OyKIE From Norway, joined Jan 2006, 2575 posts, RR: 4 Posted (7 years 4 months 2 weeks 7 hours ago) and read 3490 times:
According to Boeing 787 Dreamliner - Flying redefined, Airbus is promising similar pressurization of 6000 feet as the 787, but only for the first stage of the flight up to 35 000 feet.
1. Does this mean the pressure will be at an higher altitude for the reminder of the flight?
2. If so will Airbus try to enable the A350 to also withstand a lower pressure for the reminder of the flight?
[Edited 2006-01-07 13:07:25]
Dream no small dream; it lacks magic. Dream large, then go make that dream real - Donald Douglas
Grbld From Netherlands, joined Dec 2005, 353 posts, RR: 3 Reply 1, posted (7 years 4 months 2 weeks 7 hours ago) and read 3453 times:
Quoting OyKIE (Thread starter): 1. Does this mean the pressure will be at an higher altitude for the reminder of the flight?
Yes. If I remember correctly, the 757 has about 6000 ft of cabin altitude at FL350, and that baby has been around for almost 25 years. It would be really nice if the airplane could hold 6000 ft up to its service ceiling, around FL430 or maybe FL450.
Quoting OyKIE (Thread starter): 2. If so will Airbus try to enable the A350 to also withstand a lower pressure for the reminder of the flight?
Who knows. It's quite difficult to achieve on a larger plane. Smaller sophisticated bizjets like a Gulfstream G550 have much lower cabin altitudes (more oxygen and pressure) even up to FL510, but they have a much smaller cabin, which can be much stronger without adding too much weight in materials.
GARPD From UK - Scotland, joined Aug 2005, 2293 posts, RR: 4 Reply 2, posted (7 years 4 months 2 weeks 7 hours ago) and read 3404 times:
I struggle to see how Airbus will manage to get the A350 to maintain the same cabin alt as the 787, mainly due to the fact it's not built out of the same material. Boeing are using the greater strength engineered into their composite fuselage to offer a lower cabin alt. The A350 however is of conventional metal construction and therefore more or less limited to a higher cabin alt due to metal fatigue, despite the new use of Al-Li.
So, I'm thinking if Airbus do sell the A350 as having similar cabin alts to the 787 (The word similar is SO subjective) it will only be, as suggested on this thread, for the first stages of flight.
Otherwise the A350 will have a shorter life span than the 787.
Joni From , joined Dec 1969, posts, RR: Reply 3, posted (7 years 4 months 2 weeks 6 hours ago) and read 3377 times:
GARPD,
Two frames can have similar performance to each other even if they're not made of the same materials. Also, even if two frames are made of the same materials, their performances can be different. Doesn't this sound rather obvious?
Composites don't give you a free lunch. If the frame is engineered to be stronger than an Al-Li frame, then it will likely also weigh more. There is no universal "composites give you more strength for the same weight" rule, since in some cases metal alloys will in fact give higher strength than composites for the same weight. For many uses using composites does make sense, and for other uses metals make more sense.
Zvezda From Lithuania, joined Aug 2004, 10511 posts, RR: 66 Reply 4, posted (7 years 4 months 2 weeks 6 hours ago) and read 3351 times:
Quoting Joni (Reply 3): There is no universal "composites give you more strength for the same weight" rule, since in some cases metal alloys will in fact give higher strength than composites for the same weight.
If we limit the rule to tensile strength (which is all that matters in pressurizing an airliner) and composites to CFRP (which is what the B787 fuselage is made from) then there is such a rule. A CFRP structure of the same weight will always have greater tensile strength (typically by a factor of 3 to 5) than a corresponding metal structure engineered to do the same job.
GARPD From UK - Scotland, joined Aug 2005, 2293 posts, RR: 4 Reply 5, posted (7 years 4 months 2 weeks 6 hours ago) and read 3325 times:
Quoting Zvezda (Reply 4): If we limit the rule to tensile strength (which is all that matters in pressurizing an airliner) and composites to CFRP (which is what the B787 fuselage is made from) then there is such a rule. A CFRP structure of the same weight will always have greater tensile strength (typically by a factor of 3 to 5) than a corresponding metal structure engineered to do the same job.
Two frames can have similar performance to each other even if they're not made of the same materials. Also, even if two frames are made of the same materials, their performances can be different. Doesn't this sound rather obvious?
Composites don't give you a free lunch. If the frame is engineered to be stronger than an Al-Li frame, then it will likely also weigh more. There is no universal "composites give you more strength for the same weight" rule, since in some cases metal alloys will in fact give higher strength than composites for the same weight. For many uses using composites does make sense, and for other uses metals make more sense.
Joni, the 787 as it is just now is scheduled to have a much lower weight than the A350.
Note that I said "engineered" when refering to the strength of the 787's composite.
One of the weakest points of an aircraft fuselage is around the doors and windows. It is here, that Boeing will use the composite to its maximum effect. By strengthening these points, they can afford a lower cabin alt. They can do so by simply weaving the composite in appropriate directions. Therefore, not neccessitating a thicker fuselage skin and keeping weight down.
To provide the same ammount of stengthening on a metal fuselage would require lap joints. Therefore making the fuselage heavier.
Its the tensile strength of the composite thats going to give it the advantage in cabin alt.
OyKIE From Norway, joined Jan 2006, 2575 posts, RR: 4 Reply 8, posted (7 years 4 months 2 weeks 5 hours ago) and read 3158 times:
Quoting GARPD (Reply 7): Personaly I think they've sold well due to price and other benefits.
I am not sure how the A350 has been priced versus the 787, so you might be right on that part. It will however be very interesting to see how this battle turns out. Boeing should be able to sell the 787 at a better price and still make money
Dream no small dream; it lacks magic. Dream large, then go make that dream real - Donald Douglas
Sinlock From United States of America, joined Dec 2000, 1532 posts, RR: 3 Reply 9, posted (7 years 4 months 2 weeks 3 hours ago) and read 2987 times:
Quoting GARPD (Reply 2): The A350 however is of conventional metal construction and therefore more or less limited to a higher cabin alt due to metal fatigue, despite the new use of Al-Li.
Just to clear one thing up about 1441 Al-Li , Lithium (the lightest Solid element) is used as an alloying agent for it's lightness not it's added strength. But Al-Li does have Superplastic properties when made in certain ways. One of them is cold-rolled Sheet form so is works well as a fuselage skin as it resits the pressurization stress longer than 1163 Al (Standard fuselage Sheet)
CTHEWORLD From Mayotte, joined Dec 2004, 478 posts, RR: 3 Reply 10, posted (7 years 4 months 2 weeks 3 hours ago) and read 2971 times:
Quoting Joni (Reply 3): Composites don't give you a free lunch. If the frame is engineered to be stronger than an Al-Li frame, then it will likely also weigh more. There is no universal "composites give you more strength for the same weight" rule, since in some cases metal alloys will in fact give higher strength than composites for the same weight. For many uses using composites does make sense, and for other uses metals make more sense.
Zeke From Hong Kong, joined Dec 2006, 7723 posts, RR: 73 Reply 11, posted (7 years 4 months 1 week 6 days 17 hours ago) and read 2771 times:
Quoting OyKIE (Thread starter): 1. Does this mean the pressure will be at an higher altitude for the reminder of the flight?
Assuming that is max diff, means a max diff of about 8.3, which means
37000-cabin pressure approx 6500
39000-cabin pressure approx 7500
41000-cabin pressure approx 8000
43000-cabin pressure approx 8500
Max altitude based on max cabin diff, approx 48500.
Quoting OyKIE (Thread starter): 2. If so will Airbus try to enable the A350 to also withstand a lower pressure for the reminder of the flight?
Doubt it, standard to have the cabin altitude to increase as altitude increases.
However I would assume that the flight time below 35000 could be a several hours looking at the trend of current newer aircraft when operating at max weights.
We are addicted to our thoughts. We cannot change anything if we cannot change our thinking – Santosh Kalwar
OyKIE From Norway, joined Jan 2006, 2575 posts, RR: 4 Reply 12, posted (7 years 4 months 1 week 6 days 7 hours ago) and read 2571 times:
Quoting Zeke (Reply 11): However I would assume that the flight time below 35000 could be a several hours looking at the trend of current newer aircraft when operating at max weights.
Thank you Zeke! This was very informative.
Dream no small dream; it lacks magic. Dream large, then go make that dream real - Donald Douglas
Shenzhen From United States of America, joined Jun 2003, 1701 posts, RR: 2 Reply 13, posted (7 years 4 months 1 week 6 days 6 hours ago) and read 2525 times:
Quoting OyKIE (Reply 6): So this means that Airbus will not be able to promise 6000 feet cabin pressure for the hole flight once they freezes the design this spring?
I guess the question is what would the 787 cabin pressure be at 35K feet... 4000 feet? Guess we'll have to wait for the pressurization schedule.
Tod From Denmark, joined Aug 2004, 1682 posts, RR: 3 Reply 14, posted (7 years 4 months 1 week 6 days 1 hour ago) and read 2391 times:
I've flown on 744 that have maintained 5600 all day long, so I seriously doubt it a design issue. Operators fly with higher cabin altitude because it's cheaper.
Aerosol From Germany, joined Oct 2000, 543 posts, RR: 0 Reply 15, posted (7 years 4 months 1 week 6 days 1 hour ago) and read 2382 times:
Just one question:
Isn`t the material of the frame for the pressurized cabin irrelevant?
I always thought of the cabin as a pressurized tube within the "hull of the plane".
Tod From Denmark, joined Aug 2004, 1682 posts, RR: 3 Reply 16, posted (7 years 4 months 1 week 6 days ago) and read 2359 times:
Quoting Aerosol (Reply 15): Isn`t the material of the frame for the pressurized cabin irrelevant?
I always thought of the cabin as a pressurized tube within the "hull of the plane".
In simplified terms, the pressure vessel is the combintion of frames, stringers and skin.
Art From Lebanon, joined Feb 2005, 2937 posts, RR: 0 Reply 17, posted (7 years 4 months 1 week 6 days ago) and read 2299 times:
Quoting Zvezda (Reply 4): A CFRP structure of the same weight will always have greater tensile strength (typically by a factor of 3 to 5) than a corresponding metal structure engineered to do the same job.
If I understand you correctly, a structure made of metal with weight 100 tons could be made of composite with weight 20-33.3 tons.
DfwRevolution From , joined Dec 1969, posts, RR: Reply 18, posted (7 years 4 months 1 week 6 days ago) and read 2274 times:
Quoting Art (Reply 17): If I understand you correctly, a structure made of metal with weight 100 tons could be made of composite with weight 20-33.3 tons.
Do I understand you correctly?
Perhaps, but no inherently conservative OEM is going to use composites that extensivly. Like I said in another thread, the 787 is likely being way overbuilt as the DC-9 and other early aircraft were.
Some new frigates and cruisers are using composite armor and shedding tons off their displacement weight.
Joni From , joined Dec 1969, posts, RR: Reply 19, posted (7 years 4 months 1 week 5 days 23 hours ago) and read 2234 times:
Quoting Zvezda (Reply 4): If we limit the rule to tensile strength (which is all that matters in pressurizing an airliner) and composites to CFRP (which is what the B787 fuselage is made from) then there is such a rule. A CFRP structure of the same weight will always have greater tensile strength (typically by a factor of 3 to 5) than a corresponding metal structure engineered to do the same job.
Boeing's senior VP disagrees with you:
generally accepted assumptions that composites would weigh significantly less and cost significantly more than aluminum were found to be not universally true.
Ikramerica From United States of America, joined May 2005, 21025 posts, RR: 60 Reply 20, posted (7 years 4 months 1 week 5 days 23 hours ago) and read 2201 times:
Quoting Joni (Reply 19): generally accepted assumptions that composites would weigh significantly less and cost significantly more than aluminum were found to be not universally true.
that's an interesting way to quote that.
it does NOT say that the composites don't have more tensile strength? Where do you read that?
It says that there are new alloys of aluminum that are just as light as composite in their application, not that they are just as strong in TENSILE STRENGTH.
the statement you quote from above says exactly the same thing. ENGINEERED TO DO THE SAME JOB means that at the same weight, even it is suitable for the same job (aircraft fuselage for example), it will still have MUCH GREATER TENSILE strength. nowhere did it say it would need to be heavier (Al) to be used.
The discussion is about tensile strength, because that is one of the main forces that act upon a fuselage when pressurized.
further, this "quote" from the engineer is not a quote, but a summary by the article author of his words. the actual quote speaks only to weight and price, not to strength.
Before you dig up "quotes" to prove someone wrong, it's best to read and understand their words and the article you quote.
Of all the things to worry about... the Wookie has no pants.
Ikramerica From United States of America, joined May 2005, 21025 posts, RR: 60 Reply 21, posted (7 years 4 months 1 week 5 days 23 hours ago) and read 2190 times:
BTW - the article is also about Al-Li, not composites, and seems to only mention the composites to further the agenda of the article re: aluminium.
It is also over 2 years old, and much more has been learned and developed (on both fronts) since then.
Of all the things to worry about... the Wookie has no pants.
Joni From , joined Dec 1969, posts, RR: Reply 22, posted (7 years 4 months 1 week 5 days 22 hours ago) and read 2155 times:
Quoting Ikramerica (Reply 20): It says that there are new alloys of aluminum that are just as light as composite in their application, not that they are just as strong in TENSILE STRENGTH.
Well it ought IMO to be obvious that strength (tensile or otherwise) is the "application" in this case, with respect to weight. In other words, for the same weight you get similar "application" = strength and other relevant properties.
Quoting Ikramerica (Reply 21): BTW - the article is also about Al-Li, not composites, and seems to only mention the composites to further the agenda of the article re: aluminium.
Well at the opening it states:
The Boeing 7E7 structure will include several varieties of composites, such as graphite/epoxy and graphite/titanium composites.
so I'd tend to disagree with you here and say that it's primarily about composites.
Glacote From France, joined Jun 2005, 409 posts, RR: 2 Reply 23, posted (7 years 4 months 1 week 5 days 19 hours ago) and read 2047 times:
Quoting Zvezda (Reply 4): A CFRP structure of the same weight will always have greater tensile strength (typically by a factor of 3 to 5) than a corresponding metal structure engineered to do the same job.
- to the same weight is the keyword here
- (not implying that what you say is wrong) would you have (even estimated) figures on the strength of both aircrafts? Perhaps by infering from the mass? I am not good enough to do this myself... Thank you if you can.
Eilennaei From , joined Dec 1969, posts, RR: Reply 24, posted (7 years 4 months 1 week 5 days 9 hours ago) and read 1904 times:
Quoting Ikramerica (Reply 20): The discussion is about tensile strength, because that is one of the main forces that act upon a fuselage when pressurized.
If all that is required of an a/c hull were the tensile strength vs weight, the hull would probably be made of thin steel sheets...
I disagree with IkrAmericas "the 787 will be structurally overbuilt", admitting he allows for the word "probably" as an insurance. Seems people have a hard time understanding the bottom line of the composites. They are not automatically something incredibly light, tough and resilient, but a tool to achieve "right-built" structures. First, the need is analyzed, then the structure built to suit the need, and the result verified. There's no need to "overbuild" anything, unless you are actually unable to understand what you're trying to achieve.
He's also not goming to grips that there's necessarily no single "tensile strength" for a complex composite material, in other words, there can be a directionality built-in. "Tensile strenght" is a metal-era term for a homogeneous material.
[Edited 2006-01-09 11:22:20]
[Edited 2006-01-09 11:26:13]
25 Zvezda: If you're talking about a hypothetical structure that is submitted only to tensile stresses (never to compressive or torsional stresses), then yes. H
26 Kangar: Saying something is not universally true implies that it is true in some situations, very different from saying something is universally not true....
27 Joni: I agree, "not universally true A < B" means that there are cases where A < B and other cases where A > B. Obviously, using composites in planes makes
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