MAWEPS 00-801-80 
AIRPLANE PERFORMANCE 
The various items of airplane performance 
result from the combination of airplane and 
powerplant characteristics. The aerodynamic 
characteristics of the airplane generally define 
the power and thrust requirements at various 
conditions of flight while the powerplant 
characteristics generally define the power and 
thrust available at various conditions of flight. 
The matching of the aerodynamic configura- 
tion with the powerplant will be accomplished 
to provide maximum performance at the speci- 
fic design condition, e.g., range, endurance, 
climb, etc. 
STRAIGHT AND LEVEL FLlGHT 
When the airyJane is in steady, level flight, 
the condition of equilibrium must prevail. 
The unaccelerated condition of flight is 
achieved with the airplane trimmed for lift 
equal to weight and the powerplant set for a 
thrust to equal the airplane drag. In certain 
conditions of airplane performance it is con- 
venient to consider the airplane requirements 
by the thnr$t required (or drag) while in other 
cases it is more applicable to consider the 
power re@red. Generally, the jet airplane will 
require consideration of the thrust required 
and the propeller airplane will require consid- 
eration of the power required. Hence, the 
airplane in steady level flight will require lift 
equal to weight and thrust available equal to 
thrust required (drag) or power available equal 
to power required. 
The variation of power required and thrust 
required with velocity is illustrated in figure 
2.20. Each specific curve of power or thrust 
required is valid for a particular aerodynamic 
configuration at a given weight and altitude. 
These curves define the power or thrust re- 
quired to achieve equilibrium, Jift-equal- 
weight, constant altitude flight at various 
airspeeds. As shown by the curves of figure 
2.20, ifit is desired to operate the airplane at 
the airspeed corresponding to point A, the 
power or thrust required curves define a par- 
ticular value of thrust or power that must be 
made available from the powerplant ~to achieve 
equilibrium. Some different airspeed such as 
that corresponding to point B changes the 
value of thrust or power required to achieve 
equilibrium. Of course, the change of air- 
speed to point B also would require a change 
in angle of attack to maintain a constant lift 
equal to the airplane weight. Similarly, to 
establish airspeed and achieve equilibrium at 
point C will require a particular angle of attack 
and powerplant thrust or power. In this case, 
flight at point C would be in the vicinity of 
the minimum flying speed and a major portion 
of the ,thrust or power required would be due 
to induced drag. 
The maximum level flight speed for the air- 
plane will be obtained when the power :or 
thrust required equals the maximum power or 
thrust available from the powerplant. The 
minimum level flight airspeed is not usually 
defined by thrust or power requirement since 
conditions of, stall or stability and control 
problems generally predominate. 
CLIMB PERFOLWANCE 
During climbing flight, the airplane gains 
potential energy by virtue of elevation. This 
increase in potential energy during a climb is 
provided by one, or a combination, of two 
means: (1) expenditure of propulsive energy 
above that required to maintain level flight or 
(2) expenditure of airplane kinetic energy, i.e., 
loss of velocity by a zoom. Zooming for alti- 
tude is a transient process of trading kinetic 
energy for potential energy and is of considera- 
ble importance for airplane configurations 
which can operate at very high levels of kinetic 
energy. However, the major portions of climb 
performance for most airplanes is a near steady 
process in which additional propulsive energy 
is converted into potential energy. The funda- 
mental parts of airplane climb performance in- 
volve a flight condition where the airplane is 
in equilibrium but not at constant altitude. 
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