T-tail (stabiliser on top of the fin) — dimension sheet Source: Xem Studio, https://xemstudio.com/objects/t-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 T-tail mounts the horizontal stabiliser on top of the fin, which keeps the elevator above most propeller downwash and wing/fuselage wake and clear of engine exhaust (FAA PHAK ch.6). The horizontal surface also end-plates the fin, so the fin can be slightly smaller (Kitplanes T-Tails; Scholz 2021). - The penalty is deep stall: at high angle of attack the tail can drop into the stalled wing's wake, and FAA notes deep stalls are more likely on T-tails (PHAK ch.6). The BAC Trident was lost to an unrecoverable deep stall (Kitplanes). - Putting the stabiliser's mass at the fin tip raises flutter loads, so the fin must be stiffer and the structure 'significantly heavier' than a conventional tail (PHAK ch.6; Kitplanes). With no propwash on the tail, more elevator is needed to raise the nose at low speed (PHAK ch.6). - Used on: BAC Trident, DC-9, C-141, C-5, C-17, Piper PA-32RT-300 Lance II, Grob G-109, Piper PA-44 Seminole. - 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 Tail volume reduction allowed for T-tail about 4% Scholz 2021 Horizontal arm vs vertical arm on T-tails about 23% longer Scholz 2021 Sailplane Vh / Vv (T-tails nearly universal on sailplanes) 0.50 / 0.02 HAW Hamburg Table 2.1; Kitplanes T-Tails Reference build Sh 38,400 mm^2 (Vh 0.50 less 4%), Sv 15,360 mm^2, arm 500 mm computed 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 - Kitplanes (B. Wainfan): Design Process: T-Tails (2022) — web — Publisher's page; dimensions are facts — https://www.kitplanes.com/design-process-t-tails/ - 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 - LibreTexts (Arnedo, Fundamentals of Aerospace Engineering): 2.2.3 Empennage — web — Publisher's page; dimensions are facts — https://eng.libretexts.org/Bookshelves/Aerospace_Engineering/Fundamentals_of_Aerospace_Engineering_(Arnedo)/02%3A_Generalities/2.02%3A_Parts_of_the_aircraft/2.2.03%3A_Empennage Free files (Xem Studio Design License, Xem Studio; STEP + STL, 1 parts): https://xemstudio.com/files/hardware/t-tail/index.json API: https://xemstudio.com/api/geometry?object=t-tail