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JP Aerospace and rotating sun toy
I note that the first airship pictured at:
http://www.hobbyspace.com/AAdmin/arc...alAirship.html it looks like a dark blue in the front part of the V and then silver in the 2 back parts. On my shelf next to my desk I have one of these toys that spins in sunlight. Probably most people are familiar with it, there are 4 little plates that are black on one side and white on the other that spin in a glass bulb with a partial vacuum. So I wondered if this is related to the JP Aerospace propulsion system. My toy moves away from the black side. Basically molecules bounce away faster from the hotter black side and so push on it more. But this would push the airship backwards as it is colored now. So this does not seem to be it, unless the builder got things backwards. Still, this force seems like it could be some fun for airships at high altitudes. Imagine a single cylinder shaped airship that is black in the back half and white in the front half, with something inside separating the two halves. Imagine that it is moving perpendicular to the sun and rolling like a rotisserie to even out the heat. So the back half that is black would be hotter and would have a net thrust. Anyone know how to calculate this thrust? -- Vince |
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JP Aerospace and rotating sun toy
On Sat, 08 May 2004 21:52:04 -0700, Vincent Cate wrote:
snip Still, this force seems like it could be some fun for airships at high altitudes. Imagine a single cylinder shaped airship that is black in the back half and white in the front half, with something inside separating the two halves. Imagine that it is moving perpendicular to the sun and rolling like a rotisserie to even out the heat. So the back half that is black would be hotter and would have a net thrust. Anyone know how to calculate this thrust? All I know is that it's miniscule. The dark colored surface absorbs more energy from the light source and thus heats the adjacent air layers a bit more than the white colored side does. When the air on the black side rises and is replaced by cooler air, I believe that generates a net force on the plate pushing against it. IMHO, most of the heat probably is reflected or radiated out though and doesn't contribute to the motion of the system. Karl Hallowell |
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JP Aerospace and rotating sun toy
The toy is called a Radiometer and the effect is the
"radiometric effect". You can see a picture of one at: http://store.yahoo.com/explo/radiometer.html The rest is some notes I made about URLs I found with google. - Vince http://www.globalwarmingsolutions.co...otheoscope.htm several orders of magnitude greater than solar sail force 10E-3 to 10E-4 atmospheres "Reynolds and Maxwell proposed an explanation involving 'thermal transpiration' but even today there is still no complete explanation of how this little toy works." "There has been no attempt to harness the rotational energy to measure the efficiency of conversion but I suspect that solar is converted into rotational energy with very high efficiency in the radiometer." http://www.betrisey.ch/presbok11.htm "The mechanism by which it operates is very complex and frequently stated incorrectly." Experiments seem to indicate "thermal transpiration" is at least most of what is going on. http://students.cec.wustl.edu/~sapph...adiometer.html AMSAT people used radiometric effect to induce 1/2 rpm in 3 weeks time http://eotvos.dm.unipi.it/nobili/ope...r_PRD_2001.pdf Left side of page 2 has formula for "radiometric effect" given temp, pressure, ... http://eotvos.dm.unipi.it/nobili/ope...pe_revised.pdf Has formula http://science.howstuffworks.com/question239.htm Crookes' radiometer http://math.ucr.edu/home/baez/physic...ight-mill.html Thermal transpiration / light-mill Thrust comes at the edges - discounts many other explanations http://sargentwelch.com/product.asp?pn=WL1734%5FEA $10 - 99% evacuated - gas expands on black side and so pushes This looks like the one I have http://scientificsonline.com/product.asp_Q_pn_E_3116000 Hand made radiometers. "Energy is released as the heated molecules kick away at great speeds, causing the vanes to revolve within the vacuum." |
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