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T-tail (stabiliser on top of the fin)
What is a T-tail and why do aircraft use it? · Standard part · basis: Design rules and figures from the cited sources; example geometry by Xem Studio
Also called: t-tail, t tail aircraft, t-tail deep stall, t-tail vs conventional tail, t tail rc plane, high tail, t-tail advantages disadvantages, why gliders have t-tails, t-tail flutter, t tail sailplane
Exact dimensions. True size, with no printing tolerance added.
- sizes
- 4 in table
Notes
- 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.
T-tail size chart
| 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 |
Where the files are
Other publishers' files are linked, not hosted. "verify" = check the license at the link before commercial use.
| FAA | Pilot's Handbook of Aeronautical Knowledge (FAA-H-8083-25), Ch. 6 Flight Controls | web | Publisher's page; dimensions are facts |
| Kitplanes (B. Wainfan) | Design Process: T-Tails (2022) | web | Publisher's page; dimensions are facts |
| 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 |
| 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 |
| LibreTexts (Arnedo, Fundamentals of Aerospace Engineering) | 2.2.3 Empennage | web | Publisher'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
| t-tail-tail | t tail layout: horizontal span 384 × chord 100, vertical 140 × 110 mm on a 500 mm boom, NACA 0009 surfaces | STEP · STL |
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.Plain text: sheet.txt · JSON: /api/geometry?object=t-tail
Fits with
Questions
Why do most gliders have T-tails?
The single main wheel and slim aft fuselage would put a low tail on the ground when the glider rests wing-down (Kitplanes T-Tails).
What is a deep stall?
At high angle of attack the wing wake blankets the T-tail, removing pitch-down authority so the aircraft can stay stalled (FAA PHAK ch.6).