Why does raising the sail reef angle slow the windmill down?

Reefing (increasing the pitch angle β) is the historical way a miller shed power in strong wind — it lowers the power coefficient Cp at a given tip-speed ratio, cutting the aerodynamic torque driving the sails and letting the rotor settle at a lower, safer speed.

What happens when the millstone is engaged?

Engaging the millstone adds a load torque that grows with the square of rotor speed. That extra resistance pulls the tip-speed ratio toward the value where the power coefficient peaks, which is why real windmills are loaded rather than left to free-wheel.

Home▸Engineering & Materials▸Dutch Windmill Farm: Wind Power & Grain Milling (2D)

Dutch Windmill Farm: Wind Power & Grain Milling (2D)

2D windmill-farm lab: a real turbine power-coefficient curve, tip-speed ratio, sail reefing and grindstone load drive rotor speed and mechanical power output as wind speed changes.

Engineering & Materials2DModerate60 FPS📱 Mobile-adapted⇄ 3D version

This 2D companion swaps the 3D scene's orbiting sunset view for the actual physics behind it: a real turbine power-coefficient curve maps wind speed, sail radius and reef angle to aerodynamic torque, the rotor's own moment of inertia integrates that torque into angular velocity frame by frame, and engaging the millstone loads the shaft with a speed-squared resistance so you can watch tip-speed ratio, power coefficient, mechanical power and an illustrative grain-milling rate all respond together as conditions change.

⚙ Under the hood

2D windmill-farm lab: a standard Cp(λ,β) turbine power-coefficient curve, rotor inertia integration and a speed-squared grindstone load drive rotor speed and mechanical power output as wind speed, sail radius and reef angle change.

wind powerpower coefficienttip-speed ratioenergy conversionwindmillgrindstone load

2D · HTML5 Canvas 2D · 60 FPS target · runs fully client-side, no install