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#31
posted to rec.boats.cruising
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Buoyancy is Imaginary
On Oct 1, 11:36*am, Goofball_star_dot_etal
wrote: The point is not that I am a "clever clogs" but that you publish stuff as an "expert" and get it plain wrong. As it happens I am just "an oily rag". For the record: I have never claimed to be an expert on aerodynamics and I'm not. I'm just a writer. I've also never claimed to have "discovered" anything new about the subject as has often been claimed. I wrote a couple of articles on the subject once that an aviation magazine published and a professor of aerodynamics found useful as an introduction to the subject. I'll also agree BTW that the web page with the circulation animation isn't very good. I'd forgotten it was there until you brought it up. The text isn't from the article but something I threw together quickly to present the animation (which is from wind tunnel photographs and not my interpretation of any physics) when the question of flow around sails came up here quite a while ago. The page isn't linked on my web site and therefore not really "published". Some of your comments are valid and I'm going to rewrite it if I ever decide to provide a direct link to it. -- Roger Long |
#32
posted to rec.boats.cruising
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Buoyancy is Imaginary
Roger Long wrote:
On Oct 1, 11:36 am, Goofball_star_dot_etal wrote: The point is not that I am a "clever clogs" but that you publish stuff as an "expert" and get it plain wrong. As it happens I am just "an oily rag". For the record: I have never claimed to be an expert on aerodynamics and I'm not. I'm just a writer. I've also never claimed to have "discovered" anything new about the subject as has often been claimed. I wrote a couple of articles on the subject once that an aviation magazine published and a professor of aerodynamics found useful as an introduction to the subject. I'll also agree BTW that the web page with the circulation animation isn't very good. I'd forgotten it was there until you brought it up. The text isn't from the article but something I threw together quickly to present the animation (which is from wind tunnel photographs and not my interpretation of any physics) when the question of flow around sails came up here quite a while ago. The page isn't linked on my web site and therefore not really "published". Some of your comments are valid and I'm going to rewrite it if I ever decide to provide a direct link to it. -- Roger Long There is a lot to like about your animations and presentations. I particulary like "Removancy". It is expressions like "energy forces" that spoil it for me. It does not mean anything, outside perhaps a seance. My home PC is bust so you will have peace over the weekend. |
#33
posted to rec.boats.cruising
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Work is not Imaginary (was Buoyancy is Imaginary)
Goofball_star_dot_etal wrote:
.... Hmmmm. a mostly reasonable review - but the idea that force times distance is not equal to work is somewhat radical, don't you think? I said no work was done *on the (air)plane*. Since we only have the airplane and the air, the work done by the thrust of the engine moving the airplane through a distance all goes into the air as (kinetic) energy or heat in its wake. If I push a sled over snow with force F for distance D it's usually accounted that the work I did ON the sled is F X D ....but I won't beat the topic down.... :-) Brian W |
#34
posted to rec.boats.cruising
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Work is not Imaginary (was Buoyancy is Imaginary)
On Oct 2, 8:02*pm, brian whatcott wrote:
Goofball_star_dot_etal wrote: ... Hmmmm. a mostly reasonable review - but the idea that force times distance *is not equal to work is somewhat radical, don't you think? I said no work was done *on the (air)plane*. Since we only have the airplane and the air, the work done by the thrust of the engine moving the airplane through a distance all goes into the air as (kinetic) energy or heat in its wake. If I push a sled over snow with force F for distance D it's usually accounted that the work I did ON the sled is F X D ...but I won't beat the topic down.... :-) Brian W In regard to sudden gusts, why not use a breakaway strap like some rock climbers use whose stitches break at some load allowing the sail to be let out all the way. How many boats get knocked down anyway? I mean cruising boats, racers intend to be on the edge. My own boat, a 28' S2, if a sudden gust came up, I'd never be able to hold the tiller and she'd round up into the wind before getting knocked down. |
#35
posted to rec.boats.cruising
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Work is not Imaginary (was Buoyancy is Imaginary)
On Fri, 2 Oct 2009 17:42:17 -0700 (PDT), Frogwatch
wrote: How many boats get knocked down anyway? I mean cruising boats, racers intend to be on the edge. My own boat, a 28' S2, if a sudden gust came up, I'd never be able to hold the tiller and she'd round up into the wind before getting knocked down. There are limits to that. If you get knocked down hard enough and fast enough, the boom will hit the water and prevent the mainsail from being eased. That's where the fun starts, and some boats will tend to stay on their beam ends once they get knocked flat with the mast in the water. |
#36
posted to rec.boats.cruising
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Work is not Imaginary (was Buoyancy is Imaginary)
On Oct 2, 8:42*pm, Frogwatch wrote:
In regard to sudden gusts, why not use a breakaway strap like some rock climbers use whose stitches break at some load allowing the sail to be let out all the way. That was a huge issue and we did a lot of analysis on it back during the sailing school vessel research in the early 80's. The sail and rig forces caused by wave motion and rolling often exceed the forces that would cause knockdown although only for brief periods. If you put "fuses" in the rig, you would have stuff breaking constantly. -- Roger Long |
#37
posted to rec.boats.cruising
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Work is not Imaginary (was Buoyancy is Imaginary)
On Fri, 2 Oct 2009 17:42:17 -0700 (PDT), Frogwatch
wrote: On Oct 2, 8:02*pm, brian whatcott wrote: Goofball_star_dot_etal wrote: ... Hmmmm. a mostly reasonable review - but the idea that force times distance *is not equal to work is somewhat radical, don't you think? I said no work was done *on the (air)plane*. Since we only have the airplane and the air, the work done by the thrust of the engine moving the airplane through a distance all goes into the air as (kinetic) energy or heat in its wake. If I push a sled over snow with force F for distance D it's usually accounted that the work I did ON the sled is F X D ...but I won't beat the topic down.... :-) Brian W In regard to sudden gusts, why not use a breakaway strap like some rock climbers use whose stitches break at some load allowing the sail to be let out all the way. How many boats get knocked down anyway? I mean cruising boats, racers intend to be on the edge. My own boat, a 28' S2, if a sudden gust came up, I'd never be able to hold the tiller and she'd round up into the wind before getting knocked down. Not really a problem to design a boat that won't be knocked down. Good form or ballast stability and a small rig. Of course, as soon as the bloke buys this no-knock-down marvel he will get a cruising gennaker, a storm spinnaker and fit a topmast so he can fly a topsail. Probably it is impossible to build a vessel that is impossible to knock down if the owner is in any way adventurous. After all they once built an airplane that wouldn't spin and wouldn't stall. It wasn't immensely popular. Even full rigged ships quite frequently could send down their topmasts in bad weather. Cheers, Bruce (bruceinbangkokatgmaildotcom) |
#38
posted to rec.boats.cruising
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Work is not Imaginary (was Buoyancy is Imaginary)
On Fri, 2 Oct 2009 17:42:17 -0700 (PDT), Frogwatch
wrote: On Oct 2, 8:02*pm, brian whatcott wrote: Goofball_star_dot_etal wrote: ... Hmmmm. a mostly reasonable review - but the idea that force times distance *is not equal to work is somewhat radical, don't you think? I said no work was done *on the (air)plane*. Since we only have the airplane and the air, the work done by the thrust of the engine moving the airplane through a distance all goes into the air as (kinetic) energy or heat in its wake. If I push a sled over snow with force F for distance D it's usually accounted that the work I did ON the sled is F X D ...but I won't beat the topic down.... :-) Brian W In regard to sudden gusts, why not use a breakaway strap like some rock climbers use whose stitches break at some load allowing the sail to be let out all the way. How many boats get knocked down anyway? I mean cruising boats, racers intend to be on the edge. My own boat, a 28' S2, if a sudden gust came up, I'd never be able to hold the tiller and she'd round up into the wind before getting knocked down. Guess again! |
#39
posted to rec.boats.cruising
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Work is not Imaginary (was Buoyancy is Imaginary)
Roger Long wrote:
On Oct 2, 8:42 pm, Frogwatch wrote: In regard to sudden gusts, why not use a breakaway strap like some rock climbers use whose stitches break at some load allowing the sail to be let out all the way. That was a huge issue and we did a lot of analysis on it back during the sailing school vessel research in the early 80's. The sail and rig forces caused by wave motion and rolling often exceed the forces that would cause knockdown although only for brief periods. If you put "fuses" in the rig, you would have stuff breaking constantly. Most of the Nonsuch's (unstayed catboats) were built with aluminum masts that tapered near the top. The marketing folks made a big point of how the tip would flex to leeward and spill wind in gusts. Indeed, it worked well and was helpful since it was easy to overpower the large mainsail in gusty weather. (I learned to reef before going out, since it was a lot easier to shake out than take in a reef!) At the end of the production run they shifted to fiberglass masts that were stiffer. The marketing folks stressed how this gave better pointing ability in strong wind. |
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