It may be pertinent to point out at this juncture that the paper talks about max lift coefficient, NOT max L/D (which would indeed be contrary to fluid dynamics). Vortex lift is seriously draggy, but offers the possibility of improving lift at AoA where a conventional wing would already be stalled - the drag is taken care of by high T/W ratio. As the paper mentions, the low aspect ratio is also beneficial to supersonic drag thanks to improved longitudinal distribution of cross sectional area and low t/c ratio.
Aerodynamics thread
- Thread starter siegecrossbow
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To change the flight path of the aircraft, you need to generate a force in the desired direction. The bigger this force, the faster the aircraft will change direction. On a typical aircraft configuration, the aerodynamic surfaces capable of generating by far the largest lift force are the wings, so the best approach to a hard turn is to bank and point the wing lift vector where you intend to go. You're never going to fly a 9g turn with the lift created by the fuselage sides in side slip (never mind that you'd probably snap the pilot's neck, if you did!).
I never chased these figures down before, so doing the lazy thing and asking, but do you know how drag induced from vortices compare to drag from increasing the wing’s aspect ratio?
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That's too broad a question because it comes down to design priorities. For the purpose of low speed turning at AoA > 20° you aren't exactly spoilt for choices - it's either vortex lift or none at all (and a high aspect ratio wing able to survive the buffet loads may well be weight prohibitive). For best subsonic loiter or range at 1g, high aspect ratio will decrease drag, hence airliner wings and VG on some fighters which strongly emphasize patrol endurance.
I was being broad on purpose here. Of course the answer will vary based on flight regime, *but* that’s also why lift and drag curves are often defined as relationships across a range of flight conditions. I was mostly curious about what those relationships looked like, in comparison to each other, across different flight regimes.
Brumby
Major
I have reviewed your arguments and I could make a substitution wording that instead of “general air superiority: and have it replaced by “multi role” and would still fit within the arguments that you have provided.
The legitimacy of your preferred description is predicated on the evidence that you can provide in direct support of air superiority and not by any critical evaluation of how others have got it wrong with their description. “Air superiority’ carries the function of air dominance whether in BVR or WVR i.e. it is an “Alpha” platform.
It is my opinion that your description needs to satisfy two tests i.e. the design test and the performance metrics test.
An airframe doesn’t become air superiority by accident but by design and that include trade-offs and optimisation of certain performance at the expense of others not critical to air superiority. The question therefore is whether you can provide any evidence in support of the fact that the J-20 was conceived as an air superiority platform from design. The AVIC poster in my view is more of an advertising description then a design description.
Aerodynamic performance especially air superiority function and stealth properties are not necessarily compatible and the reason why the F-117 ended up with the “Wobbly Goblin” description. That said, an “Alpha” platform is designed to go into a dogfight to prevail and that means it has to have the performance metrics to match its intended primary function. I am not a fan of aerodynamics but in a dogfight it is common to note two key metrics, instantaneous and more importantly sustained turn rates. The question is, does the J-20 have those kind of performance measures to qualify it as an air superiority fighter viz a viz similarly class air superiority fighters? The F-35 which is a multi-role fighter has often been criticised (incorrectly) as a fighter that cannot dogfight but to my knowledge it can execute a 28 degree sustained pedal turn, a feat that I believe very few other fighters can match.
The overall body of my thesis has been available in various forms for a while now, the most recent of which I have published here:
The summation of different indicators over time act together for why I base my position as where it is, with the main indicators including:
-J-20 pilot and test pilot testimonies regarding its maneuvrability
-AVIC's official brochure from last year
-Dr Song's paper
Supplementary indicators which are more peripheral/complementary to the main indicators include:
-Rumours about J-XX's role back in the mid 2000s consistently stating its role was to be that of an air superiority fighter.
-The doctrinal logic of seeking an aircraft for the air superiority mission first, before seeking other roles and missions that require the the ability to achieve/contest air superiority to be able to conduct.
The above points together form the basis my position which I think is an accurate reflection of the summation of relevant information WRT J-20's role to the best of our knowledge at present.
Edit: I have no issue if you wanted to call J-20 a multirole fighter aircraft either. There are few modern aircraft in the world which are single role.
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A pilot said the J-20 had equivalent subsonic maneuverability (with its current engines, presumably) to the F-16. The F-16, which was designed as an energy fighter, is commonly regarded as a fighter with the best sustained turn rates of its generation.
So by this logic we should call BS every time a US pilot (or commentator) goes at effusive lengths about how the F-22 is unparalleled in dog fighting. You don’t need to believe anecdotal testimony from a Chinese pilot. It’s not foolproof information, but the same standards of validity apply to all anecdotal testimony, not just ones from Chinese sources.