J-20... The New Generation Fighter II

Discussion in 'Air Force' started by Asymptote, Jan 10, 2011.

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  1. siegecrossbow
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    siegecrossbow Brigadier
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    This is the abstract of Dr. Song Weng Cong's article. Let me briefly summarize:

    The "future fighter" will not only have good manoeuvrability at medium and low heights but have the ability to supercruise. The future fighter mentioned in the article is, in essence, a stealth fighter whose design will reduce drag as well as maximize lift.

    I just find it funny that Dr. Song's work, presumably the result of 10s of thousands of hours of windtunnel testing, could be so easily dismissed by visual inspections of a few photographs.
     
  2. johnqh
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    johnqh Junior Member

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    Some other interesting points in Dr Song's paper.

    Dual all-moving vertical stabilizers, relative size of 10% to 13% (normally 20% to 25%).
    Use of movable LEX to control under high AoA. (I guess it is possible to use canards for the same purpose)
    Some charts shows testing result with AoA as high as 60%.
     
  3. MiG-29
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    MiG-29 Banned Idiot

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    LEX or LERX stands for leading edge root extention, in the english language it does not matter the size, however the size and shape will affect some aerodynamic qualities of the aircraft, long thin LERXes increase pitch up tendencies, LERXes have the function of increase lift at high AoA but they add bit of drag too
     
  4. MiG-29
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    Those are LERXes you can not deny it, LERX stand for leading edge root extention, therefore the Rafale has LERXes, size and shape do matter that is true, longer they are increase pitch up tendencies, however LERX are called sometimes strakes, shape also matters higher angles of sweep increase the vorticity strength, that is the reason you have very sharp LERXes on the Su-27, LERXes also move the main wing center of lift forward, so they add a degree of relaxed stability to the whole design.

    Since LERXes were used and studied in the West first specifically F-5, F-16 and later on MiG-29, the technical terminology is Western in origin regadless in China they use another one.
     
  5. siegecrossbow
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    siegecrossbow Brigadier
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    never mind
     
    #2645 siegecrossbow, May 27, 2011
    Last edited: May 27, 2011
  6. MiG-29
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    MiG-29 Banned Idiot

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    The only moveable LERXes in existance are find on the T-50 and Naval LCA and these are called LEVCON
    LEVCON


    LEVCON ( Leading Edge Vortex CONtroller ) is a deflectable aerodynamic device in wing apex region LEVCON surface is deflected +20 (down) to 30 (up) from its neutral position.Downward deflection of LEVCON is used for reducing aproach speed for carrier landing



    And effectively canards do the same thing LEVCONs do however the LEVCON does not increase the drag as canards do since they do not generate downwash
    [​IMG]

    [​IMG]
     
    #2646 MiG-29, May 27, 2011
    Last edited: May 27, 2011
  7. MiG-29
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    MiG-29 Banned Idiot

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    The drag equation states that drag (D)is equal to a drag coefficient (Cd) times the density of the air (r) times half of the square of the velocity (V) times the wing area (A).
    D = .5 * Cd * r * V^2 * A

    pay attention Drag is equal to times the wing area (A).
    area is importat since it is multiplying a bigger area makes for a bigger result, thus the J-20 having a longer fuselage will have higher drag, of course shape matters but since both designs have similar cross sections they won`t have a big difference in shape you can not expect the J-20 to have lesser drag just a relatively higher but not by much in the best case
     
  8. Schumacher
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    Schumacher Senior Member

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    Now you know. Dr Song and his J20 have ruffled some serious feathers.
    Hell hath no fury like a fanboy scorned. LOL
     
  9. Quickie
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    The equation doesn't tell you anything without the required data. The Cd is different for different aircraft wings. This is in addition to different Cds for different aircraft bodies.
     
  10. Quickie
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    All vortex generating surface increases drag, including the LEVCON, although the vortex generated may in the end reduce the overall drag. The canard or tail elevator both generate downwash/upwash for pitch control reason.
     
    #2650 Quickie, May 27, 2011
    Last edited: May 27, 2011
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