RC Airplane Tail Sizing Calculator
Enter the wing, tail moment arms, existing tail areas, and target tail-volume coefficients. The calculator checks the current coefficients and reverse-solves buildable tapered tail dimensions.
Required horizontal tail area (in²)65.33
- Wing reference area (in²)
- 384
- Mean aerodynamic chord (in)
- 8.17
- Current horizontal tail volume
- 0.61
- Current vertical tail volume
- 0.04
- Required vertical tail area (in²)
- 32.06
- Horizontal area change
- -18.33%
- Vertical area change
- -10.96%
- Suggested horizontal tail dimensions
- 16.17 in full span, 5.05 in root chord, 3.03 in tip chord
- Suggested vertical tail dimensions
- 7.16 in height, 5.97 in root chord, 2.98 in tip chord
- Tail sizing comparison
- Horizontal tail volume is above the selected target; vertical tail volume is above the selected target.
Use one length unit consistently; volume coefficients are dimensionless only when all lengths and areas use the same unit system.
Treat vertical area as the combined projected area when twin fins are used.
Strongly swept, elliptical, compound, multi-panel, canard, tandem-wing, tailless, and V-tail aircraft need geometry or stability analysis beyond this straight-taper conventional-tail estimate.
How to use this calculator
- Choose inches or centimeters and use that unit system for every length and area entry.
- Enter the full wingspan plus root and tip chords for the straight-tapered wing model.
- Enter the horizontal and vertical tail moment arms measured quarter-chord to quarter-chord.
- Enter existing tail areas and target coefficients from a comparable, proven aircraft.
- Set aspect ratio and taper ratio to get suggested root and tip chords for each tail.
How the tail size is calculated
This calculator uses the tail-volume coefficient method, a preliminary geometry check used before detailed stability and control analysis. It assumes a straight trapezoidal wing and conventional horizontal and vertical tails. For a full wing span b, root chord cr, tip chord ct, and wing taper ratio lambdaW = ct / cr, the wing reference area is:
Sw = b * (cr + ct) / 2
The mean aerodynamic chord for the same straight-tapered wing is:
cBar = (2 * cr / 3) * ((1 + lambdaW + lambdaW^2) / (1 + lambdaW))
With existing horizontal tail area Sh, vertical tail area Sv, horizontal arm lh, and vertical arm lv, the current coefficients are:
VH = Sh * lh / (Sw * cBar)
VV = Sv * lv / (Sw * b)
The targets reverse those equations. The required areas are ShReq = VHt * Sw * cBar / lh and SvReq = VVt * Sw * b / lv. Area change is reported as 100 * (required - existing) / existing; if the existing area is zero, the calculator shows the required area but marks the percentage change as not applicable.
Turning area into buildable dimensions
For each required tail area S, selected aspect ratio AR, and taper ratio lambda, the suggested span or vertical height is B = sqrt(AR * S). The root chord is Croot = 2S / (B * (1 + lambda)), and the tip chord is Ctip = lambda * Croot. A taper ratio of 1 gives a rectangular stabilizer.
A longer tail moment arm lowers the required area because the tail has more leverage. A larger wing area, larger mean aerodynamic chord, or higher target coefficient raises the required horizontal tail area. Vertical tail area responds most to wing span, wing area, vertical tail arm, and the selected vertical volume target.
What this tool leaves out
Tail volume is not a complete design approval. It does not model airfoil pitching moment, downwash, tail efficiency, fuselage side area, propwash, control-surface authority, structural stiffness, flutter, or center-of-gravity range. Strongly swept, elliptical, compound, or multi-panel wings need separately calculated wing area and mean aerodynamic chord. Do not apply conventional-tail targets automatically to canards, tandem wings, tailless aircraft, or V-tails.
Worked example
Suppose a model has a 48 in span, 10 in root chord, 6 in tip chord, a 24 in horizontal tail arm, and a 23 in vertical tail arm. The wing area is 48 * (10 + 6) / 2 = 384 in², and the mean aerodynamic chord is about 8.17 in.
With an existing 80 in² horizontal tail and 36 in² vertical tail, the current coefficients are about 0.612 and 0.0449. Targets of 0.50 horizontal and 0.040 vertical require about 65.33 in² of horizontal tail area and 32.06 in² of vertical tail area. With the default aspect and taper ratios, the suggested horizontal tail is about 16.17 in span with 5.05 in root chord and 3.03 in tip chord.
Common questions
What is tail volume coefficient on an RC airplane?
Tail volume coefficient is a dimensionless measure of tail area and leverage compared with wing size. The horizontal coefficient uses wing area and mean aerodynamic chord, while the vertical coefficient uses wing area and wingspan. It is useful for comparing similar aircraft, not for proving that a design is stable.
How do I choose horizontal and vertical tail-volume targets?
Use measured or published values from a proven model with similar layout, size, speed range, and handling goals. The defaults are only starting points for a conventional RC airplane. A trainer, pattern model, glider, racer, and scale design can legitimately use different targets.
Where should the tail moment arm be measured?
Measure from the wing quarter-chord point to the tail quarter-chord point. Use the horizontal tail quarter-chord for the horizontal arm and the vertical tail quarter-chord for the vertical arm. Keep the same length unit as the wing entries.
Does elevator or rudder area count toward stabilizer area?
For this preliminary sizing method, enter the projected planform area of the whole stabilizing surface, including movable elevator or rudder portions. Do not double-count overlapping fuselage area unless your comparison aircraft was measured the same way. Be consistent when comparing current and target designs.
How do I enter a twin-fin design?
Enter the combined projected area of all vertical fins. For example, two identical 18 in² fins should be entered as 36 in² of existing vertical tail area. The suggested single-fin dimensions are an equivalent-area starting point, not a required layout.
Can this calculator size a V-tail or canard?
Not directly. V-tails, canards, tandem wings, and tailless aircraft need different geometry and stability assumptions. Use this calculator only as a conventional-tail comparison unless you have separately converted the design into equivalent horizontal and vertical stabilizing areas.