Page:Popular Science Monthly Volume 92.djvu/72

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Why is the lower wing narrower than the upper? There is a kind of interference between upper and lower wings. The air is "caught," as it were, between the superposed surfaces, if the lower wing is narrowed this interference is largely prevented. But there are structural reasons, too, for narrowing the width of the lower plane. Note in the drawing that the struts are triangular in form and that the