PLANAR FLEXBEAM UNIT
A planar flexbeam unit ( 1, 40 ) as interface between a rotor shaft ( 2 ) and a multi-blade rotor, especially for a multi-blade main rotor of a helicopter. The planar flexbeam unit ( 1, 40 ) comprises a plurality of essentially planar torque arms ( 3 - 7, 41 - 46 ), each torque arm ( 3 - 7, 41 - 46 ) having essentially a concave profile ( 8 ) along its radial extension and being integral with its adjacent torque arms ( 3 - 7, 41 - 46 ). Each of said torque arms ( 3 - 7, 41 - 46 ) comprises two bundles ( 10 - 14 ) of straight, essentially uni-directional fibers agglomerated by a hardened synthetic resin and arranged along the essentially concave profile ( 8 ) along its radial extension. Each of said bundles passing into two essentially opposed torque arms ( 3 - 7, 41 - 46 ) without remarkable change of direction.
1 . A planar flexbeam unit that interfaces between a rotor shaft and a multi-blade rotor, especially for a multi-blade main rotor of a helicopter, comprising
four or more essentially planar torque arms, each torque arm having a concave profile along its radial extension and being integral with its adjacent torque arms,
each of said torque arms comprising
two bundles of straight, essentially uni-directional fibers agglomerated by a hardened synthetic resin and arranged along the concave profile along its radial extension,
each of said bundles passing essentially symmetrical with regard to a respective radial axis of one of said torque arms from said respective torque arm into two essentially opposed torque arms with an essentially constant curvature,
a power transmission element for transmitting power from said rotor shaft to said multi blade rotor, said power transmission element being flexible about any axis perpendicular to the rotor shaft and said power transmission element being provided with rods,
said rods being respectively articulated with a first end to an inner ring at said rotor shaft and with a second end to an outside circumference between two of said torque arms of said multi blade rotor or with a second end to the center between or aligned with said torque arms.
2 . The flexbeam unit according to claim 1 , wherein its center is provided with an essentially circular opening.
3 . The flexbeam unit according to claim 1 , wherein each torque arm has an essentially triangular shape at its root area next to its adjacent torque arms.
4 . The flexbeam unit according to claim 3 , wherein the root area has a thickness to width ratio smaller than 1:3 rectangular to the essentially planar torque arms.
5 . The flexbeam unit according to claim 3 , wherein the root area has at least one hole through the essentially planar torque arms.
6 . The flexbeam unit according to claim 3 , wherein the root area comprises a shear stiff or quasi-isotropic layered structure next to the essentially planar torque arms.
7 . The flexbeam unit according to claim 1 , wherein the torque arms comprise 5 or 6 torque arms.
8 . The flexbeam unit according to claim 2 , wherein its center is provided with integrated connection means to the rotor shaft.
9 . The flexbeam unit according to claim 1 , wherein said rods are arranged respectively radially or tangentially to said inner ring at said rotor shaft.