# H-tail / twin fin tail

> What is an H-tail (twin tail) and why use one?

- 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/h-tail-twin-tail/ · JSON: https://xemstudio.com/api/geometry?object=h-tail-twin-tail · Plain text: https://xemstudio.com/objects/h-tail-twin-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

- An H-tail puts two fins at the ends of the horizontal stabiliser. Bhattacharya et al. list redundancy and fins less affected by wing/fuselage downwash and fuselage turbulence as benefits, with propwash drag and boom weight as costs.
- The stabiliser end-plates the fins in the same way a T-tail's stabiliser end-plates a single fin (Kitplanes T-Tails), and splitting the fin area keeps each fin short.
- Arnedo describes twin (H) tails as 'much less common' than conventional, cruciform and T-tails.
- Used on: Consolidated B-24, B-25 Mitchell, Avro Lancaster, Handley Page Halifax, Petlyakov Pe-2.
- 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 |
|---|---|---|
| Fin area split | total Sv shared by two fins (each 8,000 mm^2 in reference build) | computed from Vv 0.04 |
| Reference build | Sh 40,000 mm^2, two fins 100 x 80 mm | computed |

## Where the files are

- engrXiv (Bhattacharya et al., ICMMM 2023): [Design and Computational Analysis of Y-tail Configuration for Maritime UAV](https://engrxiv.org/preprint/download/6582/10812/9153) — 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
- Kitplanes (B. Wainfan): [Design Process: T-Tails (2022)](https://www.kitplanes.com/design-process-t-tails/) — 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/h-tail-twin-tail/index.json · license: https://xemstudio.com/files/hardware/h-tail-twin-tail/LICENSE.md

- h-tail-twin-tail-tail: [STEP](https://xemstudio.com/files/hardware/h-tail-twin-tail/h-tail-twin-tail-tail.step) · [STL](https://xemstudio.com/files/hardware/h-tail-twin-tail/h-tail-twin-tail-tail.stl) — h tail layout: horizontal span 400 × chord 100, vertical 100 × 80 mm on a 500 mm boom, NACA 0009 surfaces

## Questions

**Why did WWII bombers use H-tails?**

Twin fins give redundancy and sit outside fuselage turbulence (Bhattacharya et al.); examples include the B-24, B-25 and Lancaster.

## 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/)
- [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/)