ferpe
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The 787 Weight, How It Got There

Mon Sep 26, 2011 4:27 pm

Hi all,

I would very much appreciate a sensible discussion (not A vs B or 787 vs YYY) about the way the weight of the 787 came to be. We all know that it is higher then one would want (which A/C turned out lighter then planned   ) but it is still the lightest A/C per it's payload-range capability now delivered to an Airliner.

In a way I would like to discuss the practical life realities of today's aircraft designers   .


So here the things I would like to discuss (or any other thing that can high-light how the weight came about):

1. What is the detail behind the weight growth other then the increase in pax capacity from typical 220 to 240?

- how much is due to less then optimal design principles e.g. for in program fixes

- are the first frames over strength in parts due to incomplete FEM models?

- how much has damage tolerance added? Has one learned how to better handle this for later frames with e.g. different lay-up methods?

- how much is due to lightning protection and has one learned how to solve this better for later frames?


2. What would be a good rule of thumb for the weight gain of a CFRP structure part exposed to external damage and lightning vs the same part made in classical aluminum construction.

- Typical studies pre 787 pointed to -20% in weight, would -15% be more of the truth today.

- I don't want to discuss the extreme cases where it brings nothing, I am interested in the general case and what would be the practical weight gain overall.


Thanks for chipping in  bigthumbsup 

[Edited 2011-09-26 09:33:13]
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Stitch
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RE: The 787 Weight, How It Got There

Mon Sep 26, 2011 5:19 pm

The "lessons learned" document Airbus released lists the various MEW weight growth (where Airbus could identify it) from the original plan of 92t (7E7 concept) to 100t of ZA001. It's on Page 12.
 
wingscrubber
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RE: The 787 Weight, How It Got There

Mon Sep 26, 2011 6:34 pm

Here is a link to what I think Stitch is talking about

http://www.planebusiness.com/buzz/airbus2.pdf

To give a little bit of an insiders perspective, here's a timeline of how I think this typically goes:
-OEM decides to build new airplane, wants to improve on previous designs, so requirements are written with new super optimistic low weight targets, sends out RFPs/RFQs to engine/systems manufacturers. Meanwhile OEM quotes to media how many hundreds of pounds it will save with the new revolutionary design.
-Component/System manufacturer recieves RFP and reviews requirements; response to weight target is either;
-Bid realistic weight which exceeds target but with sensible price, hoping for no weight penalties later.
(honest, but losing strategy)
-Bid a component which meets weight target, but jack up the price in order to achieve it, ignore potential penalties.
(devious, but winning strategy)

Next, the systems provider solicits quotes for it's own parts from its own vendors, parses down weight requirements, and the same thing happens again. BOMs are written based on weights which will never be met, and hopelessly optimistic proposals are submitted.

Ultimately, the OEM chooses the lightest proposed solution (despite expense) and development begins.
Later in the program, bad news, the system provider discovers vendor cannot meet weight target, causing domino effect;
-Component overweight, resulting in overweight system
-System overweight, resulting in overweight airframe
-Airframe overweight, so in order to meet range requirements, more fuel must be carried.
-Range is met, but seat/mile targets are missed, surpirising and angering the customer airline who ordered their plane based on impossibly optimistic performance numbers.

Later, during detail design, engineers discover they did not account for all cable ties/hose clamps/check valves/insert misc component here, so the weight increases again as components which were simply not accounted for earlier have to be added to the design.

Eventually, weight concessions or penalties are issed by the OEM as the design setbacks delay the program and it will cost more to attempt to meet the weight than to just eat the weight and carry on. The program reaches the design freeze, and everybody starts building their first production configuration parts.

Next it's qualification testing time, oh no more bad news at component, system and/or OEM, component x/y/z has failed fatigue/vibration/proof/HIRF testing and needs reinforcement/additional vibration mounts/brackets etc etc
Weight increases even more. This happens to the airframe or individual components.

Eventually more weight concessions have to be made in order to achieve qualification, and ultimately complete the qual testing and then later flight testing. Finally flight testing is complete, but holy crap the engines aren't as efficient as was promised, reducing the effective operating range, customer airline angered more. Some may even cancel or defer order. (think Cargolux).

Finally the airplane is certified, delivered and enters service! But wait it gets worse... design flaw x/y/z suddenly becomes apparent with dangerous potential consequences. Emergency AD mandates installation of emergency mousetrap/whoopy cushion/auxiliary banana etc
Later, as the aircraft ages, structural repairs must be made, aircraft continues to slowly gain weight, new airworthiness bulletins/directives insist on new reinforced cockpit doors, special fuel tank lining and so on.

So ultimately, though I am clearly exaggerating for effect, what ultimately happens is wishful thinking and unfulfilled promises lead to aircraft which are maybe not quite as efficient or revolutionary as was hoped, but still pretty darn good nonetheless.
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ferpe
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RE: The 787 Weight, How It Got There

Mon Sep 26, 2011 7:36 pm

Thanks Sticht, I reread the A document with interest, it gives more the what but perhaps not the how.

Wingscrubber, excellent post, I understand you are an insider and I enjoyed your description on how things goes on the systems side.

Anyone with inside from the structural side?
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BE77
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RE: The 787 Weight, How It Got There

Tue Sep 27, 2011 6:13 pm

Quoting Wingscrubber (Reply 2):
though I am clearly exaggerating for effect

Uhhh, i challenge your statemen about exaggeration, so can you point to the part you exaggerated, as it all seems correct to me.

Always bid the contract as if it can be achieved how the client describes it in the RFP, since you can always get a change order when it becomes obvious that the client forgot to include reality in the contract (sometimes legal, sometimes physics). If you bid the job (any industry) how it should be or will be done, you won't get the work, and it is very seldom that once the process starts that the client will admit to, or be able to afford to, back out and go to a different supplier, especially if it was a client spec in the first place. Penalty for reality in the bid is a lost bid most of the time. Reward for bidding the rfp is lots of change orders at cost plus.
If the client is smart and has their act together in preparing the contract or RFP, then this won't work...but it doesn't happen all that often!
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ferpe
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RE: The 787 Weight, How It Got There

Mon Oct 03, 2011 3:21 pm

Here the best link I have found on what actually happened to the MEW and therefore OEW of the 787-8:

http://www.aspireaviation.com/2011/1...omes-reality/#.Tom5vKn9khA.twitter

"According to Aspire Aviation‘s two sources at the US airframer, the first 787 prototype, dubbed ZA001 which carries the registration N787BA, is 9.8 tonnes (21,500 lbs) overweight, a significant figure when considering the aircraft’s specific maximum zero fuel weight (MZFW) of 161,025 kg (355,000 lbs).

Line number 7 to 19 (LN7-LN19), the same sources confirm, are considerably less overweight at 6.1 tonnes (13,500 lbs). Line number 20 (LN20), the first 787 to feature increased maximum take-off weight (MTOW) from 219,539 kg (484,000 lbs) to 227,930 kg (502,500 lbs) to recover some of the payload/range capabilities lost owing to the overweight issue, is around 4 tonnes (8,800 lbs) overweight.

Line number 34 (LN34), dubbed ZA380 and the first 787 earmarked for China Southern Airlines, along with LN50 for Ethiopian Airlines, are block points for further weight reductions.

Line number 90 (LN90) will be the first 787-8 meeting the aircraft’s original weight target with no overweight issue, the sources say."

8% of the planned MEW of 100t is way much, even 5% which remains until frame no 50-90 or so is a lot. This would mean the planned OEW of 114,7 would be close to 120t for frame no 7-20 and 118-119t after that finally landing at 115t at about frame 90-100. Let's see what this means for the payload-range diagram when if finally appears.

[Edited 2011-10-03 08:22:40]
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nomadd22
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RE: The 787 Weight, How It Got There

Mon Oct 03, 2011 7:02 pm

Quoting ferpe (Reply 5):
8% of the planned MEW of 100t is way much, even 5% which remains until frame no 50-90 or so is a lot.

4 tonnes overweight comes to 3.7% of the original 109 tonne OEW for the post LN20 frames. Am I missing something?
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Stitch
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RE: The 787 Weight, How It Got There

Mon Oct 03, 2011 9:57 pm

Quoting ferpe (Reply 5):
Here the best link I have found on what actually happened to the MEW and therefore OEW of the 787-8:

I'm skeptical of those weight numbers. Seems far too high. Last I heard ZA001 was about 2.5 tons overweight.
 
ferpe
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RE: The 787 Weight, How It Got There

Tue Oct 04, 2011 5:25 am

Quoting nomadd22 (Reply 6):
4 tonnes overweight comes to 3.7% of the original 109 tonne OEW for the post LN20 frames. Am I missing something?

Depends on what one say is the right MEW, if 114,7t would be the desired OEW of the 228t MTOW craft one can estimate the MEW (which the framers don't publicize to mere mortals like us) by setting the furnishing per seat to 63kg (a more realistic furnishing for an airliner would be 80kg for a std long-haul craft, this is the spec figure). Now 240*63kg is 15t so then the desired MEW would be about 100t therefore my weight % numbers.

A MEW of 109t for the 787-8 would mean an OEW of 124t, it would be a catastrophe as it would only leave 36t MSP where the pax would take 23t and a realistic outfitting 5t ie you would have 8t for cargo at a MZFW range of say 5000nm or alternatively it would leave you 76t fuel on a max pax only flight. 76t fuel gives you a 14t endurance or 6800nm range, not what you would accept for over LN20 frames.
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ferpe
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RE: The 787 Weight, How It Got There

Tue Oct 04, 2011 5:30 am

Quoting Stitch (Reply 7):
I'm skeptical of those weight numbers. Seems far too high. Last I heard ZA001 was about 2.5 tons overweight.

More realistic numbers would then be appreciated, you should be able to get it from your contacts.

Aspire aviation is normally very positive to B so IMO he would not publicize this without reasonable confidence in his sources, that is why I put in the thread. But the numbers are very high indeed (or perhaps more correctly very much higher then Bs original targets, whether the numbers are high or not one has to analyze with a fraction analysis).

Could you try and come up with verified numbers for frames around 10, frames > 20 and finally late frames like say >80?



[Edited 2011-10-03 23:19:07]
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ferpe
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RE: The 787 Weight, How It Got There

Tue Oct 04, 2011 4:22 pm

So here a check of what those weight figures would mean compared to a frame which would have an OEW of 114,7t, the last official figure from B:

Payload (Maxpax)/MTOW ratio compared to other 8000nm competitors (all normalized to 8000nm):
..........787-8...787+6t...787+4t...787+2t...77W....358....359....3510
%:.......10,5.......8,2.........9,0........9,8........9,6.....11,7...11,5...12,3

Please observe that this has nothing to do with the cost like CASM etc or trip cost, it just values the frame vs payload weight, it can therefore be construed as a first efficiency value for the frame. Note that it would reach the alu 77W ratio when past 50 frames or so.


Running the figures in Piano-X gives the following spec ranges (242 pax+bags with engines within 1%):
..........787-8...787+6t w 120t MTOW...787+4t...787+2t
knm.....8,1................6,8......................7,6.........7,8

At about 6800nm with 242 pax the ANA 787-8 is a inferior in pax and range to the latest 332 (minus 10 pax and 450nm) with a fuel burn which is 10% better, not to exciting for ANA, but it will be better, once you are past block no 20 things normalize.



[Edited 2011-10-04 09:27:46]
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ferpe
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RE: The 787 Weight, How It Got There

Thu Oct 06, 2011 7:17 pm

The EASA type certificate is an interesting reading as it states some weights that the FFA does not. Here it is:

easa.europa.eu/.../type-certificates/docs/aircrafts/EASA-TCDS-A.115_(IM)_Boeing_787-01-26082011.pdf - 2011-08-24

And here the weights for the certified frame:

Maximum Taxi Weight 486,000 LB 220,445 KG

Maximum Takeoff Weight 484,000 LB 219,538 KG

Maximum Landing Weight 370,000 LB 167,829 KG

Maximum Zero Fuel Weight 345,000 LB 156,489 KG

Minimum Flight and Zero Fuel Weight 229,500 LB 104,100 KG

As can be seen the type certificate is for the 220t variant, the engines are the 69,194 lbs RR T1000 (ie forget everything about a 64klbs variant), the MZFW is 5t lower then the 228t variant. The minimum flight and zero fuel weight could be the MEW, it would fit with about 14-18t furnishing, who knows, it is most probably the minimum certified weight for ferry flights without a furnished cockpit.

B needs a new type certificate (or an amended one) for LN20.
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Stitch
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RE: The 787 Weight, How It Got There

Sat Oct 08, 2011 1:41 pm

I expect the engine thrust is the maximum, not the only. I see no reason why an airline could not de-rate the engines just as they're allowed to de-rate the MTOW.

As maximum weights and thrusts increase, the Type Certificate will be amended to reflect this.
 
tdscanuck
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RE: The 787 Weight, How It Got There

Sat Oct 08, 2011 2:33 pm

Quoting ferpe (Reply 11):
As can be seen the type certificate is for the 220t variant, the engines are the 69,194 lbs RR T1000 (ie forget everything about a 64klbs variant),

The type cert on the engines is the max for the engine, not the engine-airframe combination. The first 787-8 delivered was a 64k engine.

Tom.
 
474218
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RE: The 787 Weight, How It Got There

Sat Oct 08, 2011 3:21 pm

Quoting ferpe (Reply 11):
As can be seen the type certificate is for the 220t variant, the engines are the 69,194 lbs RR T1000
Quoting tdscanuck (Reply 13):
The first 787-8 delivered was a 64k engine.

Actually your both right:

The Trent 1000A has a "maximum takeoff thrust of 69,194" and a maximum continuous thrust of 64,722.
 
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RE: The 787 Weight, How It Got There

Sun Oct 09, 2011 3:04 am

Quoting ferpe (Reply 10):
Running the figures in Piano-X

Wow. You are armed and dangerous 
 
ferpe
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RE: The 787 Weight, How It Got There

Mon Oct 10, 2011 4:07 pm

Quoting WingedMigrator (Reply 15):
You are armed and dangerous

Don*t know if I shall take this as a compliment or a bit ironic or both, but what the heck  , flatter is so uncommon I stay with that   .
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RE: The 787 Weight, How It Got There

Wed Oct 12, 2011 5:45 am

It was a compliment tinged with more than a bit of jealousy.  
 
PolymerPlane
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RE: The 787 Weight, How It Got There

Wed Oct 12, 2011 8:44 am

Quoting ferpe (Reply 11):
B needs a new type certificate (or an amended one) for LN20.

I don't know if they do or don't need a new type certificate, but i don't think it is a big deal at all. Have you seen the weight variants of A330? there are a lot of them. I bet Boeing does it too, although Airbus lists them in the airport planning documents, while Boeing does not.
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RE: The 787 Weight, How It Got There

Wed Oct 12, 2011 10:10 am

Quoting polymerplane (Reply 18):
Have you seen the weight variants of A330? there are a lot of them. I bet Boeing does it too, although Airbus lists them in the airport planning documents, while Boeing does not.

Hmmm. That seems odd. Any explanation why? Would seem a good idea for that bit of information to be available????
 
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Stitch
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RE: The 787 Weight, How It Got There

Wed Oct 12, 2011 12:34 pm

Boeing seems to offer flexibility on what MTOW an airline can (paper) certify for, so perhaps they feel it unnecessary to show anything but the maximum?

Assuming Airbus allows the same, they might just list various block point updates.
 
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RE: The 787 Weight, How It Got There

Wed Oct 12, 2011 12:54 pm

Quoting polymerplane (Reply 18):
Have you seen the weight variants of A330? there are a lot of them. I bet Boeing does it too, although Airbus lists them in the airport planning documents, while Boeing does not.

The airport planning documents are not an approved by the regulatory agencies. Boeing lists the MTOW in the AFM (an approved document) and it s/n specific. I am sure Airbus does the same.
 
tdscanuck
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RE: The 787 Weight, How It Got There

Wed Oct 12, 2011 1:57 pm

Quoting polymerplane (Reply 18):
Quoting ferpe (Reply 11):
B needs a new type certificate (or an amended one) for LN20.

I don't know if they do or don't need a new type certificate, but i don't think it is a big deal at all.

There's no way they need a new type certificate, just an amendment. The difference between 787 LN8 and 787LN20 is waaaaaaaaaaay less than, say, a 747-100 to a 747-8 and those are on the same type certificate.

Quoting Stitch (Reply 20):
Boeing seems to offer flexibility on what MTOW an airline can (paper) certify for, so perhaps they feel it unnecessary to show anything but the maximum?

It's not Boeing that feels its unnecessary...the FAA doesn't care. The TCDS captures limits. A paper limit is just what it sounds like...paper. The aircraft can be "returned" to full limits with paper too, so it's not appropriate to have that limit on the TCDS.

Tom.
 
ferpe
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RE: The 787 Weight, How It Got There

Wed Oct 12, 2011 5:08 pm

Quoting tdscanuck (Reply 22):
There's no way they need a new type certificate, just an amendment. The difference between 787 LN8 and 787LN20 is waaaaaaaaaaay less than, say, a 747-100 to a 747-8 and those are on the same type certificate.


Sure, I understood this, actually given that Dynamicsguy said there are no structural reinforcements for the 228t LN20, why not certify to the 228t limit directly? Where the test aircraft not representative for a 228t craft?
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dynamicsguy
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RE: The 787 Weight, How It Got There

Wed Oct 12, 2011 6:33 pm

Quoting ferpe (Reply 23):
actually given that Dynamicsguy said there are no structural reinforcements for the 228t LN20

Just to clarify, that is the case for the parts of the airplane my part of Boeing builds, not necessarily the whole airplane.
 
ferpe
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RE: The 787 Weight, How It Got There

Fri Oct 14, 2011 12:14 pm

Quoting dynamicsguy (Reply 24):
Just to clarify, that is the case for the parts of the airplane my part of Boeing builds, not necessarily the whole airplane.

So what parts are you then building?
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Stitch
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RE: The 787 Weight, How It Got There

Fri Oct 14, 2011 1:45 pm

Since dynamicsguy is flying Aussie colors, I expect he's with Boeing' Hawker de Havilland unit, which builds the movable trailing edges and inboard flaps.

Other Boeing-built components for the 787 include the vertical fin at Fredrickson in WA and the wing to body fairing assembly, aft pylon fairings, wing to body fairings and the main landing gear doors, all of which are built at Boeing Canada in Winnipeg.
 
ferpe
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RE: The 787 Weight, How It Got There

Fri Oct 14, 2011 11:17 pm

Now I have been playing with Piano-x to try and figure out what is behind the following stated by B in the present technical information on their website:

Spec range with max spec seating:
250 pax+bags@210lb = 7650nm

Spec range with min spec seating:
210 pax+bags@210lb = 8200nm

I have further assumed that engines are at -1% SFC.

Playing with OEW and induced drag I find it hard to get those data points to fit with the OEW of 115t with Aspire aviations extra weights added in. It is not so that it strives toward less OEW or induced drag, rather the contrary! The sensitivity of the 787 to payload is clearly above what the Piano-x model predicts, one can get the max range point to fit but then the model predicts to long range with 250 pax even with induced drag or OEW raised considerably (they both increase the sensitivity to load). Within reasonable changes of these values I just can't get the model to fit, anyone have and idea what to change in addition?

In my reasoning:

- changing base drag or SFC just traverses the range scale

- changing OEW or induced drag changes the sensitivity to load

- any other thing one should play with? (One can edit directly in the adjustment files so one can fiddle with a lot)

Now of course the Piano-x model could be pretty far of but in general it predicts pretty linear stuff, I am a bit intrigued by the above.

I have also plotted the above in a range-payload diagram, it makes for a payload sensitive curve there as well, the range decrease for an additional 1t of payload is per B figures -14,4nm. Now going from the 8200nm payload of 20.003kg to an assumed max payload with a 219t OEW (LN20+) of 42t would yield 8200-42*14,4= 5000 nm.

The 788 is clearly more sensitive (+44%) to payload then the 332 (looses 10nm per 1t payload).

[Edited 2011-10-14 17:20:41]
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Stitch
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RE: The 787 Weight, How It Got There

Sat Oct 15, 2011 12:53 am

Quoting ferpe (Reply 27):
Playing with OEW and induced drag I find it hard to get those data points to fit with the OEW of 115t with Aspire aviations extra weights added in.

I think the 115t OEW is with Aspire Aviations' extra weight.

Airbus claimed three years ago that ZA001 had an MWE (Manufacturer Weight Empty - an airplane with no customer interior) of 102t, which is 9 tons heavier than Boeing's original design goal of 93t.

When Boeing announced firm configuration for the 787-8 in 2005, the OEW in a Boeing Configuration of 224 seats was 110t. Add the extra 6 tons of LN007-LN019, and you're at 116t OEW, which is a bit more than the 115t OEW listed in September 2008 and would reflect additional structural changes.

So NH's two deliveries would not have OEWs of 121t in a 224-seat Boeing configuration, but instead 116t. And LN090 would not have an OEW of 115t in a 224-seat Boeing configuration. It would have an OEW below 110t.
 
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RE: The 787 Weight, How It Got There

Sat Oct 15, 2011 5:48 am

Quoting Stitch (Reply 26):

Since dynamicsguy is flying Aussie colors, I expect he's with Boeing' Hawker de Havilland unit, which builds the movable trailing edges and inboard flaps.

Yep, though we haven't been called HdH for a while - it's Boeing Aerostructures Australia now. On the 787 we build inboard and outboard flaps, flaperon and aileron in Melbourne, and various parts for the 777, 737, 747-8, F/A 18 C/D, C-130, and others. Used to do a fair bit of Airbus work as well (winglets and wingtips, gear doors and some fuselage structure), but we're going Boeing-only now.
 
ferpe
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RE: The 787 Weight, How It Got There

Sat Oct 15, 2011 7:36 am

Quoting Stitch (Reply 28):
I think the 115t OEW is with Aspire Aviations' extra weight.

While I would like to believe that all the check calculations one can make contradicts that. Even Bs own spec figures does. I have found 2 errors in my previous post but they don't explain your assumptions:

1. I wrote 14,4nm per ton, it should be 144nm per ton (write fault when I took the values from my Excel) which was also used in my calculations. This slope of the payload-range curve is given by Boeing, not by me nor Piano-X. It depicts a frame which is sensitive to payload changes or more positively expressed; convert 1t of payload on the 788 to fuel and it will fly 44% longer on it then the frame it replaces. Rising the OEW with the spec points given by B per definition lowers the fuel burn fraction, therefore the curve describes a high OEW craft compared to MTOW and a low fuel burn (can be good SFC or low base drag or both). High OEW means here more then 50% of MTOW, i.e. over 0,5*228=114t for the spec config of 242 seats.

2. When one put in the two spec points that B have given (210 pax and 250 pax) one does also have to adjust the OEW accordingly for the change in furnishing weight, I didn't do that in the previous post. Having checked the relationship between MEW to OEW for numerous frames (the OEM spec values) the factor seems to be around 63kg per seat. Here then the furnishing values for the different seat configs B have given us:

First B APAC guide, 242pax together with 114,7t OEW. Deduce 15246kg and you have the MEW at 99450kg.
For the 250 pax data point add the furnishing of 15750kg and you have an OEW of 115200kg.
For the 210pax data point add the furnishing of 13230kg and you have an OEW of 112680kg.

Summary: the 210pax frame has an OEW of 2,5t lower then the 250pax seating version.

Using these differences in Piano-x the fit gets better at OEWs that range around 114,7 + 4t, your stated 5t lower OEWs and a MEW of 93t for the present craft does not fit at all with the above, you get a craft that flies 9000nm or more and a frame that has no relations to Bs figures.


I wish we could get more clarity in this, I am not out to prove 787 heavy, I think it is an elegant design, I just would like to have the baseline figures confirmed so one can predict what it can do or not with reasonable accuracy.

[Edited 2011-10-15 01:39:26]
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Stitch
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RE: The 787 Weight, How It Got There

Sat Oct 15, 2011 4:27 pm

It is supported by Airbus' analysis, and Airbus' objective should be to paint the 787 in the worst light possible. So if they could say that ZA001 was 17 tons overweight, one would think they would have said that as opposed to 8 tons.

I also can't see ZA001 suddenly gaining 8 tons of additional empty weight between October 2008 and October 2011.

And by extension, if ZA001 gained 8 tons from Change Incorporation and Re-Work since October 2008, so should every other 787 airframe produced by October 2008 as they all would have had the same Change Incorporation and Re-Work. And yet the first tranche of production frames magically lost 2 tons of that CI&RW weight and the second tranche magically lost another 2 tons on top of that and I am sure some of them were complete by October 2008.

[Edited 2011-10-15 09:29:55]
 
baroque
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RE: The 787 Weight, How It Got There

Sun Oct 16, 2011 3:24 am

Quoting Stitch (Reply 31):
It is supported by Airbus' analysis, and Airbus' objective should be to paint the 787 in the worst light possible. So if they could say that ZA001 was 17 tons overweight, one would think they would have said that as opposed to 8 tons.

Dunno there. If ZA001 was 17 tons overweight A would be so torn between laughing over that and crying with fear over having the same fate attend the A350, that they would be unable to say anything very much!   

But, jests aside you have to be right. This weight issue, does seem to be surrounded by a near impenetrable fog. With the various break points in design/production, where do the actual as opposed to predicted weights become apparent? After EIS or before it?

One presumes customers are a little less in the dark than various folk on these threads who normally would be expected to be a bit more certain????
 
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RE: The 787 Weight, How It Got There

Sun Oct 16, 2011 5:44 am

Quoting ferpe (Reply 30):
I just would like to have the baseline figures confirmed so one can predict what it can do or not with reasonable accuracy

It's not just about mass, either-- you have a similar guessing game for aero and propulsion efficiency, the other two legs of the stool. Without inside information, it's going to be hard to nail these down.
 
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Stitch
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RE: The 787 Weight, How It Got There

Sun Oct 16, 2011 12:43 pm

Quoting Baroque (Reply 32):
Dunno there. If ZA001 was 17 tons overweight A would be so torn between laughing over that and crying with fear over having the same fate attend the A350, that they would be unable to say anything very much!     

At one point, Boeing's own evaluation of the A350XWB program supposedly had the A350-900 17 tons over design MWE. If such a claim was ever true, they really would have been whistling past the    at that moment.



Quoting Baroque (Reply 32):
One presumes customers are a little less in the dark than various folk on these threads who normally would be expected to be a bit more certain????

They must know exactly what their planes weigh. And NH have stated they weigh more than planned - to the point they're not really ready (at least with Package A engines) for long-haul operations.

But if they were 6 tons heavier than Boeing said they would have been when they started building them, I can't see even the Japanese being quietly polite about that. And AAB should be spitting nails since his first frames would be multiple tons heavier than planned.
 
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RE: The 787 Weight, How It Got There

Sun Oct 16, 2011 1:12 pm

Quoting Stitch (Reply 34):
But if they were 6 tons heavier than Boeing said they would have been when they started building them, I can't see even the Japanese being quietly polite about that. And AAB should be spitting nails since his first frames would be multiple tons heavier than planned.

Agreed with all you say. What puzzles is why B (at this stage A does not have a figure because it has not yet built one, but when the time comes, them too) has not released more definite information on weights. They can hardly be worse than some of the speculations. And they could also indicate their weight loss program. But I guess this just shows why I don't work in the aircraft industry. And they talk about needing a one armed geologist because of our habit of saying well on the one hand it could be A and on the other hand it could be B!   
 
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RE: The 787 Weight, How It Got There

Sun Oct 16, 2011 2:07 pm

Quoting Stitch (Reply 34):
But if they were 6 tons heavier than Boeing said they would have been when they started building them, I can't see even the Japanese being quietly polite about that. And AAB should be spitting nails since his first frames would be multiple tons heavier than planned.

Agreed! We were less than 1,500 lbs overweight on our prototype. Immediately a weight saving plan was installed. Parts were redesigned, fasteners were changed, assemblers were retrained in sealant application and bonuses were given for weight saving suggestions that were implemented!

One item I remember was a washer like retainer, 14 were used on the leading edge slats. It was originally 1 inch diameter and made of steel. The redesigned retainer was 3/4" in diameter and made of aluminum.
 
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RE: The 787 Weight, How It Got There

Sun Oct 16, 2011 6:32 pm

Quoting WingedMigrator (Reply 33):
t's not just about mass, either-- you have a similar guessing game for aero and propulsion efficiency, the other two legs of the stool. Without inside information, it's going to be hard to nail these down.

Well apart from the weight we have a better info and rumor mill on the aero and SFC side. The only rumor on the aero side is that the wing is if anything better then predicted,if there were issues it would feed a stronger rumor mill via the airliners, they are pretty disillusioned right now and would leak such things to prep up their damages negotiations. For the SFC we know within a percent where they are, they publicize it openly.

For the weight side we have 2 data points:

1. Bs famous ACAP where they state 114.7t OEW. I don't have this one, does anyone else? I guess this was with 119t MTOW and 156t MZFW ie the first version with spec 220 seats.

2. Airbus competitive slide-set referenced above. There we know that the 119t frame was labeled as 100t MWE and the 228t as 101.6t. This is interesting as it gives the weight penalty for going from 156t to 161t MZFW and an extra 9t MTOW as 1.6t. This seems plausible for a frame which has an over-strong CFRP fuselage (due to among other things damage control).

As stated in the Aviation thread things fit with the 101.6t MWE and the furnishing addition for 242 pax of 15.2t. Then the OEW/MTOW ratio is about right at 51% (firs acid test) and the Piano-X checks also work.

We will see what B finally reveals, I don't think they will reveal the OEW at all due to the issues we discuss, they will wait until after LN90.
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sunrisevalley
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RE: The 787 Weight, How It Got There

Sun Oct 16, 2011 11:13 pm

Quoting ferpe (Reply 37):
As stated in the Aviation thread things fit with the 101.6t MWE and the furnishing addition for 242 pax of 15.2t. Then the OEW/MTOW ratio is about right at 51% (firs acid test) and the Piano-X checks also work.

In his blog in www.flightglobal.com dated Feb. 19th 2010 titled "Boeing to finalise 787-9 configuration in June..." John Ostrower says in the penultimate paragraph ..quote "To combat the increased weight Boeing disclosed an increased MTOW of the baseline 787-8 to 227,900kg up 8400kg from the initially planned 219,500kg starting with aircraft 20 " to help us to meet the expectations of our customers'" Based on the ratio of MTOW to OEW of .51 this would put the OEW at LN20 at about 116.2 t.
 
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RE: The 787 Weight, How It Got There

Thu Oct 27, 2011 6:52 pm

It was sneaking over to the local Dunkin Donuts and getting some lemon filled donuts and iced coffee. I warned it that doing so would make it gain weight, but the 787 just had to fill that late night craving. I tried to get it to do some laps around Vancouver after midnight to lose some of the weight, but it got caught by the night guard trying to sneak out.




On a serious note, any time your models for CFRP do not match destructive testing results, such as modulus, strain, etc., you end up with flawed calculations. When the actual testing shows a lower strength than the model, you either fix the model (early on) or add reinforcements to ensure the sections will behave as the initial models. If you do the latter, you are going to add the weight of the fasteners, additional panels/reinforcements, etc. One way to reduce the weight on existing frames it to match the model to the physical results, go back and analyze the entire structure, and see where some areas can be thinned or modified post-installation. It is possible to refine the models to a tight enough accuracy to go back and redesign some small components that would have minimal cost for modification, modify those components through machining or new build, and re-install. It will not solve the entire problem, but you can reduce some of the weight and get it back closer to the target weight.

Now, you would have to find components that are easily removable, not at critical design load points, and can be either re-worked or remade in new molds and do so at areas that are not going to affect the CG of the aircraft to a large degree. This would be complex, but it can be done. I would be willing to bet that they could shave a ton or so of the excess weight with about 6 months of re-evaluation, re-work, and re-installation.

Now, as for certification of those parts, etc., that could be more challenging. The design and construction can be easier than the certification.
 
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RE: The 787 Weight, How It Got There

Thu Oct 27, 2011 8:56 pm

Quoting trigged (Reply 39):
Now, as for certification of those parts, etc., that could be more challenging. The design and construction can be easier than the certification.

Thanks for this description, if you do a new variant like the 787-9 you can apply your refined and calibrated model approach to most parts as I understand it, that is why the 787-9 can be so much closer to what the 787 should have been from the outset as you are going to do a new certification anyway.
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trigged
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RE: The 787 Weight, How It Got There

Fri Oct 28, 2011 4:00 pm

Quoting ferpe (Reply 40):
Thanks for this description, if you do a new variant like the 787-9 you can apply your refined and calibrated model approach to most parts as I understand it, that is why the 787-9 can be so much closer to what the 787 should have been from the outset as you are going to do a new certification anyway.

Quite welcome! I am not that familiar with the certification process, just the engineering. I do know that the certification process may be simple or very complicated based on what part or component is re-designed/replaced. I would imagine the certifying bodies would give the go-ahead to components that are not in critical areas, have refined models to demonstrate a match to physical testing, and possibly some replacement/testing on test aircraft.

But then again I try to leave bureaucratic things to bureaucrats.  
 
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RE: The 787 Weight, How It Got There

Tue Nov 01, 2011 10:00 pm

We have a number of posts which give some good insight to plausible reasons for the 787-8 overweight, I would like to add a speculative one my-selves.

Let me first qualify a bit from which viewpoint I do this, I have participated in quite a few large programs (some of these where (military) A/C programs) in different management roles. In my experience your complexity in optimizing the programs result increases with the number of participating organizations and cultures. The whole cycle of detecting a problem, get consensus on what to do and then getting things done efficiently slows down. In other words things need more time.

Given the murder time-plan that the 787 was put to sea with, the slow cycle times as per above, add new technologies and the other factors that was highlighted above I think it is fully plausible that parts can end up on average 6-7% heavier then forecast, there is simply no time for very optimal engineering (meaning many iterations before committing to manufacture). I think the fact that B can trim it down quite fast when getting more time validates this point in addition to the others.

[Edited 2011-11-01 15:02:40]
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ferpe
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RE: The 787 Weight, How It Got There

Thu Dec 01, 2011 1:53 pm

Just to complete our discussion the the thrust of the 787-8 engines, the T1000 for the final 228t version of the 787-8 will be rated at 70klbf. So 64klbf is fine for the 219t initial frames but you have 70k to get 228t version, 5% more weight and 10% more engine thrust, wonder why.

The power to weight ratio goes from 26,5% to 28% which is in line with e.g. the A350 series P/W ratio.
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Stitch
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RE: The 787 Weight, How It Got There

Thu Dec 01, 2011 4:32 pm

Quoting ferpe (Reply 43):
So 64klbf is fine for the 219t initial frames but you have 70k to get 228t version, 5% more weight and 10% more engine thrust, wonder why.

The A350-800HGW needs 12% more thrust (83k vs. 74k) to support 4% more TOW. (259t vs. 248t).

I wonder why, since the A350-800 is supposed to have better aerodynamics than the 787-8...   
 
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RE: The 787 Weight, How It Got There

Thu Dec 01, 2011 5:59 pm

Quoting Stitch (Reply 44):
I wonder why, since the A350-800 is supposed to have better aerodynamics than the 787-8...  

I have since 1 year back stated that the 788 with 64klbf was under-powered. Would like to know the hot and high performance of MSN 7-19, not to great IMO.
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tdscanuck
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RE: The 787 Weight, How It Got There

Fri Dec 02, 2011 4:24 am

Quoting ferpe (Reply 45):
I have since 1 year back stated that the 788 with 64klbf was under-powered.

Compared to what? If you order the 64K engines you're obviously not running the plane at certified MTOW. Given that lots of airlines purchase MTOW decreases anyway, it's very important to note which aircraft and airline you're talking about.

It's no different than the multitude of thrust ratings available on any other aircraft. The lower ratings are obviously underpowered relative to the max for the model.

Quoting ferpe (Reply 45):
Would like to know the hot and high performance of MSN 7-19, not to great IMO.

Again, relative to what? As good as a 757? No, probably not...but it was never built to be either.

Tom.
 
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RE: The 787 Weight, How It Got There

Mon Dec 05, 2011 9:40 am

Quoting tdscanuck (Reply 46):
Compared to what? If you order the 64K engines you're obviously not running the plane at certified MTOW. Given that lots of airlines purchase MTOW decreases anyway, it's very important to note which aircraft and airline you're talking about.
OK, so that mean ANA has despeced the first 788 MTOW to some 208t, it limits fuel+payload to some 90t. In the case of a full payload they have 50t of fuel to play with, some 9h fligth time, ie 4300nm range.

The reason I assume the 788 must at least have the same power/MTOW ratio as the 350 (28%) is that the 788 have higher wing loading in it's 219t version and about the same at 208t (600kg/m2), further they are very similar in their wing high lift design. I would assume the customers would like them to have about the same field performance.

[Edited 2011-12-05 02:12:38]
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Stitch
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RE: The 787 Weight, How It Got There

Mon Dec 05, 2011 1:41 pm

Quoting ferpe (Reply 47):
OK, so that mean ANA has despeced the first 788 MTOW to some 208t, it limits fuel+payload to some 90t. In the case of a full payload they have 50t of fuel to play with, some 9h fligth time, ie 4300nm range.

The first two frames are meant for domestic / regional operations so a 4300nm maximum range would be plenty for them, even if they wanted to send it down to Southeast Asia.
 
sunrisevalley
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RE: The 787 Weight, How It Got There

Mon Sep 03, 2012 12:35 am

I believe this thread is worth re-opening. Aspire Aviation published a new article last week that has updates relative to the theme of this thread. Go to their website www.aspireaviation.com and

click on "Boeing 787 Dreamliner program starts to soar"

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