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Pilot's Handbook of Aeronautical Knowledge
Weight and Balance
Balance, Stability, and Center of Gravity

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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 pilot should always be aware of the consequences of
overloading. An overloaded aircraft may not be able to leave
the ground, or if it does become airborne, it may exhibit
unexpected and unusually poor flight characteristics. If not
properly loaded, the initial indication of poor performance
usually takes place during takeoff.

Excessive weight reduces the flight performance in almost
every respect. For example, the most important performance
deficiencies of an overloaded aircraft are:
• Higher takeoff speed
• Longer takeoff run
• Reduced rate and angle of climb
• Lower maximum altitude
• Shorter range
• Reduced cruising speed
• Reduced maneuverability
• Higher stalling speed
• Higher approach and landing speed
• Longer landing roll
• Excessive weight on the nose wheel or tail wheel

The pilot must be knowledgeable about the effect of weight
on the performance of the particular aircraft being flown.
Preflight planning should include a check of performance
charts to determine if the aircraft's weight may contribute
to hazardous flight operations. Excessive weight in itself
reduces the safety margins available to the pilot, and becomes
even more hazardous when other performance-reducing
factors are combined with excess weight. The pilot must
also consider the consequences of an overweight aircraft if
an emergency condition arises. If an engine fails on takeoff
or airframe ice forms at low altitude, it is usually too late to
reduce an aircraft's weight to keep it in the air.

Weight Changes
The operating weight of an aircraft can be changed by
simply altering the fuel load. Gasoline has considerable
weight—6 pounds per gallon. Thirty gallons of fuel may
weigh more than one passenger. If a pilot lowers airplane
weight by reducing fuel, the resulting decrease in the range
of the airplane must be taken into consideration during flight
planning. During flight, fuel burn is normally the only weight
change that takes place. As fuel is used, an aircraft becomes
lighter and performance is improved.

Changes of fixed equipment have a major effect upon the
weight of an aircraft. The installation of extra radios or
instruments, as well as repairs or modifications may also
affect the weight of an aircraft.

Balance, Stability, and Center of Gravity

Balance refers to the location of the CG of an aircraft, and is
important to stability and safety in flight The CG is a point
at which the aircraft would balance if it were suspended at
that point.

The primary concern in balancing an aircraft is the fore and
aft location of the CG along the longitudinal axis. The CG
is not necessarily a fixed point; its location depends on the
distribution of weight in the aircraft. As variable load items are
shifted or expended, there is a resultant shift in CG location.
The distance between the forward and back limits for the
position of the center for gravity or CG range is certified for
an aircraft by the manufacturer. The pilot should realize that
if the CG is displaced too far forward on the longitudinal
axis, a nose-heavy condition will result. Conversely, if the
CG is displaced too far aft on the longitudinal axis, a tail
heavy condition results. It is possible that the pilot could not
control the aircraft if the CG location produced an unstable
condition. [Figure 9-1]

Location of the CG with reference to the lateral axis is also
important. For each item of weight existing to the left of the
fuselage center line, there is an equal weight existing at a
corresponding location on the right. This may be upset by
unbalanced lateral loading. The position of the lateral CG
is not computed in all aircraft, but the pilot must be aware
that adverse effects arise as a result of a laterally unbalanced
condition. In an airplane, lateral unbalance occurs if the fuel
load is mismanaged by supplying the engine(s) unevenly from
tanks on one side of the airplane. The pilot can compensate
for the resulting wing-heavy condition by adjusting the
trim or by holding a constant control pressure. This action
places the aircraft controls in an out-of-streamline condition,
increases drag, and results in decreased operating efficiency.
Since lateral balance is addressed when needed in the aircraft
flight manual (AFM) and longitudinal balance is more
critical, further reference to balance in this handbook means
longitudinal location of the CG. A single pilot operating a
small rotorcraft, may require additional weight to keep the
aircraft laterally balanced.

Lateral and longitudinal unbalance.
Figure 9-1. Lateral and longitudinal unbalance.