DEVELOPMENT OF LARGE ROTORCRAFT TRANSMISSIONS

This program demonstrated the feasibility of high power gearboxes for large rotorcraft and provided a new technology for gear design. One of the primary requirements for the successful completion of this program was the development of spiral bevel gears capable of carrying single mesh power far in excess of any existing design. Previous experience had pointed out serious deficiencies in conventional analytical techniques applied to high power spiral bevel gears. To more accurately predict the load capacity of these gears an extensive Finite Element Method (FEM) system was developed. This includes pre- and post-processing .programs for automated model development and data evaluation, respectively. The program utilized an existing U.S. Army HLH aft rotor transmission. This transmission was tested for 100 hours. It includes, in addition to bevel gearing, a high contact ratio (HCR) planetary system and high speed, heavy section, tapered roller bearings. Gearbox condition was monitored by full-flow debris detectors. The successful testing demonstrated resolution of earlier deficiencies in the bevel gearing. The test program included static and dynamic strain surveys of bevel and planetary gear teeth. These data were compared to Boeing Vertol experience levels in making the decision to operate at full design torque and power during the endurance portion of the program. Later, the FEM analysis was related to actual measured stresses as a verification of this new gear design tool. This paper will present brief summaries of both the test and analytical phases of this program. A substantial portion of this effort, including the FEM development, was accomplished under NASA-Lewis sponsorship (Contract NAS3-22143), "Large Rotorcraft Transmission Technology Development Program", The NASA Project Engineer was Mr. N. Samanich. The Boeing Vertol Project Engineer was Mr. J.C. Mack. Mr. R.J. Drago was Technology Manager.