Hmmmm... I thought that was one advantages of the Chinese fighters, which all have been designed to optimize maneuverability...
Maneuvarability at what speeds and altitudes, and what kinds of maneuvers? I suppose now would be a good occasion as any to dump what I think I've figured out about the J-20's design...
I've done A LOT of reading in the last few months, especially since I've realized that Chinese BBSes have A LOT more informative discussions if I dig for them (but also a lot more rationalizing, baseless conjectures, and bs to filter through), but also since a keypub thread on fighter maneuverability and performance really helped frame this topic so that I have a better idea of what to look for.
There are still a lot of unknowns, so it's really impossible to draw any concrete consclusions, but my general understanding now is that short of further optimizations and maybe design breakthroughs (and there could very well be some since 2011's aerodynamics are going to be a bit different than 2001 and 2002's) the J-20 may have a superior high speed (trans and supersonic) performance but inferior low speed (subsonic) performance to the F-22.
From what I've managed to read, the aggregate of studies on these different aerodynamic configurations generally indicate that the F-22's (and to a different extent the F-35's) solution may well be superior in lift coefficients and lift to drag ratios to both a canard configuration and a canard+lerx+lift body configuration at increasing angles of attack at low subsonic speeds (party because of drag effects, though canards are generally much better for supersonic speeds due to lower trim drag). These differences may be compounded by the J-20's lower aspect ratio higher sweep wings, which generally speaking generates lower lift coefficients at low subsonic speeds all else held equal, but are less draggy and therefore better for supersonic speeds (Wing area alone misses the point. Wing area is important for wing loading and at high altitudes, but differences in wing area only matter all else held equal. Lift and drag coefficients and therefore wing geometry are far more important). Lift and drag ratios and lift coefficients are important because the latter (to my understanding) dictates how much force can act upon the plane's center of moment when maneuvering (at the specific air speeds, altitudes, and angles of attack) and the former indicates how sustained those motions can be (how energy efficient that maneuver is).
Now, none of these features should be used independently to judge a design, because ultimately it's the nonlinear combination of features which matter, which is why the lift properties of different shapes must be determined and confirmed experimentally. Furthermore, only results from within studies should be compared to one another. Results from different studies might have non specific differences in testing models. Therefore, its tenuous how much one can conclude by applying these very general principles to specific designs.
What also shouldn't be overlooked is that there is A LOT of room for optimization (so it's possible that two different design approaches may in fact have similar performances if they were optimized differently) and then other factors of performance metrics like thrust to weight ratio, so none of this stuff should be taken definitively. For all I know, it turns out that the engineers at CAC have found a way to overcome the limitations of specific designs and are able to achieve comparable lift coefficients and lift to drag ratios at subsonic speeds for the J-20, or Lock-Mart has appropriately optimized the F-22 so that its supercruising abilities are still comparable to other designs that on sight would seem more specialized.
Assuming, however, that these general aspects of different designs do tell us something about how the J-20's aerodynamics compares to the F-22's, we can maybe gain some insight into how the two might approach an engagement. Plawolf once told me that a lot of fighter combat hinges on energy management. How high and fast you are determine how much energy your airframe has to maneuver (height and speed store potential energy), and as you maneuver you lose that energy. Generally speaking the one with the lowest energy will find itself in the worst position. That's why the F-22's high altitude, thrust, climbing, and supercruise abilities are such immense advantages.
If the J-20 is indeed more optimized for supercruise than the F-22, assuming that its engines are good enough to generate comparable T:W ratios and climbing ability, and it has comparable high altitude performance due to its large wing area (the J-20, if you actually measure it out, actually has plenty of wing area, again it's the geometry of the wing and corresponding lift coefficients that matter more!), a supercruise advantage should mean that while the two fighters are closing on one another, the J-20 will have more potential energy available, which translates to advantages in the kinetic energy of the missile, maneuverability at the start of the merge, and energy management of the air frame.
However, as the engagement continues and both fighters lose altitude and air speed the J-20 is likely to bleed off more of that energy than the F-22 (especially as the engagement becomes subsonic). At lower subsonic speeds, the advantage probably switches towards the F-22. At that point, in those conditions, the J-20 may still maintain an advantage in instantaneous maneuvers, but its lower lift to drag ratios at those speeds means that it loses energy even more quickly. That means the J-20 will still have a very small window to land a kill and survive the engagement, but once its bled off too much energy, it becomes a sitting duck to its opponent, whose airframe has much better energy management at those speeds.
This is why I'm not sure a prolonged engagement that results in a closed in knife fight is necessarily favourable to the J-20. That said, this is only a very rough hypothetical that barely touches on other factors like transient agility (nose pointing ability) and the capability of sensors and weapons. Speaking of which, interestingly, I believe that the size of the J-20's radar, if it's going to be as big as it seems, fits rather well with the scenario I described. A bigger more powerful radar would help negate some of the radar evasion abilities of an opponent stealth fighter and get a lock earlier in engagement, when the fighters are further apart J-20 may still have its aerodynamic advantage in a supersonic flight regime. Meanwhile, at lower speeds and altitudes, the J-20 may depend on superior electro optical sensors, situation awareness, and HOBs capabilities to mitigate its specific disadvantage at those flight regimes.
Finally, it bears emphasizing that it's not what you have, but how you use it. After studying this subject a bit more, I've truly come to appreciate just how much of fighter design is about choosing your compromises, and how very hard it is to ever say for sure that one design must be superior to the other. The J-20 and F-22 have appeared to prioritize different flight characteristics, and are going to adopt tactics towards each other that try to best emphasize their particular advantages. I
Anyways, take this loongggg entry with a healthy grain of salt. I'm no expert on this stuff, and the lack of a holistic understanding about and formal training in any subject will tend to lead to an inability to parse information accurately. Nonetheless, thought it might do some good to provoke a deeper discussion rather than paper over very real and serious considerations with generic descriptions.
