We analyse some of the main challenges in the geared mechanical transmissions of modern aeroengines such as large-bypass-ratio turbofans, open rotors and turboshafts/ turboprops in terms of efficiency, power density, weight, and reliability down to their casualties and present related models from recent research. We demonstrate limits to the existing architectures and, following basic principles of mechanics, we discuss how different topologies and interface geometries may help affect force- and torque-transfer to produce better efficiency, material utilisation, power density and light weight, insensitivity to errors and perturbations, including fail-safety, and ultimately higher reliability and lower cost. Beyond its strict disciplinary focus, we use the presented case to raise questions regarding how to approach design effectively at the level of architecture and how to reconcile simplicity, where one may hope to find design intent, with complexity and the realm of “the details”, where the devil proverbially resides.
