# Cruciform tail (stabiliser part-way up the fin)

> What is a cruciform tail?

- 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/cruciform-tail/ · JSON: https://xemstudio.com/api/geometry?object=cruciform-tail · Plain text: https://xemstudio.com/objects/cruciform-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 cruciform tail mounts the horizontal stabiliser part-way up the fin, forming a cross when seen from behind (Arnedo).
- It is used to keep the horizontal surfaces out of the engine wake while avoiding many of the T-tail's drawbacks (Arnedo), such as the heavy, flutter-prone fin needed to carry a stabiliser at its tip (FAA PHAK ch.6).
- Because it is neither fully out of the wing wake nor carried at the fin tip, sizing sits between the conventional and T-tail cases; the published coefficients are for conventional tails and T-tails (Scholz 2021).
- 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 basis | use conventional class values (e.g. homebuilt 0.50 / 0.04) | HAW Hamburg Table 2.1 |
| Reference build | same areas as conventional example; stabiliser at mid-fin | computed |

## Where the files are

- 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
- 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
- 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

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

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

- cruciform-tail-tail: [STEP](https://xemstudio.com/files/hardware/cruciform-tail/cruciform-tail-tail.step) · [STL](https://xemstudio.com/files/hardware/cruciform-tail/cruciform-tail-tail.stl) — cruciform layout: horizontal span 400 × chord 100, vertical 140 × 114 mm on a 500 mm boom, NACA 0009 surfaces

## Questions

**Why choose a cruciform tail?**

To lift the stabiliser out of engine wake without the T-tail's structural and deep-stall penalties (Arnedo).

## 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/)
- [T-tail (stabiliser on top of the fin)](https://xemstudio.com/objects/t-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/)