Aerodynamics thread

[Brumby]

Some basics, from what I’ve gathered over the years, about dogfighting that I think are probably necessary to keep in mind if we ever hope to have constructive conversations about fighter designs.

STR is most important for defensive maneuvers and gun-fighting. The defensive aspect comes from needing to make tight sustained turns outside the maneuver envelope of an incoming missile. The missile may have much higher maneuverability but a combination of the missile’s need to close a distance to hit its target and its much more limited burn time means there are potential windows of escape, depending on the conditions the missile was launched in relative position of each fighter. The tighter and faster your sustained turn the better your chances of exploiting that window of escape. STR matters for gun fighting because it’s not enough to get a position in a gun fight. That position must be held long enough to ensure a kill.

Good energy management and recovery, which feeds into STR but includes many more attributes, is similarly important for preserving defensive maneuvers and for prolonged engagements. If an engagement goes beyond an initial exchange at the merge the fighter that has, and is able to preserve, the most energy has a maneuver advantage. Similarly, if you are trying to escape a locked missile your odds are better, and your maneuver advantage can be better maintained, if you have higher initial speed, better acceleration, or faster climb.

ITR and nose pointing is mainly needed for getting into a kill position in a missile fight. The trade-off is that these kinds of maneuvers can often bleed energy really quickly. This is where good energy recovery can trump good energy preservation, as recovering energy can allow a fighter to expend its energy in an expensive maneuver and then try again if it has failed, or needs to attack multiple adversaries.

Energy advantages are mainly acquired through a combination of speed and altitude. They’re essentially about maximizing the potential energy of your kinematics. Energy preservation is attained by minimizing drag during maneuvers, and in a relative sense from either starting at a higher initial speed or higher altitude than your adversary. Energy recovering is mainly attained through climbing and acceleration. However, for a fighter it’s not enough to be able to preserve and recover energy. Attaining higher PE is mostly useless if you aren’t able to also maneuver well in those higher energy states. This is why a Mig-28, despite having a raw energy advantage, is practically useless against the F-15 past the initial point of intercept. It’s also why transsonic and supersonic maneuverability, as well as high altitude maneuverability, are advantages that have received so much emphasis with newer fighter designs.

There is no such thing as a fighter that excels at all of the above relative to other fighters. All designs make compromises and trade-offs on some of these parameters in order to excel at others. The rest is left to tactics, sensors, and the capability of the kill vehicle. That’s why it’s really dumb and simplistic to try to assert, in broadbased generic terms, the superiority of one fighter design over another. At best what we can say is that fighters that can maintain and recover greater kinematic energy should have advantages over fighters that can’t, but even that isn’t always so cut and dry in practice. The specific flight envelope fighters find themselves in at a point of encounter can drastically alter the balance of advantages and disadvantages each design might have.

Thanks for outlining an excellent framework that is meaningful within the context of maneuvering in a dogfight as oppose to maneuverability in an air show Based on what I know, survivability in a dogfight is dependent on energy maneuvers and management. Like you I want to enter into a constructive and objective discussion on the subject. Unfortunately statements like being more or less maneuverable is somewhat arbitrary in language especially when we are attempting to benchmark across different platforms and to understand their relative performance. There are different situations and different starting points to consider. It is for these reasons I have advocated the metrics ITR and more importantly STR because even though it is not fully representative it is a good and objective representation of energy maneuver performance - one that we can objectively benchmark across platforms. ..

Also worth noting here that as the above pertains to the J-20 interceptor thesis, if the J-20 is indeed meant to perform an interceptor role with high speed at the merge, *but* also has good (perhaps even excellent or "unparalleled") supersonic maneuverability, then that effectively means the J-20 would be used in combat scenarios where it not only is supposed to start with an energy advantage *but* be able to convert that energy advantage into a maneuver advantage, *which* would effectively mean that it is not designed to be the same kind of traditional "interceptors" we tend to think of like the Mig-28 or Mig-31. In fact, this sort of engagement profile would line up quite cleanly with testimonies we've heard about how the F-22 has been utilized in dogfighting exercises, and that in turn would be suggestive against the notion that the J-20's design is geared towards the kind of "pure" interceptor role that it's often been assigned.

I think you summarised well my thoughts. If the J-20 is designed with the view of air superiority and not interception than the output in performance metrics should reflect an outcome that is closer to where other platforms are that has similar role of air superiority. In other words, let the facts speak for itself.

Here Mr. Brumby, I'm going to agree with Blitzo, Dr. Song's excellent design paper, citing the F-22 as the platform he was aiming at when designing the J-20, (read Siege's excellent translation of Dr. Song's paper).... the J-20 went with distant coupled canards to increase "pitch rate" as OVT was likely to be unavailable, and the ventral fins to assist the J-20 with post stall maneuverability and recovery...

J-20 Designer Yang Wei, Dr. Song's protégé, went with all of those elements to aerodynamically allow the J-20 to achieve "super maneuverability" in the absence of OVT, and the end product is the beautiful J-20.....

I could cite the "roll-over breakout" at Zhuhai on the last day of the show as visual proof, of the J-20's excellent roll rate and "departure resistance".. seeing this we could probably agree that Dr. Song was able to see his vision largely achieved...

Frankly I am agnostic on the issue. I am merely positing the view that if a certain position is advocated then we should be seeing the evidence. I am simply asking did the design paper point to such a position and secondly does the performance metrics support such a position. Sometimes outcome may not necessarily live up to intentions due to various reasons.

For example, it is said that Dr. Song was aiming at the F-22. It is natural because when you are top dog everybody else is gunning at you. In STR, the F-22 is able to execute 28 degree/sec and to my understanding that has no equal. I think the F-16 can only manage around 20 degree/sec STR according to this chart.

Likewise, the F-35 can execute a 28 degree/sec sustained pedal turn. Admittedly it is not equivalent to a conventional STR but the effect is still the same even though that there may be certain qualifiers in flight regime. I am not saying that the J-20 has to meet these numbers but if its performance metrics are closer to this region than further from it, then it better supports the notion that it's maneuverability is that of air superiority rather than that of interceptor.

 

[latenlazy]

Thanks for outlining an excellent framework that is meaningful within the context of maneuvering in a dogfight as oppose to maneuverability in an air show Based on what I know, survivability in a dogfight is dependent on energy maneuvers and management. Like you I want to enter into a constructive and objective discussion on the subject. Unfortunately statements like being more or less maneuverable is somewhat arbitrary in language especially when we are attempting to benchmark across different platforms and to understand their relative performance. There are different situations and different starting points to consider. It is for these reasons I have advocated the metrics ITR and more importantly STR because even though it is not fully representative it is a good and objective representation of energy maneuver performance - one that we can objectively benchmark across platforms. ..

Glad we’re on the same page about how we should be approaching these discussions. I do have some niggle with your emphasis on ITR though. As a matter of EM kinematics STR actually sets the baseline for good EM performance, because it tells you the lowest energy state a fighter can sustain (or rather, the rate of energy depletion during a maneuver), which in turn is suggestive of transient maneuvering performance. While the physics is actually a lot more complicated in general terms, all else held equal a fighter with good STR should have better recovery from an intensive ITR maneuver than one that doesn’t. Either way though, I think neither ITR or STR alone should receive emphasis in gauging how good a design is at air superiority roles. As I mentioned earlier, I think rather than any one attribute, it’s the whole set of kinematic attributes, taken collectively with other parts of the package, and then combined with tactical discretion, that ultimately matters. I think we can mislead ourselves a lot by nitpicking and cherrypicking individual parameters in exclusion of a more holistic analysis.

I think you summarised well my thoughts. If the J-20 is designed with the view of air superiority and not interception than the output in performance metrics should reflect an outcome that is closer to where other platforms are that has similar role of air superiority. In other words, let the facts speak for itself.

My point here though is that *the way* the J-20’s design seems to be meant to conduct interception missions is actually conducive to the performance parameters we’d expect with an air superiority role.

Frankly I am agnostic on the issue. I am merely positing the view that if a certain position is advocated then we should be seeing the evidence. I am simply asking did the design paper point to such a position and secondly does the performance metrics support such a position. Sometimes outcome may not necessarily live up to intentions due to various reasons.

The design paper, if you read it, does in fact stipulate an emphasis on air superiority, *not* interception. You can believe what you want about how well they executed the design but every public commentary we’ve gotten suggests the PLAAF is *very* happy with the J-20’s performance. I believe one of our typical big shrimps (yankeesama) has even mentioned to the effect that within the PLAAF’s fighter fleet only the Su-35 has better subsonic maneuverability, and this is obviously a nod to the Su-35’s TVC, which from what we can tell through the typical sources the J-20 is intended to have when the WS-15 becomes available.

For example, it is said that Dr. Song was aiming at the F-22. It is natural because when you are top dog everybody else is gunning at you. In STR, the F-22 is able to execute 28 degree/sec and to my understanding that has no equal. I think the F-16 can only manage around 20 degree/sec STR according to this chart.
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Likewise, the F-35 can execute a 28 degree/sec sustained pedal turn. Admittedly it is not equivalent to a conventional STR but the effect is still the same even though that there may be certain qualifiers in flight regime. I am not saying that the J-20 has to meet these numbers but if its performance metrics are closer to this region than further from it, then it better supports the notion that it's maneuverability is that of air superiority rather than that of interceptor.

There’s been some debate about whether the F-22 can in fact sustain a 28 degree STR (there were some pretty testy debates about this on keypub. Don’t really have the time these days to search for them but in previous debates about maneuverability I’ve linked to some of them in old comments). We also don’t know what part of the flight envelope that turn was executed in, so it’s hard to take anything meaningful about comparative combat performance from such anecdotes. My thinking, from perusing a lot of those kinds of debates, is that most claims for any fighter outside of 22-24 degrees per second don’t represent true STR, where altitude and speed are maintained during the turn, but a kind of prolonged transient turn rate where the plane is still bleeding speed and/or altitude but trading it for a tighter turn. This is meaningful for aerial combat, especially if you have good acceleration and climb characteristics to recover that energy, but our inability to parse what kind of “STR” at what condition a claim is really referring to can muddle the debate quite a bit when we try to draw comparisons, especially when referring back to EM diagrams that are meant to show a “true” STR figure rather than a “transient” one. Transient EM performance is of course probably the most important performance metric to understand for practical combat situations, but it’s also the hardest thing to pin down, and it’s the sort of information that would likely be treated with some kind of intel discretion. Undoubtedly the F-22’s TVC can greatly help it in executing those sorts of turns just by function of expanding the maneuver envelope outside of what aerodynamic control surfaces can do by themselves, but it’s important to keep in mind that these sorts of maneuvers still have EM penalties beyond a “true” STR and don’t always present as absolute advantages.

WRT the J-20’s performance vis a vis these fundamental principles of EM combat, my thinking is that the J-20 is probably not in fact *airframe limited* from having comparable performance characteristics to the F-22 on net, with better performance in some conditions but worse in others. However, while it is still using interim engines it will face penalties especially in lower energy flight regimes, and with the interim engines in higher energy flight regimes while it might have better EM conservation performance (something hinted at in Song’s design paper) than comparable designs it will have worse EM recovery. This does not cripple it’s ability to perform air superiority roles, but it can condition it’s abilities in those roles through the tactical and maneuver ranges necessary to maximize the airframes capabilities when conducting air superiority missions, and as a result constrain to a degree the scenarios and situations where it can execute air superiority effectively, especially against a peer design. I think this all goes away when the J-20 gets the WS-15 though. This distinction between *current* performance as stipulated by what’s in operation, and *potential* performance as stipulated by the design’s capabilities, is an important one, and it’s something that can get lost in the noise when we have these debates.

 

[latenlazy]

As an addendum to my general assessment of the J-20’s fit for air superiority roles using interim engines, a lot changes if the current J-20 in operation is in fact lighter than what many believe and in line with what some unverified sources have suggested. If the current design in operation does indeed make some other tradeoffs to save weight then the current J-20 in operation may in fact not be limited by its engines, and instead may be taking penalties elsewhere like airframe service cadence, longevity, or payload.

 

[Totoro]

which is a perfectly reasonable idea. at this point in service history, heavy payload isn't needed for these early airframes. neither is airframe lifespan important. especially if some variant produced from 2020s could incorporate performance changes. Soviets had quite a bit of models where the early variant saw few numbers and was retired fairly early. even eurofighter has somewhat similar issue with its tranche 1 planes within RAF (that was for different reasons but still)

 

[Air Force Brat]

As an addendum to my general assessment of the J-20’s fit for air superiority roles using interim engines, a lot changes if the current J-20 in operation is in fact lighter than what many believe and in line with what some unverified sources have suggested. If the current design in operation does indeed make some other tradeoffs to save weight then the current J-20 in operation may in fact not be limited by its engines, and instead may be taking penalties elsewhere like airframe service cadence, longevity, or payload.

If its a 7G airframe such as F-18, F-35B as opposed to a 9G airframe like the F-22, F-35A, then yes you can save a little weight, and it wouldn't surprise me if indeed they went that route??

but, there is no way that 3D printing reduced the actual weight of the J-20 by 25%, and to be honest, as expensive as each 5Gen airframe actually is, there's no way they would aim for a reduced service life.. do you occasionally end up with cracking and issues in places you didn't want to??

ask the Gents who decided to replace the heavy titanium main bulk head in the F-35B, with a lighter aluminum bulkhead in order to bring the weight under the target empty weight?, yep, they did indeed introduce cracking and stress fractures into that component, I'd say its a bad move.

The J-20 has been designed and built as an air superiority fighter, it is currently hindered by a lack of the designed thrust due to the older generation Russian AL-31FN, while that may indeed reduce terminal performance fractionally, the J-20 remains one of the most advanced fighters in the world.
The Chinese pilots are thrilled with it, and why wouldn't they be??

 

[latenlazy]

If its a 7G airframe such as F-18, F-35B as opposed to a 9G airframe like the F-22, F-35A, then yes you can save a little weight, and it wouldn't surprise me if indeed they went that route??

but, there is no way that 3D printing reduced the actual weight of the J-20 by 25%, and to be honest, as expensive as each 5Gen airframe actually is, there's no way they would aim for a reduced service life.. do you occasionally end up with cracking and issues in places you didn't want to??

ask the Gents who decided to replace the heavy titanium main bulk head in the F-35B, with a lighter aluminum bulkhead in order to bring the weight under the target empty weight?, yep, they did indeed introduce cracking and stress fractures into that component, I'd say its a bad move.

The J-20 has been designed and built as an air superiority fighter, it is currently hindered by a lack of the designed thrust due to the older generation Russian AL-31FN, while that may indeed reduce terminal performance fractionally, the J-20 remains one of the most advanced fighters in the world.
The Chinese pilots are thrilled with it, and why wouldn't they be??

Weight reduction may lead to a reduction of structures which are needed to buffer against higher forces, but smaller weight also reduces overall strain on the air frame structures. This is a balancing act, and there’s always a way to reduce weight without impacting performance if you are willing to make a few sacrifices. Smaller payload and shorter airframe life cycles are all reasonable approaches to this problem. An airframe that is meant to withstand up to a certain use-time of high G maneuvers at a certain weight can have that use-time or payload reduced without impacting its ability to conduct such maneuvers.

Your F-35 example is a faulty reference point for whether the J-20 could have saved 25% weight in its titanium bulkheads through 3D printing, because in that example they didn’t just reduce the weight, but *they changed the material*. Anyways. I would leave it to the mechanical engineers to figure out whether they could have found up to 25% of weight savings using 3D printing. I don’t think your or mine inexpert opinions count for much.

 

[Air Force Brat]

Weight reduction may lead to a reduction of structures which are needed to buffer against higher forces, but smaller weight also reduces overall strain on the air frame structures. This is a balancing act, and there’s always a way to reduce weight without impacting performance if you are willing to make a few sacrifices. Smaller payload and shorter airframe life cycles are all reasonable approaches to this problem. An airframe that is meant to withstand up to a certain use-time of high G maneuvers at a certain weight can have that use-time or payload reduced without impacting its ability to conduct such maneuvers.

Your F-35 example is a faulty reference point for whether the J-20 could have saved 25% weight in its titanium bulkheads through 3D printing, because in that example they didn’t just reduce the weight, but *they changed the material*. Anyways. I would leave it to the mechanical engineers to figure out whether they could have found up to 25% of weight savings using 3D printing. I don’t think your or mine inexpert opinions count for much.

No my friend, in by78's post #5423 in the middle photo the J-20 is carrying 4, count em 4 600 gallon fuel tanks on hard points, that's 2400 gallons of external fuel, multiply that by 6lbs per gallon, that's over 14,000 lbs of external fuel, doesn't count the tremendous internal fuel of the J-20....

So no, Yang Wei did not reduce the size or weight of structures and compromise this airframes payload or service life, didn't happen, do you have any idea the load that taxing out for take-off with 4 600 gallon tanks has on the J-20's wing and center section, what about landing gear?? you don't do you, but I do!

here again the J-20 carries 4 large air to air missiles internally in the center weapons bay, and 1 short range air to air missile in each side bay, so no, I don't buy your structurally lightened airframe, and I sure as heck don't buy a 25% overall weight reduction to comparable fighters of other manufacturers..

In fact the high payload, and large fuel load is the main reason I would suspect the J-20 is a 7G airplane, not structural lightening...

and my F-35 reference is spot on, you have 3 different airframes, of a similar size and planform... now if you are talking a 25% reduction in specific components, its possible on some non structural or low load components, possibly even on the external skin, but bulkheads, center fuse, wing and landing gear attach points, its just not gonna happen, it can't.

not with the materials and construction methods currently employed

 

[latenlazy]

No my friend, in by78's post #5423 in the middle photo the J-20 is carrying 4, count em 4 600 gallon fuel tanks on hard points, that's 2400 gallons of external fuel, multiply that by 6lbs per gallon, that's over 14,000 lbs of external fuel, doesn't count the tremendous internal fuel of the J-20....

So no, Yang Wei did not reduce the size or weight of structures and compromise this airframes payload or service life, didn't happen, do you have any idea the load that taxing out for take-off with 4 600 gallon tanks has on the J-20's wing and center section, what about landing gear?? you don't do you, but I do!

here again the J-20 carries 4 large air to air missiles internally in the center weapons bay, and 1 short range air to air missile in each side bay, so no, I don't buy your structurally lightened airframe, and I sure as heck don't buy a 25% overall weight reduction to comparable fighters of other manufacturers..

In fact the high payload, and large fuel load is the main reason I would suspect the J-20 is a 7G airplane, not structural lightening...

and my F-35 reference is spot on, you have 3 different airframes, of a similar size and planform... now if you are talking a 25% reduction in specific components, its possible on some non structural or low load components, possibly even on the external skin, but bulkheads, center fuse, wing and landing gear attach points, its just not gonna happen, it can't.

not with the materials and construction methods currently employed

Is the J-20 meant to hit max G maneuvers with 4 fuel tanks? Very unlikely. I don’t think any fighter is designed to pull max Gs at max load without risking some kind of structural damage. You’re conflating “can carry 14,000 lbs of external fuel” with “can carry 14,000 lbs of external fuel while doing max Gs”. 14,000 lbs of external fuel plus a standard A2A payload and full internal fuel would be roughly 2-3X the empty weight of the plane. A 9G maneuver is equivalent to 9X whatever the weight of the plane is in flight. 2-3X empty weight of the plane is not even close to the strain of a 9G maneuver. That the J-20 can carry 4 external fuel tanks is not strong evidence against the possibility that they lightened the design for interim performance reasons.

Is 4 AIM-120 sized missiles+2 AIM-9 sized missiles a heavy payload? No. No matter how much you characterize the PL-15s as “large” missiles (while totally ignoring that PL-15 and PL-10 aren’t much bigger than comparable missiles from other services) a 6 A2A missile configuration would never be large enough to even come close to the max payload for any modern day fighter today.

You talk with the confidence of someone who actually did the structural engineering for the J-20’s airframe, but I’m going to guess that unless you’e hiding something from us you have no more clue about the specifics of how the J-20’s airframe was put together and what load tolerances it was designed for anymore than the rest of us.

 

[Air Force Brat]

Is the J-20 meant to hit max G maneuvers with 4 fuel tanks? Very unlikely. I don’t think any fighter is designed to pull max Gs at max load without risking some kind of structural damage. You’re conflating “can carry 14,000 lbs of external fuel” with “can carry 14,000 lbs of external fuel while doing max Gs”. 14,000 lbs of external fuel plus a standard A2A payload and full internal fuel would be roughly 2-3X the empty weight of the plane. A 9G maneuver is equivalent to 9X whatever the weight of the plane is in flight. 2-3X empty weight of the plane is not even close to the strain of a 9G maneuver. That the J-20 can carry 4 external fuel tanks is not strong evidence against the possibility that they lightened the design for interim performance reasons.

Is 4 AIM-120 sized missiles+2 AIM-9 sized missiles a heavy payload? No. No matter how much you characterize the PL-15s as “large” missiles (while totally ignoring that PL-15 and PL-10 aren’t much bigger than comparable missiles from other services) a 6 A2A missile configuration would never be large enough to even come close to the max payload for any modern day fighter today.

You talk with the confidence of someone who actually did the structural engineering for the J-20’s airframe, but I’m going to guess that unless you’e hiding something from us you have no more clue about the specifics of how the J-20’s airframe was put together and what load tolerances it was designed for anymore than the rest of us.

No need to put words in my mouth, I'm a pilot, I well understand gross weight, payload, and fuel..... at no point did I suggest the J-20 would enter combat carrying 14,000 lbs of external fuel, so lets not put words in my mouth? but it will be doing combat air patrol, if it is scrambled, it will be going supersonic, and it will be jettisoning those tanks and hard points as it comes into the "combat zone"!

but it will be taxing out for take-off on a bumpy taxiway, and then lining up for taking and accelerating to approx. 140 to 160 knots down the runway, the maximum structural down ward load will be bouncing up and down in that process, once the wings begin to provide lift, that load will shift to the whole wing. No external ordinance, as those 4 large fuel tanks and internal weapons bring the J-20 to the max gross weight.

The aircraft I fly are all licensed in the normal category at gross weight, and in the utility category for stalls, spins, lazy eights and turn's around a point etc....

In fact I operated in the utility category on my flight last week, doing power on stalls and air work...

I've never made any such outlandish claims, but I do know what the hell I'm talking about, I have and continue to work on aircraft out of necessity. In the past I got paid to do so, yes, I do understand aircraft design, prototyping, production, and operation, and maintenance, no I don't care about the math. I do understand why the F-35A is designed to 9G's, the F-35B is designed to 7G's, and the F-35C is designed to 7.5G's, I understand why the structural limits are different on each of those extremely similar airframes.

I merely pointed out that J-20 carrying 4 600 gallon fuel tanks is proof positive that it has been designed as a "heavy fighter", any talk about reduced structure, and reduced service life in order to achieve a level of performance goes out the window when you know and understand the stress that places on an airframe, particularly in ground operations.....

you will also note that on nearly every video of the J-20 preparing to land, we see a massive fuel dump, as aircraft have a designed take off weight, and a max landing weight, which is always less, hence the need to dump fuel.

and lets be more specific, 2400 Gallons US of JP actually weighs around 16,800 lbs!

 

[latenlazy]

No need to put words in my mouth, I'm a pilot, I well understand gross weight, payload, and fuel..... at no point did I suggest the J-20 would enter combat carrying 14,000 lbs of external fuel, so lets not put words in my mouth? but it will be doing combat air patrol, if it is scrambled, it will be going supersonic, and it will be jettisoning those tanks and hard points as it comes into the "combat zone"!

but it will be taxing out for take-off on a bumpy taxiway, and then lining up for taking and accelerating to approx. 140 to 160 knots down the runway, the maximum structural down ward load will be bouncing up and down in that process, once the wings begin to provide lift, that load will shift to the whole wing. No external ordinance, as those 4 large fuel tanks and internal weapons bring the J-20 to the max gross weight.

The aircraft I fly are all licensed in the normal category at gross weight, and in the utility category for stalls, spins, lazy eights and turn's around a point etc....

In fact I operated in the utility category on my flight last week, doing power on stalls and air work...

I've never made any such outlandish claims, but I do know what the hell I'm talking about, I have and continue to work on aircraft out of necessity. In the past I got paid to do so, yes, I do understand aircraft design, prototyping, production, and operation, and maintenance, no I don't care about the math. I do understand why the F-35A is designed to 9G's, the F-35B is designed to 7G's, and the F-35C is designed to 7.5G's, I understand why the structural limits are different on each of those extremely similar airframes.

I merely pointed out that J-20 carrying 4 600 gallon fuel tanks is proof positive that it has been designed as a "heavy fighter", any talk about reduced structure, and reduced service life in order to achieve a level of performance goes out the window when you know and understand the stress that places on an airframe, particularly in ground operations.....

you will also note that on nearly every video of the J-20 preparing to land, we see a massive fuel dump, as aircraft have a designed take off weight, and a max landing weight, which is always less, hence the need to dump fuel.

and lets be more specific, 2400 Gallons US of JP actually weighs around 16,800 lbs!

You’re obfuscating. At the end of the day the point is that a max payload takeoff for any fighter is a small fraction of the total strain the airframe is designed to handle. Just as a matter of physics how much payload a fighter can take off with doesn’t tell us much of anything about where the structural limits of an airframe are.