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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




If maximum specific range is desired, the flight condition must
provide a maximum of speed per fuel flow. While the peak value
of specific range would provide maximum range operation,
long-range cruise operation is generally recommended at some
slightly higher airspeed. Most long-range cruise operations are
conducted at the flight condition that provides 99 percent of
the absolute maximum specific range. The advantage of such
operation is that one percent of range is traded for three to five
percent higher cruise speed. Since the higher cruise speed has
a great number of advantages, the small sacrifice of range is
a fair bargain. The values of specific range versus speed are
affected by three principal variables:
1. Aircraft gross weight
2. Altitude
3. The external aerodynamic configuration of the

These are the source of range and endurance operating data
included in the performance section of the AFM/POH.

Cruise control of an aircraft implies that the aircraft is operated
to maintain the recommended long-range cruise condition
throughout the flight. Since fuel is consumed during cruise, the
gross weight of the aircraft will vary and optimum airspeed,
altitude, and power setting can also vary. Cruise control means
the control of the optimum airspeed, altitude, and power setting
to maintain the 99 percent maximum specific range condition.

At the beginning of cruise flight, the relatively high initial
weight of the aircraft will require specific values of airspeed,
altitude, and power setting to produce the recommended cruise
condition. As fuel is consumed and the aircraft's gross weight
decreases, the optimum airspeed and power setting may
decrease, or, the optimum altitude may increase. In addition,
the optimum specific range will increase. Therefore, the pilot
must provide the proper cruise control procedure to ensure
that optimum conditions are maintained.

Total range is dependent on both fuel available and specific
range. When range and economy of operation are the principal
goals, the pilot must ensure that the aircraft is operated at the
recommended long-range cruise condition. By this procedure,
the aircraft will be capable of its maximum design-operating
radius, or can achieve flight distances less than the maximum
with a maximum of fuel reserve at the destination.

A propeller-driven aircraft combines the propeller with the
reciprocating engine for propulsive power. Fuel flow is
determined mainly by the shaft power put into the propeller
rather than thrust. Thus, the fuel flow can be related directly
to the power required to maintain the aircraft in steady, level
flight and on performance charts power can be substituted
for fuel flow. This fact allows for the determination of range
through analysis of power required versus speed.

The maximum endurance condition would be obtained at the
point of minimum power required since this would require the
lowest fuel flow to keep the airplane in steady, level flight
Maximum range condition would occur where the ratio of
speed to power required is greatest. [Figure 10-10]

Effect of weight.
Figure 10-11. Effect of weight.

The variations of speed and power required must be monitored
by the pilot as part of the cruise control procedure to maintain
the L/DMAX. When the aircraft's fuel weight is a small part of
the gross weight and the aircraft's range is small, the cruise
control procedure can be simplified to essentially maintaining
a constant speed and power setting throughout the time of
cruise flight However, a long-range aircraft has a fuel weight
that is a considerable part of the gross weight, and cruise
control procedures must employ scheduled airspeed and
power changes to maintain optimum range conditions.