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Old 01-22-2016, 02:58 PM   #11  
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Originally Posted by JohnBurke View Post
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.
There is no advantage to having to ALL flights be pressurized to Sea Level Pressure, but there is an advantage to having airplanes with that capability: Passenger comfort. Imagine flying from JFK to DXB and never feeling the effects of a pressurization system because the cabin was kept at sea level pressure the whole time....

Quote:
If you'd prefer to figure out world population by cities and location, cite each one, and do the math, more power to you.
It's already been done.

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How does increasing cabin pressure increase humidity?
Denser air holds more water. If you've ever owned an air compressor you would know this because the tank of an air compressor must be drained often to ensure the inside does not rust.

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Why do composite aircraft have more wiring than conventional airframes?
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.
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Old 01-22-2016, 03:56 PM   #12  
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Originally Posted by andrewtac View Post
That doesn't make sense (above); what if everyone in those countries live on the coast.
They don't, and you're arguing for arguing's sake. I think you get the point.

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.

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Originally Posted by threeighteen View Post

It's already been done.
Then by all means, show it.

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Originally Posted by threeighteen View Post

Denser air holds more water. If you've ever owned an air compressor you would know this because the tank of an air compressor must be drained often to ensure the inside does not rust.
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?

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?

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Originally Posted by threeighteen View Post
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.
As is everything on an airbus, for the most part. 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?
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Old 01-22-2016, 04:27 PM   #13  
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Quote:
Originally Posted by JohnBurke View Post
They don't, and you're arguing for arguing's sake. I think you get the point.

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.
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.
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Old 01-22-2016, 04:37 PM   #14  
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Originally Posted by JohnBurke View Post
They don't, and you're arguing for arguing's sake. I think you get the point.

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.
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.
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Old 01-22-2016, 05:01 PM   #15  
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Quote:
Originally Posted by JohnBurke View Post
Then by all means, show it.
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.

Quote:
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?
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.

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In a shop compressor, why does condensation occur? Think about it.
Denser air holds more water.

Quote:
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.
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.

Quote:
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?
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.

Quote:
Corrosion is greater on composite airplanes, is it?
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.

Quote:
Condensation greater? Electrical corrosion? You're guessing this, or it's based on a lifetime of maintenance experience?
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.

Last edited by threeighteen; 01-22-2016 at 05:20 PM.
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Old 01-22-2016, 05:18 PM   #16  
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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.
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Old 01-22-2016, 06:14 PM   #17  
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Quote:
Originally Posted by JamesNoBrakes View Post
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.
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.
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Old 01-22-2016, 06:24 PM   #18  
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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.
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.
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Old 01-22-2016, 07:12 PM   #19  
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Originally Posted by JohnBurke View Post
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.
No, I'm just calling you out on a nonsense claim you made.
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Old 01-22-2016, 08:17 PM   #20  
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Originally Posted by JohnBurke View Post
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.
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.
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