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Nose wheel scales - 1,202 lbs, tare 14 lbs
Determine the Loaded CG
Beginning with the basic empty weight and EWCG and
using a chart such as the one in Figure 4-11, the loaded
weight and CG of the aircraft can be determined. [Figure
4-10]
The aircraft is loaded as shown here:
Fuel (140 gal).................... 840 lbs
Front seats......................... 320 lbs
Row 2 seats....................... 310 lbs
Fwd. baggage.................... 100 lbs
Aft. baggage........................ 90 lbs
Chart Method Using Weight, Arm, and Moments
Make a chart showing the weight, arm, and moments of
the airplane and its load.
Figure 4-11. Determining the loaded center of gravity of the airplane
in Figure 4-10.
The loaded weight for this flight is 5,064 pounds, and the
CG is located at 42.47 inches aft of the datum.
To determine that the weight and CG are within the
allowable range, refer to the CG range chart of Figure 4-
12. Draw a line vertically upward from 42.47 inches from
the datum and one horizontally from 5,064 pounds. These
lines cross inside the envelope, showing that the airplane is
properly loaded.
Figure 4-10. Twin-engine airplane weight and balance diagram.
4–
Figure 4-12. Center of gravity range chart.
Determining the CG in Percent of MAC
Refer again to Figures 4-10 and 4-11.
The loaded CG is 42.47 inches aft of the datum.
The MAC is 61.6 inches long.
The LEMAC is located at station 20.1.
The CG is 42.47 - 20.1 = 22.37 inches aft of LEMAC.
Use this formula:
The loaded CG is located at 36.3% of the mean
aerodynamic chord.
The Chart Method Using Weight and Moment Indexes
As mentioned in the previous chapter, anything that can
be done to make careful preflight planning easier makes
flying safer. Many manufacturers furnish charts in the
POH/AFM that use weight and moment indexes rather
than weight, arm, and moments. They further help reduce
errors by including tables of moment indexes for the
various weights.
Consider the loading for this particular flight:
Cruise fuel flow = 16 gallons per hour
Estimated time en route = 2 hours 10 minutes.
Reserve fuel = 45 minutes = 12 gallons
Total required fuel = 47 gallons
The pilot completes a chart like the one in Figure 4-13
using moment indexes from tables in figure 4-14 through
4-16.
The moments/100 in the index column are found in the
charts in Figure 4-14 through 4-16. If the exact weight
is not in the chart, interpolate between the weights
that are included. When a weight is greater than any of
those shown in the charts, add the moment indexes for a
combination of weights to get that which is desired. For
example, to get the moments/100 for the 320 pounds in the
front seats, add the moment index for 100 pounds (105) to
that for 220 pounds (231). This gives the moment index of
336 for 320 pounds in the front seats.
Use the moment limits vs. weight envelope in Figure 4-
17 on page 4-8 to determine if the weight and balance
conditions will be within allowable limits for both takeoff
and landing at the destination.
The Moment limits vs. Weight envelope is an enclosed
area on a graph of three parameters. The diagonal line
representing the moment/100 crosses the horizontal line
representing the weight at the vertical line representing
the CG location in inches aft of the datum. When the lines
cross inside the envelope, the aircraft is loaded within its
weight and CG limits.
Takeoff - 3,781 lbs and 4,310
moment/100
Landing - 3,571 lbs and 4,050
moment/100
Locate the moment/100 diagonal line for 4,310 and
follow it down until it crosses the horizontal line for
3,781 pounds. These lines cross inside the envelope at
the vertical line for a CG location of 114 inches aft of the
datum.
The maximum allowable takeoff weight is 3,900 pounds,
and this airplane weighs 3,781 pounds. The CG limits for
3,781 pounds are 109.8 to 117.5. The CG of 114 inches
falls within these allowable limits.
4–
Figure 4-13. Typical weight and balance loading form.
Figure 4-14. Weight and moment index for occupants. Figure 4-15. Weight and moment index for baggage.
4–
Figure 4-16. Weight and moment
index for fuel.
Figure 4-17. Moment limits vs.
weight envelope.
5–
5 Chapter Center of Gravity Change after
Repair or Alterations
The largest weight changes that occur during the lifetime
of an aircraft are those caused by alterations and repairs. It
is the responsibility of the aircraft mechanic or repairman
doing the work to accurately document the weight change
　
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