THE PITCH CHANGE MECHANISM :

The cylinder backplate. The disc shaped backplate provides a mounting for the pitch change cylinder. This backplate fits in front of the propeller hub and it has four clearance holes to permit movement of the operating link assembly for the blades. It is secured to the hub by the transfer sleeve housing which screws into the hub and is locked by the washer as shown below.

Transfer sleeve housing. One end of the sleeve is screwed into the hub so that the sleeve surrounds the front end of the oil tubes. The sleeve flange which secures the cylinder backplate against the front of the hub, has slots to accept the spanner used for fitting or removing the sleeve housing. A ring of holes is drilled through the wall of the sleeve, just in front of the external flange. These holes transfer governor pressure oil to the rear side of the pitch change piston which slides upon the outer surface of the sleeve.

The cylinder . The shaped cylinder is flanged and drilled at the rear for mating with, and bolting to, the cylinder backplate. The cylinder provides a working surface for the pitch change piston and a shoulder towards the front forms one part of the ground fine pitch stop. The front of the cylinder is bored to obtained access to the propeller retaining nut and to permit fitting of the pitch lock mechanism. The mouth of the bore screw threaded internally to match the lock retaining nut and the pitch change cylinder is sealed by the pitch lock cylinder cover which beds onto a seal and is secured in position by a ring nut, locking plate and circlip. Finally, a screwed plug is fitted to the hole in the centre of the pitch lock cylinder cover.

Blade operating link assembly. The operating link assembly provides the means of converting the axial movement of the piston into rotary movement to turn each blade around its axis so that the blade angle is changed by pitch change piston movement. The assembly consists of an eyebolt sleeve, eyebolt and an operating link. Each eyebolt fits inside an eyebolt sleeve which provides a working surface in the bushed hub shell. The front end of each eyebolt is secured to the pitch change piston and its rear end is attached to the front of an operating link by a pivot or link pin. The bushed rear end of each operating link fits snuggly over a pin attached to the root end face of a propeller blade. Slots in the rear of each eyebolt and sleeve allow for articulation of the operating link caused by the radial movement of the blades as the pitch change piston moves forward and backwards in its cylinder.