CONTROLLABLE PITCH PROPELLER

 The CPP consists of a flange mounted hub inside which a piston arrangement is moved fore and aft to rotate the blades by a crank arrangement.The piston is moved by hydraulic oil applied at high pressure (typically 140 bar) via an Oil transfer tube (OT tube) This tube has and inner and outer pipe through which Ahead and astern oil passes. The tube is ported at either end to allow oil flow and segregated by seals.

Oil is transfered to the    tube via ports on the shaft circumference over which is mounted the OT box. This sits on the shaft on bearings and is prevented from rotation my a peg. The inner bore of the box is seperated into three sections. The ahead and astern and also an oil drain which is also attached to the hydraulic oil header to ensure that positive pressure exists in the hub and prevents oil or air ingress

The OT tube is rigidly attached to the piston, as the piston moves fore and aft so the entire length of the tube is moved in the same way. A feedback mechanism is attached to the tube, this also allows for checking of blade pitch position from within the engineroom  .  

 

Advantages 

 

• Allow greater manoevrability 

• Allow engines to operate at optimum revs 

• Allow use of PTO alternators

•   Removes need for reversing engines 

• Reduced size of Air Start Compressors and receivers 

• Improves propulsion efficiency at lower loads