Aerodynamics thread

[Brumby]

You’re obfuscating. At the end of the day the point is that a max payload takeoff for any fighter is a small fraction of the total strain the airframe is designed to handle. Just as a matter of physics how much payload a fighter can take off with doesn’t tell us much of anything about where the structural limits of an airframe are.

In my simplistic world, I don't really care about weight or thrust or the various aerodynamic properties because the sum of the different variables (and their associated trade offs) produce an end product that has certain performance metrics. How it performs is what matters. It can add weight or reduce weight but if it can't deliver the appropriate performance then it is rather moot. One can cheat with weight but may well be at the expense of meaningful useful life or the need for heavy maintenance.

I just have a simple measure when it comes to maneuverability because it is measurable and reasonably objective and that is STR. Any airframe that can generate a low 20's performance is considered highly maneuverable comparted to what is out there. Is there any evidence that the J-20 can deliver that type of performance?

 

[latenlazy]

In my simplistic world, I don't really care about weight or thrust or the various aerodynamic properties because the sum of the different variables (and their associated trade offs) produce an end product that has certain performance metrics. How it performs is what matters. It can add weight or reduce weight but if it can't deliver the appropriate performance then it is rather moot. One can cheat with weight but may well be at the expense of meaningful useful life or the need for heavy maintenance.

I just have a simple measure when it comes to maneuverability because it is measurable and reasonably objective and that is STR. Any airframe that can generate a low 20's performance is considered highly maneuverable comparted to what is out there. Is there any evidence that the J-20 can deliver that type of performance?

Yes. One unconfirmed testimony we have where a pilot said the J-20’s subsonic maneuverability was comparable to the F-16’s and that ironically made it the best gun fighter, even though it doesn’t have a gun. It’s not just the F-16 comparison that’s significant in that comment, but the way the comparison is qualified.

 

[siegecrossbow]

Yes. One unconfirmed testimony we have where a pilot said the J-20’s subsonic maneuverability was comparable to the F-16’s and that ironically made it the best gun fighter, even though it doesn’t have a gun. It’s not just the F-16 comparison that’s significant in that comment, but the way the comparison is qualified.

I think you conflated Xi Yazhou's (no relations to the PRC president) article with a statement by Chinese pilots. There are two interview testimonials by Chinese pilots:

1) An interview with pilot Zhang Hao claims that the J-20 has pretty decent subsonic maneuverability but excellent supersonic maneuverability and that no [Chinese fighters] could match it in the supersonic regime.
2) A Xinhua interview with Li Gang claiming that the J-20 has comparable agility to the J-10. The same interview confirmed that the J-20 uses a side-stick controller because it allows better handling under higher-Gs than the center-stick.

 

[latenlazy]

I think you conflated Xi Yazhou's (no relations to the PRC president) article with a statement by Chinese pilots. There are two interview testimonials by Chinese pilots:

1) An interview with pilot Zhang Hao claims that the J-20 has pretty decent subsonic maneuverability but excellent supersonic maneuverability and that no [Chinese fighters] could match it in the supersonic regime.
2) A Xinhua interview with Li Gang claiming that the J-20 has comparable agility to the J-10. The same interview confirmed that the J-20 uses a side-stick controller because it allows better handling under higher-Gs than the center-stick.

I’m thinking of a third one that is more dubious, which is why I keep caveating it.

 

[ZeEa5KPul]

I think you conflated Xi Yazhou's (no relations to the PRC president) article with a statement by Chinese pilots. There are two interview testimonials by Chinese pilots:

1) An interview with pilot Zhang Hao claims that the J-20 has pretty decent subsonic maneuverability but excellent supersonic maneuverability and that no [Chinese fighters] could match it in the supersonic regime.
2) A Xinhua interview with Li Gang claiming that the J-20 has comparable agility to the J-10. The same interview confirmed that the J-20 uses a side-stick controller because it allows better handling under higher-Gs than the center-stick.

Where do comparisons of the J-20 and F-16 come from? Have Chinese pilots flown Pakistani F-16s or is it just assumed that the J-10 and F-16 have comparable manoeuvrability?

 

[siegecrossbow]

Where do comparisons of the J-20 and F-16 come from? Have Chinese pilots flown Pakistani F-16s or is it just assumed that the J-10 and F-16 have comparable manoeuvrability?

It is from an article by Xi Yazhou. No official source directly compared the J-20 with the F-16.

Another thing to keep in mind is that different aircraft may be optimized to maneuverability in different flight regimes. The F-18 is heavily optimized for subsonic speeds whereas Mirage-2000 is optimized for super and high subsonic speeds.

 

[PiSigma]

However, as I've previously stated, the J-20 would need inlet modifications to support the WS-15, given that inlet flow requirements between the WS-10 / AL-31 and WS-15 likely differ. We may end up seeing inlets more similar to the original J-20 prototype inlets due to the flow requirements.

Are you referencing yourself here and taking it as the truth?

The J20 is designed for the WS15 from the beginning, small modifications were made to it to use WS10. Once WS15 becomes available, you will see very minor and no differences from the outside.

 

[Richard Santos]

Are you referencing yourself here and taking it as the truth?

The J20 is designed for the WS15 from the beginning, small modifications were made to it to use WS10. Once WS15 becomes available, you will see very minor and no differences from the outside.

The WS-15 almost certainly ingest more air flow, compress it more and burn it hotter than WS-10. Since J-20 seems to have fixed inlet, I suspect some changes to inlet was made to adapt it for lower airflow WS-10

 

[Inst]

Are you referencing yourself here and taking it as the truth?

The J20 is designed for the WS15 from the beginning, small modifications were made to it to use WS10. Once WS15 becomes available, you will see very minor and no differences from the outside.

In the prototype version, the DSI bump was significantly smaller than on the final version. I've also done measurements of the J-20's inlets, as well as of the F-22 and F-35.

The F-35 seems to have about 1 m^2 inlet area (combined), presumably being sufficient for a 190 kN engine like the F135. The J-20, in contrast, has something closer to .67 m^2 inlet area per engine, which is roughly the same as that on the Su-27 (i.e, sufficient to fuel a Al-31).

The point being made isn't that the J-20 isn't designed for the WS-15, but that the inlets likely saw modification to optimize them for the Al-31/WS-10. Excessively large inlets tend to lead to spillage drag as airflow either overflows the inlets or is bled out through vents.

 

[latenlazy]

The WS-15 almost certainly ingest more air flow, compress it more and burn it hotter than WS-10. Since J-20 seems to have fixed inlet, I suspect some changes to inlet was made to adapt it for lower airflow WS-10

Might not require a change in the external geometry. The J-20 seems to have bleeds on the inlet sides, and we don’t know whether the inlet capture area actually maximizes the external geometry of the inlet mouth.