Cabin pressurization [1] is a process in which air is pumped into the cabin / cabin of an airplane or spacecraft to create a safe and comfortable environment for people at high altitudes.
In airplanes , air is usually taken from a compressor of a working gas turbine engine ; for a spacecraft, air is brought in compressed or liquefied form.
Need for boost
Safe (by air pressure) is considered an altitude of less than 4 km. Any climb to a height of more than 4 km requires the use of various life support systems.
With a rise to a height of more than 3 km, a person shows signs of oxygen starvation (you want to sleep). At altitudes of more than 9 km, gas bubbles (aeroembolism) may be released from the body fluid. At heights of more than 19 km, subcutaneous fluid boils. Air temperatures above 11 km can reach β60 Β° C. For flying on an aircraft in such adverse conditions for life, it was required to create airborne life support systems.
Aviation
Signs of oxygen starvation in humans depend on many factors (see Hypoxia ). Air humidity has a significant effect: at high humidity, deterioration of well-being occurs even at altitudes of 1000-1500 meters.
Most aircraft are equipped with a sophisticated air conditioning system (Rus. SLE, Eng. ECS). The hot air drawn from the engines is cooled, drained, dosed, mixed and fed into the cabin. The pressure in the cabin is regulated by an automatic valve that discharges excess air into the outboard space.
It should be noted that when flying by plane to an altitude of about 2000 meters, there is usually no cabin pressurization (although there are exceptions), then the system begins to supply air, maintaining a constant pressure of approximately 570 mm. Hg. Art. to heights in the region of 7000-8000 meters. With a further rise, the air conditioning system maintains a variable pressure, gradually decreasing with increasing height. So, at an altitude of 11 km, the pressure in the cabin will be about 0.7 from normal.
In airplanes, to control the air pressure in the cockpit, a height and differential pressure indicator (UVPD) is used, and to simplify, the term cockpit height is used - that is, air pressure corresponding to a certain height.
Of course, it would be preferable to maintain normal, at ground level, pressure in the cabin throughout the flight, but this is not done for a number of reasons. One of the significant reasons is the technical problem of ensuring the strength of the fuselage. The design must withstand excess pressure in rarefied air at high altitude, and with increasing boost pressure, the fuselage becomes more complicated and heavier.
In military aircraft, air was initially supplied solely for the purpose of heating - for glazing the cockpit and at the feet of the pilot (as an example), and crews always used oxygen masks when flying above 4 km. Gradually, on almost all types of military aircraft, they also introduced an air-conditioning system that works like passenger liners, but during combat missions a special combat boost mode is provided. In combat mode, the pressure in the cockpit will be significantly reduced - this is done to prevent barotrauma from the crew during sudden depressurization at high altitudes in the case of, for example, shells. The entire flight crew uses oxygen masks or is equipped in high-altitude suits, and the boost system for the most part maintains the temperature regime in the cabin.
Damage to the pressurized cabin by machine-gun and fighter cannons during flight at high altitudes caused explosive decompression and the death of crews of bombers of World War II.
Cosmonautics
In Soviet / Russian manned spacecraft, the atmosphere is fully consistent with the Earth.
In American spacecraft, the atmosphere was initially completely oxygen, with reduced pressure, which made it easier to design. After an oxygen fire at the Apollo 1 spacecraft, NASA used a gas mixture of 40% nitrogen and 60% oxygen at the launch of the ship, with the transition to pure oxygen in space.
The ISS uses a nitrogen-oxygen atmosphere with normal pressure.
See also
- Helmet
- Oxygen equipment
- Air conditioning system (aviation)
- Germocabin
- Altitude sickness