# Dual-element (two-element) rear wing

> What is a dual-element wing and why does it make more downforce?

- Category: Car design › Car aero
- Kind: Standard part
- Basis: Design rules and figures from the cited sources; example geometry by Xem Studio
- Page: https://xemstudio.com/objects/rear-wing-dual-element/ · JSON: https://xemstudio.com/api/geometry?object=rear-wing-dual-element · Plain text: https://xemstudio.com/objects/rear-wing-dual-element/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 dual-element wing adds a flap behind the main plane, separated by a small slot. The slot lets fresh air energise the flap's suction side so the pair can run far more camber before stalling than one element could.
- In Southampton's ground-effect tests the optimum slot was a 3.2% chord gap with 2.4% chord overlap, and the wing reached CL 3.03 (Zhang & Zerihan). In UIUC open-wheel front-wing tests, raising flap angle from 14 to 24 deg lifted CL from 1.95 to 2.37 (Jasinski & Selig).
- HP Academy pairs dual-element rear wings with 500-600 hp cars and larger splitters, i.e. more downforce means more drag and needs front balance to match.
- Used on: Champ Car and F1 front-wing configurations tested at UIUC.
- The file is a reference example built by Xem Studio from the numbers above (Geometry of the Zhang & Zerihan test wing; aoa is its 1 deg reference incidence.). Sizes the sources do not fix are illustrative; scale the example to your own vehicle.

## Sizes

| parameter | value or range | source |
|---|---|---|
| Main element chord | 223.4 mm (~0.59c) | Zhang & Zerihan |
| Flap chord | 165.7 mm (~0.44c) | Zhang & Zerihan |
| Reference (combined) chord / span | 380 mm / 1100 mm, AR 2.89 | Zhang & Zerihan |
| Optimum gap | 0.032c (12 mm) | Zhang & Zerihan |
| Optimum overlap | 0.024c (9 mm) | Zhang & Zerihan |
| Max CL, high flap angle | 3.028 at h/c 0.079 | Zhang & Zerihan |
| Flap deflection range tested | 4-44 deg (3D), 6-41 deg (2D) | Jasinski & Selig (UIUC) |
| CL at alpha 6 deg | 1.95 (flap 14 deg), 2.37 (flap 24 deg) | Jasinski & Selig (UIUC) |
| Swan-neck LMP wing, flap +8 deg | 1413 lb downforce | Mulsanne's Corner |

## Where the files are

- University of Southampton / AIAA Journal: [Aerodynamics of a Double-Element Wing in Ground Effect (Zhang & Zerihan, AIAA J. 41(6), 2003)](https://eprints.soton.ac.uk/22605/1/AIAA-2057-653.pdf) — web — Publisher's page; dimensions are facts
- University of Illinois / SAE: [Experimental Study of Open-Wheel Race-Car Front Wings (Jasinski & Selig, SAE 1998)](https://m-selig.web.engr.illinois.edu/pubs/JasinskiSelig-1998-MSEC-SAE-Trans-V107-S6.pdf) — web — Publisher's page; dimensions are facts
- High Performance Academy: [Aerodynamic performance devices for club level cars: front splitters](https://www.hpacademy.com/courses/aerodynamics-fundamentals/aerodynamic-performance-devices-for-club-level-cars-front-splitters) — web — Publisher's page; dimensions are facts
- Mulsanne's Corner: [The Rise of the Swan Neck (2009 LMP rear wing CFD study)](https://www.mulsannescorner.com/rearwingLMPCFD2009.html) — web — Publisher's page; dimensions are facts

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

Index: https://xemstudio.com/files/hardware/rear-wing-dual-element/index.json · license: https://xemstudio.com/files/hardware/rear-wing-dual-element/LICENSE.md

- rear-wing-dual-element-rear-wing: [STEP](https://xemstudio.com/files/hardware/rear-wing-dual-element/rear-wing-dual-element-rear-wing.step) · [STL](https://xemstudio.com/files/hardware/rear-wing-dual-element/rear-wing-dual-element-rear-wing.stl) — dual element rear wing: span 1100 × chord 380 mm at 1°, endplates 200 mm, inverted NACA 4412 section (mounts from below)

## Questions

**What gap should a two-element wing use?**

The Southampton ground-effect test found 0.032c gap and 0.024c overlap optimal for its geometry (Zhang & Zerihan). Treat that as a starting point and test.

## Fits with

- [Single-element rear wing (race car)](https://xemstudio.com/objects/rear-wing-single-element/)
- [Swan-neck rear wing mount](https://xemstudio.com/objects/swan-neck-wing-mount/)
- [Gurney flap / wickerbill](https://xemstudio.com/objects/gurney-flap-wickerbill/)
- [Wing endplates / side dams](https://xemstudio.com/objects/wing-endplates/)
- [Front splitter](https://xemstudio.com/objects/front-splitter/)
- [Splitter tunnels (front diffuser)](https://xemstudio.com/objects/splitter-tunnels-front-diffuser/)