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Pilot's Handbook of Aeronautical Knowledge
Aircraft Performance

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Pilot's Handbook of Aeronautical Knowledge



Table of Contents

Chapter 1, Introduction To Flying
Chapter 2, Aircraft Structure
Chapter 3, Principles of Flight
Chapter 4, Aerodynamics of Flight
Chapter 5, Flight Controls
Chapter 6, Aircraft Systems
Chapter 7, Flight Instruments
Chapter 8, Flight Manuals and Other Documents
Chapter 9, Weight and Balance
Chapter 10, Aircraft Performance
Chapter 11, Weather Theory
Chapter 12, Aviation Weather Services
Chapter 13, Airport Operation
Chapter 14, Airspace
Chapter 15, Navigation
Chapter 16, Aeromedical Factors
Chapter 17, Aeronautical Decision Making




The maximum angle of climb would occur where there
exists the greatest difference between thrust available and
thrust required; i.e., for the propeller-powered airplane, the
maximum excess thrust and angle of climb will occur at some
speed just above the stall speed. Thus, if it is necessary to
clear an obstacle after takeoff, the propeller-powered airplane
will attain maximum angle of climb at an airspeed close to—if
not at—the takeoff speed.

Of greater interest in climb performance are the factors that
affect the rate of climb. The vertical velocity of an aircraft
depends on the flight speed and the inclination of the
flightpath. In fact, the rate of climb is the vertical component
of the flightpath velocity.

For rate of climb, the maximum rate would occur where
there exists the greatest difference between power available
and power required. [Figure 10-8] The above relationship
means that, for a given weight of an aircraft, the rate of climb
depends on the difference between the power available and
the power required, or the excess power. Of course, when the
excess power is zero, the rate of climb is zero and the aircraft
is in steady, level flight. When power available is greater
than the power required, the excess power will allow a rate
of climb specific to the magnitude of excess power.

Power versus climb rate.
Figure 10-8. Power versus climb rate.

During a steady climb, the rate of climb will depend on excess
power while the angle of climb is a function of excess thrust.
The climb performance of an aircraft is affected by certain
variables. The conditions of the aircraft's maximum climb
angle or maximum climb rate occur at specific speeds,
and variations in speed will produce variations in climb
performance. There is sufficient latitude in most aircraft that
small variations in speed from the optimum do not produce
large changes in climb performance, and certain operational
considerations may require speeds slightly different from
the optimum. Of course, climb performance would be most
critical with high gross weight, at high altitude, in obstructed
takeoff areas, or during malfunction of a powerplant. Then,
optimum climb speeds are necessary.

Weight has a very pronounced effect on aircraft performance.
If weight is added to an aircraft, it must fly at a higher angle
of attack (AOA) to maintain a given altitude and speed. This
increases the induced drag of the wings, as well as the parasite
drag of the aircraft. Increased drag means that additional
thrust is needed to overcome it, which in turn means that less
reserve thrust is available for climbing. Aircraft designers
go to great effort to minimize the weight since it has such a
marked effect on the factors pertaining to performance.

A change in an aircraft's weight produces a twofold effect on
climb performance. First, a change in weight will change the
drag and the power required. This alters the reserve power
available, which in turn, affects both the climb angle and the
climb rate. Secondly, an increase in weight will reduce the
maximum rate of climb, but the aircraft must be operated at a
higher climb speed to achieve the smaller peak climb rate.

An increase in altitude also will increase the power required
and decrease the power available. Therefore, the climb
performance of an aircraft diminishes with altitude. The
speeds for maximum rate of climb, maximum angle of climb,
and maximum and minimum level flight airspeeds vary with
altitude. As altitude is increased, these various speeds finally
converge at the absolute ceiling of the aircraft. At the absolute
ceiling, there is no excess of power and only one speed will
allow steady, level flight Consequently, the absolute ceiling
of an aircraft produces zero rate of climb. The service ceiling
is the altitude at which the aircraft is unable to climb at a rate
greater than 100 feet per minute (fpm). Usually, these specific
performance reference points are provided for the aircraft at
a specific design configuration. [Figure 10-9]

In discussing performance, it frequently is convenient to use
the terms power loading, wing loading, blade loading, and disk
loading. Power loading is expressed in pounds per horsepower
and is obtained by dividing the total weight of the aircraft by
the rated horsepower of the engine. It is a significant factor
in an aircraft's takeoff and climb capabilities. Wing loading
is expressed in pounds per square foot and is obtained by
dividing the total weight of an airplane in pounds by the wing
area (including ailerons) in square feet. It is the airplane's
wing loading that determines the landing speed. Blade loading
is expressed in pounds per square foot and is obtained by
dividing the total weight of a helicopter by the area of the
rotor blades. Blade loading is not to be confused with disk
loading, which is the total weight of a helicopter divided by
the area of the disk swept by the rotor blades.