The need for more efficient aircraft has led to the conception of innovative engine configurations, such as the combined-cycle engine proposed by Delft University of Technology or the Water-enhanced turbofan developed by MTU and Pratt & Whitney. The evaluation of the potential benefits of these novel engine concepts requires detailed performance studies considering weight and drag penalties as figures of merit. At present, no weight estimation tools with sufficient level of accuracy and flexibility are publicly available, apart from WATE++, a tool developed by NASA. However, this software is subject to export control restrictions and cannot be used outside the USA. For this reason, the development of a new component-based preliminary engine design tool, "Weight EStimation of gas Turbine engines" (WEST), was started. The goal of WEST is to predict the weight of novel engine architectures with a reasonable level of accuracy, accounting for design parameters like turbine inlet temperature, overall pressure ratio, mass flow rate, and turbomachinery configuration, with a minimal set of geometry inputs specified by the user. A previous work demonstrated that WEST can effectively predict the weight of turbofan gas generators. As only the main components are modeled, the WEST estimates account for approximately 70-90% of the actual engine weight.

The capabilities of WEST were expanded in this study to allow for the design of small-scale turboshaft engines. To this purpose, a methodology to design radial compressor disks was implemented, and successfully verified against FEM results. Regarding the modeling of the complete turboshaft, it was found that the predictions of the tool account for only 60-70% of the actual engine weight. Such result was, however, expected, as WEST does not take into account the particle separator and the integrated gearbox, which may account for up to $30\%$ of the engine's total weight.