NAVWEPS 00-8OT-80 
AIRPLANE PERFORffANCE 
The cffcct of nrnzuay slope on takeoff distance 
is due to the component of weight along the 
inclined path of the airplane. A runway 
slope of 1 percent would provide a force com- 
ponent along the path of the airplane which is 
1 percent of the gross weight. Of course, an 
upslope would contribute a retarding force 
component while a downslope would contri- 
bute an accelerating force component. For 
the case of the upslope, the retarding force 
component adds to drag and rolling friction to 
reduce the net accelerating force. Ordinarily, 
a 1 percent runway slope can cause a 2’tO 4 
percent change in takeoff distance depending 
on rhe airplane characrerisrics. The airplane 
with the high thrust-to-weight ratio is least 
affected while the airplane with the low thrust- 
to-weight ratio is most affected because the 
slope force component causes a relatively 
greater change in the net accelerating force. 
The effect of runway slope must be consid- 
ered when predicting the takeoff distance but 
the effect is usually minor for the ordinary run- 
way slopes and airplanes with moderate 
thrust-to-weight ratios. In fact, runway slope 
considerations are of great significance only 
when the runway slope is large and the airplane 
has an intrinsic low acceleration, i.e., low 
thrust-to-weight ratio. In the ordinary case, 
the selection of the takeoff runway will favor 
the direction with an upslope and headwind 
rather than the direction with a downslope 
and tailwind. 
The effect of proper takeoff t&city is important 
when runway lengths and takeoff distances are 
critical. The takeoff speeds specified in the 
flight handbook are generally the minimum 
safe speeds at which the airplane can become 
airborne. Any attempt to take 05 below the 
recommended speed may mean that the air- 
craft may stall, be difficult to control, or have 
very low initial rate of climb. In some cases, 
an excessive angle of attack may not allow 
the airplane to climb out of ground effect. On 
the other hand, an excessive airspeed at takeoff 
may improve the initial rare of climb and 
“feel” of the airplane but will produce an un- 
desirable increase in takeoff distance. Assum- 
ing that the acceleration is essentially un- 
affected, the takeoff distance varies as the 
square of the takeoff velocity, 
s* vz.2 -= - 
0 J-1 v, 
Thus, 10 percent excess airspeed would increase 
the takeoff distance 21 percent. In most criti- 
cal takeoff conditions, such an increase in 
takeoff distance would be prohibitive and the 
pilot must adhere to the recommended takeoff 
speeds. 
The effect of prcs~wc altitude and ambient 
rcmpcraturc is to define primarily the density 
altitude and its effect on takeoff performance. 
While subsequent corrections are appropriate 
for the effect of temperature on certain items 
of powerplant performance, density altitude 
defines certain effects on takeoff performance. 
An increase in density altitude can produce a 
two-fold effect on takeoff performance: (I) in- 
creased takeoff velocity and (2) decreased 
thrust and reduced net accelerating force. If 
a given weight and configuration of airplane is 
taken to altitude above standard sea level, the 
airplane will still require the same dynamic 
pressure to become airborne at the takeoff lift 
coefficient. Thus, the airplane at altitude will 
take 05 at the same equivalent airspeed (EAS) 
as at sea level, but because of the reduced 
density, the true airspeed (TAS) will be 
greater. From basic aerodynamics, the rela- 
tionship between true airspeed and equivalent 
airspeed is as follows: 
TAS 1 
EAS=F 
where 
TAS= true airspeed 
EAS= equivalent airspeed 
n=altitude density ratio 
0 = Plpo 
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