AIR CONDITIONING, ANTI ICING & DE-ICING IN AIRCRAFTS

NS ASAD A. JANJUAPC MUBASHIR SHARIFGC HAFIZ MUDASSIRNS DANISH IFTIKHAR

AC & REFRIGERATION PRESENTATION

AIR CONDITIONING IN AIRCRAFTS

PURPOSE

• Like any other air condition system to provide passengers with comfortable air

• Pressure

• Temperature

• Humidity

• Cleanliness

WHERE DOES THE CONDITIONING AIR COME FROM?

• The air source in aircraft ECS (Environmental control system) is ultimately outside air.

• ECS take compressed air from main engines (before the combustion chambers, instead of having dedicated compressors to pump outside air (but B787 is based on the latter). This is known as the bleed air.

• The conditioning air temperature is obtained by mixing

• The hot source is the bleed air

• A cold air source from the heat exchangers

STEPS1. Air compression

2. Cooling the compressed air

AIR TEMPERATURE CONTROL SYSTEM• Can be operated

• Automatically

• Manually

WHY CANT WE USE THE AIR DIRECTLY?• To keep the cabin pressurized

• It is easier to cool hot air than warm cold air.

• Temperature at high altitudes are dramatically very low.

PRESSURIZING THE CABIN

• Cabin pressurization is the pumping of compressed air into an aircraft cabin to maintain a safe and comfortable environment for crew and passengers when flying at altitude.

• Pressurization becomes necessary at altitudes beyond 10,000 feet (3,000 m) above sea level to protect crew and passengers from the risk of a number of physiological problems caused by the low outside air pressure above that altitude; it also serves to generally increase passenger comfort.

• Examples of problems, Hypoxia, Altitude sickness, Decompression sickness

• The fuselage is pressurized from the front to the back of the cabin.

• Pressure and its rate is controlled by the amount of air outboard.

• The pressure can be controlled

• Automatically

• Manually by the flight crew

AUTOMATIC PRESSURIZATION

• Automatic pressurization controls the pressure of the cabin in accordance with the altitude of the aircraft.

• It changes with the altitude automatically and also changes during the ascend and the decent transition periods

AIRCRAFT ANTI-ICING/ DE-ICING SYSTEMS

NEGATIVE EFFECTS OF ICE BUILDUP

• Destroys smooth flow of air over wing, leading to severe decrease in lift and increase in drag forces

• As angle of attack is increased to compensate for decreased lift, more accumulation can occur on lower wing surface

• Causes damage to external equipment such as antennae and can clog inlets, and cause impact damage to fuselage and engines

• Considered a cumulative hazard because as ice builds up on the wing, it increasingly changes the flight characteristics

TYPES OF ICE

• Rime: “has a rough milky white appearance and generally follows the surface closely”

• Clear/Glaze: “sometimes clear and smooth but usually contain some air pockets that result in a lumpy translucent appearance, denser, harder and more difficult to break than rime ice”

ICE DETECTION

• Electronic ice detection common, but can give false readings

• After mass of probe has increased due to additional ice, anti-icing systems are alerted and turned on

• This increases fuel efficiency and system life as de-icing systems are only turned on as required by conditions

TYPES OF ICE REMOVAL• Anti-Icing

• Preemptive, turned on before the flight enters icing conditions

• Includes: thermal heat, prop heat, pitot heat, fuel vent heat, windshield heat, and fluid surface de-icers

• De-Icing

• Reactive, used after there has been significant ice build up

• Includes surface de-ice equipment such as boots, weeping wing systems, and heated wings

PROPELLER ANTI-ICERS• Ice usually appears on propeller before

it forms on the wing

• Graphite electric resistance heaters on leading edges of blades can also be used

WINDSHIELD ANTI-ICERS

• Liquids used include: ethylene glycol, propylene glycol, Grade B Isopropyl alcohol, urea, sodium acetate, potassium acetate, sodium formate, and chloride salts

• Chemicals are often bad for the environment

• Usually uses resistance heat to clear windshield or chemical sprays while on the ground

THERMAL HEAT

• Air Heated• Bleed air from engine heats inlet cowls

to keep ice from forming

• Bleed air can be ducted to wings to heat wing surface as well

• Ice can also build up within engine, so shutoff valves need to be incorporated in design

• Usually used to protect leading edge slat, and engine inlet cowls

• Resistance heater• Used to prevent ice from forming on

pitot tubes, stall vanes, temperature probes, and drain masts Airplane Design, Book 4, Roskam

BOOTS

• Inflatable rubber strips that run along the leading edge of wing and tail surfaces

• When inflated, they expand knocking ice off of wing surface

• After ice has been removed, suction is applied to boots, returning them to the original shape for normal flight

• Usually used on smaller planes

WEEPING WING• Fluid is pumped through mesh screen on leading

edge of wing and tail

• Chemical is distributed over wing surface, melting ice

• Can also be used on propeller blades and windshields

ELECTRO-IMPULSE DEICING

• Electromagnetic coil under the skin induces strong eddy currents on surface

• Delivers mechanical impulses to the surface on which ice has formed

• Strong opposing forces formed between coil and skin

• Resulting acceleration sheds ice from the surface

• Can shed ice as thin as 0.05”

•http://www.idiny.com/eidi.html

TYPICAL ANTI-ICING• C-130:

• Engine bleed air used for anti-icing wing and empennage leading edges, radome, and engine inlet air ducts.

• Electrical heat provides anti-icing for propellers, windshield, and pitot tubes.

• 777:

• Engine bleed air used to heat engine cowl inlets. If leak is detected in Anti-Ice duct, affected engine Anti-Ice valves close.

• Wing Anti-Ice System provides bleed air to three leading edge slats on each wing. Wing Anti-Ice is only available in flight.

QUESTIONS

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