AIRCRAFT WEIGHT AND BALANCE
DEFINITION OF TERMS
CG
The CG or
Centre of Gravity is the point (or station), at which the total weight is
assumed to be concentrated or the CG is the point
at which an aeroplane would balance if suspended.
Centre of gravity limitations are the specified
forward and aft points (range) beyond
which the CG must not be located
during take-off, flight,
or landing. These limitations
are found in the envelope
on the balance chart.
Arm
The term ARM refers to the distance
between an object or
(precisely said: the CG of
an object) and the reference datum. Arms ahead of the datum are negative
and those aft of the datum are positive.
Datum
The DATUM is a reference point and may (theoretically) be located anywhere
the manufacturer/designer chooses. A common location for the datum is a specified distance forward of the aeroplane. This simplifies mass &
balance calculations.
Weight
WEIGHT is a force. For an aeroplane, weight is always
directed towards the centre of the
earth. The magnitude of this force
depends on the mass of the aeroplane, plus the amount
of fuel, and payload (revenue-generating, eg passengers, baggage, cargo,
etc). The weight is evenly
distributed throughout the aeroplane, but it acts through
the centre of gravity (CG). In flight,
the aeroplane.
Moment
A MOMENT
is a force that tries to cause rotation and is the product
of the weight of an object and its arm.
Index
The INDEX is a moment divided
by a constant factor. The division
is done to transform large moment
numbers into something
workable. For example, B737-200 ADV has
a DOI of +491.
MAC
The MAC or Mean Aerodynamic Chord is an (imaginary) line drawn over the wing of
the aeroplane on which the CG can be expressed. The length of the line is the average distance from the leading edge to the wing's trailing edge. The MAC is expressed in a percentage of that line.
Station
A STATION is a location in the aeroplane which is identified by a number designating its distance in inches from the datum. The datum is therefore identified as station zero. The station and the arm are usually identical.
WEIGHT DEFINITIONS
During load planning / loadsheet process, technical terms and
abbreviations are used.
It is important to familiarize yourself with these terms.
DOW
The DOM or Dry Operating Mass is the weight of the empty aeroplane with all
necessary items that are needed to operate
the flight (e.g. crew/catering/crew bags/navigation materials / technical
spare parts etc. The
ZFW
The ZFW or Zero Fuel Weight is
the weight of the aeroplane
(DOM) including the payload.
ZFW = DOM plus the payload.
The ZFW can fall into three categories namely:
• EZFW or Estimated Zero Fuel weight is the DOM plus payload.
• AZFW or Actual Zero Fuel weight is the DOM plus the actual
payload.
• MZFW or
Maximum Zero Fuel weight is the maximum ZFW
to which an aeroplane can be dispatched. This weight is
either regulated by the structural limitations of the aeroplane
or could be any operational limitations like
temperatures.
MAX RAMP MASS
The MRM or Taxi Mass is the weight
of the aeroplane, parked on the ramp, completely loaded and fuelled, ready for pushback.
MRM = ZFM plus fuel onboard (Block fuel)
TOW
The TOW or Take Off Weight is the weight
of the aeroplane at the beginning of the
runway at the moment
the pilot releases the brakes and initiates the take-off roll.
TOW = MRM minus the taxi
fuel or; TOW = ZFW plus the take-off fuel.
LAW
The LAW or Landing Weight is the weight of the aeroplane at the moment it touches
down on the runway at its
original destination.
LAW = TOW minus the fuel used during the flight
(trip fuel) or;
LAW = ZFM plus the remaining fuel at landing.
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