737NGs have cracked 'pickle forks' after finding several in the jets.
Not the first time
Pickle fork cracking was an issue on the 767. IIRC, depending on the extent of the damage, a repair consisted of removing some materiel or complete replacement of the affected pickle fork.
Either way it was a pig of a job.
Either way it was a pig of a job.
Yeah. When I was doing mechanical design we used to say 'You can have it right or you can have it now, but you can't have it right now'. Pretty sure that still applies.
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The patent for pickle forks as aircraft wing-to-fuselage joint dates to 2013:
It is not clear what mechanism was used for the NG prior to this. It is also not clear when this was first used on the NG (or some variant prior to the current patent).
My guess is that to achieve 35,000 flight cycles (assuming less than a decade of use) would require some kind of test aircraft, not normal passenger service.
It is not clear what mechanism was used for the NG prior to this. It is also not clear when this was first used on the NG (or some variant prior to the current patent).
My guess is that to achieve 35,000 flight cycles (assuming less than a decade of use) would require some kind of test aircraft, not normal passenger service.
Sorry the patent is strictly about a suspension method design to REPLACE the boeing ' standard " picklefork design used on 737,747,757,767 and 777. Dont know about the 787 but suspect it is similar. This is not to say parts are interchangeable between the models.
Typically the pickle fork is used in conjunction with as common BA part-technique called a PLUS CHORD which joins the wingbox to the wing skin panels- so called since it looks like a plus sign or double plus sign from an end view of a long slightly curved "bar" running fore and aft
As to the 35,000 hours - depending on airline, a usage of 10 hours/day average would give 3600 hours/year and 36,000 hours in about 10 years.
The NG has been around in service for about two decades- and I would be surprised if the pickle fork for the MAX was much different than the NG. Cheaper that way
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There is nothing inherently wrong with changing from batch to lean manufacturing. I've been involved with many lean implementation efforts, in an ISO 9001 compliant environment, from small (one part moving from machined to cast, similar to this one, but the size of your fist, and no lives on the line), to entire production lines.
You need to do your homework, use rigorous techniques and processes, and at the end of it, test final parts and assemblies as rigorously as the original. A complex, utterly critical part like this one would need a herculean effort to get right. I'm not full of the warm fuzzies about Boeing's ability to execute an effort like this in the last 20 years, from what I've read here and elsewhere about Boeing's strategic realignments.
You need to do your homework, use rigorous techniques and processes, and at the end of it, test final parts and assemblies as rigorously as the original. A complex, utterly critical part like this one would need a herculean effort to get right. I'm not full of the warm fuzzies about Boeing's ability to execute an effort like this in the last 20 years, from what I've read here and elsewhere about Boeing's strategic realignments.
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A picture of the pickle fork attachment.
According to reddit.com
https://www.reddit.com/r/news/commen...al_boeing_737/
According to reddit.com
https://www.reddit.com/r/news/commen...al_boeing_737/
Wing bending load increase with Split Scimitar Winglets
There is also the possibility/probability that the addition of the Split Scimitar winglets has had an adverse effect on the wing bending loads carried by the pickle forks.
Apparently the spanwise lift distribution has shifted the centre of lift further outboard on the wings which would necessarily give rise to greater wing bending loads at the wing attachment points from both static flight and gust loads.
Possibly those B737s that were designed from the outset to have Split Scimitar winglets might have strengthened pickleforks to account for the increase in bending loads.
But those B737s (eg, 800, NG) that were fitted with the after-market mod Scimitar installation (without beefing up the wing attach load path design) would necessarily suffer a reduced wing attachment fatigue life due to the higher loads imposed by the addition of the Split Scimitar winglets.
Perhaps more engineering learned members than I might like to comment?
Apparently the spanwise lift distribution has shifted the centre of lift further outboard on the wings which would necessarily give rise to greater wing bending loads at the wing attachment points from both static flight and gust loads.
Possibly those B737s that were designed from the outset to have Split Scimitar winglets might have strengthened pickleforks to account for the increase in bending loads.
But those B737s (eg, 800, NG) that were fitted with the after-market mod Scimitar installation (without beefing up the wing attach load path design) would necessarily suffer a reduced wing attachment fatigue life due to the higher loads imposed by the addition of the Split Scimitar winglets.
Perhaps more engineering learned members than I might like to comment?
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But those B737s (eg, 800, NG) that were fitted with the after-market mod Scimitar installation (without beefing up the wing attach load path design) would necessarily suffer a reduced wing attachment fatigue life due to the higher loads imposed by the addition of the Split Scimitar winglets.
Perhaps more engineering learned members than I might like to comment?
Perhaps more engineering learned members than I might like to comment?
I do know that one of the arguments re winglets for the first NG types was just that- increased bending loads. While one could assume that was properly taken care of- the viral infection of the MDC types in the aero design groups coupled with the cheaper-faster- mantra may well have overlooked that issue.
It remains to be seen just where the cracks were found.
Interesting point, 'FlexibleResponse'. I seem to recall that the wingtip extensions fitted to Buccaneers were said to have contributed to the wing spar fatigue failure in 1980.
However, as 'Sailvi767' says, cracks occur in most structures; the trick is to know how and when to inspect before these become critical.
However, as 'Sailvi767' says, cracks occur in most structures; the trick is to know how and when to inspect before these become critical.
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During a recent inspection, workers found a severely cracked pickle fork on a Boeing 737NG. The plane is relatively young, having logged approximately 35,000 flight cycles when the damage was found.
A retired Boeing engineer who asked to remain anonymous tells us, "It's unusual to have a crack in the pickle fork. It's not designed to crack that way at all. Period."
He says it's particularly concerning because it was found so early in the plane's service.
Another source tells us Boeing quickly reported the issue with the single plane to the FAA last week, and now more planes with similar cracking have been found.
A retired Boeing engineer who asked to remain anonymous tells us, "It's unusual to have a crack in the pickle fork. It's not designed to crack that way at all. Period."
He says it's particularly concerning because it was found so early in the plane's service.
Another source tells us Boeing quickly reported the issue with the single plane to the FAA last week, and now more planes with similar cracking have been found.
"Teams in Seattle and Washington, D.C are working on this. A source within the federal government says FAA inspectors were excited and happy to get the call from Boeing.
The source says they are "...elated that the bloodline of safety is alive at Boeing." That same source worries about how economic concerns for Boeing impact safety."
That reads as if the FAA had/have doubts about the bloodline of safety at Boeing - then the last sentence doubt the CEO's public statements on safety at Boeing.
The retiree - seems to think it is pretty urgent - even a grounding of a small number of NG's would create a serious issue for Boeing - the FAA will need to be VERY transparent with the other regulators over this, especially if the cracking is due to some of the manufacture allegations floating around.
The retired engineer tells KOMO the cracks were really surprising, used an expletive, then said, "This is not good news," and added, "It's really urgent to investigate."
The source says they are "...elated that the bloodline of safety is alive at Boeing." That same source worries about how economic concerns for Boeing impact safety."
That reads as if the FAA had/have doubts about the bloodline of safety at Boeing - then the last sentence doubt the CEO's public statements on safety at Boeing.
The retiree - seems to think it is pretty urgent - even a grounding of a small number of NG's would create a serious issue for Boeing - the FAA will need to be VERY transparent with the other regulators over this, especially if the cracking is due to some of the manufacture allegations floating around.
The retired engineer tells KOMO the cracks were really surprising, used an expletive, then said, "This is not good news," and added, "It's really urgent to investigate."
D) in general- the steps are 1) drill a hole slightly smaller than final size 2) insert a thin sleeve into hole 3) insert a special mandrel such that when pulled back thru the hole it expands the sleeve and hole. 4) Ream the hole which will usually be slightly out of round to final size.
On assembly, insert bolt as a tight fit.
E) in some cases and sizes, the same process can be used without a sleeve but with a expanding mandrel.
.......
On assembly, insert bolt as a tight fit.
E) in some cases and sizes, the same process can be used without a sleeve but with a expanding mandrel.
.......
Is the sleeve effectively swaged into place and then reamed, rather than the parent metal?
I have seen something similar using a roller reamer. That is, a process that just swages the parent metal to size.
But have never encountered use of a sleeve.
Note! Not to be confused with roller reamers as used in oil drilling.
Just interested in the process.
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Wing lift distribution effect
Yes, wing lift distribution affects the max bending moment but it does not affect the loads transfered to the fuselage. The total lift is not affected by the distribution. What might cause a slight difference is the larger displacements caused by larger moment but as a guess that is not the first concern.
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To me it reads as sarcasm or damning by faint praise. They are "elated" that Boeing informed them of a (potential) problem with the doohickey that holds the wings onto the plane?
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The fact that this has been discovered in relatively low cycle aircraft suggests to me that this is a manufacturing/materials issue rather than time-dependant metal fatigue.
Also, only certain aircraft are being inspected which makes me think that they have very quickly established a commonality among the affected airframes which could be a single production batch, a single production location or a single supply of raw materials.
Also, only certain aircraft are being inspected which makes me think that they have very quickly established a commonality among the affected airframes which could be a single production batch, a single production location or a single supply of raw materials.
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Have to wonder if this will expand to the 757 and 767 with the new winglets added assuming the scimitar is the cause.
Last edited by b1lanc; 29th Sep 2019 at 15:25.
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Is the sleeve of the same material as the parent metal?
Is the sleeve effectively swaged into place and then reamed, rather than the parent metal?
I have seen something similar using a roller reamer. That is, a process that just swages the parent metal to size.
But have never encountered use of a sleeve.
Note! Not to be confused with roller reamers as used in oil drilling.
Just interested in the process.
Is the sleeve effectively swaged into place and then reamed, rather than the parent metal?
I have seen something similar using a roller reamer. That is, a process that just swages the parent metal to size.
But have never encountered use of a sleeve.
Note! Not to be confused with roller reamers as used in oil drilling.
Just interested in the process.
the other way is to burnish the surface, typical burnishing tools are like a bar with many smaller rollers around it that then compress the host material to size, this is often done as the finishing process for bearing journals in aluminium used on camshafts etc.
here's some example tools: https://monaghantooling.com/precisio...ng/burnishing/