Global Journal of Researches in Engineering, A: Mechanical & Mechanics, Volume 22 Issue 1

Figure 5: Effective Wing Depth, d Schikantz and Scholz (8) undertook a study that examined the conflicting requirements of obtaining aerodynamic efficiency and static longitudinal stability for the Box Wing aircraft. They stated that to ensure the stability of their model, the fore wing lift coefficient was increased thereby increasing the ratio of the fore and aft wing lift coefficients. Furthermore, the centres of gravity of the airframe, engines, fuel and, payloads were carefully manipulated so they are located at approximately the same position. In a related study, Demasi (9) investigated the conditions for a minimum induced drag of closed wing systems and c-wings using the Lifting Line Theory and Small Perturbation Acceleration Potential. Applying numerical and analytical solution methods, Demasi (9) established that closed- wing systems (like biplanes) have practically the same induced drag as c-wings. This result is similar to what Kroo (12) obtained in his investigation of non-planar wing concepts. Burkhalter et al. (13) investigated the downwash effects for Joined-Wing aircraft using experimental and theoretical aerodynamic approaches. The study revealed that there is only a 12% difference between the experimental and the semi-empirical methods. This suggests that there will be no need to develop new methodologies for designing the Box-Wing Aircraft. This is because existing design and analysis methods have proven that they could be used without loss of accuracy. Corneille’s (11) conducted a wind-tunnel experiment to compare the aerodynamic performance of a Joined-Wing and Conventional Aircraft. The study finds that the Joined-Wing configuration is aerodynamically superior to conventional cantilever wing aircraft. This finding agrees with the results from previous studies by Wolkovitch (1), Prandtl (4), and Frediani (5). However, just like those studies, Corneille’s (11) focused only on the aerodynamic performance of the Box-Wing Aircraft over Conventional Aircraft and neglected other disciplines. Since aircraft is a complex mix of multiple disciplines including aerodynamics, structures, and stability and control; there is the need to investigate the combined effect of some of these disciplines on a configuration to arrive at a holistic conclusion. Consequently, Jansen et al. (12) performed a single-discipline aerodynamic optimization and multidisciplinary aero-structural optimization of non- planar lifting surfaces. For the aero-optimization, both the Box-Wing and Joined-Wing aircraft were optimal. However, when aero-structural optimization was performed, only the conventional configuration with a winglet was optimal. Jansen et al. (12) Study highlights the difficulty in developing a Joined Wing Aircraft with optimal multidisciplinary characteristics. Nangia and Palmer (16) analyzed the effects of forward-swept outboard wings on a Joined/Box-Wing aircraft. They observed that a forward-swept outboard wing produces favourable lift distribution on the forward and aft wing through a forward placement of the Centre of Pressure. Yechout et al. (18) embarked on an aerodynamic evaluation and optimization of a joined wing concept model aircraft. They used general engineering rules of thumb and a University of Missouri biplane design to optimize the performance of Joined Wings aircraft. The authors varied the negative decalage angle and the taper ratio to less than one. Additionally, they increased gap, decreased the wing sweep and decreased the stagger. Yechout et al. (18) Study concludes that a wing gap of 4.75 inches and a decalage angle of -1.5 degrees will create optimal configuration for higher lift coefficients and a shallower drag polar. However, it was observed that Joined-Wing configurations create negligible performance advantage over a monoplane. Khalid and Golson (18) undertook an aerodynamic analysis of a Box-Wing configuration for an An Analysis of Aerodynamic Design Issues of Box Wing Aircraft © 2022 Global Journals Global Journal of Researches in Engineering (A ) Volume XxXII Issue I Version I 32 Year 2022