Abstract: The invention provides a hydraulic servo-control device which performs the same functions as a conventional device but is much cheaper to manufacture and maintain.For this purpose, the control device comprises a cylinder device formed by a cylinder and a piston rigid with a rod and a hydraulic control unit whose body is rigid with the cylinder. The body of the hydraulic control unit defines a cavity for receiving the cylinder of the cylinder device and this cylinder is made in two main parts, namely a case partly received in the cavity and fixed to the body of the hydraulic control unit, and a tubular sleeve which is axially and radially positioned inside the case and the cavity and cooperates with the piston.Application in particular in the control of the pitch of the blades of a helicopter or the ailerons of a light aircraft.

Abstract: The device comprises a directional valve body which is movable with respect to guide means, and a spool which is slidably mounted in the body and connected to a control lever. The latter is pivotally mounted on a pin which is fixed relative to the body. This pin is carried by a support which is mounted on the body and means are provided for adjusting the position of the support relative to the body.

Abstract: The piston comprises two annular members which are mounted without clearance on a tubular rod. The main annular member receives in a counter bore the other annular member without clearance. The assembly is achieved by means of a mutual forming over of the two annular members which pre-stresses a rigid ring in a groove in the rod, this ring being interposed between the two annular members. The main annular member has a second formed over portion which is engaged in a groove in the rod and is capable of performing the function of the first mentioned forming over in the event of failure of the latter.Application in control cylinder devices of helicopters.