Things you always wanted to know the answer to [Vol. 5]

[RizzoTheRat]

popeyewhite said:

As cabins are pressurised it shouldn't make much difference. I think my ears may 'pop' sometimes but i don't keep score. Perhaps you have an old or chronic eardrum injury?

They're usually pressurised to around 8000 feet, enough that you should be able to notice but it shouldn't give discomfort unless you have blocked eustachion tubes or sinuses.

[captain_cynic]

RizzoTheRat said:

popeyewhite said:

As cabins are pressurised it shouldn't make much difference. I think my ears may 'pop' sometimes but i don't keep score. Perhaps you have an old or chronic eardrum injury?

They're usually pressurised to around 8000 feet, enough that you should be able to notice but it shouldn't give discomfort unless you have blocked eustachion tubes or sinuses.

Modern widebodies are pressurised to 5000-6000ft.

Taking off from Bogota last week it was fun to see the altimeter start out at 8,300 ft, the plane I was on (A350) can be pressurised at a lower altitude (5,500 ft).

[Halmyre]

Trustmeimadoctor said:

Rusty Old-Banger said:

Trustmeimadoctor said:

Rich Boy Spanner said:

audi321 said:

Roofless Toothless said:

Halmyre said:

You're allowed to store small bags under the seat in front, are you not? I've never had any bother.

The seat in front? Surely it goes under your own seat. The passenger in the foremost seat hasn’t got a seat in front and would have to use his own seat to stow away luggage, and so on all the way to the back of the plane.

It’s supposed to go under the seat in front of you.

The passengers in the foremost seats have to stow their luggage in the overhead lockers as they’re going to be exit seats.

Note also that different aircraft types have different seat options to the airline. Some have more space under them than others. An A320 generally has more under seat space that a B737. Also, if you are on an airline with in-seat power or IFE the boxes for those can take a chunk of your space away.

yep very hard to store my bags under the lay flat bed of the person in front but thats why we get more locker space and more cupboards

The cringe.

jealousy i tell you!
i will get my man servant to come and educate you

Is that a euphemism?

[popeyewhite]

RizzoTheRat said:

popeyewhite said:

As cabins are pressurised it shouldn't make much difference. I think my ears may 'pop' sometimes but i don't keep score. Perhaps you have an old or chronic eardrum injury?

They're usually pressurised to around 8000 feet, enough that you should be able to notice but it shouldn't give discomfort unless you have blocked eustachion tubes or sinuses.

Anyone who scuba dives will have experience of how unpleasant change of pressure can be without equalisation. As a sidenote if you do have blocked tubes and want to clear them going underwater for a few seconds will do the trick. Can lead to some 'murky' swimming pool water though.

[RizzoTheRat]

captain_cynic said:

Modern widebodies are pressurised to 5000-6000ft.

Interesting, is that to improve passenger comfort? I believe altitude makes DVT more likely, dunno if there are other medical issues at those kind of altitudes.

[popeyewhite]

The risk is sitting still for a length of time.

[captain_cynic]

RizzoTheRat said:

captain_cynic said:

Modern widebodies are pressurised to 5000-6000ft.

Interesting, is that to improve passenger comfort? I believe altitude makes DVT more likely, dunno if there are other medical issues at those kind of altitudes.

Largely yes. Not just DVT but a whole host of issues (hypoxia, barotrauma, altitude sickness). 8000ft was always a compromise between comfort, safety and the technology to pressurise cabins.

Cabin air is still dryer than a cream cracker at a chemsitry teachers comedy night (there is just not that much moisture in the air at 30-40,000 ft no matter how much you compress it). Staying hydrated is a huge factor in passenger comfort.

[Trustmeimadoctor]

captain_cynic said:

RizzoTheRat said:

captain_cynic said:

Modern widebodies are pressurised to 5000-6000ft.

Interesting, is that to improve passenger comfort? I believe altitude makes DVT more likely, dunno if there are other medical issues at those kind of altitudes.

Largely yes. Not just DVT but a whole host of issues (hypoxia, barotrauma, altitude sickness). 8000ft was always a compromise between comfort, safety and the technology to pressurise cabins.

Cabin air is still dryer than a cream cracker at a chemsitry teachers comedy night (there is just not that much moisture in the air at 30-40,000 ft no matter how much you compress it). Staying hydrated is a huge factor in passenger comfort.

and not with alcohol!

[popeyewhite]

Trustmeimadoctor said:

captain_cynic said:

RizzoTheRat said:

captain_cynic said:

Modern widebodies are pressurised to 5000-6000ft.

Interesting, is that to improve passenger comfort? I believe altitude makes DVT more likely, dunno if there are other medical issues at those kind of altitudes.

Largely yes. Not just DVT but a whole host of issues (hypoxia, barotrauma, altitude sickness). 8000ft was always a compromise between comfort, safety and the technology to pressurise cabins.

Cabin air is still dryer than a cream cracker at a chemsitry teachers comedy night (there is just not that much moisture in the air at 30-40,000 ft no matter how much you compress it). Staying hydrated is a huge factor in passenger comfort.

and not with alcohol!

The link between DVT and altitude in healthy individuals has not been established AFAIA. I don't know the very latest research (this was last year) but that's what my partner's cardiologist told her.

[Granadier]

Probably just showing my stupidity, only just thought of this question: I always assumed an aircraft cabin in flight was airtight (and obviously rigid in shape/size), so how is the air pressure inside the cabin affected by the air pressure outside? Why doesn't being in a rigid, sealed, airtight container prevent you from feeling the change in external air pressure?

[popeyewhite]

If you were fed outside air to breathe the plane could only climb as high as there was enough oxygen outside to breathe in the plane. Planes go higher generally so passengers are given conditioned air.

[Clockwork Cupcake]

Granadier said:

Probably just showing my stupidity, only just thought of this question: I always assumed an aircraft cabin in flight was airtight (and obviously rigid in shape/size), so how is the air pressure inside the cabin affected by the air pressure outside? Why doesn't being in a rigid, sealed, airtight container prevent you from feeling the change in external air pressure?

A sealed airtight aircraft would not contain enough air for all the occupants for the duration of the flight.

[captain_cynic]

Clockwork Cupcake said:

Granadier said:

Probably just showing my stupidity, only just thought of this question: I always assumed an aircraft cabin in flight was airtight (and obviously rigid in shape/size), so how is the air pressure inside the cabin affected by the air pressure outside? Why doesn't being in a rigid, sealed, airtight container prevent you from feeling the change in external air pressure?

A sealed airtight aircraft would not contain enough air for all the occupants for the duration of the flight.

Yep. It's not a completely sealed system. You're still cycling air from the outside for oxygen (bleed air from the engine compressors in most aircraft, a separate pump system in B787s)

The pressure changes as you climb, even though it's at a different rate. It is possible to maintain pressure at sea level but we don't becuse of the amount of power it would take and risks that would occur in the event of a sudden depressurisation.

[popeyewhite]

Clockwork Cupcake said:

Granadier said:

Probably just showing my stupidity, only just thought of this question: I always assumed an aircraft cabin in flight was airtight (and obviously rigid in shape/size), so how is the air pressure inside the cabin affected by the air pressure outside? Why doesn't being in a rigid, sealed, airtight container prevent you from feeling the change in external air pressure?

A sealed airtight aircraft would not contain enough air for all the occupants for the duration of the flight.

Is the poster asking whether the integrity of the aircraft hull is good or not? Ie is it sealed completely airtight? Not sure I understand the question correctly...

[Granadier]

Thanks everyone. I had stupidly assumed that an aircraft was sealed and carried all the air it would need inside it, like a spacecraft or a submarine would. I recall that spacecraft have oxygen tanks and also devices that convert carbon dioxide into oxygen. But I see now that, unlike spacecraft and submarines, an airliner has the advantage of travelling through air, even if it's low-pressure air... so I assume it takes air from outside and pressurises it with pumps?

[stemll]

Submarines don't carry all the oxygen either. They extract it from the water

[Granadier]

stemll said:

Submarines don't carry all the oxygen either. They extract it from the water

Excellent, I reveal myself as being more wrong with every reply I post! It's good to learn things, anyway.

[RizzoTheRat]

Granadier said:

so I assume it takes air from outside and pressurises it with pumps?

Gas turbines are essentially like a turbo charger on a car, compressor at the front driven by a turbine at the back, but with multiple stages and usually on 2 or 3 separate shafts. Most aircraft take air from one of the low pressure compressor stages, where it's will be at several bar pressure and possible a couple of hundred Celsius, and then filter and cool it before be piped in to the cabin. Although as Captain Cynic says above some aircraft have separate pumps which I hadn't realised.

[Clockwork Cupcake]

stemll said:

Submarines don't carry all the oxygen either. They extract it from the water

Generally only nuclear submarines generate oxygen from water via electrolysis, as it is very power-hungry. Traditional diesel-electric submarines use a combination of pressurised tanks and chemical processes that yield oxygen. And, of course, CO2 scrubbers.

[C n C]

captain_cynic said:

Clockwork Cupcake said:

Granadier said:

Probably just showing my stupidity, only just thought of this question: I always assumed an aircraft cabin in flight was airtight (and obviously rigid in shape/size), so how is the air pressure inside the cabin affected by the air pressure outside? Why doesn't being in a rigid, sealed, airtight container prevent you from feeling the change in external air pressure?

A sealed airtight aircraft would not contain enough air for all the occupants for the duration of the flight.

Yep. It's not a completely sealed system. You're still cycling air from the outside for oxygen (bleed air from the engine compressors in most aircraft, a separate pump system in B787s)

The pressure changes as you climb, even though it's at a different rate. It is possible to maintain pressure at sea level but we don't becuse of the amount of power it would take and risks that would occur in the event of a sudden depressurisation.

Ok - so am I correct that from reading the various replies on this thread, taking that a common airliner is pressurised to 8000 feet, assuming that it takes off from sea level, the changes in air pressure which can cause discomfort/ears popping etc.. should all occur due to the pressure drop as it climbs from take-off to 8000 feet? Once it climbs above 8000 feet, the cabin air pressure is stabilised, so there should be no further air pressure changes as it goes beyond 8000 feet up to whatever its cruising altitude is?

The reverse happens when it descends - no presure change until it gets down to 8000 feet, then the air pressure will increase from 8000 feet down to whatever altitude the runway is at.

By the sound of it, some more recent planes are pressurised to lower altitudes (5000 feet), so there is less of a pressure change on these?