T-tail CG calculator

With the stab on top of the fin, a T-tail flies in clean air away from the wing's wake. Enter your sizes and get the CG and a drawing with the T-tail on top.

1 · Layout

Start from Units

2 · Wing section half wing, centre to tip

Measure from the wing leading edge at the centre line, with spans measured flat, as seen from above. S is how far each panel's tip leading edge sits behind its root. A plain tapered wing needs one panel; an elliptical or polyhedral wing needs 2–5.

Root chord R at the centremm Wing position

Panel	Span W	Tip chord T	Sweep S	Dihedral

3 · Fuselage section

Length no spinnermm Max widthmm Nose to wing LEmm Fuselage in the result

4 · Tail section

Stab root chordmm Wing LE to stab LEmm V angle from horizontal° Tail effectiveness

Panel	Span W	Tip chord T	Sweep S

5 · Fin section

Heightmm Root chordmm Tip chordmm

6 · Balance section

Target static margin

% MAC

Flying weight optional, for wing loadingg VTOL front lift motors optionalmm VTOL rear lift motors from wing LEmm

Results also update as you type.

Balance point—

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.

Top view · scale drawing

WingFuselageTailFin

Safe CG rangeCG and MACNeutral pointPanel joints and hinges

Front view

Side view

7 · Weight & balance helper

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

Your CG now—

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 t-tail

Because the stab sits above the wing's wake, a T-tail works a little better than a low stab. The calculator uses a tail effectiveness of 0.95 for it, which you can change.

The fin carries the stab, so it must be stiff. Check the fin volume in the results.

CG calculator by layout