J-20 5th Gen Fighter Thread VI

[manqiangrexue]

The weight you give for both is their empty weight, more relevant would be combat weight or even MTOW. I suspect J-20 to have a similar if not higher MTOW than F-22.

I used empty weight cus that's what we were discussing but I know jets don't go into battle empty. I assumed they would go into battle with the same stuff on.

MTOW is the upper limit of the design for ability to lift off. The higher the MTOW the better; that means you have the choice to take off with more fuel/ordinance, but it doesn't mean you have to.

Combat weight is the figure that determines the weight when jets meet to down each other at. So if the F-22 has an empty weight of 19.7T and the J-20 is 16T, and if they carry equal missiles and fuel, J-20 is still lighter by the same amount. The only way J-20 would start getting heavier is if it carried more missiles or more fuel. J-20 does not carry more missiles than F-22. J-20 may carry more fuel than F-22 but only if it chooses to do so (as it might if it needs to engage an enemy at a further location, possibly further than F-22 is even capable of) but it will likely burn off that fuel to reach the fight and get its TWR back up.

Were you suggesting that J-20 has higher combat weight than F-22 or just MTOW? Not sure by your writing.

 

[Blitzo]

I used empty weight cus that's what we were discussing but I know jets don't go into battle empty. I assumed they would go into battle with the same stuff on.

MTOW is the upper limit of the design for ability to lift off. The higher the MTOW the better; that means you have the choice to take off with more fuel/ordinance, but it doesn't mean you have to.

Combat weight is the figure that determines the weight when jets meet to down each other at. So if the F-22 has an empty weight of 19.7T and the J-20 is 16T, and if they carry equal missiles and fuel, J-20 is still lighter by the same amount. The only way J-20 would start getting heavier is if it carried more missiles or more fuel. J-20 does not carry more missiles than F-22. J-20 may carry more fuel than F-22 but only if it chooses to do so (as it might if it needs to engage an enemy at a further location, possibly further than F-22 is even capable of) but it will likely burn off that fuel to reach the fight and get its TWR back up.

Were you suggesting that J-20 has higher combat weight than F-22 or just MTOW? Not sure by your writing.

Well, I'd first like to add that I'm not sure about the reliability of J-20's empty weight numbers

Secondly, I do expect J-20 to have a higher MTOW than F-22.

And lastly, in terms of combat weight, I would consider measuring it in terms of both aircraft having the same % of their maximum internal fuel. I believe the J-20 has a higher internal fuel capacity than F-22, meaning in terms of absolute weight, J-20's internal fuel weight would be greater than that of F-22.



In any case, I am skeptical of the idea that a J-20 with non-WS-15 engines can compete with F-22 kinematic performance.

 

[manqiangrexue]

Well, I'd first like to add that I'm not sure about the reliability of J-20's empty weight numbers

Secondly, I do expect J-20 to have a higher MTOW than F-22.

And lastly, in terms of combat weight, I would consider measuring it in terms of both aircraft having the same % of their maximum internal fuel. I believe the J-20 has a higher internal fuel capacity than F-22, meaning in terms of absolute weight, J-20's internal fuel weight would be greater than that of F-22.



In any case, I am skeptical of the idea that a J-20 with non-WS-15 engines can compete with F-22 kinematic performance.

Why would you compare them with similar percentage of internal fuel? The aircraft ranges are completely different. If aircraft A has a range of 2,000km and B has a range of 1,000km, it's unfair to compare their weights both at max fuel. It's much more meaningful to compare what they would weigh if they were both assigned to intercept a target say 600km away in which case aircraft A would need a much lower percentage of its total fuel limit to achieve. Otherwise, you're basically penalizing aircraft A for having the ability to strike farther.

I think that if WS-15 really is a 180kN engine for J-20, it would make J-20 out.of.this.world. A WS-10IPE with 155+kN would already be stunning assuming they could get the dry thrust to a good amount over 100kN to give it really nice super-cruise.

If WS-15 were really a 100kN engine for the J-20, I could think of 3 reasons to mount a pair of those:
1. The dry thrust is extremely high (130+kN) and they would allow J-20 to operate almost exclusively on fuel-saving dry thrust with fantastic performance. Afterburners would only be used for situations like out-running a missile, emergency intercept of far away target, or extremely short take-off.
2. They intend to add flat stealth nozzles for all-aspect stealth, which would shave off a significant percentage of engine performance, leaving unacceptable thrust to all but the most powerful engines.
3. J-20, being voluminous, is highly upgrade-able and adding monstrously powerful engines allows for heavier, much more capable or multi-missioned equipment to be added inside when they are ready, which would balloon the weight compared to today's J-20s.

Of course this is all assuming that J-20 is fantastically light; if it's false and J-20 is some 23T or something, then I see why WS-15 is a must. I agree that we have only 1 report so it's not perfectly reliable but unless we get something more official that dismisses it, I would cautiously accept it. I would sound less cautious, though, when debating with someone who seems to outright dismiss it based on nothing but "gut feeling."

 

[Blitzo]

Why would you compare them with similar percentage of internal fuel? The aircraft ranges are completely different. If aircraft A has a range of 2,000km and B has a range of 1,000km, it's unfair to compare their weights both at max fuel. It's much more meaningful to compare what they would weigh if they were both assigned to intercept a target say 600km away in which case aircraft A would need a much lower percentage of its total fuel limit to achieve. Otherwise, you're basically penalizing aircraft A for having the ability to strike farther.

If an aircraft with a greater internal fuel load is compared with an aircraft with a lower internal fuel load, I think the only fair way to compare them would be if both aircraft met each other with a similar % of internal fuel under their respective combat load outs.

In such a scenario, the thought experiment is how each aircraft would compare with each other in a combat scenario rather than how best each aircraft can go and intercept a given target under the same conditions.

Given this, I would say that J-20's likely higher internal fuel load is a net positive for its performance as having greater endurance and range in the likely theatre of conflict we are thinking of (western pacific, over the ocean). It likely will be less maneuvrable than an F-22 when both are operating with equal % of internal fuel loads, but it will likely have far more tactical flexibility and "freedom to maneuver" by lieu of greater endurance whereas F-22's ability to maneuver will be restricted by reduced endurance.

I think that if WS-15 really is a 180kN engine for J-20, it would make J-20 out.of.this.world. A WS-10IPE with 155+kN would already be stunning assuming they could get the dry thrust to a good amount over 100kN to give it really nice super-cruise.

If WS-15 were really a 100kN engine for the J-20, I could think of 3 reasons to mount a pair of those:
1. The dry thrust is extremely high (130+kN) and they would allow J-20 to operate almost exclusively on fuel-saving dry thrust with fantastic performance. Afterburners would only be used for situations like out-running a missile, emergency intercept of far away target, or extremely short take-off.
2. They intend to add flat stealth nozzles for all-aspect stealth, which would shave off a significant percentage of engine performance, leaving unacceptable thrust to all but the most powerful engines.
3. J-20, being voluminous, is highly upgrade-able and adding monstrously powerful engines allows for heavier, much more capable or multi-missioned equipment to be added inside when they are ready, which would balloon the weight compared to today's J-20s.

Of course this is all assuming that J-20 is fantastically light; if it's false and J-20 is some 23T or something, then I see why WS-15 is a must. I agree that we have only 1 report so it's not perfectly reliable but unless we get something more official that dismisses it, I would cautiously accept it. I would sound less cautious, though, when debating with someone who seems to outright dismiss it based on nothing but "gut feeling."

That's the thing -- I believe the thrust for WS-15 and WS-10IPE are fairly well established and agreed upon, and reasonable to believe... but J-20's empty weight

 

[manqiangrexue]

If an aircraft with a greater internal fuel load is compared with an aircraft with a lower internal fuel load, I think the only fair way to compare them would be if both aircraft met each other with a similar % of internal fuel under their respective combat load outs.

In such a scenario, the thought experiment is how each aircraft would compare with each other in a combat scenario rather than how best each aircraft can go and intercept a given target under the same conditions.

Given this, I would say that J-20's likely higher internal fuel load is a net positive for its performance as having greater endurance and range in the likely theatre of conflict we are thinking of (western pacific, over the ocean). It likely will be less maneuvrable than an F-22 when both are operating with equal % of internal fuel loads, but it will likely have far more tactical flexibility and "freedom to maneuver" by lieu of greater endurance whereas F-22's ability to maneuver will be restricted by reduced endurance.






That's the thing -- I believe the thrust for WS-15 and WS-10IPE are fairly well established and agreed upon, and reasonable to believe... but J-20's empty weight

Thought experiment:
If our weights are correct, then J-20 with 6 missiles (4 x PL-12 + 2 x PL-10 = 4 x 180kg +2 x 90kg = 900kg) plus 8 tonnes fuel is less than 24.9 tonnes. F-22 with 6 missiles (4 x AIM-120 + 2 x AIM-9 = 4 x 152kg + 2 x 85kg = 778kg) plus 8 tonnes fuel is about 28.5 tonnes. 2 x 137kN/24.9 tonnes = 11.00kN/tonne for J-20. 2 x 156kN (assuming no penalty for stealth nozzles)/28.8 tonnes = 10.95kN/tonne for F-22.

Is WS-10IPE well-established?? I was just thinking there's no solid evidence that it exists much less what the thrust is. If you have more info on this, please let me know. Is WS-15 thrust 180kN established? I've heard numbers ranging from 165-197kN thought 180 is the median. If it really is 180kN, it would seem more fitting for a single-engined fighter from my perspective to be honest.

 

[Blitzo]

Thought experiment:
If our weights are correct, then J-20 with 6 missiles (4 x PL-12 + 2 x PL-10 = 4 x 180kg +2 x 90kg = 900kg) plus 8 tonnes fuel is less than 24.9 tonnes. F-22 with 8 missiles (6 x AIM-120 + 2 x AIM-9 = 6 x 152kg + 2 x 85kg = 1082kg) plus 8 tonnes fuel is about 28.8 tonnes. 2 x 137kN/24.9 tonnes = 11.00kN/tonne for J-20. 2 x 156kN (assuming no penalty for stealth nozzles)/28.8 tonnes = 10.83kN/tonne for F-22.

Is WS-10IPE well-established?? I was just thinking there's no solid evidence that it exists much less what the thrust is. If you have more info on this, please let me know. Is WS-15 thrust 180kN established? I've heard numbers ranging from 165-197kN thought 180 is the median. If it really is 180kN, it would seem more fitting for a single-engined fighter from my perspective to be honest.

I think WS-10IPE is established.

WS-15's thrust I think is not as high as 180kN, but rather with the top end being about 170kN. I.e.: a 16-17 ton class engine.



IMO "if our weights are correct" is a very big if in the case of J-20. The notion that J-20's empty weight is merely in the "15 ton class" is one we should all take very skeptically IMO, until one day we receive overwhelming evidence suggesting otherwise.


As for comparing the "combat load" of J-20 and F-22, again, I believe the fuel load for both aircraft should be at an equal % of each aircraft's maximum internal fuel load rather than an equal absolute internal fuel load.

for example, F-22's maximum internal fuel load is given at 8.2 tons online. For the sake of discussion let's say J-20's max internal fuel load is 10 tons.

In that case, it would make sense to calculate each aircraft's internal fuel load in combat conditions as an equal percentage of each aircraft's fuel load.

 

[manqiangrexue]

I think WS-10IPE is established.

WS-15's thrust I think is not as high as 180kN, but rather with the top end being about 170kN. I.e.: a 16-17 ton class engine.



IMO "if our weights are correct" is a very big if in the case of J-20. The notion that J-20's empty weight is merely in the "15 ton class" is one we should all take very skeptically IMO, until one day we receive overwhelming evidence suggesting otherwise.


As for comparing the "combat load" of J-20 and F-22, again, I believe the fuel load for both aircraft should be at an equal % of each aircraft's maximum internal fuel load rather than an equal absolute internal fuel load.

for example, F-22's maximum internal fuel load is given at 8.2 tons online. For the sake of discussion let's say J-20's max internal fuel load is 10 tons.

In that case, it would make sense to calculate each aircraft's internal fuel load in combat conditions as an equal percentage of each aircraft's fuel load.

WS-10IPE is established? I like to hear that. But could you point me to a good source? What's its thrust (dry and AB)?

If WS-15 is 165kN then it would be a great engine for the J-20, not overwhelmingly powerful like 180kN would be.

I realize that the 15 tonne class figure is far from guaranteed, but it's the best figure we have and all my calculations used a 16 tonne figure instead of 15 tonnes to top out the 15 tonne class. So at this point, it's 16 tonnes or nothing. No thought experiment LOL.

Why should their fuel be equal percentages of each other? If F-22 goes 400nm on half fuel and J-20 goes 600nm on half fuel, you are in fact giving weight penalty to J-20 for having the option to go further. If you calculate things that way, an aircraft could come out on top in your analysis simply by removing its normal fuel tanks and installing very small ones. A fair measure would be how much fuel they need to meet each other at equal distance; if at 400nm, then F-22 at half fuel and J-20 at 1/3. Obviously, I made these numbers up as an example but whatever it takes to get there and I think it's generally agreed on that J-20 is likely to have larger fuel tanks and greater range than F-22. This is all on top of the fact that we don't know J-20's fuel capacity so that's a number we basically have to make up and we all know how much that's worth LOL.

The only time when it would be fair to compare percentage of max fuel would be if their max range was similar thus, fairly penalizing the design with poorer fuel efficiency, forcing it to carry more fuel to achieve the same distance.

On top of that, I'd like to point out that how much fuel is loaded at take off is not how much fuel aircraft meet each other at. Good planners would try to get the aircraft as close to empty fuel as safely possible for when the actual encounter happens to increase its TWR. From my calculations of equal fuel and missile load, J-20 was about equal, if not, marginally better in TWR than F-22 but the closer they get to empty weight (plus missiles), the more the TWR advantage shifts to J-20 because of its much lower empty weight (if it is true).

 

[Blitzo]

WS-10IPE is established? I like to hear that. But could you point me to a good source? What's its thrust (dry and AB)?

Jobjed's translated a few posts from an insider whose statements I think sound reasonable.
https://www.sinodefenceforum.com/chinese-engine-development.t252/page-418#post-440450

WS-10IPE should be a 14 ton engine

If WS-15 is 165kN then it would be a great engine for the J-20, not overwhelmingly powerful like 180kN would be.

I realize that the 15 tonne class figure is far from guaranteed, but it's the best figure we have and all my calculations used a 16 tonne figure instead of 15 tonnes to top out the 15 tonne class. So at this point, it's 16 tonnes or nothing. No thought experiment LOL.

Tbh I think it would be better to have nothing in that case.

Why should their fuel be equal percentages of each other? If F-22 goes 400nm on half fuel and J-20 goes 600nm on half fuel, you are in fact giving weight penalty to J-20 for having the option to go further. If you calculate things that way, an aircraft could come out on top in your analysis simply by removing its normal fuel tanks and installing very small ones. A fair measure would be how much fuel they need to meet each other at equal distance; if at 400nm, then F-22 at half fuel and J-20 at 1/3. Obviously, I made these numbers up as an example but whatever it takes to get there and I think it's generally agreed on that J-20 is likely to have larger fuel tanks and greater range than F-22. This is all on top of the fact that we don't know J-20's fuel capacity so that's a number we basically have to make up and we all know how much that's worth LOL.

The only time when it would be fair to compare percentage of max fuel would be if their max range was similar thus, fairly penalizing the design with poorer fuel efficiency, forcing it to carry more fuel to achieve the same distance.

On top of that, I'd like to point out that how much fuel is loaded at take off is not how much fuel aircraft meet each other at. Good planners would try to get the aircraft as close to empty fuel as safely possible for when the actual encounter happens to increase its TWR. From my calculations of equal fuel and missile load, J-20 was about equal, if not, marginally better in TWR than F-22 but the closer they get to empty weight (plus missiles), the more the TWR advantage shifts to J-20 because of its much lower empty weight (if it is true).

I believe it would be fair to compare both aircraft at an equal internal fuel percentage, because that would most accurately reflect the mission orientation and the balance of range vs kinematic capability that the designers intended for each respective aircraft to achieve in their respective mission profiles.


The problem IMO is that you are thinking of it as a competition of only "maneuverability" rather than the combination of maneuverabiltiy, speed, endurance/range, that I think can be summed up as "kinematic persistence".
The aircraft's kinematic persistence in turn then interacts with things like sensors and weapons systems and datalinking to derive a final "combat effectiveness" score.

So for J-20 and F-22, at an equal % of internal fuel, hypothetically let's say J-20's "maneuverability" is only 85% that of F-22's, but that J-20's range is 150% that of F-22.

Well in such a scenario, the J-20's kinematic persistence would be somewhere between equal or perhaps even superior to that of J-20.

 

[Air Force Brat]

Many features on the F-22 had been tried and tested on the F-117A. Does that make the F-22 less revolutionary? It certainly does not. The design of the F-35 is also based on many features tested on the F-22. Does that make the F-35 less remarkable? It certainly does not. Advances in techs are typically incremental and based on previous work.

To say one design is "simply" an incorporation of "some others' work" would be a gross underestimation of the hard work that has been invested in any engineering project of this scale.

If designing and manufacturing a 5th stealth fighter is so simple and requires only "kitchen sink" kind of work, I challenge you to find more than 2 designs in the world that may match the J-20. At this point, only the F-22 is unquestionably superior to the J-20. No one can definitively say about other 5th gen fighters. If the J-20 is such an inferior design, other countries with much more extensive aeronautical experience should put together something superior to the J-20 in no time since they have all the kitchen sink parts available and can simply grab whatever they need off the shelf...

Keep in mind that China has been and still is under arms embargo. They had had little access to most of the "kitchen sink parts" in your analogy. Unlike other countries, the Chinese either had to come up with their own design from scratch, or had to "acquire" certain knowledge through other means, which is a testament of the effectiveness of their intelligence services. To continue with your kitchen sink analogy, while other US allies can simply go to an appliance store owned by the US and pick parts off the shelf, the Chinese had to design / make / steal every screw, nut and pipe themselves (quite literally). Just imagine buying grocery at your local store vs. having to plant vegetables and raising cattle for every of your meal...



Having a novel idea is not the definition of a doctoral dissertation. A doctoral dissertation means a complete project, while a master's dissertation focuses on only part of it. For instance, a master's project would be to figure out how to make a weapons bay work. Another master's project would be to figure out how the landing gear functions properly. Designing and manufacturing a complete plane is a doctoral dissertation by any means.

No one, I mean no one, can work in a vacuum and come up with revolutionary designs. It's all incremental. To this day, I have not seen a single doctoral dissertation that is so revolutionary, completely brand new, and completely novel. Even Nobel laureates' works have almost always been inspired by previous work. Hence the famous saying "standing on the shoulders of giants".

Do we get completely novel ideas? Yes, once in a few centuries, we get an Einstein or a Newton who can completely revolutionize their fields. But that is an anomaly, not the norm. Everyone else has to work with kitchen sinks. If you can mount the faucet from an angle, that might be enough to get you a Science paper. If you can figure out how to install a garbage disposal in the sink, that might be novel enough to win you a Nobel price...

Exactly so,,, I never diminish those hard working designers/engineers, even of other countries, and as our friend Vesicles has reminded us, EVERYTHING is incremental, and to add to that, the US do NOT and will likely NEVER share the F-22 technology even with our close allies, Japan and Israel wished to purchase the F-22, and still would today, but some dumb Democrat congressman passed a rule forbidding F-22 export, in order to make the F-35 the only game in town,

The F-22 was very lean financially, and so called "pork" was already spent, the F-35 is a very "Porky" bird, with everybody benefitting from her various parts and pieces...hence my nick-name for the F-35 as the "ThunderHoggeII".

 

[Shaolian]

I'm no expert, but after reading manqiangrexu's explanation, I'd tend to agree with it. If, and only if, the J-20 is indeed having an empty weight of 15-plus metric tons, then we should deduce that armaments being equal with the F-22, then the J-20 should naturally have an "engagement" weight that is less than the F-22.

An analogy would be a Formula-1 race car. They always calibrate their fuel to last no more than a couple laps after the finishing line. Anything more than that would be extremely bad fuel management on their part.