Small and Micro Aerial Vehicles: How Much Span is Too Much Span?

摘要

This paper explores at what point a further span increase, while maintaining a constant wing area and loading,nresults in a reduction in aerodynamic performance. Especially in the case of small and micro aerial vehicles, a spannincrease can be realized with only a minor weight penalty. Of particular interest are the maximum lift-to-drag rationand the minimum power required. The existence of such extrema with respect to the aspect ratio is based on thennotion that, while increasing the span decreases the induced drag, it also increases the profile drag as a result of thendecreasing chord Reynolds number. The increasing profile drag eventually leads to a performance loss despitenthe growing aspect ratio. This behavior is investigated using an analytical and a computational approach.Whereasnthe analytical approach does not reveal distinct limits in beneficial aspect ratios, the computational approachnindicates the existence of such limits, especially for lower flight masses below 500 g. The computations suggest, for an100 g wing with fixed span, that doubling the aspect ratio from one to two results in a 20% endurance increase.