Definition of the Center of Gravity for Aviation

Center of Gravity

• The weight of an airplane is not actually concentrated at one specific spot -- it is distributed throughout the airplane based on the weight of its parts and what it is carrying, including the fuel and the payload. However, the average location of the weight as a whole can be calculated by using a mathematical formula, establishing a single point in the airplane as the center of gravity. The airplane actually rotates around this point while in flight.

Calculating the Center of Gravity

• The weight of any individual part of the airplane (such as a wing) can be calculated by taking the mass of the part and multiplying it by 32.2 feet per square second, the gravitational constant. Once this formula is applied to all of the individual parts (including payload and fuel), they can be added together to determine the total weight. Next, a point outside the airplane is selected as the reference line. The weight of each individual part of the airplane is multiplied by its distance from the reference line, and then those sums are added together. This final sum will be equal to the weight of the entire airplane multiplied by the center of gravity. (See References 2)

Importance of the Center of Gravity

• Knowing an airplane's center of gravity is essential to safe flight, because the center of gravity is the point around which the airplane moves when it is aloft. If the center of gravity is too far to the front of the airplane, the pilot may find it hard to get the tail down when bringing the plane in. This can also put too much stress on the nose wheel structure, and may be exhausting for the pilot. When the center of gravity is too far to the back of the airplane, the plane can spin out of control or even suffer structural failure.

Finding the Correct Center of Gravity

• Every airplane has a range in which the center of gravity can fall and still allow the airplane to be operated safely. These are the center of gravity limits. The center of gravity limits are different for different types of planes, so it is important for a pilot to check them when flying a new model. Each aircraft should come with a chart known as Chart E, which contains the center of gravity limits for that particular plane. If the center of gravity is calculated and found to fall outside the limits for that plane, then the weight must be redistributed.