Originally published at: 3D-printed engine fan fails spectacularly | Boing Boing
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Yeah, they should team up with the SloMo guys.
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We seem to be picking up a slight shimmy.
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You owe me a coffee, sir.
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Next time you’re up here in Joshua Tree, the cup’o’mud is on me.
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I’m surprised the fan got anywhere close to that speed, and also surprised the blade fragments had enough energy to shatter the cowl like that. The printer must have been set to “extra strong”.
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It was probably PETG, that stuff has very high bond strength. The cowling was probably a very thin wall print to reduce weight.
But, yeah, I’m surprised it survived at anywhere near those power levels. The rubbing between the cowling and the blades at low speed was problematic as it not only shows poor tolerencing in the print, but each time a blade hits the cowling, it’s like striking a tuning fork. There’s going to be a speed where the strikes are at the right frequency to constructively reenforce and that’s going to make the blades vibrate strongly. I’m curious if that’s why this failed or if it just hit the tensile limits of the plastic due rotational acceleration. Oh, and the cowling can ‘ring’ too, but that’s unlikely to do much bad.
The blades shouldn’t have rubbed at low speed. I know the tolerances need to be close so there’s minimal leakage of air around the turbine, but you have to leave room for the blades to stretch when they get to speed. If you don’t, the blades will strike the cowling harder and harder as it spins faster and faster.
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Come for the thrust, stay for the shrapnel.
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At least his stash is still safe in that freezer. Ain’t no one breaking into that.
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I’d been doing some small detail work at my desk, so I watched that over the top of reading glasses perched on my nose. I noticed that while waiting for the fan to come apart, I kept tilting my head back to get my eyes behind the glasses.
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I knew a guy back in the 80s who was a rear seater in the air force. Viet Nam era jets. Anyway he was saying that sort of thing happened in real life and they could tell cause the fins would sever the hydraulic lines and the landing gear would just meh and drop.
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I spent most of the time looking at the power cord and the microwave in front of the duct-taped fridge. Who tests in a room full of hazards like that? 
My guess is someone who hasn’t seen a lot of accidents involving pedestal and ceiling fans (with blades moving at slower speeds).
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ENGAGE SAFETY SQUINTS!
-AvE
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I was wondering what forces would cause the duct/cowling to explode like that. I’m thinking the Venturi effect of the high speed airflow caused strong inward forces on the sides of the plastic duct. You could see the duct increasingly vibrate as the air speed increased. Maybe the inward forces acting in opposition to the flex forces of the plastic caused the duct to resonate, peak displacement increasing with air speed, until it struck the tips of the spinning blades.
If a jet engine exploded three feet away from your head, wouldn’t you also be able to, like, hear it?
the cowling didnt explode on its own. the fins of the turbine all failed in a cascade and shot through the cowling.
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There was a link in the video to trial #6 of this fan. It was producing 20kg of thrust, & it tilted the refrigerator against the wall!.
According to the link in the article, PETG is exactly what he is using for the blades. Apparently, they are removable, so that different pitches can be used. The cowling is in separate pieces & appears to be pretty substantial.
Judging from the comments in the above-referenced video, this is in his apartment.
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