# Fowler flap

> What makes a Fowler flap different?

- 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/fowler-flap/ · JSON: https://xemstudio.com/api/geometry?object=fowler-flap · Plain text: https://xemstudio.com/objects/fowler-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 Fowler flap slides aft on tracks before drooping, increasing both wing area and camber; early extension adds lift with little drag, late extension adds drag with little lift (FAA PHAK ch.6).
- Its section CLmax increment is 1.3 x c'/c, where c' is the extended chord; double-slotted Fowler reaches 1.6 x c'/c and triple-slotted 1.9 x c'/c (Arnedo, Franchini data).
- 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 c'/c | Arnedo (Franchini) |
| Double slotted Fowler | 1.6 c'/c | Arnedo |
| Triple slotted Fowler | 1.9 c'/c | Arnedo |
| Typical CLmax/cos(sweep), Fowler flap | 2.0-2.2 takeoff (15 deg) / 2.5-2.9 landing (40 deg) | Arnedo |
| Reference build | chord 100, 30% flap, 40 deg | illustrative |

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

- fowler-flap-wing-segment: [STEP](https://xemstudio.com/files/hardware/fowler-flap/fowler-flap-wing-segment.step) · [STL](https://xemstudio.com/files/hardware/fowler-flap/fowler-flap-wing-segment.stl) — fowler flap: wing segment 100 mm chord × 300 mm, 30 % chord surface deflected 40°

## Questions

**Why do airliners use Fowler flaps?**

They add area and camber, giving the highest CLmax of common flaps (Arnedo).

## Fits with

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