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Elite Radio Control

Free calculator

RC Plane Center of Gravity (CG) Calculator

Enter your wing's measurements to get the mean aerodynamic chord, where to mark the center of gravity and the wing loading of your RC plane.

CG from the leading edge, at the root

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Mean aerodynamic chord (MAC)
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MAC position from the fuselage
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Wing area
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Wing loading
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Mark the CG at the wing root, measured from the leading edge, on both sides of the fuselage. Balance the plane ready to fly, battery installed. Your manual always comes first.

How to use the calculator

  1. Measure the root chord (the wing’s width next to the fuselage) and the tip chord.
  2. Measure the total wingspan, from tip to tip.
  3. If the wing has sweep, measure how far the tip’s leading edge sits behind the root’s. For a straight wing, leave it at 0.
  4. Pick the percentage of the mean chord where you want the CG. Use your manual’s figure; if you don’t have one, 25% is a common starting point.

Work in inches and ounces or in millimeters and grams: choose the units at the top. The calculator gives you the distance at which to mark the CG from the leading edge, at the wing root. Mark that point on both sides of the fuselage and balance the plane there on your fingertips or a CG balancer.

The formulas

For a tapered wing (each half is a trapezoid), with Cr the root chord, Ct the tip chord and λ = Ct / Cr:

  • Mean aerodynamic chord: MAC = 2/3 × Cr × (1 + λ + λ²) / (1 + λ)
  • MAC position from the fuselage: Y = (span / 2) / 3 × (1 + 2λ) / (1 + λ)
  • MAC leading edge: sweep × Y / (span / 2) behind the root leading edge
  • CG: MAC leading edge + percentage × MAC
  • Wing loading: weight / area, with area = (Cr + Ct) / 2 × span

On a straight wing (Cr = Ct and no sweep) the MAC is simply the chord, and the CG sits at the chosen percentage of it.

Before the first flight

  • Balance the plane complete and ready to fly, with the battery installed: it’s the heaviest part and the one most often moved to correct the CG.
  • Slightly nose-heavy is better than tail-heavy: a tail-heavy plane can be uncontrollable.
  • Flying wings and unconventional designs may need different values: always follow the designer’s instructions.

Building your own? See how to build a homemade RC plane.

Frequently asked questions

Where should the CG be on an RC plane?

Wherever the manual says. If you don't have that figure, a common starting point is 25% of the mean aerodynamic chord, measured from the leading edge, then adjust it based on how the plane flies.

What is the mean aerodynamic chord?

The chord of a rectangular wing equivalent to yours. On a straight wing it equals the chord; on a tapered or swept wing it sits a little toward the tip and is worked out from the root and tip chords.

What is wing loading?

The plane's weight divided by its wing area, usually in ounces per square foot in the US. The lower it is, the slower the plane can fly and the gentler it feels.

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