text: (5) The structural complexity and aero- 
  elastic problems created by sweepback are of 
  great importance. First, there is the effect 
  shown in figure 3.17 that swept wing has a 
  greater structural span than a straight wing 
  of the same area and aspect ratio. This effect 
  increases wing 
  since 
  greater bending and shear material must be 
  distributed in the wing to produce the same 
  design strength. An additional problem is 
  created near the wing 
  root and “carry- 
  through” structure due to the large twisting 
  loads and the tendency of the bending stress 
  distribution to concentrate toward the trail- 
  ing edge. Also shown in figure 3.17 is the 
  influence of wing deflection on the spanwise 
  lift distribution. Wing bending produces 
  tip rotation which 
  tends to unload the tip 
  and move the center of pressure forward. 
  Thus, the same effect which tends to allay 
  divergence can make an undesirable contri- 
  bution to longitudinal stability. 
  EFFECT OF ASPECT RATIO AND TIP 
  SHAPE. 
  to wing sweep, plan- 
  form properties such as aspect ratio, and tip 
  shape, can produce significant effects on the 
  aerodynamic characteristics at high speeds. 
  There is no particular effect of aspect ratio on 
  critical Mach number at high or medium 
  aspect ratios. The aspect ratio must be less 
  than four or five to produce any apparent 
  change in critical Mach number. This effect 
  is shown for a typical 9 percent thick sym- 
  metrical airfoil 
  in the graph of figure 3.18. 
  Note that very low aspect ratios are required 
  to cause a significant increase in critical Mach 
  number. Very low aspect ratios create the 
  extremes of three dimensional flow and sub- 
  sequent increase in free stream speed to create  (4) As described previously, sweepback 
  contributes to lateral stability by producing 
  stable rolling moments with sideslip. The 
  lateral stability contribution of sweepback 
  the amount of wing sweepback 
  varies with 
  lift coefficient-large sweepback 
  and wing 
  and high 
  lift coefficients producing large 
  contribution to lateral stability. While sta- 
  bility is desirable, any excess of stability will 
  For the majority of 
  reduce controllability. 
  airplane configurations, high 
  lateral sta- 
  is neither necessary nor desirable, but 
  bility 
  adequate control in roll is absolutely neces- 
  sary for good flying qualities. An excess of 
  lateral stability from sweepback can aggra- 
  problems and produce 
  vate “Dutch  roll” 