Aircraft weight and balance basics
Weight and balance is mostly a running total of weights and moments. The arithmetic is simple; the important part is using the correct aircraft-specific loading data and comparing the final result with the approved envelope.
Weight, arm and moment
The arm is the distance from the aircraft datum to the item. Add the moments for the empty airplane, occupants, fuel, baggage and any other loading stations.
Find the center of gravity
The result is only useful when compared with the approved CG envelope for the airplane at that weight.
Fuel changes the loading
Fuel burn changes both weight and moment. Depending on tank location, the CG can move as fuel is consumed. A single takeoff calculation does not automatically prove the airplane remains within limits through landing.
Profiles save time, not verification
PilotDesk aircraft profiles can remember common station arms and empty-weight data on your device. Treat saved values as a convenience. Verify them against the current aircraft records and POH/AFM before relying on them.
Add the station moments
This generic arithmetic example is not data for a real aircraft. Assume an empty-aircraft entry of 1,500 lb at arm 40 in, a 180 lb pilot at 37 in, a 160 lb passenger at 73 in, 50 lb baggage at 95 in, and 30 US gal of fuel at 6 lb/gal located at arm 48 in.
| Item | Weight | Arm | Moment |
|---|---|---|---|
| Empty aircraft | 1,500 lb | 40 in | 60,000 lb-in |
| Pilot | 180 lb | 37 in | 6,660 lb-in |
| Passenger | 160 lb | 73 in | 11,680 lb-in |
| Baggage | 50 lb | 95 in | 4,750 lb-in |
| Fuel | 180 lb | 48 in | 8,640 lb-in |
Total weight is 2,070 lb; total moment is 91,730 lb-in. CG = 91,730 ÷ 2,070 = 44.3 in aft of datum (rounded). If 9 gal are then consumed from that same assumed tank, remove 54 lb and 2,592 lb-in: landing weight is 2,016 lb, moment 89,138 lb-in, and CG about 44.2 in. Here the CG moves slightly forward because the fuel arm is aft of the starting CG.
Use actual measured aircraft empty weight and moment, the aircraft's own station arms, the correct fuel weight, and the approved envelope at both departure and landing. Never use this made-up loading example to determine aircraft limits.
Why both weight and CG matter
Being under maximum gross weight does not automatically mean the loading is acceptable. A CG that is too far forward or aft can affect control forces, stability, stall behavior, rotation, flare, and recovery characteristics. Use the current aircraft weight-and-balance record and POH or AFM limits rather than a generic preset.