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 capacity and efficiency. In order to advance rotorcraft propulsion system technology, NASA Glenn Research Center (NGRC) contracted Boeing Vertical Lift to perform system level benefit assessments of designing composite materials into rotorcraft transmission gear and shaft systems. In general, the environment inside a typical rotorcraft transmission creates issues for typical composite materials. In flight critical gears and shafts, design challenges and safety risks associated with introducing composite materials must be understood and accounted for in the design. Boeing was able to develop a technical approach for the system study that covered a relatively large population of rotorcraft main transmissions. This technical approach evaluated rotorcraft from various size classes and configurations and applied parametric estimating methods to assess the performance impact of composite hybrid technologies inside transmissions, in the rotating frame. Parametric weight estimating showed that composite hybrid technologies account for an average 9% weight savings over the baseline transmissions. More weight savings may be observed when various other aircraft systems are considered. Tandem and Tilt-rotor aircraft use similar transmissions at the forward/aft rotor head and left/right side of the aircraft, respectively, doubling estimated weight savings of a single transmission. Other aircraft systems, such as airframe, landing gear, and fuel systems benefit from reduced propulsion system weight, and, therefore, lighter weight aircraft are possible when propulsion system weight is reduced. In this paper, a systems level technical approach is summarized which was used to assess the performance impacts of introducing composite materials inside helicopter transmissions, in the rotating frame. Existing composite technologies, technical challenges, and general material selection guidance were used to develop the technical approach. Transmissions from a multitude of rotorcraft configurations and power classes were studied to build a database of expected performance gains. Component designs were developed using composite materials to varying levels of fidelity in order to develop data used for parametric weight estimating. The component designs are compiled and averaged with similar, existing designs in order to build a robust dataset for weight estimating purposes. Using information developed during the component design phase, technical challenges were defined.