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

[Corsair1963]

I recall a Desert Storm engagement where the F-15 pilot said he took 12g's.

Amazing, though I dunno if I'd try that all these years later!

Yep older jets with no enforced limits - in the heat of battle the pilots gonna pull whatever required even if they risk black out and airframe write off - so there are many accounts from Israeli Mirage III pilots to Mig pilots etc - well the ones that recovered from blackout.

If the airframe is over G'd past its design limits then the damage will vary - for example engines in the F-4 coming off the mounts - but the longer the G is sustained then the damage will likely be more.

F-16 9G limit should be sustained - in the example of the F-15 pulling 12Gs that was probably under 2 seconds - any more and the pilot blacks out and likely more damage will incur.

The Navy have historically set lower G limits on jets - possibly to preserve the airframe life - so the F-35C limit of 7.5G should be computer enforced - like the FA-18EF also 7.5G below defined GW ( FA-18A had an 8G limit. )

No possibly about it the aforementioned aircraft (Hornet, Super Hornet, and F-35C) are limited to 7.5G's in peace time to extended the service lives of the aircraft. Yet, can exceed those limits at anytime.........

[basher54321]

No possibly about it the aforementioned aircraft (Hornet, Super Hornet, and F-35C) are limited to 7.5G's in peace time to extended the service lives of the aircraft. Yet, can exceed those limits at anytime

Yes the SH has an override - but anything over the threshold +8G is still considered an over G requiring inspection according to the NATOPS. Its designed sustained limit is stated as +7.5G under 42Klbs.

[basher54321]

F-16s can depart too, but the F/A-18A-D is known for having a sudden, hard departure if the pilot makes large inputs at high-AoA. An inexperienced F/A-18 pilot in a sudden departure would be a heartbeat away from joining the Martin-Baker fan club.

The reason would be to point the jet at the bandit. The F/A-18 doesn't need to do a full on departure, but the SH has a pirouette mode that comes in handy in a knife fight.

A known mishap with a F-22 being over-G'd didn't cause LO skin damage, but the USAF didn't want to spend the money on a proper laser inspection needed to check for airframe misalignment so the jet was retired. Subsequent inspection revealed slight permanent twisting of the airframe.

It was an A-37B that I'm pretty sure would have been modified/strengthened as needed. It had been fully structurally refurbished when restored, and phase inspections completed. I was suggesting that the rare times the jet exceeded 6Gs didn't result in major cracks in the airframe. This particular jet gave more than a few pilots their first taste of a high performance jet as kids, including the owners' kids, and they wouldn't risk their lives with anything less than full maintenance on that jet.

Cool thanks for the info

[disconnectedradical]

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?

[Corsair1963]

No possibly about it the aforementioned aircraft (Hornet, Super Hornet, and F-35C) are limited to 7.5G's in peace time to extended the service lives of the aircraft. Yet, can exceed those limits at anytime

Yes the SH has an override - but anything over the threshold +8G is still considered an over G requiring inspection according to the NATOPS. Its designed sustained limit is stated as +7.5G under 42Klbs.

Yes, but the point is it can be overrided by the pilot..........

[neurotech]

No possibly about it the aforementioned aircraft (Hornet, Super Hornet, and F-35C) are limited to 7.5G's in peace time to extended the service lives of the aircraft. Yet, can exceed those limits at anytime

Yes the SH has an override - but anything over the threshold +8G is still considered an over G requiring inspection according to the NATOPS. Its designed sustained limit is stated as +7.5G under 42Klbs.

Yes, but the point is it can be overrided by the pilot..........

Doesn't the F-16 have a FLCS Override too? Even test pilots will have some major explaining to do (& a mishap investigation) if they exceed/override the G-Limits without a darn good reason.

[Raptor_claw]

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.

[Raptor_claw]

Yes the SH has an override - but anything over the threshold +8G is still considered an over G requiring inspection according to the NATOPS. Its designed sustained limit is stated as +7.5G under 42Klbs.

Yes, but the point is it can be overrided by the pilot..........

Doesn't the F-16 have a FLCS Override too? Even test pilots will have some major explaining to do (& a mishap investigation) if they exceed/override the G-Limits without a darn good reason.

No, there's nothing in the F-16.
The F-35C does have the capability (Navy insisted), but it's clearly a "warranty-ending" event if it's ever used. 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. In other words, if the ONLY two choices are complete destruction of the aircraft (and, I'm assuming, the pilot), or just bending/breaking it, then the "extra" is there for a last ditch effort. I would be surprised if any ship that over-g'd like that ever flew again.
Also, it's not something a pilot can "accidently" do - it takes two distinct, deliberate actions to engage, so "I just pulled too hard" wouldn't fly. As far as using it in real no-kidding wartime, I really don't have any insight, but I guess the same "damage instead of total destruction" justification could, at least theoretically, be applied.

[disconnectedradical]

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.

[Gums]

Salute!

First, the only way to override the Viper FLCS is when in a deep stall - AoA over 30 degrees or so. The switch is then acvtive and by holding it you can "rock" the jet outta the deep stall.

Back to the discussion:

So going thru the military.com news I see some folks wanting a longer range Slammer. See:

http://defensetech.org/2014/02/18/test- ... e-aim-120/

Sheesh. I guess that's great for an engagement when there's no possibility of blue-on-blue, but good grief. At 100 miles you just about have to use the datalink unless the tgt is an Airbus or Boeing. Otherwise, I guess you could hose away and let the missiles pick their own targets way out there. Secondly, the thing slows down once the motor quits, so about the only use for an extremely long range would be a face shot.

On this thread we're mostly talking about knife fights or evasive capability. However, I can see the Navy wanting a Phoenix-like capability for fleet defense when the enema is coming at you and there's no problem with blue-on-blue. Additionally, the face shot helps shorten time-of-flight. The Great White Hope (Sparrow) could not catch us if the Eagles fired beyond about 15 miles. We could do the bat turn and run away. Slammer much better, but I can't see launching over 20 or 30 miles away, and surely not entering a furball. Lastly, the point-and-shoot capability of the Slammer is great. Not necessarily pointing at the target, but just launching and not using datalink. Works great, from what I hear.

Gums sends...

[neurotech]

Yes, but the point is it can be overrided by the pilot..........

Doesn't the F-16 have a FLCS Override too? Even test pilots will have some major explaining to do (& a mishap investigation) if they exceed/override the G-Limits without a darn good reason.

No, there's nothing in the F-16.
The F-35C does have the capability (Navy insisted), but it's clearly a "warranty-ending" event if it's ever used. 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. In other words, if the ONLY two choices are complete destruction of the aircraft (and, I'm assuming, the pilot), or just bending/breaking it, then the "extra" is there for a last ditch effort. I would be surprised if any ship that over-g'd like that ever flew again.
Also, it's not something a pilot can "accidently" do - it takes two distinct, deliberate actions to engage, so "I just pulled too hard" wouldn't fly. As far as using it in real no-kidding wartime, I really don't have any insight, but I guess the same "damage instead of total destruction" justification could, at least theoretically, be applied.

I'm not nearly as familiar with the FLCS on the F-16.

F/A-18s have flown past 9.5Gs, inspected and flown again without damage. One of our jets pulled 9.8Gs when an aggressor pilot departed trying to avoid a mid-air. The jet didn't have wing tanks or stores during the mishap. The Navy grounded the jet and the depot found no bending or cracks but still kept the jet in storage. We got the jet delivered in a crate, and after a full structural inspection and standard SLEP, the jet was cleared for chase duties and flew for years.

My understanding is that most damaging over-G mishaps are not caused by pilots "pulling back too hard" but exceeding the rolling G limit at high alpha with stores on the wings. Also, wake turbulence causing a departure from controlled flight has permanently grounded jets before.

[Gums]

Salute!

Better get John Will in here to tell all about rolling gee/rate effects.

We didn't get modified FLCS laws for a few years. We were treating the jet as if it was the A2A loadout, which was unrestricted. Our straight ahead gee was not limted, but AoA limit was reduced, as was roll rate when pulling. The additional control law was as much about departures as it was about stress on the wings.

The F-35 has the benefit of the old dogs at Ft Worth that have not retired ( like John-boy has), plus over 30 years of experience with the Viper. Secondly, the stores for most missions are internal and close to the centerline. That should give the jet better, less-limiting roll versus gee than the Viper or the Superbug.

Gums...

[johnwill]

As I understood, the F-16Ns were retired early because they didn't allocate funds to fully inspect and refurbish the jets. Those jets were flown hard, but with minimal external stores. It would have made economic sense to keep them flying, if budgeted.

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. Some parts of the airplane had an easier time of that (weapon hardpoints, for example), but some parts had a more severe experience of high g events. The N airplanes were delivered with titanium wing attach brackets in place of aluminum brackets on the A/B. The Navy would not pay for a full analysis and durability test of those parts, since they were easily inspected. Bad idea, as the brackets started cracking at a relative young age.

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.

[johnwill]

The essence of this question gets back to the "design g usage spectrum" that johnwill referred to just above. When you design a structure you have to have some estimate as to how it's gonna be used. To really oversimplify: let's say the customer lays out the expected usage (say, based on every 10 flights): max G once , 80% G three times, to 50% six times, and the rest of the time it's just tooling around at "low" G. So, you design the structure based on that usage. If you have that requirement, but you actually design it to go to max G every flight, then you would have over-designed, and the extra weight is hurting something else (performance, most likely). On the flip side, if the customer requirements call out a more modest usage spectrum and then they wind up flying much more aggressively, there's gonna be problems.

Excellent explanation in layman's terms, raptor claw. I would not have been able to do that without getting far too complicated. There's hope for you flight control troops yet.

[johnwill]

Salute!

Better get John Will in here to tell all about rolling gee/rate effects.

We didn't get modified FLCS laws for a few years. We were treating the jet as if it was the A2A loadout, which was unrestricted. Our straight ahead gee was not limted, but AoA limit was reduced, as was roll rate when pulling. The additional control law was as much about departures as it was about stress on the wings.

The F-35 has the benefit of the old dogs at Ft Worth that have not retired ( like John-boy has), plus over 30 years of experience with the Viper. Secondly, the stores for most missions are internal and close to the centerline. That should give the jet better, less-limiting roll versus gee than the Viper or the Superbug.

Gums...

As usual, Gums is right on target. High g rolls are usually more critical to a structure than a straight pullup or level turn. The air to air F-16 requirements were 9g turn and a 5.86g full stick 360 roll with at any internal fuel load, speed,or altitude. Critical structure in the turn is bending moment in the wing root. High g roll critical structure is the entire wing in combined bending and torsion (twist), bending in the horizontal tails, and bending and torsion in the vertical tail and aft fuselage. You can tell from the critical areas that high g rolls are important for almost the entire airplane. Wing torsion comes from the deflected flaperons loading the wing trailing edge. H tail loads are from differential deflection for rolling and symmetric deflection to trim the g. V tail loads are from using the rudder to minimize sideslip in the roll.

The F-15 also encountered problems with high g rolls in service. Without any g or roll limiters, it was not difficult to overload the airplane, usually in a high g roll. Damaged wings resulted in MDD coming up with an overload warning system that gave the pilot a clue when he was applying too much roll command at high g.

The modified FCLS control laws Gums mentioned were needed for maintaining control with heavy external loads while rolling at low airspeeds. Those lower roll rates naturally resulted in lower wing and hardpoint loads.