Table Of Content031 AIRCRAFT MASS & BALANCE
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TABLE OF CONTENTS
Introduction
The Composition of Aeroplane Weight
The Calculation of Aircraft Weight
Weight and Balance Theory
Centre of Gravity Calculations
Adding, Removing and Repositioning Loads
The Mean Aerodynamic Chord
Structural Limitations
Manual and Computer Load/Trim Sheets
Joint Aviation Regulations
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TABLE OF CONTENTS
The Weighing of Aeroplanes
Documentation
Definitions
CAP 696 - Loading Manual
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Introduction
1. As a professional pilot you will deal with aircraft loading situations on every flying day of
your working life. The course that you are about to embark upon considers the inter-relationship
between aircraft loading and other related subjects (principally aircraft performance and flight
planning), and the very important airmanship aspects of proper aircraft loading. In general (non-
aircraft type specific) terms, the ways in which the centre of gravity of both unladen and laden
aircraft can be determined and checked as being within safe limits will be discussed. As and when
you are introduced to new aircraft types, both during your flight training and during your
subsequent career, you will be taught the loading procedures which are specific to that particular
aircraft type.
2. In the Aircraft Performance book the problem of determining the maximum permitted take-
off weight for an aircraft in a given situation is addressed. The Flight Planning book addresses the
determination of the maximum payload, which can be carried on a given flight. In Aircraft Loading
the problems of distributing the load within the aircraft such that the resultant centre of gravity is,
firstly, within the safe limits laid down for the aircraft and, secondly, positioned so as to enhance the
efficient performance of the aircraft, are addressed.
3. The Joint Aviation Authority has the task of ensuring that all public transport aircraft,
irrespective of size or number of engines, are operated to the highest possible level of safety. To
discharge this commission the JAA periodically introduces legislation in the form of operating rules
or regulations and minimum performance requirements, which are complementary. All public
transport aircraft are divided into Classes in which the types have similar levels or performance.
There is a set of rules and requirements for each Class of aeroplanes, which dictate the maximum
mass at which an aeroplane may be operated during any particular phase of flight.
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4. With the introduction of the Joint Aviation Authority syllabus the word ‘mass’ is used instead
of the word ‘weight’. In all British and American publications, weight is still preferred and used to
express the downward force exerted by mass. The reason the JAA use mass is because weight = mass
x acceleration i.e. weight = mass x 1. Therefore weight and mass are synonymous. Throughout this
book the word ‘weight’ has been used and may be exchanged for the word ‘mass’ if preferred.
5. In addition to this the metric system of measuring weight and volume is preferred by the JAA
and it may be necessary to convert Imperial or American quantities to metric equivalents. If such is
the case use the following method.
Conversion between Weight and Volume
6. The weights and volumes obtained for the purpose of centre of gravity calculations are
frequently given as a mixture of metric and imperial measures. For example a British or American
built aircraft may well have its weights presented in the Aeroplane Flight Manual (AFM) in pounds
and when loaded on the continent the load may be quoted in kilograms. Fuel is delivered in litres,
imperial gallons or US gallons, but of course must figure in the load sheet calculations in pounds or
kilograms. Although the conversion between differing units of weight and volume, and indeed the
conversion between volume and weight for fluids with a given specific gravity, is covered elsewhere
in the course, the following paragraphs are included in this manual for your guidance.
7. To convert a volume of liquid to weight and vice versa the density of the liquid must be
considered. The density is expressed as a specific gravity (SG). 1 litre of pure water weighs 1 kg and
1 imperial gallon pure water weights 10 lb. The SG of pure water is taken as the datum SG of 1.0.
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8. When converting litres of any liquid to kilograms the volume must be multiplied by the
specific gravity, or when converting kilograms to litres the weight must be divided by the specific
gravity. Similarly, when converting imperial gallons to pounds the volume must be multiplied by (10
x the specific gravity), or to convert pounds to imperial gallons the volume must be divided by (10 x
the specific gravity) of the liquid.
9. Aviation fuels and oils are lighter than pure water, therefore their specific gravities will be less
than 1.0.
10. The diagram at Figure 0-1 may help you with these conversions. When using the diagram at
Figure 0-1 and moving in the direction of the arrows, multiply (as shown). Conversely, when moving
in the opposite direction, divide.
Volume Conversions
11. In some problems the oil is measured in quarts. They may be in Imperial measurements or
American. It does not matter, the conversion is the same as shown below in Paragraph 12.
12.
2 Pints = 1 Quart
4 Quarts = 1 Gallon
8 Pints = 1 Gallon
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FIGURE 0-1
Weight/Volume
Conversion
13. When travelling in the direction of the arrows multiply, when travelling in the opposite
direction divide.
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