The Influence of Sweep on the Span Wise Lift Distribution of Wings

Abstract

N METHODS for computing the spanwise lift distribution of a monoplane wing with arbitrary chord distribution have been worked out. However, the lift distribution furnished by these methods agrees well with experimental results only if the line containing the centers of pressure of the wing sections (approximately the quarter chord line) is straight and at a right angle to the direction of flight. Sweep back of the wing increases the load at the wing tips. This effect has an unfavorable influence on the stalling characteristic of the wing unless it is compensated for by giving the wing a suitable twist. The problems connected with the spanwise lift distribution of a swept-back wing are of twofold nature: Either the shape of a wing is given, and the lift distribution has to be found, or it may be asked what twist has to be given to a swept-back wing in order to get a certain lift distribution. The first problem is dealt with in paper's by Crean and by Weinig. The present paper is devoted to the second problem, which may be formulated more precisely as follows: A straight wing with a certain lift distribution may be given sweep back by sliding each section back; then find the angle of attack at which the swept-back wing sections have to be placed in order to preserve the original lift distribution. For this new angle of attack a formula is found here, which expresses the angle in terms of the given lift distribution. In deriving this formula the present paper follows closely the procedure of Crean; but whereas Crean's paper restricts itself to small angles of sweep back, no such restriction has been made here. Weinig likewise assumes small sweep back and, furthermore, considers only wings with rectangular lift distribution. The coordinate system is taken in the usual way: x-axis in the direction of flight, ^-axis to starboard,