Forum: F-35 Lightning II

It's a good thing the B variant isn't dying anytime soon. Now that it's coming out of probation maybe we'll start seeing some more promising results.

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Lightndattic wrote:

Because they'll say anything you want them to provided you write it on a cheque for a few million $. It's well known theme here that Thomspon would stand in front of a smouldering wreck of a F-35A and spin it as a 100% improvement in landing distance.

If it's so well known that they'll write anything for money, can you provide some examples where they've hyped something akin to a smouldering wreck = improvement in landing distance?

wrightwing wrote:

Lightndattic wrote:

Because they'll say anything you want them to provided you write it on a cheque for a few million $. It's well known theme here that Thomspon would stand in front of a smouldering wreck of a F-35A and spin it as a 100% improvement in landing distance.

If it's so well known that they'll write anything for money, can you provide some examples where they've hyped something akin to a smouldering wreck = improvement in landing distance?

The example that came directly to mind (and I'm trying to find it) was after the generator failure on AF-4 at Edwards, the boys at LI spun it as "This is what the testing program is meant to find and that the backup systems on the aircraft enabled a safe landing". Which of course it did, but in almost the same breath, they were spouting that the additional testing was unnecessary and was the reason the program was so far behind schedule. Around the time of the disclosure of the bulkhead failure during durability testing, another "All's well with the F-35 and no major design problems have been found" statement came out. Perhaps by including 'major' in that statement provides enough wiggle-room in their minds, but a major structural piece forming the core of the aircraft failing at anything less than 100% of it's intended lifespan is a design problem.

Don't get me wrong, I'm not in Sweetman's 'F-35 is the devil' camp. I want the program to proceed and I love to sit out on the end of the runway here in Ft Worth and watch them fly off to their home bases, but I won't stand for a paid shill telling me the sky is yellow when I can see it's not.

With all due respect, you wouldn't know if the sky was yellow if it hit you in the face. A bulkhead failure in a durability test program is not only expected, it's a indication the airplane is not grossly over-designed. You obviously know little if anything about how airplanes are developed, so you may not understand this. If an airplane sails through durability and static test with NO failures, that's a good sign it is over-designed and weighs more than it should. (That is not the same thing as over weight). A crack is NOT a test failure, it is a test success, for the purpose of the test is to locate problem areas and fix them before flying airplanes run into the same problem.

Plus, passing a durability test requires the airframe reach from 200% to 400% of its design lifetime, not a measly 100%.

Before you criticize a development program, it might be wise to learn a little bit about how they work.

johnwill wrote:

With all due respect, you wouldn't know if the sky was yellow if it hit you in the face. A bulkhead failure in a durability test program is not only expected, it's a indication the airplane is not grossly over-designed. You obviously know little if anything about how airplanes are developed, so you may not understand this. If an airplane sails through durability and static test with NO failures, that's a good sign it is over-designed and weighs more than it should. (That is not the same thing as over weight). A crack is NOT a test failure, it is a test success, for the purpose of the test is to locate problem areas and fix them before flying airplanes run into the same problem.

Plus, passing a durability test requires the airframe reach from 200% to 400% of its design lifetime, not a measly 100%.

Before you criticize a development program, it might be wise to learn a little bit about how they work.

Interesting. Did the F-16, F-15, F-18 (gen 1 or 2), F-22 have any structural (bulkhead) failures discovered at similar points in their development?

Don't know about the 18 or 22, but the 16 certainly did have bulkhead cracks. As I said, cracks in durability test are expected. A crack is not a structural failure, but only an indication of a potential future failure.

In order to call the F-35 program a "normal acquisition program" one really might wish to define normal. There is nothing normal about a program this large. It's still not back in Milestone B which is certainly not normal. The unprecedented amount of concurrency between testing and development is far from normal.

One can certainly be very hopeful about the F-35 and assume it's a game changing strike fighter; however, this does not preclude being critical of certain aspects of the program. One can assume that all major issues will be ironed out by the end of testing but this does not mean there does not still remain issues over the entire testing phase. In any case the number one issue remains cost and this is not my opinion but rather those at DOD overseeing the program. When the final results of the review some time this year we'll know a lot more.

johnwill wrote:

With all due respect, you wouldn't know if the sky was yellow if it hit you in the face. A bulkhead failure in a durability test program is not only expected, it's a indication the airplane is not grossly over-designed. You obviously know little if anything about how airplanes are developed, so you may not understand this. If an airplane sails through durability and static test with NO failures, that's a good sign it is over-designed and weighs more than it should. (That is not the same thing as over weight). A crack is NOT a test failure, it is a test success, for the purpose of the test is to locate problem areas and fix them before flying airplanes run into the same problem.

Plus, passing a durability test requires the airframe reach from 200% to 400% of its design lifetime, not a measly 100%.

Before you criticize a development program, it might be wise to learn a little bit about how they work.

Informative post. If an airframe made with through the tests without any problem, would they then go about paring off a bit of weight here and there int the hope of improving performnce? Where do you draw the line?

No, not worth the cost of redesign and retest. You just accept the results and use the excess capacity for future inevitable weight growth. The F-16 for example grew about a pound a day for its first fifteen years of service.

lb wrote:

In order to call the F-35 program a "normal acquisition program" one really might wish to define normal. There is nothing normal about a program this large. It's still not back in Milestone B which is certainly not normal. The unprecedented amount of concurrency between testing and development is far from normal.

One can certainly be very hopeful about the F-35 and assume it's a game changing strike fighter; however, this does not preclude being critical of certain aspects of the program. One can assume that all major issues will be ironed out by the end of testing but this does not mean there does not still remain issues over the entire testing phase. In any case the number one issue remains cost and this is not my opinion but rather those at DOD overseeing the program. When the final results of the review some time this year we'll know a lot more.

I believe what they mean by normal is merely on the superficial level in which the fact that the F-35 development has been suffering from some issues here and there along with the cost overruns but in the end the F-35's issues will be solved in time and the aircraft will enter service and not be cancelled after only 50 airframes.

The F-15 and F-16 had issues in development and they were fixed over time just like what the article thinks the F-35 will experience.

johnwill wrote:

With all due respect, you wouldn't know if the sky was yellow if it hit you in the face. A bulkhead failure in a durability test program is not only expected, it's a indication the airplane is not grossly over-designed. You obviously know little if anything about how airplanes are developed, so you may not understand this. If an airplane sails through durability and static test with NO failures, that's a good sign it is over-designed and weighs more than it should. (That is not the same thing as over weight). A crack is NOT a test failure, it is a test success, for the purpose of the test is to locate problem areas and fix them before flying airplanes run into the same problem.

Plus, passing a durability test requires the airframe reach from 200% to 400% of its design lifetime, not a measly 100%.

Before you criticize a development program, it might be wise to learn a little bit about how they work.

John, I've been following Aircraft development since the early 80's, so while I'm not directly involved with the programs, I've done all I can to familiarize myself with the process. Not just reading what's published, but actually touring Vought's facility here in Dallas and seeing them do structural component testing on aircraft structures. I do believe I've familiarized myself with the program more than a little bit.

I do understand durability testing is supposed to find the actual lifespan of a component and these components are required to meet far more than 100% of the anticipated lifespan. That doesn't dismiss the fact that something designed for 8000 flight hours failed at 20% of that anticipated lifespan much less the end goal of 2 or 4 times that lifespan.

All that being said, my criticism wasn't of the testing or development program, it was about those that spin anything critical of said program as good news.

Sorry I got a little carried away with my reaction to your criticism. I've been hearing uninformed comments on test programs for a long time, and sometimes I over-react. Nothing personal, I assure you.

I still feel you have no clue as to the detail processes required to design and verify the structural integrity of a military airplane. Looking at a Vought component test is certainly interesting, but I don't see how that provides you with much insight on what it takes to get to that point, plus how the test results are used to further improve the structure. Be that as it may, I agree that those who spin results to be more positive than reality should be called out, but that is human nature, everywhere. They do it, I do it, you do it.

Here's the problem. There are a million different places where a crack might form in a structure, maybe a billion. You cannot possibly do a detail analysis of all those locations, so you pick maybe a thousand points. Those points are not just randomly selected, but are the result of a very detailed static stress analysis. What are the odds of missing a bad point? Almost 100%. The durability test programs are designed locate the bad spots and fix them. The fix most likely is a very minor redesign of a few locations where cracks appear early. If a crack forms at 20% of one lifetime, you say, great, we found a problem, let's fix it, and press on.

Forum: F-35 Lightning II

Bad News For F-35 Critics: ...A Normal Acquisition Program