Airfoil data based loop propeller
Description
Loop propellers are known to run more efficient and also quieter than propellers with classical blades. However they are hard to get and far away from a final superior design. So experimenting with them should bring some insights and definitely a lot of fun. Dating back to two German patents (DE63661A, DE53013A) from 1890/1991 the principle has been revised and re-patented several times in the last 130 years. An image search "loop propeller" in the internet brings up hundreds of different designs and approaches that modify the idea of a propeller with looped blades into many directions and deformation principles. In my view the design and 3D printing of propellers is generally a supreme discipline that goes along with a bunch of challenges. The design usually demands some freestyle extrusion connected with a lot of math and nasty calculations - especially, as airfoil data are involved. As for the printing, these complex forms tend to demand extensive support structures that usually lead to unsatisfying results - often unstable and much too weak to be fit for use. Therefore, the goal for this design was to create a loop propeller based on proper airfoil data, with pitch, camber, and twist that can be printed easily and without any demand for support structures. However, there is no free lunch. The propeller needs some strong (two component) glue for assembling. I implemented the design using OpenSCAD on the basis of some of my libraries that do most the nasty work, like sweep-based free-style extrusion [Naca_sweep.scad](https://www.thingiverse.com/thing:900137) and producing NACA-based airfoils [Naca4.scad](https://www.thingiverse.com/thing:898554). Further I used my favorite library [ShortCuts.scad](https://www.thingiverse.com/thing:644830) that speeds up programming so much and minimizes the foot print of the code to a minimum. Download those files into the same directory as the file rotLoop.scad containing the production code for the design. Follow the links to find some of my elder posts with further explanations of the library usage and functions. Customizing the parameter set in the production code file you get a propeller with 2 up to 6 loops that has a radius of 90mm. At best use a scaling factor for your print if you head for some other radius. Among other features the code lets you alter the tilting angle as well as the airfoil thickness and cord length. Have fun.
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