Composites for Advanced Drive Systems, A Systems Analysis-Revolutionary Vertical Lift Technology (RVLT)

Rotorcraft propulsion systems are continually looking to improve power density; that is reducing weight and increasing power throughput. In order to advance rotorcraft propulsion system technology, NASA Glenn Research Center (NGRC) contracted Boeing Vertical Lift (Contract #NNA15AB12B, Task Order NNA16BE07T) to perform system level benefit assessments for incorporation of composite materials into rotorcraft transmission gear and shaft systems, in the rotating frame. In general, the environment inside a typical rotorcraft transmission is aggressive for typical composite materials. Design challenges in the rotating frame and related safety risks must be understood and accounted for in the design. Boeing developed a technical approach that evaluated a relatively large population of rotorcraft main transmissions. This technical approach took rotorcraft from various size classes and configurations and applied parametric weight estimating principles to assess the performance impact of composite hybrid technologies inside transmissions, in the rotating frame. Parametric weight estimates showed that composite hybrid technologies account for an average 9% weight savings over the baseline transmissions. More weight savings may be observed when accounting for quantity of transmissions in an aircraft configuration and benefits to airframe, landing gear, and fuel systems. A weight reduction of 595 lbs was calculated for NASA's Large Civil Tilt Rotor (LCTR2) by utilizing composite hybrid components inside the Prop-Rotor Transmission in the rotating frame and accounting for design changes to the airframe, landing gear, and fuel system. In order to develop composite hybrid technologies, sub-scale and full-scale testing should continue, building on the work that NGRC has begun. Design and testing efforts should focus on technical challenges, such as joint and attachment interfaces, temperature effects, inspection procedures, and fault detection. It is recommended to address technical challenges with targeted research and development efforts, conducted at relevant scale, prior to incorporating composite hybrid technologies within the rotating frame of helicopter transmissions.