Aerodynamic Optimization Trade Study of a Box-Wing Aircraft Configuration

Abstract

This study investigates the aerodynamic trade-o s of a box-wing aircraft configuration using highfidelity aerodynamic optimization. A total of five optimization studies are conducted, where each study extends the previous one by progressively adding a combination of design variables and constraints. Examples of design variables include wing twist and sectional shape; examples of constraints include trim and stability requirements. In all cases the objective is to minimize inviscid drag at a prescribed lift and a Mach number of 0.78. Aerodynamic functionals are evaluated based on the discrete solution of the Euler equations, which are tightly coupled with an adjoint methodology incorporating a gradient-based optimizer. For each study an equivalent conventional tube-and-wing baseline is similarly optimized in order to enable direct comparisons. It is found that the transonic box-wing aircraft considered here, whose height-to-span ratio is about 0.2, produces up to 43% less induced drag than its conventional counterpart. The unique capability of the box wing to redistribute its optimal lift distribution contributes significantly to this benefit as it enables trim and other constraints to be satisfied with almost no performance degradation. The impact of nonlinear aerodynamics on the box wing is explored further through a series of subsonic optimization studies.

Wake-Model Effects on Induced Drag Prediction of Staggered Boxwings

“…These limits a realistic representation of the possible range of streamwise separations. A height-to-span ratio value of (h/b) = 0.20 was selected, which is similar to that of other references [7,11,31,32,34,35]. The lifting surfaces of the higher-order potential-flow model have zero thickness, whereas the Euler-flow model uses a thin and symmetrical NACA 0004 airfoil.…”

“…Highly non-planar configurations, such as boxwings or c-wings, have the potential to significantly reduce induced drag and, thus, have repeatedly been in the focus of research [7][8][9][10][11][12]. The inviscid aerodynamic advantage of these configurations can primarily be related to the bound circulation being distributed over a larger effective wingspan.…”

Aerodynamic Shape Optimization of a Box-Wing Regional Aircraft Based on the Reynolds-Averaged Navier-Stokes Equations

“…In another recent study done by Gagnon and Zingg [68], aerodynamic shape optimization based on the Euler equations was used to evaluate the aerodynamic performance of a boxwing regional aircraft. The box wing was designed for a cruise Mach number of 0.78 and an altitude of 36,000 ft, and was based on the Bombardier CRJ-1000.…”

“…Gagnon and Zingg [68,69] used one such method, and suggested that the box wing is capable of providing greater improvements to aerodynamic efficiency, and therefore fuel economy, than indicated by the findings of Andrews and Perez. However, aerodynamic shape optimization at least based on the RANS equations will be necessary for capturing the intricacies of flow separation, a powerful and real phenomenon that can dictate the performance of an aircraft design [44,47].…”

“…Given that the advantages of the box-wing configuration come primarily from its wing system, the aircraft geometries will only include the wing, and the horizontal stabilizer where applicable, as done by Gagnon and Zingg [68,69]. However, in order to better represent the relative performance of the complete aircraft, the weight and viscous drag contributions from the fuselage and the vertical stabilizer will be included post-optimization.…”