{
 "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": "pitch-diameter-ratio",
 "name": "Pitch-to-diameter ratio",
 "kind": "standard",
 "category": "Aircraft design",
 "group": "Propellers",
 "year": null,
 "question": "What pitch-to-diameter ratio should I use for speed vs aerobatics?",
 "tags": [
  "vehicle design",
  "propellers",
  "rc design",
  "aerodynamics"
 ],
 "aliases": [
  "pitch to diameter ratio",
  "prop pitch ratio",
  "square prop",
  "low pitch prop 3d",
  "high pitch prop speed",
  "best prop for speed rc",
  "best prop for 3d",
  "p/d ratio propeller",
  "pitch speed"
 ],
 "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/pitch-diameter-ratio/",
 "sheet_txt": "https://xemstudio.com/objects/pitch-diameter-ratio/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": [
   "Pitch ratio (pitch divided by diameter) sets what the prop is good at. APC recommends a near-square ratio such as 9x9 for high-speed use and a low ratio such as 13x4 for aerobatics and hovering (Model Aviation, APC Q&A).",
   "Low-pitch props let the engine reach high rpm and maximum thrust at low speed, the same reason full-size constant-speed props use low blade angle for takeoff and higher pitch for cruise (FAA Powerplant Handbook).",
   "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": [
    [
     "Speed example",
     "9x9 (P/D = 1.0)",
     "Model Aviation (APC)"
    ],
    [
     "Aerobatics / hover example",
     "13x4 (P/D = 0.31)",
     "Model Aviation (APC)"
    ],
    [
     "Full-size takeoff vs cruise",
     "low blade angle takeoff; higher pitch cruise",
     "FAA Powerplant Handbook"
    ],
    [
     "Reference build",
     "13 x 4, 2 blades",
     "APC example"
    ]
   ]
  }
 },
 "sheet_text": "Pitch-to-diameter ratio — dimension sheet\nSource: Xem Studio, https://xemstudio.com/objects/pitch-diameter-ratio/  (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- Pitch ratio (pitch divided by diameter) sets what the prop is good at. APC recommends a near-square ratio such as 9x9 for high-speed use and a low ratio such as 13x4 for aerobatics and hovering (Model Aviation, APC Q&A).\n- Low-pitch props let the engine reach high rpm and maximum thrust at low speed, the same reason full-size constant-speed props use low blade angle for takeoff and higher pitch for cruise (FAA Powerplant Handbook).\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\nSpeed example  9x9 (P/D = 1.0)  Model Aviation (APC)\nAerobatics / hover example  13x4 (P/D = 0.31)  Model Aviation (APC)\nFull-size takeoff vs cruise  low blade angle takeoff; higher pitch cruise  FAA Powerplant Handbook\nReference build  13 x 4, 2 blades  APC example\n\nFiles elsewhere (not hosted by Xem Studio; license as stated by the publisher):\n- Model Aviation (AMA), J. Smith with APC Propellers: Common Questions with APC Propellers (Mar 2021) — web — Publisher's page; dimensions are facts — https://www.modelaviation.com/node/2115\n- FAA: Aviation Maintenance Technician Handbook - Powerplant, Ch. 7 Propellers — web — Publisher's page; dimensions are facts — https://www.faa.gov/sites/faa.gov/files/09_amtp_ch7.pdf\n\nFree files (Xem Studio Design License, Xem Studio; STEP + STL, 1 parts): https://xemstudio.com/files/hardware/pitch-diameter-ratio/index.json\nAPI: https://xemstudio.com/api/geometry?object=pitch-diameter-ratio\n",
 "sources": [
  {
   "publisher": "Model Aviation (AMA), J. Smith with APC Propellers",
   "title": "Common Questions with APC Propellers (Mar 2021)",
   "url": "https://www.modelaviation.com/node/2115",
   "formats": [
    "web"
   ],
   "license": "Publisher's page; dimensions are facts",
   "license_verified": true,
   "hosted": false
  },
  {
   "publisher": "FAA",
   "title": "Aviation Maintenance Technician Handbook - Powerplant, Ch. 7 Propellers",
   "url": "https://www.faa.gov/sites/faa.gov/files/09_amtp_ch7.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": [
  "propeller-diameter-vs-pitch",
  "propeller-blade-count",
  "propeller-helix-angle-blade-twist",
  "propeller-slip-efficiency",
  "apc-propeller-rpm-limits",
  "apc-propeller-naming"
 ],
 "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 prop for a 3D plane?",
   "a": "A low pitch ratio like 13x4 (APC via Model Aviation)."
  }
 ],
 "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": "pitch-diameter-ratio-propeller",
   "formats": [
    "step",
    "stl"
   ],
   "price_usd": 0,
   "license": "Xem Studio Design License",
   "step": "https://xemstudio.com/files/hardware/pitch-diameter-ratio/pitch-diameter-ratio-propeller.step",
   "stl": "https://xemstudio.com/files/hardware/pitch-diameter-ratio/pitch-diameter-ratio-propeller.stl",
   "note": "13×4 in propeller, 2 blades: each section set at the geometric pitch angle atan(P / 2πr); chord and section illustrative"
  }
 ],
 "markdown": "https://xemstudio.com/objects/pitch-diameter-ratio/index.md"
}