First flight: if your plans or kit show a CG further forward than this, use the more forward one. Move it back later in 3–5 mm steps.
Where does the battery go?
List your parts with their weight and position. Position is measured from the wing leading edge at the root: minus means in front of it. The helper finds your real CG and tells you how far to move the battery.
| Part | Weight | Position | Battery |
|---|
How to use it
- Pick your layout. An example plane loads so you can see how it works.
- Enter the root chord, then one row per wing panel: span, tip chord, sweep and dihedral. Add panels for elliptical, cranked or polyhedral wings.
- Do the same for the tail. For a V-tail, enter the panel length along the panel and the V angle. For a canard, the distance is negative.
- Balance the plane at the CG shown. With your fingers under the wing next to the fuselage, use the "measure at fuselage side" number: on a swept wing the leading edge there is further back than at the centre line.
- Use the weight & balance helper to find the battery position.
- Check side-to-side balance too: hold the plane by the spinner and the tail. If one wing drops, add a little weight to the other wing tip.
- For a VTOL quadplane, enter the front and rear lift motor positions. The CG must also sit near the middle of them for a steady hover.
Tail effectiveness
A tail sitting in the wing's wake or behind a fat fuselage works less well than one in clean air. Auto uses 0.85 for most tails, 0.95 for a T-tail and 1.0 for a canard. These lean to the safe side. Pick a lower value for a short tail close to the wing.
MAC, neutral point and static margin
The mean aerodynamic chord (MAC) is the average chord of the whole wing, including every panel. The neutral point is where the CG would make the plane neutrally stable. The static margin is the gap between the CG and the neutral point, as a percentage of the MAC: 10–20 % suits a plane with a tail, 5–10 % a flying wing or delta.
Typical values
| Plane type | CG (% MAC) | Tail volume |
|---|---|---|
| Trainer, high wing | 25–30 % | 0.5–0.7 |
| Sport / FPV cruiser | 25–33 % | 0.4–0.6 |
| Glider, V-tail glider | 30–38 % | 0.35–0.6 |
| 3D aerobatic | 30–35 % | 0.3–0.5 |
| Flying wing (swept) | 15–20 % | none |
| Delta | 15–22 % | none |
| Canard | ahead of the wing LE | negative |
Starting points. The static-margin check uses your real sizes. Always confirm the CG in flight, moving back in small steps.
Balancing a v-tail
A V-tail panel tilted at angle Γ from horizontal only gives part of its area as a horizontal stab. The calculator uses the standard area × cos²Γ, the more cautious of the common methods, so the CG it gives errs on the safe side.
Most V-tails sit at 30–40° from horizontal (100–120° between the panels). A flatter V gives more pitch stability; a steeper V gives more yaw stability.
Questions
How do I measure a V-tail for the CG calculator?
Measure the panel length along the panel from the root to the tip, the root and tip chord, and the angle of the panel up from horizontal.
Why does a V-tail need a different CG?
Only part of a tilted panel acts as a horizontal stab, so the neutral point is further forward than for a flat stab of the same size. The CG must move forward with it.
Can I use this for a polyhedral glider?
Yes. Add up to five wing panels, each with its own dihedral angle.
Keep designing
Flight time calculator
Endurance and range from weight, props and battery, with hover and cruise power.
Open tool →Wing loading calculator
Wing loading, stall and landing speed, and whether your weight is normal for your build.
Open tool →Battery pack calculator
Voltage, capacity, energy, weight and safe current for any S and P pack.
Open tool →