online courses can be found
at the following link. Highly recommend doing
the icing course it may help with Thursday’s
quiz.
• https://www.faasafety.gov/login/reg/Register.aspx
SUPER-COOLED WATER
DROPLETS
• When ice crystals are warmed to above freezing
temperatures, they melt. On the other hand,
when water droplets are cooled to below freezing
they will not freeze until very cold temperatures
are reached. Water droplets in this state are
called “super-cooled”. If these droplets impact
on an aircraft at below freezing temperatures, the
jar will cause them to freeze and they will coat
the aircraft with ice.
ICING ON AIRCRAFT
• Ice disrupts the smooth laminar flow over
airfoils or rotors causing a decrease of lift
and an increase in the stalling speed.
• Also increases the drag and weight of the
aircraft.
ICING ON AIRCRAFT
• Uneven shedding of ice from propellers or
rotors can cause destructive vibrations.
• Water can freeze around control surfaces
and restrict their movement. Pitot heads
and static vents can be blocked causing
erroneous altimeter, airspeed and VSI
indications
ICING ON AIRCRAFT
• Antennas can break off with resultant loss
of communications and navaids.
• Ice can cover windscreens and block vision
(storm window)
• Undercarriage and brakes can freeze from
splach during take-off and become
inoperative.
• Power can be lost from engines.
ICING ON AIRCRAFT
• Fuel consumption will increase because of
increased drag and weight.
• Even the use of de-icing/anti-icing will
increase the fuel consumption due to the
amount of energy required to eliminate the
ice.
• After time de-ice/anti-icing equipment
reduce in affectiveness.
AIRFRAME ICING
• Results when super-cooled water strikes
portions of the airframe that are colder than
0 degrees C. The greater the amount of
super-cooled water, the worse the icing.
• The larger the liquid water content in a
cloud the more severe the icing.
• In most cases you need to be flying through
visible water such as rain or cloud
droplets in order to have structural icing.
LIQUID WATER CONTENT
• I’ve flown a PA-31T in Argentina
through a developing TCU with liquid
water content so high you could see the
ice forming on the leading edges of the
wings. In 15 seconds we had 5 inches
of ice.
• Strong vertical currents are necessary
to prevent large droplets from falling
out of a cloud.
LIQUID WATER CONTENT
• Strongest icing can be suspected in TS, in
clouds formed by abrupt orographic lift and
in lee wave clouds (mountain waves).
• In the winter environment aircraft structural
icing is most likely to have the highest rate
of accumulation in Thick stratified clouds
producing continuous rain. Especially near
the top of the clouds.
TEMPERATURE EFFECTS
• Warm air can hold more water vapour
than cold air. For this reason, the
amount of water droplets condensed
out is greater in cloud formed in warm
air masses. The warmer the cloud base
suspect more severe icing.
TEMPERATURE EFFECTS
• Larger droplets begin to freeze
spontaneously to ice crystals at around
-10 C and as droplets get smaller,
colder temps are required to freeze
them. By -40 C virtually are droplets
will have frozen.
• The rate of freezing increases
dramatically at temperatures just below
-15 C
TEMPERATURE EFFECTS
TEMPERATURE EFFECTS
• When water droplets and ice crystals exist
together in a cloud, there is a tendency for the
water droplets to evaporate and for the resulting
water vapor to sublimate on the ice crystals. The
crystals therefore, grow rapidly and begin to
settle downward. As they fall, they rapidly
deplete the liquid water content throughout the
cloud.
TEMPERATURE EFFECTS
• When ice crystals start to form and fall from above
the risk of sever icing greatly decreases.
• Icing tends to be heaviest near cloud tops unless the
tops are quite cold. Heaviest near -15 to -5 C
• Expect ice between 2 to -20 C
THE FREEZING PROCESS
• The rate of freezing after impact depends on the
temperature of the aircraft skin and on the air
temperature
RIME CLEAR MIXED ICE
TYPES OF ICE
• Three types of Ice: Rime, Clear, and Mixed
• Rime is ice which is rough, milky and opaque in
appearance and is formed by the almost
instantaneous freezing of small super-cooled
water dropeltes. It will usually form only on the
leading deges of airfoils and tends to build
forward into the air-stream, forming finger and
ridges. Tends to be lighter in weight
• Easy to remove (brittle) with de-icing equipment
such as boots.
• More common to form in Stratified Clouds
RIME ON A CONVAIR
TYPES OF ICE
• Clear ice has high advesive and cohesive
properties (harder to get rid of). Unlike rime it
can spread from the leading edges, and in sever
cases may cover the whole surface of the aircraft.
• Can look very transparent and glass-like to a
very tough opaque surface. Clear ice is formed
when large super-cooled water droplets collide
with the air frame and freeze slowly after impact.
• The free water then flows back over the airfoil
surfaces as it freezes at temperaturs not far below
freezing. Tends to be heavier in weight than
rime ice
CLEAR
• More common to
form in
Cummuliform
Clouds
TYPES OF ICE
• Mixed Ice is a mixture of Rime and clear ice
• frequently the temperature and the range of
droplet sizes are such that the ice formed is a
mixture.
ICING SEVERITY
INTENSITY OF ICING
• Trace - Ice becomes perceptible. The rate of
accretion is slightly greater than the rate of
sublimation. It is not hazardous even though deicing/anti-icing equipment is not utilize, unless
encountered for an extended period of time (over
1 hour)
• Light - The rate of accretion may create a
problem if flight is prolonged in this environment
(over one hour). Occasional use of de-icing/antiicing equipment removes/prevents accretion.
INTENSITY OF ICING
• Moderate - the rate of accretion is such that even
short encounters become potentially hazardous
and the use of de-icing/anti-icing equipment, or
diversion, is necessary.
• Severe - the rate of accretion is such that deicing/anti-icing equipment fails to reduce or
control the hazard. Immediate diversion is
necessary.
• What is considered moderate icing for one
aircraft may be only light for another.
IT’S BAAADDD!
• 1. Increases weight
• 2. Reduces lift - changes the shape of
the airfoil
• 3. Decreases thrust - effects prop
• 4. Increases drag - sticks up into the
wind
TO GET ICING
• 1. Must have visible water
• 2. Aircraft must be below freezing
• Icing is most frequent between +2C
and -20C
• 3000 ft up or down will normally
get you out of the ice.
LOOKS LIKE ICE TO ME, ZEKE
Better chance of icing
INDUCTION SYSTEM ICING
• Induction areas have small radius
edges allowing ice to build up more
rapidly
• Jet engine nacelles have heat
• Reciprocating engines have
alternate air doors and carb heat
CARBURATOR ICE
• Adiabatic expansion in the venturi
lowers air temp
• Moisture freezes restricting air flow
• Usually accumulates in curves or
where there are obstructions in the flow
ICING AND CLOUD TYPES
• Low and middle clouds is usually
where the ice is located
• freezing rain is the most hazardous
icing condition
• High clouds have very little chance of
icing since these clouds are composed
of ice crystals
WHERE IS THE ICE?
• Ice is usually found within 5000 feet
above the freezing level
• Usually only about 2000 - 3000 feet
thick between 0º C and -15º C
• More rain means more ice when below
freezing
SUPERCOOLED WATER
• May be found at temps as low as - 40º F (C)
• Freezing of pure water is called
spontaneous nucleation
• enough molecules must join together in a
ridged pattern to form an ice crystal
• it must grow to a critical size then other
molecules will attach and the whole drop
freezes
TERRAIN
• Mountain areas are good place to find
ice
• up currents lift water droplets above
the freezing level
• your usually flying higher to avoid the
terrain and Presto ice
GROUND ICING
• Taxiing through puddles when temp is at or
below 32
• accumulate water and or mud
• problem for retracts
• warm hanger is the only remedy
• deicing the wing may be accomplished with
a 50/50 mix of isopropyl alcohol and water
• watch out for aircraft washers in winter
FREEZING RAIN
• Rain and drizzle tend to form severe clear ice.
FREEZING RAIN
• With a warm front approaching ice pellets on the
surface generally lead to freezing rain on the
surface or aloft prior to frontal passage.
FREEZING DRIZZLE
• Drizzle evaporates to some extent
as it falls to the ground so the icing
will be the most severe just near the
cloud base.
• Ice pellets encounter during flight
normally indicate warm air
above
SNOW AND ICE CRYSTALS
• Dry snow and ice crystals will not adhere to an
aircraft and will not normally cause icing. If the
portion of the aircraft skin that they strike is
above freezing, they may melt and freeze as they
flow back over below-freezing portions of the
aircraft.
• Flying in ice crystals can create a lot of static
making radio communication difficult.
Especially in the anvial of a TS.
• High clouds normally have a much lower ice
accumulation rate.
ICING IN CLEAR AIR
• Hoar Frost - This term is used to indicate a white,
feathery, crystalline formation that can cover the
entire surface of the aircraft. It is similar to the
ice that occasionally forms on metal surfaces
such as car roofs during clear cool winter nights.
• Hoar frost forms by sublimation or, by water
vapour which changes directly into ice crystals
without going through the water stage. Occurs
when moist air comes in contact with an object at
temperatures below freezing.
ICING IN CLEAR AIR
• Hoar froast is typically going to
form on aircraft when their surfaces
are at temperatures sufficiently
below freezing and the surround air
is warmer and moist.
• Can also form in flight, especially
during descents into warmer, moist
air. Usually near fuel tanks.
FROST
• Collects when the surface and the Dew
point are below freezing and the temp
cools to the dew point
• little crystals form fingers that interrupt
the boundary layer
• polish the frost smooth then your good
to go
• Frost can cause early airflow separation
resulting in a loss of lift.
AERODYNAMIC FACTORS
• Three things affect how much ice a wing will
obtain.
• Curvature radii of wing, aircraft speed, and
droplet size.
AERODYNAMIC FACTORS
• The large curvature radii (thick wings) creates
less ice. The slower you are flying creates less
ice. The smaller the droplet size = less ice.
AERODYNAMIC FACTORS
• Aerodynamic heating in faster aircraft can
actually be to the point of making it impossible
for ice to form on leading edges.
ENGINE ICING
• Carburetor Icing - frequently causes engine
failure without warning. Can occur under
conditions where structural icing may not occur
and even in cloud less skys with temperatures as
high as 25-30 degrees C.
• Carburetor Ice forms during vaporization of fuel,
combined with the expansion of air as it passes
through the carburetor. Of the two cooling
processes, fuel vaporization causes the greater
temperature drop. This may amount to as much
as 40 degrees C
CARBURETOR ICING
DEICING AND ANTIICING
• Deicing-used to remove ice from a surface.
• Anti-icing- the prevention of ice from forming
BOOTS
DEICING AND ANTIICING
• Deicing-used to remove ice from a
surface. Hot Props, Leading
edge/trailing edge boots, ice doors
• Anti-icing- the prevention of ice
from forming. Alcohol chemicals,
pitot-heat, stall warning vain heat,
static port heat, wepping
wings/windshield/props etc.
ACCUMULATES ON SMALL
THIN AREAS FIRST
TAIL STALLS
ICING TIPS
BRAKING ACTION
QUESTIONS
• #1. Can water droplets exist as
super-cooled water at temperatures
below zero degrees C?
• yes
• #2. Name the three types of ice?
• Rime, Clear, Mixed
QUESTIONS
• #3 Which is easier to shed from an
aircraft Rime or Clear Ice?
• Rime
• #4. If you have Ice pellets on the
surface what can you have aloft?
• Freezing Rain
QUESTIONS
• #5. What are the four intensities of
icing?
• Trace, Light, moderate, severe
• #6. Aerodynamic heating can keep the
aircraft skin above freezing and
prevent ice, but speeds in excess of 500
knots may be required (true/false)?
• True
QUESTIONS
• #7. Collection efficiency of wings is
high for (sharp/shallow) leading edges,
(high/low) speeds, and (large/small)
droplets.