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 anywhere
the manufacturer chooses, most small training helicopters
have the horizontal reference datum 100 inches
forward of the main rotor shaft centerline. This is to keep all
the computed values positive.
7-4
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 usually
is referred to as inches aft of the datum.
Conversely, if the component or object is located forward
of the datum, it is indicated as a negative number
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 carried,
you can determine the point where a loaded helicopter
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 operation
of a helicopter, it is important to know how to
check this condition for each loading arrangement.
Most helicopter manufacturers use one of two methods,
or a combination of the methods, to check weight
and balance conditions.
COMPUTATIONAL METHOD
With the computational method, you use simple mathematics
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 center
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, passengers,
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 conditions.
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 longitudinally
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
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