J-20... The New Generation Fighter III

TBH I would caution reading too much into the take off distances. An F15 with an airshow fuel load could probably take off in a shorter distance than a fully tanked F16. What would that tell us about the TWR of the two planes?

Remember all those pictures of the J20 dumping fuel? Well if the people at CAC had completely whatever tests required that, they could be having the J20 take off with a much smaller internal fuel load and that would account for the shorter take off stance.

Similar thing with the J10s, if the J10S is half tanked while the J10A had full tanks, that would result in a shorter take off run for the J10S.

Even if the fuel load was not changed, the J20 pilot could have been taking it easy with her initially. I really doubt the J10A's trademark vertical climb right after take off was sth the test pilots tried out early in the J10's development programme.

Flight tests programmes are actually very methodical to the point of being very tedious. The test pilots are usually on a very tight leash and have very strict limits on how far they are allowed to push their planes. The fighter might be able to pull 30 degrees/s, but the pilot will not pull one more degree than he is cleared to. As more flights are completed, more and more of the plane's flight envelope is opened up and cleared, the pilots might be given a little more slack.

We are still in a very early stage of the J20 flight testing stage, and I would expect that it is not flying to anywhere close to it's limits yet. Hell, it could well be that the J20 will never fly at the very limit of what we is capable of because of pilot endurance issues - an increasingly common limit for modern fighters.

The take-off distances is dependent on quite a few factors that's not readily known but all these videos will still give useful info on the aircrafts' ballpark range of capabilities. It seems like the planes' took off without the AB, so the takeoff distances should be even shorter with full AB.

I also noticed the engine nozzles of the J-10s seem to be as short as that of the WS-10A. Anymore info on this?

plawolf said:

TBH I would caution reading too much into the take off distances. An F15 with an airshow fuel load could probably take off in a shorter distance than a fully tanked F16. What would that tell us about the TWR of the two planes?

Remember all those pictures of the J20 dumping fuel? Well if the people at CAC had completely whatever tests required that, they could be having the J20 take off with a much smaller internal fuel load and that would account for the shorter take off stance.

Similar thing with the J10s, if the J10S is half tanked while the J10A had full tanks, that would result in a shorter take off run for the J10S.

Even if the fuel load was not changed, the J20 pilot could have been taking it easy with her initially. I really doubt the J10A's trademark vertical climb right after take off was sth the test pilots tried out early in the J10's development programme.

Flight tests programmes are actually very methodical to the point of being very tedious. The test pilots are usually on a very tight leash and have very strict limits on how far they are allowed to push their planes. The fighter might be able to pull 30 degrees/s, but the pilot will not pull one more degree than he is cleared to. As more flights are completed, more and more of the plane's flight envelope is opened up and cleared, the pilots might be given a little more slack.

We are still in a very early stage of the J20 flight testing stage, and I would expect that it is not flying to anywhere close to it's limits yet. Hell, it could well be that the J20 will never fly at the very limit of what we is capable of because of pilot endurance issues - an increasingly common limit for modern fighters.

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Before about 1955 test pilots often died young, especially those testing military aircraft. But then, it seems, it dawned on people that test pilots as well as the aircraft being tested were really valuable. And also that it cost less time to test the aircraft slowly and thoroughly.

Quickie said:

The take-off distances is dependent on quite a few factors that's not readily known but all these videos will still give useful info on the aircrafts' ballpark range of capabilities. It seems like the planes' took off without the AB, so the takeoff distances should be even shorter with full AB.

I also noticed the engine nozzles of the J-10s seem to be as short as that of the WS-10A. Anymore info on this?

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Yep, I noticed that (the apparently non-Russian engines) as soon as I saw the yellow J-10's appearing on the video.

see above!

AssassinsMace said:

Here's nice pic.

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for the life of me, i just don't get the chinese obsession with the ventral fin thing. it's like they're afraid to fly a jet without them. these things must be a huge detriment to stealth. can any 'expert' here explain why the chinese find these to be necessary when other industries have found them not to be?

Subedei said:

for the life of me, i just don't get the chinese obsession with the ventral fin thing. it's like they're afraid to fly a jet without them. these things must be a huge detriment to stealth. can any 'expert' here explain why the chinese find these to be necessary when other industries have found them not to be?

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I think the reasons probably differ on a case by case basis. In the J-20's, maybe it allows the vertical tails to be smaller or something.

Or maybe it's just design trends and comfort zones of experience. Sort of like how the USA seems to love the traditional layout in its planes. Despite testing a lot of radical concepts, they usually stick to their guns when they finally settle on a design.

Well, you lower infrared of you engine on the side. It increases AOA control. And that little RCS increase is only on certain angles that are not important. These planes fly high and you do not get them very close unless you are almost shot down...

Subedei said:

for the life of me, i just don't get the chinese obsession with the ventral fin thing. it's like they're afraid to fly a jet without them. these things must be a huge detriment to stealth. can any 'expert' here explain why the chinese find these to be necessary when other industries have found them not to be?

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Detriment to stealth? The ventral fins shield the nozzles and are angled to deflect radar signal away from the signal source. Removing the ventral fins would be a detrimental of stealth.

Subedei said:

for the life of me, i just don't get the chinese obsession with the ventral fin thing. it's like they're afraid to fly a jet without them. these things must be a huge detriment to stealth. can any 'expert' here explain why the chinese find these to be necessary when other industries have found them not to be?

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The J20 is a continuation and refinement of the aerodynamic concepts developed on the J10.

The main reason ventricle fins are added to a design is to improve directional stability, especially at high speed, and could allow for smaller vertical tails as a result.

I could be wrong, but I also believe that the ventricle fins on the J10 and J20 can aid in the high alpha handling of the plane.

A canard-delta generally has better nose pointing ability than a conventional layout design because with canards, you are directly pushing the nose of the plane instead of pushing the entire plane to turn the nose - the movement arm is much shorter, thus the same applied force would yield a far greater turning force, with mass the same, greater force = more velocity => faster nose turning. Basic physics.

However, if your tail start sliding out, the situation is reverse, thus canards are not as efficient in controlling the back end of a plane compared to a conventional layout design. This would be exacerbated in high alpha maneuvers, when the wing and fuselage of the fighter would block airflow to much, if not all of the vertical tails, thus removing the primary means to control directional stability on a tailless canard-delta in level flight.

This is a very preliminary assessment, and may be affected by many other factors I do not know about, but on the face of it, I would suspect that the J10 would have better sustained turning and energy conservation properties compared to the likes of the Typhoon or Rafale that does not have ventricle fins. The flip side would be that the Eurocanards should have the edge in instantaneous turning capabilities.

I would also expect the J20 to have similar good high-alpha maneuverability and controllability, which would incidentally, be in line with the very rudimentary assessment some model makes reached when they built a RC J20 model.

As has already been pointed out, the designers at CAC did not miss the opportunity to make additional use of the ventricle fins, and have cleverly worked their design so that the ventricle fins block direct line of sight to the engine nozzles from the side-on aspect of the J20, thus allowing it to have a far bigger stealthy aspect even with conventional engine nozzles.

Looking at the picture you quoted, would it make any difference what the actual shape of the engine nozzles are from that angle?

I am unfamiliar with the effect the ventricle fins might have on drag. Would it be higher because there are more fins, or lower because the reduction in size possible to the vertical tails because of the addition of the ventricle fins is larger than the additional drag created by the extra fins?

My gut tells me that the ventricle fins and smaller vertical fins would allow for lower drag, both because the smaller fins would benefit from the low drag shock cone effect (is that what it's called?) caused by the nose and body of the plane, and also be because having fins on both the top and bottom of the plane makes for a much more even distribution of drag. With only vertical tails, all the drag would be on the top of the plane. This would push the nose up, and force the FBW to pitch the plane's nose down to maintain level flight, which causes more drag.

With fins top and bottom, some of the nose-up force is cancelled out by the drag on the ventricle fins pulling the nose down. This would this require less of a pitch-down movement from the other control surfaces and thus would help to reduce drag. But, once again it's all down to the sizes of the different forces. If the combined drag from top and down fins is greater than vertical fins and pitch-down, ventricle fins are more draggy and less if the situation was reversed. Maybe the only way to know for sure is to stick different designs in a wind tunnels dn test them out. But on the face of it, I think the J20 is less draggy for the ventricle fines.

That's my understanding of it anyways. Maybe someone more familiar with drag can help me out there if I got anything wrong.