NAVWEPS 00-801-80 
AIRPLANE PERFORMANCE 
is at a minimum, (LID),. Thus, for maxi- 
mum steady-state angle of climb, the turbojet 
aircraft would be operated at the speed ,for 
(L/D),. This poses somewhat of a problem 
in determining the proper procedure for ob- 
stacle clearance after takeoff. If the obstacle 
is a considerable distance from the takeoff 
point, the problem is essentially that of a long 
term gain and steady state conditions will pre- 
dominate. That is, acceleration from the take- 
off speed to (L/D), speed will be favorable 
because the maximum steady climb angle can 
be attained. However, if the obstacle is a rela- 
tively short distance from the takeoff point, 
the additional distance required to accelerate 
to (L/D),, speed may be detrimental and the 
resulting situation may prove to be a short 
term gain problem. In this case, it may prove 
necessary to begin climb out at or near the take- 
off speed or hold the aircraft on the runway 
for extra speed and a subsequent zoom. The 
problem is su&ciently varied that no general 
conclusion can be applied to all jer aircraft and 
particular procedures are specified for each air- 
craft in the Flight Handbook. 
Of greater general interest in climb per- 
formance are the factors which affect the rate of 
climb. The vertical velocity of an airplane 
depends on the flight speed and the inclination 
of the flight path. In fact, the rate of climb 
is the vertical component of the flight path 
velocity. By the diagram of figure 2.21, the 
following relationship is developed: 
since 
RC- 101.3 V sin y 
then 
RC=101.3 V 
a& 
2-v with Pa=% 
and Pr=& 
where 
RC=rate of climb, f.p.-. 
P11=power available, h.p. 
Pr=power re 
W=weight, 1 % 
uired, h.p. 
s 
and 
V=true airspeed, knots 
33,000 is the factor converting horsepower 
to ft-lbs/min 
101.3isthefactorconvertingknocstof.p.m. 
The above relationship states that, for a given 
weight airplane, the rate af climb (RC) depends 
on the difference between the power available 
and the power required (Pd- Pr), or excess 
power. Of course, when the excess power is 
zero (Pa-Pr=O or Pa== PI), the rate of climb 
is zero and the airplane is in steady level flight. 
When the power available is greater than the 
power required, the excess power will, allow a 
rate of climb specific to the magnitude of excess 
power. Also, when the power available is 
less than the power required, the deficiency of 
power produces a rate of descent. This rela- 
tionship provides the basis for an important 
axiom of flight technique: “For the conditions 
of steady flight, the power setting is the pri- 
mary control of rate of climb or descent”. 
One of the most important items of climb 
performance is the maximum rate of climb. 
By the previous equation for rate of climb, 
maximum rate of climb would occur where 
there exists the greatest difference between 
power available and power required, i.e., 
maximum (Pa- Pr). Figure 2.21 illustrates 
the climb rate performance with the curves of 
power available and power required versus 
velocity. The power required curve is again a 
representative airplane which could be powered 
by either a turbojet or propeller type power- 
plant. The power available curves included 
are for a characteristic propeller powerplant 
and jet powerplant operating at maximum 
output. 
The power curves for the representative pro- 
peller aircraft show a variation of propulsive 
power typical of a reciprocating engine-pro- 
peller combination. The maximum rate of 
climb for this aircraft will occur at some speed 
154 
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