Sponsor Message:
Aviation Technical / Operations Forum
My Starred Topics | Profile | New Topic | Forum Index | Help | Search 
B787 More Humid Air Conditioning  
User currently offlineTristarSteve From Sweden, joined Nov 2005, 4354 posts, RR: 33
Posted (8 years 10 months 3 weeks 2 days 1 hour ago) and read 6693 times:

Does anyone understand how this is?
The normal jet aircraft air conditioning pack takes all the water out of the air.
The old B737-200/300 type had a bag type water separator, which just about worked when it was new, and then a 35degF sensor that kept the air above freezing to stop the remaining water freezing in the heat exchangers.
Later packs from B757/ B734/A320 onwards had really efficient water extractors which guaranteed that all the water was removed. The packs could then run down into Minus temps, and M15degC is not unusual. This greatly increased the efficiency of the pack. On the ground in the humid Middle East this was greatly appreciated.
But the air in the cabin was very dry as a result. Hunidifiers were tried on some long haul aircraft for the flight deck, but not very successfully.
Now long ago I remember flying on the Gulf Air VC10s, and when we descended into BAH the roof vents rained on us as we descended into the humid air of the Gulf. Not very nice! The VC10 had rootes blowers instead of engine bleed air to produce the air supply. The B787 has something similar, but electric powered instead of driven off the engine gearbox. Perhaps this is how they get more humidity in the cabin (but hopefully not too much!)

All this is OK below say 10000ft.
But 90pc of the B787 flying will be at 37000ft where the air is dry outside. Where will the more humid air come from? Will they carry water on board? Or is there something I don't understand?

Another point from the roll out show was the claim that the B787 can be more humid because carbon fibre does not corrode so much and aluminium aircraft must be kept dry!
Well I meet B777 that arrive from the Far East where it rains a lot. As they taxy in there is water draining out of all the fuselage drains. Water that was on the freight as it was loaded, and had drained into the bilges, and is now draining out as the aircraft has depressurised. If aircraft had to be kept dry, everyone would fit these Swedish Dryers that are advertised in Flight, but very few do.

Yours confused of Tunbridge Wells.

5 replies: All unread, jump to last
User currently offlineWingedMigrator From United States of America, joined Oct 2005, 2370 posts, RR: 56
Reply 1, posted (8 years 10 months 3 weeks 1 day 15 hours ago) and read 6585 times:

Quoting TristarSteve (Thread starter):
Where will the more humid air come from?

Evaporated perspiration and moisture in exhaled breath. The resulting humidity of the cabin is controlled by how much of this moisture you remove; in practice there is never a need to humidify the cabin.

I've also wondered how the higher humidity level (and corresponding condensation on the inner surface of the fuselage skin) would be feasible. I once lived in a top-floor apartment with poor roof insulation, and the ceiling was constantly moist in the winter. Sure enough, after two years I had a massive bloom of mold. How will the growth of various hardy organisms behind the cabin walls (and potential cabin air contamination) be prevented?

User currently offlineAvt007 From Canada, joined Jul 2000, 2132 posts, RR: 4
Reply 2, posted (8 years 10 months 3 weeks 1 day 14 hours ago) and read 6553 times:

Just today I was training some guys, and was telling them about a Dash8 that had proximity sensor problems, that in the end were due to condensation ( a big Dash problem) dripping on to the computer, producing faults that grounded the aircraft. The Dash8 often drips condensation onto the pax from the overhead. There's an aircraft that certainly doesn't need more humidity!

User currently offlineZeke From Hong Kong, joined Dec 2006, 10814 posts, RR: 76
Reply 3, posted (8 years 10 months 3 weeks 1 day 12 hours ago) and read 6536 times:

The specs I have seen for the 787 say the cockpit humidifies are an optional item, I know for example Air Mauritius also has the Airbus optional humidifiers on their A343s.

BTW I dont see the 787 spending most of its time at 39000ft, I expect it initial cruise to be low 30s on long haul operations, much the same as a 773ER.

We are addicted to our thoughts. We cannot change anything if we cannot change our thinking – Santosh Kalwar
User currently offlineMD11Engineer From Germany, joined Oct 2003, 14968 posts, RR: 61
Reply 4, posted (8 years 10 months 3 weeks 1 day 12 hours ago) and read 6534 times:

We also often have GPS, ATC and TCAS problems on the 737NG due to moisture from condensation entering the antenna plugs.


Je Suis Charlie et je suis Ahmet aussi
User currently offlineTrent1000 From Japan, joined Jan 2007, 711 posts, RR: 1
Reply 5, posted (8 years 10 months 3 weeks 1 day 12 hours ago) and read 6530 times:

Quoting MD11Engineer (Reply 4):
BTW I dont see the 787 spending most of its time at 39000ft, I expect it initial cruise to be low 30s on long haul operations, much the same as a 773ER.

This might be the case. Wasn't part of the 787 marketing that it would fly higher than other current commercial aircraft and that this would also result in a smoother ride (less turbulence)?

Top Of Page
Forum Index

Reply To This Topic B787 More Humid Air Conditioning
No username? Sign up now!

Forgot Password? Be reminded.
Remember me on this computer (uses cookies)
  • Tech/Ops related posts only!
  • Not Tech/Ops related? Use the other forums
  • No adverts of any kind. This includes web pages.
  • No hostile language or criticizing of others.
  • Do not post copyright protected material.
  • Use relevant and describing topics.
  • Check if your post already been discussed.
  • Check your spelling!
Add Images Add SmiliesPosting Help

Please check your spelling (press "Check Spelling" above)

Similar topics:More similar topics...
Air Conditioning "packs" posted Tue Jun 6 2006 06:35:32 by AirWillie6475
Air Conditioning X Pressurization posted Mon Feb 9 2004 20:14:25 by S.p.a.s.
How Does The Air-Conditioning System Work? posted Wed Jun 20 2001 04:06:04 by United Airline
B707 Air Conditioning posted Sat Jun 2 2001 11:10:27 by EDR 374
Air Conditioning System In Aircrafts posted Thu May 31 2001 03:51:17 by Jm-airbus320
Air Conditioning posted Mon May 14 2001 19:51:46 by Ngr
No More Alitalia Cargo Operated By Atlas Air? posted Fri Oct 21 2005 19:24:46 by B744F
Oregon Man Flies Lawn Chair XC (lighter-than-air) posted Tue Jul 10 2007 02:45:04 by KELPkid
ATR-72-500 Hot Air Bypass Valve posted Mon Jul 2 2007 14:09:04 by Radimz
Raked Wingtip On B773ER / B787 / B764 posted Mon Jun 25 2007 07:26:57 by JetMech

Sponsor Message:
Printer friendly format