Study on Strength of Blade Fastening Bolt of a Large Controllable Pitch Propeller

Abstract

A study is performed on the fatigue life of the blade fastening bolt for the large controllable pitch propeller, based on the analysis of stress applied to the bolt and fatigue strength of the materials for the bolts. A full size controllable pitch propeller model was employed in the test to estimate the working stress in the bolts. Forces equivalent to the estimated fluid and centrifugal forces were statically given to the model propeller blade (diameter of hub : 437.5 mm) and its edge respectively. As the strength of the bolt seems to vary in accordance with the fatigue strength of materials and its rigidity, highly anti-corrosive materials such as stainless steel SUS 44 B, and copper alloys AMB 102 F and ABB-2 were employed for the test. Full size bolt head models of the three materials were also tested to estimate fatigue strength under the direct stress condition. Following conclusions are derived from the tests mentioned above. (1) The working load is distributed over the blade fastening bolts in a way quite different from that assumed by the ordinary calculating method. (2) Loads in the front side bolts of the driving face are larger than those of the other bolts. (3) Distributed load of each bolt decreases asymptotically to a certain value as the initial tightening force increases. (4) There exists the optimum combination of the hub diameter, bolt pitch diameter and blade flange thickness to make the working load of each bolt minimum. (5) The SUS 44 B shows the highest fatigue strength while the AMB 102 F and ABB-2 were lower and the lowest, respectively. (6) The optimum tightening force is found with the aid of the working load∼initial tightening force diagram and endurance limit diagram of the bolt.