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Air Hat
Propeller Beanie - Invisible Umbrella Effect | |
It's a rainy day and as usual you've left the brolly sitting in a basket by the door; no problem: press the button on top of your propeller beanie and with a whirring sound it transforms itself from a slightly eccentric fashion statement into your personal rain-free zone; the patented contoured blades
have been designed specifically to keep you dry.
Let's take a close look at the propeller... the inner (hubward) portion of each blade pushes air upwards and inwards (producing a cone shape), while the outer portion pushes air outwards and slightly upwards (producing a "brim" effect). All while being no larger than the standard beanie propeller.
Effectively, when activated the beanie makes an invisible witch's pointed hat that shoos rain away.
An earlier (but cruder) iteration
Reversible_20Fan_20...at_20_2f_20Umbrella
[FlyingToaster, Sep 13 2008]
Propellor Beanie
http://www.mcphee.com/pixlarge/10806.jpg
Erk! [wagster, Sep 14 2008]
for Ian, maybe it's American talk...
http://www.merriam-...m/dictionary/beanie
[xandram, Sep 14 2008]
[link]
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Incomprehensible: I've no idea what a "beanie" is. |
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I have linked to a propellor beanie for the less milliniristically inclined amongst us. It illustrates more than it illuminates. |
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I am intrigued by your idea that the inner and outer parts of a propeller blade do different things. Is this a new idea or have propeller designers done this for ages? |
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//have propeller designers done this//
A full-sized aircraft propeller with those properties would probably fly apart unless you made a ring at the discontinuity.
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[Ian] the propeller-beanie is an USA'ian icon from the 1940-50's; while the actual hat is a common children's toy (the propeller spins in the wind), wearing of such was portrayed in films/cartoons as denoting geekiness or social ineptitude: a younger "pocket protector" badge. |
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//I've no idea what a "beanie" is//
It's what you make coffie out of.
Duh! |
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Mabe it would be possible to employ the Coander evvect (q.v.) to create a fast-moving laminar "skin" of air which then detaches tangentially from the hat brim, carrying the raindrops with it ? |
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Whatever you use will need a fair amount of power...... |
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You lost me at //a slightly eccentric fashion statement//. |
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Oh, haven't you forgot that as you whirled out the air beneath your head you also drew in deflected mist to gather in your trousers due to negative (bad) air pressure effect? Hmmm, unless it is hydrophobic - a teflon clothing perhaps. Anyways, have a sodden bun for a truly wonderful contraption + |
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//Whatever you use will need a fair amount of power......// |
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Maybe it could be powered by lots of people pedalling in a gym.... towed behind the hat...? |
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I can imagine there will be a couple of major issues to deal with to pull this off. |
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First, where are you planning to put the motor that powers the prop? Considering how much upward thrust needs to be generated to deflect raindrops you'll need a pretty big motor. My guess is this will become less of a beanie and more like a top hat or stovepipe hat. |
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My second issue concerns the torque this rather large (for something sitting on top of one's head) motor. Air Hat wearers will likely suffer from a sore neck after using their device. It will take a lot of regular repeated use to build up their neck muscles. There will be a side benefit from this, though - wearers would no longer be called "pencil-necked geeks". |
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Well, for science I went to that source of all scientific knowledge... Wikipedia, and moderate rain is 1-4mm/hr at a speed of 5m/s. That's actually very little weight that has to be moved on a second-by-second basis. Though we're trying to do this with a small (say 6" dia) propeller to cover a relatively large area (say 2' diameter), I'd like to do it without resorting to extendable blades which would impart a pretty hefty precession-ready weight.
[8th] trying to keep the wearer dry, not just the hat.
[rotary] I don't think the raindrops will break down as far as "mist". |
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The problem is that you won:t be moving the weight directly. You're trying to make the air hit the rain. Nothing less than a vertible tornado will do, but we don't need something the size of an airplane engine. You can do it with a very high quality turbine engine in a top hat with something to hold your hair down. Only liquid hydrogen has something near the energy density to let you carry it around without an accompanying nuclear reactor. You can carry the hydrogen tank in a back-pack with 20 pounds of catylist. |
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[Voice] I can do it easiest by making extensible blades that physically hit the rain: <3,000rpm will do fine for a 4blade, but that's a bit bulky, and treading on the "centrifugal umbrella" post.
The basic pseudo-mechanics are that the cone breaks up the rain into smaller-but-not-mistlike droplets which are easily shed by the "brim". |
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