A mechanical damper has been developed to control edgewise vibration on blades of stall regulated wind turbines, claims Colin Anderson of blade manufacturer Aerpac UK. Edgewise vibration can cause a loss of energy capture and is associated particularly with rotors of 40 m diameter and above. Concern has been expressed that the problem could be a warning that the industry was reaching the end of one level of technology. Aerpac's solution is a tuned absorber inserted inside the rotating tip brake. Results show the damper can increase the annual rotor energy output by 5%, says Anderson.