Hughes Helicopters, Inc.

Robert E Head

Samuel S Yao

Debashis Banerjee

A universal joint for use in a pitch cone rotor system in a helicopter is comprised of crossed lift beams, one beam of which is coupled to the rotor hub and the other beam of which is coupled to the driven rotor shaft. The two crossed lift beams are coupled to each other through a cruciform case. The cruciform case in turn is coupled to each of the crossed lift beams by means of a plurality of flexures. The flexures and cruciform case are made of composite fiber materials and the flexures are soft enough to permit angular and translational deflections of the crossbeams with respect to each other thereby tending to smooth out and reduce sudden changes in rotor speed between the shaft and rotor system and thereby tending to make rotor speeds more uniform. The crossed lift beams are further coupled together at the center of their crossing by a flexible elastomeric tension link which conducts rotor loads between the two beams when the rotor develops negative lift loads on the ground and in flight. A hollow laminated elastomeric compression fitting is placed between the beams at their center to transmit the rotor lift force between them.

All composite, constant speed universal joint for use in a shaft driven

A fiberglass-epoxy flexbeam extends from tip to tip of each opposed blade pair, carrying the blade centrifugal forces so that none of the centrifugal loading is carried by the hub. The primary load-carrying connector between the flexbeam and the hub is a set of elastomeric pads. These provide a soft mount between the flexbeam and the hub to keep the primary bending moments within the flexbeams where the filaments are designed to accommodate them. The elastomeric pads are also effective in isolating the hub from chordwise loads which include the steady driving torque and the 'C' mode and 'S' modes of coriolis vibration. The elastomeric hub mount damps these vibrations and tunes their frequencies to values well separated from the rotor frequency.

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Palos Verdes Estates, CA, United States of America

Robert E Head