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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
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 the lateral
moments for the front doors on a
206 would be –12 for the left and
+12 for the right. Below is a lateral
C of G calculation for the 206:
Item Wt Arm Mom
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:
340 Canadian Professional Pilot Studies
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 1 ½ 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.
To find a change in C of G:
D = X x d
W
Performance
The regulations require you to
ensure that your aircraft has
adequate performance for any
proposed flight. The "performance"
of an aircraft describes its ability to
maintain certain rates of climb
against distance, so you can avoid
hard objects (obstacles), particularly
when you can't see them. As a result,
the charts will emphasise rates and
angles of climb very strongly (climb
requirements are established with
one engine working hard for a
specified time).
There are reasons for multiple
engines, of course. One is that you
get more power and can lift more,
but another is for safety – failure of
an engine should not affect the
continued safe operation of the
flight, or another one, which is why
there are isolation arrangements in
the engine compartment of
helicopters. It follows that the less
the weight of the machine, the better
it can fly with less power.
The take-off and landing phases are
the most critical, demanding the
highest skills from crews and placing
the most strain on the aircraft.
Because of this, strict regulations
govern the information used for
　
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