J-20 Stealth Fighter Design Balances Speed And Agility

What was it DefSec Gates said about not seeing the first of such threat aircraft until 2020 or so?

It has design features that are a straight ripoff of the F-35. It also looks very similar to the C160 design iteration.

Good article Bill, but there are a few mistakes.

One of which, is engines -- are you aware of the WS-15 turbofan? The current engines J-20 uses, whatever they are, are only meant to be interim. WS-15 is the F119 class turbofan under development meant to give it truly competitive levels of supercruise and maneuverability.

Also, what evidence is there of Chinese interest for Kh-58? I've heard no reports of any such thing. It isn't like China lacks the industry to develop their own stand off munition with folding fins either.

Windshield is also still in one piece, they've only added a reinforcing metal frame in the middle like F-35.

On weapons: lack of a visible gunport is not evidence of lack of a gun. Given historical PLAAF focus on WVR engagement, I doubt they wouldn't put a gun on their premiere air superiority fighter. More than likely, it is mounted similar to F-22 in a shoulder position above the air intake. But we'll probably never know until we see a CCTV documentary on J-20.
Missile number is also something to keep in mind; I wouldn't be surprised if prototypes 2011 and 2012 had expanded its width slightly to accommodate six PL-15s, given the significance of other changes we've seen from 2001 and 2002.

Finally, I think your opinion regarding J-20's roles are too constrained to the A2AD role. While I agree that J-20 is definitely meant to have much greater range and endurance than F-22, I do not see it only as a killer for ISR and tankers -- certainly not once it is equipped with WS-15s. You say yourself it is deliberately meant to have good agility as well and its aerodynamic configuration attests to it. That, combined with its greater fuel capacity, says to me PLAAF basically wanted a longer range F-22, i.e.: competitive maneuverability, competitive supercruise, but all with a longer range. This makes sense given PLAAF would've known they needed future stealth fighters to have longer range (given their lack of tankers but also given close to shore bases may be destroyed by strike). The biggest contention lies in J-20's maneuverability, and that depends on the thrust of its engines, and few mainstream aviation watchers seem to even know about WS-15. Logic would dictate that it be immensely unreasonable if PLAAF did not desire a fighter that could survive or defeat their most significant threat, the F-22 in close encounters.
I suspect they might have gone for a conventional configuration like F-22 if they didn't have to bother with interim engines and could produce something like F119 immediately, but alas they knew WS-15 would be delayed a number of years behind the airframe, so chose an unconventional aerodynamic solution to best leverage whatever interim engine they could muster up on the first batch of J-20s.

Also, the underfuselage EO sensors are part of a 360 degree spherical EO detection system, with a similar arrangement of apertures as F-35's EODAS.
http://i.imgur.com/JjGljvh.png
http://i.imgur.com/6oNqcW5.jpg

Whether J-20's "DAS" features the same surveillance, tracking, and display capability as F-35 is another matter, but I think it's pretty obvious it's meant to have a similar spherical coverage.

Blitzo@
Do you have any source on the WZ-15?
The Su-35SK deal with China are on the doorstep.
With that deal, there will be some spare 117S engines.
Russia will not export its ToT on their engines, so in any case what China will do with their 117S engine is limited.
Its not that easy to copy jet engines, and China will have to stick to their contracts, or they will not recieve any followup deal and will get blasted in Contract breach.. Which could mean no more AL-31F and AL-31FN export to China.

With those Ventral Strakes on the J-20, it means its eighter quite directional unstable and/or the current FBW/FCS is not able to control the jet enough.

AL31F are quite long at 196-199 inches. Comparatively, the F119 is 203 inches but almost a quarter of that is freestream nozzle sidewall with only about 160 inches inside the airframe.

Put a weapons bay ahead of a last-gen engine and you have a quite long fuselage body.

The choice of engine cycle and cruise mode will also dictate TSFC for throttle setting with the Soviet engine being generally behind the latest equivalent American metallurgy and design SOA by about .5 generations at this point and yet for all that (24 vs. 32:1 differential in OPR and 257 vs. 247 lb/sec mass flow on a .5 vs. .36 BPR), it has superior IRT specific fuel consumption on the order of .6 vs. .75 on the F100-PW-229 and .9 on the F119.

Furthermore, it is considerably (500lbs) -lighter- than the U.S. engine for similar overall levels of thrust, both military and max. Which means you can throw it out further from the CG for comparable levels of body flex.

Overall, this is indicative to me of a different approach to sub vs. supercruise problem because you cannot afford a large BPR, low massflow and much lower TET in a supercruise powerplant. It just won't work.

Here too, we must remember that the AL-41F1 (117) of today is _not_ the AL-41F of the MiG 1.44 project but rather a derivation of the AL-31 core.

I have feeling that this reflects that same line of reasoning that the YF120/YF119 design choices on variable geometry came to (high speed all the time over a median radius with VG 'leaks' effecting operating efficiencies or a selectively longer radius overall but with a much shorter SSC percentage of same).

If so, it is important to remember because the AL-31 core design is so much older that, even with a lot of major changes to it's core, the 117 variant is going to 'inherit' a lot of artifacted features that are also incompatible with sustained SSC.

Cutting down the inlets (reducing mass flow) to improve forebody aerodynamics and/or front sector LO is further indicative of this because you are losing intake capture area and this will show up as the difference between the AL-31 equivalent F100 (254) and AL-41F matched F119 (310) pound/sec mass flows.

The backend of the second series of J-20 prototypes are shaped like they are due to boat tail wave drag pressure recovery issues and perhaps inverse ruling effects. Again, the F-22 gets away with it's shape because the taper occurs so much farther forward on the fuselage, in front of the majost aft tail boom structure (the extended J-20 booms are likely drag devices like the fairings on the F-102 aft fuselage).

Where the J-20 initial prototypes likely had an F-111 problem; recontouring the aft fuselage with such a deep cutout likely proscribes any further consideration of 3D TVC as the engine fairing cover panels over any residual centerline keel likely just isn't have the rigidity to resist the torsional loads imposed by thrust vectoring.

In this, it is important to note that the F-22's 6-7G turn capability at high Mach _directly_ drove the squat, 'body builder', look of the airframe with the need to keep the TVC, stabs and wing TE control effectors as close in line with each other and at as short a coupling distance from the wing CL as possible to minimize airframe bending effects on supersonic maneuver within a very strong structural box.

The J-20 may choose to come at this problem 'nose first', with carefully tuned vortices flows off the canards and LEX tractoring the wing through turns rather than flipping it from the aft end but I would still not count on such a long fuselage body as having anywhere near the structural rigidity to be capable of supersonic cruise and maneuver.

IMO, by itself, this takes the J-20 out of the OCA fighter class and puts it firmly in the interceptor category of a MiG-31 or even as a simple replacement for the F-8 Finback. Which is fine because China has a lot of hinterland to cover and not many bases to do it from. But does not make the airframe a Bogeyman threat.

I don't qualify as a LO expert but my understanding of the F-35 tail issue is that the combination of a longer moment arm (no TVC = stabs further back on the boom) and the 5-7` dihedral effect are what makes the F-35 less than best as an 'integrated RF shape'. The J-20 is in the same position with multiple surface intersections and it's canards being angled up so that their tip vortices don't beat on the wing center panels too much.

But the fact remains that, where the F-35 has a tail RCS problem, the J-20 has a _front sector_ equivalent. So unless they have changed the 'shape-shape-shape-materials' rule of the Denys Overholser days with new approaches to active masking of complex surface geometries, it's a virtual guarantee that the J-20 takes a signature hit in exactly the worst place you want to be doing so: coming at the enemy rather than leaving him behind.

Finally, if the aluminum doped paint and colored ribbon around the control surfaces are truly indicators that the second series prototypes are starting to pay the VLO price of major RCS treatments (which supposedly add 5-7,000lbs of design increment empty weight penalty) we should also be seeing changes in things like a production ECS capable of handling heat exchanger venting, post-flight venting to dump waste heat stored in the fuel and an overall change in the energeticness/throttle settings of the aircraft on takeoff and landing.

Are we?

The difference between the J-20's normal takeoff weight (70,750) and the sum of the J-20's OEW (42,750) and internal fuel (25,000) is 3,000 lb, a figure 500 lb less than that of the F-22.

In a Senate hearing on 7 May 1991 the Assistant Secretary of the Navy Gerald Cann testified the payload of an Navalized ATF fully loaded at 70,000 lb, flying a hi-lo-lo-hi profile - 200 ft at 100 NM from target - for a 650 NM combat radius mission would be zero. The Navalized ATF's zero fuel, zero stores weight was estimated to be between 50,000 and 55,000 lb though.

Without the weight penalty of navalization and flying hi-hi-hi-hi, what would be the J-20's combat radius fully loaded at 70,750 lb, carrying 3,000 lb stores?

Many who know a lot about it have written that the U.S. will have a good counter to stealth in ten years. By the time the J-20 appears in numbers it will be just an expensive target.

Plus, the current world strategic situation makes it very unlikely there would be conflict in the next ten years. I would be surprised it the Chinese can sell an airliner overseas in the next ten years. Or an automobile.

Also, it would be interesting to see how well the J-20 matches up against the F-35. The J-20 operating Al-31 engines almost definitely will be a dog in WVR, but so is the F-35. F-35 advocates claim that the F-35 has EODAS so turning is irrelevant, but so does the J-20, and the J-20 has a larger radar aperture to give it better WVR performance.

So even the J-20 interceptor variant will be better than the F-35 in an air superiority mission. Little wonder that the Japanese are rushing to their ATD-X project, the Air Force is hiding behind their F-22s and counter-stealth tactics, and the Navy is hiding behind its EW aircraft and future F/A-XX project.

Ban Lockheed from military contracts for 20 years!

Image analysis: J-31's resemblence with F-35 and F-22 Raptor

http://www.aviationanalysis.net/2014/12/chinese-j-31-resemblence-with-f-...