# Computational Investigation of a Novel Box-Wing Aircraft Concept
## 5 Conclusions  
The present work focused on the so-called SmartLiner aircraft concept, which is a novel variant of a Box-Wing Aircraft (BWA). Differing from more typical, biplane BWA concepts, it comes as a triplane comprising backward and forward swept wings. The aerodynamic performance and structural characteristics of this BWA/SL conceptual aircraft were here assessed through numerical simulation, using Computational Fluid Dynamics (CFD) and Fluid-Structure Interaction (FSI) calculations.  
First, the computational approach was carefully validated using NASA's Common Research Model (CRM) aircraft. No less than 20 simulations were achieved, several of which were validated against experimental and numerical results coming from the literature. In a second time, the computational methodology was applied to the BWA/SL aircraft, so as to compare its aero-structural merits to those of its CRM counterpart. In the lack of any prior knowledge, the BWA/SL flight envelope was first explored by simulating an extensive set of flight conditions and aerodynamics settings--with no less than 45 computations performed. For the most relevant cases, the aerodynamic performance was then assessed, both quantitatively and qualitatively.  
Results show that although its design is still preliminary and lacks optimization, this BWA/SL aircraft exhibits very decent aerodynamic performance, with higher lifting capacities and a reasonable lift-to-drag ratio (L/D). In its current state of design, the BWA/SL aircraft can fly optimally at a cruise speed of Mach 0.7 and an altitude of 43,000 ft, with an overall L/D of about 15.7. This aerodynamic performance is expected to be significantly improved through further optimization of the BWA/SL planform, upon  
Figure 24: BWA/SL aircraft in flight conditions S\({}_{3}\) and S\({}_{4}\) (M = 0.7 at 43,000 ft and sea level, respectively) with an angle-of-attack \(\alpha=0^{\circ}\). Deflections (**left**) and stress (**right**) exerted by the aircraft planform.  
preliminary results from an ongoing study. Whether or not this will be enough for the current (triplane) BWA/SL concept to actually outperform its competitors (traditional or biplane BWA aircraft) remains an open question.  
Aside from this, the BWA/SL aircraft demonstrates superior structural characteristics, including under extreme loading scenarios. In particular, thanks to the higher stiffness inherited from its closed-frame character, the planform exhibits only small amounts of tip deflection and stress concentration. Combined with its increased lifting capacity, this more robust planform allows the BWA/SL aircraft to carry higher payloads than actual and more traditional tube-and-wings aircraft, such as the CRM.  
Based on this preliminary aero-structural analysis, and considering the room left for its further optimization, the BWA/SL conceptual aircraft appears as a promising alternative for the development of more environmentally friendly airliners. On the other hand, whether this promise can translate into a tangible reality remains an open question, which can only be answered by further assessing this concept from an aero-structural perspective and exploring its viability through other lenses (e.g., stability and control, propulsion, commercial exploitation, and so on).  
The authors declare no conflict of interest.