text: braking friction will bring both airplanes to 
  a stop in the same distance. The heavier ait- 
  plane will have the gteater mass to decelerate 
  but the greater normal force will provide a 
  greater retarding friction 
  force. As a result, 
  both airplanes would have identical accelera- 
  tion and identical stop distances from a given 
  the heavier airplane 
  velocity. 
  would have a greater kinetic energy to be dis- 
  sipated by the brakes and the principal differ- 
  ence between the two airplanes as they reach 
  a stop would be that 
  the heavier airplane 
  would have the hotter brakes. Therefore, 
  one of the factors of braking performance is the 
  ability of the brakes to dissipate energy with- 
  out developing excessive temperatures and 
  losing effectiveness. 
  
  However, 
  
  if the net retarding force increases in the 
  same proportion as the .weight, the accel- 
  eration is unaffected. 
  the effect of these items on landing dis- 
  tance is, 
  
  To appreciate the effectiveness of modern 
  brakes, a 30,000-lb. aircraft 
  landing at 175 
  knots has a kinetic energy of 41 million ft.-lbs. 
  In a minimum 
  at the instant of touchdown. 
  distance landing, 
  the brakes must dissipate 
  most of this kinetic energy and sach brake must 
  absotb an input power of approximately 1,200 
  for 25 seconds. Such requirements for 
  h.p. 
  brakes are extreme but the example serves to 
  illustrate 
  the ptoblems of brakes for high 
  performance airplanes. 