text: In this sense, an angle of attack indicator is 
  especially useful for night or instrument takeoff 
  conditions as well as. the ordinary day VFR 
  takeoff conditions. Acceleration errors of the 
  attitude gyro usually preclude accurate pitch 
  rotation under these conditions. 
  
  FACTORS AFFECTING TAKEOFF PER- 
  FORMANCE. 
  In addition to the important 
  factors of proper technique, many other vari- 
  ables affect the takeoff performance of an air- 
  plane. Any 
  item which alters the takeoff 
  velocity or acceleration during takeoff roll will 
  affect the takeoff distance. 
  In order to evalu- 
  ate the effect of the many variables, the prin- 
  cipal relationships of uniformly accelerated 
  motion,will be assumed and consideration will 
  be given to those effects due to any nonuni- 
  formity of acceleration during the process of 
  takeoff. Generally, in the case of uniformly 
  accelerated motion, distance varies directly 
  with the square of the takeoff velocity and in- 
  versely as the takeoff acceleration. 
  
  Thus, a given airplane in the takeoff configura- 
  tion at a given gross weight will have a specific 
  takeoff speed (EAS or CAS) which is invariant 
  with altitude, temperature, wind, etc. because 
  a certain value of 4 is necessary to provide lift 
  equal to weight at the takeoff CL. As an ex- 
  ample of the effect of a change in gross weight 
  a 21 percent increase in takeoff weight will 
  require a 10 percent increase in takeoff speed to 
  support the greater weight. 