Tail moment arm (tail lever arm ratios) — dimension sheet Source: Xem Studio, https://xemstudio.com/objects/tail-moment-arm/ (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 - The tail moment arm is the distance from the wing's aerodynamic centre (or c.g.) to the tail's aerodynamic centre; it multiplies every newton of tail lift into pitching or yawing moment (Kitplanes, Wainfan). - Statistics of 30 transport aircraft put the horizontal-tail arm at about 46% of fuselage length and the fin arm at about 42%, with the horizontal arm about 5% longer than the vertical on conventional tails and about 23% longer on T-tails (Scholz 2021). - For light aircraft, Pazmany's data give tail arms of 11.8-15.5 ft on wings with 4.17-5.33 ft MAC, i.e. roughly 2.5-3 MAC (EAA Chapter 62). A short arm needs a bigger tail; Sadraey notes fighters use short arms and transports long arms (quoted in HAW Hamburg thesis). - Used on: Piper J-3 Cub, Luscombe Silvaire, Ryan Navion. - 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 Horizontal tail arm / fuselage length (30 aircraft) 46.2% (SD 2.8) Scholz 2021 / HAW Hamburg Vertical tail arm / fuselage length (30 aircraft) 41.8% (SD 4.8) Scholz 2021 Engines on wing: Lh / Lv 47.0% / 44.7% of fuselage length Scholz 2021 Engines on aft fuselage: Lh / Lv 44.6% / 36.1% of fuselage length Scholz 2021 T-tail: horizontal arm vs vertical arm about 23% longer Scholz 2021 Conventional: horizontal arm vs vertical arm about 5% longer Scholz 2021 Piper J-3: Lh, MAC 13.2 ft, 5.33 ft (Lh/MAC = 2.48, derived) EAA62 (Pazmany) Luscombe Silvaire: Lh, MAC 11.8 ft, 4.17 ft (Lh/MAC = 2.83, derived) EAA62 Ryan Navion: Lh, MAC 15.5 ft, 5.22 ft (Lh/MAC = 2.97, derived) EAA62 Sh/Sw (J-3, Silvaire, Navion) 13.7%, 15.5%, 23.3% EAA62 Sv/Sw (J-3, Silvaire, Navion) 5.7%, 7.6%, 7.9% EAA62 Files elsewhere (not hosted by Xem Studio; license as stated by the publisher): - INCAS Bulletin / HAW Hamburg (D. Scholz): Empennage sizing with the tail volume complemented with a method for dorsal fin layout (2021) — web — Publisher's page; dimensions are facts — https://www.fzt.haw-hamburg.de/pers/Scholz/Aero/AERO_PUB_INCAS_TailVolume_Vol13No3_2021.pdf - HAW Hamburg (Aircraft Design and Systems Group): Empennage sizing: tail lever arm as % of fuselage length (thesis; Table 2.1 typical tail volume coefficients) — web — Publisher's page; dimensions are facts — https://www.fzt.haw-hamburg.de/pers/Scholz/arbeiten/TextMcDavid.pdf - EAA Chapter 62 (Stan Hall, from Pazmany 'Light Airplane Design'): How Big The Tail — web — Publisher's page; dimensions are facts — https://eaa62.org/technotes/tail.htm - Kitplanes (B. Wainfan): Design Process: Horizontal Tail (2022) — web — Publisher's page; dimensions are facts — https://www.kitplanes.com/?p=177046 Free files (Xem Studio Design License, Xem Studio; STEP + STL, 1 parts): https://xemstudio.com/files/hardware/tail-moment-arm/index.json API: https://xemstudio.com/api/geometry?object=tail-moment-arm