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Today we will learn more about a very important system in airplanes, we will talk about the pressurization that offers safety and comfort to travelers.
We have previously reviewed in this blog important topics about pressurization and the air we breathe on airplanes., but this time we will have another vision of this fundamental system in thousands of flights and planes in the world.
Post written by: William Casalins
Aeronautic engineer
FIA Foundation
Our friend the pressurization
The term PRESSURIZATION is well known in most of the passengers and clearly among the crew and mechanics aircraft. Indeed, it is what the word PRESSURIZE implies. (Pressure). People immediately think of oxygen, knows that as you go up the air is less dense and its concentration decreases with height, until it is practically insufficient for the vital requirements of the human being and even for most of the animals, that's true, but it is only part of what really happens in the cabins of the plane when we venture to be in places for which we are not made and that are extremely hostile to life.
The air we breathe is made up of various types of gases and is oxygen., what, although it is in a smaller percentage (about 20%) is the most necessary for life; but it is useful as long as it can be assimilated adequately and in sufficient quantities by the alveoli of the lungs and distributed by the blood throughout the body.
The flight attendants in the instructions tell us, very smiling, what, in case of depressurization, the respective oxygen masks will drop and that we put on our own before helping someone who needs it, but they know that they will have to go down to lower levels as quickly as possible, Whats that for, if we have the masks on? That is a good question.
The answer is the same, which is why astronauts or deep-sea divers need not only oxygen but also special suits..
As we ascend we know that the pressure decreases and that the oxygen particles are scarcer (by volume) and when pressurizing (increase cabin pressure) would again be concentrated in proportions suitable for human consumption; but it turns out that if you are very high, depending on each person, even if you have an oxygen mask supplying enough air, at those flight levels your lungs would not be able to absorb enough oxygen to keep you alive, it is necessary to go down so that the body is in a less harsh and more friendly environment for life (as we know it). Regular passenger air transport implies being able to take the largest number of people from one place to another without them being Olympic athletes (or ordinary people) and that is why we must simulate as much as possible an environment where most of us feel comfortable and without the fear of suffering from all the diseases that implies being for prolonged periods at necessary flight heights (operationally) today in air navigation.
Now comes something more interesting, what would happen if we got higher and higher, like the passengers of a Concorde, un SR 71 or a high-altitude balloon? unexpected things will happen. Water, at sea level with a pressure of more or less than 29.92 inches of mercury or 14 psi (pounds per square inch) boils to 100 degrees Celsius, as we rise it boils at a lower temperature, in Bogotá, for example, it would be around 92 degrees Celsius, a 8848 meters (Everest) a 86 degrees to 11000 (at normal flight height) a 71 degrees and 19000 meters to 37 degrees. That wouldn't matter much if our bodies weren't mostly water and if our temperature wasn't more or less at 37 degrees Celsius, because that means that 19000 meters (60000 pies, almost normal flight level in a concorde) our blood would be, if it weren't for your internal pressure, about to boil, with the serious consequences that this entails for our health, we roast in our juice, literally, because saliva if it could boil.
Knowing all this, we can understand the great efforts made by aircraft designers and builders to make them fly at higher levels., or you are very tall, it brings many benefits to the flight, avoid aircraft congestion, they are usually about bad weather, engines consume less fuel and in some areas they take advantage of favorable winds (jet stream)although pressurization implies more weight, more fuel consumption, more costs to build and with more systems to operate; in addition to having to control the temperature with sophisticated air conditioning systems that are so complicated and wasteful that modern aircraft recycle part of that air through efficient filters inside the system, not to mention the drag that is generated to cool the air conditioning heat exchangers.
Now let's see how they do it, the first is a cabin fully sealed and reinforced for the pressures and cycles it must withstand, the second thing is to get an air source, nowadays, with turbine engines, it is very easy to get it from the first stages of the compressor, a pressure control system normally achieved by controlling the valve where the air exits ,If more goes in than goes out, it pressurizes, If more goes out than goes in, it depressurises ,if the same volume comes out as the one that enters, the pressure inside the cabin is maintained and is obtained automatically, semi-automatic and manual. Logically, some safety valve systems to prevent the integrity of the structure from collapsing due to overpressure or, on the contrary, due to a higher external pressure that would cause the cabin to implode in the event of a controller or human failure..
The history of pressurization, like almost all aeronautical innovations, it has its dark and painful side, the various accidents of the De Havilland Comets, due to structural failures due to cycles of pressurization and depressurization, Those disasters contributed a lot to the development of the industry in the development of the new cells and design of the windows of the modern jets that we fly today.
This was one of the topics that I often discussed with a great aviator, friend and companion Captain ALVARO MEJIA on long flights where he told me about his experiences, those that enriched the knowledge and the importance of a good and correct operation of the equipment, but the torches pass from one generation to another and now I do those discussions with a young and studious commander Cristian Cuestas, that when he arrives at the cruise he takes out his notes, adjust your chair, look back and ask House…?
Note: The Comet was not the first pressurized passenger plane., nor the first to have square windows, but due to its impressive accidents it is the one that has left the most lessons for future designs.
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