Update
August 2024: An updated version is posted at https://www.thingiverse.com/thing:6720495. Both left-handed and right-handed propellers are supported.
Sept. 30, 2023: Posted a build guide at https://www.youtube.com/watch?v=7WBZlx42M5Y
April 10, 2023: Thanks to feedback from several Science Olympiad Flight teams, I have implemented a few helpful ideas in this v3.6 release, e.g. a channel to help glue CF stem to a blade easily and accurately; a flange to help pull the two molds apart; and more parameters on the Customizer UI to tweak.
Glad to see many propellers that were built from this program performed so well in the SO Flight competition. Those winning flights were simply amazing!
Intro
Here is an OpenSCAD script for creating indoor flight propeller molds. Many parameters like Pitch/Diameter, Centerline Location, Mold Thickness, etc. are adjustable in OpenSCAD's customizer panel. Propeller blade angle is true helical. Flaring propeller is possible. Blade axis is straight. Good for alignment. There are lots of other adjustment possibilities. Open up the .scad files in OpenSCAD and see.
Usage
0> Download and install OpenSCAD at https://openscad.org/. Download PropBlade_Mold_xx.scad and Larrabee_Boor.scad files into one of your local folders. Start OpenSCAD and open PropBlade_Mold_xx.scad. Select design parameters in OpenSCAD's Customizer panel based on your flight experience, or use default values as a good starting point. After render the model in OpenSCAD, generate a .stl file and bring it to your 3d printer. Print the mold with either PLA, PLA+, or your favorite filament.
1>Use the 3d-printed male mold (without flange) as a template, cut multiple blades out of 1/32" balsa sheet.
2>Wet these balsa blades thoroughly.
3>Put balsa blades into the female mold one by one with bathroom tissue under, in between, and above. Put the male mold on top of all.
4>Weigh the whole stack down with a book or something. Wait half hour or so and change tissue.
5>After changed tissue a few times, get rid of the tissue in between blades (leave the top and bottom ones), and wait for another few hours, or overnight.
6> Check again to make sure all blades are completely dry.
7> Prepare CF stems. Place a blade and then a stem into the same female mold. Put the male mold on top. Align the stem into the slot in the male mold. Through the open channel on the male mold, apply two or three drops of CA to hold the stem to the balsa blade (not to the mold!) After a few seconds, take the whole blade-stem assembly out and add a few more drops of CA to help secure the blade to the stem. Repeat for other blades.
The formed blade-stem assemblies then go through another process to build up a propeller. For that, I use another 3d printed gadget, Propeller Pitch Gauge. Check it out at my design collection at
https://www.thingiverse.com/aeromartin/designs
Please hit the
LIKE button if you like it! Good luck with your precision propellers!
-AeroMartin
http://StarImagineering.com
Change Log:
- v3.6 Opened a channel to assist in gluing blade stem 4/9/2023
- v3.5 Added flange on the male mold & more Customizer UI options 4/9/2023
- v3.4 Added selectable parameter options on label text 4/8/2023
- v3.3 Auto-locate text on the mold 4/1/2023
- v3.2 Support Larrabee Blade Shape. (aka. blade platform, blade planform).
Larrabee propeller blade shape was developed by a MIT Professor, Eugene Larrabee, for human powered airplanes. It was later adapted by Reg Boor for indoor airplane's propellers. This implementation is based on Boor's paper. (See reference in the code.) 3/10/2023
- V3.0 Added "Wash out" angle setting.
Visually, a few degrees of washout is very subtle. Aerodynamically, washout could yield that winning edge. 01/02/2023
- V2.3 Added ventilation slots to speed up drying process. 11/24/2022
- V1.9 Original release. 11/12/2022
AeroMartin
