Why do airplanes need to be frost-proof?

Both rockets and aircraft are vehicles that fly in the sky. After a certain height from the ground, the aircraft will use air conditioners to control the temperature, so that the temperature in the cabin will not be particularly low; and the rocket needs to pass through the same height safely. Coat the outer surface with heat-resistant material to prevent it from being burned out. Why is this?

Jiang Ping from the Beijing Institute of Aerospace Systems Engineering, China Academy of Launch Vehicle Technology, told us the reason. It turns out that when rockets and airplanes fly in the sky, whether they need to be protected from freezing or heat is closely related to the Mach number they fly.

Mach number refers to the ratio of the speed of an object to the speed of sound in the surrounding air. Under the same conditions, the smaller the Mach number, the lower the surface temperature of the object; the larger the Mach number, the higher the surface temperature of the object.

Jiang Ping said that during the flight of the rocket in the atmosphere, in order to break free from the gravity of the earth and fly to higher and farther space, it will continue to accelerate the flight, the speed from subsonic, supersonic to hypersonic, at an altitude of about 10 kilometers from the ground At , the Mach number even exceeds 5, and the temperature on the surface of the rocket is more than 1,000 degrees. As the rocket's speed increases, this temperature will continue to rise until it leaves the atmosphere.

At this stage, if there are not enough anti-heat insulation measures, the metal shell of the rocket will deform or even melt, and the circuit boards, components, and precision instruments inside the rocket will burn through and deform, resulting in the failure of the entire flight mission.

Ordinary civil aircraft generally fly at subsonic speed. Also at an altitude of about 10 kilometers from the ground, the Mach number is only 0.7-0.8, and the temperature of the external atmosphere is as low as minus 55 degrees Celsius, close to the temperature within the Arctic Circle. The temperature is similar to the outside temperature. At this temperature, the aircraft must turn on the air conditioner to adjust the temperature in the cabin, otherwise the passengers of the passenger plane will be frostbitten.

In fact, if the speed of the aircraft is also increased to supersonic speed, that is, the Mach number reaches about 10, it also needs to be protected from heat. The speed of the space shuttle is similar to that of a rocket, and the surface temperature can reach as high as 2000 degrees Celsius, so a thick layer of heat-proof tiles is also installed on the surface of the space shuttle to resist the high temperature.

Why is the temperature of the pre air conditioning so cold?

Many experienced passengers will bring their own thick clothes, or ask the flight attendants for aviation blankets when boarding the plane. And no matter which airline, it will set the temperature of the air conditioner very low, so what is the reason for the airline to adjust the temperature in the cabin so much?

According to industry insiders, setting the temperature in the cabin lower is mainly to ensure that passengers will not faint in the cabin. Generally speaking, the temperature in the cabin is between 16-25 degrees Celsius, the temperature in the cockpit is about 16 degrees, and the temperature in the cabin outlet is about 24 degrees.

According to the American Society for Testing and Materials, passengers are more likely to faint and faint on the plane than on the ground. This is because on the plane, it is more likely to be deprived of oxygen, and when passengers cannot breathe enough oxygen on the plane, it will increase the possibility of fainting and fainting. At the same time, the probability of fainting and fainting during flight is also related to the air pressure and temperature in the cabin. If the temperature in the cabin is too high, it will make passengers feel more uncomfortable and increase the possibility of fainting and fainting.

And this is a common medical condition when people take a plane, especially during the ascent and descent of the plane. At this time, if the air pressure in the cabin is not adjusted accordingly, it is possible that the passengers may faint due to hypoxia due to insufficient pressure.

When the temperature in the cabin is higher than or even just at the normal temperature of the human body, it will further increase the risk of fainting and fainting of passengers. For different passengers, maintaining a comfortable temperature in the cabin is not the same. In order to ensure that each passenger does not have the risk of fainting or fainting, the airline will keep the temperature in the cabin within a lower range. Therefore, in the cabin, except for a few people who feel that the temperature is suitable, most people will feel that the temperature is relatively cold, or even extremely cold.

It cannot be denied that in order to ensure that everyone does not faint or faint, airlines may overcorrect when adjusting the temperature. At present, more and more airlines have achieved more accurate temperature adjustment through new technologies. In order to make themselves as comfortable as possible, when boarding a plane, it is better to bring an extra piece of clothing or an aviation blanket as soon as possible.