Xem Studiomeasured geometry

Library › Aircraft design › Tail configurations ·

V-tail (butterfly tail with ruddervators)

What is a V-tail and how do you size the ruddervators? · Standard part · basis: Design rules and figures from the cited sources; example geometry by Xem Studio

Also called: v-tail, v tail rc plane, ruddervator, butterfly tail, v-tail angle calculator, v tail sizing, v-tail dihedral angle, v-tail vs conventional tail, vee tail, v tail mixing, ruddervator size, v tail glider

Exact dimensions. True size, with no printing tolerance added.

sizes
8 in table

Notes

  • A V-tail replaces the stabiliser and fin with two slanted surfaces; their ruddervators move together for pitch and differentially for yaw (FAA PHAK ch.6). FAA notes it is more complex, more prone to Dutch roll, and the 'total reduction in drag is minimal'.
  • Sizing rule (McCombs, Model Aviation): effective horizontal area = 2S cos^2(a) and effective vertical area = 2S sin^2(a), where S is one panel and a the dihedral. Because cos^2 + sin^2 = 1, total V-tail area equals the sum of the conventional horizontal and vertical areas it replaces, which is also Wainfan's conclusion (Kitplanes: no net area saving).
  • Yaw input creates a roll opposite to the commanded yaw (Kitplanes), though on RC sailplanes Stackhouse calls it 'truly negligible'; ruddervators can flutter, so balance them (Kitplanes). NACA TR-823 (Purser & Campbell) is the classic test-verified V-tail theory.
  • Used on: Beechcraft Bonanza V35, Fouga CM 170 Magister, Antonov A-15.
  • The file is a reference example built by Xem Studio from the numbers above. Sizes the sources do not fix are illustrative; scale the example to your own vehicle.

V-tail size chart

parametervalue or rangesource
Typical dihedral per panel (models)about 40 degMcCombs, Model Aviation 1994
Typical dihedral (full-size)usually about 45 degKitplanes V-Tails
Effective horizontal area2S cos^2(a)McCombs 1994
Effective vertical area2S sin^2(a)McCombs 1994
Angle from required areastan^2(a) = Sv_req / Sh_reqderived from McCombs formulas
Worked example (McCombs)40 deg -> 31 deg cut effective fin area from 12.4 to ~7.96 in^2McCombs 1994
Reference build (computed)Sh_req 40,000 + Sv_req 16,000 mm^2 -> a = 32.3 deg, each panel 28,000 mm^2 (250 x 112 mm)computed
Pitch coupling fixsmall differential: more travel on the down-going ruddervatorStackhouse, CRRC

Where the files are

Other publishers' files are linked, not hosted. "verify" = check the license at the link before commercial use.

FAAPilot's Handbook of Aeronautical Knowledge (FAA-H-8083-25), Ch. 6 Flight ControlswebPublisher's page; dimensions are facts
Model Aviation (AMA), W.F. McCombsWing and Tail Dihedral for Models (Dec 1994)webPublisher's page; dimensions are facts
Kitplanes (B. Wainfan)Design Process: V-Tails (2022)webPublisher's page; dimensions are facts
Charles River Radio Controllers (D. Stackhouse)V-Tail Adverse Yaw (1999)webPublisher's page; dimensions are facts
NACA (Purser & Campbell)Experimental Verification of a Simplified Vee-Tail Theory, NACA TR-823 (1945)webPublisher's page; dimensions are facts
engrXiv (Bhattacharya et al., ICMMM 2023)Design and Computational Analysis of Y-tail Configuration for Maritime UAVwebPublisher's page; dimensions are facts

Free files

★ Free files 1 parts. Xem Studio design: free to use, print and sell things from; not to be republished as files. Xem Studio Design License. index.json

v-tail-tailv tail layout: horizontal span 250 × chord 112, vertical 0 × 0 mm on a 500 mm boom, NACA 0009 surfacesSTEP · STL
Let your AI pull this. Add https://xemstudio.com/mcp to Claude, ChatGPT, Cursor or any MCP client (free, no account, one minute) and it can look up exact sizes, mating fits and free STEP/STL from every chat.
Set it up →

Plain text: sheet.txt · JSON: /api/geometry?object=v-tail

V-tail (butterfly tail with ruddervators), isometric render of a generated part
Render of v-tail-tail from the free STEP; not to scale.

Fits with

Tail volume coefficient (horizontal and vertical tail sizing), isometric render of a generated part
Tail volume coefficient (horizontal and vertical tail sizing)19 sizes★ 1 file
Tail moment arm (tail lever arm ratios), isometric render of a generated part
Tail moment arm (tail lever arm ratios)11 sizes★ 1 file
Conventional tail (low-mounted stabiliser and single fin), isometric render of a generated part
Conventional tail (low-mounted stabiliser and single fin)5 sizes★ 1 file
T-tail (stabiliser on top of the fin), isometric render of a generated part
T-tail (stabiliser on top of the fin)4 sizes★ 1 file
Cruciform tail (stabiliser part-way up the fin), isometric render of a generated part
Cruciform tail (stabiliser part-way up the fin)2 sizes★ 1 file
Inverted V-tail (anhedral V), isometric render of a generated part
Inverted V-tail (anhedral V)2 sizes★ 1 file

Questions

What angle should a V-tail be?

Pick it from the areas you need: tan^2(a) = vertical area / horizontal area (McCombs). Models typically land near 40 deg (McCombs), full-size near 45 deg (Kitplanes).

Does a V-tail have less drag?

Not much: there is no wetted-area saving and FAA calls the total drag reduction minimal (Kitplanes; PHAK ch.6).