Aircraft Weight and Balance 3-5

Aircraft Balance and Control

• An aircraft is said to be in balance when all weight items are distributed so that the longitudinal center of gravity (cg) lies within a predetermined cg range.
• This range is defined by the forward and aft permissible cg locations, respectively.

Calculating Aircraft CG

• The cg of a group of items can be calculated when the items' weights and arms are known.
• This can be done by using moments.
• The process involves:
  • Recording the aircraft's basic weight and moment from Chart C.
  • Determining the moments of the load items by multiplying the individual weights by their arms or by recording them out of Chart E loading data.
  • Adding the weights of the items and the basic weight and adding the moments of the items and the basic moment.
  • Dividing the moment sum by the weight sum to calculate the balance arm, or cg, of the loaded aircraft.

Fuselage Station (FS)

• FS is often equal to the balance arm scale, but not always.
• Changes to the aircraft fuselage can alter the FS–balance arm relationship.
• Balance calculations should only use balance arms, not FS locations.

Percent MAC (Mean Aerodynamic Chord)

• The location of the aircraft cg is commonly expressed by percent MAC, not by balance arm.
• Percent MAC identifies a location with respect to the position of the MAC; 0.0 percent at the leading edge and 100.0 percent at the trailing edge.
• Percent MAC can be found by a simple mathematical conversion equation or tables particular to the aircraft, listed in Chart E.

Loading/Unloading and Ballast

• Loading or unloading items can have a significant effect on aircraft balance, even when the items total less than one tenth of one percent of the aircraft weight.
• Balance loading principles and techniques for determining the balance of various aircraft configurations are discussed in Section VII.
• Ballast is sometimes added to correct the aircraft cg when it exceeds its limits due to design, manufacturing, or maintenance changes.

Ballast

• Ballast is added to an aircraft when design, manufacturing, or maintenance changes cause the center of gravity (cg) to exceed its limits.
• Permanent ballast always remains in the aircraft.
• Temporary ballast is added to counter the temporary removal of an item or to balance a particular configuration.
• An equation to determine the amount of temporary ballast is provided in Section VII.
• A definition of ballast can be found in APPENDIX A.

Weight and Balance Manual

• DD Form 365: Record of Weight and Balance Personnel, provides a continuous record of personnel responsible for the correctness and maintenance of the weight and balance handbook.
• The form lists the name, grade/rate/rank, qualification information, duty station, and dates of responsibility and relief.

Chart A - Basic Weight Checklist Record

• Lists all equipment and items installed in a definite location in the aircraft, with a weight of 2 pounds or more for aircraft under 25,000 pounds and 5 pounds or more for all other aircraft.
• Items include avionics, power supply, engines, propellers, fluids, crew safety and comfort items, and personnel and cargo equipment.
• The chart lists the weight, arm, and moment of each item, and is used to correct the aircraft's basic weight and moment on Chart C as changes are made.

Completing and Using Chart A

• The manufacturer completes the chart at the time of delivery, indicating the equipment included in the aircraft's initial basic weight.
• Subsequent inventories are completed by inspecting the aircraft and noting any changes in equipment or quantities.
• Check marks are used to indicate the presence of an item in the aircraft, and zeros are used to indicate its absence.
• Partial quantities of an item are noted in the IN AIRCRAFT column.
• The chart is used to provide an inventory of items in the basic weight, and adjustments may be necessary to reflect unusable fuel or other items not installed at the time of weighing.

Chart C - Basic Weight and Balance Record

• A continuous and permanent record of the aircraft's weight, moment/index, and cg position.
• All changes to the aircraft's basic weight and moment, regardless of size, are recorded on the chart to keep it up-to-date.
• The chart is used to calculate the aircraft's loading and to determine the cg position.

Adding and Subtracting from Chart C

• Additions and subtractions to the basic weight and moment/index are recorded on the chart.
• When equipment is added or removed, the item's weight, arm, and moment are determined and recorded on the chart.
• The chart is updated to reflect changes resulting from Chart A inventories and new weighing data.

Weighing the Aircraft

• DD Form 365-2: Form B - Aircraft Weighing Record, is used to record the data obtained from actual weighing.

• The form provides instructions for computing the current weight, moment, and cg of the aircraft.

• Corrections are made for scale calibration, temperature, and equipment included in the scale reading.

• The form is used to calculate the basic weight, moment, and cg of the aircraft.### Weight and Balance Clearance

• The ADDED (+) and REMOVED (–) weight and moment totals should be summed to determine the overall weight and moment change.

• The overall change should be entered under the appropriate column (+ or –) and underlined to indicate that these values are to be added to or subtracted from the previous aircraft weight and moment to obtain the new basic weight and moment.

Accumulation of Weight and Moment Data

• Weight and moment data should not accumulate beyond 0.1 percent (0.2 percent for aircraft with a basic weight less than 35,000 pounds) of the basic weight or beyond a resulting cg change of 0.1 percent MAC (0.1 inch for rotorcraft).
• When this occurs, a new current basic weight, moment, and arm or index will be calculated, and a new WEIGHT AND BALANCE CLEARANCE FORM F will be prepared.

Exceptions for Certain Aircraft

• Aircraft that may receive a series of minor modifications without official AF TCTOs, such as N-coded test aircraft and other test bed aircraft, may accumulate a basic weight change of 0.3 percent, provided the cg change does not exceed 0.1 percent of MAC (0.1 inch for rotorcraft).

Chart C Weight and Balance Entries

• Chart C weight and balance entries regarding jet engine and afterburner replacement are allowed when the moment, arm, and weight data are available.
• In cases where the weight, arm, and moment information for the jet engine or afterburner are variable and cannot be readily ascertained, the aircraft shall be weighed by the activity making the change.
• The engine serial number and proper designating nomenclature will be entered on the Chart C, even though a specific weight entry cannot be made.

Chart E Loading Data

• The Chart E Loading Data provides the aircraft weight and cg limits and the weights and moments of all variable load items.

DD Form 365-4; Weight and Balance Clearance Form F

• The Form F is a summary of the actual disposition of the load carried by the aircraft.
• It is the official record of the computations done by the weight and balance technician to ensure the weight and cg limits are not exceeded at takeoff, during flight, or at landing due to loading conditions.

Completion of Form F

• There are two versions of the Form F: TRANSPORT and TACTICAL.
• The general use and fulfillment of either version are the same, although separate instructions for filling out each version are given.
• In the case of multi-purpose aircraft, the choice of which version to use will be the responsibility of the Using Command.
• One copy of the completed Form F must be filed in accordance with para 4-9.6, and a copy should remain in the aircraft for the duration of the flight.

Aircraft Balance

• An aircraft is said to be in balance when all weight items are distributed so that the longitudinal center of gravity (cg) lies within a predetermined cg range.
• The cg range is defined by the most forward and aft permissible cg locations, called the forward and aft cg limits.

Calculating Aircraft CG

• The cg of a group of items can be calculated when their weights and arms are known.
• Moments are used to calculate the cg, and can be calculated by multiplying the individual weights by their arms.
• The basic moment from the Chart C must be multiplied by a given constant.
• The longitudinal reference datum may not always be located forward of the aircraft, and negative arms may be encountered.

Moments

• If negative arms are encountered with added weight, the moments are negative.
• If negative arms are encountered with deleted weight, the moments are positive.
• If positive arms are encountered with added weight, the moments are positive.
• If positive arms are encountered with deleted weight, the moments are negative.
• The addition or deletion of an item at the reference datum contributes no moment change.

Fuselage Station

• Fuselage Station (FS) is often equal to the balance arm scale, but not always.
• Changes in the aircraft fuselage can alter the FS-balance arm relationship.
• Balance calculations should not be worked using FS locations, but only balance arms.

Percent MAC

• The location of the aircraft cg is commonly expressed as a percentage of the Mean Aerodynamic Chord (MAC).
• Percent MAC identifies a location with respect to the position of the MAC, with 0.0% at the leading edge and 100.0% at the trailing edge.
• Percent MAC can be found using a simple mathematical conversion equation or tables specific to the aircraft.

Loading/Unloading

• Loading or unloading items can have a significant effect on aircraft balance, even if the items are less than 0.1% of the aircraft weight.
• Balance loading principles and techniques for determining the balance of various aircraft configurations are discussed in Section VII.

Ballast

• Ballast is added to counter the effects of design, manufacturing, or maintenance changes that cause the aircraft cg to exceed its limits.
• Temporary ballast is added to balance a particular configuration, while permanent ballast always remains in the aircraft.
• An equation for determining the amount of temporary ballast is included in Section VII.

Mean Aerodynamic Chord (MAC)

• Is an engineering term used in aircraft design
• Represents an airfoil's chord
• Is a constant length
• Used in the calculation of cg location in terms of percent MAC