Center of gravity of an aircraft

The center of gravity (COG) of an aircraft is a critical parameter that designates the point at which the entire weight of the aircraft is considered to be concentrated. This point is crucial for the stability and control of the aircraft during flight. The COG affects how the aircraft behaves during pitch, roll and yaw and must be carefully maintained within certain limits to ensure safe flight performance.

Main features of the COG

Position within the CG envelope curve

The COG must be within the forward and backward limits specified by the manufacturer and certified by the aviation authorities. These limits are referred to as the CG envelope and are crucial for flight safety.

Printout of the COG

The COG is often expressed as a distance from a reference datum, either in physical units such as inches or meters, or as a percentage of the mean aerodynamic chord (MAC) for fixed-wing aircraft.

Typical expression of the COG as a percentage of the MAC

The position of the COG can be expressed as a percentage of the mean aerodynamic chord (MAC). The formula for the calculation is

[
\%CG = \left(\frac{\text{CG position} - \text{front edge of the MAC}}{\text{MAC}}\right) \times 100
]

Significance of the COG

Stability and control

A correctly positioned COG is crucial for the stability and control of the aircraft. If the COG is too far forward, the aircraft can become nose heavy, which can lead to difficulty rotating during takeoff and higher stall speeds. If the COG is too far back, the aircraft can become tail-heavy, leading to pitch instability and the risk of uncontrollable flight.

Fuel efficiency

The position of the COG also influences the fuel efficiency of the aircraft. An optimally positioned COG can reduce drag and optimize fuel consumption.

Structural security

Compliance with the COG limits is crucial for the structural safety of the aircraft. A COG outside the permissible limits can lead to excessive loads on the aircraft structure and impair safety.

Compliance with certification

Compliance with the COG limits is also a prerequisite for certification of the aircraft by the aviation authorities. Aircraft must prove that they can be operated safely within the specified COG limits.

Careful monitoring and compliance with the COG is therefore essential for the safety, efficiency and certification of aircraft.