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Old 01-22-2016, 08:32 PM   #21  
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Quote:
Originally Posted by threeighteen View Post
I've had plastic cups of iced soda collect condensation on the outside of the cup while in cruise.
Well there you go. You ARE an expert.

Ignore list for you.
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Old 01-22-2016, 10:38 PM   #22  
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Originally Posted by JamesNoBrakes View Post
No, I'm just calling you out on a nonsense claim you made.
You quoted me responding to someone else, and then answered as though it was directed to you?

You can do better than that.

I provided numbers. Do better.
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Old 01-23-2016, 07:49 AM   #23  
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Thank you, John and Adlerdriver. That is exactly the information and understanding I was looking for. You explained it in a way that is completely understandable to me. What was most interesting to me are the tradeoffs in cabin pressure and aircraft operation and maintenance.

My Dad was a retired Flying Tigers 747 Captain, and I worked for 27 years at Tigers and Fedex (in sales). I don't have any expertise in this area, obviously, but I do have a lot of interest.

I appreciate you taking the time to explain everything in layman's terms.

Thank you!

Mark
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Old 01-27-2016, 10:20 AM   #24  
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Originally Posted by JohnBurke View Post
The world's average elevation is 2,700.'
Average elevations by country...
USA: 2,500'
China: 6,000'
India: 525'
Russia: 2,000'
South Africa: 3,400'
Indonesia: 1,200'
Brazil: 1,000'
Pakistan: 3,000'
Nigeria: 1,200'
Mexico: 3,600'
Japan: 1,400'
Phillipines: 1,400'
Ethiopia: 4,300'

That's over 58% of the world population by country living at an average of 2,400 as established by word population by country, and average elevation of those countries.

I didn't try to say anything. I said it.
Global/national geographic average elevations don't reflect where people actually live. They don't live on mountain tops at all, and they tend to concentrate near oceans and rivers (ease of transport way back in the day).

From the naval power projection perspective, a large majority of the global population lives very close (helicopter/strike fighter range) to an ocean.

I'm pretty confidant that the average elevation of the global population is well under 1000', probably within a few hundred feet of sea level.

The average elevation of air travelers actually may be a bit higher...folks in the boondocks may have more need/desire to travel.
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Old 01-27-2016, 07:12 PM   #25  
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Originally Posted by rickair7777 View Post
Global/national geographic average elevations don't reflect where people actually live. They don't live on mountain tops at all, and they tend to concentrate near oceans and rivers (ease of transport way back in the day).

From the naval power projection perspective, a large majority of the global population lives very close (helicopter/strike fighter range) to an ocean.

I'm pretty confidant that the average elevation of the global population is well under 1000', probably within a few hundred feet of sea level.

The average elevation of air travelers actually may be a bit higher...folks in the boondocks may have more need/desire to travel.
Being obtuse, or you really don't get it?

You do understand that this is about cabin pressurization and not where people actually live, right?

Again, for those too slow to read the first few times, you're welcome to do the math city by city and find the actual population at sea level if you wish, but it's really irrelevant to the fact that there's no economic benefit to pressurizing cabins to sea level, nor is there a particular need given that such a large percentage of the worlds population doesn't actually live at sea level.

You go ahead and spend your evening coming up with better numbers, if it's that important to you. Until then, put up or shut up...and do try to stick with the subject of the thread, will you?
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Old 01-27-2016, 08:21 PM   #26  
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Speaking of cabin pressure, what's the procedure if a F/A reports that it's too high in coach, but OK in first class?
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Old 01-31-2016, 05:32 AM   #27  
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Most airplanes have a "CAFCBAV" to help this:

"Coach & First Class Balancing Air Vent"
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Old 02-07-2016, 08:22 PM   #28  
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Cabin pressurization is a necessary evil for airliners and nothing that a designer wants to deal with. The original Boeings had the benefit of being designed while Comets were exploding in flight. They put a lot more time into their fuselage because of it. Everything was fine until a 737 popped its top in Hawaii. After that, the FAA began paying a lot more attention to older aircraft. The entire fleet got massive doublers/patches around the L1 and R1 doors and an ongoing NDT program. DC-8 and 9 fuselages are much stronger than Boeings, they are limited more by damage than fatigue cycles. The fuse skin may gain some compression strength while pressurized but it doesnt matter because the only time it actually buckles is on hard landings. The 787 fuse is actually heavier than a metal one. Once enough material is added for omnidirectional strength and allowable damage, it is very robust. This along with excellent fatigue life of composites allow the cabins to be pumped up a little more without penalty. As far as moisture, yes, airliners are wet and nasty under the interior. Lav and galleys stay saturated and smell like dumpsters, lower insulation is usually full of "blue" water. You all should change a cabin air recirculation filter to fully appreciate your work environment.
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Old 03-05-2016, 08:51 AM   #29  
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Originally Posted by threeighteen View Post
The experience of dealing with composites is not equivalent to experience with complete carbon fiber fuselage/pressure vessel capable of lower altitudes of pressurization. The material is the same, the application of the material and the subsequent environment that it creates is drastically different.

I must regretfully step out of this debate. You call my comparisons ridiculous and then proceed to illogically compare and link unrelated items such as the average elevation of a country to the elevation at which the majority of its population lives... You also did not read anything I linked because even BOEING and AIRBUS are actively trying to find ways to reduce condensation building up in long-haul aircraft because of the humidity created inside. The pressure vessel itself in the aircraft is cold. The air inside is warmer than the physical pressure vessel. This causes condensation to build inside the pressure vessel as the flight progresses, even if the air is constantly being replaced. Just like condensation would build on a cold glass of lemonade in a room at room temperature. I've had plastic cups of iced soda collect condensation on the outside of the cup while in cruise.
The level of humidity in a airliner at cruise altitude is virtually zero. Boeing humidifies the 787 to bring the moisture level up making for a more comfortable flight. The are trying to add moisture not reduce it.
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Old 03-06-2016, 10:34 AM   #30  
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Originally Posted by WhatNow View Post
The level of humidity in a airliner at cruise altitude is virtually zero. Boeing humidifies the 787 to bring the moisture level up making for a more comfortable flight. The are trying to add moisture not reduce it.
I'll just put these here again.....

Straight from Boeing (they know a thing or two about airplanes): Controlling Nuisance Moisture in Commercial Airplanes

The rain in planes | The Economist
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