NAVWEPS OD-BOT-80  APPLICATION OF AERODYNAMICS  TO SPECIFIC PROBLEMS OF FLYING  brakes does not produce the maximum coefi-  cient of friction.  The incipient skid condi-  tion will produce the maximum coefficient of  friction but this peak is difficult to recognize  and maintain without  an antiskid system.  Judicious use of the brakes is necessary to  obtain the peak coefficient of friction but not  develop a skid or locked wheel which could  cause tire failure, loss of control, or consider-  able reduction in the friction coefficient.  One of the important factors affecting the  landing roll distance is landing touchdown  speed. Any excess velocity at landing causes  a large increase in the minimum stop distance  and it is necessary  that the pilot control the  landing precisely so to land at the appropriate  speed. When landing on the dry, hard surface  runway of adequate length, a tendency is to  take advantage of any excess runway and  allow the airplane to touchdown with excess  speed. Of course, such- errors in technique  cannot be tolerated and the pilot must strive  for precision in all landings.  Immediately  after touchdown, the airp1ar.e lift may be  considerable and the normal force on the  braking surfaces  quite low.  Thus, if excessive  braking torque is applied, the wheel may lock  easily at high speeds  and tire failure may take  place suddenly.  The capacity of the brakes must be sufficient  to create adequate braking torque and produce  the high coefficient of friction.  In addition,  the brakes must be capable of withstanding  the heat generated without fading or losing  effectiveness. The most critical requirements  of the brakes occur during landing at the  maximum allowable landing weight.  TYPICAL ERRORS OF BRAKING TECH-  NIQUE.  Errors in braking technique are usu-  ally coincident with errors of other sorts. For  example, if the pilot lands an airplane with  excessive airspeed, poor braking technique  could accompany the original error to produce  an unsafe situation.  One common error of  of braking technique is the application of  braking torque in excess of the maximum  possible rolling torque. The result will  be  that the wheel decelerates  and locks and the  skid reduces the coefficient of friction, lowers  the capability for side force, and enhances the  possibility of tire failure.  If maximum brak-  ing is necessary,  caution must be used to  modulate the braking torque to prevent lock-  ing the wheel and causing a skid.  On the  other hand, maximum coefficient of friction is  obtained at the incipient skidding condition  so sufficient brake torque must be applied to  produce maximum friction force. Intermittent  braking serves no useful purpose when the  objective is maximum deceleration because  the periods between brake application produce  only slight  or negligible  cooling.  Brake  should be applied smoothly and braking  torque modulated at or near the peak value  to insure that skid does not develop.  Landing on a wet or icy runway requires  judicious use of the brakes because of the re-  duction in the maximum coefficient of friction.  Because of reduction in the maximum attain-  able value of the coefficient of friction, the  pilot must anticipate an increase in the mini-  mum landing distance above that applicable  for the dry runway conditions.  When there  is considerable water or ice on rhe runway, an  increase in landing distance on the order of 40  to 100 percent must be expected for similar  conditions of gross weight, density altitude,  wind,  etc.  Unfortunately, the conditions  likely to produce poor braking action also  will  cause high idle thrust of the turbojet  engine and the extreme case (smooth, glazed  ice or heavy rain) may dictate shutting down  the engine to effect a reasonable stopping  distance.  During takeoff, it is necessary to monitor  the performance of the airplane and evaluate  the acceleration to insure that the airplane will  REFUSAL SPEEDS, LINE  SPEEDS, AND  CRITICAL FIELD LENGTH  391 