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[ksurf] Re: R: Aspect ratio .vs. performance

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  • Mark Frasier
    ... because of ... C-Quad is ... The CQuad is faster because it has a higher lift-drag ratio. It gets that from having fewer bumps across the back (which
    Message 1 of 3 , Sep 5, 1999
      At 08:08 AM 9/5/99 -0400, you wrote:
      >> It is true that a C-Quad pulls more than a Peel, but this is not
      because of
      >> aspect ratio difference. Many more things are involved, one of which is
      >> speed. A faster kite will pull more than a slow one due to the factor that
      >> power increase 4 times as the speed doubles. Peel is a slow kite,
      C-Quad is
      >> a fast kite.
      >So what exactly makes the C-Quad a faster kite than the Peel and the
      >N-Gen? Also, what are the other factors that make a C-Quad a higher
      >performance kite?
      >If a low aspect ratio framed single skin kite has higher performance
      >than a higher aspect ratio ram air foil kite, does it mean that framed
      >single skin kite is the better way to make a kite?

      The CQuad is faster because it has a higher lift-drag ratio. It gets that
      from having fewer bumps across the back (which create "parasitic drag"
      (whatever that means...)), a fairly high lift:drag profile, fewer bridle
      lines, a very clean leading edge and probably some other stuff. It also has
      a high coeffecient of lift, which means more lift at lower speed, which is
      a function of the profile shape (the shape of the airfoil).

      You could make a C-Quad-like kite with a higher lift:drag ratio. You might
      start by increasing the aspect ratio, using unsleeved spectra for the
      bridle, and tweaking the angle of attack. The thing is, the lift:drag is
      already good enough that it overflies the edge of the window if the wind
      isn't good. Higher L:D ratio would mean more overflying, especially for
      less experienced users. The lower aspect ratio makes the kite steer quicker
      and seems to generally improve handling (at least if you like a responsive

      Like Roberto said, there are many factors that determine kite performance.

      One interesting thing about a single skin kite is that it has less inertia,
      which means it can accelerate faster. The air inside a foil can reportedly
      have more mass than the kite itself (10 cubic feet of air = about 1 lb.).
      So I think the CQuad can reach its top speed sooner, which might mean you
      could use it on shorter lines, or at least have full power in a greater
      portion of a "sweep".

      Peter Lynn seems to think a good rigidly-framed delta can beat what we're
      using now (CQuads, Qaudrifoils, etc), at least in some conditions. Here are
      some quotes from the PL site:

      (from October 98 newsletter)
      ...by now three, large C Quads in Holland took the first three places in a
      well attended 2 day club meeting- though observers noted that a 4 sq.m.
      delta style 2 line kite was clearly fastest on the reaching legs (but not
      the upwinds) in the gusty conditions on Sunday.

      (from Buggies Boats & Peels, written in 1993. MMR is max. to min. pull
      ratio across the window)
      Rigid Frame Stunt Kites
      Before developing the "Peel" range of soft stunters I used rigid frame
      delta style stunt kites extensively for kite traction. They have
      considerable natural advantages: control is good, kites can be made in
      almost any desirable size (I built a series of 5.5m wing span stunters) or
      smaller stunters can be stacked to get sufficient pull. They have a built
      in mechanism to improve M.M.R.. By utilising spar flex and skin stretch,
      delta style stunters automatically "twist off" at their wingtips as pull
      increases giving very good M.M.R. This desirable characteristic can be
      enhanced by building stunters with extra windtip area, held out by battens,
      which only generates lift when the kite's apparent wind is low. Although
      the recent trend has been for delta form stunters to tend towards long
      tapered wingtips the reason for this has particularly to do with the rules
      and requirements for "precision" stunt kite competitions. Kites for
      traction don't need to follow this trend. One kite style that should have
      considerable potential as a traction kite, for the reasons outlined above,
      is the Volkensturmer 101 from Germany. Another design which should also
      have very good inherent M.M.R. is the speedwing from Vlieger Op in Holland.
      Lacking a spine, it contrives "twist off" in the middle of the skin again
      by spar flex and skin stretch.

      (from april 99 newsletter)
      A major new product this month; We have purchased non-exclusive rights to
      manufacture and sell the Bob Dawson (Leading Edge Kites, Coff's Harbour)
      "Osprey" series delta style 2 line traction kites. Actually this is not a
      sudden decision. We have been following Bob's work with close interest for
      some years, looking for a traction kite that excels in strong gusty winds
      to complement our Peels, NGens and C Quads. We believe that "D Wings"(our
      name for this new range) will outperform all other traction kites in some
      conditions, and not just in the Southern Hemisphere either! Their handling
      is what sets them apart; somehow Bob has retained the power, speed and gust
      responsiveness that delta's are renowned for while tightening the turns,
      eliminating almost all oversteer and building in luff resistance that just
      has to be experienced.

      (from Kitesaling)
      *DELTA style 2 line framed kite. These currently have the best automatic
      depowering characteristics of all traction kites (by twisting off at the
      tips in the same way that windsurfer sails depower by twisting off.), very
      good lift coeff�s (power for size), excellent L/D (good upwind) and unique
      luff resistance.
      On the down side, above about 5 sq.m�s, even with carbon it becomes
      difficult to make frames for deltas that are strong enough within weight
      limits for good light wind flying. Additionally, rigid frame kites like
      deltas tend to break up when swilled around in breaking waves and the
      bigger they are the worse this tendency is.

      Mark Frasier
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