STALLING OF SWEPT WINGS. (PITCHING, ROLLING AND YAWING)

The stalling characteristics of airfoil sections and straight wings along with the maximum lift coefficients are dis­cussed in Chapter IV for single element airfoils. The effects on CLX by the use of trailing edge flaps, leading edge slats and other high lift devices are covered in Chap­ters V and VI. These chapters provide the necessary basis for the study of the stall characteristics of swept wings which are very different from those of straight wings, especially when operating at high angles of attack. The stall, maximum lift, moment and drag characteristics of swept wings are generally very unfavorable and thus spe­cial attention is required in the design to achieve satisfac­tory flying qualities. The unfavorable high angle anc. stall characteristics of swept wings are accepted because of their good high speed performance and associated higher Mach number prior to the drag rise qualities discussed in Chapter XV and in the book “Fluid Dynamic Drag”.

The variation of the pitching moment with angle of attack when operating at or near maximum lift is one o: the major problems of swept wings. This problem is caused by an unstable pitch up moment of the wing at both high and low Mach numbers which leads to unsatisfactory aircraft flying qualities. For this reason, when considering the maximum lift and stalling characteristics of swept wings the variation of the pitching moment becomes of major importance.

The flow characteristics effecting the stall properties of swept wings are influenced by the aspect ratio, sweep angle, load distribution, planform and operating condi­tion. The wing design modifications used to obtain satis­factory operation are covered. These design modifications will include the use of planform changes, flaps, slats, camber, wash out, spoilers and fences. Where possible the data will be given for estimating the effects of Ihese aero-dynamic devices on the stalling characteristics of swept wings.

Definitions: Aspect ratio, taper ratio and sweep angle are defined as in Chapter XV. A simple or plain swept wing is considered to be an untwisted wing of straight tapered planform with no span wise variation of airfoil sec: ion. Such simple straight wings are also considered to have low camber airfoil sections.