Definition
A weight-and-balance calculation method used to find how far the center of gravity (CG) shifts when weight is added to or removed from an aircraft. It uses the ratio of the added or removed weight to the new total weight, multiplied by the distance between that weight's location and the original CG, to determine the CG shift.
Plain English
A simple ratio calculation that tells you how much the balance point of the aircraft moves when you add or remove cargo, fuel, or passengers. It compares the size of the change to the size of the whole airplane's weight to figure out how far the balance point shifts.
Context Anchor
Seen in weight-and-balance calculations when equipment, baggage, or other weight is added to or removed from an aircraft.
Derivation
Proportional' comes from the Latin 'proportio,' meaning 'comparative relation.' The formula works on the idea that the CG shift is in proportion to how big the weight change is compared to the total aircraft weight — a bigger change relative to the whole means a bigger shift.
Why Pilots Care
Keeps the center of gravity within certified limits after any weight change so the airplane remains stable and controllable.
Analogy
It is like using a scale drawing: if one part changes by a certain ratio, another related part changes by the same ratio. The formula uses that relationship to find the balance change.
Intuition Check
Do not read “proportional formula” as just any formula that uses numbers. Here it means a specific ratio-based method used to connect a weight change with a balance-point change.
Example Sentence 1
After unloading two passengers from the rear seats, the pilot used the proportional formula to confirm the CG had moved forward but was still within limits.
Example Sentence 2
After removing the rear seats, the crew applied the proportional formula to confirm the new CG stayed inside the forward limit.