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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    I think it is best (since I'm new) that I consult popeye first this time around. I do agree that the thread is getting ridiculously long.
     
  2. no_name
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    no_name Major

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    Reference area is only an arbitrary value that is affected by volume shape distribution. It is more of an equivalent area rather than actual area.

    In fact if area is all that mattered there wouldn't be much point in sweeping the wings of planes designed for high speed.
     
    #2732 no_name, May 28, 2011
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  3. no_name
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    In fact I just looked up on physics book, and that area is indeed the effective frontal area normal to the direction of airflow. In other words a swept wing with the same wing length will have less cross section area than a straight one when seen head on.

    In fact it is more about the area facing head on rather than longitudinal to the airflow.

    This is from Halliday's fundamentals of physica.
     
  4. MiG-29
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    MiG-29 Banned Idiot

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    you are correct and that is true, however the J-20 and F-22 have very similar volume distribution, thus they are quiet equivalent, the problem here is many want to see things that are not real, the J-20 was designed with compromises, stealth and aerodynamics not always will go hand in hand, any design will compromise, will have to chose between two different needs,
    I will put you an example, the F-35, the original F-35 concepts had several configurations one with canards other with tailplanes, the original X-32 was not different, from a tailess they decided to add tailplanes, they even studied the V tail.
    The J-20 has compromised, the canard position for example is not the best position however they can not put it higher than the wing unless the made the J-20 a middle or low wing but this will affect stealth, so the decided to add some dihedral to improve roll and pitch agility and reduce buffeting, they also added ventral fins to increase high AoA handling since these won`t be blanketed by the fuselage.
    The DSI inlet for example has other limitations if you change the inlet cowling you will affect the boundary layer divertion, so it has a lot of limitants, the DSI can not be used as a Variable Geometry inlet.
    what the J-20 shows is fighter that has compromised aerodynamics for stealth, in canard position and wing position, they have also compromised in size, the aircraft is quit large, but these allows them to carry more fuel and weapons.

    [​IMG]

    [​IMG]

    The studies done on the JSF concept yielded as a result that the advantages of the canard was only it added better pitch handling, however in drag both designs were quit similar if both designs used relaxed stability, however the backtailed design offers better stealth and less aerodynamic penalty

    [​IMG]

    On the J-20 the canard is not in the best position but still is useful if you want to improve the agility of a large aircraft like the J-20 is that has a wing quiet aft, this will improve supersonic trimming.

    If the J-20 will fly at mach 1.6 and cruise speeds of Mach 1.2-1.5 then the canard offers excellent qualities specially if you do not have TVC available

    by using a delta wing the J-20 reduces drag and it needs to reduce drag because it is larger than the F-22
     
    #2734 MiG-29, May 28, 2011
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  5. MiG-29
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    In this two videos you see the J-20 doing rolls at flight it never uses the canards differentially, and the main reason is it does not need it, the elevons are enough to do it without lift losses or drag increases as canard deflection would mean see by your self[video=youtube;89mJ9ddFqpc]http://www.youtube.com/watch?v=89mJ9ddFqpc&feature=related[/video][video=youtube;pZwJIv6mwzk]http://www.youtube.com/watch?v=pZwJIv6mwzk[/video]
    Note the J-10 when it take offs move its canards more than 15 degrees are quit noticeable, so there is not such thing they will use 1 degree of differential deflection to roll, it simply does not use canards, and it does it to keep lift at its max and leaving the elevons do the job without any loss of lift
    [video=youtube;SlLGk6GiDuA]http://www.youtube.com/watch?v=SlLGk6GiDuA[/video]

    For the J-20 the V tail will do the job of pitch control as the F-18 does it at take off[video=youtube;dcUmoLu6psw]http://www.youtube.com/watch?v=dcUmoLu6psw[/video]
     
    #2735 MiG-29, May 28, 2011
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  6. johnqh
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    johnqh Junior Member

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    Actually, at 1:46, the canards do seem to be at different angles. One side got the sun reflection first, then the other side.

    But who knows, I don't claim to have super eyes (unlike you) to say one way or the other.
     
  7. Inst
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    Inst Senior Member

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    J-20 isn't a canard delta design, however. It's a canard-lerx-delta design, as in the Rafale, so its aerodynamics are not directly comparable to the F-35 canard proposal.
     
  8. latenlazy
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    The effects of shaping count, and that factor is determined by the drag coefficient. Higher wing area*smaller drag coefficient vs Smaller wing area*higher drag coefficient. We wouldn't be able to tell which one has a greater overall drag. If we don't know the drag coefficient we can't say which plane has greater drag.

    Your attempt to rearrange the equation does not do anything to resolve your claim that the J-20 has higher drag, because in a situation like that we have two unknown variables, not one. If you find the drag coefficient by dividing all the other parameters by overall drag, you're essentially conceding that drag is an independent variable that must be measured (which we still do not know because we don't have wind tunnel data), and therefore in the equation to find drag coefficient the assumption would be that drag is independent of all those other factors.
     
    #2738 latenlazy, May 28, 2011
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  9. latenlazy
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    Show us. (No, a picture of their frontal view is not enough)

    Doesn't the J-20 have a higher sweep which should change the area facing the airflow? Also, doesn't the canards effectively change the area facing the direction of airflow.
     
    #2739 latenlazy, May 28, 2011
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  10. siegecrossbow
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    siegecrossbow Brigadier
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    The link to the discussion at CJDBY on our thread that I promised. The AP did a google translate on our discussion so people on the forum found it easier to read the English version!!!

    ÎÒÃÇÉóÃÀÆ£ÀÍÁËJ20,ÃÀ¹ú¾üÃÔ»¹ÔÚÌÖÂÛѼÒí!!!!!!(ÇéºÎÒÔ¿°) - µÚ2Ò³ - ¾üʳ©Ì¸ - ³¬¼¶´ó±¾Óª¾üÊÂÂÛ̳ - - ×î¾ßÓ°ÏìÁ¦¾üÊÂÂÛ̳ Super Military Forum Of China

    Any one feel like translating our 7 page banter for our Chinese friends :D?
     
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