Gimbaled hub with constant velocity joint (spherical bearing and elastomeric torque links)

Gimbal: The gimbal model has been used to determine the kinematic and gyroscopic properties of the rotor. It consists in a constant velocity joint, made of two universal joints, linked to the mast and to the hub respectively at one arm of each cross. The other arm of the crosses is connected to a linkage, that transmits the torque between the mast and the hub and keeps constant the distance between the two U-joints. The hub is also linked, by means of an in-line joint, to a spherical joint on the mast that allows the gimbal motion. The gimbal allows the rigid flapping of the whole rotor and, since the direction of the angular velocity tilts together with the hub, no Coriolis forces due to this motion result in the blades when the flapping is steady. At the same time, the 1 per rev. flapping motion has no stiffness due to centrifugal effects, but only that provided by a set of springs.

The CVJ should significantly reduce the in-plane lead/lag vibration resulting from Cyclical Corollas. This is because the tip path plane is basically normal to the axis of the hub side of the CVJ. Note that there will be some Cyclical Corollas because the prying action. The forces to overcome the hub springs will result in the tip path plane (plane of blades' CGs) not being quite normal to the axis of the hub side of the CVJ.

Stiffer inplane blades will help to reduce the vibration. Some amount of undersling may also help reduce the vibration

Are (some/all) elastomeric bearings self-contained items or are the outer layers of the elastomer bonded directly to hub part?

Rotor Diameter & Blade Length; On the CVJ & HS rotor, the mast centerline to grip bolt centerline is 8.1". On the Dragonfly rotor, the mast centerline to grip bolt centerline is 20.0". This is a difference of 11.9" which is 1' greater radius for same blade length.

Mast Height: Due to the greater rigidity of the rotor compared to the teetering rotor the mast has been shortened (rotor head lowered) by a few inches.

Consider three coiled and cupped springs. The coil of each will be 270º or 630º. One end of each spring will be attached to the outer hub and the other end to the ball. A elastomer will be located between the coils of the spring. The moving of the elastomer will allow for flapping where as torque will attempt to squeeze the elastomer.

The elastomeric bearings must have just as high safety factor as the final gear train, for the vary same reason.?