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787 Vs A350: Freight Capacity Question.  
User currently offlineMotorHussy From New Zealand, joined Mar 2000, 3205 posts, RR: 9
Posted (6 years 4 months 2 weeks 4 days 20 hours ago) and read 8342 times:

How does the 787 manage such a large cargo/freight capacity compared to the comparable but wider A350?

Regards
MH

[Edited 2008-05-03 22:15:34]


come visit the south pacific
13 replies: All unread, jump to last
 
User currently offlineSlz396 From , joined Dec 1969, posts, RR:
Reply 1, posted (6 years 4 months 2 weeks 4 days 19 hours ago) and read 8258 times:

It is because the 787 has a far smaller wing box than the A350.

While this is definitely to the advantage of the 787 platform when it comes to cargo space on similarly sized competing models, it also makes the 787 platform harder to grow beyond what it is just now, as an enlarged and thus heavier version will hit structural limitations well before the more capable A350 platform does.

The 787 was designed as a direct 767 replacement and was obviously never intended by Boeing to also replace the 777, but Airbus surprisingly reacted to it by attacking it from above, rather than head-on, taking out basically the entire 777 range while doing so! A good decision in my view, yet to do so the A350 needs to have a larger wing box, eating up some of the belly space which the 787 uses for cargo.

It's all about compromises really, as no platform can do it all:
the 787 is optimized for the low end of the widebody market segment, whereas the A350 is optimized for the high end of the market segment. It is also why the future of the 787 is not up, but down in my view and the whole idea of a 787-10 or even -11 should be abandoned for something like the 787-5, unless Boeing wants to relive the 767-400 experience with it.


User currently offlineMotorHussy From New Zealand, joined Mar 2000, 3205 posts, RR: 9
Reply 2, posted (6 years 4 months 2 weeks 4 days 15 hours ago) and read 8050 times:

Slz396

Thank you very much for your well considered, informative and easy to understand response. I now understand the market place far better when considering these two aircraft.

Regards
MH



come visit the south pacific
User currently offlineStitch From United States of America, joined Jul 2005, 30986 posts, RR: 86
Reply 3, posted (6 years 4 months 2 weeks 4 days 11 hours ago) and read 7769 times:
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The 787 is not exactly as crippled for expansion as some might be led to believe.

CFRP is relatively easy to reinforce, so longer (69m / 75m / 80m) frames would not require anywhere near the structural reinforcement (and weight) that would have been required if the plane was Al. Also, the wider fuselage naturally improves resistance to bending/flexing loads, which also reduces the amount of reinforcement needed. It is one of the reasons why the 777-300ER has a lower OEW then the A340-600.

The 787's wing is good for MTOW's exceeding 290t. However, field performance at high(er) MTOWs falls off at an accelerated rate, so if Boeing stayed with the standard wing, they would need to raise engine thrust to keep field performance within reasonable limits. An 82k-85k thrust engine would help address this need and Boeing could do some re-profiling or changes to the slats/flaps.

The 787's undercarriage is good for around 254t, so larger and heavier versions will need new undercarriage geometry which will affect the size of the wingbox, which will impact the cargo capacity, but it would still remain greater then the A350's. If Boeing decides to develop an all-new and larger wing, then that too would impact the wingbox design and would reduce the 787's capacity to a greater extent, though it also would remain greater.


User currently offlineBrendows From Norway, joined Apr 2006, 1020 posts, RR: 4
Reply 4, posted (6 years 4 months 2 weeks 4 days 10 hours ago) and read 7674 times:



Quoting Stitch (Reply 3):
so larger and heavier versions will need new undercarriage geometry which will affect the size of the wingbox, which will impact the cargo capacity

Not necessarily. The forward and rear cargo holds ends at the back end of section 43 and forward end of section 46 respectively. I'd guess that a new wing and/or a larger MLG would mean a stretched center wing box (section 11) and/or wheel well section (section 45,) together with a longer section 44, and that would not affect the cargo capacity.

Quoting Stitch (Reply 3):
If Boeing decides to develop an all-new and larger wing, then that too would impact the wingbox design and would reduce the 787's capacity to a greater extent

See above.


User currently offlineStitch From United States of America, joined Jul 2005, 30986 posts, RR: 86
Reply 5, posted (6 years 4 months 2 weeks 4 days 10 hours ago) and read 7663 times:
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Well that would be great, Brendows, since a 69m 787-10 will match the A350-1000 (44 LD3 positions), a 75m 787-11 would offer 8 more (52) and an 80m 787-12 would offer 16 additional positions (60).

That all should do wonders for the revenue-generation capability of the larger 787 family.


User currently offlineGlacote From France, joined Jun 2005, 409 posts, RR: 2
Reply 6, posted (6 years 4 months 2 weeks 4 days 5 hours ago) and read 7415 times:

If I understand correctly, you are saying that 1) The B787 is easy to stretch and 2) a 787 stretched beyond what was originally intended would beat the A350 which was designed afterwards and not stretched.

How is this possible? Boeing engineers being so much smarter? CFRP being so extraordinarily better? That's not what recent facts have suggested, e.g. the unforseen yet unprecedented (for a Boeing airplane) overweight issue.


User currently offlineStitch From United States of America, joined Jul 2005, 30986 posts, RR: 86
Reply 7, posted (6 years 4 months 2 weeks 4 days 4 hours ago) and read 7339 times:
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Quoting Glacote (Reply 6):
If I understand correctly, you are saying that 1) The B787 is easy to stretch and 2) a 787 stretched beyond what was originally intended would beat the A350 which was designed afterwards and not stretched.

Both the monolithic barrel construction of the 787 and the properties of the CFRP used to build those barrels will help make stretches easier to engineer and those stretches will not result in an increase of OEW measured in the tens of tons, as they have on some planes built using Al (772 to 773, 77E to 77W, A343 to A345/A346).

Airbus, in deciding to use such large wings for the A350 to help drive the efficiencies needed to (what they hope will) comprehensively eclipse the 777 family sacrificed cargo volume to do it. This is why the 787-8 holds 2 more LD3 positions then the A350-800 even though it is physically smaller and the similar-sized 787-9 holds 10 more positions. It is the same reason a 787-10 would hold 12 more LD3 positions then a 772/77E/77L even though they have similar cabin areas. The 777's wingbox is larger and intrudes into space that could be used for cargo holds.

The A350-1000 has the same number of LD3 positions as the 77W (44). In at least EK's case, the 77W still has more payload lift (about 6t worth), however. On the flip side, the A350-1000 should easily lift more then the 777-300, so it makes sense for EK to have bought 20 A350-1000s to replace and expand their 14 777-300s if such was indeed the case.

Now, the following assumes Boeing launches a 787-10HGW, 787-11 and/or a 787-12.

Thanks to the larger wing, the A350-900 and A350-1000 might enjoy a superior maximum payload in terms of raw tonnage compared to a 787-10HGW/787-11/787-12 even if the Boeing models offer significantly more payload volume. As such, if Boeing chooses not to go with a new wing for such models, it is likely they would work to either improve the wing's effectiveness at high MTOWs and/or revise the undercarriage geometry to allow engines with larger diameter fans to be fitted so as to generate more power to improve payload-range performance.

[Edited 2008-05-04 14:14:35]

User currently offlineBrendows From Norway, joined Apr 2006, 1020 posts, RR: 4
Reply 8, posted (6 years 4 months 2 weeks 4 days 3 hours ago) and read 7251 times:

One more thing:
IIRC, there's an EE bay aft of the MLG wheel well (in the front end of section 46) and aft of the NLG wheel well (in front of the forward cargo hold in section 41.) These two EE bays are the only part of the lower fuselage on the 787 that is "wasted."

Quoting Glacote (Reply 6):
1) The B787 is easy to stretch

As Stitch notes, you can beef up the barrels, wings, wing box etc by additional layers of CFRP. I don't know what they'd do with the stringers and frames tho,,.

Quoting Glacote (Reply 6):
2) a 787 stretched beyond what was originally intended would beat the A350 which was designed afterwards and not stretched.

Well, a stretched 787, as in a 787-10 would have a hard time beating the payload/range capabilities of the A350, mainly because of its lower MTOW. But in terms of cargo capacity (number of LD3 positions,) the 787 "wins", as the 787 does over the 777, unless Airbus alters the lower fuselage.

Quoting Stitch (Reply 7):
The 777's wingbox is larger and intrudes into space that could be used for cargo holds.

Yes, the center wing box is bigger, as is the wheel well for the MLG, and they take up a bigger part of the overall length of the 777. But, that's not the only reason behind the "lower" cargo capacity of the 777 compared to the 787.
First, the nose gear is positioned a lot further back on the fuselage on the 777, decreasing the available volume in the forward cargo hold (by one row of LD3s,)
Secondly, on the 777, the last LD3 position in the aft cargo hold ends right where the rear fuselage starts tapering. This is not the case on the 787, the last LD3 position ends further back (but this reduces the available bulk volume a bit.)
That's why the 789 can take two extra LD3s in the forward cargo hold and two more in the rear cargo hold compared to the 772, while being shorter. The lower fuselage is utilized better on the 787.


User currently offlineStitch From United States of America, joined Jul 2005, 30986 posts, RR: 86
Reply 9, posted (6 years 4 months 2 weeks 4 days 3 hours ago) and read 7217 times:
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Quoting Brendows (Reply 8):
As Stitch notes, you can beef up the barrels, wings, wing box etc by additional layers of CFRP. I don't know what they'd do with the stringers and frames though...

I imagine they'd just be extended, as well, as part of the extensions to each barrel section. For the 787-9, they did a 2m extension between Door 1 and Door 2 (Section 41+Section 43) and another 4m plug between Door 3 and Door 4 (Section 46+Section 47).

For a 787-10, they'd add another meter on top of that between Door 1 and 2 and then maybe put the other five meters into Section 44 along with another door. That way, they could use the 787-9's Section 46, 47 and 48.

A 787-11 would likely need extensions in each section (1m each) as would the 787-12 (2m each) over the 787-10's respective sections.


User currently offlineBrendows From Norway, joined Apr 2006, 1020 posts, RR: 4
Reply 10, posted (6 years 4 months 2 weeks 4 days 3 hours ago) and read 7174 times:



Quoting Stitch (Reply 9):
I imagine they'd just be extended, as well, as part of the extensions to each barrel section.

I wasn't thinking about the length of each stringer or the number of frames, but the load they can handle. Will increasing the thickness of each barrel be enough to carry the extra load?

Quoting Stitch (Reply 9):
For the 787-9, they did a 2m extension between Door 1 and Door 2 (Section 41 Section 43) and another 4m plug between Door 3 and Door 4 (Section 46 Section 47).

Are you sure about that? I'm pretty certain they're extending section 43 and 46 by five frames each, where the stretch is done in front of door #2 for section 43, and between door #3 and the cargo hatch for section 46.

Quoting Stitch (Reply 9):
That way, they could use the 787-9's Section 46, 47 and 48.

As far as I know, section 43 and 46 are the sections that are being extended on the 789, not section 41, 44/45/11 or 47/48  wave 


User currently offlineStitch From United States of America, joined Jul 2005, 30986 posts, RR: 86
Reply 11, posted (6 years 4 months 2 weeks 4 days 2 hours ago) and read 7149 times:
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Quoting Brendows (Reply 10):
Are you sure about that?

Don't have a clue, actually, since I have not seen a diagram of the 787-9's plug positions. I was just eye-balling Flight's mock-ups and the 787-8 and 787-9 cabin floor diagrams from Boeing (calculating the different lengths between each door).

Quote:
I'm pretty certain they're extending section 43 and 46 by five frames each, where the stretch is done in front of door #2 for section 43, and between door #3 and the cargo hatch for section 46.

Sounds good to me.

Quoting Brendows (Reply 10):
As far as I know, section 43 and 46 are the sections that are being extended on the 789, not section 41, 44/45/11 or 47/48 wave

Also sounds good to me.


User currently offlineBrendows From Norway, joined Apr 2006, 1020 posts, RR: 4
Reply 12, posted (6 years 4 months 2 weeks 3 days 11 hours ago) and read 6967 times:



Quoting MotorHussy (Thread starter):
How does the 787 manage such a large cargo/freight capacity compared to the comparable but wider A350?

To answer the original question:
the length of the cargo holds are more important than the width of the fuselage (as long as its wide enough to handle two LD3s side by side.) The fuselage of the A350 may be wider, but the cargo hold is shorter, thus the lower capacity.


User currently offlineZeke From Hong Kong, joined Dec 2006, 9101 posts, RR: 75
Reply 13, posted (6 years 4 months 2 weeks 3 days 11 hours ago) and read 6967 times:



Quoting Stitch (Reply 3):

CFRP is relatively easy to reinforce, so longer (69m / 75m / 80m) frames would not require anywhere near the structural reinforcement (and weight) that would have been required if the plane was Al. Also, the wider fuselage naturally improves resistance to bending/flexing loads, which also reduces the amount of reinforcement needed. It is one of the reasons why the 777-300ER has a lower OEW then the A340-600.

Your example is flawed.

The A346 (minus engines and pylons) is actually lighter than the 77W (minus engines and pylons). An A346 engine weighs 6451 kg, and the outer pylons 1142 kg each, all up the engines and pylons on the A346 weigh over 30,000 kg, about 65% more than the 77W.

The A346 airframe is also capable of lifting about 4800 kg more payload than the 77W. The A346 has about double the composite content than what the 77W does. The A346 keel beams used for the lengthening are made from composite, it also has active structural dampening in the flight control system.



We are addicted to our thoughts. We cannot change anything if we cannot change our thinking – Santosh Kalwar
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