The total mass of the aircraft can be said to act through one point, called the Centre of Gravity (CG) and the total lift acts through the Centre of Pressure (CP).

The position of the CP changes with speed and as alpha changes, whilst the position of CG changes as load and fuel change. When this happens, new balancing forces and trim changes will be needed.

The relative positions of the CG and CP affect the longitudinal stability of the aircraft. In practice, the CG is usually forward of the CP, thus, the more forward the CG, the more stable the aircraft in pitch. Some stability in pitch is desirable, but not too much, because the extra down force on the elevator effectively adds to the aircraft weight and requires the lift to be increased to counter it. More lift means more drag created by the trim (trim drag) and more drag means higher fuel consumption.

Aircraft manufacturers determine a safe range for the CG. The aft limit is usually just in front of the Centre of Pressure, but it provides less stability than that provided by the forward limit, but a smaller balancing tail moment will be required.

In summary, assuming that gross mass, altitude and airspeed remain unchanged, the movement of the Centre of Gravity from the forward to the aft limit:

• Increases the Rate of Climb and the Climb gradient
• Decreases TORR, TODR, ASDR, thus MTOM can be increased
• Makes the required stick forces less
• Makes rotation easier
• Decreases stall speed, which permits a higher ceiling altitude
• Makes flare easier during landing, thus decreasing LDR and increasing MLM
• Increases range and endurance, due to the decreased fuel consumption