Aircraft Weight and Balance
AIRCRAFT WEIGHT & BALANCE CONTROL
INTRODUCTION
Understanding how weight and balance affects aircraft operation is crucial for safety.
REFERENCES
Regulations and guidelines pertinent to Aircraft Weight and Balance:
14 CFR, PART 23, Airworthiness Standards: Sections 23.21, 23.23, 23.25, 23.29, and 23.31.
AC 43.13-1B, Acceptable Techniques and Practices, Chapter 10, dedicated to Weight & Balance.
FAA-H-8083-30, Airframe and Powerplant Mechanics General Handbook, Chapter 4, discussing Aircraft Weight & Balance.
PIA, Aircraft Structures Workbook, Chapter 4, for additional context.
RESPONSIBILITIES OF THE A&P MECHANIC
Following the entry of an aircraft into service, the mechanic's responsibilities include:
Providing the aircraft owner with a revised Weight & Balance (W&B) report.
Performing an actual weighing of the aircraft and preparing a new report.
The W&B report must indicate the following:
EMPTY WEIGHT
EMPTY WEIGHT CENTER OF GRAVITY (CG)
USEFUL LOAD
Utilizing this information, the pilot can accurately load and operate the aircraft.
Documenting the maintenance record entry.
EXAMPLE OF MAINTENANCE RECORD ENTRY
Sample entry from 10-22-2006:
Total Time: 5,673.7 hr.
Repainted aircraft and installed STOL kit by Airmark Enterprises per STC SA 2376 GL.
Reference FAA Form 337 for return to service documentation.
Reweighed aircraft using Evergreen Road Runner weighing scales (Model 23, Serial No. 237654, calibrated 06-23-2006).
New empty weight is 4,320 lbs. and empty weight CG is 39.2 inches.
Updated Equipment List and Flight Manual.
Signed by William Dudash (A&P License No. 2724502).
PURPOSE OF WEIGHT & BALANCE
The primary purposes include:
Safety: Ensuring safe operation of the aircraft.
Efficiency in Flight: Optimizing performance and fuel efficiency.
PROOF OF COMPLIANCE
Compliance with 14 CFR Part 23.21 regarding the determination of:
EMPTY WEIGHT and corresponding CG must be established at the time of certification.
The manufacturer is allowed to weigh one of every ten aircraft produced; others receive computed weight & balance reports.
Reports on empty weight must be clearly defined and easily replicated.
NEED FOR REWEIGHING
Reweighing is suggested under certain conditions:
For private aircraft, there is no mandatory requirement unless W&B records are lost.
Recommended circumstances include:
Notable weight gain over time.
Following repainting.
For Air Taxi and Air Carrier operations, a mandatory reweighing schedule is enforced.
NEGLIGIBLE WEIGHT CHANGE TOLERANCES
Guidelines for permissible weight changes based on aircraft weight category:
For aircraft weighing 5,000 lbs. or less: Change of 1 lb. is permissible.
For aircraft weighing between 5,000 lbs. to 50,000 lbs.: Change of 2 lbs. is permissible.
For aircraft over 50,000 lbs.: Change of 5 lbs. is permissible.
THEORETICAL ASPECTS OF WEIGHT & BALANCE
Force of Gravity: Refers to the force drawing all bodies towards the Earth’s center.
Center of Gravity (CG): Defined as the point where the nose-heavy and tail-heavy moments are equal.
Manufacturers provide a tolerance range for CG, known as the operating range.
CONDITIONS AFFECTING WEIGHT & BALANCE
Three specific conditions related to W&B:
Nose Heavy - nose has to much weight
Tail Heavy - tail has the best weight
Overweight - to much weight in general
IMPACTS OF IMPROPER LOADING
Failing to properly balance an aircraft can result in:
Reduced service ceiling.
Decreased rate of climb and speed.:
Increased fuel consumption.
Potential loss of life and destruction of property.
Excessive wear and tear on aircraft structure, leading to potential failure.
Increased required take-off distance.
Reduced maneuverability and unstable control response.
Increased costs associated with maintenance.
WEIGHT VS. STRUCTURAL LIMITS
Aircraft are designed to withstand normal and abnormal flight loads known as “G” loads:
In straight, level flight, wings experience 1 G.
In a 30° banked coordinated turn, wings support 1.5 Gs, resulting in increased load. E.g., a 4,000 lb aircraft will need to handle 6,000 lbs in such conditions.
In a 60° bank, the load increases to 2 Gs, or 8,000 lbs.
SOURCES TO FIND WEIGHT & BALANCE DATA
Aircraft Specifications and Type Certificate Data Sheets (TCDs): These documents provide vital metrics.
Approved Flight Manual and Pilot's Operating Handbook: Required documentation.
Aircraft W&B Report: Fundamental for compliance and safety checks.
KEY TERMS
Datum: An imaginary vertical line or plane used for reference in horizontal measurements.
Positioned 90° to the horizontal axis, established by the manufacturer and detailed in the TCDS.
Type Certificate Data Sheets (TCDS): Official FAA-issued specifications that determine if a device meets airworthiness criteria.
Available on the FAA website (www.faa.gov).
Arm: The horizontal distance (inches) from the datum to the CG of an item.
Positive if aft of the datum and negative if forward.
Moment: The rotational effect on an object, calculated as the weight multiplied by arm length.
Expressed in pound-inches (lb-in). To determine total moment: Total Moment = Weight x Arm.
CENTER OF GRAVITY.
The point where all weight is concentrated and where the aircraft is balanced.
Calculated by dividing the total moment by the total weight (CG = Total Moment / Total Weight).
Note that the CG shifts during flight, e.g., due to fuel consumption.
CENTER OF PRESSURE
Also known as center of lift.
Represents the point on an airfoil generating the most lift.
Shifts with changes in the angle of attack (AoA).
MAXIMUM WEIGHTS
Maximum Weight: The highest allowed aircraft weight as per TCDS.
Example: Landplane max weight = 2200 lbs (Normal), 1900 lbs (Utility).
Maximum Landing Weight: The weight limit for landing as specified in the TCDS.
Maximum Ramp Weight: Total weight constraint for ground maneuvering activities.
Maximum Take-Off Weight: Limit at the beginning of the take-off run.d
EMPTY WEIGHT (EW)
Definition: The weight of the aircraft's structure, powerplant, and fixed equipment.
Includes unusable fuel, full oil, and hydraulic fluid.
Calculated and recorded in the W&B report.
Important note: For previously Certified Aircraft under Civil Aeronautics Regulations (CAR -3), oil weight used to be excluded from the empty weight. Under CFR Part 23, oil weight is included.
USEFUL LOAD
Definition: The total weight available for cargo.
Includes the pilot, crew, passengers, baggage, and usable fuel.
Determined by subtracting the empty weight from the maximum weight.
Sometimes referred to as payload.
CALCULATING USEFUL LOAD
Example calculation:
Maximum Take Off Weight: 10,000 lbs
Empty Weight: 6,000 lbs
Useful Load:
EMPTY WEIGHT CENTER OF GRAVITY (EWCG)
The CG when the aircraft is in its empty weight condition, serving solely as a reference point.
Includes:
Airframe weight
Powerplant weight
All permanently installed equipment
All optional and special equipment
Unusable fuel
Full oil and hydraulic fluid
Fixed permanent ballast.
Does not include usable fuel, occupants, or cargo.
EWCG RANGE
Defined parameters ensuring that the EWCG falls within specified limits during normal operation.
May be specified in TCDS, allowing exceptions for forward and rearward checks under standard loading conditions.
CENTER OF GRAVITY (CG) RANGE
The allowable distance between forward and rearward limits for operation defined in TCDS.
Example: For a Cessna 170A in Normal Category, limits are from (+40.8) to (+46.4) at maximum weight of 2200 lbs.
ROUNDING CALCULATIONS
TCDS provides rounding tolerances for calculations:
Example Rounding tolerances:
To the nearest tenth, hundredth, or thousandth as needed.
CG ENVELOPE
A graphical representation demonstrating the range of CG limits as influenced by aircraft weight.
BALLAST
Weight added to achieve a favourable CG position.
Typically made from lead or depleted uranium.
Must be marked as "BALLAST".
Can be either movable or permanent, and approved technical data by FAA must be used for additions.
MEAN AERODYNAMIC CHORD (MAC)
Conceptual airfoil representation to simplify CG expressions.
Length and CG referenced as percentages in TCDS rather than inches.
AIRCRAFT ATTITUDE AND CONDITION FOR WEIGHING
Conditions during weighing:
Must be in level flight position.
Clean and in Empty Weight (EW) state.
Weighed indoors, parking brake released.
Can be weighed with or without fuel and oil.
LEVELING MEANS
Reference points ensuring aircraft is level for W&B checks found in TCDS.
LEVELING AIDS
Tools to determine level status:
Plumb bob, spirit levels, custom fixtures.
Adjustments may include using jacks, tail stands, modifying tire pressure, or using blocks/chocks.
WEIGHING SCALES
Must feature zero calibration, current calibration traceable to the National Institute of Standards and Technology (NIST).
Types include platform/mechanical and electronic scales (most accurate).
TARE WEIGHT
Defined as the weight of weighing equipment not part of the airplane's actual weight; must be removed from scale readings.
STANDARD WEIGHTS
Accepted weights for W&B calculations:
AVGAS: 6 lb/gal
Turbine fuel: 6.7 lb/gal
Oil: 7.5 lb/gal
Water: 8.3 lb/gal
Crew and passengers: 170 lbs Normal, 190 lbs Utility.
SEATING LOCATIONS
Specified in TCDS.
Example: Cessna 172K with seating for 4 (2 at +34 to +46 inches, 2 at +73 inches).
BAGGAGE WEIGHT AND LOCATIONS
Specified in TCDS:
Example: Cessna 182 N has maximum baggage limits across different serial numbers.
WEIGHING POINTS
Defined locations for scales during weighing, specified in Aircraft Specification Sheets or FAA Approved Flight Manual.
Locations can include jacking points and wheel touchpoints.
TCD WEIGHING POINT DATA
Weight specifications for various aircraft models:
Details on landing gear and associated weights/installation instructions.
MAXIMUM EXCEPTIONS TAKEOFF (METO)
Highest available power rating from reciprocating engines excluding takeoff ratings. Refer to TCDs for horsepower details.
MINIMUM FUEL
Required for operation calculated based on METO horsepower.
Example Calculation: When calculating the amount of minimum fuel required:
ZERO FUEL WEIGHT
Maximum weight of a loaded aircraft, excluding fuel weight.
Any weight above maximum zero fuel weight must consist of usable fuel.
OIL
Included in empty weight as per regulations set on March 1, 1978; previous regulations excluded oil from empty weight calculations.
USABLE FUEL
The usable portion of total fuel defined in TCDS.
Example: Fuel capacity of 42 gallons total, 37 gallons usable.
UNUSABLE FUEL
Fuel that cannot be used in normal flight; part of the empty weight.
Specification of the amount and characteristics specified in TCDS.
RESIDUAL FUEL & OIL
Refers to weights of fuel or oil that cannot be drained, typically specified in TCDS.
REQUIRED EQUIPMENT
Mandatory equipment stipulated by FAA for aircraft airworthiness is recorded in an equipment list; a current W&B report must be part of this documentation.
OPTIONAL EQUIPMENT
Equipment that is not required for aircraft safety but may be installed.
ADVERSE LOADING CHECKS
Calculative checks to ensure aircraft loading does not exceed safety margins under extreme load configurations.
Two primary computations for stability: Forward Loading Check and Rearward Loading Check.
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FORWARD CHECK GUIDELINES
Criteria for assessing forward load condition includes the following:
Aircraft is loaded nose heavy, with full use of indicated fuel and weight arrangements based on TCD specifications.
REARWARD CHECK GUIDELINES
Similar criteria as forward check but load is balanced towards the tail; ensures stability with full rear passenger and baggage allocations.
LOADING SCHEDULES
Must determine allowable passengers and baggage after accounting for fuel capacities and limitations as per TCD.
INITIAL SETUP OF WEIGHT & BALANCE PROBLEMS
Identification requires:
Data Plate: Make, Model, Serial Number, Nationally Number, Category.
Significant TCD specifics guide empty weight and CG calculations.
REQUIRED CALCULATIONS
Necessary for comprehending overall W&B:
EMPTY WEIGHT
EMPTY WEIGHT CG
USEFUL LOAD
FORWARD AND REARWARD EXTREME CHECKS
Loading schedules underpin safety and compliance.
CONDITION OF AIRCRAFT FOR EMPTY WEIGHT DETERMINATION
Condition assessments when weighing include:
Fuel levels (full/no fuel)
Oil levels (full/no oil)
Hydraulic fluid levels (full/no fluid).
FORMULA FOR ADDING OR REMOVING BALLAST
Breakdown:
LW = Loaded Weight
DO = Distance out of Range
BL = Ballast to be added or removed.
FUEL TANKS OPERATION
Header Tank: Ensures positive pressure for float-type carburetors, typically filled when other tanks contain fuel.
FUEL OPERATION REQUIREMENTS
Specified restrictions on auxiliary fuel tanks for take-off and landing; main tanks must carry minimum fuel.
LANDING GEAR RETRACTION AFFECT
The nature of CG shifts due to gear position changes during take-off and landing must be accounted for in calculations to maintain safe stability limits.
LANDING GEAR RETRACTION CALCULATION
Adjust calculations during forward and rearward checks to ensure adherence to CG limitations.
EXAMPLE CALCULATIONS
Demonstration of weight and moment calculations adhering to a specific W&B check.
Weight assessments and arm length considerations leading to CG calculations, adjusting post-retraction conditions to adhere to operational limits.
LOADING GRAPHS & CG ENVELOPES
Tools provided by the manufacturer enabling rapid assessments of CG based on various loading scenarios.
These graphs are foundational in ensuring compliance and safety in weight management.
MEAN AERODYNAMIC CORD (MAC) METHOD
A standardized method for expressing CG as a percentage of MAC, standard range typically between 16%-34% of MAC as defined in TCDS.
FINDING MAC
Calculated by measuring distances between leading edge and trailing edge chords; used to determine overall aircraft CG in simple, meaningful units.
FORMULA FOR MAC
ext{CG} - ext{LEMAC} imes 100 = ext{CG in % of MAC}
Example calculation demonstrating accessibility to performance analysis with respect to horizontal measurement accuracy.