Weight & balance limits
A CG number alone is not enough: it has to sit between the aircraft's forward and aft CG limits (from the POH/AFM). Compute the CG, then check it against both.
- In limits: forward limit ≤ CG ≤ aft limit. Good to go.
- Out the aft limit (CG too far aft): move load forward, from an aft station (baggage, rear seats) to a forward one.
- Out the forward limit (CG too far forward): move load aft.
To fix an out-of-limits CG by shifting load between two stations:
weight to shift = total weight × (distance the CG must move) / (distance between the two stations)
- Distance the CG must move = how far the CG is outside the limit (CG minus the violated limit).
- Distance between the stations = the two arms subtracted, not added.
- The shift comes out in whatever weight unit you feed in: if the weight is given in kg and the answer is asked in pounds, convert first (1 kg ≈ 2.205 lb).
- You can instead add or remove weight at one station to the same end. Either way, recompute the CG afterward and confirm it now sits inside both limits.
Trap: measuring the CG error from the wrong limit, or adding the station arms instead of subtracting them.
Source note: the CG limits are aircraft-specific givens from the POH/AFM; the numbers in a problem are supplied, not memorised.
References
- POH/AFM