What is a moment in weight and balance?

A moment is weight multiplied by arm — the distance of that weight from the aircraft's reference datum. Summing every item's moment and dividing by total weight gives the centre of gravity. Moments capture not just how heavy a load is but where it sits.

What is the arm and where does it come from?

The arm is the horizontal distance in inches or millimetres from the datum to the centre of a loading station — a seat, baggage area, or fuel tank. These arms are published in the aircraft's type certificate data sheet and pilot operating handbook loading section.

Why does CG matter as much as total weight?

An aircraft can be under its maximum weight yet still unsafe if the CG is too far forward or aft. A forward CG strains the elevator and may prevent rotation; an aft CG reduces longitudinal stability and can make the aircraft uncontrollable. Both limits must be respected.

How is the centre of gravity calculated?

CG equals total moment divided by total weight. Add every item's weight to get gross weight, add every item's moment to get total moment, then divide. If the result lies between the forward and aft limits and weight is within max, the loading is legal.

Is this a real loading chart for my aircraft?

No. This is a generic teaching tool using whatever limits you enter. Always use the actual weight-and-balance data, arms, and CG envelope from your specific aircraft's pilot operating handbook for any real flight planning. Never fly on a generic envelope.

Aircraft CG Envelope Check Tool

Loading an aircraft safely means checking two things together: that it is under its maximum weight, and that its centre of gravity falls within the certified envelope. This tool computes the moment for each item you load, sums to a gross weight and CG, and flags whether the result is inside a generic light-aircraft envelope.

How it works

Each item’s moment is its weight times its arm (distance from the datum). Summing all moments and dividing by total weight gives the CG, which is then checked against the weight and CG limits:

moment_i   = weight_i × arm_i
total_wt   = Σ weight_i
total_mom  = Σ moment_i
cg         = total_mom / total_wt
in_limits  = total_wt ≤ max_weight  AND  fwd_limit ≤ cg ≤ aft_limit

A loading is legal only when it passes all three checks: under maximum weight, not forward of the forward CG limit, and not aft of the aft CG limit.

Example and tips

Suppose an empty aircraft weighs 1,500 lb at arm 39.0, a pilot of 170 lb sits at arm 37.0, 120 lb of fuel sits at arm 48.0, and 50 lb of baggage at arm 95.0. Total weight is 1,840 lb and total moment is the sum of each weight times arm; dividing gives a CG around 41 inches. If the envelope runs 35.0 to 47.3 inches and max weight is 2,300 lb, this load is legal. Always pull the real arms and envelope from your aircraft’s pilot operating handbook — never plan a real flight on generic numbers — and recheck CG for the landing weight after fuel burn, since burning fuel shifts the CG.