Large airfoil structure and method for its manufacture

A large wind-driven power plant having a rotor blade with an airfoil structure having an upper airfoil surface and a lower airfoil surface comprising:

• three modular sections consisting essentially of a leading section defining a leading edge of said airfoil, a trailing section defining a trailing edge of said airfoil, and a spar section immediate said leading and trailing sections;
• said modular sections being separately formed and subsequently assembled together to form said airfoil structure;
• said spar section being formed to consist essentially of an upper airfoil skin segment defining a part of said upper airfoil surface, a lower airfoil skin segment defining a part of said lower airfoil surface, said parts of said upper and lower airfoil surfaces extending along the section of said airfoil structure defined by said spar section and a spar including upper and lower laminate layers and at least one foam bar unit extending completely between and supporting said laminmate layers;
• said laminate layers each consisting essentially of laminate material having a unidirectional fiber orientation and laminate material having a thrust transmitting fiber orientation connected to said laminate material having unidirectional fiber orientation;
• said foam bar unit being connected between and supporting said laminate material having a unidirectional fiber orientation;
• said laminate layers of said spar forming said upper and lower airfoil skin segments.