Center of gravity of an aircraft

If it is not, weight in the aircraft must be removed, added (rarely), or redistributed until the center of gravity falls within the prescribed limits.

In larger aircraft, weight and balance is often expressed as a percentage of mean aerodynamic chord, or MAC.

When the fore-aft center of gravity (CG) is out of range, serious aircraft control problems can occur.

The center of gravity is even more critical for helicopters than it is for fixed-wing aircraft (weight issues remain the same).

The pilot tries to perfectly balance a helicopter so that the fuselage remains horizontal in hovering flight, with no cyclic pitch control needed except for wind correction.

A forward CG may occur when a heavy pilot and passenger take off without baggage or proper ballast located aft of the rotor mast.

The helicopter will have a nose-low attitude, and the pilot will need excessive rearward displacement of the cyclic control to maintain a hover in a no-wind condition.

In this condition, the pilot could rapidly run out of rearward cyclic control as the helicopter consumes fuel.

In the event of engine failure and the resulting autorotation, the pilot may not have enough cyclic control to flare properly for the landing.

When determining whether a critical balance condition exists, it is essential to consider the wind velocity and its relation to the rearward displacement of the cyclic control.

The helicopter will have a tail-low attitude, and the pilot will need excessive forward displacement of cyclic control to maintain a hover in a no-wind condition.

If flight is continued in this condition, the pilot may find it impossible to fly in the upper allowable airspeed range due to inadequate forward cyclic authority to maintain a nose-low attitude.

In addition, with an extreme aft CG, gusty or rough air could accelerate the helicopter to a speed faster than that produced with full forward cyclic control.

In this case, dissymmetry of lift and blade flapping could cause the rotor disc to tilt aft.

This is because helicopter cabins are relatively narrow and most optional equipment is located near the center line.

This section shows data obtained from a NASA Ames research grant for large commercial transport aircraft.

The nose baggage compartment of a Fokker F.XII in 1933, avoiding the problem of heavy weights towards the rear
A sample CG-moment envelope chart, showing that a loaded plane weighing 2,367 lb (1,074 kg) with a moment of 105,200 lb⋅in (11886 N⋅m) is within the "normal category" envelope.
The center of gravity of this British Aerospace 146 shifted rearward when its engines were removed. As a result, it tipped back onto its rear fuselage in windy conditions.
CG factors for transport aircraft
CG of components and systems
CG range of typical transport aircraft