Fight's On! The origins of TOPGUN and dogfights back in the day/future prospects

[sfdistance]

So is there anyone out there who actually knows why newer Navy fighters are limited to 7.5 vice 9? So far people are guessing physiological reasons. Are the AF jet seats really built that differently, or does it just have to do with service life of the jets? What explains the difference between the versions of the F-35 in load limit?

 

[HeyJoe]

So does peanut butter, just make sure it's the creamy kind, not chunky.

Your choice, but banana is a little easier logistically and more popular for breakfast and raw peanut butter.

The old man tells me that the seat in the F-16 was put in that position because that was the only way it would freaking fit. (Same with why the canopy is backwards)

Sketch a stick man and seat at 15°, 20° and 30°. If you have a protractor, draw an arc over top of heads as you go from 15° to 30°. The difference in height is not much and hardly enough to warrant a design change. I was in the Analyst business back then and never heard anything like that. Sounds like an urban legend.

The added G Tolerance from that position was really an added bonus but didn't have anything to do with the design of the airplane. He could be feeding me a line of bull, but it makes enough sense.

Quite the opposite. Since the F-16 was designed to sustain 9Gs (Israelis have a mod to go higher than that), there was concern and an effort to do everything possible to assist the pilot to handle that type of G. I don't think he's feeding you bull. Why would he? I think it's it's an urban legend. Just Google "F-16 + ejection tilt angle design" or similar words and you'll find lots of hits on the G tolerance and even studies related to it.

 

[HeyJoe]

So is there anyone out there who actually knows why newer Navy fighters are limited to 7.5 vice 9? So far people are guessing physiological reasons. Are the AF jet seats really built that differently, or does it just have to do with service life of the jets?

Not built differently for G capability and actually, the advent of the Martin-Baker ACES (Navy version was called NACES) seats meant they were virtually identical. Tomcat was delivered with a G capability similar to Air Force jets. Aircraft can actually pull quite a bit more, but it does impact the fatigue life and require mx inspections. In case of Tomcat, NAVAIR determined that 6.5G was more conducive to service life and a NATOPS change was made.

 

[Van]

Some Rhino/Hornet driver will correct me if I'm wrong, but I'm pretty sure both aircraft "can" pull +9G's if they toggle the G-limit override which, as the name suggests, overrides the flight computer to give them a 33% increase in G loading (up to +10G's). However, doing so will pop a bit code, and require overstress inspections along with a valid reason why you did it (i.e. SAM avoidance). Of course, that doesn't mean the aircraft was "designed" to pull +9G's, but it is definitely "possible".

 

[HeyJoe]

Some Rhino/Hornet driver will correct me if I'm wrong, but I'm pretty sure both aircraft "can" pull +9G's if they toggle the G-limit override which, as the name suggests, overrides the flight computer to give them a 33% increase in G loading (up to +10G's). However, doing so will pop a bit code, and require overstress inspections along with a valid reason why you did it (i.e. SAM avoidance). Of course, that doesn't mean the aircraft was "designed" to pull +9G's, but it is definitely "possible".

They were designed to withstand much more. Many aircraft components, especially in rotary wing aircraft, are designed to withstand 20Gs so they don't come apart in a crash and injure occupants.

 

[sfdistance]

Not built differently for G capability and actually, the advent of the Martin-Baker ACES (Navy version was called NACES) seats meant they were virtually identical. Tomcat was delivered with a G capability similar to Air Force jets. Aircraft can actually pull quite a bit more, but it does impact the fatigue life and require mx inspections. In case of Tomcat, NAVAIR determined that 6.5G was more conducive to service life and a NATOPS change was made.

So the AF is just more willing to pay for the added maintenance and inspection costs and accept the likelihood of shorter service life due to pulling more G's in the jets?

 

[jarhead]

There are plenty of 9G fighters out there whose ejection seat isn't laid back like the Fighting Falcon, including the F/A-18. As mentioned, the Hornet has a G override giving it 33% more G (up to ~10G's). The G limits are based on increasing structural/fatigue life... there are also performance issues that go into that decision as to why the Hornet doesn't need >7.5 G's unless in an "emergency".

SF

 

[Alpha_Echo_606]

They were designed to withstand much more. Many aircraft components, especially in rotary wing aircraft, are designed to withstand 20Gs so they don't come apart in a crash and injure occupants.

The Mods we install are designed to withstand a minimum 20G crash. Stress has a field day always wanting more material and design is always looking to cut weight.

 

[C420sailor]

If youre in halfway decent shape and are getting significant light loss at 4 G's then your AGSM is probably lacking. Technique can be improved, and if you get jets the centrifuge helps a lot to learn how to do it right.

I guess I worded it wrong. Those numbers are sans AGSM. I was just curious if the Germans who conducted that study used a straining maneuver to obtain those results, or if my "resting" tolerance just sucks. With a half decent squeeze I can keep the lights on without a problem...

...but why explain away a perfectly good reason to eat red meat and drink dark beer? "It's for professional development, I swear."

 

[Treetop Flyer]

I guess I worded it wrong. Those numbers are sans AGSM. I was just curious if the Germans who conducted that study used a straining maneuver to obtain those results, or if my "resting" tolerance just sucks. With a half decent squeeze I can keep the lights on without a problem...

...but why explain away a perfectly good reason to eat red meat and drink dark beer? "It's for professional development, I swear."

Eat, drink and be merry!

 

[ryan1234]

I've pulled 7 G's in my Yak 52 sitting pretty much straight up and about 8.5 G's leaned back in an Su-29. I'm told the Su-29 seats lean back about 30 degrees and it was a lot easier to take the G's in that position than sitting straight up. I know the Yak 52 and Su-29 can't maintain the G's like a military fighter, but short duration being tilted back did make a difference on how it felt.

So the CJ's engine had a little 'sag' to it... just replaced the mounts. A least the metallurgy on your's is a bit better!

How'd you figure out the absolute load limit for the Yak?

 

[HeyJoe]

So the AF is just more willing to pay for the added maintenance and inspection costs and accept the likelihood of shorter service life due to pulling more G's in the jets?

Technically, having to inspect the jet after an overstress event (set limits for symmetrical or rolling G) doesn't cost the unit or service anything other than the manhours it takes to open the panels and take a look to see if any damage is apparent. Mx gets pissed off because they don't want a downed jet on the line (unless it was necessary for SAM avoidance or real world situation vice training). Some COs used to require offending aircrew help open/pull the panels. The larger cost that gets the beancounters concerned is expenditure of FLE. There was great concern in Hornet community as continual deployments burned up FLE in Marine Hornets (especially D models that were tapped for FAC (A) roles as far back as Kosovo and a parallel issue with Navy A/C Hornets (and deployed Marine A/C models) that were racking up trap/cat events, which were tracked separately and also had a limit. Then the Center Barrel issue reared its ugly head on top of having so many different Lot configurations. So it isn't a simple G limit issue at all. That said, we haven't had any fuselages break in two like the Air Force F-15s have (Navy tends to be more conservative overall even down to how we handle stop drilling cracks). Air Force has subsequently downed a lot of their F-15s as a result. Like they say on Fox...you decide...

 

[Flash]

So the AF is just more willing to pay for the added maintenance and inspection costs and accept the likelihood of shorter service life due to pulling more G's in the jets?

A very big thing to keep in mind when talking about different G limits with USAF and Navy fighters, F-15's and F-16's don't land on and take off from the boat. That adds a lot of stress to the aircraft that the USAF doesn't have to account for.

 

[sfdistance]

Technically, having to inspect the jet after an overstress event (set limits for symmetrical or rolling G) doesn't cost the unit or service anything other than the manhours it takes to open the panels and take a look to see if any damage is apparent. Mx gets pissed off because they don't want a downed jet on the line (unless it was necessary for SAM avoidance or real world situation vice training). Some COs used to require offending aircrew help open/pull the panels. The larger cost that gets the beancounters concerned is expenditure of FLE. There was great concern in Hornet community as continual deployments burned up FLE in Marine Hornets (especially D models that were tapped for FAC (A) roles as far back as Kosovo and a parallel issue with Navy A/C Hornets (and deployed Marine A/C models) that were racking up trap/cat events, which were tracked separately and also had a limit. Then the Center Barrel issue reared its ugly head on top of having so many different Lot configurations. So it isn't a simple G limit issue at all. That said, we haven't had any fuselages break in two like the Air Force F-15s have (Navy tends to be more conservative overall even down to how we handle stop drilling cracks). Air Force has subsequently downed a lot of their F-15s as a result. Like they say on Fox...you decide...

What is FLE? Guessing fatigue life expectancy?
So am I correct in assuming that published symmetric and asymmetric G-limits are decided upon based on a balance of getting a long life out of the jet while at the same time allowing pilots to regularly have experience with as much of the safe operating envelope as possible? I was the engineering type in college so this stuff interests me a lot. Thanks for all the responses from those in the know.
Also, thats a great point about the broken F-15 fuselages. I've also read about a pilot who cracked the spine of his F-16 in a 9G turn at an airshow.

 

[Jim123]

What is FLE? Guessing fatigue life expectancy?
So am I correct in assuming that published symmetric and asymmetric G-limits are decided upon based on a balance of getting a long life out of the jet while at the same time allowing pilots to regularly have experience with as much of the safe operating envelope as possible? I was the engineering type in college so this stuff interests me a lot.

You pretty much described it. Your friends doing T-34 primary get to live with this every day (we were allowed 4.5G when I went through, nowadays if I'm not mistaken some of the T-34s* are limited to much less)... which brings up the next point, that no matter what fleet aircraft you select, if you routinely max out the limits that eventually adds up later on. Not to say you should always fly like a wuss to eke out every last bit of service life- think of naval aircraft like family hand-me-down cars in rather than rental cars.


( * Never mind the ex-military T-34Bs... whole 'nother story )