What about if we find ourselves on a plane while a T-storm outside instead of a warm and cozy home? How is it possible that planes can fly safely in a storm? To answer this question, we have to dive into the materials it is made of and more.
People always dreamed of taking over the skies like birds, being like mythical Icarus. Many legends describe the pursue of the sky. One example tells how the king of Persia, Kaj Kaoss, tied eagles to his throne and flew about his kingdom. Another legend has it that Alexander the Great tied four mythical animals with wings, called Griffins, to a basket and flew around his kingdom.
These stories were also born out of deep dreams, to become free as birds. What were the first attempts to master the skies? Wings made of feathers on a light wood frame. This intricate construction was mounted directly to the arms. As a result, we can fly now. Flying is no more a legend, while it took centuries to make it real.
Mastering the flights was a revolutionary breakthrough, making traveling faster, simpler, and available to a broad social group than ever before. Thanks to the tremendous development of engineering in recent decades, aircraft make it possible to cross the ocean distance within just a few hours, making it possible to fly even though non-pleasant weather.
Flying through the T-storm
Sometimes it is challenging to predict sudden changes in the weather. Have you ever wondered what happens to the aircraft that flies through the T-storm? The lightning strike may quite easily hit the flying object. For that reason, the surface of the plane has to be resistant to large doses of electricity. Before focusing on the materials used in aerospace, let’s take a look closer at the thunder and lightning. Lightning, or thunderbolt, is a strong electrostatic discharge between atmosphere and ground.
The electric current goes through the shortest way, so most of the lightning is vertical. It spawns during a storm. In turn, thunder is a sound created by a sudden increase in air pressure and temperature that causes it to expand rapidly. Thunderstorms can produce a tremendous amount of electricity, reaching even over 1 billion Volts per thunderstrike!
And what about flying a plane during thunderstorms? Nowadays, the development of engineering has contributed to the fact that lightning strikes are not perceptible. However, in the past, this has resulted in severe damage or aircraft crashes. For example, in 1963, a plane approaching Philadelphia crashed, killing 81 people. Lightning struck one of the plane’s fuel tanks, causing an explosion. And the last such disaster happened in the USA in 1967.
Currently, similar accidents do not occur, but still, many people have concerns about flying. Pilots assure us that it is not dangerous. How is it really, are the fears right? It is estimated that most aircraft will be struck by lightning at least once in three years due to an electrical discharge.
Lightning must not lead to the loss of the plane and must not cause any significant damage that could prevent further travel. The moment of take-off and landing is essential; when weather conditions do not allow for an entirely safe landing, evacuation must be carried out. Precisely because of a possible evacuation, passengers are often asked not to use their phones. However, pilots try to avoid the storm or fly over it. As a last resort, it is possible to land at an alternate airport.
What happens when there is no way out, the plane blows into the storm and is struck by lightning? A current flows through the aircraft’s fuselage, which induces a magnetic field and an electric field inside the fuselage. During the impact also energy is released. And how is it that passengers are safe during this time?
The Faraday cage, designed in 1836, will respond to this. Everyone who has taken physics lessons has heard of it. Faraday cage is an electrostatic shield to protect against the external action of the electric field. The material from which it is made helps prevent the electric field from penetrating the inside of the cage, thanks to which there is no electric field in it.
So what is inside the cage is protected against the action of an external electric field, such as arises during a lightning strike. In airplanes, the Faraday cage is most often obtained by a suitable fuselage structure – using a dense metal mesh in its construction.
For years aircraft covers were often made of aluminum, a material that conducts electricity very well, while due to the materials science progress some other materials are recently used. Modern coating is made of composites like carbon fibers coated with nickel. Recently, even conducting polymers that are polymers conducting electricity are added into the composites. Then these constructions contain an embedded layer of conductive fibers or screens designed to carry lightning currents.
It happens, however, that pilots sometimes report temporary flickering of lights or short-term interference with instruments. The electronics are sensitive to various surges and sudden voltage spikes. Therefore, in addition to external protection, there is also internal protection in airplanes. In addition to careful screening, surge suppression devices are installed, for example, on cables. The radar in the nose of the plane is housed in conductive housing.
Another element of the aircraft that requires special protection against lightning is the fuel tank. The skin of the airplane around the fuel tanks must be thick enough to withstand burnout. The entire fuel system must be tightly protected against discharges, starting from the fuel tank and ending with the fuel supply lines to the engines. However, small private airplanes should still avoid flying in and near storms due to the accompanying turbulence. Interestingly, planes can fly through hurricanes, which often appear much closer to the ground than the storms. But such operations are so far only for scientific purposes.
On the other hand, before the aircraft is allowed to fly, it must comply with the Federal Aviation Administration (FAA) standards or similar authority in the aircraft’s country of origin regarding protection against lightning.
While the planes are on the ground, the danger is no longer as great as it is in the air. Most at risk are ground personnel. However, there are systems and tools to protect the crew. These systems detect total lightning, then alarm using stroboscopic lights and sound. Once the information reaches the crew, further actions take place according to the special procedures. It happened that a storm will immobilize the plane at the airport, while refueling, loading luggage, and using metal staircases are then dangerous. Let’s not blame the crew; just wait for the storm to end. They do it for our safety.
Summary
Due to turbulence, small airplanes should avoid flying during thunderstorms. They usually occupy small sky areas and can be successfully avoided by choosing a different air corridor. Large planes can fly during a storm, as passengers are generally not at risk. However, once the plane has landed, a storm sometimes prevents it from unloading and passengers from disembarking. It is, however, a relatively low price for fast and long-distance travel and, above all, for our safety.
This article is a joint work of Agnieszka Pregowska (Institute of Fundamental Technological Research, Polish Academy Sciences), Martyna Łuszczek (Faculty of Chemistry, University of Warsaw), and Magdalena Osial (Faculty of Chemistry, University of Warsaw) as a part of the Science Embassy project. Image Credit – Agnieszka Pregowska.
References
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[2] Mazur V, Fisher BD, Gerlach JC. (1984) Lightning strikes to an airplane in a thunderstorm, Journal of Aircraft 21,8,607-611. DOI: 10.2514/3.45030
[3] Petrov NI, Haddad A, Petrova GN, Griffiths H, Waters RT. (2012). Study of Effects of Lightning Strikes to an Aircraft, Recent Advances in Aircraft Technology, Ramesh K. Agarwal, IntechOpen, DOI: 10.5772/36634. https://www.intechopen.com/books/recent-advances-in-aircraft-technology/study-of-effects-of-lightning-strikes-to-an-aircraft (Available 13.04.2021)
[4] Christian HJ, Goodman SJ. (1987) Optical Observations of Lightning from a High-Altitude Airplane, Journal of Atmospheric and Oceanic Technology, 4(4), 701-711.
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