Rotorcraft Flying Handbook, FAA-H-8083-21

SAMPLE PROBLEM 3
The loading chart used in the sample problems 1 and 2
is designed to graphically calculate the loaded center of
gravity and show whether it is within limits, all on a
single chart. Another type of loading chart calculates
moments for each station. You must then add up these
moments and consult another graph to determine
whether the total is within limits. Although this method
has more steps, the charts are sometimes easier to use.
To begin, record the basic empty weight of the helicopter,
along with its total moment. Remember to use the
actual weight and moment of the helicopter you are flying.
Next, record the weights of the pilot, passengers,
fuel, and baggage on a weight and balance worksheet.
Then, determine the total weight of the helicopter.
Once you have determined the weight to be within prescribed
limits, compute the moment for each weight
and for the loaded helicopter. Do this with a loading
graph provided by the manufacturer. Use figure 7-7 to
determine the moments for a pilot and passenger
weighing 340 pounds and for 211 pounds of fuel.
@STA. 83.2.” Go left and read the pilot/passenger
moment (28.3 thousand lb.-inches).
Reduction factors are often used to reduce the size of
large numbers to manageable levels. In figure 7-7, the
scale on the loading graph gives you moments in thousands
of pound-inches. In most cases, when using this
type of chart, you need not be concerned with reduction
factors because the CG/moment envelope chart
normally uses the same reduction factor. [Figure 7-8]
1. Basic Empty Weight..................
2. Pilot and Front Passenger........
3. Fuel...........................................
5. Baggage...................................
Weight
(lbs.)
Moment
(lb.-ins.
/1,000)
1,102 110.8
340
211
28.3
22.9
TOTALS
1,653
162.0
MOMENT (THOUSANDS OF LBS.-IN.)
36
32
28
24
20
16
12
8
4
0
FUEL @ STA. 108.5
PILOT & PASSENGER @ STA. 83.2
100 200 300 400 500
LOAD WEIGHT (LBS)
Figure 7-7. Moments for fuel, pilot, and passenger.
Start at the bottom scale labeled LOAD WEIGHT.
Draw a line from 211 pounds up to the line labeled
“FUEL @ STA108.5.” Draw your line to the left to
intersect the MOMENT scale and read the fuel moment
(22.9 thousand lb.-inches). Do the same for the pilot/passenger
moment. Draw a line from a weight of 340
pounds up to the line labeled “PILOT & PASSENGER
LOAD MOMENT/1000
(POUNDS - INCHES)
190
180
170
160
150
140
130
120
110
Aft CG Limit
Station 101.0
100
1,100 1,200 1,300 1,400 1,500 1,600 1,700
Figure 7-8. CG/Moment Chart.
Forward CG Limit
Station 95.0
LOADED WEIGHT (POUND)
After recording the basic empty weight and moment of
the helicopter, and the weight and moment for each
item, total and record all weights and moments. Next,
plot the calculated takeoff weight and moment on the
sample moment envelope graph. Based on a weight of
1,653 pounds and a moment/1,000 of 162 pound-inches,
the helicopter is within the prescribed CG limits.
COMBINATION METHOD
The combination method usually uses the computation
method to determine the moments and center of
gravity. Then, these figures are plotted on a graph to
determine if they intersect within the acceptable envelope.
Figure 7-9 illustrates that with a total weight of
2,399 pounds and a total moment of 225,022 pound-
7-6