Abstract
In this paper, we addressed the flow patterns over a light boxplane scale model to explain the previously discovered disagreement between its predicted and experimental aerodynamic characteristics. By tuft flow and CFD visualization, we explored the causes yielding a large zero lift pitching moment coefficient, lateral divergence, difference in fore and aft elevator lift, and poor high lift performance of the aircraft. The investigation revealed that the discrepancy in the pitching moment coefficient and lateral stability derivatives can be attributed to insufficient accuracy of the used predictive methods. The difference in fore and aft elevator lift and poor high lift performance of the aircraft may occur due to the low local Reynolds number, which causes the early flow separation over the elevators and flaperons when deflected downward at angles exceeding 10°. Additionally, some airframe changes are suggested to alleviate the lateral divergence of the model.
Highlights
Model Using Tuft Flow VisualizationWith a given take-off weight, an aircraft lift-to-drag ratio can be improved by reducing its drag
Rudders are located on the vertical fins at wing tips, while elevators and flaperons were mounted on the main wings (Figure 2)
The investigation revealed that we should refine the methods for predicting the boxplane pitching moment coefficient and lateral stability derivatives
Summary
With a given take-off weight, an aircraft lift-to-drag ratio can be improved by reducing its drag. The induced drag comprises about 40% of the aircraft total drag. The shear of induced drag can reach up to 90% [1]. With respect to its induced drag according to Prandtl [2]. The boxwing is a statically indeterminate system of lifting surfaces with a larger structural depth; its structure could be lighter if compared to an equivalent monoplane, designed from the same requirements specification. The structural strength and weight of a boxwing were studied in [3,4]. Stability and aerodynamic issues arising due to the interference of the two lifting surfaces were analyzed by Schiktanz et al and Van G. et al [5,6]
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