# Swept-back wing

> Why do some wings sweep back?

- Category: Aircraft design › Wing planforms
- Kind: Standard part
- Basis: Design rules and figures from the cited sources; example geometry by Xem Studio
- Page: https://xemstudio.com/objects/swept-wing/ · JSON: https://xemstudio.com/api/geometry?object=swept-wing · Plain text: https://xemstudio.com/objects/swept-wing/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

- Sweeping the wing raises its critical Mach number, since Mcr for a swept wing scales with 1/cos(sweep) (TU Delft AE1101); sweep is mainly worth it at transonic and supersonic speed.
- Sweepback adds a stable dihedral effect that grows with lift coefficient, so swept high-wing designs may even need anhedral (Kitplanes, Wainfan).
- On a swept-back wing the local angle of attack rises toward the tip, so washout is needed to keep the tips from stalling first (R/C Soaring Digest). NACA tests of a 45 deg swept wing showed severe pitch instability without fences (NACA RM A53I21).
- Used on: B-1 (variable sweep), Boeing 737.
- 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 |
|---|---|---|
| Sweep measured at | quarter-chord line (or LE/TE angles) | ERAU (Leishman) |
| Example | sweep 40 deg with Mcr 0.7 (worked example) | TU Delft AE1101 |
| NACA test wing | 45 deg sweep, AR 5.515, taper 0.532, 10% thick | NACA RM A53I21 |
| Reference build | span 1000, root 250, tip 120, LE sweep 40 deg | illustrative (TU Delft example angle) |

## Where the files are

- TU Delft OpenCourseWare: [AE1101 Introduction to Aerospace Engineering, Aerodynamics 6](https://ocw.tudelft.nl/wp-content/uploads/AE1101-Aero-6.pdf) — web — Publisher's page; dimensions are facts
- Kitplanes (B. Wainfan): [Wind Tunnel: Roll's role in lateral stability (2008)](https://www.kitplanes.com/wind-tunnel-135/) — web — Publisher's page; dimensions are facts
- R/C Soaring Digest: [Twist Distributions for Swept Wings, Part 2 (June 2002)](https://new.rcsoaringdigest.com/2002/06/twist-distributions-for-swept-wings/[pdf].pdf) — web — Publisher's page; dimensions are facts
- NACA Ames (Cleary & Boddy), RM A53I21: [Wind-Tunnel Investigation of a 45 deg Sweptback Wing ... Including the Effects of Fences (1953)](https://ntrs.nasa.gov/api/citations/19930088248/downloads/19930088248.pdf) — web — Publisher's page; dimensions are facts
- Embry-Riddle (Leishman), Introduction to Aerospace Flight Vehicles: [Wing Shapes and Nomenclature](https://eaglepubs.erau.edu/introductiontoaerospaceflightvehicles/chapter/wing-shapes-and-nomenclature/) — web — Publisher's page; dimensions are facts

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

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

- swept-wing-wing: [STEP](https://xemstudio.com/files/hardware/swept-wing/swept-wing-wing.step) · [STL](https://xemstudio.com/files/hardware/swept-wing/swept-wing-wing.stl) — swept planform: span 1000, root 250, tip 120 mm, LE sweep 40°, dihedral 0°, NACA 2412

## Questions

**Why does a swept wing tip-stall?**

The angle of attack seen by each section rises toward the tip, so washout is needed (R/C Soaring Digest).

## Fits with

- [Rectangular (constant-chord) wing](https://xemstudio.com/objects/rectangular-wing/)
- [Tapered wing (taper ratio for minimum induced drag)](https://xemstudio.com/objects/tapered-wing/)
- [Elliptical wing](https://xemstudio.com/objects/elliptical-wing/)
- [Forward-swept wing](https://xemstudio.com/objects/forward-swept-wing/)
- [Delta wing](https://xemstudio.com/objects/delta-wing/)
- [Cranked arrow / double delta wing](https://xemstudio.com/objects/cranked-double-delta-wing/)