How does an airplane de-icing system work? The plane’s wings are sprayed with a heated, high-pressure solution of propylene glycol and water.
Planes fly throughout the year, in all kinds of weather, and there is very little that can stop them. When they fly, they have to avoid heavy storms, but rain is generally not a problem. One of the biggest things that can stop a plane from flying, or cause a flying plane to have trouble, is the cold and ice forming on the wings. Ice needs to be removed from a plane’s wings before take off and also during flight. In the last 25 years, 35 planes have crashed or had major problems because of ice. Many lives have been lost. Planes are much safer than they used to be, and de-icing has improved a lot, but there are obviously still problems.
Why does ice build up cause problems? There are three reasons. The first is that the wing has many fine control systems, such as the flaps, and a lot of sensors. Ice build up can interfere with all of these systems and make them harder to use or inoperable. The second problem is weight. A thick buildup of ice can add a lot of weight to a plane. The weight itself is probably no problem, but if it builds up on one wing more than the other, the plane can become unbalanced. The third reason is that a buildup of ice can affect the shape of the wings. A plane’s wings are carefully designed to vary the speed of the air over the top and the bottom of the wing, creating lift. If there is a buildup of ice, it will change this balance, and the plane may suddenly not be able to get enough lift.
So, what can they do? The first thing is to de-ice the planes before they take off. In very cold weather, planes sitting on the tarmac before they take off are very vulnerable. The outside of the plane’s skin can be very cold, and ice can form quickly. A plane is pretty well insulated to keep in the heat when it is at a high altitude, so heat from the cabin doesn’t melt the ice. The wings are also full of cold fuel. The first step is to check for ice, and pilots perform an inspection before they take off. The problem is that ice is difficult to see from the ground. If there is any ice, they call for a de-icing truck. A de-icing truck is basically a tanker of de-icing liquid and a hose to spray it on the plane through. The liquid is heated to about 70℃ so that it will melt any ice and snow already on the plane. There are different liquids used, but they are usually propylene glycol and water. This works because propylene glycol lowers the freezing point of water. When water is trying to freeze, the water molecules come together and form a rigid crystal structure, which is ice. Propylene glycol molecules get in the way of the water molecules and stop them forming their crystal structure, keeping them liquid. The water has to get even colder before the water molecules can overcome the propylene glycol and make ice. And, when this happens, the glycol that is excluded from the frozen water gets pushed into other areas of water, increasing their glycol concentration and lowering the freezing temperature even more. The water on the wings doesn’t freeze into one
block but freezes in places and becomes a slush that falls off the wings. This keeps the wings of the plane free of ice, but it doesn’t last forever. A ground de-icing is rated to be good for 22 minutes. If the plane hasn’t taken off before those 22 minutes are up, it needs to be de-iced again.
Ice can also form when a plane is flying, which has to be dealt with. Planes have a number of systems to remove that ice. The first one is simple. Some planes have electric heated panels in the wings that the pilot just needs to turn on. That, plus the air flowing over the wings, can be enough to knock the ice off. These panels are at the front of the wings because that is where ice usually starts. There is also a system of pipes that redirects hot air from the engines to the wings to heat them. There is another system of pipes that, when switched on, slowly pump de-icing fluid over the wings. And there is a system of inflatable boots that go on the front edge of the wing and near to vital components. They are usually made of segments, and when they are switched on, they inflate and deflate rapidly, different segments at a time. The sudden movement and changing shape is hopefully enough to shatter the ice that has formed for it to be blown off. And this is what I learned today.
Sources
https://en.wikipedia.org/wiki/Deicing
https://en.wikipedia.org/wiki/Freezing-point_depression
https://science.howstuffworks.com/deice-airplanes.htm
https://asrs.arc.nasa.gov/publications/directline/dl5_ice.htm
https://en.wikipedia.org/wiki/Category:Airliner_accidents_and_incidents_caused_by_ice
https://www.portseattle.org/blog/all-you-never-wanted-know-about-airplane-de-icing
https://en.wikipedia.org/wiki/Ice_protection_system
image By Alex Pereslavtsev – http://www.airliners.net/photo/Aeroflot—Russian/Airbus-A330-243/1710354/L/, GFDL 1.2, https://commons.wikimedia.org/w/index.php?curid=16594894