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moments by the total weights to get
the C of G. Then refer to the flight
manual to see if the figure fits into
the authorised range on the graph.
Simply take the all-up weight you
end up with, and the final C of G,
and line them up horizontally and
vertically. If they are inside the
envelope, you are OK, but don't
forget you have to land again! Your
C of G may well be fine for takeoff,
but check again after the fuel has
been used! %MAC charts, by the
way, show the limits before fuel has
been loaded.
Although charts in the exams look
more complex, it’s quite easy to read
the arm against the position it is in –
just don’t mix metric and Imperial.
For a helicopter with an external
load, bear in mind that the maximum
all-up weight with something on the
hook is often higher than it would
be for passengers only (an extra 150
Operational Procedures 83
lbs for a 206, but check the max
weight for the hook itself), and if
you take a door off, it will affect the
lateral C of G as well, which works
the same way as longitudinal C of G
does, except the figures are smaller
and easier to work with. In fact, they
may even be zeroed if the items are
in the centre, as the hook would be.
You would normally only be worried
about it when taking a door off, as
above, or hoisting, but fuel
consumption has an influence as
well. Items left of the centreline have
a negative sign, and those on the
right are positive, so lateral moments
for the front doors on a 206 would
be –12 for the left and +12 for the
right. Here’s an example lateral C of
G calculation for the 206:
Item Wt Arm Moment
Aircraft 1881 .41 773
Pilot 185 14 2590
Front pax 185 -11 -2035
Left Rear Pax 185 -16 -2960
Centre Rear Pax 185 0 0
Right Rear Pax 185 16 2960
Baggage 50 147.50 7375
Fuel 310 0 0
Total 3166 2.75 8703
Again, there will be a chart in the
Flight Manual to show you where
your plot lies.
Flight Manuals often have helpful
charts with precalculated moment
figures for fuel and baggage (the arm
figures will be excluded). They are
quite simple to use, except that the
exam will require you to interpolate
here and there. However, you should
watch for special conditions, as with
any chart, especially for maximum
weights in particular locations. There
may also be a plan view of the
aircraft with the arms displayed next
to the locations they refer to.
The figures on the outside of the
fuselage are the longitudinal
moments – those inside the seats are
the lateral ones.
If you’re overweight in one section
and want to redistribute the load,
here’s how to figure out what to
move and where:
X = W x D
d
where:
X Weight to be moved
W Total weight of aircraft
D Distance the C of G is out
d Distance between old and new
locations of load moved
So, if your gross weight is 3000 lbs,
your load is 1½ inches outside the
envelope (aft), to be moved from the
baggage compartment to the rear
seats, all of 34 inches, you need to
move 133 lbs to get back in limits:
133 = 3000 x 1.5
34
Remember that the C of G will
follow the weight, that is, if the
movement is forward, the C of G
will go that way, too.
84 Operational Flying
To find a change in C of G:
D = X x d
W
A company mass and balance
document should be raised in
duplicate for each commercial air
transport flight. One copy must be
on the aircraft, with another
available on the ground for at least 3
days. It must contain details of all
loaded items, including fuel, and
indicate whether standard or actual
values have been used. Whoever's
supervising the loading must
confirm by signature that the load
and its distribution are as stated on
the mass and balance document,
which must also have the name of
the person who prepared it. The
document must be acceptable to,
and countersigned by, the
commander, to whom late
alterations must be passed, and
entered in the ‘last minute changes’
spaces. Of course, this won’t be so
necessary if you make several trips
with loads that don’t change very
much, in which case a Load Plan
system is more practical (see below).
There are many ways of expressing
C of G position, ranging from a
simple statement of fact (like 75
inches from a specified point),
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