Load Sharing Test of the CH-53K Split Torque Main Gearbox

After careful review and consideration of the new technologies required for the development of the new CH- 53K heavy lift helicopter, an independent review panel consisting of the Program Office personnel, Sikorsky, NAVAIR, and U.S. Army technology experts has decided to assign a Technical Readiness Level (TRL) 4 to the proposed Split Torque Main Gearbox (MGB) configuration. A risk reduction test of the load sharing concept was required in order to mitigate the MGB risk to a minimum acceptable TRL 6. Balancing the loads within the redundant multiple path gear train is necessary for the aircraft gearboxes where a high power-to-weight ratio is essential. The proposed main transmission for the USMC CH-53K helicopter includes torsionally soft quill shafts to achieve uniform torque split. The quill shafts are designed to steadily and equally distribute input torque to improve durability of the transmission. The CH-53K Main Gearbox is designed to operate at 35% higher power than the CH-53E transmission. This paper describes the concept of the gear train load sharing configuration of the CH-53K Split Torque Main Gearbox including a detailed discussion of the risk reduction efforts, the tested gearbox layout, and the results of a 200 hour endurance test performed from September 2007 through February 2008.