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The science
The wind blows horizontally at speed U. The kite is a flat plate at angle of attack alpha, giving dynamic pressure q = 1/2 rho U^2 S, lift L = q CL (vertical) and drag D = q CD (downwind) with the flat-plate fits CL = 1.1 sin 2alpha and CD = 0.05 + 1.28 sin^2 alpha.
Static equilibrium: the horizontal tether force equals the drag, H = D, and the vertical force at the kite is V = L - m g, so the tether leaves the kite at tan(theta) = (L - m g)/D with tension T = sqrt(D^2 + V^2). A heavy string hangs as a parabola with constant horizontal tension; the program solves its arc length numerically so the kite height follows from the string length. Wind shear follows the power law U(z) = U10 (z/10)^0.143.
Simplifications: a rigid flat plate with no induced drag or pitch dynamics, parabolic instead of catenary string, quasi-static response with a first-order lag to gusts. The best glide angle satisfies tan^2 alpha = CD0/(CD0 + CDN).
What to try
- Press Light breeze: a big light kite still lifts; then try Heavy kite.
- Use Stalled: lift falls and drag rises, so the kite sits low and pulls hard.
- Toggle wind shear off to see how much altitude comes from the stronger wind aloft.