Have you got your ear numb when you’re moving from one altitude to another one? It may happen when you use high elevator or mostly when you’re inside a takeoff or landing aircraft. In normal circumstances the air pressure is the same on both sides of our eardrums. But when the pressure in our environment changes significantly, the pressure on the outside of the eardrum is no longer the same as that on the inside. This pressure difference is eventually regulated by the Eustachian tube, a sort of air canal that links the middle ear to the back of the throat. If your eardrum can’t take the pressure difference, It will do the same as a balloon will blown up when it fly too high.
SO how about when we’re taking aircraft? Actually the air pressure outside the aircraft at 32000 ft is about 223 mmHg which means it only has about 1/3 of oxygen compared to sea level (760 mmHg) and the temperature may drop to -44°C. In that condition, human would have serious respiratory problem and may die (For that reason, at the beginning of aircraft invented, all the passengers must use oxygen mask).
Today as we know we don’t have to use any living support tools to stay alive while flying in high altitude. It happened since our aircraft cabin is pressurized while the air temperature also maintained. But why our ear still feel pressure difference while we are flying?
I got it into my mind when I was take a flight a moment ago. By using barometer in my phone, I realized the cabin pressure is not the same as sea level. But why? After doing some search, I found that it has many reasons doing that.
First is, the higher aircraft cabin pressure the more stress aircraft frame get while flying. It’s like a balloon, it will getting bigger while flying to higher altitude (or blown up since the rubber can’t stretch anymore). It will bring aircraft lifetime drop since aircraft frame stretch and flex a bit, after hundreds of stretch, it will broken. Second is, if the aircraft windows is broken, the pressure inside cabin will drop quickly, it will harm our ear and other organs if the pressure change drastically in a moment. By making the pressure about 2/3 sea level, the pressure change will be more acceptable and our body will feel a lighter shock. The last one is, the more we need to pressurize cabin means aircraft must bring more compressed air from ground which increase the weight and power to decompress and cooling it. More power means more fuel are wasted to do that thing. For those reasons, we will still have unpleasure moment when the airplane takeoff or landing.
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