# Pitch-to-diameter ratio

> What pitch-to-diameter ratio should I use for speed vs aerobatics?

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

- 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.

## Sizes

| parameter | value or range | source |
|---|---|---|
| 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 |

## Where the files are

- Model Aviation (AMA), J. Smith with APC Propellers: [Common Questions with APC Propellers (Mar 2021)](https://www.modelaviation.com/node/2115) — web — Publisher's page; dimensions are facts
- FAA: [Aviation Maintenance Technician Handbook - Powerplant, Ch. 7 Propellers](https://www.faa.gov/sites/faa.gov/files/09_amtp_ch7.pdf) — web — Publisher's page; dimensions are facts

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

Index: https://xemstudio.com/files/hardware/pitch-diameter-ratio/index.json · license: https://xemstudio.com/files/hardware/pitch-diameter-ratio/LICENSE.md

- pitch-diameter-ratio-propeller: [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) — 13×4 in propeller, 2 blades: each section set at the geometric pitch angle atan(P / 2πr); chord and section illustrative

## Questions

**What prop for a 3D plane?**

A low pitch ratio like 13x4 (APC via Model Aviation).

## Fits with

- [Propeller diameter vs pitch](https://xemstudio.com/objects/propeller-diameter-vs-pitch/)
- [Propeller blade count (2, 3 and 4 blades)](https://xemstudio.com/objects/propeller-blade-count/)
- [Propeller helix angle and blade twist](https://xemstudio.com/objects/propeller-helix-angle-blade-twist/)
- [Propeller slip and efficiency](https://xemstudio.com/objects/propeller-slip-efficiency/)
- [APC propeller RPM limits](https://xemstudio.com/objects/apc-propeller-rpm-limits/)
- [Propeller naming suffixes (E, SF, MR, P, W, N, C)](https://xemstudio.com/objects/apc-propeller-naming/)