Study on possible solutions of a Compound-Split transmission system for the UH-60 helicopter

Recent studies showed that the variation of the main rotor speed of the Sikorsky UH-60 (Black Hawk) helicopter offers the opportunity to reduce the propulsive power demand significantly in some flight states. Since the speed range of the turboshaft engines of the helicopter is limited and several accessories, especially the two main electric generators, require constant rotational speed, Continuously Variable Transmission (CVT) in the form of a so-called Compound-Split (CS) transmission was proposed. The aim of this study is to define a feasible drivetrain architecture for the UH-60 helicopter and to quantify expected efficiency of the drivetrain. This will be done by comparing the reliability, expected mass and rotational speeds of the drivetrain components of different solutions. The best solution contains two Compound-Split modules, one in the power path of each turboshaft engine. The resulting drivetrain is described in detail. In particular the properties of the machines forming the so-called variator and the overall efficiency are investigated.