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baggage compartments to adjust the balance for certain
flight conditions. The bags are marked “Ballast XX
Pounds - Removal Requires Weight and Balance Check.”
Temporary ballast must be secured so it cannot shift its
location in flight, and the structural limits of the baggage
compartment must not be exceeded. All temporary ballast
must be removed before the aircraft is weighed.
Temporary Ballast Formula
The CG of a loaded airplane can be moved into its
allowable range by shifting passengers or cargo, or by
adding temporary ballast.
To determine the amount of temporary ballast needed, use
this formula:
Permanent Ballast
If a repair or alteration causes the aircraft CG to fall
outside of its limit, permanent ballast can be installed.
Usually, permanent ballast is made of blocks of lead
painted red and marked “Permanent Ballast - Do Not
Remove.” It should be attached to the structure so that it
does not interfere with any control action, and attached
rigidly enough that it cannot be dislodged by any flight
maneuvers or rough landing.
Figure 5-9. Load conditions for aft adverse-loaded CG check.
5–
Two things must first be known to determine the amount
of ballast needed to bring the CG within limits: the amount
the CG is out of limits, and the distance between the
location of the ballast and the limit that is affected.
If an airplane with an empty weight of 1,876 pounds has
been altered so its EWCG is +32.2, and CG range for
weights up to 2,250 pounds is +33.0 to +46.0, permanent
ballast must be installed to move the EWCG from +32.2 to
+33.0. There is a bulkhead at fuselage station 228 strong
enough to support the ballast.
To determine the amount of ballast needed, use this
formula:
A block of lead weighing 7.7 pounds attached to the
bulkhead at fuselage station 228, will move the EWCG
back to its proper forward limit of +33. This block should
be painted red and marked “Permanent Ballast - Do Not
Remove.”
5–
6–
6 Chapter Weight and Balance Control
– Helicopter
Weight and balance considerations of a helicopter are
similar to those of an airplane, except they are far more
critical, and the CG range is much more limited. [Figure
6-1] The engineers who design a helicopter determine
the amount of cyclic control power that is available, and
establish both the longitudinal and lateral CG envelopes
that allow the pilot to load the helicopter so there is
sufficient cyclic control for all flight conditions.
If the CG is ahead of the forward limit, the helicopter
will tilt, and the rotor disk will have a forward pull. To
counteract this, rearward cyclic is required. If the CG is
too far forward, there may not be enough cyclic authority
to allow the helicopter to flare for a landing, and it will
consequently require an excessive landing distance.
If the CG is aft of the allowable limits, the helicopter will
fly with a tail-low attitude and may need more forward
cyclic stick displacement than is available to maintain a
hover in a no-wind condition. There might not be enough
cyclic power to prevent the tail boom striking the ground.
If gusty winds should cause the helicopter to pitch up
during high speed flight, there might not be enough
forward cyclic control to lower the nose.
Helicopters are approved for a specific maximum gross
weight, but it is not safe to operate them at this weight
under all conditions. A high density altitude decrease the
safe maximum weight as it affects the hovering, takeoff,
climb, autorotation, and landing performance.
The fuel tanks on some helicopters are behind the CG,
causing it to shift forward as fuel is used. Under some
flight conditions, the balance may shift enough that there
will not be sufficient cyclic authority to flare for landing.
For these helicopters, the loaded CG should be computed
for both takeoff and landing weights.
Figure 6-1. Typical helicopter datum, flight stations, and butt line
locations.
6–
Figure 6-2. Typical helicopter CG envelopes.
Lateral balance of an airplane is usually of little concern
and is not normally calculated. But some helicopters,
especially those equipped for hoist operations, are sensitive
to the lateral position of the CG, and their POH/AFM
include both longitudinal and lateral CG envelopes as well
as information on the maximum permissible host load.
Figure 6-2 is an example of such CG envelopes.
Determining the Loaded CG of a Helicopter
The empty weight and empty-weight center of gravity
　
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