Half a croissant, on a plate, with a sign in front of it saying '50c'
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Safe fan

  (+6, -1)
(+6, -1)
  [vote for,

A rotating cylinder acts like an airfoil when passed through a fluid, i.e. it creates lift (see link). Therefore fan blades could be replaced by rotating cylinders. This could be easily achieved by gearing that transfers some of the energy that normally rotates the fan blades to rotate the cylinders along each of their longitudinal axes. So the cylinders would be rotating along their own axes while also rotating about a common (perpendicular) axis.

Because the sharp edges of the blades have been removed, the cage that usually surrounds an electric fan could be removed (in conjunction with a motor that slows upon detecting resistance, eg child’s hand).

xaviergisz, Jan 23 2006

Lift of rotating cylinder http://www.grc.nasa...2/airplane/cyl.html
[xaviergisz, Jan 23 2006]

Flying cylinder http://www.xzylo.com/#mid
With video [bungston, Jan 23 2006]

MAGNUS FLYER http://sln.fi.edu/wright/magnus.html
Let's Make It: Get two cups . . . [baconbrain, Jan 25 2006]

Rotating Cylidner Helicopter Rotor https://youtu.be/J1...si=WvMPsbQ34ir3T6ev
[xaviergisz, Nov 18 2023]


       Doesn't look too terribly efficient, and I think I would put quotes around the "safe" part.   

       But it definitely looks cool, and would attract double-takes. Bun for that. I really would like to find out what kind of sound it would make.
lurch, Jan 23 2006

       Current large plastic fan blades are quite safe if you stick your fingers in from the front - the trailing part of the blades pushes your fingers away from getting close to the sharp leading edges.   

       To get any sort of breeze out of the rotating cylinders, they are going to have to spin incredibly fast - so the danger is perhaps increased, not for cutting injury but for contusion, breaks and ligament damage.   

       That said, I like the idea in a halfbaked sort of way and it would look cool. Even cooler if it turns out that it sounds like a bullroarer! (+)
ConsulFlaminicus, Jan 23 2006

       I have looked and looked for a link describing the "flying coke can" toy. I am sure some of you have seen one: a can with topand bottom cut off,which can be thrown like a frisbee.   

       I think that the cylinder would have to really rotate fast.
bungston, Jan 23 2006

       Tesla had some related ideas: see the Tesla turbine.   

       BTW, you mention cylinders (plural). With more than one, you will have an in-running nip problem.
Ling, Jan 23 2006

       hmm, I'm a little puzzled by bungston and Ling's comments... I'll link to a picture of it tomorrow.   

       ConsulFlaminicus re:sticking your finger in current plastic fans; umm, you go first.
xaviergisz, Jan 23 2006

       Ah, I checked why you were puzzled, and can see what you mean. No in-running nip, of course.   

       What I meant about Tesla, was that he also made a fan without blades. Not in the same way that you propose, however.
Ling, Jan 23 2006

       Checking a bit more into the sound thing: the tubes just have *got* to be corrugated. Then it will make musical tones like those whirl-around-the-head plastic hose toys.
lurch, Jan 23 2006

       //without angled blades, how would you direct the airflow in one direction?// um, [21], if you go read the link, it gets pretty well explained.
lurch, Jan 23 2006

       /The flying soda can anno above is also incorrect. Simply spinning a cylinder won't generate lift in one direction. It flies because someone threw it./   

       Obviously, someone threw it. Flying toys that go farther than, say, a rock thrown in the same way do so because they convert some energy into lift. A frisbee is an example. The flying can toy is another. I think they have to spin - my recollection of the flyign can toy is that it took some skill to impart spin as you released the can.   

       Goaded into more searching by [21]'s comment above, I found a link to this xzylo company, which sells something that appears to be a plastic version of the flying coke can toy. I also found (under gliding cylinder) a blueprint for a paper version. The movie shows that the thing has lift - it rises as it flies.
bungston, Jan 23 2006

       I've linked to some poorly drawn pictures of the rotating cylinder fan and gearing system. This is a ceiling fan version.   

       The rotating shaft (gold) is coupled to and hence rotates the bottom toothed ring (also gold). The bottom toothed ring meshes with and hence rotates the cogs (mauve) which rotate the cylinders (grey). The top toothed ring (red/brown) is held stationary.
xaviergisz, Jan 23 2006

       /A frisbee is an example. The flying can toy is another. I think they have to spin /
These particular toys have to spin because they're not stable otherwise. The spinning creates gyroscopic stability. Once this is achieved, the shape of the object produces the lift. A frisbee and flying cylinder both produce lift by directing air downward.

       A cylinder spinning in still air will not produce lift. However, a cylinder spinning in moving air (or a cylinder spinning while moving through air) will generate lift.   

       I'm left with a question: Is this intended to operate such that each cylinder is stationary, rotating about its axis only, or will the whole assembly of rotating cylinders also rotate around a single central axis as well?   

       If it's just spinning cylinders, you'll not see any airflow aside from local boundary layer disturbance. If the whole thing spins, the cylinders will generate magnus lift, and you will get some airflow.
Freefall, Jan 23 2006

       always good larning to be had when [Freefall] weighs in.
bungston, Jan 23 2006

       Freefall, your second interpretation is correct:   

       //the whole assembly of rotating cylinders also rotate around a single central axis as well//
xaviergisz, Jan 23 2006

       Thank, Freefall, for asking the clarifying questions. I don't know why people go off on these confusing tangents.   

       The Xzylo flying cylinders have nothing to do with this idea. I have a couple, and their spin is only for stability. A similar toy can be made of paper, weighted properly, and flown without spin.   

       The toy to make to illustrate Magnus lift is pretty simple. I'll see if I can find a good link.   

       Take two paper or styrofoam cups, and tape them to together, base to base--kinda like a butterfly. Snip through a rubber band to make an elastic string. Wrap one end of the band around the join of the bases, under tension, a couple of times. Hold the cups with one hand, with the rotational axis horizontal, and the loose end of the rubber band at the bottom. Use the other hand to pull the loose end of the band tight, away from you, like a slingshot, and let go of the cups.   

       The cups go away from you, spinning, make a loop in the air, and glide to the floor. It's easy enough to do, but confuses the heck out of people.   

       It's a perfect party trick for a nerd. I'm going to try it again if I ever get invited to another party.
baconbrain, Jan 25 2006

       That's excellent [baconbrain]. Another good party trick with styrofoam cups is "McCafe Cat" - charge up your cat with static electricity (I find the quickest way to do this is to hold the cat so that the whirling blades of a plastic fan rub across it's back - about a minute gives a good charge) than put in in a cardboard box about half full of loose McDonalds coffee cups. Wait for about thirty seconds and release the cat. The cups will be stuck to its fur like glue for about two minutes. Works best on very dry days.
ConsulFlaminicus, Jan 25 2006

       You're on a streak, [xaviergisz].
pertinax, Nov 19 2023


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