# Propeller helix angle and blade twist

> Why are propeller blades twisted?

- 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/propeller-helix-angle-blade-twist/ · JSON: https://xemstudio.com/api/geometry?object=propeller-helix-angle-blade-twist · Plain text: https://xemstudio.com/objects/propeller-helix-angle-blade-twist/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

- Blade angle is the angle between a blade section's chord and the plane of rotation; the tip moves much faster than the root, so the blade is twisted (pitch distribution) to keep each section at a useful angle of attack (FAA Powerplant Handbook).
- The FAA defines geometric pitch from the blade angle at the 75% station: GP = 2 x pi x R x tan(blade angle). Rearranged, a constant-pitch blade needs angle = atan(P / (2 pi r)) at every radius r, i.e. the angle falls toward the tip (helix-angle rule, derived from the FAA formula).
- Slip is the difference between geometric and effective pitch, and propeller efficiency varies from 50% to 87% depending on slip (FAA).
- 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 |
|---|---|---|
| Geometric pitch | GP = 2 pi R tan(beta) at 75% station | FAA Powerplant Handbook |
| Blade angle for constant pitch | beta(r) = atan(P / (2 pi r)) | derived from FAA formula |
| Example (derived), 10x6 prop | beta at 75% radius (3.75 in) = atan(6/(2 pi 3.75)) = 14.3 deg | computed |
| Propeller efficiency | 50-87% | FAA Powerplant Handbook |
| Reference build | 10 x 6, 2 blades | computed example |

## Where the files are

- 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/propeller-helix-angle-blade-twist/index.json · license: https://xemstudio.com/files/hardware/propeller-helix-angle-blade-twist/LICENSE.md

- propeller-helix-angle-blade-twist-propeller: [STEP](https://xemstudio.com/files/hardware/propeller-helix-angle-blade-twist/propeller-helix-angle-blade-twist-propeller.step) · [STL](https://xemstudio.com/files/hardware/propeller-helix-angle-blade-twist/propeller-helix-angle-blade-twist-propeller.stl) — 10×6 in propeller, 2 blades: each section set at the geometric pitch angle atan(P / 2πr); chord and section illustrative

## Questions

**Where is a prop's pitch measured?**

At the 75% radius station (FAA Powerplant Handbook).

## Fits with

- [Propeller diameter vs pitch](https://xemstudio.com/objects/propeller-diameter-vs-pitch/)
- [Pitch-to-diameter ratio](https://xemstudio.com/objects/pitch-diameter-ratio/)
- [Propeller blade count (2, 3 and 4 blades)](https://xemstudio.com/objects/propeller-blade-count/)
- [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/)