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: 
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 
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 
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 
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. 
(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. 
(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