Aircraft Cabin Pressure
#11
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There is no advantage, or need, to run cabin pressure to sea level; the majority of the world's population does not live at sea level. Some world population centers are there, and eventually flights landing there will have cabin pressures matching field elevation, as is always the case; to suggest that all flights should have cabin pressure altitudes that descend to sea level, especially when the flight may never actually go to sea level, makes no sense.
If you'd prefer to figure out world population by cities and location, cite each one, and do the math, more power to you.
How does increasing cabin pressure increase humidity?
Why do composite aircraft have more wiring than conventional airframes?
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#12
Disinterested Third Party
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If you want to take the time to determine world population by city by elevation and do the calculations, be my guest, as previously stated. Again, READ.
Then by all means, show it.
Making a comparison between your air compressor operating at sea level and pressurizing an airframe at altitude is flawed and nonsensical. Pressurizing does not create humidity nor moisture. Think about it. At altitude, where do you think that air is coming from?
In a shop compressor, why does condensation occur? Think about it.
A shop compressor increases pressure, which rises and falls repeatedly as tools utilize the air, which is then pumped back up to a cut-out pressure, again and again.
In an airframe, dry air is continuously pumped through the structure while pressurized to a given value, changing the air every few seconds to minutes, and is continually being released while maintaining a given differential pressure value (which is quite low; far lower than your sea level shop compressor.
You really want to make a comparison between a 6 psid airplane utilizing dry bleed air at altitude and your 80-120 psi compressor at home?
Didn't say that they did. However most newer composite aircraft have many more electronics than their predecessors. In fact I can't think of a single one that doesn't. The 787 is the easy example, and it has far more electronics than its predecessor: the 767. Almost everything on the 787 is electric.
#13
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Statement : The worlds average elevation is 2,700msl
Conclusion: Most of the people in the world live at 2,700msl (or significantly above sea level).
There is no relationship whatsoever between those two ideas, they don't logically follow. The problems with that statement include the fact that people are not evenly dispersed across the land; people also historically tend to concentrate around low rivers, the mouth or significant forks.
The top ten cities in terms of population are:
1
Tokyo, Japan
37,833,000
101'msl
2
Delhi, India
24,953,000
751'msl
3
Shanghai, China
22,991,000
13'msl
4
Mexico City, Mexico
20,843,000
7,400msl
5 São Paulo, Brazil
20,831,000
2500'msl
6
Mumbai, India
20,741,000
26'msl
7
Osaka, Japan
20,123,000
122'msl
8
Beijing, China
19,520,000
150'msl
9
New York/Newark, United States
18,591,000
2'msl (I'm being generous, it comes up as 1 or 0 most of the time on google earth)
10
Cairo, Egypt
18,419,000
95'msl
The average of these is less than half of your figure, and Mexico City might just be an outlier, we'd have to sample more data to know. Typically, the most people in human history lived in the low lands in fertile country where the environment was not harsh, the biggest cities or metro areas in our country follow this pretty well, as with most countries, but it's not about that, it's about the statement not logically following. We know people aren't dispersed evenly by altitude.
#14
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Posts: 233
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No, I wasn't arguing for arguing, you made a statement that did not make sense to me. I tried to explain some reasons that it did not make senses. Sorry if I offended you. Good day.
#15
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One source of academic info:
Maps » Population, Landscape, And Climate Estimates (PLACE), v3: | SEDAC
Also, go look at any major airline's international route map. The majority of their destinations begin/end at or near sea level.
Uh, humans. Humans create moisture. Do you have any idea how much water a human being expels in an hour of air travel? it's about 100ml/hr. Multiply that by 200+ people packed in an airbus on a 5hr transcon and you get 100 LITERS of water built up. Higher aircraft utilization means more time spent flying around with condensation built up inside.
Pressurization does not create humidity or moisture, but it DOES allow more of it to exist in the same space.
Denser air holds more water.
Not really an applicable point. Condensation will still occur in a shop compressor even if no tools are used at all and it simply holds the pressure at whatever level is selected. Put an air compressor at 35,000 feet, set it to 8 PSI, heat it up to 60 degrees, put a human in there, and condensation will still form, even with an outflow valve.
I do wish to make that comparison. Pressurization is pressurization. The air in a cabin pressurized to 5000ft will hold more water than the air in a cabin pressurized to 8000ft. PERIOD.
No. Composites don't corrode. Electronic corrosion however will likely be greater. Stop grasping at straws by trying to put words in my mouth, making blanket statements, and by making this more complicating than it is.
Honestly your lifetime of MX experience isn't something that you can really use to "pull rank" with because composite airliners pressurized down to lower cabin altitudes haven't been around for much more than 10 years, and most mechanics haven't even touched one.
I'm not guessing, I just think it may be time for some reading on your behalf:
BOEING: Controlling Nuisance Moisture in Commercial Airplanes
The rain in planes | The Economist
Condensation is a HUGE issue in airplanes.
Maps » Population, Landscape, And Climate Estimates (PLACE), v3: | SEDAC
Also, go look at any major airline's international route map. The majority of their destinations begin/end at or near sea level.
I'm a practicing A&P mechanic and have been for more years than you've likely been alive. I drain a compressor frequently. The compressor, however, doesn't takeoff, climb to a high altitude, and refresh the air contained within it from a dry source at FL350.
Making a comparison between your air compressor operating at sea level and pressurizing an airframe at altitude is flawed and nonsensical. Pressurizing does not create humidity nor moisture. Think about it. At altitude, where do you think that air is coming from?
Making a comparison between your air compressor operating at sea level and pressurizing an airframe at altitude is flawed and nonsensical. Pressurizing does not create humidity nor moisture. Think about it. At altitude, where do you think that air is coming from?
Pressurization does not create humidity or moisture, but it DOES allow more of it to exist in the same space.
In a shop compressor, why does condensation occur? Think about it.
A shop compressor increases pressure, which rises and falls repeatedly as tools utilize the air, which is then pumped back up to a cut-out pressure, again and again.
In an airframe, dry air is continuously pumped through the structure while pressurized to a given value, changing the air every few seconds to minutes, and is continually being released while maintaining a given differential pressure value (which is quite low; far lower than your sea level shop compressor.
You really want to make a comparison between a 6 psid airplane utilizing dry bleed air at altitude and your 80-120 psi compressor at home?
You really want to make a comparison between a 6 psid airplane utilizing dry bleed air at altitude and your 80-120 psi compressor at home?
Corrosion is greater on composite airplanes, is it?
Condensation greater? Electrical corrosion? You're guessing this, or it's based on a lifetime of maintenance experience?
I'm not guessing, I just think it may be time for some reading on your behalf:
BOEING: Controlling Nuisance Moisture in Commercial Airplanes
The rain in planes | The Economist
Condensation is a HUGE issue in airplanes.
Last edited by threeighteen; 01-22-2016 at 05:20 PM.
#16
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Joined APC: Dec 2010
Posts: 3,114
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"The global distribution of the human population by elevation is quantified here. As of 1994, an estimated 1.88 x 10(9) people, or 33. 5% of the world's population, lived within 100 vertical meters of sea level, but only 15.6% of all inhabited land lies below 100 m elevation. The median person lived at an elevation of 194 m above sea level. Numbers of people decreased faster than exponentially with increasing elevation. The integrated population density (IPD, the number of people divided by the land area) within 100 vertical meters of sea level was significantly larger than that of any other range of elevations and represented far more people"
Source: Hypsographic demography: the distribution of human population by altitude.
Source: Hypsographic demography: the distribution of human population by altitude.
#17
Disinterested Third Party
Joined APC: Jun 2012
Posts: 6,247
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I don't think you get it, what you said logically makes no sense:
Statement : The worlds average elevation is 2,700msl
Conclusion: Most of the people in the world live at 2,700msl (or significantly above sea level).
There is no relationship whatsoever between those two ideas, they don't logically follow. The problems with that statement include the fact that people are not evenly dispersed across the land; people also historically tend to concentrate around low rivers, the mouth or significant forks.
The top ten cities in terms of population are:
1
Tokyo, Japan
37,833,000
101'msl
2
Delhi, India
24,953,000
751'msl
3
Shanghai, China
22,991,000
13'msl
4
Mexico City, Mexico
20,843,000
7,400msl
5 São Paulo, Brazil
20,831,000
2500'msl
6
Mumbai, India
20,741,000
26'msl
7
Osaka, Japan
20,123,000
122'msl
8
Beijing, China
19,520,000
150'msl
9
New York/Newark, United States
18,591,000
2'msl (I'm being generous, it comes up as 1 or 0 most of the time on google earth)
10
Cairo, Egypt
18,419,000
95'msl
The average of these is less than half of your figure, and Mexico City might just be an outlier, we'd have to sample more data to know. Typically, the most people in human history lived in the low lands in fertile country where the environment was not harsh, the biggest cities or metro areas in our country follow this pretty well, as with most countries, but it's not about that, it's about the statement not logically following. We know people aren't dispersed evenly by altitude.
Statement : The worlds average elevation is 2,700msl
Conclusion: Most of the people in the world live at 2,700msl (or significantly above sea level).
There is no relationship whatsoever between those two ideas, they don't logically follow. The problems with that statement include the fact that people are not evenly dispersed across the land; people also historically tend to concentrate around low rivers, the mouth or significant forks.
The top ten cities in terms of population are:
1
Tokyo, Japan
37,833,000
101'msl
2
Delhi, India
24,953,000
751'msl
3
Shanghai, China
22,991,000
13'msl
4
Mexico City, Mexico
20,843,000
7,400msl
5 São Paulo, Brazil
20,831,000
2500'msl
6
Mumbai, India
20,741,000
26'msl
7
Osaka, Japan
20,123,000
122'msl
8
Beijing, China
19,520,000
150'msl
9
New York/Newark, United States
18,591,000
2'msl (I'm being generous, it comes up as 1 or 0 most of the time on google earth)
10
Cairo, Egypt
18,419,000
95'msl
The average of these is less than half of your figure, and Mexico City might just be an outlier, we'd have to sample more data to know. Typically, the most people in human history lived in the low lands in fertile country where the environment was not harsh, the biggest cities or metro areas in our country follow this pretty well, as with most countries, but it's not about that, it's about the statement not logically following. We know people aren't dispersed evenly by altitude.
You're either obsessed with making a worthless point, you're being obtuse, or you actually misunderstood my point.
I really don't think you misunderstood my point.
There is no economic value in pressurizing aircraft to sea level from cruise altitude.
#18
Disinterested Third Party
Joined APC: Jun 2012
Posts: 6,247
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Uh, humans. Humans create moisture. Do you have any idea how much water a human being expels in an hour of air travel? it's about 100ml/hr. Multiply that by 200+ people packed in an airbus on a 5hr transcon and you get 100 LITERS of water built up. Higher aircraft utilization means more time spent flying around with condensation built up inside.
Approximately every 2-3 minutes the cabin air is completely replaced, in that it takes approximately that period of time to flow an entire cabin's volume through the packs and out the outflow valves. What's coming in is very dry air. The relative humidity at altitude is considerably less at lower altitudes.
Your ridiculous comparisons to a home air compressor on the ground, and cabin air obtained from a dry source in a low pressure cabin holds no water.
Ever wonder why one tends to dehydrate on long flights at altitude, and should keep drinking, or why skin tends to dry out on long flights? It's not a humid place at altitude, especially given the fact that large volumes of very dry air are being pumped into the cabin.
Nearly all condensation takes place at lower elevations on descent, and it's not a result of pressurization, but of condensation due to a cold fuselage descending into warmer, humid air.
As for maintenance experience with composites, you clearly wouldn't know, but we've been working composites for many decades now. You're not familiar with fiberglass work, honeycomb structures, bonding, vacuum bagging, or other common maintenance facets of constructing and repairing composite structures, but most mechanics are. Go figure.
#19
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You keep on doing that until you've accounted for more than half the world population. You're off to a good start.
You're either obsessed with making a worthless point, you're being obtuse, or you actually misunderstood my point.
I really don't think you misunderstood my point.
There is no economic value in pressurizing aircraft to sea level from cruise altitude.
You're either obsessed with making a worthless point, you're being obtuse, or you actually misunderstood my point.
I really don't think you misunderstood my point.
There is no economic value in pressurizing aircraft to sea level from cruise altitude.
#20
Gets Weekends Off
Joined APC: Dec 2010
Posts: 3,114
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What is the cabin air frefresh or replacement rate in most modern large airplanes? Do you know?
Approximately every 2-3 minutes the cabin air is completely replaced, in that it takes approximately that period of time to flow an entire cabin's volume through the packs and out the outflow valves. What's coming in is very dry air. The relative humidity at altitude is considerably less at lower altitudes.
Your ridiculous comparisons to a home air compressor on the ground, and cabin air obtained from a dry source in a low pressure cabin holds no water.
Ever wonder why one tends to dehydrate on long flights at altitude, and should keep drinking, or why skin tends to dry out on long flights? It's not a humid place at altitude, especially given the fact that large volumes of very dry air are being pumped into the cabin.
Nearly all condensation takes place at lower elevations on descent, and it's not a result of pressurization, but of condensation due to a cold fuselage descending into warmer, humid air.
As for maintenance experience with composites, you clearly wouldn't know, but we've been working composites for many decades now. You're not familiar with fiberglass work, honeycomb structures, bonding, vacuum bagging, or other common maintenance facets of constructing and repairing composite structures, but most mechanics are. Go figure.
Approximately every 2-3 minutes the cabin air is completely replaced, in that it takes approximately that period of time to flow an entire cabin's volume through the packs and out the outflow valves. What's coming in is very dry air. The relative humidity at altitude is considerably less at lower altitudes.
Your ridiculous comparisons to a home air compressor on the ground, and cabin air obtained from a dry source in a low pressure cabin holds no water.
Ever wonder why one tends to dehydrate on long flights at altitude, and should keep drinking, or why skin tends to dry out on long flights? It's not a humid place at altitude, especially given the fact that large volumes of very dry air are being pumped into the cabin.
Nearly all condensation takes place at lower elevations on descent, and it's not a result of pressurization, but of condensation due to a cold fuselage descending into warmer, humid air.
As for maintenance experience with composites, you clearly wouldn't know, but we've been working composites for many decades now. You're not familiar with fiberglass work, honeycomb structures, bonding, vacuum bagging, or other common maintenance facets of constructing and repairing composite structures, but most mechanics are. Go figure.
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.
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