text: planes 
  
  The airplane depicted by the curves of Figure 
  1.13 has a maximum lift-drag ratio of 12.5 at 
  an angle of attack of 6”. Suppose this airplane 
  is operated in steady flight at a gross weight 
  of 12,500 lbs. 
  If flown at the airspeed and 
  angle of attack corresponding to (L/D),.., 
  the drag would be 1,000 lbs. Any higher or 
  lower airspeed would produce a drag greater 
  than 1,000 lbs. Of course, this same airplane 
  could be operated at higher or lower gross 
  weights and the same maximum lift-drag ratio 
  of 12.5 could be obtained at the same angle of 
  attack of 6”. However, a change’ in gross 
  weight would require a change in airspeed to 
  support the new weight at the same lift co- 
  efficient and angle of attack. 
  
  maximum power-off glide range, jet or 
  
  Prop 
  
  interesting of these 
  The most immediately 
  items is the power-off glide range of an air- 
  plane. By examining the forces acting on an 
  airplane during a glide, it can be shown that 
  the glide ratio 
  is numerically equal to the 
  lift-drag ratio. For example, if the airplane 
  in a glide has an (L/D) of 15, each mile of alti- 
  tude is traded for 15 miles of horizontal dis- 
  tance. Such a fact implies that the airplane 
  should be flown at (L/D)- 
  to obtain the 
  greatest glide distance. 