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Lieutenant General
"Learning...fully operational"? The J-20 has been in service in LRIP already with numbers higher than the Su-57.
Chinese purchase of Su-35
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"Learning...fully operational"? The J-20 has been in service in LRIP already with numbers higher than the Su-57.
No one said TVC is completely worthless. Other members, including myself, only mentioned that placing TVC on J-10 and J-20 at the expense of thrust (assuming so) is probably not a good idea. We doubted they would do it, but seeing as they are at least planning to test them, we must have gotten it wrong somewhere.
TVC does not reduce thrust unless you're using flat nozzles. Engineer's been going off about how TVC is dumb for way too long, but it is a way to establish supermaneuverability without the drag and stealth penalties of canards. You could say it bleeds energy faster than canards, but energy bleed is good in some flight regimes (transition from supersonic to subsonic flight; at Mach 1.5 9G turns hit only 10 degrees / second, or 18 seconds to make a 180, so a fast shoot-and-scoot requires deceleration). And the funny thing is, the J-20 is built for high-speed maneuverability, not Mitsubishi Zero 300 km/h cornering speed.
Whatever drag is mitigated from control surface deflections re-manifests as a decrease in forward thrust resulted from deflection of TVC nozzles, which has the same effect as increasing aerodynamic drag with regards to the kinematics of the aircraft.
Drag is only a problem because it fights forward thrust, thus imposing a terminal velocity on the aircraft. If drag is decreased but the forward thrust is as well, there is no actual change in the terminal velocity resulting in no benefits to the aircraft's kinematics.
TVC is dumb if employed the way fanboys like them to be employed; executing fancy airshow-style manoeuvres. There are likely other reasons for CAC's interest in TVC, like as alternate controls for J-20s during level flight to allow all control surfaces to remain at optimal stealth position, or as preparation for 6th-gen fighters with fewer control surfaces to maximise stealth.
jobjed: Except that TVC imposes only weight, but not drag, penalties in level flight.
Moreover, what's the entire concept of instantaneous turn rate? That's turn rate where you're bleeding off energy. If you have TVC alongside long-coupled canards, you will gain greater instantaneous turn rate over going either with just TVC or canards. From the videos we've seen, the J-20 is definitely anemic when it comes to low-speed low-altitude flight. Adding TVC adds further agility to the aircraft.
Moreover, what's the entire concept of instantaneous turn rate? That's turn rate where you're bleeding off energy. If you have TVC alongside long-coupled canards, you will gain greater instantaneous turn rate over going either with just TVC or canards. From the videos we've seen, the J-20 is definitely anemic when it comes to low-speed low-altitude flight. Adding TVC adds further agility to the aircraft.
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Lieutenant General
Does the Su-57 has diverterless supersonic inlet (DSI)? You bet China J-20 will have the WS-15 on it before the Russian will have mass productions on the Su-57 with that over rated Levcons. The reason they are using it because they have not successfully 'learn' or been able to produce DSI onto their jets. "DSIs also crucially improve the aircraft's very-low-observable characteristics (by eliminating radar reflections between the diverter and the aircraft's skin). Additionally, the "bump" surface reduces the engine's exposure to radar, significantly reducing a strong source of radar reflection because they provide an additional shielding of engine fans against radar waves." DSI can be also found on the F-35 along with the J-20, two of the world's most advanced stealth fighters.
Stupid brain fart. Like as if PLAAF is gonna show you all the plane can do so the enemies can develop counter strategies
That must be why the definitive Su-57 engine is already flying in one of the prototypes while the WS-15 is nowhere to be seen.
A DSI is not a magic replacement for any and every other type of intake, nor is the theory behind it incredibly complicated - so the fact that the Su-57 doesn't have one can easily be (and probably is) down to other factors.
What it does is provide shaping inherently well suited to stealth at performance competitive with more traditional (fixed) intake types. For a LO aircraft this saves a bunch of weight, because you get away with far less RAM/RAS to take care of cavities and other "hot spots" which are inevitable with conventional solutions. That's all there is to it though - it neither performs better (weight saving apart) than a traditional intake nor is it impossible to achieve similar levels of RCS reduction with a traditional intake (see F-22).
If the Su-57 doesn't have a DSI, the most likely reason is that it isn't in fact the best solution for the requirements which the Su-57 is designed to fulfill - which are not necessarily the same as those the J-20 is intended to meet. It's a bit surprising in an aircraft clearly aimed a certain level of low observability, but different aims lead to different solutions - it's not as though Russia is ignorant of the technology involved (Tupolev envisaged DSIs on a mid-1990s concept for a stealthy Tu-22M-sized bomber).
Ever wondered why you never see DSIs on supersonic transport concepts? They don't need to be stealthy, so a big part of the weight saving doesn't accrue, and variable intakes are better able to provide the high efficiency over a wide Mach number range which is so important for long range supersonic cruise. Horses for courses.