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The 787 Weight, How It Got There  
User currently offlineferpe From France, joined Nov 2010, 2804 posts, RR: 59
Posted (2 years 11 months 4 weeks 1 day 8 hours ago) and read 15190 times:

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]


Non French in France
59 replies: All unread, showing first 25:
 
User currently onlineStitch From United States of America, joined Jul 2005, 30997 posts, RR: 86
Reply 1, posted (2 years 11 months 4 weeks 1 day 7 hours ago) and read 15169 times:
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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.

User currently offlineWingscrubber From UK - England, joined Sep 2001, 850 posts, RR: 0
Reply 2, posted (2 years 11 months 4 weeks 1 day 6 hours ago) and read 15102 times:

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.



Resident TechOps Troll
User currently offlineferpe From France, joined Nov 2010, 2804 posts, RR: 59
Reply 3, posted (2 years 11 months 4 weeks 1 day 5 hours ago) and read 15024 times:

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?



Non French in France
User currently offlinebe77 From Canada, joined Nov 2007, 455 posts, RR: 0
Reply 4, posted (2 years 11 months 4 weeks 6 hours ago) and read 14558 times:

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!



Tower, Affirmitive, gear is down and welded
User currently offlineferpe From France, joined Nov 2010, 2804 posts, RR: 59
Reply 5, posted (2 years 11 months 3 weeks 1 day 9 hours ago) and read 13953 times:

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]


Non French in France
User currently offlinenomadd22 From United States of America, joined Feb 2008, 1866 posts, RR: 0
Reply 6, posted (2 years 11 months 3 weeks 1 day 5 hours ago) and read 13817 times:

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?



Andy Goetsch
User currently onlineStitch From United States of America, joined Jul 2005, 30997 posts, RR: 86
Reply 7, posted (2 years 11 months 3 weeks 1 day 2 hours ago) and read 13723 times:
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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.


User currently offlineferpe From France, joined Nov 2010, 2804 posts, RR: 59
Reply 8, posted (2 years 11 months 3 weeks 19 hours ago) and read 13596 times:

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.



Non French in France
User currently offlineferpe From France, joined Nov 2010, 2804 posts, RR: 59
Reply 9, posted (2 years 11 months 3 weeks 19 hours ago) and read 13592 times:

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]


Non French in France
User currently offlineferpe From France, joined Nov 2010, 2804 posts, RR: 59
Reply 10, posted (2 years 11 months 3 weeks 8 hours ago) and read 13439 times:

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]


Non French in France
User currently offlineferpe From France, joined Nov 2010, 2804 posts, RR: 59
Reply 11, posted (2 years 11 months 2 weeks 5 days 5 hours ago) and read 13108 times:

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.



Non French in France
User currently onlineStitch From United States of America, joined Jul 2005, 30997 posts, RR: 86
Reply 12, posted (2 years 11 months 2 weeks 3 days 11 hours ago) and read 12802 times:
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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.


User currently offlinetdscanuck From Canada, joined Jan 2006, 12709 posts, RR: 79
Reply 13, posted (2 years 11 months 2 weeks 3 days 10 hours ago) and read 12793 times:

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.


User currently offline474218 From United States of America, joined Oct 2005, 6340 posts, RR: 9
Reply 14, posted (2 years 11 months 2 weeks 3 days 9 hours ago) and read 12775 times:

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.


User currently offlineWingedMigrator From United States of America, joined Oct 2005, 2213 posts, RR: 56
Reply 15, posted (2 years 11 months 2 weeks 2 days 21 hours ago) and read 12651 times:

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

Wow. You are armed and dangerous 


User currently offlineferpe From France, joined Nov 2010, 2804 posts, RR: 59
Reply 16, posted (2 years 11 months 2 weeks 1 day 8 hours ago) and read 12347 times:

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   .



Non French in France
User currently offlineWingedMigrator From United States of America, joined Oct 2005, 2213 posts, RR: 56
Reply 17, posted (2 years 11 months 1 week 6 days 19 hours ago) and read 12128 times:

It was a compliment tinged with more than a bit of jealousy.  

User currently offlinepolymerplane From United States of America, joined May 2006, 991 posts, RR: 3
Reply 18, posted (2 years 11 months 1 week 6 days 16 hours ago) and read 12100 times:

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.



One day there will be 100% polymer plane
User currently offlineBaroque From Australia, joined Apr 2006, 15380 posts, RR: 59
Reply 19, posted (2 years 11 months 1 week 6 days 14 hours ago) and read 12080 times:

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????


User currently onlineStitch From United States of America, joined Jul 2005, 30997 posts, RR: 86
Reply 20, posted (2 years 11 months 1 week 6 days 12 hours ago) and read 12047 times:
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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.


User currently offline474218 From United States of America, joined Oct 2005, 6340 posts, RR: 9
Reply 21, posted (2 years 11 months 1 week 6 days 11 hours ago) and read 12039 times:

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.


User currently offlinetdscanuck From Canada, joined Jan 2006, 12709 posts, RR: 79
Reply 22, posted (2 years 11 months 1 week 6 days 10 hours ago) and read 12015 times:

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.


User currently offlineferpe From France, joined Nov 2010, 2804 posts, RR: 59
Reply 23, posted (2 years 11 months 1 week 6 days 7 hours ago) and read 11986 times:

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?



Non French in France
User currently offlinedynamicsguy From Australia, joined Jul 2008, 873 posts, RR: 9
Reply 24, posted (2 years 11 months 1 week 6 days 6 hours ago) and read 11968 times:

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.


25 ferpe : So what parts are you then building?
26 Stitch : Since dynamicsguy is flying Aussie colors, I expect he's with Boeing' Hawker de Havilland unit, which builds the movable trailing edges and inboard fl
27 ferpe : 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 webs
28 Stitch : 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 air
29 dynamicsguy : 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, flaper
30 ferpe : 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
31 Stitch : 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
32 Post contains images Baroque : 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
33 WingedMigrator : 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 insi
34 Post contains images Stitch : 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
35 Post contains images Baroque : 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, the
36 474218 : Agreed! We were less than 1,500 lbs overweight on our prototype. Immediately a weight saving plan was installed. Parts were redesigned, fasteners wer
37 ferpe : 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 anyt
38 Post contains links SunriseValley : 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 penulti
39 trigged : 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 wei
40 ferpe : 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 under
41 Post contains images trigged : 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
42 ferpe : 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.
43 ferpe : 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 64k
44 Post contains images Stitch : 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 bet
45 ferpe : 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
46 tdscanuck : 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 de
47 ferpe : 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
48 Stitch : 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
49 Post contains links sunrisevalley : 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
50 Post contains links ferpe : I agree it can be time to look at the actual empty weight(s) of the 787 but then this thread should be the better one as this thread was meant to disc
51 777way : Will Boeing or paint manufacturers work to resolve the 787 engine colour issue? hope its not a this is it situation.
52 tdscanuck : What issue? The nacelle paint system has been set for years. Tom.
53 sweair : I think the 788 will get even lighter as an effect of the 789 parts taking over in the future, LN90 was the spec weight and it may even go below these
54 CM : The nacelles are white by design. Although an airline is free to paint their 787 nacelles any color they like, Boeing will only paint them white. As
55 777way : the fact that it cant be painted any other colour than white.
56 tdscanuck : How is that an issue? It's a design feature to improve fuel burn...calling that an "issue" is like asking when Boeing is going to fix the "issue" of
57 CM : This is not true for the nacelles (although it is for the wings & h-stab). There is nothing preventing an airline from painting the nacelles any
58 Post contains images KELPkid : ..and has warned airlines that the laminar flow in the nacelle area is so supercritical that changing the thickness of the paint coat will destroy la
59 Post contains links nomadd22 : It would not "destroy" laminar flow. Save that crap for WSJ articles. Boeing warned that other than optimal thickness of paint and having paint seams
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