text: In addition to the delay of the onset of com- 
  pressibility effects, sweepback will 
  reduce the 
  magnitude of the changes in force coefficients 
  due to compressibility. Since’ the component 
  of velocity perpendicular to the leading edge is 
  less than the free stream velocity, the magni- 
  tude of all pressure forces on the wing will be 
  reduced (approximately by the square of the 
  cosine of the sweep angle). Since compressi- 
  bility force divergence occurs due to changes in 
  pressure distribution, the use of sweepback will 
  “soften” 
  the force divergence. This effect is 
  illustrated by the graph of figure 3.14 which 
  shows the typical variation of drag coeiIicient 
  with Mach number for various sweepback 
  angles. The straight wing shown begins drag 
  rise at M=O.lO, reaches a peak near M=l.O, 
  and begins a continual drop past M= 1.0. Note 
  that the use of sweepback then deh+y~ the drag 
  rise to some~ higher Mach number and wdms 
  the magnitude of the drag rise. 
  
  general effect and contributes less damping to 
  longitudinal pitching oscillations. These ef- 
  fects can become so significant at high Mach 
  numbers that the aircraft might require com- 
  plete synthetic stabilization. 