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R.V. COLLEGE OF ENGINEERING,BANGALORE-560059(Autonomous Institution Affiliated to VTU, Belgaum)

DE-ICING OF AIRCRAFT

SELF STUDY REPORT

Submitted by BHADRI RAJASAI USN 1RV12ME023V Semester, A SectionFaculty Incharge Dr. K.BADARINARAYANProfessorDepartment of Mechanical Engineering, R V College of Engineering Submitted toDEPARTMENT OF MECHANICAL ENGINEERINGR.V. COLLEGE OF ENGINEERING, BANGALORE - 560059(Autonomous Institution Affiliated to VTU, Belgaum)

DEPARTMENT OF MECHANICAL ENGINEERING R.V. COLLEGE OF ENGINEERING, BANGALORE-560059(Autonomous Institution Affiliated to VTU, Belgaum)

CERTIFICATECertified that the Self Study work titled De-Icing of aircraft is carried out by Bhadri Rajasai (1RV12ME023), who is a bonafide student of R.V College of Engineering, Bangalore, in partial fulfillment for the Continuous Internal Evaluation (CIE) in the Self Study component for the V semester during the year 2014-2015. It is certified that all corrections/suggestions indicated for the internal assessment have been incorporated in the report deposited in the departmental library. The Self Study report has been approved as it satisfies the academic requirements in respect of Self Study work prescribed by the institution for the said subject.

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Marks awarded = (Evaluation1+ Evaluation2) =20

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Signature of Staff In-charge Signature of Head of the Department

ACKNOWLEDGEMENT

I Bhadri Rajasai would like to thank RVCE for giving me this golden opportunity to work on this project De-icing of Aircraft. Working on this project was an enriching experience. The knowledge gained throughout the development of this project was valuable and priceless.

The project would be incomplete without the help of my teachers. Their guidance and suggestions helped me script this paper.

I would also like to thank my parents, for their continuous support. Encouragement and suggestions from friends is also acknowledged. I also take this opportunity to thank my fellow group members for all their continuous support and help.

ContentsINTRODUCTION5Why Ice Is Bad5Kinds of Ice and Their Effects on Flight5Structural Ice6Wing Stall6Effects of Icing on Roll Control6What Is a Tail Stall?7Deicing and Anti-Icing Equipment7Ice Detection8Propeller Anti-Icers8Windshield Anti-Icers9Thermal Heat9Boots10Weeping Wing10Electro-impulse Deicing11Induction System11References14

INTRODUCTIONWhy Ice Is BadIce in flight is bad news. It destroys the smooth flow of air, increasing drag while decreasing the ability of the airfoil to create lift. The actual weight of ice on an airplane is insignificant when com- pared to the airflow disruption it causes. As power is added to compensate for the additional drag and the nose is lifted to maintain altitude, the angle of attack is increased, allowing the underside of the wings and fuselage to accumulate additional ice. Ice accumulates on every exposed frontal surface of the airplane not just on the wings, propeller, and windshield, but also on the antennas, vents, intakes, and cowlings. It builds in flight where no heat or boots can reach it. It can cause antennas to vibrate so severely that they break. In moderate to severe conditions, a light aircraft can become so iced up that continued flight is impossible. The airplane may stall at much higher speeds and lower angles of attack than normal. It can roll or pitch uncontrollably, and recovery might be impossible.

Ice can also cause engine stoppage by either icing up the carburetor or, in the case of a fuel-injected engine, blocking the engines air source.Kinds of Ice and Their Effects on Flight Structural ice is the stuff that sticks to the outside of the airplane. It is described as rime, clear (sometimes called glaze), or mixed. Rime ice has a rough, milky white appearance, and generally follows the contours of the surface. Much of it can be removed by deice systems or prevented by anti-ice. Clear (or glaze) ice is sometimes clear and smooth, but usually contains some air pockets that result in a lumpy, translucent appearance. The larger the accretion, the less glaze ice conforms to the shape of the wing; the shape is often characterized by the presence of upper and lower horns. Clear ice is denser, harder, and more transparent than rime ice, and is generally hard to break. Mixed ice is a combination of rime and clear ice.

Ice can distort the flow of air over the wing, diminishing the wings maximum lift, reducing the angle of attack for maximum lift, adversely affecting airplane handling qualities, and significantly increasing drag. Wind tunnel and flight tests have shown that frost, snow, and ice accumulations (on the leading edge or upper surface of the wing) no thicker or rougher than a piece of coarse sandpaper can reduce lift by 30 percent and increase drag up to 40 percent. Larger accretions can reduce lift even more and can increase drag by 80 percent or more. Even aircraft equipped for flight into icing conditions are significantly affected by ice accumulation on the unprotected areas. A NASA study (NASA TM83564) showed that close to 30 percent of the total drag associated with an ice encounter remained after all the protected surfaces were cleared. Non protected surfaces may include antennas, flap hinges, control horns, fuselage frontal area, windshield wipers, wing struts, fixed landing gear, etc.Some unwary pilots have, unfortunately, been caught by surprise with a heavy coating of ice and no plan of action. Many pilots get a weather briefing and have little or no idea how to determine where icing may occur. However, pilots can learn enough basic meteorology to understand where ice will probably be waiting after they get their weather briefing. The pilot can then formulate an ice avoidance flight plan before ever leaving the ground.

Structural IceHow quickly a surface collects ice depends in part on its shape. Thin, modern wings will be more critical with ice on them than thick, older wing sections. The tail surfaces of an airplane will normally ice up much faster than the wing. If the tail stalls due to ice and the airflow disruption it causes, recovery is unlikely at low altitudes. Several air carrier aircraft have been lost due to tail stalls. It also happens to light aircraft but usually isnt well documented.

Since a tail stall is less familiar to many pilots, it is emphasized in this advisor, but a wing stall is the much more common threat, and it is very important to correctly distinguish between the two, since the required actions are roughly opposite.

Wing StallThe wing will ordinarily stall at a lower angle of attack, and thus a higher airspeed, when contaminated with ice. Even small amounts of ice will have an effect, and if the ice is rough, it can be a large effect. Thus an increase in approach speed is advisable if ice remains on the wings. How much of an increase depends on both the aircraft type and amount of ice.

Stall characteristics of an aircraft with ice-contaminated wings will be degraded, and serious roll control problems are not unusual. The ice accretion may be asymmetric between the two wings. Also, the outer part of a wing, which is ordinarily thinner and thus a better collector of ice, may stall first rather than last.

Effects of Icing on Roll ControlIce on the wings forward of the ailerons can affect roll control. Wings on general aviation (GA) aircraft are designed so that stall starts near the root of the wing and progresses outward, so the stall does not interfere with roll control of the ailerons. However, the tips are usually thinner than the rest of the wing, so they are the part of the wing that most efficiently collects ice. This can lead to a partial stall of the wings at the tips, which can affect the ailerons and thus roll control.If ice accumulates in a ridge aft of the deice boots but forward of the ailerons, this can affect the airflow and interfere with proper functioning of the ailerons. If aileron function is impaired due to ice, slight forward pressure on the elevator may help to reattach airflow to the aileron.

What Is a Tail Stall?The horizontal stabilizer balances the tendency of the nose to pitch down by generating downward lift on the tail of the aircraft. When the tail stalls, this downward force is lessened or removed, and the nose of the air- plane can severely pitch down. Because the tail has a smaller leading edge radius and chord length than the wings, it can collect proportionately two to three times more ice than the wings and, often, the ice accumulation is not seen by the pilot. (Perkins and Reike, In- Flight Icing)

Deicing and Anti-Icing Equipment

Many aircraft have some, but not all, the gear required for approved flight into icing conditions. In some cases, the equipment has been added as an after-market modification. Although it may give the pilot more time to escape an icing encounter, it has not been tested in the full range of conditions and, therefore, does not change the aircrafts limitation prohibiting flight into icing. Plan to avoid icing conditions, but if you experience unexpected ice build up, use the equipment to escape do not depend on it for prolonged periods, particularly in moderate or heavier ice.

Ice Detection Electronic ice detection common, but can give false readings GM is developing a mass based ice detection system where ice builds up on external probe 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 conditionsTypes 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 wingsPropeller Anti-Icers Ice usually appears on propeller before it forms on the wing Can be treated with chemicals from slinger rings on the prop hub 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

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 windshieldsElectro-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

Induction System Not all aircraft ice is structural; induction icing is the cause of many accidents. There are two kinds of induction system icing: carburetor icing, which affects engines with carburetors, and air intake blockage, which affects both carbureted and fuel- injected engines. Induction icing accidents top the charts as the number one cause of icing accidents, comprising a whopping 52 percent.Unless preventive or corrective measures are taken, carburetor icing can cause complete power failure. In a normally aspirated engine, the carburetion process can lower the temperature of the incoming air as much as 60 degrees Fahrenheit. If the moisture content is high enough, ice will form on the throttle plate and venturi, gradually shut- ting off the supply of air to the engine. Even a small amount of carburetor ice will result in a power loss, indicated by reduced rpm with a fixed-pitch propeller and a loss of manifold pressure with a constant-speed propeller, and may make the engine run rough.

Carburetor icing

It is possible for carburetor ice to form even when the skies are clear and the outside air temperature is as high as 90 degrees Fahrenheit, if the relative humidity is 50 percent or more particularly when engine rpm is low. This is why, when flying most airplanes with carbureted engines, students are drilled to turn on the carburetor heat before making a significant power reduction. Carburetors can, however, ice up at cruise power when flying in clear air and in clouds. The envelope for the most severe buildups of carburetor ice is between 60 and 100 percent relative humidity and 20 to 70 degrees Fahrenheit.

At the first indication of carburetor ice, apply full carburetor heat and LEAVE IT ON. The engine may run rougher as the ice melts and goes through it, but it will smooth out again. When the engine runs smoothly, turn off the heat. (If you shut off the car- buretor heat prematurely, the engine will build more iceand probably quit because of air starvation.) The engine rpm should return to its original power setting. If the rpm drops again, fly with the carb heat on. Do not use partial heat.

With carburetor heat on, the hot air is less dense, so the mixture becomes richer, and as a result, the rpm will drop a bit further. Lean the mixture, and most of the rpm loss should return. If you dont lean, fuel consumption increases. A number of fuel exhaustion accidents have resulted from miscalculations.

If carburetor heat is used for landing and you decide to go around, advance the throttle smoothly, then remove the carb heat. This will ensure all available power for takeoff.

Fuel-injected engines have no carburetor and, therefore, no carburetor ice problem. However,when conditions are favorable for structural ice, fuel- injected engines can lose power and even fail if the air filter and intake passages are blocked by ice. (This can also occur in airplanes with carburetors.) At the first sign of power loss, activate the alternate induction air door or doors. When these doors open, intake air routes through them, bypassing the ice- blocked normal induction air pathway. Many alter- nate induction air systems activate automatically; these designs use spring-loaded doors. Suction in an ice-blocked air intake draws these alternate air doors open. Some older fuel-injected airplanes have alter- nate air doors that must be manually opened. Knobs or levers have to be physically moved to the open position in order for alternate air to reach the engine. Check the POH for your airplane to find out how and when to use this system.

Note: Both carburetor heat and alternate air sources use unfiltered air. They should be closed when on the ground, unless conditions are conducive to engine icing while taxiing.

References Airplane Design, Pt 4. Roskam http://www.aopa.org/asf/publications/sa11.pdf#search=%22anti-icing%20systems%20aircraft%22 http://www.newpiper.com/promo/PIIPS/images/PIIPSPropSlingerRing.jpg http://www.fas.org/man/dod-101/sys/ac/c-130.htm http://www.airs-icing.org/AIRS_II/AIAAReno2006/AIAA-2006-206-739.pdf#search=%22transport%20ice%20%22in%20flight%22%22 www.p2pays.org/ref/07/06047.pdf Ice Pictures http://www.idiny.com/eidi.html

DEPARTMENT OF MECHANICAL ENGINEERING