F-35B Bulkhead Cracks Found on Stress Test
Thread Starter
F-35B Bulkhead Cracks Found on Stress Test
Looks like bulkheads will require beefing up after this report on the F-35B.
Lockheed F-35 for Marines Delayed as Test Exposes Cracks - Bloomberg
Lockheed F-35 for Marines Delayed as Test Exposes Cracks - Bloomberg
Join Date: Jan 2003
Location: Leicestershire, England
Posts: 1,170
Likes: 0
Received 0 Likes
on
0 Posts
Thread Starter
You have a good heads up on the re-design RP. looks like Reuters just getting up to speed today.
UPDATE 1-F-35 cracks need redesign, Marines still on track for 2015 combat use | Reuters
UPDATE 1-F-35 cracks need redesign, Marines still on track for 2015 combat use | Reuters
Join Date: Jan 2003
Location: Leicestershire, England
Posts: 1,170
Likes: 0
Received 0 Likes
on
0 Posts
The bulkhead cracking issues were actually known about as far back as 2011 (possibly further), must've been a slow news day at Reuters and they needed some filler... 
-RP
-RP
Join Date: Jul 2006
Location: by the Great Salt Lake, USA
Posts: 1,542
Likes: 0
Received 0 Likes
on
0 Posts
Rhino - the article says this is a new cracking issue, not the same as that found in 2011:
.
However, note the following:
1. "projected lifetime, which in the case of the Marines’ F-35B is 8,000 flying hours."
2. "The ground testing aircraft had accumulated 9,480 hours when testing was stopped"
3. "To provide an extra margin of assurance, the Marine, Air Force and Navy versions of the F-35 are all required to undergo tests for the equivalent of 16,000 flight hours."
So the test aircraft was past the currently-planned service life when the cracks developed.
In many ways, this is comparable to the F/A-18A/B/C/D fatigue issue - which required replacement of the fuselage center-barrel to prevent cracking.
Remember, the original Hornets had been designed for a service life of only 6,000 hours, but were reaching their "fatigue life" (based on stresses recorded by aircraft instrumentation) in an average of 4,800 hours.
In this case, though, the need for changing the center section has been identified long before any aircraft need it.
I am confident that a proper "fix" can be developed and implemented long before any flying aircraft start developing cracks.
Yes, the F-35B has only 202lb more leeway before its weight reaches the contractual "limit".
Contrary to some assertions, this is not the "max growth weight", but the "max start-of-service" weight. There will still be "growth allowance" left, as well as future allowable weight increases as engine power is increased over time.
Originally Posted by Bloomberg article from the OP
The cracking “is significant enough to warrant changes to the design” of the bulkhead, Jennifer Elzea, spokeswoman for the Pentagon test office, said in an e-mail. “This is a new defect that must now be addressed through a production change and a retrofit plan.”
However, note the following:
1. "projected lifetime, which in the case of the Marines’ F-35B is 8,000 flying hours."
2. "The ground testing aircraft had accumulated 9,480 hours when testing was stopped"
3. "To provide an extra margin of assurance, the Marine, Air Force and Navy versions of the F-35 are all required to undergo tests for the equivalent of 16,000 flight hours."
So the test aircraft was past the currently-planned service life when the cracks developed.
In many ways, this is comparable to the F/A-18A/B/C/D fatigue issue - which required replacement of the fuselage center-barrel to prevent cracking.
Remember, the original Hornets had been designed for a service life of only 6,000 hours, but were reaching their "fatigue life" (based on stresses recorded by aircraft instrumentation) in an average of 4,800 hours.
In this case, though, the need for changing the center section has been identified long before any aircraft need it.
I am confident that a proper "fix" can be developed and implemented long before any flying aircraft start developing cracks.
Yes, the F-35B has only 202lb more leeway before its weight reaches the contractual "limit".
Contrary to some assertions, this is not the "max growth weight", but the "max start-of-service" weight. There will still be "growth allowance" left, as well as future allowable weight increases as engine power is increased over time.
So the test aircraft was past the currently-planned service life when the cracks developed.
Or possibly when the cracks were found - which would be a slightly different story !
GK, there is an error margin between actual fatigue and that experienced by the testbed, hence the higher target. The fact that the F/A-18 experienced real-world fatigue issues at an earlier point than the testbed suggested is testament to this additional margin. It would be overly optimistic to expect the F-35 to meet its projected lifetime without the planned rectification.
The presumed logic of increased thrust overcoming the weight gain is a bit shaky with the F-35B due to physical limitations of the lift fan.
The presumed logic of increased thrust overcoming the weight gain is a bit shaky with the F-35B due to physical limitations of the lift fan.
Join Date: Jan 2003
Location: Leicestershire, England
Posts: 1,170
Likes: 0
Received 0 Likes
on
0 Posts
Really not good news at all, if they are indeed 'new' bulkhead cracks...
Where's our resident ray of F-35 sunshine Spaz when we need him, to assure all is actually well...
-RP
Where's our resident ray of F-35 sunshine Spaz when we need him, to assure all is actually well...
-RP
Join Date: Jun 2009
Location: Earth
Posts: 125
Likes: 0
Received 0 Likes
on
0 Posts
Originally Posted by GreenKnight121
2. "The ground testing aircraft had accumulated 9,480 hours when testing was stopped"
The problem is real and nothing to downplay.
Join Date: Jul 2008
Location: Australia OZ
Age: 75
Posts: 2,587
Likes: 0
Received 53 Likes
on
46 Posts
For 'Nitro104':
Cracking Found in Marine Joint Strike Fighter Won’t Delay Program 24 Feb 2014 Dave Majumdar
Cracking Found in Marine Joint Strike Fighter Won't Delay Program | USNI News
Cracking Found in Marine Joint Strike Fighter Won’t Delay Program 24 Feb 2014 Dave Majumdar
"...
According to the joint statement: “9,480 durability test hours equate to more than 17 years of operational flying.”
The F-35 is required to have an airframe life of 8,000 flight hours—which must be verified via durability testing though two complete structural lifetimes...."
According to the joint statement: “9,480 durability test hours equate to more than 17 years of operational flying.”
The F-35 is required to have an airframe life of 8,000 flight hours—which must be verified via durability testing though two complete structural lifetimes...."
Join Date: Jun 2009
Location: Earth
Posts: 125
Likes: 0
Received 0 Likes
on
0 Posts
Thx.
I assumed 40 years of service life, but it appears JPO calculates with 30 years life span, which is particularly problematic at current cost rates and would bring the total fleet procurement in often cited 'next 40/50 years', to almost 200% of the current cost.
I assumed 40 years of service life, but it appears JPO calculates with 30 years life span, which is particularly problematic at current cost rates and would bring the total fleet procurement in often cited 'next 40/50 years', to almost 200% of the current cost.
Join Date: Mar 2011
Location: Sussex
Age: 66
Posts: 371
Likes: 0
Received 0 Likes
on
0 Posts
The cracks in the bulkhead (S) that have so far been found are in the lighter weight aluminium alloy that was developed to give a weight saving over the Titanium used in the A and C models.
I have not seen anyone taking about any new alloy to replace the one that has failed in a number of structures. I assume that if all the light weight aluminium was replaced by the original Titanium, that the plane would be overweight.
A bit of a quandary...
I have not seen anyone taking about any new alloy to replace the one that has failed in a number of structures. I assume that if all the light weight aluminium was replaced by the original Titanium, that the plane would be overweight.
A bit of a quandary...
Join Date: Aug 2007
Location: London, New York, Paris, Moscow.
Posts: 3,632
Likes: 0
Received 0 Likes
on
0 Posts
Na they'll just scrap everything else to pay for a [relatively] minute fleet of wonder aircraft....
...still on the good side, we splurged a dose of Harriers to the yanks for peanuts, perhaps it is time for some payback with some A-10's coming our way, perhaps even for the AAC instead of those ridiculously expensive helicopter upgrades/replacements
...still on the good side, we splurged a dose of Harriers to the yanks for peanuts, perhaps it is time for some payback with some A-10's coming our way, perhaps even for the AAC instead of those ridiculously expensive helicopter upgrades/replacements
Join Date: Dec 2006
Location: UK
Posts: 799
Likes: 0
Received 0 Likes
on
0 Posts
PhilipG,
Sorry, no - the bulkhead that has cracked has always been aluminium. The titanium bits that were replaced were the keel beams, which were that way to meet the C model requirements for catapult launch and recovery. Those were changed out to new aluminium beams on the A and B.
Structures fail for all sorts of reasons, including selection of material, but for most combat aircraft, high strength aluminium is really the best choice. The main reason structures fail is due to failings in design, mainly failing to correctly model and predict load paths and load magnitude. Fatigue also plays a massive part, and here things get really complicated, depending on how you apply fatigue spectra. Clever people all around that stuff.
I don't for one moment want to suggest that 'all is well'. It's not and fixes will have to be found. My own feeling is that a rapidly executed weight reduction programme led to some structural design features that should have been better. But I could very well be wrong.
That said, the sky is not falling in here. It's perhaps best to remember that the F-35 team set themselves a very, very high bar for achieving a complex yet light weight structure. Nobody is perfect. The designers of the Tornado wing box found that out. So did the C-5A wing team. So did the F-22 aft fuselage team. So did the Buccaneer team. So did the Hornet team. So did the Comet team.
It's easy to criticise. It's a bit harder to do.
Best Regards as ever to all those doing the doing.
Engines
Sorry, no - the bulkhead that has cracked has always been aluminium. The titanium bits that were replaced were the keel beams, which were that way to meet the C model requirements for catapult launch and recovery. Those were changed out to new aluminium beams on the A and B.
Structures fail for all sorts of reasons, including selection of material, but for most combat aircraft, high strength aluminium is really the best choice. The main reason structures fail is due to failings in design, mainly failing to correctly model and predict load paths and load magnitude. Fatigue also plays a massive part, and here things get really complicated, depending on how you apply fatigue spectra. Clever people all around that stuff.
I don't for one moment want to suggest that 'all is well'. It's not and fixes will have to be found. My own feeling is that a rapidly executed weight reduction programme led to some structural design features that should have been better. But I could very well be wrong.
That said, the sky is not falling in here. It's perhaps best to remember that the F-35 team set themselves a very, very high bar for achieving a complex yet light weight structure. Nobody is perfect. The designers of the Tornado wing box found that out. So did the C-5A wing team. So did the F-22 aft fuselage team. So did the Buccaneer team. So did the Hornet team. So did the Comet team.
It's easy to criticise. It's a bit harder to do.
Best Regards as ever to all those doing the doing.
Engines
Join Date: Mar 2011
Location: Sussex
Age: 66
Posts: 371
Likes: 0
Received 0 Likes
on
0 Posts
Engines,
Sorry if I got it wrong but the press article did say that the F35B bulkhead was one of those that is in Titanium on the A and C.
As a matter of interest do you know how much weight the aluminium saved? Also do you know if the metallurgical issues with the alloy is in the process if being solved, I say metallurgical as I assume the component is the same shape as the Titanium ones?
Philip
Sorry if I got it wrong but the press article did say that the F35B bulkhead was one of those that is in Titanium on the A and C.
As a matter of interest do you know how much weight the aluminium saved? Also do you know if the metallurgical issues with the alloy is in the process if being solved, I say metallurgical as I assume the component is the same shape as the Titanium ones?
Philip