and

ABSTRACT In an effort to advance helicopter transmission technology NASA Lewis Research Center awarded a con-Experimental tests were performed on the NASA / tract to Bell Helicopter Textron (BHT) for the design, Bell Helicopter Textron (BHT) 500-hp advanced technol- development, and manufacture of a 373-kW (500-hp) ogy transmission (ATT) at the NASA Lewis Research Cen- demonstrator transmission. The design emphasis of the ter. The ATT was a retrofit of the OH-58C helicopter NASA/BHT advanced technology transmission (ATT) was to 236-kM (317-hp) main rotor transmission, upgraded to develop a 373-kM (500-hp) version of the OH-58C 236-kW 373 kM (500 hp), with a design goal of retaining long (317-hp) main rotor transmission that would have long, life with a minimum increase in cost, weight, and i1ze. quiet life at a minimum increase in cost, weight, and Vibration, strain, efficiency, deflection, and tempera- space. This was accomplished by implementing advanced ture experiments were performed and the results were technologies that have been developed during the last, compared to previous experiments on the OH-53A, OH-58C, decade and making improvements dictated by field and UH-60A transmissions. The high-contact-ratio gears experience (2). and the cantilever-mounted, flexible ring gear of the The objective of the present study is to report ATT reduced vibration compared to that of the OH-58C. on the experimental testing performed on the NASA/BHT The ATT flexible ring gear improved planetary load 500-hp ATT and compare the results to previous experi