Conceptual Design of Distributed Electrified Boundary Layer Ingesting Propulsors for the CHEETA Aircraft Concept

This paper describes the conceptual design of a boundary layer ingesting, distributed electric propulsor system for civil aircraft, supported through NASA’s CHEETA (Center for High-Efficiency Electrical Technologies for Aircraft) program. Cryogenic hydrogen fuel cellpowered superconducting electric motors power the boundary layer ingesting ducted fans to achieve high propulsive efficiency. Sizing of the integrated propulsor system is carried out using a Geometric Programming (GP) optimization framework to capture the effects of system integration on component design. A 16-propulsor configuration is presented which can meet the requirements of the CHEETA aircraft using motors similar to a previously reported 2.5MW reference design. Analysis of configurations with different numbers of propulsors shows that the aero-propulsive benefit of distributed propulsion is limited by the thermal management requirements and constraints on the geometry of the superconducting machine which do not scale linearly with shaft power. The resulting fan and motor designs are different than if each were designed independently, illustrating the importance of simultaneous optimization in the design of novel electric propulsors.