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the reduction factor.
Determining Which Limits are Exceeded
When preparing an aircraft for flight, you must consider all
parameters and check to determine that no limit has been
exceeded.
Consider the parameters below, and determine which limit,
if any, has been exceeded.
• The airplane in this example has a basic empty weight of
9,005 pounds and a moment index of 25,934 poundinches/
100.
• The crew weight is 340 pounds, and its moment/100
is 439.
• The passengers and baggage have a weight of 3,950
pounds and a moment/100 of 13,221.
• The fuel is computed at 6.8 lbs/gal:
The ramp load is 340 gallons, or 2,312 pounds.
Fuel used for start and taxi is 20 gallons, or 136 pounds.
Fuel remaining at landing is 100 gallons, or 680 pounds.
• Maximum takeoff weight is 16,600 pounds.
• Maximum zero fuel weight is 14,000 pounds.
• Maximum landing weight is 16,000 pounds.
Take these steps to determine which limit, if any, is exceeded:
1. Determine the zero fuel weight, which is the weight of the
aircraft with all of the useful load except the fuel on board.
The zero fuel weight of 13,295 pounds is less than the
maximum of 14,000 pounds, so this parameter is
acceptable.
2. Determine the takeoff weight and CG. The takeoff weight
is the zero fuel weight plus the ramp load of fuel, less
the fuel used for start and taxi. The takeoff CG is the
(moment/100 ÷ weight)°?100.
The takeoff weight of 15,471 pounds is below the
maximum takeoff weight of 16,600 pounds, and a check
of Figure 6-12 on Page 6-16 shows that the CG at station
298.0 is also within limits.
3. Determine the landing weight and CG. This is the zero
fuel weight plus the weight of fuel at landing.
The landing weight of 13,975 pounds is less than the
maximum landing weight, of 14,000 pounds. According
to Figure 6-12, the landing CG at station 297.5 is also
within limits.
6 – 20
7– 1
Chapter 7
Weight and Balance Control—
Helicopters
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 7-1] 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. High density altitude decreases 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 7-1. Typical helicopter datum, flight stations, and butt
line locations.
7– 2
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 POHs include both longitudinal
and lateral CG envelopes as well as information on the
maximum permissible hoist load. Figure 7-2 is an example
of such CG envelopes.
Determining the Loaded
CG of a Helicopter
The empty weight and empty-weight center of gravity of a
helicopter are determined in the same way as for an airplane.
The weights recorded on the scales supporting the helicopter
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