text: Thus, the use of sweepback on a transonic 
  aircraft will reduce and delay the drag rise and 
  preserve the maneuverability of the aircraft 
  in transonic flight. 
  It should be noted that a 
  small amount of sweepback produces very 
  little benefit. If sweepback is to be used at all, 
  at least 30’ to 33’ must be used to produce any 
  significant benefit. Also note from figure 3.14 
  that 
  the amount of sweepback required to 
  d&y drag rise in supersonic flight is very large, 
  By 
  e.g., more than 60° necessary at M=2.0. 
  comparison of the drag curves at high Mach 
  numbers it will be appreciated that extremely 
  high (and possibly impractical) sweepback is 
  necessary to delay drag rise and that the lowest 
  drag is abtained with zero sweepback. There- 
  fore, the planform of a wing designed to operate 
  tend 
  continuously at high Mach numbers will 
  to be very thin, low aspect ratio, and unswept. 
  An immediate conclusion is that sweepback is 
  a device of greatest application in the regime of 
  transonic flight. 
  
  A few of the less significant advantages of 