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for an airplane. A helicopter may be properly loaded for
takeoff, but near the end of a long flight when the fuel tanks
are almost empty, the CG may have shifted enough for the
helicopter to be out of balance laterally or longitudinally.
Before making any long flight, the CG with the fuel available
for landing must be checked to ensure it will be within the
allowable range.
Airplanes with tandem seating normally have a limitation
requiring solo flight to be made from the front seat in some
airplanes or the rear seat in others. Some of the smaller
helicopters also require solo flight be made from a specific
seat, either the right or the left. These seating limitations will
be noted by a placard, usually on the instrument panel, and
they should be strictly adhered to.
As an aircraft ages, its weight usually increases due to trash
and dirt collecting in hard-to-reach locations, and moisture
absorbed in the cabin insulation. This growth in weight is
normally small, but it can only be determined by accurately
weighing the aircraft.
Changes of fixed equipment may have a major effect upon
the weight of the aircraft. Many aircraft are overloaded by
the installation of extra radios or instruments. Fortunately,
the replacement of older, heavy electronic equipment with
newer, lighter types results in a weight reduction. This weight
change, however helpful, will probably cause the CG to shift
and this must be computed and annotated in the weight and
balance data.
Repairs and alterations are the major sources of weight
changes, and it is the responsibility of the AMT making any
repair or alteration to know the weight and location of these
changes, and to compute the new CG and record the new
empty weight and EWCG in the aircraft weight and balance
data.
The AMT conducting an annual or 100-hour inspection must
ensure the weight and balance data in the aircraft records is
current and accurate. It is the responsibility of the pilot in
command to use the most current weight and balance data
when operating the aircraft.
Service ceiling: The highest altitude
at which an aircraft can maintain a
steady rate of climb of 100 feet per
minute.
Has the Aircraft Gained Weight?
As an aircraft ages, its weight usually increases. Repairs and alterations
are the major sources of weight change.
AMTs conducting an annual or 100-hour inspection must ensure the
weight and balance data in the aircraft records is current and accurate.
The pilot in command’s responsibility is to use the most current weight
and balance data when planning a flight.
Balanced laterally: Balanced in such
a way that the wings tend to remain
level.
1–4
Stability and Balance Control
Balance control refers to the location of the CG of an
aircraft. This is of primary importance to aircraft stability,
which determines safety in flight.
The CG is the point at which the total weight of the
aircraft is assumed to be concentrated, and the CG must
be located within specific limits for safe flight. Both
lateral and longitudinal balance are important, but the
prime concern is longitudinal balance; that is, the location
of the CG along the longitudinal or lengthwise axis.
An airplane is designed to have stability that allows it to be
trimmed so it will maintain straight and level flight with
hands off of the controls. Longitudinal stability is maintained
by ensuring the CG is slightly ahead of the center of lift. This
produces a fixed nose-down force independent of the
airspeed. This is balanced by a variable nose-up force, which
is produced by a downward aerodynamic force on the
horizontal tail surfaces that varies directly with airspeed.
[Figure 1-1]
As long as the CG is maintained within the allowable limits
for its weight, the airplane will have adequate longitudinal
stability and control. If the CG is too far aft, it will be too
near the center of lift and the airplane will be unstable, and
difficult to recover from a stall. [Figure 1-2] If the unstable
airplane should ever enter a spin, the spin could become flat
and recovery would be difficult or impossible.
Figure 1-3. If the CG is too far forward, there will not be
enough elevator nose-up force to flare the airplane for
landing.
Figure 1-2. If the CG is too far aft, at the low stall airspeed
there might not be enough elevator nose-down force to get the
nose down for recovery.
Figure 1-1. Longitudinal forces acting on an airplane in
flight.
If a rising air current should cause the nose to pitch up, the
airplane will slow down and the downward force on the tail
　
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