Mass and Balance
Mass and Balance tests the calculation and control of aircraft weight and centre of gravity (CG) so that performance, stability and structural limits are respected throughout the flight.
Core rules
- Weight × arm = moment; total moment divided by total weight gives the CG position.
- Maximum takeoff, landing and zero-fuel weights must not be exceeded; the zero-fuel weight excludes usable fuel.
- The CG must remain within forward and aft limits for takeoff, in flight and landing.
- A forward CG increases elevator authority needed and can increase stall speed; an aft CG reduces static stability.
Worked example
Basic empty weight 1,200 kg at 2.0 m; pilot 100 kg at 1.5 m; fuel 200 kg at 3.0 m; baggage 50 kg at 4.0 m. Total weight = 1,550 kg. Total moment = (1,200×2.0)+(100×1.5)+(200×3.0)+(50×4.0) = 2,400+150+600+200 = 3,350 kg·m. CG = 3,350 ÷ 1,550 = 2.16 m. If the limit is 1.80–2.30 m, the loading is legal.
Traps
- Forgetting the fuel moment or using volume instead of mass.
- Mixing units: kg·m versus kg·in.
- Checking only takeoff CG and not zero-fuel or landing CG.
- Assuming an aft CG is always faster and therefore better; stability margins are reduced.