Gurney flap — dimension sheet
Source: Xem Studio, https://xemstudio.com/objects/gurney-flap/  (sheet CC BY 4.0; files Xem Studio Design License, https://xemstudio.com/license/)
Basis: Design rules and figures from the cited sources; example geometry by Xem Studio
Catalog version: 2026-10-20

Sizes: see table below
- A Gurney flap is a small strip perpendicular to the trailing edge on the pressure side. Liebeck's 1978 tests used about 1.25% chord and found significant lift and drag improvement, but expected drag penalties above that height (NASA TM-4071).
- On the S1223 high-lift airfoil a 1% chord Gurney raised CLmax from 2.2 to 2.3 with similar stall (Selig & Guglielmo). On an advanced airfoil at Re 3e6 a 1.25% flap raised lift substantially but with very large drag penalties at low and moderate CL (NASA TM-4071).
- A 5% chord strip gave more max lift but a significant drag increase (Roesch & Vuillet in NASA TM-4071).
- 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.

parameter  value or range  source
Liebeck height  about 1.25% chord  NASA TM-4071
S1223 + 1% Gurney  CLmax 2.2 -> 2.3 (Re 2e5)  Selig & Guglielmo 1997
0.0125c strip on helicopter stabiliser  drag unchanged, lift up  NASA TM-4071 (Roesch & Vuillet)
0.05c strip  more CLmax, significant drag increase  NASA TM-4071
Reference build  chord 100, 1.25 mm tab, 90 deg  Liebeck height

Files elsewhere (not hosted by Xem Studio; license as stated by the publisher):
- NASA Langley (Neuhart & Pendergraft): A Water Tunnel Study of Gurney Flaps, NASA TM-4071 (1988) — web — Publisher's page; dimensions are facts — https://ntrs.nasa.gov/api/citations/19890004024/downloads/19890004024.pdf
- University of Illinois (Selig & Guglielmo), Journal of Aircraft 1997: High-Lift Low Reynolds Number Airfoil Design (S1223) — web — Publisher's page; dimensions are facts — https://m-selig.web.engr.illinois.edu/pubs/GuglielmoSelig-1997-JofAC-S1223.pdf

Free files (Xem Studio Design License, Xem Studio; STEP + STL, 1 parts): https://xemstudio.com/files/hardware/gurney-flap/index.json
API: https://xemstudio.com/api/geometry?object=gurney-flap