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.
Although the primary function of propellers is typically to produce thrust, aircraft equipped with distributed electric propulsion (DEP) may utilize propellers whose main purpose is to act as a form of high-lift device. These "high-lift propellers" can be placed upstream of wing such that, when the higher-velocity flow in the propellers' slipstreams interacts with the wing, the lift is increased. This technique is a main design feature of a new NASA advanced design project called Scalable Convergent Electric Propulsion Technology Operations Research (SCEPTOR). The goal of the SCEPTOR project is design, build, and fly a DEP aircraft to demonstrate that such an aircraft can be much more efficient than conventional designs. This paper provides details into the high-lift propeller system configuration selection for the SCEPTOR flight demonstrator. The methods used in the high-lift propeller system conceptual design and the tradeoffs considered in selecting the number of propellers are discussed.
Nomenclaturec chord length C i coefficient row vector for β surrogate model c l section lift coefficient C D0 parasite drag coefficient c i,j scalar coefficient value for β surrogate model D drag i p propeller slipstream inclination angle K L lift multiplier (i.e., ratio of blown to unblown lift) L lift L lift per unit span R radius T thrust u distance of disk upstream of wing leading edge V velocity w induced velocity from point vortex X column vector for β surrogate model, 1 u/cT α angle of attack β velocity multiplier or twist angle of local blade element Γ circulation ρ density θ swirl swirl angle
A variety of tools, from fundamental to high order, have been used to better understand applications of distributed electric propulsion to aid the wing and propulsion system design of the Leading Edge Asynchronous Propulsion Technology (LEAPTech) project and the X-57 Maxwell airplane. Three highfidelity, Navier-Stokes computational fluid dynamics codes used during the project with results presented here are FUN3D, STAR-CCM+, and OVERFLOW. These codes employ various turbulence models to predict fully turbulent and transitional flow. Results from these codes are compared for two distributed electric propulsion configurations: the wing tested at NASA Armstrong on the Hybrid-Electric Integrated Systems Testbed truck, and the wing designed for the X-57 Maxwell airplane. Results from these computational tools for the high-lift wing tested on the Hybrid-Electric Integrated Systems Testbed truck and the X-57 high-lift wing presented compare reasonably well. The goal of the X-57 wing and distributed electric propulsion system design achieving or exceeding the required " = 3.95 for stall speed was confirmed with all of the computational codes. Nomenclature Symbols # drag coefficient a angle of attack, degrees #,%&'()* drag coefficient, pylons contribution Δ delta #,,-). drag coefficient, wing contribution #,/0 drag coefficient, tip nacelles contribution Acronyms #,10" drag coefficient, high-lift nacelles contribution BSL Menter kbasic turbulence model " lift coefficient CFL pseudo time advancement Courant-Friedrichs-Lewy ",344 effective lift coefficient: " + ",%5(% DEP distributed electric propulsion ",678 maximum lift coefficient HLN high-lift nacelles ",%5(% lift coefficient from the contribution of propeller thrust in lift direction KCAS KEAS knots calibrated airspeed knots equivalent airspeed 6
As the aviation vehicle design environment expands due to the influx of new technologies, new methods of conceptual design and modeling are required in order to meet the customer's needs. In the case of distributed electric propulsion (DEP), the use of highlift propellers upstream of the wing leading edge augments lift at low speeds enabling smaller wings with sufficient takeoff and landing performance. During cruise, however, these devices would normally contribute significant drag if left in a fixed or windmilling arrangement. Therefore, a design that stows the propeller blades is desirable. In this paper, we present a method for designing folding-blade configurations that conform to the nacelle surface when stowed. These folded designs maintain performance nearly identical to their straight, non-folding blade counterparts.
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