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

[Avimimus]

Yes, the GCAP features substantially improved power generation capability compared to previous generation fighter aircraft. Nevertheless, my personal assessment is that a peak generating capacity of 1 MW is still too conservative for the J‑36, considering that according to leaks, the J‑36 places heavy emphasis on electronic warfare. Both its large airframe and two‑seat configuration are tied to its EW requirements.

The WS-15 is expected to produce more power than the WS-10... having three engines means 50% more power... and not all systems will scale in their power draw the way radar or jammers will. So, even without improvements in the ability to draw extra power from the engine - we're still talking about an 150% more power than a late model J-20 and 200% more power than an early model J-20. So it could still be a major increase in capacity even without taking any additional steps to draw more power from the engines.

Given the implied power to weight ratio and relatively limited thrust requirements in cruise they could probably add additional mechanisms to draw power from the engines... which would increase those numbers further - but I don't think it is necessarily implied that they will need to in order 'place heavy emphasis on electronic warfare'. That said, if they did plan a modified engine to allow increased electricity production... ...I wonder if the reason for the dorsal engine placement is partly to fit a larger heat exchanger for cooling electronics?

 

[bennyp]

Doesn’t the beam attenuate towards the edges of the radar? I’d imagine there will be some tradeoff form looking at head on targets.

I dont really see that as a concern. If you think of the total system then instead of each ship staring forward, each ship simply covers adjacent ships' sectors (total fused picture makes this a lot less confusing than in the past). When you bring in other offboard sensors into the picture like CCAs, AWACS, and legacy platforms, this becomes even less of an issue. Instead, it seems advantageous to me that the ownship arrays would be tailored for immediate tactical needs, and sidelooking arrays seem smart in that regard.

 

[Scott Kenny]

Doesn’t the beam attenuate towards the edges of the radar? I’d imagine there will be some tradeoff form looking at head on targets.

I'm not sure, not enough of a radar nerd to understand that.

It's my understanding that the overlap between the two arrays at ~45-50deg ~90-100deg eliminates that issue.

Edit: used sweep angle, not full included angle between arrays.

 

[F119Doctor]

Not sure I like starter-generators inside the spools, that's going to greatly suck for maintenance.

The classic "starter-generator in the inlet bolted onto the front of the compressor" like J34 and J79 may be a better option (not sure how well or even if that works with a multi-spool engine). @F119Doctor can you start a multi-spool engine by starting the LP compressor?

A two spool turbojet, maybe. A two spool turbofan is unlikely since a lot of low spool airflow bypasses the core and doesn’t assist the turning of the core. The F100-100/200/220 (0.7 BPR) requires approximately 350 KIAS speed to perform a windmill air start. I doubt a low spoil starter motor could match that level of airflow to the core rotor.

That said, there is a lot of discussion with starter / generators mounted on both the low and high spools, primarily to provide additional electrical power for aircraft systems without overly loading the high spool. Could a low spool starter help the high spool starter? Would take a ton of current to operate both.

 

[Scott Kenny]

A two spool turbojet, maybe. A two spool turbofan is unlikely since a lot of low spool airflow bypasses the core and doesn’t assist the turning of the core. The F100-100/200/220 (0.7 BPR) requires approximately 350 KIAS speed to perform a windmill air start. I doubt a low spoil starter motor could match that level of airflow to the core rotor.

I was afraid of that.

That said, there is a lot of discussion with starter / generators mounted on both the low and high spools, primarily to provide additional electrical power for aircraft systems without overly loading the high spool. Could a low spool starter help the high spool starter? Would take a ton of current to operate both.

Still means two starter-generators in very hot places that are an absolute nightmare to repair or replace.

 

[EmoBirb]

Still means two starter-generators in very hot places that are an absolute nightmare to repair or replace.

A large, highly advanced and complex tri-engine jet will be maintenance hog anyway I'd assume

 

[Alfa_Particle]

What you think about the seemingly extreme nose radome canting? Is some kind of V-shaped array possible?

Well, first it gets the radar away from glinting directly forward.

ESAs of both types have been demonstrated with 90deg between arrays (45deg "sweep") and seamless tracking as an object moves around them. One of the SPY6 versions (v3?) can handle 120deg between arrays (60deg "sweep") but apparently has some loss of data fidelity at the edges, 90deg is much preferred there.

But it'd be possible to have two arrays in there matching the ~50deg sweep of the main leading edges with no trouble. So now your nose radar is covering +-100deg across the front of the plane. Able to track a target abeam(!).

Doesn’t the beam attenuate towards the edges of the radar? I’d imagine there will be some tradeoff form looking at head on targets.

Might I also suggest – an isosceles trapezoidal arrangement (when viewed from above)? So one front-facing array flanked by two side-facing arrays (of comparable size) integrated into a single unit. Gives you even more area for the T/R modules and I imagine the implication of overlapping FoVs from a singlular radar unit is quite nice.

So basically this but significantly better.

 

[Scott Kenny]

A large, highly advanced and complex tri-engine jet will be maintenance hog anyway I'd assume

Right, but when the generator bolted onto an accessory drive fails you can unbolt it from the accessory drive housing and replace it, engine still in the plane.

While when a generator inside the spools fails you have to pull and then disassemble the engine.

That's an order of magnitude difference in how long to repair. At least.

 

[Scott Kenny]

Might I also suggest – an isosceles trapezoidal arrangement (when viewed from above)? So one front-facing array flanked by two side-facing arrays (of comparable size) integrated into a single unit. Gives you even more area for the T/R modules and I imagine the implication of overlapping FoVs from a singlular radar unit is quite nice.

I'd need to crunch specific numbers, but I think you'd get more array area with just two large "side" arrays and skipping the forward array entirely. Plus not having a forward array means you have one less RCS spike direction.

Does anyone know how deep a typical GaN TRM is, how far the TRM goes into the backing plate? 10cm? 5?

 

[siegecrossbow]

Like the face of the radar antenna is V-shaped? What benefit can you get from such a design? Better utilization of the radome volume and ability to get sideway views?

In case anyone can’t visualize what we were discussing, here is a patent showing a similar setup.

https://patents.google.com/patent/US9091745B2/en

 

[Alfa_Particle]

I'd need to crunch specific numbers, but I think you'd get more array area with just two large "side" arrays and skipping the forward array entirely. Plus not having a forward array means you have one less RCS spike direction.

Does anyone know how deep a typical GaN TRM is, how far the TRM goes into the backing plate? 10cm? 5?

I was gonna do a numerical estimate but after thinking about it, it's highly context-dependant. The exact radome shape changes a lot of things, so it's probably better off to model the different configurations in CAD then estimate it.

A v-shaped array might look like this:


And a trapezoidal one might look like this (excuse the incredibly crappy quick sketch):


Theoretically the latter gives you even more area via a more aggressive utilisation of the radome space + slight slanting. A v-shaped array might also do this BUT since the volume shrinks as you approach the front, it's probably more awkward.

Gives you more FoV, overlap, and more importantly, bistatic operation over a much wider range for LPD/LPI. A wedge array can only do that to a significantly more limited fashion frontally.

 

[Seragina]

Geometry aside Transceiver size has the final practical say. And having 3 separate ones is the better practical solution for density, aperture size & resolution, and range to the detriment of mass & power, though.

 

[Nx4eu]

I was gonna do a numerical estimate but after thinking about it, it's highly context-dependant. The exact radome shape changes a lot of things, so it's probably better off to model the different configurations in CAD then estimate it.

Two configurations.

 

[Alfa_Particle]

Two configurations.

Fantastic work. The difference is 0.08 m^2 in this case. I'll admit the wedge array is significantly easier to optimise for but I'm suretpy the tri-array arrangement can have the same (if not more?) area with a little more aggressive use of the available radome volume though, since the whole point was pushing the front array a bit forward so that the side arrays wouldn't be smaller than the wedge solution + FoV gains.

 

[lancer21]

To my very uniformed eyes, the tri-array has the apparent disadvantage of the side-arrays not seeing directly in front, with the frontal array being smaller than the radome size would allow, impacting range/EW etc. The V-shaped array however allows both arrays to see in front with the maximum number of TRMs. Of course there is some loss in lateral FOV compared to the triple solution, but still offers a much wider FOV than a conventional fixed array. It seems to be the best compromise, but i guess we'll have to wait years or decades to actually find out the solution they chose.

 

[Alfa_Particle]

To my very uniformed eyes, the tri-array has the apparent disadvantage of the side-arrays not seeing directly in front, with the frontal array being smaller than the radome size would allow, impacting range/EW etc. The V-shaped array however allows both arrays to see in front with the maximum number of TRMs. Of course there is some loss in lateral FOV compared to the triple solution, but still offers a much wider FOV than a conventional fixed array. It seems to be the best compromise, but i guess we'll have to wait years or decades to actually find out the solution they chose.

But AESAs don't need to be physically pointed towards a target. The beam is electronically steered, which is the whole point. The side arrays for the tri-array solution can of course see forward, but they don't necessarily need to (for the most part). There's the front array for that, while the side arrays can look for off-bore targets for better situational awareness.

And the thing with the v-array is that when it looks directly forward, both panels are scanning heavily off-broadside, which means (potentially significant) cosine loss. Realistically the effective aperture area is much smaller. Even if it can house more TRMs (it might not) there could be no tangible advantage since they aren't radiating efficiently in that direction.

There's also kinda an elephant in the room. The v-shaped array forms a big ahh cavity so you get a dihedral corner reflector.