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CLB Máy bay - Không quân Tài liệu về cân bằng trọng tải cho tàu bay (AIRCRAFT MASS & BALANCE)

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    1. Introduction
    2. The Composition of Aeroplane Weight
    3. The Calculation of Aircraft Weight
    4. Weight and Balance Theory
    5. Centre of Gravity Calculations
    6. Adding, Removing and Repositioning Loads
    7. The Mean Aerodynamic Chord
    8. Structural Limitations
    9. Manual and Computer Load/Trim Sheets
    10. Joint Aviation Regulations
    11. The Weighing of Aeroplanes
    12. Documentation
    13. Definitions
    14. CAP 696 - Loading Manual

    1. 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.

    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.

    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.
    2 Pints = 1 Quart
    4 Quarts = 1 Gallon
    8 Pints = 1 Gallon​


    13. When travelling in the direction of the arrows multiply, when travelling in the opposite
    direction divide.
    2. The Composition of Aeroplane Weight

    Weight Limitations

    1. The Composition of Aeroplane

    1. The total weight of an aeroplane is the weight of the aeroplane and everyone and everything
    carried on it or in it. Total weight comprises three elements, the basic weight, the variable load and
    the disposable load.

    Basic Weight. This is the aeroplane weight plus basic equipment, unusable fuel and undrainable
    oil. Basic equipment is that which is common to all roles plus unconsumable fluids such as hydraulic

    Variable Load. This includes the role equipment, the crew and the crew baggage. Role
    equipment is that which is required to complete a specific tasks such as seats, toilets and galley for
    the passenger role or roller convey or, lashing points and tie down equipment for the freight role.

    Disposable Load. The traffic load plus usable fuel and consumable fluids. The traffic load is the
    total weight of passengers, baggage and cargo, including any non-revenue load. The disposable load
    is sometimes referred to as the useful load.

    2. Although these are the weight definitions used in the load sheet there are other terms which
    are commonly used. These are:

    Absolute Traffic Load. The maximum traffic load that may be carried in any circumstances. It
    is a limitation caused by the stress limitation of the airframe and is equal to the maximum zero fuel
    weight minus the aircraft prepared for service weight.

    All Up Weight (AUW). The total weight of an aircraft and all of its contents at a specific time.

    Design Minimum Weight. The lowest weight at which an aeroplane complies with the
    structural requirements for its own safety.

    Dry Operating Weight. The total weight of the aeroplane for a specific type of operation
    excluding all usable fuel and traffic loads. It includes such items as crew, crew baggage, catering
    equipment, removable passenger service equipment, and potable water and lavatory chemicals. The
    items to be included are decided by the Operator. The dry operating weight is sometimes referred to
    as the Aircraft Prepared for Service (APS) weight. The traffic load is the total weight of passengers,
    baggage and cargo including non-revenue load. [JAR-OPS 1.607 (a)].

    Empty Weight. (Standard Empty Weight) The weight of the aircraft excluding usable fuel, crew
    and traffic load but including fixed ballast, engine oil, engine coolants (if applicable) and all
    hydraulic fluid and all other fluids required for normal operation and aircraft systems, except
    potable water, lavatory pre-charge water and fluids intended for injection into the engine (de-
    mineralised water or water-methanol used for thrust augmentation).

    Landing Weight. The gross weight of the aeroplane, including all of its contents, at the time of

    Maximum Ramp Weight. The maximum weight at which an aircraft may commence taxiing
    and its equal to the maximum take-off weight plus taxi fuel and run-up fuel. It must not exceed the
    surface load bearing strength.

    Maximum Structural Landing Weight. The maximum permissible total aeroplane weight on
    landing in normal circumstances. [JAR-OPS 1.607 (c)].

    Maximum Structural Take-Off Weight. The maximum permissible total aeroplane weight at
    the start of the take-off run. [JAR-OPS 1.607 (d)].

    Maximum Total Weight Authorised (MTWA). The maximum total weight of aircraft
    prepared for service, the crew (unless already included in the APS weight), passengers, baggage and
    cargo at which the aircraft may take-off anywhere in the world, in the most favourable circumstances
    in accordance with the Certificate of Airworthiness in force in respect of aircraft.

    Maximum Zero Fuel Weight. The maximum permissible weight of an aeroplane with no usable
    fuel. The weight of fuel contained in particular tanks must be included in the zero fuel mass when it
    is explicitly mentioned in the Aeroplane Flight Manual limitations. This is a structural limitation
    imposed to ensure that the airframe is not overstressed. [JAR-OPS 1.607 (b)].

    Payload. Anyone or anything on board the aeroplane the carriage of which is paid for any
    someone other than the operation. In other words anything or anyone carried that earns money for
    the airline.

    Total Loaded Weight. The sum of the aircraft basic weight, the variable load and disposable

    Traffic Load. The total mass of passengers, baggage and cargo, including any non-revenue load.
    [JAR-OPS 1.607 (f)].

    Zero Fuel Weight. This is the dry operating weight plus the traffic load. In other words it is the
    weight of the aeroplane without the weight of usable fuel.


    Ballast. Additional fixed weights which can be removed, if necessary, that are carried, to ensure
    the centre of gravity remains within the safe limits, in certain circumstances.

    Basic Equipment. The unconsumable fluids and the equipment which is common to all roles for
    which the operator intends to use the aircraft.

    Load Spreader. A mechanical device inserted between the cargo and the aircraft floor to
    distribute the weight evenly over a greater floor area.

    Unusable Fuel. That part of the fuel carried which is impossible to use because of the shape or
    position of particular tanks.

    Unusable Oil. That part of the oil lubrication system that cannot be removed due to the
    construction of the system.


    3. The total weight of an aeroplane comprises many different components, all of which, together
    with the appropriate lever arms, are recorded in the weight and CG Schedule.

    4. The standard empty weight of the aeroplane is the weight of the aircraft excluding the usable
    fuel, the crew and the traffic load but including any fixed ballast, unusable fuel, all engine coolant
    and all hydraulic fluid.

    5. The basic weight of an aeroplane is essentially the empty weight plus the weight of basic
    equipment, that is equipment which is common to all roles in which the aircraft may be required to
    perform. The basic weight and the corresponding CG position, together with the declared basic
    equipment showing the weight and arm of each item, are shown in Part A of the Weight and CG
    Schedule or in the Loading and Distribution Schedule as appropriate.

    6. To equip an aircraft to perform a particular role it may be necessary to fit additional
    equipment. This is known as role equipment, an example would be the passenger seats, toilets and
    galleys, which may vary in quantity for a large public transport aircraft.

    7. The role equipment (variable load) detailed in Part B may be for as many roles as the operator
    wishes, but for every role the weights and moments must be stated. The weight and moment of the
    crew is included in Part B. Under certain circumstances, standard crew (and passenger) weights are
    assumed, otherwise the weight of each crew member must be determined by weighing. The
    occasions on which standard weights may be used are discussed in the Chapter entitled ‘Joint
    Airworthiness Requirements’.

    8. With the role equipment fitted the aircraft is ready to enter service. The weight of the aircraft
    in this condition is called the Aircraft Prepared for Service (APS) weight, or the Dry Operating
    Weight (DOW). The total weight of the aeroplane comprises the APS weight plus the disposable
    load, which is made up of usable fuel and the payload.

    9. Details of the disposable load must be entered in Part C of the Weight and CG Schedule,
    which contains the lever arm of each cargo stowage position, hold and each row of passenger seats.
    Full details of all fuel and oil tanks are also included in this part of the Schedule stating the arm,
    maximum capacity and weight when full for aircraft exceeding an MTWA of 2730 kg.

    10. For an aircraft having a valid Certificate of Airworthiness a valid Weight and CG Schedule
    must be completed every time the aircraft is weighed. Each Schedule must be preserved for a period
    of six months following the subsequent re-weighing of the aircraft.

    11. If the person who is the operator ceases to be the operator, he (or his representative if he dies)
    must retain the Schedule or pass it on to the new operator for retention for the requisite period.

    Weight Limitations

    12. The factors which may limit the maximum Take-Off Weight (TOW) are:

    The Structural Limits. These are weight limits, which are imposed by the manufacturer, and
    agreed by the Authority, to ensure the aeroplane is not over-stressed. These structural weights
    include the maximum structural ramp weight, the maximum structural take-off weight, the
    maximum zero fuel weight and the maximum structural landing weight.

    The Field-Length Limited Take-Off Weight. This is the TOW as limited by the available field
    lengths and the prevailing meteorological conditions at the departure aerodrome.

    The Weight-Altitude-Temperature (WAT) Limit. This limitation is imposed on TOW by
    minimum climb gradient requirements, which are specified in Joint Airworthiness Requirements

    The En-Route Requirements. The weight of the aircraft at any stage of the flight en-route must
    be such that the aircraft can safely clear any objects within a specified distance of the aircraft’s
    intended track. Depending on the aircraft’s performance category, the loss of power from a specified
    number of engines will be assumed when determining the maximum weight at which the aircraft can
    safely clear en-route obstacles. En-route terrain clearance may impose a limitation on the take-off

    The Maximum Landing Weight. This may be dictated by the structural limitation, the Field-
    Length Limit or the WAT Limit at the destination or alternate aerodromes.

    The Maximum Take-off Weight. The lowest restricted weight of the field-length limitation, the
    WAT limitation and the structural limitation is the maximum TOW.

    13. As already discussed, the disposable load consists of the usable fuel and the traffic load. In
    order that the maximum traffic load can be carried it may be necessary to limit the amount of fuel
    which is carried to a safe minimum. Whether or not the fuel carried actually limits the traffic load, it
    is normally prudent to reduce the fuel load to a safe minimum in order to reduce the all up weight of
    the aircraft. This will result in lower operating costs, higher cruise levels, reduced thrust take-offs
    and/or easier compliance with noise abatement procedures on take-off. The total fuel required on
    any particular flight comprise the following:

    Route Fuel. This is the fuel used from departure to destination aerodromes and may be
    minimised by operating at the most economical pressure altitude accounting for the temperature and
    wind component, but not below the minimum safe altitude.

    Diversion Fuel. The fuel required to proceed from the destination to the alternate aerodrome in
    the prevailing conditions.

    Holding Allowance. The fuel required to enable the aircraft to hold at a specified pressure
    altitude and for a specified period of time.

    Contingency Allowance. An amount of fuel carried to counter any disadvantage suffered
    because of unforecast adverse conditions.

    Landing Allowance. The fuel required to be used from overhead the landing aerodrome to the
    end of the landing roll.

    14. On occasions it is advantageous to carry more than the minimum fuel for a given sector. The
    obvious example is when fuel will not be available at the destination aerodrome. Alternatively, the
    cost of fuel at the destination aerodrome may be so high that the cost differential (departure
    aerodrome fuel cost versus destination aerodrome fuel cost) may be so great that it is cheaper to
    carry the fuel for the return or subsequent sector outbound from the original departure aerodrome.
    In either event, when this is done the first sector would be termed a ‘Tankering Sector’.

    15. The size of the traffic load may be restricted by reasons other than the disposable load which
    is available once the fuel load has been decided. It may be impossible to distribute the traffic load
    such that the centre of gravity of the laden aircraft remains within the safe specified limits, in which
    case some of the traffic load may have to be off-loaded. Floor loading factors may have to be
    considered. With a payload which is light in weight but bulky it may be physically impossible to fit
    the traffic load into the aircraft.

    Operating Overweight

    16. A safely loaded aircraft is one in which the total weight of traffic load is equal to or less than
    the maximum permissible traffic load for a given flight and the distribution of that traffic load is such
    that the centre of gravity of the laden aircraft lies within the fore and aft limits of centre of gravity
    which are permitted for that aircraft operating in the specified role.

    17. The effects of operating in an overweight condition include:

    (a) Reduced acceleration on the ground run for take-off. The take-off speeds are
    increased because of the weight, and this results in an increased take-off run required
    and an increased take-off distance required.

    (b) Decreased gradient and rate of climb which decreases obstacle clearance capability
    after take-off and the ability to comply with the minimum climb gradient

    (c) Increased take-off speeds impose a higher load on the undercarriage and increased tyre
    and wheel temperatures. Together these reduce the aeroplane’s ability to stop rapidly
    in the event of an abandoned take-off.

    (d) Increased stalling speed which reduces the safety margins.

    (e) Reduced cruise ceiling which increases the fuel consumption resulting in a decreased
    operational range. It may also cause en-route terrain clearance problems.

    (f) Impaired manoeuvrability and controllability.

    (g) Increased approach and landing speeds causing a longer landing distance, landing
    ground run, increased tyre and wheel temperatures and reduced braking effectiveness.

    (h) Reduced one-engine inoperative performance on multi-engined aircraft.

    (i) Reduced structural strength safety martins with the possibility of overstressing the

    18. In addition to ensuring that the maximum permissible all-up weight of an aircraft is not
    exceeded it is of vital importance to ensure that the distribution of the permissible weight is such that
    the balance of the aircraft is not upset.
  2. hochoi

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    3. The Calculation of Aircraft Weight

    From the diagram at Figure 1-1 it can be determined that:
    • Aircraft Weight + Basic Equipment = Basic Weight
    • Basic Weight + Usable Oil = Standard Empty Weight
    • Standard Empty Weight + Optional Equipment = Basic Empty Weight (Note if no optional equipment is added, Standard Empty Weight = Basic Empty Weight).
    • Basic Empty Weight + Variable Load = Aircraft Prepared for Service Weight (APS).
    • APS Weight + Removable Ballast = Dry Operating Weight. (Note if there is no removable ballast, APS Weight = Dry Operating Weight).
    • Dry Operating Weight + Traffic Load = Zero Fuel Weight.
    • Zero Fuel Weight + Usable Fuel = All Up Weight
      Problems related to these fomulae will be met as follows: (Note optional equipment and removable ballast will not be mentioned unless it is carried).
    EXAMPLE 2-1 and 2-2:

    EXAMPLE 2-3 and 2-4:

    Weight and Traffic Load

    1. Problems concerning the traffic load capacity of an aircraft often occur in the Flight Planning,
    Navigation or Mass and Balance examination papers. The problems are not complicated because
    there is no consideration of whether the centre of gravity of the laden aircraft lies within the trim

    2. To avoid getting lost in a mass of figures and definitions, remember that the All Up Weight of
    an aircraft at any stage of flight consists of three elements:

    (a) The Aircraft Prepared for Service Weight (or Dry Operating Mass).
    (b) The weight of the Fuel Onboard.
    (c) The traffic load carried.

    3. The APS weight and the traffic load remain constant throughout the flight whereas the weight
    of the fuel will progressively decrease.

    4. In the examination you will be required to calculate the weight of the traffic load that can be
    carried, as limited by one of three limiting maximum weights:

    (a) Maximum Take-Off Weight.
    (b) Maximum Landing Weight.
    (c) Maximum Zero Fuel Weight.

    5. For an aircraft to perform a particular role it may be necessary to fit additional equipment.

    This is known as role equipment, for example the passenger seats and galleys required in a public transport aircraft, which makes the aircraft ready to enter service. The weight of the aircraft in this condition is called the Aircraft Prepared for Service (APS) weight, or the Dry Operating Weight. The
    Total Weight of the aeroplane then comprises of the APS weight plus the Disposable Load, which is made up of the usable fuel and traffic load.

    6. To answer this type of question use the layout shown in the following examples and approach
    the problem in a logical manner remembering the total weight at any time comprises the APS weight,
    the fuel and the traffic load.

    EXAMPLE 2-5


    EXAMPLE 2-6:



    EXAMPLE 2-6:



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