Chengdu J-20 5th Generation Aircraft News & Discussions
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Brainsucker
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What is the improvement of J-20A compared to the J-20?
Deino
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To admit officially AFAIK there is no difference between J-20 and J-20A, at best it is used for the WS-10-powered variant. I however prefer to use it already without confirmation since the original J-10 was the J-10, which became the slightly improved J-10A in its operational form now and since we have the J-20 demonstrators and the revised true prototypes & LRIP-birds I call the demonstrators J-20 and from the 201x-prototypes I call them J-20A.
Sorry for any confusion.
Deino
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Are you sure? That is for sure Canzhou but as far as I know that image only shows Su-30s.
Deino
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Thanks for posting this image even if I'm sorry that these birds are indeed NO J-20s: I remember that I've seen it already but I did not have it at hand.
Best,
Deino
Cookie Monster
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@Deino In this video, one of the J20s is shown taxiing with its canards in the vertical position. The tails of the J20 are also moveable in such a way along with the canards that they can be used as air breaks.
I'm curious to know if these control surfaces would be used as airbreaks for short landing(if necessary)?
Also with the addition of the WS15 engine(when it's ready) and along with its control surfaces serving as massive air brakes...is it possible that the J20 can have a STOL(Short Take Off and Landing) capability?
gambit
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Airbrake and speedbrake are used interchangeably, but the preferred is 'speedbrake'.
Now...Regarding the video. At timestamp 0:03, we see the J-20's canards are in what seems to be full deflection, but there is a crucial visual clue that most would miss: LEADING EDGE DOWN.
Whether it is leading edge (LE) down or up is important for the flight controls engineer. It depends on the MODE OF OPERATION or to put simply -- what the aircraft is doing at that moment in TRANSITION to what you want the aircraft to do.
What you want the aircraft to do implies a FUTURE mode of operation. So at the time of change, as the pilot changes cockpit switches, the jet will know how to deflect the flight control surfaces to make controls smoothly and safely.
So what is so significant about LE down?
If it is LE up, you would create a nose-up condition, which when you are moving on the ground trying to land in as short a distance as possible, a nose-up condition would be a very bad thing to do.
Further, we do not want this level of deflection while the jet is still flying. Leading Edge (LE) down is nose-down. Full LE down command while still in the air would mean a crash. So we install a safety condition call 'weight-on-wheels' (WOW). All aircrafts has WOW automatic switching. Another word is 'squat switch'.
http://www.askacfi.com/20020/squat-switch.htm
The F-16 has three WOW switches -- one per gear -- and there is a logic to this.
So if the J-20's flight controls engineer want to design a safe speedbrake system using the canards, how would he do this LOGICALLY?
If you have WOW on the main gear, that means the jet has only a PARTIAL touchdown condition. Whether the jet is in a take-off or landing mode, partial WOW means a partial ground condition. You want WOW on all three landing gear struts before the avionics fully reconfigure itself for landing.
So in general principles, the logic would be in this sequence:
- Cockpit switch activation (this essentially prepare the avionics to let the system know that you want to land)
- Main WOW switches active (this tells the avionics that the jet is partially on the ground)
- Nose WOW switch active (this tells the avionics that the jet is fully on the ground)
- Canards LE down
All three WOW switches must be active in order for the canards to deflect LE down. The avionics should not expect first main gear WOW, then nose WOW. The logic should not be a 'first-then-second' or sequential condition. The logic should be a simple 'and' condition because there will be times when a jet could land with all three landing gear making ground contact at the same time. It would not be a smooth landing but it is possible, so we just want to know when the jet is fully on the ground.
Now we come to the vertical stabilators and how they could be used as speedbrakes.
Note the F-18's vertical stabs, especially the rudders. And note that the vertical stabilator and the rudder are not the same thing, even though people uses the two words interchangeably. The stab CONTAINS the rudder. Or the rudder is a component of the stab.
The F-18 is clearly taking off as we do not see the arresting cable anywhere. The rudders are pointing inwards, or in a 'toe-in' condition. This condition assists the horizontal stabs in generating down force, which means nose-up, which assists take-off. This toe-in condition also exists on landing to generate additional aerodynamic drag.
What is the difference between 'toe-in' and 'toe-out' ? Certainly they generate some kind of forces but also certainly those forces are different in directions.
- If the vertical stabs are canted (angled) outward, rudders toe-in would generate downward force to assist nose-up. So to generate drag to slow down the jet, rudders should be toe-out.
- If the vertical stabs are canted (angled) inward, rudders toe-out would generate downward force to assist nose-up. So to generate drag to slow down the jet, rudders should be toe-in.
The above two rules are not absolute as the F-18's avionics uses toe-in and toe-out with different angle-of-attack.
So for the J-20, until someone post a video of the J-20 landing and showing from the rear perspective, we do not know for certain how the J-20's flight controls engineering staff uses the vertical stabs during landing. But we can have a high degree of confidence that the J-20's vertical stabs are used in some ways as speedbrakes. Even though the J-20 do not have rudders, the all-moving stabs can still be used in the same ways as the rudders.
This does not mean the J-20 can exhibit true S/TOL capability. Speedbrakes are used by the F-15, F-16, and F-22 and they do not have true reduced runway length landing capability. For that, we need thrust redirection, aka 'reverser'.
52051
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More rumors about initial exercises of J-20 from reputable members in fyjs, this time J-20 is not equiped with lens so the RCS is not comprised:
Rough translation:
1 J20 vs 4 J-10 in dog-fight, the J-20 leave the rear end to 4 J-10s, but climb suddenly with afterburn, all J-10 lost tracks, the J-20 have not release any countermeasures at all.
2 J20 vs defence array consist of C300/HQ-16A SAM and KJ500 AWACS and several J-10, the first J-20 take down KJ500, the second J-20 take out all SAM batteries, then they finish the mission and leave, neither J-10 nor KJ-500 have any response during the exerise, the senior engineers of the AESA radar developer for KJ-500 is very impressed about J-20's performance.
2 J20 vs 4 J-10 and KJ500 as well as a electronic warfare plane, J-20 climb to 15,000 meter ceil, locate the KJ-500 and the EW plane, rush down to finish them and then take out the 4 J-10s, the whole fight last for 46 mins.
2 J20 vs 4 J-10 and KJ500 as well as a ground radar station, same story, the J-20s climb to high ceil and take out KJ-500, then finish off the J-10s, the whole combat last for 32 mins.
Like some senior scientist in China claimed once: stealth fighter is the nuke weapon in our time.
http://www.fyjs.cn/forum.php?mod=viewthread&tid=1890684&extra=page=&page=1
Rough translation:
1 J20 vs 4 J-10 in dog-fight, the J-20 leave the rear end to 4 J-10s, but climb suddenly with afterburn, all J-10 lost tracks, the J-20 have not release any countermeasures at all.
2 J20 vs defence array consist of C300/HQ-16A SAM and KJ500 AWACS and several J-10, the first J-20 take down KJ500, the second J-20 take out all SAM batteries, then they finish the mission and leave, neither J-10 nor KJ-500 have any response during the exerise, the senior engineers of the AESA radar developer for KJ-500 is very impressed about J-20's performance.
2 J20 vs 4 J-10 and KJ500 as well as a electronic warfare plane, J-20 climb to 15,000 meter ceil, locate the KJ-500 and the EW plane, rush down to finish them and then take out the 4 J-10s, the whole fight last for 46 mins.
2 J20 vs 4 J-10 and KJ500 as well as a ground radar station, same story, the J-20s climb to high ceil and take out KJ-500, then finish off the J-10s, the whole combat last for 32 mins.
Like some senior scientist in China claimed once: stealth fighter is the nuke weapon in our time.
Brainsucker
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So basically China needs a new radar to detect stealth fighter. Because in a fight against F-22, KJ-500 is impotent. I don't know about F-35, as it has less stealth feature. But at the same time, most of AEWAC in the world also impotent to stealth fighter. Yet, it's not an excuse. Maybe that's why they allow those senior scientists who develop KJ-500 to watch the exercise.
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52051
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My take is these exericses have not involved ground anti-stealth radar array yet
Brainsucker
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They use SAM system like C-300 and HQ-16A SAM, so they use ground radar array too. But maybe not the anti stealth radar. But what is Chinese ground anti stealth radar array? And what about KJ-500? Is it not an anti stealth AWAC?
52051
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China have developed several models of anti-stealth radar, but my take is they can somehow locate the rough region where the stealth fighter could be, but dont have the accuracy required to guide missiles there, so you can regard such radar as early warning radar.
Such radar usually are tool large to put on airborne platform.
Brainsucker
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And do you see what funny with the exercise? Those Senior Engineers who develop KJ-500 are there. It just like a harsh reality that act as an eye opener to them
52051
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And do you see what funny with the exercise? Those Senior Engineers who develop KJ-500 are there. It just like a harsh reality that act as an eye opener to them
Not surprise, the stealth fighter is optimized to radar freqency that offer the highest possible resolution, whilst radar operates at other freqency may find the stealth fighter, the resolution is limited, thus they are not clear enough to locate it, maybe eventually with the aids of AI/machine learning/multi-source sensors, one can figure out a reliable way to track stealth fighters, or one may develop radar of new mechanism like China's quantum radar under R&D.
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