Theory, practice and doctored fan

About a year ago, [Wyman’s Workshop] Need a fan. But not just regular-old fans, sir. A Drain Fan you know, the fancy fan design where the stationary shroud is so close to the blade of the moving fan that there is basically no gap and a huge gain in aerodynamic efficiency? At least in theory?

Okay, in practice, you can see how it turned out in this video. (Also embedded below.) If you’re more of the “how-to-build-it” type, you’ll want to watch his build video – there’s plenty of gluing 3D prints and woodwork. But we’re in it just for the ducted fan data!

And so we write it! [Wyman] Made a nice thrust-testing rig that can pull the fan out to see how hard it is. And the goal of the theory was 652 grams of thrust, which was fairly confirmed. And then you go to power: with a 500 watt motor, he has produced 47 watts. Spoiler: He is overloading the motor, although he has used a fairly bench grinder motor.

So he redesigned the fan from scratch to better match the motor. And it performed Good It will be more than theory. A pleasurable surprise, but it means rewriting the theory with the full volume of fan blades, which has finally combined theory and practice. Which makes him design many fan blades and test them against each other.

He ended the video with a teaser showing his various inlet profiles and fan cones and similar results. But the video is a year old, so we’re not holding our breath. Still, if you’re interested in fan design and aren’t afraid of high school physics, it’s worth your time.

Don’t worry about the convenience of ducted fans, just want to make your quad look great? We got the hack for you!

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