WingedMigrator
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787 Cabin Altitude

Sat Sep 08, 2007 1:54 pm

The 787 marketing materials point out that the CFRP fuselage allows a higher cabin altitude of 6000 ft vs. 8000 ft on conventional aluminum airliners. This obviously implies a higher pressure differential between the inside and the outside, made possible by the greater strength and fatigue resistance of CFRP. I also understand that these cabin altitudes are quoted at the aircraft's ceiling altitude (43000 ft in the case of the 787).

What are the implications for the flying experience? Specifically, will the 787's cabin altitude be varied in such a way as to maintain this higher pressure differential through a wide band of cruise altitudes, well below ceiling altitude -- given that the pressure differential is the same for 6000 ft cabin @ FL430 and 3600 ft cabin @ FL350 ?

A simpler way of asking is, will the 787 cabin altitude be 6000 ft or 3600 ft when cruising at FL350 ?
 
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Jetlagged
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RE: 787 Cabin Altitude

Sat Sep 08, 2007 9:47 pm

Quoting WingedMigrator (Thread starter):
What are the implications for the flying experience? Specifically, will the 787's cabin altitude be varied in such a way as to maintain this higher pressure differential through a wide band of cruise altitudes, well below ceiling altitude -- given that the pressure differential is the same for 6000 ft cabin @ FL430 and 3600 ft cabin @ FL350 ?

I shouldn't think so. The pressure controller will probably follow previous practice and control to max Pdiff at cruise altitude, varying smoothly between this and zero during climb and descent. This gives the best comfort for the passengers. If you go straight to max Pdiff ASAP, the remainder of the climb contains quite rapid pressure changes. Better to go for a smooth and steady rate, timed to take the whole climb/descent phase.

Passengers don't really notice cabin altitude but they do notice cabin altitude (pressure) changes, because it affects their ears.
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WingedMigrator
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RE: 787 Cabin Altitude

Sun Sep 09, 2007 4:32 am

Quoting Jetlagged (Reply 1):
The pressure controller will probably follow previous practice and control to max Pdiff at cruise altitude, varying smoothly between this and zero during climb and descent.

I see; so we can expect a 3600 ft cabin at FL350. That will be nice. (so what happens if you takeoff from Denver...  Wink )
 
roseflyer
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RE: 787 Cabin Altitude

Sun Sep 09, 2007 6:40 am

I'm only a little knowledgeable on envirornmental control systems, but the pressure should always be higher than 6000ft. It probably will be in the 5,000 range. On airplanes today you see the pressure go down to 8,000ft equivalent, but usually it is in the 6500-7500 range I believe.
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Jetlagged
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RE: 787 Cabin Altitude

Sun Sep 09, 2007 8:05 am

Quoting RoseFlyer (Reply 3):
I'm only a little knowledgeable on envirornmental control systems, but the pressure should always be higher than 6000ft. It probably will be in the 5,000 range. On airplanes today you see the pressure go down to 8,000ft equivalent, but usually it is in the 6500-7500 range I believe.

Good point, the increased max Pdiff does change things a bit. There may well be a minimum cabin altitude in the logic.
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zeke
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RE: 787 Cabin Altitude

Mon Sep 10, 2007 7:57 am

Quoting WingedMigrator (Thread starter):

A simpler way of asking is, will the 787 cabin altitude be 6000 ft or 3600 ft when cruising at FL350 ?

Too hard to say, on the WB Airbus models, if your doing a regional flight you get a different cabin altitude than what you do if your long haul for the same cruise altitude. They have a higher cabin altitude for shorter flights to reduce airframe stress.

It is rare on the 340 to ever see the cabin altitude go above 6500 ft even after 12 hrs of flying, if the 787 is providing 500' lower pressure altitude, I do not know what if any physiological advantages that will have. I seem to recall 4500' being the altitude where some eyesight is effected particularly at night, 6000 or 6500 is not not going to change anything.

Should start finding out next month when the A380 goes into service with SQ, the 787 is using the same cabin pressure controllers from the A380.
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Tod
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RE: 787 Cabin Altitude

Mon Sep 10, 2007 10:38 pm

Quoting RoseFlyer (Reply 3):
On airplanes today you see the pressure go down to 8,000ft equivalent, but usually it is in the 6500-7500 range I believe.



Quoting Zeke (Reply 5):
It is rare on the 340 to ever see the cabin altitude go above 6500 ft

It is not uncommon for a 744 to not exceed 5600 - 6400 ft.

Highest cabin altitude I've seen on a commercial flight has been 8400 on a AS 734.

Tod
 
tdscanuck
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RE: 787 Cabin Altitude

Tue Sep 11, 2007 1:22 am

Quoting Zeke (Reply 5):

Should start finding out next month when the A380 goes into service with SQ, the 787 is using the same cabin pressure controllers from the A380.

Same hardware but not the same pressure profile program.

If a "normal" pressure controller maxes out at 8,000' cabin altitude and the 787 maxes out at 6,000' and we assume the pressure profiles are the same, the 787 should end up with a lower cabin altitude for a given mission than an equivalent "normal" plane.

Whether that makes any difference remains to be seen.

Tom.

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