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List of kite passive-stability factors, with intro and notes

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  • dave santos
    Each kite degree-of-freedom (DOF) is a Lyapunov unstable-periodic-orbit (UPO) with an associated exponent that is chaotic when positive. The kite is like many
    Message 1 of 2 , Dec 29, 2012
      Each kite degree-of-freedom (DOF) is a Lyapunov unstable-periodic-orbit (UPO) with an associated exponent that is chaotic when positive. The kite is like many dynamical systems, with major UPOs driving bulk dynamics, and other UPOs contributing nonlinear complexity. Multiple positive Lyapunov exponents are formally hyperchaos which drastically shorten the effective model-predictive control horizon. Eliminating maximal exponents much as possible with strong inherent stabilities makes reliable AWES control far easier. This is the "Low Complexity AWES School".

      The major DOF/UPO of a simple kite is its elevation, with the ground as literally the "ground state" of lowest energy, and major chaotic attractor ("What goes up must come down," in classic aeronautics.). Note that line extension is another DOF coupled in, but under deterministic control, as long as tension exists. The ontology only gets messier, but a dozen or so DOFs are easily found in even simple kite systems (Don't forget the wind's DOFs'. See Pyragas and OGY for chaos control theory background.

      So what are the aerodynamic stability factors that a kite designer can work with? Here is a partial list-

      General Stability Factors- 

             Compliant Damping- flexibility, porosity, visco-elasticity, minimal-mass, good-balance.

            Tether Tension Stability- maintained elastically (passive compliance) or by reeling and pay-out (active compliance).

            Form Stability- sticks or inflated shapes passively maintain geometry.

            Anchor Stability- ground or vehicle resistance to movement.

            Skin Stability- battened or stretched surfaces (including inflation pressure).

      Yaw Stability-

           Pendulum Stability- too much undamped pendulum force promotes chaotic instability.

           Rudder Stability- kite tails damp pendulum oscillation by Pyragas inputs.

           Snowplow Stability- differential wing tip drag with the leading wing developing more drag and the trailing wing "hides" from the flow.

           Arch Stability- kite staked out crosswind deterministically.

      Pitch Stability

           Fore and Aft Bridling Stability- Characteristic in kites.

           Elevator Stability- Same method as general aircraft.

           Wing Reflex Stability (TE kicked up and/or upturned nose to prevent diving).

      Roll Stability-

           Arch Stability- Scalable; cannot roll

           Cross-bridle Stability- Good roll protection but requires spreading force (stick or wind pressure)

      Bouyant or Ballasted Stability-

           LTA is passively bouyant. Ballast can stabilize a kite at the ground state.
           Neutral Bouyancy is an approximation for the lightest kites in low wind, with a thermal boost; not a stable.
      Lift Stability is the passive quality of a kite "pasted to the sky".

      Drogue Stability is the passive quality of being stretched downwind.

      Windfield Stability is a four dimensional constancy, which sometimes is approximated in natural wind.

    • Joe Faust
      OGY * Oh God, Yeah! * Chaos control studies: Ott, Grebogi and Yorke method. * http://www.scholarpedia.org/article/Controlling_chaos
      Message 2 of 2 , Dec 29, 2012


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