# T-tail (stabiliser on top of the fin)

> What is a T-tail and why do aircraft use it?

- Category: Aircraft design › Tail configurations
- Kind: Standard part
- Basis: Design rules and figures from the cited sources; example geometry by Xem Studio
- Page: https://xemstudio.com/objects/t-tail/ · JSON: https://xemstudio.com/api/geometry?object=t-tail · Plain text: https://xemstudio.com/objects/t-tail/sheet.txt
- License: dimension sheet CC BY 4.0 (Xem Studio); files Xem Studio Design License (free to use and sell from, not to redistribute as files: https://xemstudio.com/license/)
- Use in every chat: add https://xemstudio.com/mcp as a connector (https://xemstudio.com/use-with-ai/)

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

## 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.

## Sizes

| 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

- FAA: [Pilot's Handbook of Aeronautical Knowledge (FAA-H-8083-25), Ch. 6 Flight Controls](https://www.faa.gov/sites/faa.gov/files/08_phak_ch6.pdf) — web — Publisher's page; dimensions are facts
- Kitplanes (B. Wainfan): [Design Process: T-Tails (2022)](https://www.kitplanes.com/design-process-t-tails/) — 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)](https://www.fzt.haw-hamburg.de/pers/Scholz/Aero/AERO_PUB_INCAS_TailVolume_Vol13No3_2021.pdf) — 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)](https://www.fzt.haw-hamburg.de/pers/Scholz/arbeiten/TextMcDavid.pdf) — web — Publisher's page; dimensions are facts
- LibreTexts (Arnedo, Fundamentals of Aerospace Engineering): [2.2.3 Empennage](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) — web — Publisher's page; dimensions are facts

## Free STEP/STL (1 parts, Xem Studio Design License, Xem Studio)

Index: https://xemstudio.com/files/hardware/t-tail/index.json · license: https://xemstudio.com/files/hardware/t-tail/LICENSE.md

- t-tail-tail: [STEP](https://xemstudio.com/files/hardware/t-tail/t-tail-tail.step) · [STL](https://xemstudio.com/files/hardware/t-tail/t-tail-tail.stl) — t tail layout: horizontal span 384 × chord 100, vertical 140 × 110 mm on a 500 mm boom, NACA 0009 surfaces

## 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).

## Fits with

- [Tail volume coefficient (horizontal and vertical tail sizing)](https://xemstudio.com/objects/tail-volume-coefficient/)
- [Tail moment arm (tail lever arm ratios)](https://xemstudio.com/objects/tail-moment-arm/)
- [Conventional tail (low-mounted stabiliser and single fin)](https://xemstudio.com/objects/conventional-tail/)
- [Cruciform tail (stabiliser part-way up the fin)](https://xemstudio.com/objects/cruciform-tail/)
- [V-tail (butterfly tail with ruddervators)](https://xemstudio.com/objects/v-tail/)
- [Inverted V-tail (anhedral V)](https://xemstudio.com/objects/inverted-v-tail/)