A STUDY ON CORRELATION BETWEEN PROPELLER PITCH DISTRIBUTION AND IMPROVEMENT OF PROPELLER EFFICIENCY BY PBCF

PBCF (Propeller Boss Cap Fin) is a boss cap with small fins. It recovers the rotational energy in propeller slipstream by eliminating the hub vortex and improves propeller efficiency. This paper shows how propeller efficiency with PBCF changes by changing the pitch distribution of a propeller. Three model propellers, increasing pitch propeller, constant pitch propeller and decreasing pitch propeller respectively, were made, changing the pitch ratio of each root part. They were tested in uniform flow and two different non-uniform flows, with and without PBCF. Calculation of the propeller performance was made. The results obtained are; (1) Significant efficiency improvement by PBCF was obtained for all the propellers; 2 - 8% was achieved in the model test. (2) The increasing pitch propeller, which seems to be adapted to the wake, has also been improved by PBCF. (3) It may be possible to design a more efficient propeller considering PBCF and well-matched propeller pitch distribution.