Rudder Incorporated Winglet Design for Blended Wing Body Aircraft

Concern about the environmental footprint of aviation has re-sparked the interest in unconventional configurations, such as the blended wing body aircraft, BWB. While most research studies recognize the potential of the hybrid-body, they also list a number of challenges. Amongst these challenges is the need for adequate lateral-directional stability and control, which is complicated due to the concept's relative short moment arm and limited available control-volume. To refrain from further straining the trailing edge for directional control, most BWB employ either a conventional vertical tail or resort to yaw-control incorporated winglets. By combining the functionality of the vertical fin with the aerodynamic benefits of a winglet, the required control surface could be obtained without the drag penalty associated with a vertical tail. Although a number of BWB, such as the X-48B, operate these active winglets, limited information is available on the design of such a non-planar component and its influence on the stability and control characteristics. The presented research investigates these aspects aiming to provide a better understanding of the influence of the individual winglet design variables. A design methodology was devised that implements a first order panel method connected to a virtual flight test program. The information collected from the analysis of 400 configurations was used to construct response surfaces that span the entire design space. The generated winglet design program also monitors the impact of the non-planar component on the aerodynamic performance, weight, and operating cost. This enables the user to optimize the tip device, given specified stability and control requirements. It was found that implementing yaw-control incorporated winglets resulted in a statically stable aircraft that meets the requirements for crosswind landing. However, none of the tested configurations meet the dutch roll frequency criterion, corresponding to a satisfactory handling quality level. Research indicates that the tip device has little influence on ωdr, indicating the need to modify the baseline aircraft. Analysis of the response surface estimates for the asymmetric eigenmodes yields a significantly large average error and standard deviation for the spiral. Therefore, it is omitted from the study. Similar errors can be found for a number of other parameters. These parameters can generally be characterized by values that approach zero. The error and standard deviation is amplified when the parameter also changes sign. Normalization of these stability and control characteristics had little influence on the accuracy of the response surface. In recognition of the demonstrated inability of the response surface to accurately capture the behaviour of these parameters, it is concluded that further research is required to reduce the error of the estimates. Despite the indicated challenges, the system is able to explore various control surface configurations. This provides valuable insight into the behaviour of the stability and control characteristics and takes the first step towards the generation of less computational intensive models.