Why do planes de-ice?
Why do planes de-ice?
Simply put, avoid causing harm to the flight. Because the flight of the aircraft depends on the shape to generate lift, if the wing ice, the airfoil will be damaged, reducing flight safety. In the past, foreign airlines have had accidents in which the engine sucked ice off the wing and crashed the engine. In addition, a large amount of ice is attached to the fuselage, and the weight is very large, which will also reduce the performance of the aircraft and affect the economy.
When to deice?
1. Weather conditions
(a) In the event of frost or snow, anti-icing measures must be considered;
(2) At any time, according to the information provided by the meteorological department, the external atmospheric temperature is below 5 ° C and visible moisture has formed;
For example: conditions accompanied by fog, rain, snow, sleet, ice crystals with visibility of less than 1.5 km, or the presence of water, snow, ice or snow on the runway. Or the external atmospheric temperature is below 10 ° C, and the external temperature reaches or is close to the dew point. At the same time, the aircraft body and the control surfaces appear or may appear frost, snow or ice;
(3) Freezing rain and drizzle: precipitation when the outside temperature is below 0°C, and the raindrops are kept in a supercold state and are connected with the aircraft body
Form ice upon contact;
(d) frozen precipitation, ice crystals: in the event of snow, rain and snow or hail, the external atmospheric temperature is between -4°C and 1°C,
The difference between temperature and dew point temperature is usually within 1°C of each other, and wet snow has fallen on the surface of the aircraft;
(e) the outside temperature is about -8°C below, the temperature and dew point temperature difference between each other is more than 5°C, rain and snow fall on the aircraft
On the surface.
2. Ground conditions
Ice accumulation can also come from the effects of ground operations or ground conditions. Even if the weather conditions do not have the temperature conditions of ice and snow, it is still possible to cause ice and snow adhesion on the surface of the machine parts on the scene that has been frozen. If the aircraft operates on a tarmac, taxiway or runway with moisture, snow or snow; Ground winds, the operation of other aircraft, and ground auxiliary anti-icing equipment continue to blow snow.
What method of deicing is used?
Aircraft deicing mostly uses deicing liquid deicing method, that is, deicing liquid containing ethylene glycol or propylene glycol is heated to about 82 degrees Celsius, and special deicing trucks are used to spray the surface of the aircraft to remove ice on the surface of the aircraft. At the same time, after the deicing liquid is mixed with water, the freezing point will be reduced, similar to the principle that water is not easy to freeze after mixing with alcohol. The freezing point of the mixture of deicing liquid and water can be as low as minus 50 degrees Celsius, which can prevent reicing. However, this effect has a certain time limit, beyond the time limit, the anti-icing effect will fail and need to be deiced again.
In addition to the deicing fluid deicing method, there are these deicing methods:
Compressed air deicing is the use of high pressure air to blow ice off the surface of the aircraft. This method is suitable for dry snow that has not melted and is not ideal for conditions that have frozen.
Infrared heating deicing method is a new deicing method. It uses the infrared radiation emitted by the high-power infrared generator installed in a cluster to irradiate the aircraft, heat the fuselage to melt snow and ice to achieve de-icing operations. No pollutants remain in the operation process, which is an environmentally friendly operation method, but the equipment investment is large, and it is suitable for airports with long winter snow cycle and large flights.
Hot water deicing is the method used in the past, but this method has great limitations. When the ambient temperature is well below zero degrees Celsius, hot water will cool quickly in the cold fuselage and may refreeze on the surface of the aircraft, affecting the movement of moving parts and blocking flight measurement and control instruments. Therefore, only in the use of hot water deicing within 3 minutes of takeoff, can play the role of deicing and anti-icing.
What is local deicing?
There are generally three service modes for aircraft deicing at the airport, namely, aircraft deicing, fixed-point deicing, and local deicing.
As the name implies, the aircraft is parked in the aircraft position, and the deicing truck is removed to the aircraft position. This method is suitable for airports with low deicing frequency, because it takes a long time to prepare and move the deicing vehicle.
Fixed-point deicing means that the deicing platform is set not far from the take-off position of the runway. The aircraft goes to the deicing platform before taking off, and the deicing vehicle does not have to move. For airports with large flow, this deicing method is more efficient.
The above two deicing methods turn off the engine during the deicing process.
Local deicing is one of the most efficient methods of deicing at present. Simply put, it is to establish a deicing area on the taxiway of the aircraft takeoff queue, multiple deicing vehicles and other deicing equipment gathered here, the aircraft will pass the deicing area when queuing on the taxiway, multiple deicing vehicles will work at the same time, it only takes about 7-8 minutes to complete the deicing of an aircraft. After the deicing is completed, the aircraft can slide directly into the runway and take off. In the whole deicing process, the aircraft engine is in a slow running state, so it is called "slow deicing", and this deicing method needs to avoid the deicing fluid affecting the engine operation is also one of its difficulties.
