Dogfight : F35 vs F16

[nrshida]

The cracking I've read about was in the engine mounts and bulkheads of an airframe that had flown the equivalent of 7000 hours. They've also discovered cracks in the wings of the C  model. This is not unexpected, but basically by design.

Have to say I'm rather sceptical about this comment. Upon which date was it announced that a borderline airframe was in flight to investigate stress cracks through flight?

[Vraciu]

There was a lot of press about the two Aim120s fired as the F4 target drone which was the target was actually preserved and returned to base.  Many "The F35's only 2 missiles both missed" etc etc etc.  Turns out they didn't actually miss, but were right on target and closing to warhead detonation when it was decided there was no point in wasting the last F4 drone that was to be used to prove that the missile warheads worked, so they sent self destruct through the datalink connection from the F35 to the Aim120s.  That's actually a pretty interesting feature, and probably has some real world use for times in swirling combat when a pilot might wish he hadn't let one fly due a friendly or unknown all of  sudden showing up somewhere downrange. 

IMO this still all boils down to theory - does low observability, new/great sensors, and modern tech in weapons and their employment trump maneuverability, speed, and power?  I've said this before, I'm still waiting for info from a very large EX where the various versions of the F35 are used in large, as in a 4 ship or a section of a squadron versus current Red Air and other threats at say Red Flag or what have you.  The Air Force has recently joined the USMC in stating that using their F35s even with current software and restrictions is to the point now where all the other fighters (save the F22 of course) are saying it's pointless to even play, as they are dead as soon as they turn inbound during their scenarios, and never even see the F35.  I do hope that's true, this thing needs to work, regardless of how any of us feel about its design and the compromises made in building it the way it is.  There are still issues, but there are still issues with every fighter out there in some manner, and there have been more and more glimmers of hope regarding the F35 recently IMO.

Those glimmers are fool's gold.   The airplane isn't meeting its design requirements so they lowered them and put out a press release. 

Speed is life and this thing is a slug.  It will NEVER be an air superiority fighter.    Never. 

If we are lucky it will be a passable light attack jet (see A-4) for second tier regional wars.

[Vraciu]

Have to say I'm rather sceptical about this comment. Upon which date was it announced that a borderline airframe was in flight to investigate stress cracks through flight?

I can't wait to hear the answer.   Gonna be a good one.   

[GScholz]

Have to say I'm rather sceptical about this comment. Upon which date was it announced that a borderline airframe was in flight to investigate stress cracks through flight?

At least two and a half years ago... It's not a "borderline airframe" and it's not "in flight". You're making too many assumptions.

They were ground testing the airframe to simulate 8000-16000 flight hours. No flying F-35 is even close to that yet, and won't be for many years. These are test and changes done to the production line and retrofitted to existing aircraft to prevent cracking problems years from now.

“The crack was not predicted to occur by prior analyses or modeling,” she said. “We can’t know all the changes that must be made to the structures until the testing is complete, and it is not surprising when discoveries like this occur.”

The purpose of “durability testing is to intentionally stress the aircraft to its structural limits so we can identify any issues and corrective actions needed to fix them,” the Pentagon’s DellaVedova said in an e-mailed statement. “These discoveries are expected and planned for in a developmental program.”

Ground testing stresses an airframe to simulate flight conditions and determine whether a plane can reach its projected lifetime, which in the case of the Marines’ F-35B is 8,000 flying hours.

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. The Marine version was supposed to complete its second 8,000 hours of testing by the end of this year.

The ground testing aircraft had accumulated 9,480 hours “when testing was stopped to conduct root-cause analysis on discovered bulkhead cracks,” DellaVedova said.

“Because of the high hours accumulated,” this “discovery does not affect current F-35B flying operations,” he said, adding that the suspension of ground testing won’t affect the Marine Corps’ goal of declaring its first squadron operational no later than December 2015.

http://www.bloomberg.com/news/articles/2014-02-21/lockheed-f-35-for-marines-delayed-as-test-exposes-cracks

[GScholz]

There was a lot of press about the two Aim120s fired as the F4 target drone which was the target was actually preserved and returned to base.  Many "The F35's only 2 missiles both missed" etc etc etc.  Turns out they didn't actually miss, but were right on target and closing to warhead detonation when it was decided there was no point in wasting the last F4 drone that was to be used to prove that the missile warheads worked, so they sent self destruct through the datalink connection from the F35 to the Aim120s.  That's actually a pretty interesting feature, and probably has some real world use for times in swirling combat when a pilot might wish he hadn't let one fly due a friendly or unknown all of  sudden showing up somewhere downrange.

Yes I saw several articles that took that successful test and twisted it into a negative propaganda piece. Irresponsible journalism. As for missile tests in general they often replace the warhead with a telemetry package so they can gather data on the terminal performance of the missile. Unless the missile scores a direct kinetic hit the drone is preserved.

[Vraciu]

Yes I saw several articles that took that successful test and twisted it into a negative propaganda piece. Irresponsible journalism. As for missile tests in general they often replace the warhead with a telemetry package so they can gather data on the terminal performance of the missile. Unless the missile scores a direct kinetic hit the drone is preserved.

Irresponsible journalism doesn't make this airplane a Mach 1.6 Su target. 

I guess the journalists who published the "Not For Public Release"  OFFICIAL AIR FORCE PROPAGANDA DIRECTIVE were also irresponsible, eh?

https://warisboring.com/u-s-air-force-requires-airmen-to-praise-troubled-stealth-fighter-c69d918d7b02#.9dwhrkhh7

Two missiles in twelve minutes.  Lol.

When it is 7:1, "Well, you all passed math. "

[Vraciu]

At least two and a half years ago... It's not a "borderline airframe" and it's not "in flight". You're making too many assumptions.

They were ground testing the airframe to simulate 8000-16000 flight hours. No flying F-35 is even close to that yet, and won't be for many years. These are test and changes done to the production line and retrofitted to existing aircraft to prevent cracking problems years from now.

http://www.bloomberg.com/news/articles/2014-02-21/lockheed-f-35-for-marines-delayed-as-test-exposes-cracks

This is PRECISELY why you don't do DEVELOPMENT and PRODUCTION concurrently. 

This whole program was a scam from the start.  They knew it.  That's why they did it this way--so it couldn't be canceled. 

[nrshida]

You're making too many assumptions.

No more than anyone else posting here I should say. You said:-

The cracking I've read about was in the engine mounts and bulkheads of an airframe that had flown the equivalent of 7000 hours.

So I naturally assumed it was a mixture of flying and test jig.

You said it was 'basically by design'. I don't think so, which would be evidenced if the announcement that it was 'by design' coincided with the reporting of the discovery of the cracks. If it had been announced at the start of the programme it'd be a different matter.

I think more likely the programme can tolerate the unexpected by virtue of it's Cook–Craigie++ plan. Which is completely reasonable of course. But I doubt with the state of the art modelling simulations they intended a design solution incorporating an element of trial and error. Likely a mistake they've had to correct. The point is the official line might be less than frank, in this regard.

[nrshida]

Also the article you posted is entitled 'Lockheed F-35 for Marines Delayed as Test Exposes Cracks'.

[GScholz]

Bad choice of words on my part, but the word "equivalent" and the fact that no F-35 could possibly have flown 7000 hours yet should have given you pause.


“The crack was not predicted to occur by prior analyses or modeling,” she said.”

“These discoveries are expected and planned for in a developmental program.”

If it had been announced at the start of the programme it'd be a different matter.

Why would they announce anything? The only reason they've commented at all is because someone leaked/sold classified test results and it was deemed worth it to answer the bad press.

[GScholz]

Also the article you posted is entitled 'Lockheed F-35 for Marines Delayed as Test Exposes Cracks'.

Just more irresponsible journalism again. A claim directly refuted by the article itself:

“Because of the high hours accumulated,” this “discovery does not affect current F-35B flying operations,” he said, adding that the suspension of ground testing won’t affect the Marine Corps’ goal of declaring its first squadron operational no later than December 2015.

[nrshida]

Just scanning this article now. They've replaced Titanium (GR5 I assume) with Aluminium alloy in the Marine's version.


"That move was part of an effort in 2004 and 2005 to lighten the increasingly heavy Marine Corps version".

“the cracks continued to grow” until a “bulkhead severed and transferred loads, which caused cracking in the adjacent” bulkhead.


Bit alarming to my eyes.

[nrshida]

Bad choice of words on my part, but the word "equivalent" and the fact that no F-35 could possibly have flown 7000 hours yet should have given you pause.

I don't follow the programme I'm too busy with my own projects. I just pass the break times and train journeys on the AH forum for entertainment.

“The crack was not predicted to occur by prior analyses or modeling,” she said.”

Yeah because they switched materials to save weight. Quite a drastic shift of materials too.

Why would they announce anything?

They don't have to. But what's that business about anything you fail to say now which you will use in your defence later. That's all I meant with that. Important to deduce as well as extrapolate. To me anyway.

“Because of the high hours accumulated,” this “discovery does not affect current F-35B flying operations,” he said, adding that the suspension of ground testing won’t affect the Marine Corps’ goal of declaring its first squadron operational no later than December 2015.

But they also conceded it would require a lengthy redesign. They've tried to save a relatively small amount of weight with a core, structural material change. From this you infer all is well?

Respectfully I think you're missing the point. Perhaps deliberately I don't know. We're reading the same articles and you interpret all is well, according to plan. I read the same and think, Crikey, they really switched from Titanium for that little of a weight saving in an almost ad hoc stylee in the core structure, and now they've found it failed enough to pass the cracks to the neighbouring bulkhead? I hope they can solve it, because they're in a lot of trouble there with very little margin.

[GScholz]

I don't assume to know better than the people working on it. You do realize these are "second life" cracks right? Cracks that occur after the designed lifespan-hours of the aircraft have been spent. They're testing the airframe to twice the designed lifespan, just to be on the safe side.

[nrshida]

I don't assume to know better than the people working on it.

That doesn't assert the people who are working on it haven't found themselves in a unplanned and less than ideal situation and are now facing an extremely difficult set of problems to solve while trying to put a positive spin on it.

You do realize these are "second life" cracks right? Cracks that occur after the designed lifespan-hours of the aircraft have been spent. They're testing the airframe to twice the designed lifespan, just to be on the safe side.

I have an intermediate understanding of metal fatigue and materials by engineering standards. Enough to comprehend the issues quite well. It's not like there isn't a HUGE body of knowledge now about stress fatigue in airframes. Even if you only count it from the first Comet break up onwards. Why are they accepting the delay and redesigning if the aircraft will never reach this number of hours? If it's just to be on the safe side you'd typically overstress it, not overlife it. Something isn't right in that information.