Introduction
It is vital to comply with weight and balance limits
established for helicopters. Operating above the maximum
weight limitation compromises the structural integrity of
the helicopter and adversely affects performance. Balance
is also critical because, on some fully loaded helicopters,
center of gravity (CG) deviations as small as three inches can
dramatically change a helicopter’s handling characteristics.
Operating a helicopter that is not within the weight and
balance limitations is unsafe. Refer to FAA-H-8083-1 (as
revised), Aircraft Weight and Balance Handbook, for more
detailed information.
Weight and Balance
Chapter 6
Weight
When determining if a helicopter is within the weight limits,
consider the weight of the basic helicopter, crew, passengers,
cargo, and fuel. Although the effective weight (load factor)
varies during maneuvering flight, this chapter primarily
addresses the weight of the loaded helicopter while at rest.
It is critical to understand that the maximum allowable weight
may change during the flight. When operations include out of
ground effect (OGE) hovers and confined areas, planning must
be done to ensure that the helicopter is capable of lifting the
weight during all phases of flight. The weight may be acceptable
during the early morning hours, but as the density altitude
increases during the day, the maximum allowable weight may
have to be reduced to keep the helicopter within its capability.
The following terms are used when computing a helicopter’s
weight:
• Basic Empty Weight
• Maximum Gross Weight
• Weight Limitations
Basic Empty Weight
The starting point for weight computations is the basic empty
weight. This is the weight of the standard helicopter, optional
equipment, unusable fuel, and all operating fluids including
engine and transmission oil, and hydraulic fluid for those
aircraft so equipped. Some helicopters might use the term
“licensed empty weight,” which is nearly the same as basic
empty weight, except that it does not include full engine and
transmission oil, just undrainable oil. If flying a helicopter
that lists a licensed empty weight, be sure to add the weight
of the oil to the computations.
Maximum Gross Weight
The maximum weight of the helicopter is referred to its
maximum gross weight. Most helicopters have an internal
maximum gross weight, which refers to the weight within the
helicopter structure and an external maximum gross weight,
which refers to the weight of the helicopter with an external
load. The external maximum weight may vary depending
on where it is attached to the helicopter. Some large cargo
helicopters may have several attachment points for sling load
or winch operations. These helicopters can carry a tremendous
amount of weight when the attachment point is directly under
the CG of the aircraft.
Weight Limitations
Weight limits are necessary to guarantee the structural
integrity of the helicopter, enable pilots to predict helicopter
performance and insure aircraft controllability. Although
aircraft manufacturers build in safety factors, a pilot should
never intentionally exceed the load limits for which a
helicopter is certificated.
Operating below a minimum weight could adversely affect
the handling characteristics of the helicopter. During single-
pilot operations in some helicopters, a pilot needs to use a
large amount of forward cyclic to maintain a hover. By adding
ballast to the helicopter, the neutral cyclic position can be
shifted toward the center of its range, thus giving a greater
range of control outward from neutral in every direction.
When operating at or below the minimum weight of the
helicopter, additional weight also improves autorotational
characteristics since the autorotational descent can be
established sooner. In addition, operating below minimum
weight could prevent achieving the desirable rotor revolutions
per minute (rpm) during autorotations.
Operating above a maximum weight could result in
structural deformation or failure during flight if encountering
excessive load factors, strong wind gusts, or turbulence.
Weight and maneuvering limitations also are factors in
establishing fatigue life of components. Overweight, meaning
overstressed, parts fail sooner than anticipated. Therefore,
premature failure is a major consideration in determination
of fatigue life and life cycles of parts.
Although a helicopter is certificated for a specified maximum
gross weight, it is not safe to take off with this load under
some conditions. Anything that adversely affects takeoff,
climb, hovering, and landing performance may require
off-loading of fuel, passengers, or baggage to some weight
less than the published maximum. Factors that can affect
performance include high altitude, high temperature, and high
humidity conditions, which result in a high-density altitude.
In-depth performance planning is critical when operating in
these conditions.
Balance
Helicopter performance is not only affected by gross weight,
but also by the position of that weight. It is essential to load the
aircraft within the allowable CG range specified in the rotorcraft
flight manual’s (RFM) weight and balance limitations. Loading
outside approved limits can result in insufficient control travel
for safe operation.
Center of Gravity
The pilot should ensure that the helicopter is properly balanced
and within its center of gravity limitations, so that minimal
cyclic input is required during hovering flight, except for
any wind corrections. Since the fuselage acts as a pendulum
suspended from the rotor, changing the CG changes the angle
at which the aircraft hangs from the rotor. When the CG is
directly under the rotor mast, the helicopter hangs horizontally;
if the CG is too far forward of the mast, the helicopter hangs
CG Directly Under The Rotor Mast Forward CG Aft CG
CG
CG
CG
Figure 6-1. The location of the CG strongly influences how the helicopter handles.
with its nose tilted down; if the CG is too far aft of the mast,
the nose tilts up. [Figure 6-1]
CG Forward of Forward Limit
A forward CG may occur when a heavy pilot and passenger
take off without baggage or proper ballast located aft of the
rotor mast. This situation becomes worse if the fuel tanks
are located aft of the rotor mast because as fuel burns the
CG continues to shift forward.
This condition is easily recognized when coming to a hover
following a vertical takeoff. The helicopter has a nose-low
attitude, and excessive rearward displacement of the cyclic
control is needed to maintain a hover in a no-wind condition.
Do not continue flight in this condition, since a pilot could
rapidly lose rearward cyclic control as fuel is consumed. A
pilot may also find it impossible to decelerate sufficiently to
bring the helicopter to a stop. In the event of engine failure
and the resulting autorotation, there may not be enough cyclic
control to flare properly for the landing.
A forward CG is not as obvious when hovering into a strong
wind, since less rearward cyclic displacement is required than
when hovering with no wind. When determining whether a
critical balance condition exists, it is essential to consider the
wind velocity and its relation to the rearward displacement
of the cyclic control.
CG Aft of Aft Limit
Without proper ballast in the cockpit, exceeding the aft CG
may occur when:
• A lightweight pilot takes off solo with a full load of
fuel located aft of the rotor mast.
• A lightweight pilot takes off with maximum baggage
allowed in a baggage compartment located aft of the
rotor mast.
• A lightweight pilot takes off with a combination of
baggage and substantial fuel where both are aft of the
rotor mast.
A pilot can recognize the aft CG condition when coming
to a hover following a vertical takeoff. The helicopter will
have a tail-low attitude and will need excessive forward
displacement of cyclic control to maintain a hover in a no-
wind condition. When facing upwind, even greater forward
cyclic is needed.
If flight is continued in this condition, it may be 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 flapping could cause the rotor disk to tilt aft.
With full forward cyclic control already applied, a pilot might
not be able to lower the rotor disk, resulting in possible loss
of control, or the rotor blades striking the tailboom.
Lateral Balance
For smaller helicopters, it is generally unnecessary to
determine the lateral CG for normal flight instruction and
passenger flights. This is because helicopter cabins are
relatively narrow and most optional equipment is located
near the centerline. However, some helicopter manuals
specify the seat from which a pilot must conduct solo flight.
In addition, if there is an unusual situation that could affect
the lateral CG, such as a heavy pilot and a full load of fuel
on one side of the helicopter, 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 limited dramatically. Manufacturers generally account
for known lateral CG displacements by locating external
attachment points opposite the lateral imbalance. Examples
are placement of hoist systems attached to the side, and wing
stores commonly used on military aircraft for external fuel
pods or armament systems.
Horizontal
datum +−
Aviation Gasoline (AVGAS). . . . . . . . . . . . . . . . . . . . . 6 lb/gal
Jet Fuel (JP-4). . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 6.5 lb/gal
Jet Fuel (JP-5). . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 6.8 lb/gal
Reciprocating Engine Oil. . . . . . . . . . . . . . . . . . . . . 7.5 lb/gal*
Turbine Engine Oil. . . . . . . . . . Varies between 6 and 8 lb/gal*
Water. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 8.35 lb/gal
Oil weight is given in pounds per gallon while oil capacity is
usually given in quarts; therefore, convert the amount of oil to
gallons before calculating its weight. Remember, four quarts
equal one gallon.
*
Figure 6-2. 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.
Figure 6-3. While the horizontal reference datum can be anywhere
the manufacturer chooses, some manufacturers choose the datum
line at or ahead of the most forward structural point on the
helicopter, in which case all moments are positive. This aids in
simplifying calculations. Other manufacturers choose the datum
line at some point in the middle of the helicopter, in which case
moments produced by weight in front of the datum are negative and
moments produced by weight aft of the datum are positive.
Weight and Balance Calculations
When determining whether a helicopter is properly loaded,
two questions must be answered:
1. Is the gross weight less than or equal to the maximum
allowable gross weight?
2. Is the CG within the allowable CG range, and will
it stay within the allowable range throughout the
duration of flight including all loading configurations
that may be encountered?
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. Ensure that the total weight does not exceed
the maximum allowable gross weight.
To answer the second question, use CG or moment
information from loading charts, tables, or graphs in the
RFM. It is important to note that any weight and balance
computation is only as accurate as the information provided.
Therefore, ask passengers what they weigh and add a few
pounds to account for the additional weight of clothing,
especially during the winter months. Baggage should be
weighed on a scale, if practical. If a scale is not available,
compute personal loading values according to each individual
estimate. Figure 6-2 indicates the standard weights for
specific operating fluids. These values are used when
computing a helicopter’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
horizontal 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 6-3]
The lateral reference datum is usually located at the center
of the helicopter. The location of the reference datum is
established by the manufacturer and is defined in the RFM.
[Figure 6-4]
Chapter Summary
This chapter discusses the importance of computing the
weight and balance of the helicopter. The chapter also
discusses the common terms and meanings associate with
weight and balance.
Lateral datum
Front view
Top view
+ −
+ −
Figure 6-4. The lateral reference datum is located longitudinally
through the center of the helicopter; therefore, there are positive
and negative values.