this post was submitted on 09 Jan 2025
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No Stupid Questions

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By that I mean literally sucking up stuff. The vent fan above my stove only seems to actually pull anything in while it's on low; setting it to high makes it louder but stops pulling any smoke or steam up through the hood. I'm just curious how the hell that works; shouldn't a faster spinning fan suck MORE? Is there some property of aerodynamics that was forgotten when they installed this shit?

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[–] litchralee@sh.itjust.works 16 points 21 hours ago* (last edited 49 minutes ago) (2 children)

I like this answer. The only thing I would add is that when the fan blades are all stalled, it might seem then that drag and energy consumption should reduce, since there's not much air moving. But in a cruel twist (fan pun intended) of aerodynamics, the useless spinning of stalled fan blades still causes parasitic drag. So not only does the fan not move air, it's also consuming more energy than spinning a solid disk of the same moment-of-inertia.

When the engine fails for certain single-propeller aircraft, there's sometimes a mechanism to lock the propeller to make it stop rotating, since it would otherwise "windmill" in the air and waste the precious kinetic energy that's keeping the plane aloft. Or so I'm told.

[–] AnAustralianPhotographer@lemmy.world 3 points 17 hours ago* (last edited 16 hours ago) (1 children)

That could happen with propellors that have Constant Speet Units. (Propellor pitch is able to be changed) The act is called 'feathering' . This can happen on multi engine aircraft and reduce the drag of the side with the failed engine. Cheaper propellors are fixed pitch and no means exist to change them. (I believe some propellor are able to have their pitch changed by a maintainer on the ground so the aircraft can be optimized for climbing, cruising or a combination of both)

'Reverse Thrust' is also possible in so e Other aircraft. the blade reverses to the point where it pushes the wrong way so the engines assist breaking* after landing. * Typo, but I'm leaving it in =)

[–] litchralee@sh.itjust.works 2 points 14 hours ago* (last edited 7 hours ago)

Constant Speed is probably what I was thinking of. And speaking of multi engine failure, you've just reminded me of the demise of TransAsia Airways Flight 235 where the right engine feathered itself erroneously, but then the crew misdiagnosed the situation and shut down the left engine. Mentour Pilot made a video on that particular accident.

[–] FuglyDuck@lemmy.world 5 points 21 hours ago

that's a great addon, thank you.

Side note; that's why they get noisier, too.