# Slotted flap

> How does a slotted flap work?

- Category: Aircraft design › Wing features
- Kind: Standard part
- Basis: Design rules and figures from the cited sources; example geometry by Xem Studio
- Page: https://xemstudio.com/objects/slotted-flap/ · JSON: https://xemstudio.com/api/geometry?object=slotted-flap · Plain text: https://xemstudio.com/objects/slotted-flap/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 slotted flap opens a gap between wing and flap so high-pressure air from below energises the flap's upper surface; it raises the lift coefficient significantly more than plain or split flaps and is the most popular type today (FAA PHAK ch.6).
- Its section CLmax increment is about 1.3 vs 0.9 for a plain flap (Arnedo, Franchini data); large aircraft use double or triple slots (FAA).
- 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 |
|---|---|---|
| Section delta-CLmax | 1.3 | Arnedo (Franchini) |
| Wing delta-CLmax | 0.92 x dCl x (Sflapped/S) x cos(sweep) | Arnedo |
| Typical CLmax/cos(sweep), slotted flap | 1.5-1.7 takeoff (20 deg) / 1.8-2.2 landing (40 deg) | Arnedo |
| Typical CLmax/cos(sweep), double slotted | 1.7-1.95 takeoff (20 deg) / 2.3-2.7 landing (50 deg) | Arnedo |
| Reference build | chord 100, 25% flap, 40 deg | Arnedo landing setting |

## Where the files are

- 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
- LibreTexts (Arnedo, Fundamentals of Aerospace Engineering; data from Franchini et al.): [3.4.3 Increase in CLmax (high-lift devices)](https://eng.libretexts.org/Bookshelves/Aerospace_Engineering/Fundamentals_of_Aerospace_Engineering_(Arnedo)/03%3A_Aerodynamics/3.04%3A_High-lift_devices/3.4.03%3A_Increase_in_CLmax) — web — Publisher's page; dimensions are facts

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

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

- slotted-flap-wing-segment: [STEP](https://xemstudio.com/files/hardware/slotted-flap/slotted-flap-wing-segment.step) · [STL](https://xemstudio.com/files/hardware/slotted-flap/slotted-flap-wing-segment.stl) — slotted flap: wing segment 100 mm chord × 300 mm, 25 % chord surface deflected 40°

## Questions

**Does the slot matter?**

Yes; the gap flow lets the flap deflect further without separating, giving about 1.3 vs 0.9 dCLmax (Arnedo).

## Fits with

- [Plain flap](https://xemstudio.com/objects/plain-flap/)
- [Split flap](https://xemstudio.com/objects/split-flap/)
- [Fowler flap](https://xemstudio.com/objects/fowler-flap/)
- [Leading-edge slat and fixed slot](https://xemstudio.com/objects/leading-edge-slat-slot/)
- [Gurney flap](https://xemstudio.com/objects/gurney-flap/)
- [Leading-edge cuff (drooped leading edge)](https://xemstudio.com/objects/leading-edge-cuff/)