BEHAVIOUR OF A CONTROLLABLE-PITCH PROPELLER IN DIFFERENT OPERATING CONDITIONS

The Authors, of El Pardo experiment-tank, first examine the advantages of the controllable-pitch propeller, discuss some general problems of c.p. propeller design, and explain some basic concepts of flow and cavitation at a blade section. Much of the paper is then devoted to a detailed account of cavitation and other model tests carried out during the design of the c.p. propellers for a twin-screw corvette. In addition to providing a means for going astern, c.p. propellers were chosen for this ship mainly to allow only one of the two engines (geared Diesels) per shaft to be used when cruising and both engines per shaft to be used when full power was needed. Maximum efficiency was required when the propellers were absorbing the total power at rates rpm. The propellers were designed by lifting-line theory, with some corrections, based on lifting-surface theory, to pitch and camber. Four different models were tested, including one designed for a condition intermediate between full power and cruising power, and the results are presented and discussed. Some conclusions are drawn on c.p. propeller design in general and on the methods used in the design of the propellers for the corvette. Order from BSRA as No. 49,239.