Rotating Controls
Last updated
Last updated
The rotating controls convert non-rotating flight control inputs from the rotor flight control system into rotating control inputs to the rotor hub. These controls cause the resultant lifting force vector to tilt away from the main rotor shaft axis which moves the helicopter in the direction of the resulting force. It is composed of the components that follow:
The swashplate and support is located on the top of the transmission with the main rotor shaft passing through its center. The parts of this assembly are made of aluminum alloy and steel. A heavy rubber boot on the top of the swashplate assembly prevents the intrusion of foreign material. The swashplate and support assembly consists of the parts that follow:
The support assembly is bolted to the top of the transmission. At its bottom is a flange that provides the means to bolt it to the top of the transmission, and at its top is a hollow cylindrical tube through which the main rotor shaft passes. It is made of aluminum alloy and steel and has a hard anodized or tungsten carbide surface treatment on the exterior cylindrical portion that makes it wear-resistant. There is one support assembly per swashplate and support assembly.
The pivot sleeve assembly slides over the cylindrical portion of the support assembly. It is cylindrical on the bottom and has a spherical portion its top which forms the bearing surface that the swashplate rotates about. There is a slot in the center of the sphere that runs parallel to the main rotor axis that, when engaged with the stud of the outer ring, prevents the swashplate from slipping along the axis of the main rotor shaft. The parts of this assembly are made of aluminum alloy and steel. There is one pivot sleeve assembly per swashplate and support assembly.
The inner ring assembly is non-rotating and provides attachment lugs for the non-rotating vertical control rods that are actuated by the flight control system. It is separated from the outer ring by bearings and is made of aluminum alloy and steel. There is one inner ring assembly per swashplate and support assembly.
The outer ring assembly rotates and provides attachment lugs for the pitch links that attach to it and to the pitch horns on the rotor blades. It is separated from the inner ring by bearings and is made of aluminum alloy and steel. There is one outer ring assembly per swashplate and support assembly.
The V-shaped collective lever connects to the support assembly and to the pivot sleeve and is hinged in such a way that it prevents the pivot sleeve from rotating when the main rotor shaft turns. Pushing on it causes the pivot sleeve to slide up or down over the cylindrical portion of the support assembly. The parts of this assembly are made of aluminum allow and steel. There is one collective lever assembly per swashplate and support assembly.
The pitch link assemblies connect the rotating outer ring of the swashplate assembly to the pitch horns of the main rotor hub. It consists of the parts that follow:
aluminum alloy tube
corrosion resistant steel bonded inserts
corrosion resistant steel clevises
There are two pitch links per helicopter.
The swashplate drive assembly is comprised of a collar set that attaches to the drive splines on the mast assembly. The collar set attaches to an idler lever and an idler link assembly. The idler link attaches to the drive pin on the swashplate rotating outer ring. These assemblies allow the mast assembly to drive the rotating outer ring assembly of the swashplate and support assembly.
The idler link attaches to the drive lever at its top and to the swashplate rotating outer ring at its bottom. Both of these mechanical connections are assembled with bushings and threaded fasteners which allow the parts to rotate about the bushings. The parts of this assembly are made of aluminum alloy and steel. There is one idler link assembly per helicopter.
The drive lever attaches to the collar set swashplate drive assembly and to the idler link assembly. Both of these mechanical connections are assembled with bushings and threaded fasteners which allow the parts to rotate freely about the bushings. The parts of this assembly are made of aluminum alloy and steel. There is one drive lever assembly per helicopter.
The collar set swashplate drive attaches firmly to the mast assembly and with bushings and threaded fasteners to the drive lever assembly. The parts of this assembly are made of aluminum alloy and steel. There is one collar set swashplate drive assembly per helicopter.
The swashplate receives the flight control inputs from the non-rotating inner ring assembly. The flight control inputs consist of a mix of two separate inputs from the flight control system that are mixed mechanically by the mechanism of the swashplate. The swashplate converts these mixed control inputs to rotating inputs at the rotating outer ring assembly.
The two inputs mixed together are those from two independent sources: the flight control system that represent cyclical pitch commands and those that represent collective pitch commands.
The first input (cyclical) consists of two pushrods attached to the non-rotating inner ring of the swashplate. As these pushrods are pushed up and down, they tilt the swashplate which converts this non-rotating control to a rotating control that go to two pitch link assemblies which change the pitch of the main rotor blades.
The second input (collective) attaches to the collective lever assembly. It raises or lowers the push rod connected to the apex of the V shaped collective lever assembly. When this pushrod is pushed upward, this moves the pivot sleeve assembly downward since the middle of the collective lever assembly is held in place by a link attached to the support assembly that forms a hinge point. So the collective lever assembly is a see saw hinge with the pushrod at one end and the pivot sleeve assembly at the other. When this pushrod is pushed downward, this moves the pivot sleeve assembly upward. The pivot sleeve fits over the support assembly and uses the support assembly as a slide. As the pivot sleeve assembly raises or lowers so does the swashplate. As the swashplate is raised, the pushrods are moved upwards which increase the pitch of the blades, and as the swashplate is lowered, the pushrods are moved downwards which decrease the pitch of the blades.
The collar set swashplate drive assembly, drive lever assembly and idler link assembly form a multi-hinge mechanism that attaches to the main rotor at one end to the swashplate rotating outer ring assembly at the other end. This mechanism keeps the rotating outer ring assembly aligned with the main rotor shaft as it turns. This ensures that the pitch link assemblies do not slip on the main rotor shaft when the main rotor rotates. The mechanism swivels to allow the mechanism to keep the outer ring aligned with the main rotor shaft regardless of the swash plate orientation.
The main rotor shaft passes through these assemblies.