Cabin pressurization is the process by which air-conditioning is pumped into the cabin of an aircraft or spacecraft, to create a safe and comfortable environment for passengers and crews flying at high altitudes. For aircraft, this air is usually released from the gas turbine engine at the compressor stage, and for the spacecraft, it is carried in high-pressure cryogenic tanks. Air is cooled, humidified, and mixed with recirculated air if necessary, before being distributed to the cabin by one or more environmental control systems. The cabin pressure is regulated by the exit valve.
Video Cabin pressurization
Need for cabin suppression
Air pressure is becoming increasingly necessary at altitudes above 10,000 feet (3,000 m) above sea level to protect crews and passengers from the risk of a number of physiological problems caused by low external air pressure above that height. For private aircraft operating in the US, crew members are required to use oxygen masks if cabin heights remain above 12,500 feet for more than 30 minutes, or if cabin heights reach 14,000 feet at all times. At altitudes above 15,000 feet, passengers should be provided with oxygen masks as well. On commercial aircraft, the height of the cabin should be maintained at 8,000 feet or less. Giving pressure on the load holder is also required to prevent damage to pressure-sensitive items which may leak, expand, crack or destroy on re-pressurization. The main physiological problems are listed below.
- Hypoxia
- Lower partial oxygen pressure at altitude reduces alveolar oxygen pressure in the lungs and then in the brain, leading to slow thinking, dim vision, loss of consciousness, and ultimately death. In some individuals, especially those with heart or lung disease, symptoms may begin as low as 5,000 feet (1,500 m), although most passengers can tolerate a height of 8,000 feet (2,400 m) without adverse effects. At this altitude, there is about 25% less oxygen than the one at sea level.
- Hypoxia can be handled by supplemental oxygen delivery, either through an oxygen mask or through the nasal cannula. Without air pressure, sufficient oxygen can be delivered up to a height of about 40,000 feet (12,000 m). This is because a person accustomed to living at sea level requires about 0.20 bar of partial oxygen pressure to function normally and that pressure can be maintained up to about 40,000 feet (12,000 m) by increasing the oxygen mole fraction in the air. that is being inhaled. At 40,000 feet (12,000 m), ambient air pressure drops to about 0.2 bar, where maintaining a minimum oxygen partial pressure of 0.2 bar requires 100% oxygen breathing using an oxygen mask.
- Emergency oxygen supply masks in aircraft passenger compartments need not be a pressure-demand mask as most flights stay below 40,000 feet (12,000 m). Above that height, the partial pressure of oxygen will drop below 0.2 bar even at 100% oxygen and some degree of cabin pressure or rapid decline will be essential to avoid the risk of hypoxia.
- Higher disease
- Hyperventilation, the most common response to hypoxia, helps to restore partial oxygen partial pressure in the blood, but also causes carbon dioxide (CO 2 ) out-gas, increases blood pH and induces alkalosis. Passengers may experience fatigue, nausea, headaches, insomnia, and (on extended flight) even pulmonary edema. This is the same symptom experienced by mountain climbers, but the limited duration of a powerful flight causes the development of pulmonary edema unlikely. Altitude disease can be controlled by a full pressure setting with a helmet and faceplate, which completely envelopes the body in a pressurized environment; However, this is not practical for commercial passengers.
- Decompression disease
- Low partial gas pressure, especially nitrogen (N 2 ) but including all other gases, may cause dissolved gas in the bloodstream to precipitate, produce gas embolism, or bubbles in the bloodstream. The mechanism is the same as a compressed air diver on the climb from depth. Symptoms may include early symptoms of "bend" - fatigue, forgetfulness, headache, stroke, thrombosis, and subcutaneous itching - but rarely full symptoms. Decompression disease can also be controlled by a full pressure setting such as for altitude sickness.
- Barotrauma
- As the plane rises or falls, passengers may experience discomfort or acute pain when the gas trapped inside their bodies enlarges or contracts. The most common problem occurs with air trapped in the middle ear (aerotitus) or paranasal sinuses by a blocked or sinus Eustachian tube. Pain can also be experienced in the digestive tract or even teeth (barodontalgia). Usually this is not severe enough to cause actual trauma but can cause persistent ear pain after flight and may aggravate or precipitate pre-existing medical conditions, such as pneumothorax.
Maps Cabin pressurization
Cab height
The pressure inside the cabin is technically referred to as the equivalent effective cabin height or more commonly as cab height . This is defined as an equivalent height above the mean sea level which has the same atmospheric pressure according to standard atmospheric models such as the International Standard Atmosphere. So the height of the zero cabin will have the pressure found at the mean sea level, which is taken to 101.325 kilopascals (14.696 psi).
Planes
Inside the aircraft, the height of the cabin during flight is stored above sea level to reduce pressure on the plane of the pressurized aircraft; this stress is proportional to the difference in pressure inside and outside the cabin. In a typical commercial passenger flight, the cabin height is programmed to rise gradually from the height of the original airport to a maximum limit of 8,000 feet (2,400 m). The height of the cabin is maintained as the aircraft is traveling at maximum altitude and then decreases gradually as long as it drops until the cabin pressure corresponds to the ambient air pressure at the destination.
Keeping the cabin altitude below 8,000 feet (2,400 m) generally prevents significant hypoxia, altitude sickness, decompression disease, and barotrauma. The Federal Aviation Administration (FAA) Regulations in the US mandate that under normal operating conditions, cabin height may not exceed this limit at the maximum operating height of the aircraft. This mandatory maximum cabin elevation does not eliminate all physiological issues; passengers with conditions such as pneumothorax are advised not to fly until completely healed, and people suffering from colds or other infections may still experience pain in the ears and sinuses. The rate of change in cabin height greatly affects comfort because humans are sensitive to changes in pressure in the inner ear and sinus and this must be managed with care. Scuba divers fly in "non-flying" periods after diving is at risk of decompression due to the accumulated nitrogen in their body can form bubbles when exposed to reduced cabin pressure.
The height of the Boeing 767 cabin is usually about 7,000 feet (2,100 m) when it sails at 37,000 feet (11,000 m). This is typical for older jet aircraft. The design goal for many, but not all, newer aircraft is to provide a lower cabin height than the older design. This can be useful for passenger comfort. For example, the Bombardier Global Express business jet can provide a 4,500 ft (1,400 m) cabin aloft when sailing at 41,000 feet (12,000 m). The Emivest SJ30 business jet can provide sea-level cabin altitude while sailing at 41,000 feet (12,000 m). One study of 8 flights on the Airbus A380 aircraft found a median height of 6,128 feet (1,868 m) median cabin, and 65 flights on the Boeing 747-400 aircraft found an average altitude of 5,159 feet (1,572 m).
Prior to 1996, some 6,000 large commercial transport carriers were certificate-type to fly up to 45,000 feet (14,000 m) without having to meet special high-altitude conditions. In 1996, the FAA adopted the 25-87 Amendment, which imposed additional cabin cabin height specifications for the design of a new type of aircraft. Certified aircraft to operate above 25,000 ft (7,600 m) "should be designed so that residents will not be exposed to cabin pressure height of more than 15,000 ft (4,600 m) after possible failure conditions in pressurized systems". In the case of decompression resulting from "any failure conditions not proven to be highly improbable", the aircraft shall be designed so that the occupants shall not be exposed to cabin heights exceeding 25,000 feet (7,600 m) for more than 2 years. minutes, or altitudes exceeding 40,000 feet (12,000 m) at any time. In practice, the new Federal Aviation Regulation amendments impose a 40,000 foot (12,000 m) operating ceiling in most of the newly designed commercial aircraft. Aircraft manufacturers may apply for relaxation of this rule if circumstances require it. In 2004, Airbus acquired FAA's release to allow the A380's cabin height to reach 43,000 feet (13,000 m) in case of decompression incidents and exceeding 40,000 feet (12,000 m) for one minute. This allows the A380 to operate at a higher altitude than the newly designed civil aircraft.
Spacecraft
Russian engineers use a mixture of nitrogen/oxygen air, which is stored at cabin elevations near zero at all times, in Vostok 1961, 1964 Voskhod, and 1967 to present the Soyuz spacecraft. This requires the design of a heavier space vehicle, because the spacecraft's cabin structure must withstand the pressure of 14.7 pounds per square inch (1 bar) against the vacuum, and also because the inert nitrogen mass must be carried. Treatment should also be taken to avoid decompression when cosmonauts perform extravehicular activity, since soft space clothing is currently suppressed with pure oxygen at relatively low pressure to provide reasonable flexibility.
Instead, the United States uses pure oxygen atmosphere for 1961 Mercury, 1965 Gemini, and the Apollo 1967 spacecraft, primarily to avoid decompression. Mercury uses cabin heights of 24,800 feet (7,600 m) (5.5 pounds per square inch (0.38 bar)); Gemini uses a height of 25,700 feet (7,800 m) (5.3 psi (0.37 bar)); and Apollo uses 27,000 feet (8,200 m) (5.0 psi (0.34 bar)) in space. This allows the design of a lighter space vehicle. Before launch, the pressure is kept slightly higher than sea level at a constant 5.3 psi (0.37 bar) above the ambient for Gemini, and 2 psi (0.14 bar) above sea level at launch for Apollo), and diverted to the height of the room cabin while climbing. However, the high pressure pure oxygen atmosphere proved to be a fatal fire hazard in Apollo, contributing to the death of the entire Apollo 1 crew during the 1967 ground test. After this, NASA revised its procedure to use a 40% nitrogen/60% oxygen mixture at zero cabin height when launch, but store low-pressure pure oxygen in space.
After the Apollo program, the United States uses an air-like cabin atmosphere for Skylab, the Space Shuttle orbiter, and the International Space Station.
Mechanics
Pressurization is achieved by airplane designs engineered to be pressurized by a compressed air source and controlled by an environmental control system (ECS). The most common compressed air source for air pressure is air extracted from the gas turbine engine compressor stage, from the low or intermediate stage and also from the additional high stage; the exact stage may vary depending on the machine type. By the time the cold air outside has reached the air valve, the pressure is very high and has been heated to about 200 ° C (392 ° F). The control and selection of high or low blooded sources is fully automated and governed by the needs of various pneumatic systems at different stages of flight.
Part of the bleed air that is directed to the ECS is then expanded to bring it to the cabin pressure, which cools it down. The appropriate final temperature is then achieved by adding heat back from compressed heat through the heat exchanger and air cycle engine known as the packet system. On some larger airplanes, hot, hot air can be added to the air-conditioned downstream coming from the pack if necessary to warm the cabin parts cooler than others.
At least two engines provide air-pressurized air for all aircraft pneumatic systems, to provide full redundancy. Compressed air is also obtained from an additional power unit (APU), if installed, in an emergency and to supply air cabin on the ground before the main engine starts. Most modern commercial aircraft today have fully redundant duplicate electronic controllers to maintain air pressure along with manual backup control systems.
All exhaust air is discharged into the atmosphere through the outlet valve, usually at the rear of the fuselage. This valve controls the cabin pressure and also acts as a safety release valve, in addition to other safety valves. If the automatic pressure controller fails, the pilot can manually control the cabin pressure valve, according to the backup emergency procedures checklist. The automatic controller usually maintains the proper cabin pressure height by constantly adjusting the valve out position so that the cabin height is as low as practical without exceeding the maximum differential pressure limit on the plane. Pressure differences vary between types of aircraft, typical values ​​are between 7.8 psi (54 kPa) and 9.4 psi (65 kPa). At 39,000 feet (12,000 m), the cabin pressure will be automatically maintained at about 6,900 feet (2,100 m) (450 feet (140 m) lower than Mexico City), which is about 11.5 psi (79 kPa) pressure atmosphere.
Some aircraft, such as the Boeing 787 Dreamliner, have reintroduced an electric compressor previously used on piston-engined planes to provide pressure. The use of an electric compressor increases the electrical load on the engine and introduces several stages of energy transfer; therefore, it is unclear whether this improves the overall efficiency of aircraft handling systems. Nevertheless, eliminating the danger of chemical contamination of the cabin, simplifying the design of the engine, avoiding the need to run high pressure pipes around the aircraft, and provide greater design flexibility.
Unplanned decompression
The loss of unplanned cabin pressure at altitude is rare but has resulted in a number of fatal accidents. Failures range from sudden loss of plane integrity (explosive decompression) to slow leakage or equipment damage allowing cabin pressure to fall undetected to levels that may cause severe unconsciousness or decreased performance in aircrew.
Any cabin pressure failure above 10,000 feet (3,000 m) requires an emergency landing up to 8,000 feet (2,400 m) or closest to it while maintaining a Minimum Safe Height (MSA), and deploying oxygen masks for each seat. The oxygen system has enough oxygen for all on the board and gives the pilot enough time to drop below 8,000 ft (2,400 m). Without emergency oxygen, hypoxia can lead to loss of consciousness and loss of aircraft control. The time of beneficial consciousness varies according to the height. When the pressure drops the cabin air temperature may also decrease to the outdoor temperature with the danger of hypothermia or frostbite.
In jet fighter planes, the small cockpit size means any decompression will be very fast and will not allow the pilot time to wear oxygen masks. Therefore, fighter jets and aircrew pilots must wear oxygen masks at all times.
On June 30, 1971, the Soyuz 11 crew, Soviet cosmonauts, Georgy Dobrovolsky, Vladislav Volkov, and Viktor Patsayev were killed after the cabin vent valve opened accidentally before reentering the atmosphere. There was no indication of a problem until the recovery team opened the capsule and found the dead crew.
History
The aircraft that pioneered the pressurized cabin system include:
- Packard-Le PÃÆ'¨re LUSAC-11, (1920, modified French design, not really pressurized but with enriched oxygen enriched cockpit)
- Engineering Division USD-9A, modified Airco DH.9A (1921 - first aircraft flying with the addition of a pressurized cockpit module)
- Junkers Ju 49 (1931 - German experimental aircraft built to test the cabin pressure concept)
- Farman F.1000 (1932 - broke the French cockpit pressurized record, experimental aircraft)
- Chizhevski BOK-1 (1936 - Russian experimental aircraft) Lockheed XC-35 (1937 - American pressurized aircraft.) Instead of a capsule of pressure covering the cockpit, the leather monocoque plane is a pressure vessel.)
- Renard R.35 (1938 - first pressurized piston aircraft, which falls on the first flight)
- Boeing 307 (1938 - first pressurized aircraft to enter commercial services)
- Lockheed Constellation (1943 - first pressurized aircraft in broad service)
- Avro Tudor (1946 - first British pressure aircraft)
- de Havilland Comet (English, Comet 1 1949 - first jet aircraft, Comet 4 1958 - solve Comet problem 1)
- Tupolev Tu-144 and Concorde (1968 USSR and 1969 Anglo-French respectively - first operating at very high altitudes)
- SyberJet SJ30 (2005) The first civilian business jet to certify a 12.0 psi pressurization system that allows the sea surface cab at 41,000 feet (12,000 m).
In the late 1910s, efforts were made to reach higher and higher altitudes. In 1920, flight over 37,000 feet (11,000 m) was first achieved by an Lt test pilot. John A. Macready at Packard-Le PÃÆ'¨re LUSAC-11 biplane at McCook Field in Dayton, Ohio. The flight is made possible by releasing stored oxygen to the cockpit, which is released directly into the closed cabin and not to the oxygen mask, which is then developed. With this system, a flight of nearly 40,000 feet (12,000 m) is possible, but the lack of atmospheric pressure at that height causes the heart of the pilot to widen, and many pilots report health problems from such high altitude flight. Some early airlines have oxygen masks for passengers for regular flights.
In 1921, a Wright-Dayton USD-9A surveillance biplane was modified by the addition of a fully-enclosed air-enclosed space with forced air into it by a small external turbine. The chamber has a hatch of only 22 in (0.56 m) in diameter to be sealed by the pilot at 3,000 feet (910 m). The room contains only one instrument, the altimeter, while the conventional cockpit instruments are all installed outdoors, visible through five small holes. The first attempt to operate the aircraft was again made by Lt. John A. McCready, who discovered that the turbine forced air into space faster than the small release valve provided to release it. As a result, the room was quickly distressed, and the flight was abandoned. The second attempt should be abandoned when the pilot discovers at 3,000 feet (910 m) that he is too short to seal the hold hatch. The first successful flight was finally made by an Lt test pilot. Harrold Harris, making it the world's first flight with a pressurized aircraft.
The first aircraft with a pressurized cabin was the Boeing 307 Stratoliner, built in 1938, before World War II, although only ten were produced. "The pressure compartment 307 from the nose of the plane to the pressure barrier at the stern only progresses from the horizontal stabilizer."
World War II is a catalyst for aircraft development. Initially, World War II piston planes, although they often flew at very high altitudes, were not depressed and depended on oxygen masks. This becomes impractical with the development of larger bombers in which the crew is asked to move around the cabin and this causes the first bomber with a pressurized cabin (though limited to the crew area), Boeing B-29 Superfortress. The control system for this was designed by Garrett AiResearch Manufacturing Company, taking part in the patent license held by Boeing for Stratoliner.
Postwar piston forces such as Lockheed Constellation (1943) extend technology to civil service. Piston-engined aircraft generally rely on electric compressors to provide pressurized cabin air. Supercharged engines and pressurized cabins allow aircraft such as Douglas DC-6, Douglas DC-7, and Constellation to have a certified service ceiling of 24,000 feet (7300 m) up to 28,400 feet (8,700 m). Designing a pressurized fuselage to overcome that height range in current engineering and metallurgical knowledge. The introduction of jet aircraft requires a significant increase in the height of the yacht to the range of 30,000-41,000 feet (9,100-12,500 m), where jet engines are more fuel efficient. That the increase in the height of a yacht requires far more stringent aircraft engineering, and at first not all engineering problems are fully understood.
The first commercial jet aircraft in the world was British de Havilland Comet (1949) designed with a 36,000ft (11,000m) service ceiling. This is the first time a large, pressurized ship with a window has been built and flown at this altitude. Initially, the design was very successful but two massive fuselage failures in 1954 resulted in a total loss of aircraft, passengers and crew down to what became the world's jet fleet. Extensive investigations and innovative engineering analysis of the wreck caused a number of significant engineering advances that solved the basic problem of aircraft design at pressurized altitudes. The critical issue proved to be a combination of inadequate understanding of the effects of progressive metal fatigue when the aircraft experienced a recurring stress cycle coupled with misconceptions about how skin aircraft pressure is distributed around openings in the fuselage such as windows and rivet holes.
Principles of critical engineering on metal fatigue learned from the Comet 1 program are applied directly to the design of Boeing 707 (1957) and all subsequent jet aircraft. One of the most visible legacies of the Comet disaster is the oval window on every jet plane; Crack metal fatigue that destroys Comet begins by the corners of a small radius in a window almost as wide as Comet 1. The Comet body was redesigned and Comet 4 (1958) later became a successful aircraft, pioneering the first transatlantic jet service, but the program never really recovered from this disaster and followed by Boeing 707.
Concorde has to deal with very high pressure differences because it flies at very high altitudes (up to 60,000 feet (18,000 m)) and maintains a 6,000 feet (1,800 m) cabin altitude. This makes the aircraft much heavier and contributes to the high flight costs. Concorde also has smaller cabin windows than most other commercial passenger aircraft to slow down the decompression rate if the window fails. High cruising altitudes also require the use of high-pressure oxygen and demand valves in emergency masks unlike the continuous flow masks used on conventional aircraft.
The height of the operating cabin designed for new aircraft falls and this is expected to reduce the remaining physiological problems.
See also
- Aerotoxic syndrome
- Air cycle machine
- Atmosphere (unit)
- Compressed air
- Smoke event
- Rarefaction
- Room settings
- Useful awareness time
Footnote
General reference
-
Seymour L. Chapin (August 1966). "Garrett and Pressurized Flight: A Business Built with Thin Air". Pacific History Reviews . 35 (3): 329-43. doi: 10.2307/3636792. JSTORÃ, 3636792. - Seymour L. Chapin (July 1971). "Patent Interference and Technology History: A Very Flying Example". Technology and Culture . 12 (3): 414-46. doi: 10.2307/3102997. JSTORÃ, 3102997.
- Cornelisse, Diana G. Beautiful Vision, Purpose Unbearable; Developing Air Force For The United States Air Force During The First Century Powerful Flight . Wright-Patterson Air Force Base, Ohio: U.S. Air Force Publications, 2002. ISBN: 0-16-067599-5. pp.Ã, 128-129.
- Parts of the United States Navy Aviation Surgery Manual
- "Dead 121 in Greek Air Crash", CNN
External links
- Videos with Cabin Pressure Demo on Civil Aircraft on YouTube
Source of the article : Wikipedia
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