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Pilot's Handbook of Aeronautical Knowledge
Aerodynamics of Flight
Weight and Balance

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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




Effect of Weight on Flight Performance
The takeoff/climb and landing performance of an aircraft are
determined on the basis of its maximum allowable takeoff and
landing weights. A heavier gross weight results in a longer
takeoff run and shallower climb, and a faster touchdown
speed and longer landing roll. Even a minor overload may
make it impossible for the aircraft to clear an obstacle that
normally would not be a problem during takeoff under more
favorable conditions.

The detrimental effects of overloading on performance are not
limited to the immediate hazards involved with takeoffs and
landings. Overloading has an adverse effect on all climb and
cruise performance which leads to overheating during climbs,
added wear on engine parts, increased fuel consumption,
slower cruising speeds, and reduced range.

The manufacturers of modern aircraft furnish weight and
balance data with each aircraft produced. Generally, this
information may be found in the FAA-approved AFM/POH
and easy-to-read charts for determining weight and balance
data are now provided. Increased performance and load carrying
capability of these aircraft require strict adherence
to the operating limitations prescribed by the manufacturer.
Deviations from the recommendations can result in structural
damage or complete failure of the aircraft's structure. Even
if an aircraft is loaded well within the maximum weight
limitations, it is imperative that weight distribution be
within the limits of CG location. The preceding brief study
of aerodynamics and load factors points out the reasons for
this precaution. The following discussion is background
information into some of the reasons why weight and balance
conditions are important to the safe flight of an aircraft.

In some aircraft, it is not possible to fill all seats, baggage
compartments, and fuel tanks, and still remain within
approved weight or balance limits. For example, in several
popular four-place aircraft, the fuel tanks may not be filled to
capacity when four occupants and their baggage are carried.
In a certain two-place aircraft, no baggage may be carried
in the compartment aft of the seats when spins are to be
practiced. It is important for a pilot to be aware of the weight
and balance limitations of the aircraft being flown and the
reasons for these limitations.

Effect of Weight on Aircraft Structure
The effect of additional weight on the wing structure of an
aircraft is not readily apparent. Airworthiness requirements
prescribe that the structure of an aircraft certificated in the
normal category (in which acrobatics are prohibited) must
be strong enough to withstand a load factor of 3.8 Gs to take
care of dynamic loads caused by maneuvering and gusts. This
means that the primary structure of the aircraft can withstand
a load of 3.8 times the approved gross weight of the aircraft
without structural failure occurring. If this is accepted as
indicative of the load factors that may be imposed during
operations for which the aircraft is intended, a 100-pound
overload imposes a potential structural overload of 380
pounds. The same consideration is even more impressive in
the case of utility and acrobatic category aircraft, which have
load factor requirements of 4.4 and 6.0, respectively.

Structural failures which result from overloading may
be dramatic and catastrophic, but more often they affect
structural components progressively in a manner that
is difficult to detect and expensive to repair. Habitual
overloading tends to cause cumulative stress and damage
that may not be detected during preflight inspections and
result in structural failure later during completely normal
operations. The additional stress placed on structural parts
by overloading is believed to accelerate the occurrence of
metallic fatigue failures.

A knowledge of load factors imposed by flight maneuvers
and gusts emphasizes the consequences of an increase in
the gross weight of an aircraft. The structure of an aircraft
about to undergo a load factor of 3 Gs, as in recovery from
a steep dive, must be prepared to withstand an added load
of 300 pounds for each 100-pound increase in weight. It
should be noted that this would be imposed by the addition
of about 16 gallons of unneeded fuel in a particular aircraft.
FAA-certificated civil aircraft have been analyzed structurally
and tested for flight at the maximum gross weight authorized
and within the speeds posted for the type of flights to be
performed. Flights at weights in excess of this amount are
quite possible and often are well within the performance
capabilities of an aircraft. This fact should not mislead the
pilot, as the pilot may not realize that loads for which the
aircraft was not designed are being imposed on all or some
part of the structure.

In loading an aircraft with either passengers or cargo, the
structure must be considered. Seats, baggage compartments,
and cabin floors are designed for a certain load or
concentration of load and no more. For example, a light
plane baggage compartment may be placarded for 20 pounds
because of the limited strength of its supporting structure
even though the aircraft may not be overloaded or out of CG
limits with more weight at that location.