# Computational Investigation of a Novel Box-Wing Aircraft Concept
###### Abstract  
With regard to the current needs for greener aviation, this study focuses on a novel concept of Box-Wing Aircraft (BWA). Labelled SmartLiner (BWA/SL), this conceptual aircraft comes as a triplane comprising backward and forward swept wings. The aerodynamic performance and structural characteristics of this BWA/SL aircraft are here explored through numerical simulation, using Computational Fluid Dynamics (CFD) and Fluid-Structure Interaction (FSI). The computational approach is first validated using NASA's Common Research Model (CRM) aircraft, which is then taken as a reference solution against which to compare the aero-structural merits of the BWA/SL concept. Results show that, although its design is still preliminary and lacks optimization, the BWA/SL aircraft exhibits very decent aerodynamic performance, with higher lifting capacities and a reasonable lift-to-drag ratio. Moreover, thanks to the closed frame of its peculiar planform, it demonstrates superior structural characteristics, including under extreme loading scenarios. Based on this preliminary analysis and considering the room left for its further optimization, this conceptual aircraft thus appears as a potentially promising alternative for the development of more environmentally friendly airliners. g = [color=gray!50, linecolor=gray!50, linecolor=gray! performances than a conventional 'tube-and-wing' configuration. Indeed, different from a conventional aircraft whose lift is produced by a single wing, a box-wing aircraft relies on multiple lifting surfaces (wings, but also horizontal tail) that are connected one to the others, with these connections reducing the drag induced by wingtip vortices. The benefits are expected to be multi-fold, namely (i) more lift produced (i.e., more payload allowed and/or shorter wingspan required), (ii) less induced-drag generated (i.e., less fuel consumption entailed) and then, (iii) higher structural integrity (i.e., less weight from structural reinforcement)--all of which would ultimately lead to better performances and thus lower emissions. The last decade saw active research on box-wing aircraft, worldwide. One can cite the BWA concept currently explored by Lockheed Martin (see Figure 1) under the Environmentally Responsible Aviation Project (ERAP) initiative by NASA [8]. The proposed concept advantageously combines a box-wing design, advanced lightweight composite materials, and highly efficient engines (with a bypass ratio almost five times greater than that of current engines). It is claimed that this BWA aircraft would offer a lift-to-drag ratio that would be 16% higher than that of a conventional aircraft, along with reduced noise emissions. One can also mention several large-scale projects conducted under the aeg of the European Commission, namely PARSIFAL [9; 10; 11; 12; 13; 14; 15; 16; 17] and IDINTOS [18; 19]. In particular, the recent EU project PARSIFAL explored rather extensively the so-called Prandtl Plane concept, which was investigated from various angles, including market perspectives [9], conceptual design viewpoints [10; 11; 12], and more technical aspects (e.g., performance [13], stability [14], aerodynamics [15; 16], structures [17]). Additionally, more specific studies were conducted by several universities, worldwide; several works investigated the BWA concept from design perspectives [20; 21; 22; 23; 24; 25; 26; 27] whereas others focused on more specific things such as the aerodynamic efficiency of the box-wing itself [28; 29; 30; 31; 32; 33; 34], as well as structural [35; 36] and stability [37; 38; 39; 40] aspects. All these pioneering studies paved the way to the possible emergence of a BWA aircraft era. This being said, there are still many venues to explore for such an unconventional aircraft concept can be further consolidated and optimized. Besides, these conceptual early days are the perfect timeframe for further thinking out of the box (-wing), for instance by exploring even more disruptive BWA concepts.