NAVWEPS 00401-80  APPLICATION OF AERODYNAlvllCS  TO SPECIFIC PROBLEMS OF FLYING  achieve the takeoff speed in the specified dis-  tance. If it is apparent that the airplane is  not accelerating normally or that the airplane  or powerplant is not functioning properly,  a decision must be made to refuse or continue  takeoff. If the decision to refuse takeoff is  made early in the takeoff roll, no problem  exists because the airplane has not gained  much speed and a large portion of runway  distance is unused. However, at speeds near  the takeoff speed, the airplane has used a large  portion of the takeoff distance and the distance  required to stop is appreciable. The problem  which exists is to define the highest speed  attained during takeoff acceleration  from which  the airplane may be decelerated to a stop on  the runway length remaining, i.e., the “refusal  speed.  ’ ’  The refusal speed will be a function of take-  off performance, stopping performance, and  the length of available runway.  The ideal  situation would be to have a runway length  which exceeds the total distance required to  accelerate  to the takeoff speed then decelerate  from the takeoff speed. In this case, the  refusal speed would exceed the takeoff speed  and there would be little concern for the case  of refused takeoff. While this may be the  case for some instances, the usual case is that  the runway length is less than the “accelerate-  stop” distance and the refusal speed is less than  the takeoff speed. A graphical representation  of the refused takeoff condition is illustrated  in figure 6.12 by a plot of velocity versus dis-  tance. At the beginning of the runway, the  airplane starts accelerating and the variation  of velocity and distance is defined by the  takeoff acceleration profile. The deceleration  profile describes  the variation of velocity with  distance where the airplane is brought to a  stop at the end of the runway.  The inter-  section of the acceleration and deceleration  profiles then defines the refusal speed and the  refusal distance along the runway.  Of course,  an allowance must be made for the time spent  at the refusal speed as the power is reduced  and braking action is initiated.  During takeoff, the airplane could be accel-  erated to any speed up to the refusal speed,  then decelerated to a stop on- the runway  remaining.  Once past the refusal speed, the  airplane cannot be brought to a stop on the  runway remaining and the airplane is com-  mitted to an unsafe stop.  If takeoff is refused  when above the refusal speed, the only hope  is for assistance  from the arresting gear, run-  way barrier, or an extensive overrun at the  end of the runway.  This fact points to the  need for planning of the takeoff and the require-  ment to monitor the takeoff acceleration.  If the refusal speed data are not available,  the following equations may be used to ap-  proximate the refusal speed and distance:  where  and for the appropriate takeoff configuration,  V,= refusal speed  S,= refusal distance  V,*= takeoff speed  S,,= takeoff distance  V,= landing speed  J,=landing  distance  R. = runway length available  These approximate relationships do not ac-  count for the time spent at the refusal point and  must not be used in lieu of accurate handbook  data.  In the case of the single-engine airplane, the  pilot must monitor the takeoff performance  to  recognize malfunctions or lack of adequate ac-  celeration prior to reaching the refusal speed.  Obviously, it is to advantage to recognize rhe  3 ’ 92 