Mathematical Modeling and Internal Clearance Optimization of Helicopter High Speed Bearing Systems Considering Temperature Variations

In this work, a comprehensive analytical model is established to study the performance of the bearings of a helicopter high speed input gear shaft. The high speed shaft, rotating above 15,000 rpm, transmits power to the second stage through a bevel gear that is straddle mounted by a duplex ball bearing and a cylindrical roller bearing. The effects of centrifugal forces, the change of bearing internal clearances due to interference fits and uneven thermal expansions are considered in the outlined approach. Then the influence of temperature elevations (that may arise due to inadequate cooling) on the performance of high speed bearings is explored by employing the proposed model. This study points out that bearing internal clearances are very critical in assessing the performance of the high speed system; and optimal manufactured bearing clearances are greatly dependent on the operating conditions. Thus, a bearing internal clearance optimization study is carried out considering different operating temperatures. This optimization study provides "operation condition maps" for high speed bearings and guides the designer for the optimal selections of bearing clearances by considering different operating conditions.