Kite Flight Physics (2D): Lift, Torque & a Sagging Tether

Wind

Wind speed 1.10

Gustiness 0.80

Wind angle from horizontal 10°

Tether

Line length 18.0 m

Flight

Readouts

Altitude

0.0 m

Line tension

0 N

Angle of attack

0°

Wind speed

0.0 m/s

How the physics works

The kite is a rigid body with position, velocity, orientation and angular velocity. Each frame:

Relative wind = wind field − kite velocity; angle of attack = angle between the kite's face normal and that relative wind.
Lift coefficient C_L = sin(2·AoA), drag coefficient C_D from a stall-shaped curve — both act through the centre of mass.
The bridle point is offset from the centre of mass. When it strays past the line length, a spring–damper tension pulls it back — that off-centre pull is the only source of torque, exactly like a real kite weathervaning on its line.
The tether itself is a separate Verlet-integrated chain of segments hanging under gravity, so the line visibly sags rather than being drawn as a straight rod.

C_L = sin(2·AoA)
C_D = 0.18 + 0.45·(1 − cos(2·AoA))
τ = (bridle − CoM) × F_tension

Tether (Verlet chain) Kite sail Tail ribbon