{
 "version": "2026-10-20",
 "license": "Dimension sheets: CC BY 4.0. Standard and published-size files: CC BY 4.0. Xem Studio's own designs (files_license = Xem Studio Design License): free to use and sell things from, not to redistribute as files — https://xemstudio.com/license/. Other publishers' files: their own license, linked beside them.",
 "slug": "gurney-flap",
 "name": "Gurney flap",
 "kind": "standard",
 "category": "Aircraft design",
 "group": "Wing features",
 "year": null,
 "question": "What is a Gurney flap?",
 "tags": [
  "vehicle design",
  "wing features",
  "rc design",
  "aerodynamics"
 ],
 "aliases": [
  "gurney flap",
  "wickerbill",
  "gurney flap height",
  "gurney tab",
  "trailing edge strip",
  "gurney flap rc",
  "gurney flap lift increase",
  "liebeck flap",
  "lift tab"
 ],
 "overall_mm": {
  "length": null,
  "width": null,
  "height": null
 },
 "official_cad": false,
 "xem_status": "free-files",
 "les": false,
 "free_files": 1,
 "url": "https://xemstudio.com/objects/gurney-flap/",
 "sheet_txt": "https://xemstudio.com/objects/gurney-flap/sheet.txt",
 "sheet": {
  "basis": "Design rules and figures from the cited sources; example geometry by Xem Studio",
  "overall_mm": {
   "length": null,
   "width": null,
   "height": null
  },
  "notes": [
   "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."
  ],
  "table": {
   "columns": [
    "parameter",
    "value or range",
    "source"
   ],
   "rows": [
    [
     "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"
    ]
   ]
  }
 },
 "sheet_text": "Gurney flap — dimension sheet\nSource: Xem Studio, https://xemstudio.com/objects/gurney-flap/  (sheet CC BY 4.0; files Xem Studio Design License, https://xemstudio.com/license/)\nBasis: Design rules and figures from the cited sources; example geometry by Xem Studio\nCatalog version: 2026-10-20\n\nSizes: see table below\n- 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).\n- 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).\n- A 5% chord strip gave more max lift but a significant drag increase (Roesch & Vuillet in NASA TM-4071).\n- 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.\n\nparameter  value or range  source\nLiebeck height  about 1.25% chord  NASA TM-4071\nS1223 + 1% Gurney  CLmax 2.2 -> 2.3 (Re 2e5)  Selig & Guglielmo 1997\n0.0125c strip on helicopter stabiliser  drag unchanged, lift up  NASA TM-4071 (Roesch & Vuillet)\n0.05c strip  more CLmax, significant drag increase  NASA TM-4071\nReference build  chord 100, 1.25 mm tab, 90 deg  Liebeck height\n\nFiles elsewhere (not hosted by Xem Studio; license as stated by the publisher):\n- 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\n- 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\n\nFree files (Xem Studio Design License, Xem Studio; STEP + STL, 1 parts): https://xemstudio.com/files/hardware/gurney-flap/index.json\nAPI: https://xemstudio.com/api/geometry?object=gurney-flap\n",
 "sources": [
  {
   "publisher": "NASA Langley (Neuhart & Pendergraft)",
   "title": "A Water Tunnel Study of Gurney Flaps, NASA TM-4071 (1988)",
   "url": "https://ntrs.nasa.gov/api/citations/19890004024/downloads/19890004024.pdf",
   "formats": [
    "web"
   ],
   "license": "Publisher's page; dimensions are facts",
   "license_verified": true,
   "hosted": false
  },
  {
   "publisher": "University of Illinois (Selig & Guglielmo), Journal of Aircraft 1997",
   "title": "High-Lift Low Reynolds Number Airfoil Design (S1223)",
   "url": "https://m-selig.web.engr.illinois.edu/pubs/GuglielmoSelig-1997-JofAC-S1223.pdf",
   "formats": [
    "web"
   ],
   "license": "Publisher's page; dimensions are facts",
   "license_verified": true,
   "hosted": false
  }
 ],
 "xem": {
  "status": "free-files",
  "sheet_free": true,
  "mesh_price_usd": null,
  "step_price_usd": null,
  "tolerance_mm": null
 },
 "related": [
  "plain-flap",
  "split-flap",
  "slotted-flap",
  "fowler-flap",
  "leading-edge-slat-slot",
  "leading-edge-cuff"
 ],
 "fits": [],
 "dimensions": "exact (nominal, no printing tolerance)",
 "dimension_rule": "All geometry on Xem Studio is exact (nominal, true size) with no printing tolerance. Where a part meets another part, the object lists its mating features (feature, exact size, what it mates with, fit class: press, slide, run, socket, clamp or designed). Apply your process's allowance to those features only; 'designed' gaps are part of the design and stay as drawn.",
 "mating": [],
 "faq": [
  {
   "q": "How tall should a Gurney flap be?",
   "a": "Around 1-1.25% chord; taller adds drag (Liebeck via NASA TM-4071)."
  }
 ],
 "files_license": {
  "name": "Xem Studio Design License",
  "holder": "Xem Studio",
  "url": "https://xemstudio.com/license/",
  "note": "Xem Studio's own design: free to use, print, modify and sell things made from it; not to be republished or redistributed as files."
 },
 "offers": [
  {
   "file": "gurney-flap-wing-segment",
   "formats": [
    "step",
    "stl"
   ],
   "price_usd": 0,
   "license": "Xem Studio Design License",
   "step": "https://xemstudio.com/files/hardware/gurney-flap/gurney-flap-wing-segment.step",
   "stl": "https://xemstudio.com/files/hardware/gurney-flap/gurney-flap-wing-segment.stl",
   "note": "Wing segment with a Gurney flap 2 mm high (2 % chord) at the trailing edge"
  }
 ],
 "markdown": "https://xemstudio.com/objects/gurney-flap/index.md"
}