Blades and Brakes

In “Wind Energy for the Rest of Us,” noted wind energy authority Paul Gipe describes six approaches for early wind turbines to protect themselves from spinning at dangerously high speeds.

1.	Ailerons, or flaps, that adjust along the trailing edge of a blade to reduce performance of the rotor (blades).
2.	Tip brakes that deploy automatically at the end of the blade, adding drag to the rotor. Photo: NREL
3.	Pitchable blade tips that automatically extend and rotate, adding drag to the rotor but also eliminating the lift along the important last few feet of the blade. This is on display here on the upper blade.
4.	Air brakes, or spoilers, that automatically extend outward from the rear face of the blade. This is on display here on the lower blade.
5.	Parachutes that deployed to substantially add drag to an overspeeding rotor.
6.	Full span pitch of the blade, where the entire blade rotates its pitch angle from a high performance position to “feather,” where the blade’s leading edge faces into the wind. In feathered position, air moves equally over both sides of the blade, leading to no performance.

The early wind machines of the 1980s used passive means of achieving these protections, many using springs whose holding force was overcome by the centrifugal force generated by the fast-moving rotor. As time passed, the designs became more automated and controlled, using computers, sensors, actuators, and gears.