Parametric Folding Propellor Generator

I have an FPV Shadow RC plane from Banggood that I bought a while ago. The standard kit includes a bunch of 6 inch diameter x 4.5 inch pitch propellors. For a while I would break a prop (and often rip the motor off) each time I landed because there was nothing to stop the propellor motoring over or being in a vertical position when it touched down. I alleviated the problem by adding two largish coreflute tails that extended below the plane a bit like twin keels on a surfboard. It looks pretty ugly but helps prevent the damage to motor mount and props that I was experiencing. BUT what I felt it really needed was a folding prop. After hunting high and low for quite some time I finally concluded that small 6x4.5 folding props did not exists, and so I decided to see if I could come up with a parametric folding prop that could be 3D printed. This OpenSCAD script is the result.

If you would prefer a regular non-folding propellor, go here: Parametric Multi-Blade Propellor Generator

This was written in OpenSCAD 2015 and uses coding that will not work in older versions. I suspect the Thingiverse customiser may have problems with it so I would suggest you download the .scad file and use it directly in OpenSCAD.

The model is for the blade only. If you are brave you could try a 3D printed spinner too. I notice there are several on Thingiverse.

The airfoil for the blade profile is the NACA4412. This produces a very thin blade which may be a bit too flexible. I will be testing this blade once I have built a test rig. It may be that after a bit of testing I may replace this with a thicker airfoil. If you want to use a different airfoil look for the line;

Airfoil_points = [[1000,1.3],[950,14.7],
  .....,[950,-1.6],[1000,-1.3]];  

... and replace it with your preferred airfoil. The base scale is 1000 units, so you will need to adjust your preferred airfoil to conform with this. I got the points for this airfoil from the airfoil archive http://m-selig.ae.illinois.edu/ads/archives/coord_seligFmt.tar.gz, and used the following file: http://m-selig.ae.illinois.edu/ads/coord/naca4412.dat. I have created a Python3 based Airfoil .dat file to OpenSCAD conversion tool on my website. You can find it here: Airfoil .dat to OpenSCAD Conversion Tool

With regard to printing, you may find the trailing edge gets too fine to print so it may be truncated a little. You can see this happening in the photos where the last 0.5 – 1mm has been lost. I have not tried this on an FDM printer but feel that some sort of support will be required.

All parameters are mm unless otherwise stated. The exception is the blade diameter and pitch which you can fill out with either metric or imperial values. Refer to the diagrams and list below.

Here is a run down of the parameters used.

The fundamentals
Pitch: Use PitchI for Imperial measurement, or PitchM for metric values.
Diameter: Use DiamI for Imperial measurement, or DiamM for metric values.
Blade Maximum Width (mm): MaxChdW

Calculation Factors
Statns: This is the number of stations along the blade where the size and twist is calculated. A higher number will improve the smoothness of the shape but add to the calculations. You may need to fiddle with this when dealing with larger diameter blades to counter the appearance of a gap of pointy bit around the hinge area that sometimes happens.
SectRes: The number of intermediate steps between stations. The higher the number the smoother the shape is but it adds significantly to the calculation time.

Pitch Adjustment
The pitch adjustment was originally introduced to de-rate the pitch angle so that my calculated pitch angles would match what I was measuring from a commercial propellor. As it turns out I must have been measuring the commercial propellor pitch poorly and I should have just run with my unadjusted pitch angles. So, leave these both set to 1.0. It is left here because it may be useful for adding washout to the propellor.
PitchAdjHub: Pitch adjustment factor at the hub end.
PitchAdjTip: Pitch adjustment factor at the hub end.

More Blade and Hub Parameters
BldCtr: This is the position of blade centreline about which the blade is scaled and twisted. It is expressed as a % of the distance along the blade chord measured from the leading edge.
SpinHPinRad: This is distance from the shaft centerline to the centreline of the propellor hinge pin.
SpinPinD: Hinge pin diameter
SpinHubD: This is difficult to describe but is the diameter of the bit of the blade base around the pin. See the diagrams for a clear guide.
SpinHL: This is the width of the hinge section.
SpinHubVTweak: this factor will allow you to move the hinge pivot forward or backward on the blade to suit your needs. This may have advantages when making pusher type folding props.

There are a number of other parameters but they are variables for use in the code. You are welcome to put numbers in them, but they will be overwritten anyway and have no effect. They are: Poz1, Poz2, StrtAngi, EndAngi, StepLi, StrtWi, and EndWi.

Good luck.

22 March 2019 - Added a "Glitch Guide Image" to explain the method for eliminating the occasional appearance of artefacts around the hinge by tweaking the Statns parameter.