J-20 5th Generation Fighter VII

So... anything else Yankee and Shilao discussed about in that limited-access podcast on the WS-15-equipped J-20A? I believe there should be more intriguing new information... even if there are non-J-20-related information...

latenlazy said:

Still trying to square how 110 kN military thrust at a bypass ratio of 0.25 translates to a wet thrust of 180 kN.

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Am I thinking in the opposite direction than you?

The only reason of higher BPR is to use the fan to increase thrust (dry thrust), but once afterburner is lightened, the aircraft is in supersonic regime, the fan and higher BPR becomes useless in contributing to threst (wet thrust). Therefor I think higher BPR gives higher dry thrust for the same wet thrust, meaning the diff is lower. So for the same dry thrust of 110kN, BPR 0.25 should have a higher wet thrust than BPR 0.3.

taxiya said:

Am I thinking in the opposite direction than you?

The only reason of higher BPR is to use the fan to increase thrust (dry thrust), but once afterburner is lightened, the aircraft is in supersonic regime, the fan and higher BPR becomes useless in contributing to threst (wet thrust). Therefor I think higher BPR gives higher dry thrust for the same wet thrust, meaning the diff is lower. So for the same dry thrust of 110kN, BPR 0.25 should have a higher wet thrust than BPR 0.3.

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No because at a higher BPR you have a lot more air that hasn’t been combusted being dumped into the AB. Higher BPR gets you a lot more specific thrust because it’s a more efficient use of the thermal cycle, which means both higher dry thrust and wet thrust. The issue is that your non AB thrust curves drop faster at higher speeds because of greater fan drag and lower thrust impulse.

latenlazy said:

No because at a higher BPR you have a lot more air that hasn’t been combusted being dumped into the AB. Higher BPR gets you a lot more specific thrust because it’s a more efficient use of the thermal cycle, which means both higher dry thrust and wet thrust. The issue is that your non AB thrust curves drop faster at higher speeds because of greater fan drag and lower thrust impulse.

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yes I am aware of that advantage that bigger bypass duct can bring in more oxygen into the AB, but that is only before mach 1. Once above mach 1, the fan stopped accelerating air, but acts like an air brake because the fan just like a propeller can not move air faster than speed of sound, so a bigger fan doesn't bring in more oxygen into AB for thrust generation any more. Higher BPR is more efficient in thermal cycle but only when the fan works. That is why turbojet is always more suitable for supersonic flight, both in terms of thrust and efficiency.

taxiya said:

yes I am aware of that advantage that bigger bypass duct can bring in more oxygen into the AB, but that is only before mach 1. Once above mach 1, the fan stopped accelerating air, but acts like an air brake because the fan just like a propeller can not move air faster than speed of sound, so a bigger fan doesn't bring in more oxygen into AB for thrust generation any more. Higher BPR is more efficient in thermal cycle but only when the fan works. That is why turbojet is always more suitable for supersonic flight, both in terms of thrust and efficiency.

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Well sure, but presumably the reported thrust figures are static thrust figures, so that still doesn’t answer the question of why 110 kN of dry thrust at a bpr of 0.25 is yielding a wet thrust of 180 kN. The reported dry thrust is slightly lower than the F119’s, the reported BPR is also lower, but the wet thrust is higher. Even if we *assume* (and I think this is a huge stretch) that the 180 kN is wet thrust at supersonic speeds, that only makes the dry thrust to wet thrust discrepancy even more glaring, because without fan contribution to thrust the overall thrust gain from AB should go down. I think there are ways to explain these numbers but without further elaboration they don’t seem to line up with how these parameters usually work in relation to one another.

Gloire_bb said:

Erm, this is a very bad example, because the lack of EF-111 replacement (now rushed in EW form of F-15EX) is currently seen as a core deficit of USAF structure, and EA-6 was directly replaced by F-18G(also with complaints that it isn't enough for deck use, since there is no guarantee larger USAF EW assets will be there to back it up).
And that's USAF with its large existing F-35 fleet, and USN with both. They still complain that chosen solution was at least a partial downgrade(navy) or a complete capability gap(USAF).

F-35 is an unlucky comparison here - as it is capable of only more or less automatic electronic attacks attacking ahead, in one band.
In this case, it isn't even a straightforward improvement over discrete systems of the previous generation - yes, the jammer itself is more capable and advanced, but again - only ahead, only one band, and pilot(who's effectively attacking) won't have much attention - or, likely, skill and education - to spare.

Frankly speaking, the fact that 2010s(oh that dangerous topic) fighters can do electronic attacks with their main array should be more viewed in the general picture(vastly improved EW order of battle, and expectation to significantly suppress all fire control systems under our attack...assuming they won't reply in kind), rather than replacement or even substitution to 360 deg systems with dedicated operators with special education and skills.

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EF-111 and EA6B are both absolutely relevant as they are excellent examples of past dedicated EW aircraft whose capabilities can now be done with less aircrew in the cockpit, as a result of advancements in technology and automation.

In context of the original discussion for how "EW certainly requires more than one crew" the best way to view the trend of EW capabilities being distributed to more tactical aircraft is that more aircraft have EW capabilities and can take on the EW role than the past.

I personally think that the current J-20, as it is, is absolutely disastrous as a dedicated EW platform. It won't escort anything, it won't be able to degrade opponents' SA picture, comms, anything.
Its twin development can be made to carry pods from the J-16(their more independent and automated evolution) - but it still will be bad, simply because there are just 4 parallel(mutually interfering) underwing suspension points to play...which are also needed for oversized munitions and fuel tanks. Yes, flanker platform is bright as F on a radar screen, but for a plane that is supposed to be a blinding-bright sun on as many screens as possible, it just works.

However, J-20 (as, again, expected of the plane of its generation) is probably an absolute troll at mixing kinetic and centimeter- electronic attacks when it turns hot to engage. And in this form, it's a very brutal development for A2A(expected), but also SEAD/DEAD.

p.s. but the main point for me personally is still the professional operator(1) with time(2) and dedicated hardware(3). In this order.
I.e. among current fighter planes, there is one sorta- EW battlestar - that's Su-57 again. But because of (1) and (2) it's still ultimately a fighter, regardless of hardware - and the commander using it instead of a proper EW will suffer.
Much like eurocanards with their fancy suites - survivable, but even escort jamming is realistically beyond them.

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I disagree, I think the single seat J-20 can absolutely function well as a dedicated EW aircraft, second only to the J-16D and that's only because J-16D has dedicated EW pods. But in terms of the in built ESM capabilities of each aircraft and the EW capabilities of their primary radar, I would be surprised if J-20 was inferior.
J-20 even has some tactical advantages due to being stealthy and better able to maintain higher speeds than J-16D which are absolutely consequential to the tactical dedicated EW role.


Going back to the original point, which is my contesting of the "EW certainly requires more than one crew" statement (which I note for some reason you chose not to quote in your reply despite it making up about half of my word count in my last reply), my overall point is
1: for the dedicated EW mission today, you can absolutely do that with only one crew member due to advances in technology and automation, especially in 5th generation aircraft. The proliferation of capable EW subsystems are a trend where modern fighter aircraft can fulfill the dedicated EW mission if their mission profile was oriented for it, at the expense of the other roles in what is nominally a multirole fighter aircraft.
2: however, if your aircraft has more than one crew member, it will perform significantly better in the dedicated EW mission than if the same aircraft had only one crew member.

The above applies to J-20 single seater variants and the twin seater variant if the PLA should go for the latter.

taxiya said:

Am I thinking in the opposite direction than you?

The only reason of higher BPR is to use the fan to increase thrust (dry thrust), but once afterburner is lightened, the aircraft is in supersonic regime, the fan and higher BPR becomes useless in contributing to threst (wet thrust). Therefor I think higher BPR gives higher dry thrust for the same wet thrust, meaning the diff is lower. So for the same dry thrust of 110kN, BPR 0.25 should have a higher wet thrust than BPR 0.3.

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Thrust increases linearly with exhaust speed but flow energy increases quadratically. Therefore it is better to accelerate more air to slower speeds, as long as target aircraft speed doesn't get too close to the exhaust speed. In jet engines, this is done by sapping energy from a high-energy flow using a turbine and feeding that energy to more air by a larger fan. The turbine is not 100% efficient, neither so the fan. Therefore some energy is lost but efficiency gained more than makes up for that. Therefore in a higher BPR afterburning turbofan, the afterburner gets cooler slower and less burnt air. Higher BPR benefits the afterburner too

BoraTas said:

Thrust increases linearly with exhaust speed but flow energy increases quadratically. Therefore it is better to accelerate more air to slower speeds, as long as target aircraft speed doesn't get too close to the exhaust speed. In jet engines, this is done by sapping energy from a high-energy flow using a turbine and feeding that energy to more air by a larger fan. The turbine is not 100% efficient, neither so the fan. Therefore some energy is lost but efficiency gained more than makes up for that. Therefore in a higher BPR afterburning turbofan, the afterburner gets cooler slower and less burnt air. Higher BPR benefits the afterburner too

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That is only true below speed of sound where fan can accelerate air in front of it to a higher speed behind it. After the sound barrier, fan doesn't work.

taxiya said:

That is only true below speed of sound where fan can accelerate air in front of it to a higher speed behind it. After the sound barrier, fan doesn't work.

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Yeah but again, we are not talking about thrust at the speed of sound here. The parameter discrepancies we're talking about look even more pronounced even if we allow for that analytical condition to be what these figures represent.

latenlazy said:

Well sure, but presumably the reported thrust figures are static thrust figures, so that still doesn’t answer the question of why 110 kN of dry thrust at a bpr of 0.25 is yielding a wet thrust of 180 kN. The reported dry thrust is slightly lower than the F119’s, the reported BPR is also lower, but the wet thrust is higher. Even if we *assume* (and I think this is a huge stretch) that the 180 kN is wet thrust at supersonic speeds, that only makes the dry thrust to wet thrust discrepancy even more glaring, because without fan contribution to thrust the overall thrust gain from AB should go down. I think there are ways to explain these numbers but without further elaboration they don’t seem to line up with how these parameters usually work in relation to one another.

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I think the problem isn't really lack (or confusing) of information of WS-15 but rather lack of information of F-119. The discrepency should be that F-119's wet thrust is "too" low at around 156kN compared to WS-15's 185kN (or 180?) with almost equal dry thrust. However, 156kN o F-119 is likely the thrust under super-sonic regime. I have seen 168kN of F-119 quoted by Lin Zuoming in 2000. That is a big difference between 156 adn 168. It could be that 156 is the thrust attainable in supersonic regime, while 168kN is the static thrust on the ground from P&W.

Here is the paper ", see the right most column. It is 113 vs 168. 113 is very close to 116 in wikipedia. It is reasonable since intermediat thrust is less affected by incoming airspeed. So WS-15 gained some 10% wet thrust (185 vs 168) by lower BPR (83%) and higher in-let temperature (>4%, based on early paper >2000K, could be higher according to recent rumor). That is very reasonable IMO.
[edit] also considering F-119's 2D nozzle has a higher penalty, swithing to a round nozzle, the wet static thrust could go over 170kN, the discrepency is even smaller.