# Selig S1223 airfoil

> What is the S1223 high-lift 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/selig-s1223-airfoil/ · JSON: https://xemstudio.com/api/geometry?object=selig-s1223-airfoil · Plain text: https://xemstudio.com/objects/selig-s1223-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

- S1223 was designed to exceed CLmax 2 at Re 200,000 for small UAVs; wind-tunnel tests gave 2.2 clean (Selig & Guglielmo, J. Aircraft 1997), 25% above the FX 63-137's 1.75.
- The design uses concave pressure recovery with aft loading, giving a strongly nose-down moment (Cm c/4 about -0.29 predicted) (Selig & Guglielmo).
- Stall is moderate when clean; a 1% Gurney raised CLmax to 2.3, while vortex generators made the stall abrupt with hysteresis (Selig & Guglielmo).
- Used on: Pointer UAV (target class).

## Sizes

| parameter | value or range | source |
|---|---|---|
| Design target | CLmax > 2 at Re 2e5 | Selig & Guglielmo 1997 |
| Measured CLmax (clean) | 2.2 (Table 1: 2.23) | Selig & Guglielmo 1997 |
| Cm c/4 (predicted) | -0.29 | Selig & Guglielmo 1997 |
| With 1% Gurney flap | CLmax 2.3 | Selig & Guglielmo 1997 |
| Design Re range | 2e5-5e5 | Selig & Guglielmo 1997 |
| FX 63-137 / M06-13-128 CLmax | 1.75 / 1.52 | Selig & Guglielmo 1997 |
| Coordinates source | Table 2 of the paper | Selig & Guglielmo 1997 |

## Where the files are

- University of Illinois (Selig & Guglielmo), Journal of Aircraft 1997: [High-Lift Low Reynolds Number Airfoil Design (S1223)](https://m-selig.web.engr.illinois.edu/pubs/GuglielmoSelig-1997-JofAC-S1223.pdf) — web — Publisher's page; dimensions are facts

## Questions

**Why is S1223 popular for heavy-lift RC?**

It reaches CLmax about 2.2 at Re 200k (Selig & Guglielmo), far above typical sections, at the cost of a large nose-down moment.

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