Aviation weight and balance is the study of how an aircraft's load affects its stability and control. Every airplane has a maximum weight and an approved center of gravity range that must be respected before flight. If the airplane is too heavy or the center of gravity is outside limits, it may not climb, turn, flare, or recover safely.
Pilots calculate weight and balance so the aircraft handles as the designers intended.
Key Facts
- Weight is the force of gravity on the aircraft and everything loaded in it.
- Moment = Weight x Arm
- Center of gravity location = Total moment / Total weight
- Forward center of gravity increases stability but can make it harder to raise the nose.
- Aft center of gravity reduces stability and can make stalls and recovery more dangerous.
- An aircraft is safe to fly only if total weight and center of gravity are within the approved limits.
Vocabulary
- Center of Gravity
- The center of gravity is the point where the aircraft's total weight can be considered to act.
- Arm
- Arm is the distance from a chosen reference point to the location of a weight.
- Moment
- Moment is the turning effect produced by a weight located some distance from a reference point.
- Datum
- The datum is the fixed reference line used to measure arms in an aircraft weight and balance calculation.
- CG Envelope
- The CG envelope is the approved range of total weight and center of gravity positions for safe flight.
Common Mistakes to Avoid
- Adding weights without calculating moments is wrong because the location of each weight matters as much as the amount of weight.
- Using the wrong arm for baggage or fuel is wrong because even a small distance error can shift the calculated center of gravity outside limits.
- Assuming a forward center of gravity is always safer is wrong because too much forward loading can prevent proper rotation, climb, or landing flare.
- Ignoring fuel burn is wrong because fuel weight changes during flight and can move the center of gravity into or out of the safe range.
Practice Questions
- 1 An airplane has an empty weight of 1,400 lb at an arm of 40 in, two passengers totaling 320 lb at an arm of 37 in, and baggage of 80 lb at an arm of 70 in. Find the total weight, total moment, and center of gravity location.
- 2 A training aircraft has a total weight of 2,000 lb and a total moment of 92,000 lb in. What is its center of gravity location? If the safe CG range is 43 in to 47 in, is it within limits?
- 3 Explain why an aft center of gravity can make an airplane feel more responsive but less stable, especially during a stall recovery.