• Friday, December 13, 2019

Translation of J-20 Article by Dr. Song Wencong

Discussion in 'Chinese Defence Forum' started by siegecrossbow, Mar 13, 2012.

  1. siegecrossbow

    siegecrossbow PDF THINK TANK: ANALYST

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    Dr. Song Wencong was the chief designer of the J-10 program and mentor to Yang Wei, who was in charge of both the JF-17 and the J-20. The paper I translated was a theoretical document written in 2001 discussing the aerodynamic considerations of a "future fighter". Hopefully my translation could shed some light on the role and design considerations of the J-20 fighter.

    Link to original article in Chinese: ¡¶Ò»ÖÖСչÏұȸßÉýÁ¦·É»úµÄÆø¶¯²¼¾ÖÑо¿¡·_°Ù¶ÈÎÄ¿â

    Original diagrams from the text. Posted here for reference:

    [​IMG]

    [​IMG]

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    [​IMG]

    [​IMG]

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    [​IMG]
     
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  2. siegecrossbow

    siegecrossbow PDF THINK TANK: ANALYST

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    Posting the remaining three diagrams (can't post them in the original thread due to limit on # of diagrams):

    [​IMG]

    [​IMG]

    [​IMG]
     
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  3. FairAndUnbiased

    FairAndUnbiased SENIOR MEMBER

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    And certain high school dropout maintainence boys and a few illiterate people think that they're smarter than DR Song.
     
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  4. DrSomnath999

    DrSomnath999 SENIOR MEMBER

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    well the article emphasizes more on the advantage of LERX rather than canards:lol:
     
  5. siegecrossbow

    siegecrossbow PDF THINK TANK: ANALYST

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    Not true. If you look closely it covers how the combination of LERX, Canards, and lift-body contribute to greater lift than each could do independently. Check out this diagram:

    [​IMG]
     
  6. DrSomnath999

    DrSomnath999 SENIOR MEMBER

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    well what about turn rate & at what speed ?? thats important
    supersonic drag is the most important thing .well article also states the importance of TVC also
     
  7. gambit

    gambit PROFESSIONAL

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    And there are many on the Chinese side here who believe they know more than all the DRs and engineers at Lockheed.
     
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  8. DrSomnath999

    DrSomnath999 SENIOR MEMBER

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    One more thing crossbow what is the stealth penalty for having CANARD + LERX combination ????
    is it minimal or large
     
  9. j20blackdragon

    j20blackdragon FULL MEMBER

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    From JAST To J-20

    [​IMG]

    [​IMG]
     
  10. siegecrossbow

    siegecrossbow PDF THINK TANK: ANALYST

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    Turn rate is correlated to lift generation. Under high AOA conditions the body and inner portions of the wing, according to the article, contribute to most of the lift.

    TVC is important and the production engine, WS-15, will be equipped with TVC. The reason that Dr. Song adapted a complex aerodynamic configuration is to assist safe recovery from high AOA conditions should the TVC fail during flight.

    Dr. Song's paper didn't go into too much detail on stealth shaping/rcs calculations. He mentioned that Caret intakes similar to the ones on the F-22 will be beneficial for RCS reduction and he also talked about using canted stabilizers to reduce lateral RCS. I don't think he did any RCS measurements in this paper.
     
  11. DrSomnath999

    DrSomnath999 SENIOR MEMBER

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    well obviously LERX + CANARD can contribute to lift no doubt about it ,

    well at what speed needs to be seen at supersonic speed or not and TVC is important for faster recovery from post stall or high angle of
    attack manuveur





    well he couldnt becoz it's very difficult thing to calculate & u have to keep in mind more u give criteria to manuverabilty more is ur penalty for
    stealth ,It is a very difficult thing to achieve complete stealth with good aerodyamic manuverabilty
     
  12. gambit

    gambit PROFESSIONAL

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    This statement is questionable...

    ...In its explanation of interferences, constructive and destructive.

    From a lateral RCS contributorship perspective, the SR-71's twin vertical stabs in their inward canted configuration enlarged the corner reflector structures, reducing their RCS contributorship from this view. However, their inward canted configuration created a sort of 'box' with the fuselage which could create constructive interference and increase RCS contributorship when view top down and slightly off angle. For the SR-71, this perspective is unlikely because of its mission and operational altitude but not for a fighter whose entire EM perspectives can be available at any time for anyone. So for the fighter, the outward canted configuration is the better option.
     
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  13. DrSomnath999

    DrSomnath999 SENIOR MEMBER

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    well true , but unfortunately j20 has outward canted vertical stabilizers i think
     
  14. gambit

    gambit PROFESSIONAL

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    It does. Out of tactical necessity.
     
  15. gambit

    gambit PROFESSIONAL

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    I suggest...

    ...Changing 'contradictions' to 'conflicts' or 'conflicting'. To say 'contradicting' is to imply no possible elimination or even compromises of factors that create said problems, which we have seen is very possible for many problems.

    I also noticed that over at your playground, there is some chatter going on about the (odd) positions of the canards during turns, particularly in these two shots...

    http://img28.imageshack.us/img28/5103/j208.jpg
    http://img3.imageshack.us/img3/6126/271698625f2882571f40410.jpg

    Pay attention to what one participant said...

    It is the flight control laws that made possible the 'harmonization' or 'coordination' of the various flight control elements that reduced the pilot's workload by that factor of 100, which is not an absurd figure.

    The first aircrafts, from the Wright Flyer to WW I era bi-planes, were negative stability designs...

    Elevator - Wright 1903 Flyer
    It took extraordinary efforts and constant attention by the pilot to maintain stable flight, whereas today an F-15 pilot can read or even nap across the ocean while his aircraft does the 'rut' work for him.

    But here is where the NASA/Wright Flyer blurb is applicable to the J-20's somewhat 'odd' and 'counter-intuitive' positions during turns...

    Now look at this shot of the canard-ed F-15 ACTIVE flight control system research and development aircraft...

    [​IMG]

    Look at the canards' positions during this landing approach.

    Why are they leading edge DOWN? Should they not be leading edge UP to maintain a safe nose-up attitude for TO/L?

    When speaking of flight control elements, use 'leading' and 'trailing' edges terminologies instead of simply 'upward' or 'downward'. Much clearer.

    By the way, the canards for the F-15 ACTIVE aircraft came from the F-18. They basically structurally reinforced the fuselage to take on the additional weight because the researchers NEEDED a surface large enough to 'blank' out or remove as much air flow across the wing as possible. The F-18's rear horizontal stab fitted the bill perfectly.

    Anyway, the canards working in conjunction or 'harmonization' with the other flight control elements calculated their necessary positions for ANY and ALL flight maneuvers. So to maintain pitch attitude stability, be it in TO/L or violent maneuvers, the canards will be 'positioned' or commanded to displace in angles that will seems to be counter-intuitive to what we believe 'should be'. Leading edge down will force the nose down or displace pitch down -- yes. But not if the elevons -- from aft -- are working to force nose up or pitch up. The canards' leading edges down is to balance out the elevons' trailing edges up. And vice versa. This is a closed loop operation in the flight control laws in that pitot/static, gyroscopes, acceleremeters, and control surfaces current positions inputs are calculated prior to and external to this loop.

    The entire process must work flawlessly if the goal is maintain contrability in an inherently negative stability design. We have a mechanical counterpart to this set of virtual laws in the F-111's and F-15's pitch-roll mixer assembly, which is a set of physical laws.

    1966 USAF Serial Numbers
    http://www.f-15.nl/hist.html
    For the F-111 and the F-15, the pitch-roll mixer assembly reduced the pilot's workload considerably when he command any maneuver. Pito/static, gyroscopes, accelerometers, and current flight control surfaces' positions are calculated prior to and external to this set of mechanical flight control laws, which is a closed loop operation. The concept works and is carried into the programming of virtual FLCS laws.

    For other delta designs that uses canards, their aerodynamics and flight control system philosophies may be -- and probably is -- different from the J-20 and that will dictate different and probably opposite commands for their canards. Virtual FLCS laws are much more flexible than mechanical ones but they are more prone to 'Byzantine faults'...

    The Risks Digest Volume 24: Issue 3
    The greater the amounts of flight control effectors, which includes thrust vectoring controls, the greater the odds of 'Byzantine faults' to occur and when they do occur, it is usually catastrophic.

    The question about the J-20's canard positions during maneuvers and why they seems to be 'odd' and counter-intuitive crosses many disciplines in avionics and programming, from philosophy to practical engineering, in flight control system designs. This is why it is no less a 'monumental' achievement by any country to R/D its own modern aircraft, military or civilian.
     
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