While on the topic of Aircraft structures, and having used the term ‘pressurization cycle’ not too long ago, it would be practical to cover the topic of pressurization.
First off, I think we understand the need for pressurization of aircraft’s flying at high altitudes. In plain terms, pressurization helps maintain a positive pressure in the passenger cabin, one that is comfortable for passengers to breathe normally in.
What is slightly less known, is that the cabin pressure is not maintained at sea level pressure, that is, the pressure your body might experience at sea level.
So why take all the pains to pressurize the cabin at all, if we cannot keep it at a pressure which is most favorable for the human body?
The answer lies in the structural ability of the aircraft cabin (fuselage) to withstand differential pressures. Ok, now that deserves an explanation!
As we move upwards from the surface of the earth, atmospheric pressure decreases as the air becomes rarer. As mentioned, to overcome the effects of this on the human body, the aircraft is pressurized. So, while the atmospheric pressure (pressure outside the aircraft fuselage) is very low, pressure within the fuselage is quite a bit higher.
Imagine a balloon being inflated, Yes an ordinary birthday balloon! Now, if the pressure within the balloon becomes critically high, in relation to the atmospheric pressure surrounding the balloon, it will…well, burst! This example simply helps appreciate that by pumping air into a balloon we are increasing it’s internal pressure, and when it(differential pressure between internal and external of the balloon) gets beyond that which the balloon is capable of holding, it bursts.
Similarly, an aircraft structure can only withstand a limited amount of differential pressure between the (internal) cabin and the (external) atmosphere….before it, well,… I think we know now!
If you read between the lines, there are 2 factors at play here, between which we must run a compromise. First, the human requirement for cabin/fuselage pressure to be at a level where human physiological functions (mainly breathing) can occur normally. And second, a differential pressure (between cabin/fuselage pressure and external atmospheric pressure) that the aircraft structure can withstand.
Strange dichotomy! Well, if you are an aviation professional, you are probably already quite accustomed to such compromises, technically speaking that is!! Ok, Lets proceed.
So, to meet both these requirements, the cabin pressure is basically set at what you might experience on earth at about 6000 to 8000feet above sea level. This pressure seems quite comfortable for a wide range of people. At the same time, this seems reasonably comfortable for the aircraft structure to withstand without…. The problem is actually compounded the higher the aircraft flies; but, let’s put that away for the moment, lest we put your brain under a cornucopia of information, compelling it to…!
The next time your doctor advises you against flying due to a medical condition, the consequences of this reduced pressure on your body, is probably what he is highlighting.
First off, I think we understand the need for pressurization of aircraft’s flying at high altitudes. In plain terms, pressurization helps maintain a positive pressure in the passenger cabin, one that is comfortable for passengers to breathe normally in.
What is slightly less known, is that the cabin pressure is not maintained at sea level pressure, that is, the pressure your body might experience at sea level.
So why take all the pains to pressurize the cabin at all, if we cannot keep it at a pressure which is most favorable for the human body?
The answer lies in the structural ability of the aircraft cabin (fuselage) to withstand differential pressures. Ok, now that deserves an explanation!
As we move upwards from the surface of the earth, atmospheric pressure decreases as the air becomes rarer. As mentioned, to overcome the effects of this on the human body, the aircraft is pressurized. So, while the atmospheric pressure (pressure outside the aircraft fuselage) is very low, pressure within the fuselage is quite a bit higher.
Imagine a balloon being inflated, Yes an ordinary birthday balloon! Now, if the pressure within the balloon becomes critically high, in relation to the atmospheric pressure surrounding the balloon, it will…well, burst! This example simply helps appreciate that by pumping air into a balloon we are increasing it’s internal pressure, and when it(differential pressure between internal and external of the balloon) gets beyond that which the balloon is capable of holding, it bursts.
Similarly, an aircraft structure can only withstand a limited amount of differential pressure between the (internal) cabin and the (external) atmosphere….before it, well,… I think we know now!
If you read between the lines, there are 2 factors at play here, between which we must run a compromise. First, the human requirement for cabin/fuselage pressure to be at a level where human physiological functions (mainly breathing) can occur normally. And second, a differential pressure (between cabin/fuselage pressure and external atmospheric pressure) that the aircraft structure can withstand.
Strange dichotomy! Well, if you are an aviation professional, you are probably already quite accustomed to such compromises, technically speaking that is!! Ok, Lets proceed.
So, to meet both these requirements, the cabin pressure is basically set at what you might experience on earth at about 6000 to 8000feet above sea level. This pressure seems quite comfortable for a wide range of people. At the same time, this seems reasonably comfortable for the aircraft structure to withstand without…. The problem is actually compounded the higher the aircraft flies; but, let’s put that away for the moment, lest we put your brain under a cornucopia of information, compelling it to…!
The next time your doctor advises you against flying due to a medical condition, the consequences of this reduced pressure on your body, is probably what he is highlighting.
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