Helicopter rotor flexbeam

A flexbeam of enhanced out-of-plane, in-plane and torsional flexibility, for mounting a helicopter rotor blade to a hub therefor, said flexbeam being characterized by:

• first and second generally parallel, spaced beams adapted for accommodating therebetween, a pitch change shaft disposed generally parallel thereto and generally coplanar therewith;
• each of said beams including an inboard root end, an outboard tip end and adjacent inboard and outboard regions disposed therebetween:
• said inboard region being of a first geometry and having a first characteristic stiffness which, under dynamic operating conditions, renders said inboard region more compliant than said outboard region in an out-of-plane mode of vibration;
• and
• said outboard region being of a second geometry and having a second characteristic stiffness which, under dynamic operating conditions, renders said outboard region more compliant than said inboard region in in-plane and torsional modes of vibration,
• whereby the natural frequencies of vibration of said flexbeam in said in-plane and out-of-plane modes may be spaced from one another, below the range of frequencies of rotor rotation.