A conceptual design study of a distributed electric propulsion transport aircraft is presented. The objective is to study the applicability of distributed electric propulsion configurations to aircraft serving thin-haul airline routes. A hybrid powertrain is selected, such that shorter routes can be flown operated electric, while longer routes can be operated with a range extender, to reduce the required battery size. Two range extender options are examined: a modern turbodiesel and an advanced recuperated turbogenerator. Conventional fuel-powered aircraft are designed in parallel to the same mission and constraints, to illustrate the impact of the electric propulsion configurations on the chosen metrics. An operating cost model is assumed, to estimate the commercial viability of the different designs. The advanced concepts are generated and analyzed using purpose-built conceptual design tools, with optimization employed to minimize a weighted average operating cost of a short battery-powered flight and a longer hybrid-powered flight. The analysis tools are also used to model existing aircraft for comparison. Plots of various trade studies are presented. The results suggest that the configurations examined in this study present an advantage in operating costs over conventional aircraft, in addition to assumed noise and emissions advantages. Nomenclature APropeller disk area A u Propeller disk area less obscured area AR Wing aspect ratio AR j Aspect ratio of blown wing segment bWingspanMotor diameter eSpan efficiency e 0Oswald efficiency J Propeller advance ratio M Propeller figure of merit m wing Mass of the wing M s Propeller figure of merit (not including swirl losses) N z Ultimate load factor P min Minimum engine size P shaft Shaft power * Aeronautical Engineer, 340 Woodpecker Ridge, AIAA Member. † Chief Aerodynamicist, 340 Woodpecker Ridge, AIAA Member.

Theoretical and numerical aspects of aerodynamic efficiency of propulsion systems coupled to the boundary layer of a fuselage are studied. We discuss the effects of local flow fields, which are affected both by conservative flow acceleration as well as total pressure losses, on the efficiency of boundary layer immersed propulsion devices. We introduce the concept of a boundary layer retardation turbine that helps reduce skin friction over the fuselage. We numerically investigate efficiency gains offered by boundary layer and wake interacting devices. We discuss the results in terms of a total energy consumption framework and show that efficiency gains of any device depend on all the other elements of the propulsion system.