Aircraft Weight & Balance
Centre-of-gravity and balance-limit calculation, the weighing procedure and precautions, and the weight-and-balance documentation.
Weight & balance, summary notes
- Weight and balance establishes the aircraft's empty weight and centre of gravity (CG) and confirms the CG stays within the forward and aft limits for every loading, a CG outside limits makes the aircraft unstable or uncontrollable.
- The DATUM is a defined reference plane; the ARM is the horizontal distance of a weight from the datum, and the MOMENT is weight × arm. The CG is the total moment divided by the total weight, measured from the datum.
- Weighing procedure: use the approved weighing schedule, put the aircraft in the defined configuration (fuel and fluids drained or accounted for, specified equipment fitted/removed, state recorded), and use calibrated, in-date load cells or scales at the jacking or wheel points.
- Weigh in a closed, draught-free, dry hangar to avoid wind and rain errors, and level the aircraft to its datum using the built-in level provision.
- Record the reaction at each weighing point and its arm; sum the moments and divide by the total weight to find the empty-weight CG, then compare against the limits.
- Account for TARE, the weight of chocks, jacks and adapters on the scales, and subtract it, and record the true empty-weight configuration.
- The weight-and-balance report and the loading/mass-and-balance documentation are updated and certified after any weighing or major modification affecting weight.
- ⚠ Exam trap: Moment = Weight × Arm, and CG = Σ Moments ÷ Σ Weights measured from the datum, and remember to remove tare.
- Moment
- Moment = Weight × Arm
- Centre of gravity
- CG = Σ Moments ÷ Σ Weights (from the datum)
- Net weight
- scale reading − tare = actual reaction
Datum at the nose. Nose gear 500 kg at arm 1.0 m; main gear 1500 kg at arm 5.0 m. Find the CG.
Total weight = 2000 kg. Total moment = (500 × 1.0) + (1500 × 5.0) = 500 + 7500 = 8000 kg·m. CG = 8000 ÷ 2000 = 4.0 m aft of the datum.
Why is the aircraft weighed in a closed hangar and levelled to its datum?
Wind produces aerodynamic lift or download and rain adds weight, both falsifying the reading, so the hangar must be draught-free and dry. Levelling to the datum ensures the arms used in the calculation match the schedule; an out-of-level aircraft gives wrong arms and therefore a wrong CG.
Weight & balance concept map
Weight & Balance
Weight & balance quiz
Weight & Balance, quiz
1. An aircraft weighs 2400 kg with its centre of gravity 2.5 m aft of datum. The total moment about datum is:
6000 kg·m960 kg·m2402.5 kg·m2. Total moment is 9000 kg·m and total weight is 3000 kg. The centre of gravity lies:
3.0 m aft of datum27 000 m aft of datum0.33 m aft of datum3. An aircraft of 2000 kg has its CG at 2.0 m. Adding 100 kg of baggage at 4.5 m moves the CG to approximately:
2.12 m2.25 m3.25 m4. Moment in a weight-and-balance calculation equals:
Weight × armWeight ÷ armWeight + arm5. Centre of gravity is:
Total moment ÷ total weightTotal weight ÷ total momentThe heaviest point6. The arm is the distance of a weight from the:
DatumNose gearWing tip7. Nose gear 500 kg at 1 m, mains 1500 kg at 5 m. The CG is:
4.0 m from datum3.0 m5.0 m8. An aircraft is weighed in:
A closed, draught-free, dry hangarThe open, in any weatherA pressurised chamber9. Before recording weights, the aircraft is:
Levelled to its datumFully fuelledJacked to maximum height10. Tare weight on the scales is:
Subtracted from the readingAdded to the readingIgnored