Abstract: A hollow rotor hub is provided at the top of the rotor shaft for a multi-bladed helicopter. The blades being mounted to the rotor hub on spherical elastomeric bearings which provide for coincident rotor blade hinges for blade pitch, flap and lead-lag motions. The invention discloses a lead-lag damper contained in a housing at the center of the hollow rotor hub. The damper consists of a series of damping plates, each plate being connected to one of the rotor blades. The damping plates are separated from each other and from the damper housing by elastomeric layers bonded to the plates and to the housing. Lead-lag damping is provided by the shear in the elastomeric layers. The damper may be fastened to the air frame in a conventional manner, it may be mounted on a spindle for rotation about the rotor axis independent of rotor shaft rotation or may be free-floating and attached only to the rotor blades and not to the rotor shaft.

Abstract: In the control system for a helicopter rotor a rotating diaphragm driveably connects a rotating swashplate ring to the rotor shaft or to the underside of the rotor hub. The diaphragm is flexible with respect to displacement along and rotation about the rotor shaft axis. A centering plate connected to the stationary ring of the swashplate provide a small gap at the rotor shaft circumference sufficient to permit swashplate tilting and to maintain an acceptable tolerance. A stationary diaphragm connects the stationary ring of the swashplate to the airframe to prevent rotation of the stationary ring and to fix the radial portion of the ring centered about the rotor shaft.

Abstract: A spherical bearing for a helicopter rotor connects a rotor blade to a rotor hub. The bearing includes an outer race supported on the hub and an inner race spaced axially from the outer race supported by a shackle attached to the blade root. Each race defines a concentric spherical surface. Multiple laminates of elastomer and shims of metal are arranged alternately between the races. The laminates and shims are bonded to each other to form an assembly that is bonded to the races at radially opposite ends. Each laminate has an opening formed at its center extending through its thickness. A coupon of elastomer, whose damping characteristics exceed those of the laminates, is fitted within each opening with suitable dimensions to minimize control loads and flapwise damping, yet the coupon increases lead-lag damping.

Abstract: A redundant rotor blade retention system is disclosed. A secondary load path is provided in the event the primary load path of the rotor blade retention system fails. Both the primary and the secondary load path permit rotation of the rotor blade about its pitch axis. The rotor blade is connected to a shaft which forms a portion of the rotor hub. The shaft is pivotally connected to the housing of the rotor hub by a tie-bar, tension-torsion strap, or the like. Flanges which form an integral part of the hub housing and the shaft overlap and are spaced apart from one another. In the event the tie-bar or tension-torsion strap fails, the flanges come in contact with one another and act as a secondary load path. Lubrication is provided so that relative motion about the rotor blade pitch axis may occur between the two flanges thus permitting rotor blade pitch motion.