Gaut From Belgium, joined Dec 2001, 344 posts, RR: 2 Posted (10 years 1 week 21 hours ago) and read 5653 times:
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.
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.
Pihero From France, joined Jan 2005, 4886 posts, RR: 78
Reply 7, posted (10 years 1 week 18 hours ago) and read 5388 times:
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.
Katekebo From United States of America, joined Apr 2001, 711 posts, RR: 6
Reply 8, posted (10 years 6 days 19 hours ago) and read 5252 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.
UAL747 From , joined Dec 1969, posts, RR:
Reply 9, posted (10 years 6 days 19 hours ago) and read 5239 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.
Zvezda From Lithuania, joined Aug 2004, 10512 posts, RR: 63
Reply 13, posted (10 years 23 hours ago) and read 4907 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.
ZRH From Switzerland, joined Nov 1999, 5578 posts, RR: 34
Reply 14, posted (10 years 22 hours ago) and read 4902 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.
McGoose From Sweden, joined Aug 2004, 37 posts, RR: 0
Reply 15, posted (9 years 11 months 4 weeks 1 day 4 hours ago) and read 4727 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.
Trex8 From United States of America, joined Nov 2002, 5176 posts, RR: 14
Reply 16, posted (9 years 11 months 3 weeks 2 days 18 hours ago) and read 4573 times:
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????
YUL332LX From Canada, joined Feb 2004, 820 posts, RR: 1
Reply 17, posted (9 years 11 months 1 week 6 days 19 hours ago) and read 4349 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 ...
Areopagus From United States of America, joined Sep 2001, 1376 posts, RR: 1
Reply 18, posted (9 years 11 months 1 week 5 days 16 hours ago) and read 4279 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.