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B787 Cabin Humidity  
User currently offlineGaut From Belgium, joined Dec 2001, 344 posts, RR: 2
Posted (9 years 5 months 1 week 6 days 7 hours ago) and read 5117 times:

Hi all,

In the B787 family internet pages, Boeing says that: Passengers will also see improvements with the new airplane, from an interior environment with higher humidity to increased comfort and convenience.

I understand that the extensive use of composite in the new aircraft reduce the corrosion problem but in an aircraft, the moisture condense between the cabin panels and the cold fuselage. It create a number of problem. These include added dead weight, deterioration of the wiring insulations, microbial growth and drips through the liner onto the occupants and furnishings bellow!

How Boeing will manage to avoid those problem?

In current aircraft, humidity = 5 to 25%. What are the B787 numbers.

Thanks for your answers,

Gaut


«Horum omnium fortissimi sunt Belgae.»
18 replies: All unread, jump to last
 
User currently offlinePipoA380 From Switzerland, joined May 2005, 1594 posts, RR: 51
Reply 1, posted (9 years 5 months 1 week 6 days 6 hours ago) and read 5092 times:
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I guess they managed better insulation.


It's not about AIRBUS. it's not about BOEING. It's all about the beauty of FLYING.
User currently offlineDfwRevolution From United States of America, joined Jan 2010, 989 posts, RR: 51
Reply 2, posted (9 years 5 months 1 week 6 days 6 hours ago) and read 5053 times:

Quoting Gaut (Thread starter):
These include added dead weight,

If the water is in vapor form or condensation form... it's the same amount of weight. You can't just create matter  Wink

Quoting Gaut (Thread starter):
These include added dead weight, deterioration of the wiring insulations, microbial growth and drips through the liner onto the occupants and furnishings bellow!

It's an airplane, not Houston!  Wink

You're exaggerating the amount of condensation that can form just a bit...

Quoting PipoA380 (Reply 1):
I guess they managed better insulation.

Bingo... not even "better" per say.


User currently offlineGaut From Belgium, joined Dec 2001, 344 posts, RR: 2
Reply 3, posted (9 years 5 months 1 week 6 days 6 hours ago) and read 4999 times:

Well Im not a specialist. I was reading this presentation when this question arose.

Better insulation usualy means more weight (IMHO).

Gaut



«Horum omnium fortissimi sunt Belgae.»
User currently offlineDfwRevolution From United States of America, joined Jan 2010, 989 posts, RR: 51
Reply 4, posted (9 years 5 months 1 week 6 days 6 hours ago) and read 4977 times:

Quoting Gaut (Reply 3):
Well Im not a specialist

And you expect us to be? If the presentation is available online, it's a good bet the publisher is too. Ask'em.

Quoting Gaut (Reply 3):
Better insulation usualy means more weight (IMHO).

How did you come to that conclusion? That's like saying, to build something stronger, it must be heavier. The best insulator in the world (aerogel) is one of the lightest substances ever manufactured. The 787 won't have aerogel blankets, but its a wild to assume that a better insulation is heavier.


User currently offlineFriendlySkies From United States of America, joined Aug 2004, 4115 posts, RR: 5
Reply 5, posted (9 years 5 months 1 week 6 days 6 hours ago) and read 4955 times:

Quoting DfwRevolution (Reply 2):
You can't just create matter

No, but according to Einstein you can turn it into energy...maybe Boeing is playing with quantum physics...


User currently offlineGaut From Belgium, joined Dec 2001, 344 posts, RR: 2
Reply 6, posted (9 years 5 months 1 week 6 days 6 hours ago) and read 4945 times:

DFW,

You are right, this topic is in the wrong forum. This Civil forum only admit 'A vs B' or 'US vs EU' topics.

Anyway thanks for your interesting inputs.

Gaut



«Horum omnium fortissimi sunt Belgae.»
User currently offlinePihero From France, joined Jan 2005, 4608 posts, RR: 77
Reply 7, posted (9 years 5 months 1 week 6 days 4 hours ago) and read 4852 times:
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Gaut,
It is a matter of physics :the humidity in the 787 should be higher than on another airplane as basically the conditioning system will start its cycle with an unheated volume of air : on a normal airplane tne air used comes from the engines compressor: due to the compression heat, the relative humidity of that air drops to a very low value, then it is piped into the air cycle machine and a condenser that draws out the last amount of water vapour which is left.
As I understand,on the 87 the air is just pumped from the outside and compressed just enough to satisfy pressurisation needs and in principle, the drop in relative humidity is just the result of raising the -55°C air to the +22°C or thereabout for a/c purposes.Whether they will include a humidifier system is unknown.
But as you pointed out, the corrosion risks are higher for the cabin systems and the wirings rather than the common thought about fuselage...After all, aluminium quickly stops corroding after the film of alumine, AlO2, has formed on the surface .

By the way, thanks for a very informative, though yukkie link !
Now I know why passengers at the back enjoy more humidity :it comes from the sweat, the breath......of the pax in front.
Sobering thought.

Regards



Contrail designer
User currently offlineKatekebo From United States of America, joined Apr 2001, 704 posts, RR: 6
Reply 8, posted (9 years 5 months 1 week 5 days 5 hours ago) and read 4716 times:

I am not an aviation expert, and I have not studied this subject in depth, but I am mechanical engineer and have my 2 cents:

1) Aluminum is an excellent heat transfer material, while composites are generally a good heat insulator. Therefore is can be expected that the inner wall of a composite fuselage will be "warmer" than an aluminum wall (which essentially would be as cold as the air outside). This could be enough to avoid condensation on the interior wall. With an aluminum wall, internal humidity must be maintained at a level such that the dew point is equal or within few degrees from the exterior temperature to avoid condensation on the interior surface. As a composite wall provides some degree of thermal insulation, you can afford higher humidity without risk of condensation.

2) Insulation materials are also getting more advanced and surely today Boeing can come up with wall insulation which is thinner and lighter than materials available 10 years ago when airliners such as B777 or A330/340 were designed.

3) Corrosion is greatly increased when there is condensation. Given that the new composite fusalege will provide some degree of thermal insulation compared to aluminum, even cables and other systems located right next to the wall would not be subject to condesation even at (slightly) higher relative humidity.

4) Regarding humidifiers, this will probably not be necessary. Modern airliners recirculate some portion of the air and people exhale significant amount of moisture with every breath. This amount of mositure should be enough to maintain the required relative humidity inside the plane.


User currently offlineUAL747 From , joined Dec 1969, posts, RR:
Reply 9, posted (9 years 5 months 1 week 5 days 5 hours ago) and read 4703 times:

I think that Boeing is trying to fix the issue of cabin air dryness. On long flights, the air often times becomes very dry. In fact, they say you should drink one glass of water for every hour you are on the plane so you won't become dehydrated.

UAL


User currently offlineTod From Denmark, joined Aug 2004, 1729 posts, RR: 3
Reply 10, posted (9 years 5 months 1 week 4 days 9 hours ago) and read 4638 times:

Quoting DfwRevolution (Reply 2):
You're exaggerating the amount of condensation that can form just a bit...

Unless properly controlled with drains, condensation in the cond air ducting can rain down on pax.

Quoting UAL747 (Reply 9):
should drink one glass of water for every hour you are on the plane so you won't become dehydrated.

To be effective, instead of just being a frequent lav visitor, try to get well hydrated prior to flight in addition to during the flight.


User currently offlineYUL332LX From Canada, joined Feb 2004, 820 posts, RR: 1
Reply 11, posted (9 years 5 months 1 week 2 days 7 hours ago) and read 4547 times:

Quoting Gaut (Thread starter):
In current aircraft, humidity = 5 to 25%. What are the B787 numbers.

The 25% figure for today's aircraft at 8,000ft. seems a bit farfetched. Even the 787 will be nowhere near 25% at 6,000ft. Accurate numbers are in the neighbourhood of 5-15%.

Boeing's goal for the 787 is 16% relative humidity at 6,000ft.

The impact of higher humidity alone will be quite limited though. Boeing has acknowledged this by reducing the expected compound level in the cabin, which will also reduced dehydration symptoms.



E volavo, volavo felice più in alto del sole, e ancora più su mentre il mondo pian piano spariva lontano laggiù ...
User currently offlineHAWK21M From India, joined Jan 2001, 31692 posts, RR: 56
Reply 12, posted (9 years 5 months 1 week 1 day 18 hours ago) and read 4485 times:

Quoting DfwRevolution (Reply 4):
The best insulator in the world (aerogel) is one of the lightest substances ever manufactured.

Tell me more about Aerogel pls.
regds
MEL



Think of the brighter side!
User currently offlineZvezda From Lithuania, joined Aug 2004, 10511 posts, RR: 64
Reply 13, posted (9 years 5 months 6 days 9 hours ago) and read 4371 times:

Quoting Tod (Reply 10):
Unless properly controlled with drains, condensation in the cond air ducting can rain down on pax.

I experienced this once in a J31/41. Most of the passengers were quite alarmed to be "rained upon" while sitting in their seats. I think about one liter of water passed into the cabin in a period of perhaps a minute.


User currently offlineZRH From Switzerland, joined Nov 1999, 5569 posts, RR: 36
Reply 14, posted (9 years 5 months 6 days 8 hours ago) and read 4366 times:

I doubt that the airlines really want to have more humidity. I agree that it is better for the passengers and more comfortable but if you had to moisten the air you would have to carry this water extra. And as we no every kilogram more costs a lot.

User currently offlineMcGoose From Sweden, joined Aug 2004, 37 posts, RR: 0
Reply 15, posted (9 years 4 months 4 weeks 1 day 14 hours ago) and read 4191 times:

If you are interested in issues concerning humidity you should have a look at CTT Systems who offers two systems, the Zonal drying for removing condensation and the Cair-system for adding humidity in the cabin. Recently Air Mauritius chose to become the launch-customer for the Cair-system. I believe more carriers will follow.

User currently offlineTrex8 From United States of America, joined Nov 2002, 4791 posts, RR: 14
Reply 16, posted (9 years 4 months 3 weeks 3 days 4 hours ago) and read 4037 times:
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Quoting YUL332LX (Reply 11):
Boeing's goal for the 787 is 16% relative humidity at 6,000ft.

this weeks Flight Intl article on A350 in the Paris 05 section, " Airbus will offer humidity levels of 15-20% and a typical cabin altitude of 6000 ft until the late stages of long haul flights, when higher flight levels are usual practice"

so it seems the difference between the 2 may be pretty minimal, anyone want to educate those technically challenged such as myself why the higher altitude at later cruise will affect the cabin altitude? Is this because it can only pressurize to a certain pressure differential to the outside????


User currently offlineYUL332LX From Canada, joined Feb 2004, 820 posts, RR: 1
Reply 17, posted (9 years 4 months 2 weeks 5 hours ago) and read 3813 times:

Quoting Trex8 (Reply 16):
so it seems the difference between the 2 may be pretty minimal, anyone want to educate those technically challenged such as myself why the higher altitude at later cruise will affect the cabin altitude? Is this because it can only pressurize to a certain pressure differential to the outside????

Pretty much. Fatigue problems occur as the differential increases. To overcome these problems, current aircraft need more structural strength, which translates into thousands of pounds of additional weight.

However, the effects of fatigue on a composite fuselage are marginals according to Airbus and Boeing. Therefore, with their new projects, both Airbus and Boeing will have the ability to pressurize the A350 and 787 at 6,000ft without weight penalty.



E volavo, volavo felice più in alto del sole, e ancora più su mentre il mondo pian piano spariva lontano laggiù ...
User currently offlineAreopagus From United States of America, joined Sep 2001, 1371 posts, RR: 1
Reply 18, posted (9 years 4 months 1 week 6 days 2 hours ago) and read 3743 times:

Quoting YUL332LX (Reply 17):
However, the effects of fatigue on a composite fuselage are marginals according to Airbus and Boeing. Therefore, with their new projects, both Airbus and Boeing will have the ability to pressurize the A350 and 787 at 6,000ft without weight penalty.

Airbus is using AlLi for the A350 fuselage.


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