As boring as propeller designs may seem to the average person, occasionally there’s a bit of a dust-up in the media about a ‘new’ design that promises at least a few percent improvement in performance, decreased noise profile, or any combination of such claims. Naturally, if you’re [Daniel Riley] of RCTestFlight, then you have to 3D print a few of them, and make a video covering a handful. Most famous of these is probably the toroidal propeller that made waves a while ago, mostly in the field of flying drones, but commercial toroidal boat props exist too.
Test results of the different boat propeller designs. (Credit: rctestflight)
Interestingly, the 2-blade FDM-printed propeller ended up performing the best, while the bi-blade design (with two sets of blades positioned one after the other) performed worse — but better than the toroidal design. Here the last two designs were professionally printed in nylon, rather than printed at home in a standard FDM printer with all of the surface sanding and treatment required. Even so, the surface treatment did not seem to noticeably affect the results in further testing.
Hints at the root cause of the problem came from the bubble tests. In a bubble test, air is blown in front of the spinning propeller to visualize the flow of the water. This revealed some stalling on the bi-blade and the toroidal design too, which would explain so ..
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