Shenyang / Chengdu "6th Gen" Aircraft - General Discussion and Speculation

Looking back at the whole topic, you'll notice that a lot of people are discussing the usage of sixth-generation fighters using the combat style of fourth-generation jets and the design of fifth-generation jets.
Yep. This whole forum inevitably falls back to the fly high fly fast paradigm and that always ends up becoming a comparison of engines, planforms and payload. Just not the only things or even the most important things that matter anymore.
Additionally, I lean toward the idea that the drones accompanying the J36 would be AI-autonomous fighters. They might be able to identify and attack enemy aircraft on their own, and work with other drones to autonomously choose the best attack strategy based on the movement of enemy planes, then relay it back to the J36's co-pilot commander for real-time adjustments.
Being able to coordinate, respond and actively plan and execute a collaborative task is trivial if one were ready to allow it. While teaming technology continues to be studied, there is sufficient tech there already for it to happen.

As it stands, no one is making CCAs that are semi-autonomous either. Truly semi-autonomous control is used for the purpose of dev and verification. Otherwise It completely defeats the purpose of collaborative combat if every paired cca itself cannot decide how to execute an attack on a target and requires the human to micromanage it. Especially in an extremely dense and complex environment, the pilot should simply be designating targets and assigning / directing attack groups when needed. The 6th gen pilot is more of an AWACS controller than a drone mission planner.

What isnt trivial though is how your AI system reacts when the information being gathered is sparse, theres plenty of jamming and deceptive signals, and what targets you pick up are of varying quality and then having to build awareness and execute plan of actions based off that.

The problem imo is also a matter of how that information flows to the processor, who is doing the processing, and how do you process it well enough to build the required situational awareness to act accordingly. That means each individual unit must be able to take action alone as well as in a group and that gets complex really quick. How complex a model you use depends now on how much electric generation your main processing node has. How much autonomy now depends on how much power generation your drones have too.

Then theres also the problem of how the human affects and is affected by the fight under this framework, because when your teaming AI is taking over, are you, the pilot in the 6th gen still retaining control or are you yourself being commanded by the AI in order to win the fight?

So autonomy and teaming itself is easy, and no CCA user is not going to have this capability. Its when you add in the rest of these problems that its no longer easy. differences in 6th gen fighters and CCAs will be in the quality of the onboard solutions to these problems.

I should also add especially for readers notoriously concerned about kinematic and physical requirements of aircraft - given the likely density of flying targets in a future air war, awareness and appropriate cordination is increasingly more important than having range or kinematics. Id even venture enough to say that kinematics quite frankly take second seat to awareness and reaction.

Even if you can shoot to kill at 300 miles, you need to engage and send to defensive all the opposing enemies that are engaging your force at that 300 mile mark in order to keep them at 300 miles. You also have to have these targets fixed by someone across the missiles flight profile and up until pitbull. Otherwise you wont be able to stop an opposing force from closing in and, if close enough, obtaining a firing solution on you esp with the amount of targets both LO and VLO flying around. Being able to fly faster and higher means absolutely nothing when you with the more exquisite and less numerous force simply cant cover all the required geometries to prevent leakers. Hell being able toshoot first isnt even all that valuable anymore when theres something you havent engaged yet already pushing your position. This is why an appropriate level of sophistication and amassability is far more valuable than increased kinetic and kinematic capability with regards to CCAs.
 
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There are a lot of problems, but there are also quite a few solutions. And since the main sixth-generation fighter manufacturing countries are pretty secretive about this, I don't think we'll have answers to these issues right now. But there's no doubt that once they've decided to build these fighters, they definitely have concrete solutions in mind. No doubt, future air battles are going to get even bloodier.
 
This video argues that the triple-engine layout may be to provide power generation for onboard systems while it also operates with loyal wingmen (images are the usual collection of AI slop and more serious renders that are uncredited).
While I'm sure that a 3rd engine helps with electrical power, I'm equally sure that the primary reason for the 3rd engine was power-to-weight at 50% fuel.

J-36 is a hecking big plane, I'm guesstimating 125klbs MTOW (Su34 is 100k, FB-111 is 105k). But China doesn't have 45klb class engines, at least not openly demonstrated. They do have a couple of 32-35klb engines, though, and 3x32>2x45. So the monster plane has ~96-105klbs of thrust. So, after burning 20,000lbs of fuel, the plane has a T:W of 1.0. It could burn another 20klbs of fuel and still have 10-20klbs for weapons.

If the J-36 was not intended as a fighter, instead if it were a "stealthy F-111", it would only need 2 engines for straightline speed.
 
J-36 is a hecking big plane, I'm guesstimating 125klbs MTOW (Su34 is 100k, FB-111 is 105k). But China doesn't have 45klb class engines, at least not openly demonstrated. They do have a couple of 32-35klb engines, though, and 3x32>2x45. So the monster plane has ~96-105klbs of thrust. So, after burning 20,000lbs of fuel, the plane has a T:W of 1.0. It could burn another 20klbs of fuel and still have 10-20klbs for weapons.
WS-15 is a 40 klbs thrust class engine. It wouldn’t be too hard to upgrade it to 45 klbs by raising the bypass ratio and making other tweaks. I don’t think twin 45 klbs engines can satisfy the needs of the J-36, especially since it has relatively small forebody sweep and leading edge sweep angles.

We can use this chart for reference. A forebody sweep angle between 65 and 68 degrees, paired with a 50 degree wing leading edge sweep angle, corresponds to a takeoff weight of 85000lbs to 90000 lbs. With a thrust to weight ratio in this range, the top speed will end up being pretty underwhelming.
 

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3).The propulsion system needs to balance specific fuel consumption (SFC) and supersonic thrust. If optimal values for both cannot be achieved simultaneously, prioritize lowering SFC and moderately relax the requirement for intermediate thrust.
Three adaptive cycle engines represent the fully mature configuration for the J-36. Prior to this engine swap, the J-36 is tailored to prioritize long range capabilities. Taking into account past rumors surrounding the J-XDS focusing on supersonic performance, alongside papers detailing its intake optimized for 1.8 Mach, the J-36 and J-XDS clearly follow divergent design priorities. I suspect they will utilise distinct variants of the WS-15 during their early service phases.

As shown in Figure 2, the longer the mission leg distance, the greater the impact of lift to drag ratio and SFC on aircraft weight. For fighters with a combat radius of around 1000 km, even if we moderately relax the lift to drag ratio and SFC targets to meet demands such as high angle of attack maneuvering and steep climb rate, the aircraft weight will still fall within a viable design window of roughly 20 tonnes. By contrast, for designs targeting a far longer combat radius (for instance, the 2200 km sought by Japan), varying combinations of lift coefficient K and SFC can lead to weight differences of up to 10 tonnes or even dozens of tonnes, exerting a disruptive, make or break effect on the viability of the overall design scheme.
With SFC set to 1 and K set to 15, 55 tonnes gives a combat radius of 3700 km on this chart
 

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WS-15 is a 40 klbs thrust class engine. It wouldn’t be too hard to upgrade it to 45 klbs by raising the bypass ratio and making other tweaks. I don’t think twin 45 klbs engines can satisfy the needs of the J-36, especially since it has relatively small forebody sweep and leading edge sweep angles.

We can use this chart for reference. A forebody sweep angle between 65 and 68 degrees, paired with a 50 degree wing leading edge sweep angle, corresponds to a takeoff weight of 85000lbs to 90000 lbs.
That's quite a bit lighter than I was expecting.



With a thrust to weight ratio in this range, the top speed will end up being pretty underwhelming.
Not necessarily. Blackbird has an in-flight TWR of about 0.58. A-5 has a TWR of about 0.79 (both at roughly half fuel)
 
That's quite a bit lighter than I was expecting.




Not necessarily. Blackbird has an in-flight TWR of about 0.58. A-5 has a TWR of about 0.79 (both at roughly half fuel)
Northrop once developed a concept for the F/A-XX supersonic strike fighter featuring a double-swept wing configuration and engines analogous to the F119. To achieve a combat radius of 1,200 nautical miles (2,222 kilometres) and a maximum take-off weight approaching 100,000 pounds (45.4 tonnes), the design required a leading-edge wing sweep angle of roughly 35° to boost lift-to-drag ratio, which capped the aircraft’s top speed at approximately Mach 1.5. Evidently, the performance limits of existing low-bypass-ratio turbofan engines are insufficient to meet the operational requirements of next-generation high-performance fighter jets.
The 85000‑90000 number I mentioned is the weight from this chart for a twin sweep fighter powered by two F119 class engines. It has TWR close to the J‑36, with roughly matching forebody sweep and leading‑edge sweep angles. Perhaps you haven’t seen this chart?

Edit: Maximum speed is indeed mainly determined by the sweep angles,my earlier wording was not precise ,2 × 45000 ÷ 125000 = 0.72. At this point, the maximum takeoff weight corresponding to two F119 engines should be 97000 lbs, and this value falls off‑scale on this chart so we cannot read it. My conclusion remains the same. At this sweep angle, this low TWR leaves little practical design value for the configuration.

Anybody got relatively solid figures for J‑36 forebody sweep angle? My current estimate is just within the 65‑70 degrees range.
 

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While I'm sure that a 3rd engine helps with electrical power, I'm equally sure that the primary reason for the 3rd engine was power-to-weight at 50% fuel.

J-36 is a hecking big plane, I'm guesstimating 125klbs MTOW (Su34 is 100k, FB-111 is 105k). But China doesn't have 45klb class engines, at least not openly demonstrated. They do have a couple of 32-35klb engines, though, and 3x32>2x45. So the monster plane has ~96-105klbs of thrust. So, after burning 20,000lbs of fuel, the plane has a T:W of 1.0. It could burn another 20klbs of fuel and still have 10-20klbs for weapons.

If the J-36 was not intended as a fighter, instead if it were a "stealthy F-111", it would only need 2 engines for straightline speed.
Also could be for altitude. The higher you fly the further you can see. Giant wing and lots of power you can still turn decently at higher altitudes.
 
The 85000‑90000 number I mentioned is the weight from this chart for a twin sweep fighter powered by two F119 class engines. It has TWR close to the J‑36, with roughly matching forebody sweep and leading‑edge sweep angles. Perhaps you haven’t seen this chart?
No, I hadn't seen that before you posted it yesterday


Anybody got relatively solid figures for J‑36 forebody sweep angle? My current estimate is just within the 65‑70 degrees range.
@Deino ? Weren't you working on a CAD model of the J36?
 
Also could be for altitude. The higher you fly the further you can see. Giant wing and lots of power you can still turn decently at higher altitudes.

Indeed... and at high speed the angle of attack should be within limits for a dorsal air intake. It is likely that its supersonic turn performance is determined mainly by whether the airframe can handle 7g.

P.S. Anyone reading this should realise that supersonic turns are not very sharp to begin with.
 
(Via ACuriousPLAFan/SDF)
Excerpts from a patent document on a forward landing gear setup, published by Chengdu AC and could be related to the J-36. Posted by @一定会对蛙动手 on Weibo.
 

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The reason it has three engines is they used an existing engine instead of having to design a larger engine, which takes a long time to develop. Also, by using an existing engine it aids with spare parts commonality with the other aircraft using the same engine. It's not as complicated as they want to make it. It's like asking why the Vulcan bomber had four engines instead of two.
 
The reason it has three engines is they used an existing engine instead of having to design a larger engine, which takes a long time to develop. Also, by using an existing engine it aids with spare parts commonality with the other aircraft using the same engine. It's not as complicated as they want to make it. It's like asking why the Vulcan bomber had four engines instead of two.

Also, I think I said this before but if there is a notional 350 J-XDS and 150 J-36 then the number of engines (by having a three engine J-36) goes from 1000 engines to 1150 engines... which is only a 15% increase in procurement - and economies of scale as well as logistics commonality reduce that cost further... so one gets a significant increase in capability for a small increase in cost.

It is also worth noting that it might be possible to extract a lot more power from a three engine setup (e.g. for radars and jammers).
 

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