F-35 air-to-air - Pro and Con

Discuss the F-35 Lightning II
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sferrin

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Unread post19 Feb 2014, 14:21

disconnectedradical wrote:
Raptor_claw wrote:
disconnectedradical wrote:Raptor_claw, I'm curious about your statement that g-limits of modern flight control systems like on the F-22/F-35 is not as conservative as they were in the F-16. I'm not quite sure what you mean by that. I mean, aren't they all just limited to 9 g?
I wasn't referring to the g-limits being less conservative, I was alluding to the margin in the structural design. There has been a trend toward reduced margins in certain regards, in the never-ending quest to limit weight. The justification (as I understand it) has a lot to do with the increase in complexity and fidelity of the structural models (predictive, math models, not physical ones) and the massive increase to the sheer quantity of analysis that can be generated with the computing power available now.


Interesting. I guess it's more dangerous and risky nowadays to over-g an F-22 than an F-16.



I would be surprised if an F-22 couldn't handle more G's than the F-16. That F-22 mentioned earlier pulled a LOT of G's to be put on the shelf.
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Unread post19 Feb 2014, 16:15

johnwill wrote:
But there is more to the story. USAF uses a structural technology called fracture mechanics to track crack growth and allows airplanes to keep flying with cracks so long as the cracks remain within specified lengths. The Navy, being old fashioned and ultra conservative still used fatigue crack rules which say that any crack is reason for grounding. Because fatigue analysis and test is much more primitive than fracture mechanics, it requires a more conservative approach. So if USAF had those same F-16N airplanes, they would not have grounded them.


Interesting. I wonder if the F-15 that snapped in half inflight was under a monitoring program.
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outlaw162

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Unread post19 Feb 2014, 17:45

Its primary justification is to give the guy a little more capability if he finds himself headed at the ground and thinks he can't avoid it.


....it takes two distinct, deliberate actions to engage....


That's comforting. :shock:
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Unread post19 Feb 2014, 19:18

maus92 wrote:
johnwill wrote:
But there is more to the story. USAF uses a structural technology called fracture mechanics to track crack growth and allows airplanes to keep flying with cracks so long as the cracks remain within specified lengths. The Navy, being old fashioned and ultra conservative still used fatigue crack rules which say that any crack is reason for grounding. Because fatigue analysis and test is much more primitive than fracture mechanics, it requires a more conservative approach. So if USAF had those same F-16N airplanes, they would not have grounded them.


Interesting. I wonder if the F-15 that snapped in half inflight was under a monitoring program.


Yes it was, since all AF fighters are monitored. The problem with the F-15 was not a design or severe usage situation, but an unknown manufacturing flaw that resulted in an undersized cockpit sill longeron for some airplanes. All structural analysis and test of a good longeron showed no problems. So there was no reason to suspect it would fail in flight, therefore it was not monitored or inspected closely. I believe the F-16 was the first AF airplane to be designed to fracture mechanics criteria, so the F-15 (at least early ones) may have been designed to fatigue criteria.

Fracture mechanics was initially developed to help solve a severe cracking problem with F-111 wing pivot high strength steel parts. The steel was extremely strong, but small cracks could grow very fast and result in failures. It could be described as "brittle", since it behaved something like glass - very strong, but intolerant of cracks.
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Unread post19 Feb 2014, 22:21

johnwill wrote:
neurotech wrote:As I understood, the F-16Ns were retired early ........

Long story there, I'll try to be as brief as possible. The design mission usage of the F-16A/B was 55% air to air, 45% air to ground, but the F-16N was used almost 100% air to air in aggressor training.......


Hi I picked the following off the net years ago (Link is now dead).

Is he correct about the claimed 800KIAS overstress?

Which brings me to (wait for it): The Worst Overstress I Ever Had
...
And so it came to pass one day that I, in an F-16N, and my wingman, in an F-5E, were fragged for a 2v2 sweep mission against a pair of Homestead Air Force Base F-16s. Long story short, we gained an offensive advantage at medium range, and our adversaries were forced to run away, which the F-16 does wonderfully well.
And I attempted to catch them, which the F-16 does equally well. Leaving my F-5 wingman panting in the dust, I gained radar locked on a guy several miles away, hauling the mail and going for the deck. He was out of range for a missile attack, but I could hear him and his wingman chattering on the radio. They had lost visual mutual support, and were attempting to regain situational awareness and formation.
I was going 800 knots, which was as fast as you were allowed to go. If my man turned so much as 30 degrees or so to rejoin with his wingie, I would be all over him like a cheap suit. Like white on rice. Like a bad rash. Like… you get the picture.
So yeah, I was bringing the heat.
It’s a lot of fun to go that fast, down low, with your adversary right there in front of you, totally defensive and your finger on the trigger. There is a buzzing sound in the inlet, and your canopy howls with the dynamic stress of the airflow. The wave tops below flash by like the trestles on a high-speed train.
At that speed, you are unconcerned with virtually anything but that which is right in front of you. Things behind you will not be a factor (unless you turn, oh please turn) and things beside you will soon be behind you.
The fighter’s wingie called on the radio and said he was right three o’clock, one mile. The lead called “blind,” meaning he didn’t him.
“HAH!” thought I, “not only is he defensive, but he is blind as a bat!”
“RIGHT THREE O’CLOCK, WINGFLASH!” the wingie emphasized his position call by rocking up on his wing, at ninety degrees to the horizon – showing himself in planform for his lead – a wingflash.
“Blind!”
And that sort of put me to thinking. Even Elmer Fudd should have been able to see an F-16 in planform from 1 mile away.
So if the wingie was flying along beside an F-16, and that F-16 was not his lead, then who could he be flying next to?
A quick glance to my right three o’clock told me who.
Apparently the same notion worked its way through the wingie’s wetware, since as I began my rapid windup break turn into him, he began to turn into me.
At least I’m pretty sure he did. Because that’s when the lights went low.
The F-16N was rated for 9 g’s. You could easily get more, at 800 knots. I did.
At very high g, and especially at high g-onset rates, the blood drains from your head to your lower extremities. Your optic nerves are especially sensitive to blood loss, so your vision progressively narrows until it looks like you’re peering at the world through soda straws – all peripheral vision is lost. And if you keep it up, pretty soon the lights go out, and sometimes when that happens you lose consciousness. When that happens, your limp hands fall from the controls until you regain consciousness. Sometimes you wake up dead.
Your g-suit is specifically designed to combat that tendency, by forcing air into it’s bladders from a weighted (and g-sensitive) valve, the blood is forced back into your upper torso, where by galvanic contortions (not unlike dealing with the worst case of constipation in medical history), you attempt to move it a little higher. And all the while, your average 175-pound pilot feels the apparent weight of 1960 pounds pushing him down in his seat. His ten-pound head will feel like it weighs 110 pounds (and gets kind of hard to move around).
That’s at 11.2 g’s.

I don’t know if I’ve mentioned before that this hurts. A lot. In a really, really good way, normally. You live for pulling g’s, as a fighter pilot.But 11.2 g’s isn’t normal.

Somehow my new adversary and I manage to blunder into a merge without clacking into one another. I ease g for a moment at the merge to check his intentions, and see him going vertical.Which is a good thing, because that means you’ll lose airspeed, even in an F-16. And I don’t want any more airspeed. I want to make the bad thing stop.So I join him in the vertical, still pulling hard for a while, because you don’t lose 800 knots right away. We get into a particularly violent and thankfully, short fight, in which I emerged victorious (hey, it’s my story). Shortly after that, his lead shot me like a coward, in the back, from my six o’clock, and unobserved.But that’s his story. And that’s all I have to say, about that.

Good clean fun, and I’m off to the field with my wingman in tow. On the way back, I’ve got to call maintenance and confess my fault (“forgive me, base, for I have sinned.”)”620 five minutes out, down jet.”"What are you down for?”"Overstress.” Here’s where I might get lucky. Maybe they don’t ask me how bad the overstress was – I’d only ever heard of one overstress worse than that. Maybe all the ready-room cowboys lining the wall around the SDO desk won’t get to hear what a plumber Lex is.
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Unread post19 Feb 2014, 22:34

What a great story from LEX - Vale. BZ Sir. :mrgreen:
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Unread post20 Feb 2014, 00:16

The F-16 g limiter is not perfect and it can be defeated by a small amount, maybe .6 to .8 g. There is no way it would let you go to 11.2g in a turn. However there are two factors which may have led him to believe he did. First, his g meter is in the HUD and is driven by an accelerometer in the HUD electronics. The flight control accelerometer is about 5 feet behind the pilot, so those two units may give different values. Second, if he was rolling at high g, the roll rate and acceleration may affect either accelerometer and result in false readings. Pitch acceleration can also make false g reading.

So he may well have seen 11.2g but he likely did not really get there.
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Unread post20 Feb 2014, 00:42

Salute!

John-boy points out what we saw in the early days on FCF's.

The maximum displayed gee would vary from 8.7 or so to 9.2 or so when doing the "bat turn". The HUD display retained the max gee for the mission and another display for current gee. Then there were the recorders we had that no other jet had at the time. So you couldn't fool the accident board or anyone else. One of them was in the ejection seat and the solid state memory had lottsa stuff on it.

I never saw anything above 9 gees on my tapes, and I pulled very hard on one particular mission in a break turn. So onset rate might account for an excursion above 9 gees if you are going the speed of stink.

Gums recalls....
Gums
Viper pilot '79
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lamoey

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Unread post20 Feb 2014, 04:50

Gums wrote:John-boy points out what we saw in the early days on FCF's.

The maximum displayed gee would vary from 8.7 or so to 9.2 or so when doing the "bat turn". The HUD display retained the max gee for the mission and another display for current gee. Then there were the recorders we had that no other jet had at the time. So you couldn't fool the accident board or anyone else. One of them was in the ejection seat and the solid state memory had lottsa stuff on it.

I never saw anything above 9 gees on my tapes, and I pulled very hard on one particular mission in a break turn. So onset rate might account for an excursion above 9 gees if you are going the speed of stink.


I once saw 9.9g on the hud tape after an FWIT mission in Denmark in 85'. When the pilot, Tank-Nilsen, told me about this I must have displayed doubt because he grabbed my arm and pulled me in to the Ops room to show me the HUD tape. Low and behold, while being real close to an Eagle, at 6 o'clock, the G indicated flickered a lot and the max G indicated stopped at 9.9. Who knows if that was as far as the display could go. Needless to say, being the lone Norwegian flight control guy at this NATO FWIT competition, I was not popular when we had to take the Viper apart for a full G-check, to be ready for the next days missions.

I conferred with my superiors in Norway and the available documentation. I found that the system could on rare occasions allow up to 9.5G, and full G check starts at 9.8G. There were no error lights or messages of any kind, so to make the squadron and the pilot happy I changed the main FLCS computer. However, it all happened again the following day, so my standing in the bar fell even lower. I started to search for where the G indication in the HUD came from and found it was not from the flight control system, but a separate accelerometer in front of the cockpit, handled by the radar guys that was responsible for the HUD. I asked them the change their accelerometer and the problem was eliminated. I don't remember how much G was pulled, but it was cool to see 9.9G and the two Eagle burners up close on the HUD tape.
Former Flight Control Technican - We keep'em flying
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Unread post20 Feb 2014, 20:11

Great discussion - thanks guys
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Unread post21 Feb 2014, 15:41

spazsinbad wrote:OK now you say what if a merge is inevitable. I say 'get it out of your head'. The F-35 ain't gonna merge. OK? :D


Are you saying they will abort.
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Unread post21 Feb 2014, 19:30

'rkap' I'm not sure if you read all the posts on the forum or only visit irregularly not reading threads. Whatever. However in simple terms I'll restate what is said over and over and not just by me. The F-35s will be in groups of four, co-operating together to dictate terms of any BVR engagement to do their work as required. No need to merge - ever. Go figure.
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Unread post22 Feb 2014, 23:44

spazsinbad wrote:'rkap' I'm not sure if you read all the posts on the forum or only visit irregularly not reading threads. Whatever. However in simple terms I'll restate what is said over and over and not just by me. The F-35s will be in groups of four, co-operating together to dictate terms of any BVR engagement to do their work as required. No need to merge - ever. Go figure.



The problem a lot of people have about the "never merge" statement is, it has yet to happen.

Not only that but it is a statement that has been repeated over and over again since the advent of BVR air-air missiles.

Who knows, maybe this time around it will finally become a reality.

But until then "Never say never" (not a fan of Justin Beiber just so we're clear)

Here's a thought though, the fact that even Raptor pilots hone their skills continiously practicing on the Merge speaks volumes on what the possible scenarios are. Unless we're sugesting that they simply like to waste gas.

The insistance on placing a gun on even the most sophisticated 5th gen fighters underscores the need for a weapon within the R-min range.

So, unless we can convince the USAF/USN/USMC to stop wasting gas on 1v1, gun fighting and merge fights,

since hey, the F-35 will never need it anyway, I think it would be safe to assume that they still consider it a possibility and it would be best for us to respect their assesment instead of trying to make up our own.

The enemy always has a vote in the battlefeild, and it will not always pan out entierly the way you planned.
Right now the Enemy will do everything they can to force a megre, because that is the only way they can atleast have a chance against F-22/35s.

We often think of Migs and Sukhois as low tech airshow planes but they're not, with their arsenal of modern sensors, avionics, data linking, proper GCI support and competent pilots, sure, they may be successful in forcing the Merge at times.

But again they will only give the F-35s more ways of killing them once they do get into the merge.
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Unread post23 Feb 2014, 00:26

Probably this idea has been restated a few times also. Fighter pilots train for all situations - even unlikely scenarios. ACM is an excellent way to get to know your aircraft. DACT is an excellent way to get to know your aircraft against dissimilar aircraft. And on and on. However the plan is as I described. Then there are fallback plans, then there is.... I'm reminded also of RED FLAG scenarios where adversaries against the F-22 became fed up with being taken out of the game without ever seeing the F-22s. And so it goes. Then there is the RAAF exchange pilot in an F-15 complaining about not being able to lock up on an F-22 in DACT (because I guess the rules of the DACT allowed this to occur). The frustration with the F-22 when you are against it must be incredible. Sure we will wait for the F-35. And we will hear about the ACM/DACT & Red Flags and whatnots.
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Unread post23 Feb 2014, 01:00

Thats right, I agree that going into a merge against an F-22\35 is highly Improbable ,

Infact the only likely way for you to get close to the F22/35 is if they choose to, perhaps because they ran out of AMRAAMs or because of ROEs or what not.

But remember, the F-22/35 is not getting any stelthier, Detection technology and computer filtering however are progressing like crazy these days,

So again, preparing for the "unlikely scenario" may be the smart thing to do
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