Icing of the aircraft - conditions, causes and consequences

2024 Author: Howard Calhoun | [email protected]. Last modified: 2023-12-17 10:16

Statistics show that the percentage of deaths in air crashes is much lower than in cases with other modes of transport. Aircraft icing is a common cause of accidents, so the fight against it is given increased attention. In the event of a train, ship or car accident, people have a fairly high chance of surviving. The fall of air liners, with rare exceptions, leads to the death of all passengers.

What causes icing

The following parts of the aircraft body are most often exposed to icing:

• tail and wing leading edges;
• engine air intakes;
• propeller blades for respective engine types.

The formation of ice on the wings and tail leads to an increase in drag, a deterioration in the stability and controllability of the aircraft. In the worst cases, the controls (ailerons, flaps, etc.) can simply freeze to the wing, and the control of the aircraft will be partially or completely paralyzed.

Icing of the air intakes disrupts the uniformity of the air flows entering the engines. The consequence of this is the uneven operation of the motors and the deterioration of traction, failures in the operation of the units. Vibrations appear that can lead to the complete destruction of engines.

In propeller-fan and turboprop aircraft, icing on the edges of the propeller blades causes a serious reduction in flight speed due to a drop in the efficiency of the propellers. As a result, the vessel may not “make it” to its destination, as the fuel consumption at a lower speed remains the same or even increases.

Aircraft ground icing

Icing can be on the ground or in flight. In the first case, the aircraft icing conditions are as follows:

• In clear weather at sub-zero temperatures, the surface of an aircraft cools more than the surrounding atmosphere. Because of this, the water vapor contained in the air turns into ice - frost or frost occurs. The thickness of the plaque usually does not exceed a few millimeters. It can be easily removed even by hand.
• At near-zero temperatures and high humidity, supercooled water contained in the atmosphere settles on the body of the aircraft in the form of plaque. Depending on specific weather conditions, the coating varies from transparent at higher temperatures to a matte frost-like coating at lower temperatures.
• Freezing on the surface of the aircraft fog, rain or sleet. It is formed not only as a result of precipitation, but also when snow and slush hit the hull from the ground during taxiing.

There is also such a kind of phenomenon as "fuel ice". When the kerosene in the tanks has a lower temperature than the surrounding air, atmospheric water begins to settle in the area where the tanks are located and ice forms. The layer thickness sometimes reaches 15 mm or more. This type of aircraft icing is dangerous because the sediment is most often transparent and difficult to notice. In addition, sediment forms only in the fuel tank area, while the rest of the aircraft body remains clean.

Icing in the air

Another type of aircraft icing is the formation of ice on the ship's hull during the flight. Occurs when flying in cold rain, drizzle, sleet or fog. Ice forms most often on wings, tails, engines and other protruding body parts.

The rate of formation of an ice crust varies and depends on both weather conditions and aircraft design. There have been cases of plaque formation at a speed of 25 mm per minute. The speed of the aircraft here plays a dual role - up to a certain threshold, it contributes to an increase in the icing of the aircraft due to the fact that more moisture falls on the surface of the aircraft per unit time. But then, with further acceleration, the surface heats up from friction with the air, and the intensity of ice formation decreases.

Icing of an aircraft in flight occurs most often at altitudes up to 5,000 meters. Therefore, in advance, utmost attention is paid to the study of weather conditions in the area.takeoff and landing. Icing at high altitudes is extremely rare, but still possible.

De-icing with POL

The main role in the prevention of icing is played by the treatment of aircraft with anti-icing fluid (AFL). The leaders in the production of deicing agents are the American The Dow Chemical Company and the Canadian Cryotech Deicing Technology. Companies are constantly expanding and improving the line of their reagents.

Priority areas of research are the speed of deicing and the duration of aircraft deicing. Different types of anti-icing fluid are responsible for these processes, so the processing of the aircraft is always carried out in two stages. In total, there are four types of reagents that are used in the processing of an aircraft. Fluids of the first type are responsible for removing existing ice from the aircraft body. Compositions II, III and IV types serve to protect the body from icing for a certain time.

Processing the aircraft on the ground

First, the aircraft is treated with type I fluid diluted with hot water to a temperature of 60-80 0C. The concentration of the reagent is chosen based on weather conditions. A dye is often included in the composition so that the maintenance personnel can control the uniformity of the coating of the aircraft with liquid. In addition, the special substances that make up the POL improve the coverage of the product.

The second stage is the processing of the nextfluid, most commonly type IV. It is generally identical to the type II composition, but is produced using more modern technology. Type III is most commonly used for de-icing aircraft of various local airlines. Type IV liquid is sprayed neat and, unlike type I, at a low velocity. The purpose of the treatment is to ensure that the aircraft is evenly coated with a thick film of compound that does not allow water to freeze on the surface of the aircraft.

During the action, the film gradually "melts", reacting with precipitation. Manufacturers are conducting research designed to increase the duration of the protective layer. The possibilities of minimizing the impact of harmful components of anti-icing fluids on the environment are also being studied. In general, the AOL remains the best way to deal with aircraft icing at the moment.

Anti-icing systems

The compositions that aircraft are handled on the ground are specially made so that during takeoff they are “blown away” from the surface of the body so as not to reduce lift. Then the baton is taken over by the aircraft's icing sensors. At the right time, they give a command to take action on systems that prevent the formation of ice during the flight. They are divided into mechanical, chemical and thermal (air-thermal and electro-thermal).

Mechanical systems

Based on the principle of artificial deformation of the outer surface of the ship's hull, as a result of which the ice breaks up and is blown away by the oncoming air flow. For example, on wingsThe empennage of the aircraft is reinforced with rubber protectors with a system of air chambers inside. After the aircraft starts icing, compressed air is first supplied to the central chamber, which breaks the ice. Then the side compartments are inflated and the ice is thrown off the surface.

Chemical systems

The action of such a system is based on the use of reagents that, in combination with water, form mixtures with a low freezing point. The surface of the desired section of the aircraft body is covered with a special porous material, through which a liquid is supplied that dissolves the ice. Chemical systems were widely used on aircraft in the middle of the 20th century, but now they are used mainly as a backup method for cleaning windshields.

Thermal systems

In these systems, icing is eliminated by heating the surface with hot air and exhaust gases taken from engines, or by electricity. In the latter case, the surface is heated not constantly, but periodically. Some ice is allowed to freeze, after which the system is turned on. Frozen water separates from the surface and is carried away by the air current. Thus, the melted ice does not spread over the body of the aircraft.

The most modern development in this area is the electrothermal system invented by GKN. A special polymer film with the addition of liquid metal is applied to the wings of the aircraft. It takes energy from the aircraft's on-board system and maintains the temperature on the wing surface from 7 to 21 0C. This latest system is widely used on Boeing aircraft.787.

Despite all the "fancy" security systems, icing requires the utmost attention on the part of the person. Little inattention often led to big tragedies. Therefore, despite the rapid development of technology, the safety of people still largely depends on themselves.