Why does air pressure difference make us have airplane ears during a flight, if airliners are pressurized?
In: Physics
Aircraft aren’t pressured to the same as sea level, at cruising altitude there’s still a noticeable difference between ground level air pressure and cabin air pressure.
Airliners are not pressurized to the pressure of the airport you take off from or to sea level pressure. The requirement is the pressure should be at least what it is at 8,000 ft (2,438 m) which is close to 75% of the pressure at sea-level
The reason is the higher the pressure difference between the inside and outside the higher the force the hull needs to handle. You could build the airplane so it is pressurized to sea-level pressure, it is allowed and not hard at all, the problem is it would make the airplane heavier, which means it costs more to operate. Some airplanes are pressurized to a slightly lower altitude but I do not think any is to sea-level
The required pressure is picked so humans do not get sick from it. The problem with air is one of pressure change and there are rules of how fast the pressure can drop and increase.
Airplanes are pressurized so the cabin environment is equivalent to no more that 8,000ft of altitude, that’s still 8,000 feet to adjust for your ears.
Translate to absolute figures, on the ground level it’s 1 ATM, up at cruising altitude of around 33,000 feet, it’s 0.2-0.3 ATM outside and 0.8 ATM inside, the ears have to vent out 20% of air during climb and take in 20% air during descent. If your ears can’t adjust quick enough, pressure builds up on your eardrums and it hurts.
Better materials like carbon fiber is used in construction of newer planes, so they can be designed to take more pressure differential, they can be pressurized to the equivalent of maybe 6,000 feet of air pressure inside the cabin, this reduces fatigue for occupants and maybe less stress for your ears.
A great example of what people are talking about below – bring a bag of chips and water bottle on your next flight.
In the middle of the flight check them out, your bag of chips will be HUGE and swollen like my ego. Drink half the water and put the bottle back in your bag. When you the land the bottle will get all shrunken and crushed like a puppy on the highway.
Other people have commented about the 8000 foot pressurization, so I’ll ignore that in my comment. Another thing to add is that the cabin pressure can rapidly change when the engines spin up or down. Cabin pressure is maintained by bleeding air from the high pressure turbines just before combustion. Even if they are targeting 8000 feet of elevation, this drop or increase in pressure can be felt by your ears.
Its also why one of the first signs of a bird strike is the distinct aroma of fried chicken in the cabin.
If you are rich enough, you can buy a jet with 0 changes of cabin pressure! The disadvantage of this is, that the whole airplane needs to be rated for a higher pressure difference. This makes it heavier.
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In a way it’s the same reason you get those when driving in mountainous or very hilly terrain. It’s just the change in pressure. The airplane takes you to the top of the mountain and then gives you pressurized air after that. When you land and you start coming down the mountain you come down fast and your ears can’t adjust.
I use Afrin nose spray on every flight and my ears “pop” so much faster with a lot less pain.. I used to hate flying and my ears would not pop until the next day… sucked so bad especially if I had to take multiple flights, those puddle jumper flights were so bad.
They are only pressurized to a point. They don’t pressurize above the equivalent of 8000 feet altitude.
Pressurization is stressful on the fuselage, they need to strike a balance between passenger comfort and fuselage weight.
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