The COG envelope, or center of gravity envelope, is a graphical representation that shows the allowable combinations of aircraft weight and center of gravity (COG) positions for safe flight. This representation is crucial to ensure that the aircraft is operated within the permissible limits, which is essential for the stability and safety of the flight.
Representation of the COG envelope:
2D diagram:
The COG envelope is displayed in a two-dimensional diagram that includes the following axes:
X-axis: Position of the center of gravity, expressed as a percentage of the mean aerodynamic chord (%MAC) or as a distance in inches from a reference datum.
Y-axis: Weight of the aircraft, given in kilograms or pounds.
Approved COG range:
The shaded or outlined area within the diagram represents the approved COG range.
Within the limits Combinations of weight and COG positions that are safe to fly.
Outside the borders: Combinations that are not certified and can lead to unsafe or unstable flight.
Purpose of the COG Envelope:
Stability, controllability and structural security:
The COG envelope ensures that the aircraft is operated within the limits necessary for stability, controllability and structural safety.
Aids for flight crews and dispatchers:
The COG Envelope helps flight crews and dispatchers with the determination:
- Whether the current load is safe.
- Whether trim weights or ballast are required to keep the COG within the permissible limits.
- Whether fuel or cargo needs to be redistributed to optimize the balance of the aircraft.
Related concepts:
COG area:
The COG range defines the limits of the center of gravity position at different weights and is an essential component of the COG envelope.
Important weight definitions:
- ZFW (Zero Fuel Weight): The weight of the aircraft without fuel.
- MTOW (Maximum Takeoff Weight): The maximum weight at which the aircraft can take off safely.
- MLW (Maximum Landing Weight): The maximum weight at which the aircraft can land safely.
These weights are typically displayed on the COG envelope to provide additional reference points for flight planning.
Flight range limits:
Flight envelope limits are used in conjunction with the COG envelope to calculate the actual COG for given loads. This helps to accurately plan the loading and distribution of cargo and passengers.
The COG Envelope is therefore an indispensable tool for flight planning and execution, ensuring that the aircraft is operated within the permissible limits and thus guaranteeing the safety and efficiency of flight operations.
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