Aerodynamics thread

Discussion in 'Air Force' started by siegecrossbow, Mar 12, 2012.

  1. Pmichael
    Offline

    Pmichael Junior Member

    Joined:
    Mar 6, 2014
    Messages:
    278
    Likes Received:
    192
    Canards lead to less drag because it means to generate more lift with less wing area (compared to a more traditional American twin tailed aircraft), especially with movable canards. See all the Eurocanard designs which are generally described as extremly low drag aircraft.
     
    Air Force Brat likes this.
  2. Air Force Brat
    Offline

    Air Force Brat Brigadier

    Joined:
    Dec 7, 2011
    Messages:
    8,484
    Likes Received:
    9,935
    I'll give you a like, because anybody who is honestly trying to understand aerodynamics, is well ahead of the average internet poster, but I disagree, the J-20 is NOT a Euro-Canard, it has a very large canard in comparison, and it is also a "distant coupled" canard, so its large enough to add significantly to the total lift, as well as total drag, but its extremely long moment arm, (to massively increase "pitch rate"), places it into "clean" high pressure air, and while it does indeed create a strong lift enhancing vortex, the main wing is almost all in "clean" high pressure air as well.....

    The only way we can honestly assess real world drag is by the ability to super cruise or not, the F-22 is the fastest supercruiser on the planet, it also makes more dry thrust than anything else on the planet, when the J-20 gets its WS-15, we may actually be able to discuss honestly which of these airplanes is "cleaner", but for now, we will just have to wait and see....
     
  3. Pmichael
    Offline

    Pmichael Junior Member

    Joined:
    Mar 6, 2014
    Messages:
    278
    Likes Received:
    192
    You are mixing some things together.

    The J-20 has for its size a relative small wing area. All aerodynamic devices on that thing basically only exist to compensate for the lack of lifting surfaces and still provide the J-20 with fighter characteristics.
    Especially the coupled canard of the J-20 is basically optimized to generate lift.

    What does that mean for the J-20? In combination of the unique length to width ratio and with some eyeballing, I would assume that the J-20 was designed under the premisse to have as low drag as possible while providing enough lift as necessary. The recent western analysis of the J-20 being a long-range interceptor to attack crucial assets like AWACS or tankers aren't that off of my opinon regarding the J-20. It's not a traditional interceptor "fast but can't turn" but the J-20 was mostly designed for that transsonic/supersonic evelope which makes the lack of competive engines even worse.
     
    Air Force Brat likes this.
  4. latenlazy
    Offline

    latenlazy Colonel

    Joined:
    Jun 24, 2008
    Messages:
    4,234
    Likes Received:
    3,367
    At least according to Song Wencong’s design study insofar as wing area was reduced it was done so because the vortex coupling method the design uses actually generates less lift if wing area passes a certain size due to the vortices acting on a smaller proportion of the wing. In a plane ultimately what matters to total lift isn’t wing area alone but (wing area)*(lift coefficient). If the wing area is smaller but the lift coefficient is higher that works just as fine as a wing with greater area but lower lift coefficient. The size of the J-20’s canards isn’t optimized for generating lift, but actually optimized for pitch authority. That authority comes from how much lifting force the canards can generate. The J-20’s design needs it because of how much they relaxed the plane’s stability.

    Good supersonic and transonic turning performance is actually a strength for dogfighting. It’s their agility and maneuverability in those regimes where designs like the Typhoon and the F-22 derive most of their combat advantages against 4th generation fighters. Most legacy planes that were “optimized” for the supersonic envelope were optimized to maintain speed, not to have good turning performance. In that sense the J-20’s “transonic” and “supersonic” optimization is very different from, say, a Mig-31’s. Assuming the J-20 can attain good turning performance at the subsonic, supersonic, and transonic regimes with inferior engines (as was stated to be the goal in the design study), that obviates less capable engines as a detriment and actually highlights the aerodynamic design as an advantage.
     
    Air Force Brat likes this.
  5. Air Force Brat
    Offline

    Air Force Brat Brigadier

    Joined:
    Dec 7, 2011
    Messages:
    8,484
    Likes Received:
    9,935
    Not at all, especially when you add the area of the canards to the total wing area, then factor in the lifting body effect, the J-20 is right were it ought to be, compare the F-22 and the F-35A..

    The J-20 turns very nicely thank you, take a look at that "roll-over-break-out" at Zhuhai!

    yes it definitely needs the WS-15, I suppose that is the most likely answer, explaining why the fleet seems to be around 20 or so flying aircraft?

    I'm not insisting on this number of aircraft, but I really don't see any real evidence of a larger fleet?
     
  6. Air Force Brat
    Offline

    Air Force Brat Brigadier

    Joined:
    Dec 7, 2011
    Messages:
    8,484
    Likes Received:
    9,935
    Actually the canard's are an optimal size for generating lift coupled with the lift generated by the forward fuselage, you are correct in stating they are primarily for optimizing and maximizing "pitch transitions"... they perform each of these functions admirably, and they do indeed generate a very effective vortex adding to the total lift produced by the aft mounted delta main wing..

    come on, less capable engines are a disappointment to any honest assessment of the J-20, more capable engines will indeed very likely produce enough thrust to allow the J-20 to supercruise, as well as enough thrust to increase its medium altitude turning performance, and boost it into an upper level fight that's not going to happen on the present turbines....
     
  7. latenlazy
    Offline

    latenlazy Colonel

    Joined:
    Jun 24, 2008
    Messages:
    4,234
    Likes Received:
    3,367
    I’m not saying less capable engines aren’t overall a detriment to the J-20’s performance, just that if J-20’s airframe design with interim engines enables overall better performance than China’s 4 and 4.5 gen airframes then the engine isn’t making anything “worse”. Sure, the current engine is probably limiting what the airframe is capable of overall, but my point is that that hardly makes the current J-20 a slouch.

    Also, as you’re probably already aware, I’d make the case that we have some good reasons for not ruling out the possibility that the J-20 even with its interim engines can supercruise.
     
    #1107 latenlazy, Mar 29, 2019
    Last edited: Mar 29, 2019
    Air Force Brat and gelgoog like this.
  8. PhilFYW
    Offline

    PhilFYW New Member
    Registered Member

    Joined:
    Feb 6, 2019
    Messages:
    23
    Likes Received:
    21
    I thought what the study mentions is more of aspect ratio than absolute wing area. What was mentioned is that a smaller aspect ratio wing i.e. wider wing is not as efficient at generating vortexes compared to a larger aspect ratio wing i.e. narrower wing.

    But I agree, stronger vortexes could allow smaller wing to generate the same amount of lift compared to a larger wing, therefore allowing smaller wing to be used while retaining manoeuvrability. However, the paper by Dr Song is not focused on the use of smaller wing but more on the possibility to use a larger aspect ratio wing which has better area ruling but usually possesses a poorer lift coefficient compared to a smaller aspect ratio wing which usually has a better lift coefficient but poorer area ruling. The eventual solution was use of three coupled vortexes migrates the necessity of choice as a larger aspect ratio wing is able to meet a greater lift coefficient, but not the use of a smaller wing which is not mentioned as a solution.

    Perhaps this is a misunderstanding of Dr Song's study?
     
    Air Force Brat likes this.
  9. Air Force Brat
    Offline

    Air Force Brat Brigadier

    Joined:
    Dec 7, 2011
    Messages:
    8,484
    Likes Received:
    9,935
    Nice Response Bub, Dr. SongYang Wei designed the J-20 with likely hood that he would be initially operating on the AL-31's, with less thrust than say an F-119 and without OVT......

    That was the main impetus in the large distant couple canards, coupled with the aft ventral fins,,, those two aerodynamic features would allow the J-20 to be recovered from post stall maneuvering with out OVT.

    The far forward location of the "distant coupled" canards enhances pitch control and "pitch rate" in every speed regime..

    I also agree that its likely the J-20 is deceptively slippery just as the F-22, it may well supercruise in the low Mach numbers???
     
  10. Air Force Brat
    Offline

    Air Force Brat Brigadier

    Joined:
    Dec 7, 2011
    Messages:
    8,484
    Likes Received:
    9,935
    possibly you could post the section of Dr. Song's paper you are referring to, so that we might better understand your own translation of Dr. Song's ideal design??
     
Loading...

Share This Page