text: value, or, if reverse thrust is available, a maxi- 
  mum negative value for minimum landing dis- 
  tance. Lift and drag are produced as long as 
  the airplane has speed and the values of lift 
  and drag depend on dynamic pressure and 
  angle of attack. Braking friction results when 
  there is a normal force on the braking wheel 
  surfaces and the friction force is the product of 
  the normal force and the coe&cient of braking 
  The normal force on the braking 
  friction. 
  surfaces is some part of the net of weight and 
  lift, 
  i.e., some other part of this net may be 
  distributed to wheels which have no brakes. 
  The maximum coefficient of braking friction 
  is 
  primarily a function of the runway surface con- 
  dition (dry, wet, icy, etc.) and rather inde- 
  pendent of the type of tire for ordinary condi- 
  tions (dry, hard surface runway). However, 
  the operating coefficient of braking friction 
  is 
  controlled by the pilot by the use of brakes. 
  
  The acceleration of the airplane during the 
  landing roll is negative (deceleration) and will 
  be considered to be in that sense. At any in- 
  stant during the landing roll the acceleration 
  is a function of the net retarding force and the 
  airplane mass. From Newton’s second law of 
  motion: 