The pitch of the blades of an air‐screw is adjustable by means of a movable cylinder which is mounted beyond the end of the hub and moves over a fixed piston to either side of which an actuating liquid is conveyed down the hollow airscrew shaft and the cylinder has an axial extension which takes a bearing inside that shaft. The air screw shaft a4 is hollow and driven by gearing from the engine shaft a2. Inside the shaft are fitted two concentric tubes ƒ, ƒ1 of which the tube ƒ is secured to the shaft a4 by teeth ƒ2 and the mounting includes steady bearings ƒ6 which are serrated to allow oil to pass, and further steady sleeves between the two tubes are provided at ƒ3. The outer end of tube ƒ is attached to a piston g secured thereto by a nut g1. Over the piston is a cylinder h having a closed end h1 and an inner axial extension sleeve h2 which takes a bearing on the outside of the pipe ƒ on annular rings h3 and also on the inside of the shaft h4. The end of the space between the concentric tubes is closed by a plug h3. When liquid pressure is applied to either side of the piston, movement of the cylinder is transmitted to the pins m4 on the blade roots by the bolts m and links m3, the connection of the two linkages is formed as a slipper movable within a guide m5. For the purpose of ensuring oil tightness the junctions of the supply pipes j1, j2 with the supply tubes ƒ, ƒ1 are formed with spring‐held glands j4, j5, j10, j9.
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