NAVWEPS DD4OT-80  APPLICATION OF AERODYNAMICS  TO SPECIFIC PROBLEMS OF FLYI ’ NG  possibility of a refused takeoff before exceed-  ing the refusal speed. To this end, the pilot  must carefully evaluate airplane and power-  plant performance and judge the acceleration  of the airplane by the use of “line  speeds.”  The accelerated  motion of the airplane during  takeoff roll will define certain relationships be-  tween velocity and distance when the acceler-  ation of the airplane is normal. By comparison  of predicted and actual speeds  at various points  along the runway, the pilot can evaluate the  acceleration and assess the takeoff perfotm-  axe.  An example of an acceleration profile is  shown by the second  illustration of figure 6.12,  where the variation of velocity and distance is  defined for the case of uniformly accelerated  motion, i.e., constant acceleration. While the  case of uniformly accelerated  motion doesnot  correspond exactly to the takeoff performance  of all airplanes, it is sufficiently applicable to  illustrate the principle of line speeds and ac-  celeration checks. If the takeoff acceleration  of the airplane were constant, the airplane  would develop specific  percentages  of the take-  off speed at specific percentages  of the takeoff  distance.  Representative values from figure  6.12 are as follows:  As an example of this uniformly accelerated  motion, the airplane upon reaching the half-  way point of takeoff roll would have spent  70.7 percent of the total takeoff time and ac-  celerated to 70.7 percent of the takeoff speed.  If the airplane has not reached a specific speed  at a specific distance, it is obvious that the ac-  celeration is below the predicted value and the  airplane surely will not achieve the takeoff  speed in the specified takeoff distance. There-  fore, properly computed line speeds  at various  (2) Critical engine jaih~~ speed: A speed  achieved during the takeoff roll at which fail-  ure of one engine will require the same distance  to continue accelerating with the operative en-  gines to accomplish safe takeoff or refuse  takeoff and decelerate to a stop utilizing the  airplane brakes. At critical engine failure  (1) Takeoff and initial climb speed: A speed,  usually a fixed percentage  above the stall speed,  at which the airplane will become  airborne and  best clear obstacles immediately after takeoff.  For a particular airplane in the takeoff con-  figuration, this speed (in EAS or CM) is a  function of gross weight but in no circumstances  should it he less than the minimum directional  control speed for the critical asymmetrical  power condition.  Generally, the takeoff and  initial climb speed is referred to as the “V,”  speed.  The fundamental principles of refusal speeds  and line speeds  are applicable equally well to  single-engine  and multiengine airplanes. How-  ever, in the case of the multiengine airplane  additional consideration must be given to the  decision to continue or refuse takeoff when  engine failure occurs during the takeoff roll.  IF failure of one engine occurs prior to reaching  the-refusal speed, takeoff should be discon-  tinued and the airplane brought to a stop on  the remaining runway. If failure of one engine  c~curs after exceeding the refusal speed, the  airplane is committed to continue takeoff with  the remaining engines operative or an unsafe  refused  take&.  Sn some cases,  the remaining  runway may not be sufficient to allow acceler-  ation to the takeoff speed and the airplane can  neither takeoff or stop on the runway rcmain-  ibg. To facilitate consideration of this prob-  lem, several specific  defmitions are necessary.  points along the runway will allow the pilot  to monitor the takeoff performance  and recog-  nize a deficiency of acceleration.  Of course,  a deficiency of acceleration must be recognized  prior to reaching some point along the runway  where takeoff cannot be safely achieved or  refused  394  Pmmr  0,  ‘ &Ofl  diJh?%Z  Pmmr  of r ‘ iko~  "docit~  PInmr  0, &off  rim  0  0  0  25  so. 0  50.0  SO  70.7  70.7  75  86. 5  86.5  100  100  100 