Automatic control of propeller pitch

Abstract

The object of this study was to determine the feasibility of automatically controlling propeller pitch to reduce RPM fluctuations caused by variations in propeller speed of advance. The investigation was made ignoring the reduced frequency effect and power plant governing. A Victory Ship (AP2) was chosen as a prototype and a feedback system controlling the pitch of a controllable pitch propeller was developed. A non-linear analogue computer program approximating the system and the propeller characteristics is presented. Electronic difficulties prevented obtaining total system response from this program. The computer study indicated that a linear analysis would be useful. The linear analysis indicated that, for the prototype, in order to achieve a reduction in RPM fluctuation of 10% of that present in the fixed pitch case, a hydraulic pump consuming over 300 HP would be needed. Systems utilizing RPM, shaft torque, and thrust are analyzed. Thrust sensing provided the poorest response and in fact increased the RPM fluctuation for lower frequencies. RPM governing by automatic control of propeller pitch was found to be inadvisable unless major design changes are made to reduce the spindle torque of presently available controllable pitch propellers.