# Clark Y airfoil

> What is the Clark Y airfoil?

- Category: Airfoils › Airfoils
- Kind: Standard part
- Basis: Design rules and figures from the cited sources; example geometry by Xem Studio
- Page: https://xemstudio.com/objects/clark-y-airfoil/ · JSON: https://xemstudio.com/api/geometry?object=clark-y-airfoil · Plain text: https://xemstudio.com/objects/clark-y-airfoil/sheet.txt
- License: dimension sheet CC BY 4.0 (Xem Studio); files CC BY 4.0 or their publisher's 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

- The Clark Y has a maximum thickness of 11.7% and a lower surface flat from 30% chord aft (Mason, Virginia Tech, citing Riegels). The flat bottom makes it easy to build on a flat board.
- NACA tested it widely, including TR-431 on very low aspect ratios (0.5-3), which found stall delayed and maximum lift increased at aspect ratios around 1 (NACA TR-431).
- NASA's 1979 PAR ground-effect model used a 12% Clark-Y section (NASA TM-78793).
- Used on: NASA PAR WIG test model (TM-78793).

## Sizes

| parameter | value or range | source |
|---|---|---|
| Max thickness | 11.7% chord | Mason (Virginia Tech) |
| Lower surface | flat from 30% chord aft | Mason (Riegels 1961) |
| Low-AR tests | AR 0.5-3; CLmax higher near AR 1 | NACA TR-431 |
| Coordinates source | Mason / Riegels; NACA R 427, 428, 431 | Mason |

## Where the files are

- Virginia Tech (W.H. Mason): [Airfoil definitions (Configuration Aerodynamics notes)](https://archive.aoe.vt.edu/mason/Mason_f/C23AirfoilDefinitions.pdf) — web — Publisher's page; dimensions are facts
- NACA (C.H. Zimmerman): [Characteristics of Clark Y Airfoils of Small Aspect Ratios, NACA TR-431 (1933)](https://ntrs.nasa.gov/citations/19930091504) — web — Publisher's page; dimensions are facts
- NASA Langley / DTNSRDC (Thomas, Paulson & Margason): [Powered Low-Aspect-Ratio Wing in Ground Effect (WIG) Aerodynamic Characteristics, NASA TM-78793 (1979)](https://ntrs.nasa.gov/api/citations/19790022970/downloads/19790022970.pdf) — web — Publisher's page; dimensions are facts

## Questions

**Why is Clark Y popular with builders?**

Its lower surface is flat from 30% aft, so ribs sit on a flat board (Mason).

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