Optimization of an Intermeshing Rotor Transmission System Design

Abstract

An intermeshing rotor drive system of the K-MAX Helicopter has been analyzed and optimized for various rotor output speed applications. The purpose of this paper is to identify different rotor speed designs and to minimize transmission weights under similar stress and component life conditions. The project is divided into two sections, analysis and synthesis. The analysis reproduces the existing K-MAX Intermeshing Rotor System, including gear dimensions, strength, durability and power carrying capacity. The synthesis provides optimal results for a constant engine input power and input speed with different rotor output speeds. The optimal design is selected analytically as a function of the best transmission weight, tooth bending stresses, contact stresses and rotor speeds. Three output rotor speeds (200, 271.4 and 350 RPM) are selected for the design study. More than 150 design cases are generated and inspected. During the optimal design, a new transmission with the best cost function constraints has been achieved. Results show that better designs for least weight and proper stress values can be obtained. At 350 RPM output speed, transmission is 11% lighter and stress values are less than the baseline design. In this study it is found that the existing K-MAX transmission is an optimum design. The re-design 271.4 RPM case for the optimum planetary gear has a new transmission weight 3% heavier than the baseline design. At 200 RPM speed design, the drive train is 28% heavier than the baseline and the stress level at each design stage is not acceptable.