Balance lift, drag, weight and line tension. Find the lowest wind that lets the kite fly and see what stall does.
The science
Aerodynamic force. The wind pushes on the kite with dynamic pressure q = 1/2 rho U^2 (rho = 1.225 kg/m3). A tilted plate at angle of attack alpha feels a normal force N = q A C_N(alpha), with C_N = (2 pi / (1 + 2/AR)) sin(alpha) below stall (finite-wing lift slope) and a sharp drop beyond about 18 degrees. Lift is N cos(alpha), drag N sin(alpha) plus a small friction term.
Equilibrium. In steady wind the line must cancel lift, drag and weight: tan(theta) = (L - W) / D and T = sqrt(D^2 + (L - W)^2), where W includes the kite plus half of the line mass. If lift is below weight the kite cannot rise; the minimum flying wind is where L = W.
Gusts. The animation lets the kite swing on the line (a damped pendulum driven by the instantaneous aerodynamic force) in a wind U(t) built from three sines. The check compares this dynamic response with the algebraic equilibrium.
Simplifications. Rigid kite at fixed angle of attack (no bridle flex or tail), quasi-steady aerodynamics, straight line with a visual sag only, 2D side view with no sideways motion. Not a safety guide: keep kites away from power lines and airports.