{
 "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": "tail-moment-arm",
 "name": "Tail moment arm (tail lever arm ratios)",
 "kind": "standard",
 "category": "Aircraft design",
 "group": "Tail configurations",
 "year": null,
 "question": "How long should the tail moment arm be on an aircraft?",
 "tags": [
  "vehicle design",
  "tail configurations",
  "rc design",
  "aerodynamics"
 ],
 "aliases": [
  "tail moment arm",
  "tail lever arm",
  "how long should fuselage be rc plane",
  "tail arm length rule of thumb",
  "tail arm to MAC ratio",
  "fuselage length vs wingspan",
  "stabilizer distance from wing",
  "tail arm percentage fuselage length",
  "rc plane fuselage length formula"
 ],
 "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/tail-moment-arm/",
 "sheet_txt": "https://xemstudio.com/objects/tail-moment-arm/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": [
   "The tail moment arm is the distance from the wing's aerodynamic centre (or c.g.) to the tail's aerodynamic centre; it multiplies every newton of tail lift into pitching or yawing moment (Kitplanes, Wainfan).",
   "Statistics of 30 transport aircraft put the horizontal-tail arm at about 46% of fuselage length and the fin arm at about 42%, with the horizontal arm about 5% longer than the vertical on conventional tails and about 23% longer on T-tails (Scholz 2021).",
   "For light aircraft, Pazmany's data give tail arms of 11.8-15.5 ft on wings with 4.17-5.33 ft MAC, i.e. roughly 2.5-3 MAC (EAA Chapter 62). A short arm needs a bigger tail; Sadraey notes fighters use short arms and transports long arms (quoted in HAW Hamburg thesis).",
   "Used on: Piper J-3 Cub, Luscombe Silvaire, Ryan Navion.",
   "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": [
    [
     "Horizontal tail arm / fuselage length (30 aircraft)",
     "46.2% (SD 2.8)",
     "Scholz 2021 / HAW Hamburg"
    ],
    [
     "Vertical tail arm / fuselage length (30 aircraft)",
     "41.8% (SD 4.8)",
     "Scholz 2021"
    ],
    [
     "Engines on wing: Lh / Lv",
     "47.0% / 44.7% of fuselage length",
     "Scholz 2021"
    ],
    [
     "Engines on aft fuselage: Lh / Lv",
     "44.6% / 36.1% of fuselage length",
     "Scholz 2021"
    ],
    [
     "T-tail: horizontal arm vs vertical arm",
     "about 23% longer",
     "Scholz 2021"
    ],
    [
     "Conventional: horizontal arm vs vertical arm",
     "about 5% longer",
     "Scholz 2021"
    ],
    [
     "Piper J-3: Lh, MAC",
     "13.2 ft, 5.33 ft (Lh/MAC = 2.48, derived)",
     "EAA62 (Pazmany)"
    ],
    [
     "Luscombe Silvaire: Lh, MAC",
     "11.8 ft, 4.17 ft (Lh/MAC = 2.83, derived)",
     "EAA62"
    ],
    [
     "Ryan Navion: Lh, MAC",
     "15.5 ft, 5.22 ft (Lh/MAC = 2.97, derived)",
     "EAA62"
    ],
    [
     "Sh/Sw (J-3, Silvaire, Navion)",
     "13.7%, 15.5%, 23.3%",
     "EAA62"
    ],
    [
     "Sv/Sw (J-3, Silvaire, Navion)",
     "5.7%, 7.6%, 7.9%",
     "EAA62"
    ]
   ]
  }
 },
 "sheet_text": "Tail moment arm (tail lever arm ratios) — dimension sheet\nSource: Xem Studio, https://xemstudio.com/objects/tail-moment-arm/  (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- The tail moment arm is the distance from the wing's aerodynamic centre (or c.g.) to the tail's aerodynamic centre; it multiplies every newton of tail lift into pitching or yawing moment (Kitplanes, Wainfan).\n- Statistics of 30 transport aircraft put the horizontal-tail arm at about 46% of fuselage length and the fin arm at about 42%, with the horizontal arm about 5% longer than the vertical on conventional tails and about 23% longer on T-tails (Scholz 2021).\n- For light aircraft, Pazmany's data give tail arms of 11.8-15.5 ft on wings with 4.17-5.33 ft MAC, i.e. roughly 2.5-3 MAC (EAA Chapter 62). A short arm needs a bigger tail; Sadraey notes fighters use short arms and transports long arms (quoted in HAW Hamburg thesis).\n- Used on: Piper J-3 Cub, Luscombe Silvaire, Ryan Navion.\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\nHorizontal tail arm / fuselage length (30 aircraft)  46.2% (SD 2.8)  Scholz 2021 / HAW Hamburg\nVertical tail arm / fuselage length (30 aircraft)  41.8% (SD 4.8)  Scholz 2021\nEngines on wing: Lh / Lv  47.0% / 44.7% of fuselage length  Scholz 2021\nEngines on aft fuselage: Lh / Lv  44.6% / 36.1% of fuselage length  Scholz 2021\nT-tail: horizontal arm vs vertical arm  about 23% longer  Scholz 2021\nConventional: horizontal arm vs vertical arm  about 5% longer  Scholz 2021\nPiper J-3: Lh, MAC  13.2 ft, 5.33 ft (Lh/MAC = 2.48, derived)  EAA62 (Pazmany)\nLuscombe Silvaire: Lh, MAC  11.8 ft, 4.17 ft (Lh/MAC = 2.83, derived)  EAA62\nRyan Navion: Lh, MAC  15.5 ft, 5.22 ft (Lh/MAC = 2.97, derived)  EAA62\nSh/Sw (J-3, Silvaire, Navion)  13.7%, 15.5%, 23.3%  EAA62\nSv/Sw (J-3, Silvaire, Navion)  5.7%, 7.6%, 7.9%  EAA62\n\nFiles elsewhere (not hosted by Xem Studio; license as stated by the publisher):\n- INCAS Bulletin / HAW Hamburg (D. Scholz): Empennage sizing with the tail volume complemented with a method for dorsal fin layout (2021) — web — Publisher's page; dimensions are facts — https://www.fzt.haw-hamburg.de/pers/Scholz/Aero/AERO_PUB_INCAS_TailVolume_Vol13No3_2021.pdf\n- HAW Hamburg (Aircraft Design and Systems Group): Empennage sizing: tail lever arm as % of fuselage length (thesis; Table 2.1 typical tail volume coefficients) — web — Publisher's page; dimensions are facts — https://www.fzt.haw-hamburg.de/pers/Scholz/arbeiten/TextMcDavid.pdf\n- EAA Chapter 62 (Stan Hall, from Pazmany 'Light Airplane Design'): How Big The Tail — web — Publisher's page; dimensions are facts — https://eaa62.org/technotes/tail.htm\n- Kitplanes (B. Wainfan): Design Process: Horizontal Tail (2022) — web — Publisher's page; dimensions are facts — https://www.kitplanes.com/?p=177046\n\nFree files (Xem Studio Design License, Xem Studio; STEP + STL, 1 parts): https://xemstudio.com/files/hardware/tail-moment-arm/index.json\nAPI: https://xemstudio.com/api/geometry?object=tail-moment-arm\n",
 "sources": [
  {
   "publisher": "INCAS Bulletin / HAW Hamburg (D. Scholz)",
   "title": "Empennage sizing with the tail volume complemented with a method for dorsal fin layout (2021)",
   "url": "https://www.fzt.haw-hamburg.de/pers/Scholz/Aero/AERO_PUB_INCAS_TailVolume_Vol13No3_2021.pdf",
   "formats": [
    "web"
   ],
   "license": "Publisher's page; dimensions are facts",
   "license_verified": true,
   "hosted": false
  },
  {
   "publisher": "HAW Hamburg (Aircraft Design and Systems Group)",
   "title": "Empennage sizing: tail lever arm as % of fuselage length (thesis; Table 2.1 typical tail volume coefficients)",
   "url": "https://www.fzt.haw-hamburg.de/pers/Scholz/arbeiten/TextMcDavid.pdf",
   "formats": [
    "web"
   ],
   "license": "Publisher's page; dimensions are facts",
   "license_verified": true,
   "hosted": false
  },
  {
   "publisher": "EAA Chapter 62 (Stan Hall, from Pazmany 'Light Airplane Design')",
   "title": "How Big The Tail",
   "url": "https://eaa62.org/technotes/tail.htm",
   "formats": [
    "web"
   ],
   "license": "Publisher's page; dimensions are facts",
   "license_verified": true,
   "hosted": false
  },
  {
   "publisher": "Kitplanes (B. Wainfan)",
   "title": "Design Process: Horizontal Tail (2022)",
   "url": "https://www.kitplanes.com/?p=177046",
   "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": [
  "tail-volume-coefficient",
  "conventional-tail",
  "t-tail",
  "cruciform-tail",
  "v-tail",
  "inverted-v-tail"
 ],
 "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": "What is a good tail arm for an RC plane?",
   "a": "Light aircraft in Pazmany's data run 2.5-3 MAC from wing to tail (EAA62); use that with a tail volume coefficient to set tail area."
  }
 ],
 "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": "tail-moment-arm-tail",
   "formats": [
    "step",
    "stl"
   ],
   "price_usd": 0,
   "license": "Xem Studio Design License",
   "step": "https://xemstudio.com/files/hardware/tail-moment-arm/tail-moment-arm-tail.step",
   "stl": "https://xemstudio.com/files/hardware/tail-moment-arm/tail-moment-arm-tail.stl",
   "note": "conventional layout: horizontal span 400 × chord 100, vertical 140 × 114 mm on a 500 mm boom, NACA 0009 surfaces"
  }
 ],
 "markdown": "https://xemstudio.com/objects/tail-moment-arm/index.md"
}