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