V-tail (butterfly tail with ruddervators) — dimension sheet Source: Xem Studio, https://xemstudio.com/objects/v-tail/ (sheet CC BY 4.0; files Xem Studio Design License, https://xemstudio.com/license/) Basis: Design rules and figures from the cited sources; example geometry by Xem Studio Catalog version: 2026-10-20 Sizes: see table below - 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. parameter value or range source Typical dihedral per panel (models) about 40 deg McCombs, Model Aviation 1994 Typical dihedral (full-size) usually about 45 deg Kitplanes V-Tails Effective horizontal area 2S cos^2(a) McCombs 1994 Effective vertical area 2S sin^2(a) McCombs 1994 Angle from required areas tan^2(a) = Sv_req / Sh_req derived from McCombs formulas Worked example (McCombs) 40 deg -> 31 deg cut effective fin area from 12.4 to ~7.96 in^2 McCombs 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 fix small differential: more travel on the down-going ruddervator Stackhouse, CRRC Files elsewhere (not hosted by Xem Studio; license as stated by the publisher): - FAA: Pilot's Handbook of Aeronautical Knowledge (FAA-H-8083-25), Ch. 6 Flight Controls — web — Publisher's page; dimensions are facts — https://www.faa.gov/sites/faa.gov/files/08_phak_ch6.pdf - Model Aviation (AMA), W.F. McCombs: Wing and Tail Dihedral for Models (Dec 1994) — web — Publisher's page; dimensions are facts — https://library.modelaviation.com/article/wing-and-tail-dihedral-models - Kitplanes (B. Wainfan): Design Process: V-Tails (2022) — web — Publisher's page; dimensions are facts — https://www.kitplanes.com/design-process-v-tails/ - Charles River Radio Controllers (D. Stackhouse): V-Tail Adverse Yaw (1999) — web — Publisher's page; dimensions are facts — https://charlesriverrc.org/articles/design-and-construction/aircraft-design/tail-design-and-structure/vtail-adverse-yaw/ - NACA (Purser & Campbell): Experimental Verification of a Simplified Vee-Tail Theory, NACA TR-823 (1945) — web — Publisher's page; dimensions are facts — https://ntrs.nasa.gov/citations/19930091901 - engrXiv (Bhattacharya et al., ICMMM 2023): Design and Computational Analysis of Y-tail Configuration for Maritime UAV — web — Publisher's page; dimensions are facts — https://engrxiv.org/preprint/download/6582/10812/9153 Free files (Xem Studio Design License, Xem Studio; STEP + STL, 1 parts): https://xemstudio.com/files/hardware/v-tail/index.json API: https://xemstudio.com/api/geometry?object=v-tail