Repositioning the CG: Mass-Shift Formula and Practical Corrections

031-05-03Pablo Asensio Martínez2026-04-011 min

Shifting Mass

If the calculate CG is outside the limits, load (passengers or cargo) can be moved to bring the CG back into the safe envelope.

The Formula

The change in CG position ($\Delta CG$) is proportional to the mass moved and the distance it is moved, relative to the total mass of the aircraft.

$ \Delta CG = \frac{\text{Mass Moved} \times \text{Distance Moved}}{\text{Total Mass}} $

  • Mass Moved: The weight of the item being shifted.
  • Distance Moved: The distance between the old location and the new location of the item.
  • Total Mass: The total mass of the aircraft (which remains constant during a shift).

Direction of Shift

The CG moves in the same direction as the mass being moved.

  • Move load Aft $\rightarrow$ CG moves Aft.
  • Move load Forward $\rightarrow$ CG moves Forward.

Example

  • Total Mass: 10,000 kg
  • Current CG: 200 inches (Too far aft)
  • Desired CG: 195 inches (Need to move CG 5 inches forward)
  • Distance available to move cargo: 200 inches (e.g., from rear hold at 300" to fwd hold at 100")

How much cargo must be moved?

$ \Delta CG = 5 \text{ inches} $ $ 5 = \frac{\text{Mass Moved} \times 200}{10,000} $ $ \text{Mass Moved} = \frac{5 \times 10,000}{200} = 250 \text{ kg} $

Action: Move 250 kg from the rear hold to the forward hold.