A Functional Evaluation of a Thrust Carrying Cylindrical Roller Bearing Design

A special 60 mm bore cylindrical roller bearing was designed to support the radial and thrust loads developed by a spiral bevel input in a Blackhawk size helicopter transmission. Two prototype bearings were fabricated and tested in a laboratory environment at various loads and speeds simulating that of the application, culminating in a combined load of 7.12 kN radially and 6.79 kN axially at 21,500 rpm. Lubrication was provided by circulating Mil-L-23699 synthetic lubricant into the bearing from jets located on each side and through inner ring supply holes directing the flow to the flange surfaces. Thirty-two hours of operation were accumulated. Detailed examination of the bearing surfaces conducted visually and using the scanning electron microscope established that no abnormal deterioration of the load-supporting contact surfaces had been experienced. It was concluded that the bearing performed satisfactorily and warrants further consideration for application in helicopter transmissions. In addition, an experimental test series was conducted to evaluate bearing performance under predominant thrust loading. This was completed at 1.3 × 106 Dn maintaining the applied axial load at 6.79 kN while reducing the radial load until a thrust to radial load ratio of 9.5 was achieved without difficulty. The condition of the load-supporting contact surfaces after this test was again quite good although the contact patterns were altered. It was concluded that the bearing design also has the potential to operate in this more severe loading environment.