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which measurements can be made. But because the aerodynamic
characteristics of a wing relate to its chord length,
pilots and flight engineers are more concerned with the
location of the CG relative to the chord; and because the mean,
or average, physical chord of a tapered wing is difficult to
measure, the mean aerodynamic chord (MAC) is used. The
allowable CG range is expressed in percentages of the MAC.
Figure 3-9. The MAC is the chord drawn through the
geographic center of the plan area of the wing.
Chord: A straight-line distance
across a wing from leading edge to
trailing edge.
MAC and CG
The location of the CG with respect to the mean aerodynamic chord
is important to the flight crew because it predicts the handling
characteristics of the aircraft.
Mean aerodynamic chord (MAC):
The chord of an imaginary airfoil
that has the same aerodynamic
characteristics as the actual airfoil.
The relative positions of the CG and the aerodynamic center
of lift of the wing have critical effects on the flight characteristics
of the aircraft. Consequently, relating the CG location
to the chord of the wing is convenient from a design and
operations standpoint. Normally, an aircraft will have
acceptable flight characteristics if the CG is located
somewhere near the 25% average chord point. This means the
CG is located one-fourth of the total distance back from the
leading edge of the wing section. Such a location will place
the CG forward of the aerodynamic center for most airfoils.
3–8
In order to relate the percent MAC to the datum, all weight
and balance information includes two items: the length of
MAC in inches and the location of the leading edge of MAC
(LEMAC) in inches from the datum.
The weight and balance data of the airplane in Figure 3-10
states that the MAC is from stations 1022 to 1198 and the
CG is located at station 1070.
MAC = 1198 – 1022 = 176 inches
LEMAC = station 1022
CG is 48 inches behind LEMAC (1070 – 1022 =
48 inches)
The location of the CG expressed in percentage of MAC is
determined using this formula:
It is sometimes necessary to determine the location of the CG
in inches from the datum when its location in % MAC is known.
The CG of the airplane is located at 27.3% MAC
MAC = 1198 – 1022 = 176 inches
LEMAC = station 1022
Determine the location of the CG in inches from the datum
by using this formula:
Figure 3-10. Large aircraft weight and balance calculation diagram.
Leading edge of MAC (LEMAC):
Leading Edge of the Mean
Aerodynamic Chord.
TEMAC: Trailing Edge of the Mean
Aerodynamic Chord.
The CG of the airplane is located at 27.3% MAC.
The CG of this airplane is located at station 1070 which is
1,070 inches aft of the datum.
It is important for longitudinal stability that the CG be located
ahead of the center of lift of a wing. Since the center of lift is
expressed as a percentage of the MAC, the location of the
CG is expressed in the same terms. See Chapter 6 for more
about using % MAC in weight and balance technology, in
“Weight and Balance Control—Large Aircraft.”
4– 1
Chapter 4
General Aviation Aircraft Operational
Weight and Balance Computations
Weight and balance data allows the pilot to determine the
loaded weight of the aircraft and determine whether or not
the loaded CG is within the allowable range for the weight.
See Figure 4-1 for an example of the data necessary for these
calculations.
Determining the Loaded Weight and CG
An important part of preflight planning is to determine that
the aircraft is loaded so its weight and CG location are within
the allowable limits. [Figure 4-2] There are two ways of
doing this: by the computational method using weights,
arms, and moments; and by the loading graph method,
using weight and moment indexes.
Figure 4-1. Weight and balance data needed to determine
proper loading of a 14 CFR, Part 23 airplane.
Figure 4-2. Airplane loading diagram.
Computational Method
The computational method uses weights, arms, and moments
and relates the total weight and CG location to a CG limits
chart similar to those included in the TCDS and the POH/
AFM.
A worksheet such as the one in Figure 4-3 provides space for
all of the pertinent weight and balance data. Data is included
for the airplane weight, CG, and moment along with the arms
of the seats, fuel, and baggage areas.
4–2
Figure 4-3. Blank weight and balance worksheet.
To determine that the airplane is properly loaded for this
　
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