A 12 m long glass fiber blade has been developed for use as outer wing panels in the two Danish Nibe windmills. The outer wing is composed of a glass-fiber-reinforced plastic, in the form of a NACA 4412 section at the tip and a NACA 4420 section at the root and with chord and section thickness varying linearly along the wing. In bending tests of a 4-m portion of the blade, a compression stress of 137.5 MN/sq m was found to cause failure, and a flapwise bending moment was calculated. Natural frequencies of combined flapwise and chordwise bending have been calculated for the blade fixed at the root face and 1 m from the root face and have been verified experimentally. Aerodynamic calculations have also been performed of the power coefficient as a function of tip speed ratio for various tip chord angles for blades used in a 3-bladed and a 2-bladed rotor configuration with a diameter of 26 m.
|Publication status||Published - 1980|