CG Directly Under The Rotor Mast
Aft CG
Figure 7-1. The location of the center of gravity strongly influences how the helicopter handles.
7-3
sive forward displacement of cyclic control to maintain
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 flapping
could cause the rotor disc to tilt aft. With full forward
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 cabins
are relatively narrow and most optional equipment
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 maximum
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 allowable
CG range shown in the rotorcraft flight manual.
It is important to note that any weight and balance computation
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 baggage
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 standard
weights for specific operating fluids.
The following terms 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
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