Optimal Design of Composite Helicopter Power Transmission Shafts with Axially Varying Fiber Layup

The optimal design of supercritical composite drive shafting was developed with the goal of minimum weight. A numerical optimization scheme was employed to achieve the lightest possible shaft consistent with geometric, strength, and stability constraints. In the initial stage of this research, the use of optimization methods in the design of graphite—epoxy composite power transmission shafts was effectively demonstrated, where the fiber lay‐up was held constant over the length of the shaft. This effort investigates the additional benefits associated with allowing the fiber lay‐up and thickness to vary as a function of axial position along the shaft. The method was applied to the redesign of tail rotor driveshafts (AH‐64 Apache and UH‐60 Blackhawk) and synchronization shafts (CH‐47 Chinook) to illustrate potential weight savings. The results showed that though dramatic weight savings could he achieved through the use of supercritical composite shafts, it is also possible to design subcritical composite shaft systems that are significantly lighter than current aluminum designs.