text: airplane is operated at the proper approach 
  speed-not too low or too high an airspeed. 
  In addition to the tise of the angle of attack 
  indicator during approach and landing, 
  the 
  instrument may te used as a principal reference 
  during takeoff. The use of the angle of attack 
  indicator to assume the proper takeoff angle 
  of attack will prevent both over-rotation and 
  excess takeoff speed. Also, the angle of at- 
  tack indicator may be applicable to assist in 
  control of the airplane for conditions of range, 
  endurance, maneuvers, etc. 
  
  A particular advantage of an angle of attack 
  indicator is that the indicator is not directly 
  affected by gross weight, bank angle, load 
  factor, velocity, or density altitude. The 
  typical 
  lift curve of figure 6.3 illustrates the 
  variation of lift coefficient, C,, with angle of 
  attack. a. When a particular aerodynamic 
  configuration is in subsonic flight, each angle 
  of attack produces a particular value of lift 
  coefficient. Of course, a point of special 
  interest on the lift curve is the maximum lift 
  coefficient, C,,,,. Angles of attack greater 
  than that for C,,,, produce a decrease in lift 
  coefficient and constitute the stalled condition 
  of flight. Since Cz,., occurs at a particular 
  angle of attack, any device to provide a stall 
  warning should be predicated on the function 
  of this critical angle of, attack. Under these 
  conditions, stall of the airplane may take place 
  at various airspeeds depending on gross weight, 
  load factor, etc., but always the same angle of 
  attack. 