Por que as cabines de aeronaves não são pressurizadas à pressão do nível do mar?

Question

Por que as cabines de aeronaves não são pressurizadas à pressão do nível do mar?

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5

De um artigo on WHO's website:

Although aircraft cabins are pressurized, cabin air pressure at cruising altitude is lower than air pressure at sea level. At typical cruising altitudes in the range 11 000–12 200 m (36 000–40 000 feet), air pressure in the cabin is equivalent to the outside air pressure at 1800–2400 m (6000–8000 feet) above sea level.

Why aren't cabins completely pressurized, but instead to 6000-8000', seeing that many passengers wouldn't have to endure às vezes painful popping in the ears?

pressão da cabine

por William R. Ebenezer 14.07.2019 / 19:40

3 respostas

The higher the pressure differential between inside and outside, the more stress is put on the plane, which reduces lifespan, and the stronger it needs to be, which increases weight. More weight means more fuel burn and shorter range. All of these factors would combine to increase the overall cost of operation--and eventually fares.

Many passengers don't even notice the higher cabin altitude, especially the frequent fliers who account for the vast majority of airline revenue, so there is little financial incentive to change.

15.07.2019 / 00:28

Because the extra air would add extra weight!

In all seriousness the weight of the extra air might well be on par with a layer of paint, or heavier, and we are often told that airliners are sometimes left partially unpainted (e.g. on undersides) to save weight.

Of course the extra structure required by the extra pressurization would also add weight.

14.07.2019 / 23:30

Tags pressão da cabine

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score 7 · Accepted Answer

Two reasons: Longevity and weight. Which really come down to just weight.

Airframes have a limited fatigue life, measured in flight cycles. The main driving factor for airliner airframe wear is pressurizing and depressurizing them. Each millibar of difference between cabin pressure and outside pressure effectively consumes some percentage of the airframe's fatigue life.

Reducing the cabin altitude means increasing this pressure difference, and thus consuming more of the airframe's life. This could be compensated for with sturdier construction, which adds weight. It would also consume a little more bleed air, requiring slightly heavier packs, which, as well as weight, means a loss of efficiency.

Luxury business jets often maintain a lower cabin altitude, such as 4,000 ft. This eats into their flight cycles, so they can still be switched to the usual 8,000 ft for flights without the owner/VIP inside.
Carbon fiber has a much longer fatigue life, so CFRP fuselages can afford to lower the cabin altitude to 6,000 ft. This pressure altitude can also be maintained in other airliners at flight levels well below their ceiling.

The optimum compromise point is sujeito a muito debate. The highest cabin altitude that could be permitted is 15,000 ft, above which hypoxia-induced loss of consciousness can occur. The regulatory bodies have settled at 8,000 ft, so that's what the manufacturers targeted with most of their aluminum airliners, and that's where airlines prefer to run them even if they have a choice, to get more life out of their planes.