Centre of Gravity (CG) Limitations: Stability, Control, and Recovery Margins

031-01-02Pablo Asensio Martínez2026-04-012 min

Centre of Gravity (CG) Concept

The Centre of Gravity (CG) is the point through which the force of gravity is considered to act on the aircraft. It is the point where the aircraft would balance if suspended. Its position is critical for stability and control.

Importance of CG Limits

The CG must remain within a specified range (the CG envelope) defined by the manufacturer. This range ensures the aircraft is stable and controllable throughout all phases of flight.

Weight and balance chart

Effects of Forward CG

A CG located near the forward limit creates a "nose-heavy" condition.

  • Increased Stability: The aircraft is more longitudinally stable (harder to displace from trim).
  • Reduced Manoeuvrability: Control inputs must be larger to change pitch.
  • Higher Fuel Consumption: The tailplane must produce more downward force (negative lift) to balance the nose-down moment. The wings must produce more lift to support the aircraft weight plus the tail downforce, increasing induced drag.
  • Increased Stall Speed: Due to higher wing loading required to balance the tail downforce.
  • Difficulty in Flare: High stick forces may be required to raise the nose for landing.

Effects of Aft CG

A CG located near the aft limit creates a "tail-heavy" condition.

  • Reduced Stability: The aircraft becomes less logically stable (easier to displace). If the CG moves behind the Neutral Point, the aircraft becomes unstable.
  • Increased Manoeuvrability: Smaller control forces are needed.
  • Lower Fuel Consumption: The tailplane produces less downward force (or even upward force), reducing the lift required from the wings and thus reducing induced drag.
  • Decreased Stall Speed: Lower wing loading.
  • Difficulty in Stall Recovery: Aft CG makes it harder to lower the nose to recover from a stall. Spin recovery may become impossible if the CG is too far aft.

CG Movement

The CG moves during flight due to:

  • Fuel Consumption: Depending on fuel tank location relative to the CG.
  • Landing Gear Retraction/Extension: Shifting mass of the gear.
  • Movement of Payload: Passengers or crew moving in the cabin (though usually negligible in large aircraft).

The pilot must ensure the CG remains within limits for both take-off and landing.