text: PLANFORM EFFECTS. The development 
  of surfaces for high speed involves considera- 
  tion of many items in addition to the airfoil 
  sections. Taper, aspect ratio, and sweepback 
  can produce major effects on the aerodynamic 
  characteristics of a surface in high speed flight. 
  Sweepback produces an unusual effect on the 
  high speed characteristics of a surface and has 
  basis in a very fundamental concept of aero- 
  dynamics. A grossly simplified method of 
  visualizing the effect of sweepback is shown in 
  figure 3.14. The swept wing shown has the 
  streamwise velocity broken down to a com- 
  ponent of velocity perpendicular to the leading 
  edge and a component parallel to the leading 
  edge. The component of speed perpendicular 
  to the leading edge is less than the free.stream 
  speed (by the cosine of the sweep angle) and 
  it is this velocity component which determines 
  the magnitude of the pressure distribution. 
  
  In view of the preceding discussion, sweep- 
  back will have the following principal ad- 
  vantages : 
  
  (1) Sweepback will delay the onset of all 
  compressibility effects. Critical Mach num- 
  ber and force divergence Mach number will 
  increase since the velocity component affect- 
  is less than the 
  ing the pressure distribution 
  free stream velocity. Also, the peak of drag 
  rise is delayed to some higher supersonic 
  speed-approximately 
  the speed which pro- 
  duces sonic flow perpendicular to the leading 
  edge. Various sweeps applied to wings of 
  .moderate aspect ratio will produce these 
  approximate effects in transonic flight: 