Development of a Conceptual Design Model for Aircraft Electric Propulsion with Efficient Gradients

Research on electric aircraft propulsion has greatly expanded in the last decade, revealing new insights on the unique features of the electric aircraft design problem, and identifying shortcomings in existing analysis techniques and tools. In this paper, we survey currently-available analysis codes for aircraft with electric propulsion. We introduce a new conceptual design and optimization toolkit-OpenConcept-built for aircraft incorporating electric propulsion. Open Concept consists of three parts: a library of simple, conceptual-level models of common electric propulsion components; a set of analysis routines necessary for aircraft sizing and optimization; and several example aircraft models. All of Open Concept's codes have been analytically differentiated, enabling the use of OpenMDAO 2's efficient Newton solver, as well as gradient-based optimization methods. Open Concept supports parametric cost modeling and waste heat management at the component level, enabling realistic thermal and economic constraints in optimization studies. We present a case study involving the electrification of existing turboprop airplanes. We model the Daher TBM 850 and Beechcraft King Air C90GT in Open Concept, and validate the sizing, weights, fuel burn, and takeoff field length analyses. We then define a series hybrid electric propulsion architecture for the King Air, and perform a retrofit study. Finally, we perform multidisciplinary design optimization to minimize both fuel burn and trip cost for varying design ranges and assumed battery specific energy levels. We ran more than 750 multidisciplinary optimization cases with full mission analysis. Each optimization runs in approximately 2 minutes on a typical notebook PC. We demonstrate that Open Concept is a flexible and efficient way of performing conceptual-level analysis of aircraft with unconventional propulsion architectures.