DEVELOPMENT OF THE TRIFLEX ROTOR HEAD.

This paper reviews the development of a new hingeless rotor hub named Triflex. This hub is made of composite materials and features flexible arms that provide blade retention, flap/lag/pitch degrees of freedom through structural deflection, and lag damping. A large part of the Triflex hub design effort has been devoted to determinationof the flexible arm characteristics, since these strongly affect the behavior of the rotor in flight. The Triflex hub dynamic characteristics were carefully checked during laboratory and whirl stand tests and found to be in agreement with theoretical predictions. Flight tests of the Triflex rotor on a Gazelle helicopter were successful in demonstrating the feasibility of the concept. Though rotor lag damping was found to be weak, no insurmountable stability problems were encountered, and the flying qualities of the Gazelle helicopter fitted with the Triflex hub were good. The next phase of the Triflex hub development will be aimed at improving the hub's structural damping characteristics and at optimizing the manufacturing process.