Distributed Electric Propulsion (DEP) technology uses multiple propulsors driven by electric motors distributed about the airframe to yield beneficial aerodynamic-propulsioninteraction. The NASA SCEPTOR flight demonstration project will retrofit an existing internal combustion engine-powered light aircraft with two types of DEP: small "high-lift" propellers distributed along the leading edge of the wing which accelerate the flow over the wing at low speeds, and larger cruise propellers located at each wingtip for primary propulsive power. The updated high-lift system enables a 2.5x reduction in wing area as compared to the original aircraft, reducing drag at cruise and shifting the velocity for maximum lift-to-drag ratio to a higher speed, while maintaining low-speed performance. The wingtip-mounted cruise propellers interact with the wingtip vortex, enabling a further efficiency increase that can reduce propulsive power by 10%. A tradespace exploration approach is developed that enables rapid identification of salient trades, and subsequent creation of SCEPTOR demonstrator geometries. These candidates were scrutinized by subject matter experts to identify design preferences that were not modeled during configuration exploration. This exploration and design approach is used to create an aircraft that consumes an estimated 4.8x less energy at the selected cruise point when compared to the original aircraft. Nomenclature = coefficient of drag 0 = coefficient of drag at zero lift = coefficient of lift = maximum coefficient of lift ⁄ = ratio of drag to dynamic pressure = battery specific energy = energy use per unit distance, conventional configuration = energy use per unit distance, distributed electric propulsion configuration = aircraft gross weight ℎ = altitude above mean sea level = induced drag constant ⁄ = ratio of lift to drag ( ⁄ ) = maximum ratio of lift to drag = mass of battery pack = power consumption of aircraft at cruise = specific excess power (instantaneous rate of climb capability) = rate of descent = range parameter at cruise power, no reserves = efficiency multiplier = velocity at cruise 0 = stall speed in the landing configuration , ∞ = airspeed velocity

One promising application of recent advances in electric aircraft propulsion technologies is a blown wing realized through the placement of a number of electric motors driving individual tractor propellers spaced along each wing. This configuration increases the maximum lift coefficient by providing substantially increased dynamic pressure across the wing at low speeds. This allows for a wing sized near the ideal area for maximum range at cruise conditions, imparting the cruise drag and ride quality benefits of this smaller wing size without decreasing takeoff and landing performance. A reference four-seat general aviation aircraft was chosen as an exemplary application case. Idealized momentum theory relations were derived to investigate tradeoffs in various design variables. Navier-Stokes aeropropulsive simulations were performed with various wing and propeller configurations at takeoff and landing conditions to provide insight into the effect of different wing and propeller designs on the realizable effective maximum lift coefficient. Similar analyses were performed at the cruise condition to ensure that drag targets are attainable. Results indicate that this configuration shows great promise to drastically improve the efficiency of small aircraft.

The Leading Edge Asynchronous Propeller Technology (LEAPTech) demonstrator is a wing design for a four-place general aviation aircraft with high wing loading to reduce cruise drag and improve ride quality. Takeoff and landing performance is maintained by distributing 18 small propellers across the leading edge of the wing that blow the wing and increase the dynamic pressure during takeoff and landing. This configuration presented a complicated aerodynamic design problem because the relationship of design variables such as propeller tip speed and diameter to the realized blown wing performance (most importantly, lift) is difficult to accurately predict using low-order models such as momentum theory. Therefore, the design process involved the use of various higher-order aerodynamic simulation tools, particularly the STAR-CCM+ and FUN3D RANS codes and the VSPAERO vortex lattice code. The propellers are modeled with actuator disks, although the details of these actuator disk models differ. Experimental results were then obtained by constructing the wing at full scale, mounting it above a truck on a vibration-damping frame, and driving it along a runway at the design stall speed. A comparison of these experimental test results with computational results from these analysis tools is presented. Nomenclature C L lift coefficient C M pitching moment coefficient C Lmax maximum lift coefficient Symbols α angle of attack

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.

NASA's X-57 "Maxwell" flight demonstrator incorporates distributed electric propulsion technologies in a design that will achieve a significant reduction in energy used in cruise flight. A substantial portion of these energy savings come from beneficial aerodynamicpropulsion interaction. Previous research has shown the benefits of particular instantiations of distributed propulsion, such as the use of wingtip-mounted cruise propellers and leading edge high-lift propellers. However, these benefits have not been reduced to a generalized design or analysis approach suitable for large-scale design exploration. This paper discusses the rapid, "design-order" toolchains developed to investigate the large, complex tradespace of candidate geometries for the X-57. Due to the lack of an appropriate, rigorous set of validation data, the results of these tools were compared to three different computational flow solvers for selected wing and propulsion geometries. The comparisons were conducted using a common input geometry, but otherwise different input grids and, when appropriate, different flow assumptions to bound the comparisons. The results of these studies showed that the X-57 distributed propulsion wing should be able to meet the as-designed performance in cruise flight, while also meeting or exceeding targets for high-lift generation in low-speed flight.