sive forward displacement of cyclic control to main-
tain a hover in a no-wind condition. If there is a wind,
you need even greater forward cyclic.
If flight is continued in this condition, you may find it
impossible to fly in the upper allowable airspeed range
due to inadequate forward cyclic authority to maintain a
nose-low attitude. In addition, with an extreme aft CG,
gusty or rough air could accelerate the helicopter to a
speed faster than that produced with full forward cyclic
control. In this case, dissymmetry of lift and blade flap-
ping could cause the rotor disc to tilt aft. With full for-
ward cyclic control already applied, you might not be
able to lower the rotor disc, resulting in possible loss of
control, or the rotor blades striking the tailboom.
LATERAL BALANCE
For most helicopters, it is usually not necessary to
determine the lateral CG for normal flight instruction
and passenger flights. This is because helicopter cab-
ins are relatively narrow and most optional equip-
ment is located near the center line. However, some
helicopter manuals specify the seat from which you
must conduct solo flight. In addition, if there is an
unusual situation, such as a heavy pilot and a full
load of fuel on one side of the helicopter, which could
affect the lateral CG, its position should be checked
against the CG envelope. If carrying external loads in
a position that requires large lateral cyclic control
displacement to maintain level flight, fore and aft
cyclic effectiveness could be dramatically limited.
WEIGHT AND BALANCE
CALCULATIONS
When determining whether your helicopter is properly
loaded, you must answer two questions:
1. Is the gross weight less than or equal to the max-
imum allowable gross weight?
2. Is the center of gravity within the allowable CG
range, and will it stay within the allowable range
as fuel is burned off?
To answer the first question, just add the weight of the
items comprising the useful load (pilot, passengers,
fuel, oil, if applicable, cargo, and baggage) to the basic
empty weight of the helicopter. Check that the total weight
does not exceed the maximum allowable gross weight.
To answer the second question, you need to use CG or
moment information from loading charts, tables, or graphs
in the rotorcraft flight manual. Then using one of the
methods described below, calculate the loaded moment
and/or loaded CG and verify that it falls within the allow-
able CG range shown in the rotorcraft flight manual.
It is important to note that any weight and balance com-
putation is only as accurate as the information provided.
Therefore, you should ask passengers what they weigh
and add a few pounds to cover the additional weight of
clothing, especially during the winter months. The bag-
gage weight should be determined by the use of a scale, if
practical. If a scale is not available, be conservative and
overestimate the weight. Figure 7-2 indicates the stan-
dard weights for specific operating fluids.
The following terms are used when computing a heli-
copter’s balance.
REFERENCE DATUM —Balance is determined by the
location of the CG, which is usually described as a
given number of inches from the reference datum. The
horizontal reference datum is an imaginary vertical
plane or point, arbitrarily fixed somewhere along the
longitudinal axis of the helicopter, from which all hori-
zontal distances are measured for weight and balance
purposes. There is no fixed rule for its location. It may
be located at the rotor mast, the nose of the helicopter,
or even at a point in space ahead of the helicopter.
[Figure 7-3]
Aviation Gasoline (AVGAS) . . . . . . . . . . . . . . . . . . .6 lbs. / gal.□
Jet Fuel (JP-4) . . . . . . . . . . . . . . . . . . . . . . . . . . . . 6.5 lbs. / gal.□
Jet Fuel (JP-5) . . . . . . . . . . . . . . . . . . . . . . . . . . . . 6.8 lbs. / gal.□
Reciprocating Engine Oil . . . . . . . . . . . . . . . . . . 7.5 lbs. / gal.*□
Turbine Engine Oil . . Varies between 7.5 and 8.5 lbs. / gal.*□
Water . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .8.35 lbs. / gal.□
□
* Oil weight is given in pounds per gallon while oil capacity□
is usually given in quarts; therefore, you must convert the□
amount of oil to gallons before calculating its weight.□
□
Figure 7-2. When making weight and balance computations,
always use actual weights if they are available, especially if
the helicopter is loaded near the weight and balance limits.
Datum +–
Figure 7-3. While the horizontal reference datum can be any-
where the manufacturer chooses, most small training heli-
copters have the horizontal reference datum 100 inches
forward of the main rotor shaft centerline. This is to keep all
the computed values positive.
The lateral reference datum, is usually located at the
center of the helicopter. The location of the reference
datums is established by the manufacturer and is
defined in the rotorcraft flight manual. [Figure 7-4]
ARM—The horizontal distance from the datum to any
component of the helicopter or to any object located
within the helicopter is called the arm. Another term
that can be used interchangeably with arm is station.
If the component or object is located to the rear of the
datum, it is measured as a positive number and usu-
ally is referred to as inches aft of the datum.
Conversely, if the component or object is located for-
ward of the datum, it is indicated as a negative num-
ber and is usually referred to as inches forward of the
datum.
MOMENT— If the weight of an object is multiplied by
its arm, the result is known as its moment. You may
think of moment as a force that results from an object’s
weight acting at a distance. Moment is also referred to
as the tendency of an object to rotate or pivot about a
point. The farther an object is from a pivotal point, the
greater its force.
CENTER OF GRAVITY COMPUTATION—By totaling the
weights and moments of all components and objects car-
ried, you can determine the point where a loaded heli-
copter would balance. This point is known as the center
of gravity.
WEIGHT AND BALANCE METHODS
Since weight and balance is so critical to the safe oper-
ation of a helicopter, it is important to know how to
check this condition for each loading arrangement.
Most helicopter manufacturers use one of two meth-
ods, or a combination of the methods, to check weight
and balance conditions.
COMPUTATIONAL METHOD
With the computational method, you use simple math-
ematics to solve weight and balance problems. The first
step is to look up the basic empty weight and total
moment for the particular helicopter you fly. If the cen-
ter of gravity is given, it should also be noted. The
empty weight CG can be considered the arm of the
empty helicopter. This should be the first item recorded
on the weight and balance form. [Figure 7-5]
Next, the weights of the oil, if required, pilot, passen-
gers, baggage, and fuel are recorded. Use care in
recording the weight of each passenger and baggage.
Recording each weight in its proper location is
extremely important to the accurate calculation of a
CG. Once you have recorded all of the weights, add
them together to determine the total weight of the
loaded helicopter.
Now, check to see that the total weight does not exceed
the maximum allowable weight under existing condi-
tions. In this case, the total weight of the helicopter is
under the maximum gross weight of 3,200 pounds.
Figure 7-4. The lateral reference datum is located longitudi-
nally through the center of the helicopter; therefore, there are
positive and negative values.
Weight Arm Moment□
(pounds) (inches) (lb/inches)
Basic Empty Weight□
Oil□
Pilot□
Forward Passenger□
Passengers Aft□
Baggage□
Fuel□
Total□
CG
1,700□
12□
190□
170□
510□
40□
553□
3,175
116.5□
179.0□
65.0□
65.0□
104□
148□
120□
□
109.9
198,050□
2,148□
12,350□
11,050□
53,040□
5,920□
66,360□
348,918
Max Gross Weight = 3,200 lbs. CG Range 106.0 – 114.2 in.
Figure 7-5. In this example, the helicopter’s weight of 1,700
pounds is recorded in the first column, its CG or arm of 116.5
inches in the second, and its moment of 198,050 pound-
inches in the last. Notice that the weight of the helicopter,
multiplied by its CG, equals its moment.
Lateral□
Datum
+ –
+ –
Front View
Top View
Once you are satisfied that the total weight is within
prescribed limits, multiply each individual weight by
its associated arm to determine its moment. Then, add
the moments together to arrive at the total moment for
the helicopter. Your final computation is to find the
center of gravity of the loaded helicopter by dividing
the total moment by the total weight.
After determining the helicopter’s weight and center
of gravity location, you need to determine if the CG
is within acceptable limits. In this example, the
allowable range is between 106.0 inches and 114.2
inches. Therefore, the CG location is within the
acceptable range. If the CG falls outside the accept-
able limits, you will have to adjust the loading of the
helicopter.
LOADING CHART METHOD
You can determine if a helicopter is within weight and
CG limits using a loading chart similar to the one in
figure 7-6. To use this chart, first subtotal the empty
weight, pilot, and passengers. This is the weight at
which you enter the chart on the left. The next step is to
follow the upsloping lines for baggage and then for fuel
to arrive at your final weight and CG. Any value on or
inside the envelope is within the range.
SAMPLE PROBLEM 1
Determine if the gross weight and center of gravity are
within allowable limits under the following loading
conditions for a helicopter based on the loading chart
in figure 7-6.
To use the loading chart for the helicopter in this exam-
ple, you must add up the items in a certain order. The
maximum allowable gross weight is 1,600 pounds.
ITEM POUNDS
Basic empty weight 1,040
Pilot 135
Passenger 200
Subtotal 1,375 (point A)
Baggage compartment load 25
Subtotal 1,400 (point B)
Fuel load (30 gallons) 180
Total weight 1,580 (point C)
1. Follow the green arrows in figure 7-6. Enter the
graph on the left side at 1,375 lb., the subtotal of
the empty weight and the passenger weight.
Move right to the yellow line. (point A)
2. Move up and to the right, parallel to the baggage
compartment loading lines to 1,400 lb. (Point B)
3. Continue up and to the right, this time parallel to
the fuel loading lines, to the total weight of 1,580
lb. (Point C).
Point C is within allowable weight and CG limits.
SAMPLE PROBLEM 2
Assume that the pilot in sample problem 1 discharges
the passenger after using only 20 pounds of fuel.
ITEM POUNDS
Basic empty weight 1,040
Pilot 135
Subtotal 1,175 (point D)
Baggage compartment load 25
Subtotal 1,200 (point E)
Fuel load 160
Total weight 1,360 (point F)
Follow the blue arrows in figure 7-6, starting at 1,175
lb. on the left side of the graph, then to point D, E, and
F. Although the total weight of the helicopter is well
below the maximum allowable gross weight, point F
falls outside the aft allowable CG limit.
As you can see, it is important to reevaluate the balance
in a helicopter whenever you change the loading. Unlike
most airplanes, where discharging a passenger is
unlikely to adversely affect the CG, off-loading a pas-
senger from a helicopter could make the aircraft unsafe
to fly. Another difference between helicopter and air-
plane loading is that most small airplanes carry fuel in
the wings very near the center of gravity. Burning off
fuel has little effect on the loaded CG. However, heli-
copter fuel tanks are often significantly behind the center
of gravity. Consuming fuel from a tank aft of the rotor
mast causes the loaded helicopter CG to move forward.
As standard practice, you should compute the weight
and balance with zero fuel to verify that your helicopter
remains within the acceptable limits as fuel is used.
A B
1,600□
□
1,500□
□
1,400□
□
1,300□
□
1,200□
□
1,100
104 105 106 107 108 109
Baggage Compartment□
Loading Lines
Fuel Loading□
Lines
Figure 7-6. Loading chart illustrating the solution to sample
problems 1 and 2.
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 helicop-
ter, along with its total moment. Remember to use the
actual weight and moment of the helicopter you are fly-
ing. 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 pre-
scribed 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.
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/pas-
senger moment. Draw a line from a weight of 340
pounds up to the line labeled “PILOT & PASSENGER
@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 thou-
sands of pound-inches. In most cases, when using this
type of chart, you need not be concerned with reduc-
tion factors because the CG/moment envelope chart
normally uses the same reduction factor. [Figure 7-8]
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 computa-
tion 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 enve-
lope. Figure 7-9 illustrates that with a total weight of
2,399 pounds and a total moment of 225,022 pound-
FUEL@
STA.108.5
PILOT
&
PASSENGER
@
STA.83.2
0 100 200 300 400 500
MOMENT (THOUSANDS OF LBS.-IN.)
LOAD WEIGHT (LBS)
Figure 7-7. Moments for fuel, pilot, and passenger.
1,100 1,200 1,300 1,400 1,500□
□
1,600 1,700
LOADED WEIGHT (POUND)
LOAD MOMENT/1000
(POUNDS - INCHES)
1. Basic Empty Weight..................□
□
2. Pilot and Front Passenger........
3. Fuel...........................................
5. Baggage...................................
TOTALS
□
Weight□
(lbs.)
Moment□
(lb.-ins.□
/1,000)
1,102 110.8
28.3340
22.9211
162.01,653
Aft CG Limit□
Station 101.0
Forward CG Limit□
Station 95.0
Figure 7-8. CG/Moment Chart.
inches, the CG is 93.8. Plotting this CG against the
weight indicates that the helicopter is loaded within
the longitudinal limits (point A).
CALCULATING LATERAL CG
Some helicopter manufacturers require that you also
determine the lateral CG limits. These calculations are
similar to longitudinal calculations. However, since the
lateral CG datum line is almost always defined as the
center of the helicopter, you are likely to encounter
negative CGs and moments in your calculations.
Negative values are located on the left side while posi-
tive stations are located on the right.
Refer to figure 7-10. When computing moment for the
pilot, 170 pounds is multiplied by the arm of 12.2 inches
resulting in a moment of 2,074 pound-inches. As with
any weight placed right of the aircraft centerline, the
moment is expressed as a positive value. The forward
passenger sits left of the aircraft centerline. To compute
this moment, multiply 250 pounds by –10.4 inches. The
result is in a moment of –2,600 pound-inches. Once the
aircraft is completely loaded, the weights and moments
are totaled and the CG is computed. Since more weight
is located left of the aircraft centerline, the resulting
total moment is –3,837 pound-inches. To calculate CG,
divide –3,837 pound-inches by the total weight of 2,399
pounds. The result is –1.6 inches, or a CG that is 1.6
inches left of the aircraft centerline.
Weight Arm Moment□
(pounds) (inches) (lb/inches)
Basic Empty Weight□
Pilot□
Fwd Passenger□
Right Fwd Baggage□
Left Fwd Baggage□
Right Aft Passenger□
Left Aft Passenger□
Right Aft Baggage□
Left Aft Baggage□
□
Totals with Zero Fuel□
Main Fuel Tank□
Aux Fuel Tank□
□
Totals with Fuel□
CG
1,400□
170□
250□
□
185□
50□
50□
□
2,105□
184□
110□
□
2,399
107.75□
49.5□
49.5□
44□
44□
79.5□
79.5□
79.5□
79.5□
□
106□
102□
□
93.8
150,850□
8,415□
12,375□
14,708□
3,975□
3,975□
□
194,298□
19,504□
11,220□
□
225,022
Longitudinal
2,500□
2,300□
2,100□
1,900□
1,700□
1,500
91 93 95 97 99 101 103
1,100□
1,050□
1,000□
950□
900□
850□
800□
750□
Fuselage Station (CM from Datum)
Gross Weight - lb.
Gross Weight - KG
Fuselage Station (in. from Datum)
Main□
Rotor
Most Fwd□
CG with□
Full Fuel
Longitudinal
(Point A)
Figure 7-9. Use the longitudinal CG envelope along with the computed CGs to determine if the helicopter is loaded properly.
Figure 7-10. Computed Lateral CG.
Weight Arm Moment□
(pounds) (inches) (lb/inches)
Basic Empty Weight□
Pilot□
Fwd Passenger□
Right Fwd Baggage□
Left Fwd Baggage□
Right Aft Passenger□
Left Aft Passenger□
Right Aft Baggage□
Left Aft Baggage□
□
Totals with Zero Fuel□
Main Fuel Tank□
Aux Fuel Tank□
□
Totals with Fuel□
CG
1,400□
170□
250□
□
185□
50□
50□
□
2,105□
184□
110□
□
2,399
12.2□
–10.4□
11.5□
–11.5□
12.2□
–12.2□
12.2□
–12.2□
□
–13.5□
13□
□
–1.6
2,074□
–2,600□
–2,257□
610□
–610□
□
–2,783□
–2,484□
1,430□
□
–3,837
Lateral
Lateral CG is often plotted against the longitudinal CG.
[Figure 7-11] In this case, –1.6 is plotted against 93.8,
which was the longitudinal CG determined in the previ-
ous problem. The intersection of the two lines falls well
within the lateral CG envelope.
8R□
6R□
4R□
2R□
2L□
4L□
6L□
8L
Fuselage Station (CM from Datum)
Lateral - in.
Lateral CG - CM
Fuselage Station (in. from Datum)
Lateral
3R□
1R□
1L□
3L
Main□
Rotor
(Point A)
91 93 95 97 99 101 103
Figure 7-11. Use the lateral CG envelope to determine if the
helicopter is properly loaded.