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Old 21-12-2009, 19:52   #151
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But the pitot tube and anemometer do not work on the same principles.

The pitot tube measures the dynamic pressure of the air relative to the pitot tube by slowing the air to zero movement and measuring the pressure.
Both are converting the energy into work. They do look very different but if you aligned the pitot tube into the wind the pitot tube and the anemometer would read the same value due to the same physics.


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The anemometer balances the drag on the cups facing into and away from the wind. They are built with practically frictionless bearings and remove a negible amount of energy from the air.
That's very true but only by the conversion of energy to work could we read anything at all. The amount of energy converted is irrelevant.

At this point I think we'll just settle on round-worlders and flat-worlders.
I have never seen anyone change their mind on the internet, including me, so why should this be any different?
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Old 21-12-2009, 20:47   #152
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At this point I think we'll just settle on round-worlders and flat-worlders.
I have never seen anyone change their mind on the internet, including me, so why should this be any different?
Then we'll have to leave it at that. We did get pretty off topic by the end here.
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Old 21-12-2009, 21:10   #153
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Quote:
Originally Posted by zydecotoad View Post
But the pitot tube and anemometer do not work on the same principles.

The pitot tube measures the dynamic pressure of the air relative to the pitot tube by slowing the air to zero movement and measuring the pressure.

The anemometer balances the drag on the cups facing into and away from the wind. They are built with practically frictionless bearings and remove a negible amount of energy from the air.

Check this link for the equations of motion. See page 33 or so. http://www.ieawind.org/Task_11/Recom...econdPrint.pdf

Todd

Indeed the equations to calculate rotational torque do include air density. If you note the requirements for calibration all require the precise knowledge of the air density or barometric pressure so that the anemometer can be calibrated. Note the density variables in the dynamic equation of motion on page 35, and the mean wind speed equation on page 41. It is clear to me that the air density at 10000 feet is substantially less than the air density at sea level. In actuality it is about 2/3 sea level density.

The cup anemometer differs substantially from the pitot tube, but is still affected by air density. The cup anemometer is essentially insensitive to wind direction in the horizontal plane, which makes it highly useful in a boat. I guess those of you who sail those tippy boats do have a bit of a calibration issue at times. The Pitot tube is very sensitive to direction and would be essentially useless in a boat. Also the Pitot tube works by comparing the dynamic pressure of the air entering the the pitot tube to the static pressure of the air in the static system.
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Old 22-12-2009, 06:23   #154
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.........
I have never seen anyone change their mind on the internet, including me, so why should this be any different?
Hey Ex-C, you are seriously under selling CF, mate. This is one site where I have learnt some stuff including, would you believe, that I actually don't know everything and that there are some people by the way of reasoned and logical argument can lead me to consider another way of understanding - but perhaps I am just a internet bunny....

But I suspect your post was partly tongue in check .
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Old 22-12-2009, 12:16   #155
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Hey Ex-C, you are seriously under selling CF, mate. This is one site where I have learnt some stuff including, would you believe, that I actually don't know everything and that there are some people by the way of reasoned and logical argument can lead me to consider another way of understanding - but perhaps I am just a internet bunny....

But I suspect your post was partly tongue in check .

Keeping my tongue in check is something I still have to learn...
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Old 22-12-2009, 14:25   #156
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Reminder to self, proof read posts better - cheek - or use TLA's like TIC
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