NAVWEPS 00-801-80 
AIRPLANE PERFORMANCE 
the effect of these items on takeoff dis- 
tance is 
or 
g+?)x(Z) 
J-2 WY2 a -= - J-1 ( ) WI 
(ut 1eaJt this effect because weight will 
alter the net accelerating force) 
This result approximates the e5ect of gross 
weight on takeoff distance for airplanes with 
relatively high thrust-to-weight ratios. In 
effect, the takeoff distance will vary at least 
as the square of the gross weight. For ex- 
ample, a 10 percent increase ,in takeoff gross 
weight would cause: 
a 5 percent increase in takeoff velocity 
at least a, 9 percent decrease in acceleration 
at least a 21 percent increase in takeoff 
distance 
For the airplane with a high thrust-to-weight 
ratio, the increase in takeoff distance would 
be approximately 21 to 22 percent but, for 
the airplane with a relatively low thrust-to- 
*eight ratio, the increase in takeoff distance 
would be approximately 25 to 30 percent. 
Such a powerful effect requires proper con- 
sideration of gross weight in predicting takeoff 
distance. 
The effect of wind on takeoff distance is large 
and proper consideration also must be provided 
when predicting takeoff distance. The effect 
of a headwind is to allow the airplane to reach 
the takeoff velocity at a lower ground velocity 
while the effect of a tailwind is to require the 
airplane to achieve a greater ground velocity 
to attain the takeoff velocity. The effect of 
the wind on acceleration is relatively small 
and, for the most part, can be neglected. To 
evaluate the effect of wind on takeoff distance, 
the following relationships are used: 
the effect of a headwind is to reduce the 
takeoff ground velocity by the amount of 
the headwind velocity, VW 
the effect of wind on acceleration is 
negligible, 
the effect of these items on takeoff distance 
is 
where 
Xi= zero wind takeoff distance 
Sa=takeoff distance into the head- 
wind 
V,= headwind velocity 
VI= takeoff ground velocity with zero 
wind, or, simply, the take05 
airspeed 
As a .result of this relationship, a headwind 
wh,ich is 10 percent of the takeoff airspeed will 
reduce the takeoff distance 19 percent. How- 
ever, a tailwind (or negative headwind) which 
is 10 percent of the take05 airspeed will in- 
crease the takeoff distance 21 percent. In the 
case where the headwind velocity is 50 percent 
of the takeoff speed, the takeoff distance would 
be approximately 25 percent of the zero wind 
takeoff distance (75 percent reduction). 
The e5ect of wind on landing distance is 
identical to the effect on takeoff distance. 
Figure 2.33 illustrates the general dfect of 
wind by the percent change in takeoff or land- 
ing distance as a function of the ratio of wind 
velocity to takeoff or landing speed. 
188