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CG calculator

Measure one wing half and enter the numbers. The calculator finds the mean aerodynamic chord (MAC) and puts the balance point at the percentage you choose.

Front to back at the wing root (centre of the model).
Front to back at the wing tip.
How far the tip's leading edge is behind the root's leading edge. 0 for a straight leading edge.
Root to tip, measured straight out (half the wingspan).
25% is a safe start for most models. Flying wings 15-20%. Many sport models fly well at 28-33% once trimmed.

Result

Fill in the numbers above to see the result.

How it works

The mean aerodynamic chord (MAC) is the chord of an imaginary straight wing that behaves like yours. For a tapered wing it is longer than the average chord and sits nearer the root.

MAC = 2/3 × root × (1 + λ + λ²) / (1 + λ), where λ is tip chord ÷ root chord. It sits (half span ÷ 3) × (root + 2 × tip) ÷ (root + tip) out from the root, and sweep moves its leading edge back by the same proportion.

The balance point is then the chosen percentage of the MAC behind the MAC's leading edge. We show it measured from the leading edge at the root, which is the easiest place to mark on a real model.

Balance the model on your fingertips at that mark, nose very slightly down. Always check against the manual - designers sometimes give a different CG.

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