Title: Positive Tail Loads for Minimum Induced Drag of Subsonic Aircraft
Abstract: By applying Prandtl's relation for the induced drag of a biplane to typical wing-tail combinations, it can be shown that the minimum induced drag occurs with a positive upload. This fact has been overlooked because the reduction in the total induced drag by a download was overestimated by using the total downwash of the on the tail, while neglecting the downwash produced on the by the tail. It is proved that, regardless of the relative size of the tail, the downwash produced by a download increases the induced drag of the so as to cancel the additional tail thrust, and keep the mutually induced drag of a wing-tail combination the same as that induced upon the alone when it is in the wing's Trefftz-plane. At any finite length the bound circulation vortex of the produces a downwash that increases the induced drag of a upload. However, the circulation vortex system of the upload produces an upwash on the that results in a wing thrust component that cancels the increased drag on the so that the total induced drag is a minimum with a positive load. In order to facilitate the calculation of the mutually induced drag of typical wing-tail combinations, an explicit relation is derived for the limiting case of a small-span at any distance above or below a large-span wing.
Publication Year: 1978
Publication Date: 1978-12-01
Language: en
Type: article
Indexed In: ['crossref']
Access and Citation
Cited By Count: 33
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