The strip is a chain of 24 point masses with inextensible links (position-based constraints) and a bending spring between every second node. Each node feels gravity and a flat-plate aerodynamic force from the wind component normal to the local cloth: Fn = ½ ρ Cn w Δs (urel·n)|urel·n| with C_n = 1.2, plus a small tangential skin drag. The wind is U(t) = U0(1 + gust · [0.6 sin(2πt/3.1) + 0.4 sin(2πt/1.3 + 1)]).

For a stiff (rigid) strip hinged at the boom the torque balance gives sinθ / cos²θ = ρ Cn w U² / (2 μ g); this is the orange dashed line and the lower graph. A flexible strip flaps about it. Simplifications: 2D slice (no cross-flow), quasi-steady aerodynamics with no added mass or vortex shedding, so true flutter frequencies are only qualitative. Educational model.