h a l f b a k e r yWhat's a nice idea like yours doing in a place like this?
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I'm sure you've all seen the magnelev toy. Well why not use a magnetically levitating compressor wheel on a Ramjet. I mean it will elininate the need to carry oil and increase the efficiency of the engines power output
High Temperature Magnetic Bearings for Gas Turbines
http://www.grc.nasa...5000/5930kascak.htm
Nasa work from a decade ago [lurch, Mar 02 2008]
LEVITRON® - The Amazing Anti-Gravity Top
http://www.levitron.com/
the magnelev toy? [baconbrain, Mar 02 2008]
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You're talking about magnetic bearings, then? |
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Since a ramjet has no compressor wheel, I'm sure it doesn't matter much what you levitate it with. Stick it to the top of the cockpit with chewing gum, if you like. |
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What lurch said. By its very design, a ramjet needs no compressor. Magnetic bearings do exist, though. |
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I'm not getting it, either. Is this just a joke? Anyone else? |
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I don't think it's a joke - I think he/she is
thinking of a different type of engine
(maybe a conventional jet?), and proposing
magnetic bearings for the fans. |
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I agree [MB]. But the toy and the magnetic bearings needed for a compressor wheel have many differences, and not just in size. I'm rating this as "magic magnets", by someone not very technical. |
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This is a classic example of amateur stream of consciousness engeneering. Use technical words to try to mate two technologies that you don't understand to "increase efficiency, power output". This is is epitomized by bastard perpetual motion machines: Somehow there is a combination of technologies that can "increase efficiency, power output" to more than 100%. |
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So, [bacon] and [WcW], based on lurch's
link, should this be MFDd on the grounds
of its being magic, or being baked? |
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If the poster was simply confused about the makeup of types of jet engines, then it's a valid combo of technologies - but not original, and not an exceedingly good combo. |
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However, since that's not what's written, I don't see a problem with this getting an "[m-f-d] hair curlers for bowling balls". |
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I think we could assume that he has simply
used the term "Ramjet" wrongly through
ignorance, if we were feeling kindly
disposed. It may not be original, but
neither is it really baked. It may not be a
very good idea either, but it was
presumably good enough for NASA to
invest tens of dollars (if not more) in,
which suggests it's not a really awful idea. |
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But it's an idea along the lines of saying, "NASA should build bigger rockets." It's got nothing about how to, and two big technical errors (and several writing and spelling errors). It's also about something fairly obvious--using magnets as frictionless supports--which we get about once a week here. |
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It's not necessarily bad, there's just nothing good in it. Magnetic bearings may not be magic to NASA, maybe, but they were to [SIVOLC]. I'm not marking for deletion, but this isn't a HB-worthy idea. |
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It's not really like saying "NASA should
build bigger rockets" - it's more like
saying "NASA apparently has or had a fairly
large programme dedicated to this, so it's
not really "magic magnets" nor "stream of
consciousness". |
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I'm not saying it's a great idea, just that
both possible MFD grounds seemed
unreasonably harsh to me. |
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No, sorry, you are the one who noticed NASA was working on it. [SIVOLC] didn't know that, didn't look for and had never heard of magnetic bearings. And it was magic to him. |
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Here's a sentence from the linked article. "A probe senses the position of the rotor, and a feedback controller keeps it centered in the cavity." There's nothing like that concept in the idea or in the toy referred to. |
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I'm not MFDing for anything, I seldom do. I just think it's a poor idea. Good discussion, though. Thanks. |
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//And it was magic to him.// Well, I
think it was naive of him, to extrapolate
from a toy magnetic bearing to a real
one, but I don't see that that makes it
magic to him. |
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The early annos were pretty unanimous
(after pointing out that he didn't mean
'ramject') that magnetic bearings for
serious heavy applications were silly or
impossible. They may be impossible,
but they're clearly neither silly nor
magic. |
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Anyway, it looks as if we scared him off
back in '04, so us old gits can go back
to discussing custard in peace. |
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I still think this is pointless attempt to hybridize two concepts that are not compatable. Magnetic bearings make sense when the forces are easily contained and where weight is not a factor. In a jet engine weight is a huge factor as are the forces involved. Unless these are hyper powerfull super lightweight bearings then the idea simply does not fly. I will post a link with a cutaway of a jet engine and let people judge for themselves. Remeber for jet bearings to float free they must repulse the entire force produced by the engine and any side loads to sub-millimeter clearance. The compressor cannot move inside the housing due to close tollerences and the fact that rotating out of plane would fataly destabilize the assembly. |
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The idea as stated does not make sense in a conventional jet either, as the compressor wheel would simply fly out of the front of the engine if you don't hold it in. |
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In a jet engine the gravitational weight of the components becomes insignificant once the engine is spinning. I would imagine that the airflow is calibrated so that the axle would still stay in almost exactly the same place if you removed the bearings. |
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However, the major force in play in a jet is thrust, which only ever pushes the rotor forwards, so applying a repusive electromagnetic force to the bearing as the thrust increases would reduce the sideways load on the bearing. It could even be done mechanically using induction from the rotor. |
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Any magnetic force that you add to a traditional bearing to discourage the axle from leaving centre will reduce the load on the bearing. If the rotor weighs a tonne, repelling it vertically with a tonne of force will help, albeit minimally once it's up to speed. |
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