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Hi Jeff. Thanks for putting together your ideas and questions on this topic and asking for my thoughts. Your questions are good ones, and ones that many people have puzzled over before.
I have started thinking about your questions. I expect to have some thoughtful answers in a day or two. I will probably post my answers on my User talk page, adjacent to your questions. Cheers Dolphin51 ( talk) 04:15, 21 June 2008 (UTC)
Hi Jeff. I have now finished my responses to your questions. You will find them on my User talk page. If you have any further questions don't hesitate to fire them at me. Cheers. Dolphin51 ( talk) 04:20, 27 June 2008 (UTC)
Hi Jeffareid. It may provoke strong reactions on WP if you edit (or reformat) your own or others comments on an article's talk page, after other people have reacted. See WP:REDACT and WP:TALK#Editing_comments. Personally, in your case it is OK with me (and it also appears to be with Dolphin51), since you seem to to do this in good faith and try to make thinks clearer. But that may not be the case with everybody, so be aware of that. Also, a talk page is just a work place to assist editing the article itself. So it is less important to have things written there very neatly. Cheers, Crowsnest ( talk) 21:33, 9 September 2008 (UTC)
Hi Jeffareid. I archived the talk page of Bernoulli's principle because it was getting long (85 kilobyte). I don't intent to archive again (but I do not know what others will do) until it gets long again. Best regards, -- Crowsnest ( talk) 20:05, 22 September 2008 (UTC)
Either I missed it in the article, or the article left out the key factor in self stability, which is trail. This is easily demonstrated on bicycles where the front wheel can be turned backwards; by turning the front wheel backwards (assuming forward offset forks, the trail is increased a lot and the bicycle will almost come to a complete stop before falling over. Jeffareid ( talk) 01:55, 18 October 2008 (UTC)
On a side note, too little trail is one source of speed wobble. This was an issue for the first year production of Honda's 900 RR motorcycle, where speed wobble was an issue when these motorcycles were raced. In the second and later years, the forks were adjusted 3/8" back to increase the trail and eliminate the speed wobble issue. Jeffareid ( talk) 01:55, 18 October 2008 (UTC)
You are raising excellent points about the article. Thanks for taking a look at it. -
AndrewDressel (
talk)
14:10, 18 October 2008 (UTC)
Perhaps you could help out here when you get the time?
Regarding bicycles (or motocycles) I've alway's thought that main source of self stability was fork trail. I've read this in numerous articles, that included the results of actual testing of real bicycles where the trail was varied from negative (no stability) to very positive (lots of stability). However, Andrew Dressel appears to be disputing a relationship between trail snd self stability.
I've added the following section to the talk page:
I'm also confused about the capsize speed, since I've never experienced this. The eigenvalues section includes a diagram showing that some model of a bicycle will go unstable at around 18mph. However this speed seems slow. A winning racing bicyclist often goes hand free at the end of a race, well over 30mph, with no apparent instability. Motorcycle races sometimes fall off their bikes at high speeds, and the bikes continue on with no apparenty instability.
Jeffareid ( talk) 19:20, 18 October 2008 (UTC)
I've experienced turning a motorcycle at 100mph (not all out, but at about 80% of maximum grip), and the main difference is that the bike tends to hold it's lean angle (lean stability) as opposed to straightening up (vertical stability), when I wasn't applying any torque to the handle bars. I had to use the same amount of inwards counter steering to straighten up as outwards counter steering to lean over. It was similar to flying a plane with no dihedral effects, once banked, it just held the bank angle (the motorcycle at 100mph). At slower speeds, the motorcycle tends to straighten up and requires a constant amount of outwards counter-steering torque in order to hold a lean angle.
I've always thought that the tendency to straighten up is due to the inwards yaw torque on the steering due to fork trail effect. Regarding the transition into lean stability at high speeds, I've always though that it was due to gyroscopic effets.
Jeffareid ( talk) 19:33, 18 October 2008 (UTC)
Article explaining camber thrust: tyres
Tiny graph in this link: motorcycle tire information
Experiment disputing camber thrust: wheels that don't turn Scroll down web page for this link. It's currently broke though. A description of the experiment: Terry made a rig that consisted of two paper cups and a frame. The axles of the paper cups were parallel to each other. Even though the "outer" diameters of the paper cups were larger than the "inner" diameters, the rig rolled in a straight line.
A cone segment shaped tire turns in a circle because it's contact patch generates an inwards yaw torque as the tire rolls forwards, which causes the tire to turn (yaw) over time and travel in a circular path. The contact patch deforms in normal slip angle mode. As speed increases, the radius will become larger because the slip angle increases with centripetal force, which increases relative to speed^2. The point here is that the cone aspect of the tire creates a (yawing) torque, not a (centripetal) force.
Now expand this to a vehicle with two cone segment shaped tires. The inwards yaw torque from the rear tire produces an inwards force on the front tire. The inwards yaw torque from the front tire is more complicated because the front wheel can yaw (steer). It would produce an outwards force on the rear tire if the steering angle was fixed or resisted by a rider. The net difference in these forces, could be considered camber thrust. These camber related forces would be added to the centripetal related forces on the tires, eventually ending up as conventional slip angle related deformations. Note that the inwards yaw camber torque at the front tire causes it to steer inwards, and this may be factor in capsize speed in the case of a riderless bicycle. Camber torque must be relatively small, because it doesn't prevent a riderless bicycle from being stable within reasonable speed range, and it doesn't exhibit itself as a significant torque felt at the handlebars by a rider.
If the two cone shaped tire vehicle had parallel axis, then I'm not sure what happens. Terry Colon did an experiment using paper cups, but the friction was low allowing slippage, and it's possible that the straight line was really a circle with a very large radius. Note that the yawing torque from each tire is resisted by a sideways force by the other tire, so I don't know if there is any net torque or force on the overall vehicle. I wonder what would happen if only one of the tires was cone like and the other was flat?
Jeffareid ( talk) 21:02, 20 October 2008 (UTC)
I can find several examples of authors that claim that side slip causes centripetal force, instead of merely being a symptom of centripetal force. The best treatment I know of online is at http://www.dinamoto.it/ - AndrewDressel ( talk) 01:29, 21 October 2008 (UTC)
I've found several examples of Bernoulli princicple being "demonstrated" by having a stream of air blow across the top of straw with the other end drawing up water from glass implying that the pressure in the stream of air is below ambient.
Realizing that aircraft use static ports to sense the pressure of moving air, I decided to create my own static port using by inserting the end of the straw through a spool of thread and attaching it to a piece of carboard. Links to pictures of my "static port":
If the breeze is strong, then you'd want to cut down the size of the cardboard, or use wood. However at this point, note that real static ports can be purchased for less than $20 (USA):
I then repeated the pressure measurement test using a blow dryer and a straw in water. With just the straw, the water rises indicating lower pressure in the straw. With the static port there was virtually no movment of the water.
I then noted a surface tension and friction effect was resisting vertical movement within the straw, so I mixed in a small amount of liquid soap into the water. This changed the surface within the straw from convex to concave, and for some reason raised the water a slight amount (capillary like effect?). Retesting with the "static port" the water receded a small amount, indicating a slighly higher than ambient pressure in the output stream of the blow dryer.
The blow dryer source is also problematic, because it has a tapered nozzle, acting as a venturi to cause a Bernoulli type exchange of speed for pressure.
If the nozzle wasn't tapered, then the wash from the fan would have higher than ambient pressure, unless there is some special design of fan or propeller that reduces pressure fore of the prop more than than it increases pressure across the prop disc. This Nasa link explains what I'm getting at (prop increases pressure, air continues to accelerate after the prop as it's pressure returns to ambient):
I'm not sure what is going on with the exposed end of the straw in a stream other than it interferes with the stream while the static port doesn't (apparently it's "hiding" in the boundary layer of air near the surface around the port). It's how the exposed end of the straw inteferes with the stream that has me puzzled, does it generate a vortice with corresponding low pressure? Jeffareid ( talk) 04:11, 26 January 2009 (UTC)
Hi Jeff. On 1 March 2009 you made the following entry in response to one of mine, both at Talk:Lift (force)#Upwash:
causing the particle to finish where it started. - This conflicts with the fact that the particles that the wing passes under end up displaced from the particles that the wing passes over.
I agree with you. When I wrote my comment about particles finishing where they started I was obviously thinking about a sphere (or a cylinder). Non-rotating spheres and cylinders don't generate lift so particles finish where they started. The same is true with an airfoil generating zero lift. When an airfoil is generating lift there is cleavage of the flow and, as described by the Kutta condition, the flow over the top of the airfoil moves very fast and never returns to its starting position. (Maybe the flow under the lower surface of the airfoil moves a little too slow and also never returns to its starting position. I need to think about that one.)
I have noticed that a number of contributors to Talk:Lift (force), including you, are inclined to add a new comment right in the middle of some other User's text. (Your comment on 1 March, described in the para above, is an example.) As a result it becomes almost impossible for readers to determine who wrote what because part of each User's text becomes separated from his signature block. I would appreciate it if you always add your comments immediately after someone else's signature block, rather than in the middle of someone else's text. Many thanks! Best regards. Dolphin51 ( talk) 23:51, 17 March 2009 (UTC)
Hi Jeffareid. I archived the talk page of "Lift (force)", because of its length (137 kB). Unfortunately that also moved your contribution of April 7 to the Upwash section there. I will try to create the streamline plot you requested (but cannot promise whether I will succeed and when). Shall we discuss here? Or create an "Upwash (cont'd)" section at the talk page of "Lift (force)", at the moment that may be needed? Further, the WikiProject "Fluid dynamics" has been revived as a task force, see WP:FDTF. If you like to join in, you can do so there. Best regards, Crowsnest ( talk) 18:19, 10 April 2009 (UTC)
(unindent) Why do you expect the streamlines to become vertical lines far from the airfoil? Comment: also note the streamline spacing increases with distance to the airfoil, so the velocities and other effects reduce with distance from the airfoil. The airfoil only significantly disturbs the fluid in its neighbourhood. -- Crowsnest ( talk) 09:48, 14 April 2009 (UTC)
I like the other one and animation, since they show the displacement of the air by the passage of the airfoil (Darwin drift). The schematic one is a bit too "schematic", in my opinion, see the velocity vectors in the top-right picture above. -- Crowsnest ( talk) 15:49, 29 April 2009 (UTC)
Hi Jeff,
I responded in two places to comments/questions you posed at the following location:
http://en.wikipedia.org/wiki/Talk:Bernoulli%27s_principle
Today is my first day ever to post on wikipedia, so I'm not sure how to include the pointers to the comments or if it's even necessary. I know I can put something inside pairs of square brackets, but not sure what should go in there. Anyway, I suppose you will sort it out.
-Kim
Kimaaron ( talk) 06:22, 9 September 2009 (UTC)
Leave a message by clicking here.
Don't forget to sign your message with ~~~~.
Or leave an email: email:Jeffareid
Hi Jeff. Thanks for putting together your ideas and questions on this topic and asking for my thoughts. Your questions are good ones, and ones that many people have puzzled over before.
I have started thinking about your questions. I expect to have some thoughtful answers in a day or two. I will probably post my answers on my User talk page, adjacent to your questions. Cheers Dolphin51 ( talk) 04:15, 21 June 2008 (UTC)
Hi Jeff. I have now finished my responses to your questions. You will find them on my User talk page. If you have any further questions don't hesitate to fire them at me. Cheers. Dolphin51 ( talk) 04:20, 27 June 2008 (UTC)
Hi Jeffareid. It may provoke strong reactions on WP if you edit (or reformat) your own or others comments on an article's talk page, after other people have reacted. See WP:REDACT and WP:TALK#Editing_comments. Personally, in your case it is OK with me (and it also appears to be with Dolphin51), since you seem to to do this in good faith and try to make thinks clearer. But that may not be the case with everybody, so be aware of that. Also, a talk page is just a work place to assist editing the article itself. So it is less important to have things written there very neatly. Cheers, Crowsnest ( talk) 21:33, 9 September 2008 (UTC)
Hi Jeffareid. I archived the talk page of Bernoulli's principle because it was getting long (85 kilobyte). I don't intent to archive again (but I do not know what others will do) until it gets long again. Best regards, -- Crowsnest ( talk) 20:05, 22 September 2008 (UTC)
Either I missed it in the article, or the article left out the key factor in self stability, which is trail. This is easily demonstrated on bicycles where the front wheel can be turned backwards; by turning the front wheel backwards (assuming forward offset forks, the trail is increased a lot and the bicycle will almost come to a complete stop before falling over. Jeffareid ( talk) 01:55, 18 October 2008 (UTC)
On a side note, too little trail is one source of speed wobble. This was an issue for the first year production of Honda's 900 RR motorcycle, where speed wobble was an issue when these motorcycles were raced. In the second and later years, the forks were adjusted 3/8" back to increase the trail and eliminate the speed wobble issue. Jeffareid ( talk) 01:55, 18 October 2008 (UTC)
You are raising excellent points about the article. Thanks for taking a look at it. -
AndrewDressel (
talk)
14:10, 18 October 2008 (UTC)
Perhaps you could help out here when you get the time?
Regarding bicycles (or motocycles) I've alway's thought that main source of self stability was fork trail. I've read this in numerous articles, that included the results of actual testing of real bicycles where the trail was varied from negative (no stability) to very positive (lots of stability). However, Andrew Dressel appears to be disputing a relationship between trail snd self stability.
I've added the following section to the talk page:
I'm also confused about the capsize speed, since I've never experienced this. The eigenvalues section includes a diagram showing that some model of a bicycle will go unstable at around 18mph. However this speed seems slow. A winning racing bicyclist often goes hand free at the end of a race, well over 30mph, with no apparent instability. Motorcycle races sometimes fall off their bikes at high speeds, and the bikes continue on with no apparenty instability.
Jeffareid ( talk) 19:20, 18 October 2008 (UTC)
I've experienced turning a motorcycle at 100mph (not all out, but at about 80% of maximum grip), and the main difference is that the bike tends to hold it's lean angle (lean stability) as opposed to straightening up (vertical stability), when I wasn't applying any torque to the handle bars. I had to use the same amount of inwards counter steering to straighten up as outwards counter steering to lean over. It was similar to flying a plane with no dihedral effects, once banked, it just held the bank angle (the motorcycle at 100mph). At slower speeds, the motorcycle tends to straighten up and requires a constant amount of outwards counter-steering torque in order to hold a lean angle.
I've always thought that the tendency to straighten up is due to the inwards yaw torque on the steering due to fork trail effect. Regarding the transition into lean stability at high speeds, I've always though that it was due to gyroscopic effets.
Jeffareid ( talk) 19:33, 18 October 2008 (UTC)
Article explaining camber thrust: tyres
Tiny graph in this link: motorcycle tire information
Experiment disputing camber thrust: wheels that don't turn Scroll down web page for this link. It's currently broke though. A description of the experiment: Terry made a rig that consisted of two paper cups and a frame. The axles of the paper cups were parallel to each other. Even though the "outer" diameters of the paper cups were larger than the "inner" diameters, the rig rolled in a straight line.
A cone segment shaped tire turns in a circle because it's contact patch generates an inwards yaw torque as the tire rolls forwards, which causes the tire to turn (yaw) over time and travel in a circular path. The contact patch deforms in normal slip angle mode. As speed increases, the radius will become larger because the slip angle increases with centripetal force, which increases relative to speed^2. The point here is that the cone aspect of the tire creates a (yawing) torque, not a (centripetal) force.
Now expand this to a vehicle with two cone segment shaped tires. The inwards yaw torque from the rear tire produces an inwards force on the front tire. The inwards yaw torque from the front tire is more complicated because the front wheel can yaw (steer). It would produce an outwards force on the rear tire if the steering angle was fixed or resisted by a rider. The net difference in these forces, could be considered camber thrust. These camber related forces would be added to the centripetal related forces on the tires, eventually ending up as conventional slip angle related deformations. Note that the inwards yaw camber torque at the front tire causes it to steer inwards, and this may be factor in capsize speed in the case of a riderless bicycle. Camber torque must be relatively small, because it doesn't prevent a riderless bicycle from being stable within reasonable speed range, and it doesn't exhibit itself as a significant torque felt at the handlebars by a rider.
If the two cone shaped tire vehicle had parallel axis, then I'm not sure what happens. Terry Colon did an experiment using paper cups, but the friction was low allowing slippage, and it's possible that the straight line was really a circle with a very large radius. Note that the yawing torque from each tire is resisted by a sideways force by the other tire, so I don't know if there is any net torque or force on the overall vehicle. I wonder what would happen if only one of the tires was cone like and the other was flat?
Jeffareid ( talk) 21:02, 20 October 2008 (UTC)
I can find several examples of authors that claim that side slip causes centripetal force, instead of merely being a symptom of centripetal force. The best treatment I know of online is at http://www.dinamoto.it/ - AndrewDressel ( talk) 01:29, 21 October 2008 (UTC)
I've found several examples of Bernoulli princicple being "demonstrated" by having a stream of air blow across the top of straw with the other end drawing up water from glass implying that the pressure in the stream of air is below ambient.
Realizing that aircraft use static ports to sense the pressure of moving air, I decided to create my own static port using by inserting the end of the straw through a spool of thread and attaching it to a piece of carboard. Links to pictures of my "static port":
If the breeze is strong, then you'd want to cut down the size of the cardboard, or use wood. However at this point, note that real static ports can be purchased for less than $20 (USA):
I then repeated the pressure measurement test using a blow dryer and a straw in water. With just the straw, the water rises indicating lower pressure in the straw. With the static port there was virtually no movment of the water.
I then noted a surface tension and friction effect was resisting vertical movement within the straw, so I mixed in a small amount of liquid soap into the water. This changed the surface within the straw from convex to concave, and for some reason raised the water a slight amount (capillary like effect?). Retesting with the "static port" the water receded a small amount, indicating a slighly higher than ambient pressure in the output stream of the blow dryer.
The blow dryer source is also problematic, because it has a tapered nozzle, acting as a venturi to cause a Bernoulli type exchange of speed for pressure.
If the nozzle wasn't tapered, then the wash from the fan would have higher than ambient pressure, unless there is some special design of fan or propeller that reduces pressure fore of the prop more than than it increases pressure across the prop disc. This Nasa link explains what I'm getting at (prop increases pressure, air continues to accelerate after the prop as it's pressure returns to ambient):
I'm not sure what is going on with the exposed end of the straw in a stream other than it interferes with the stream while the static port doesn't (apparently it's "hiding" in the boundary layer of air near the surface around the port). It's how the exposed end of the straw inteferes with the stream that has me puzzled, does it generate a vortice with corresponding low pressure? Jeffareid ( talk) 04:11, 26 January 2009 (UTC)
Hi Jeff. On 1 March 2009 you made the following entry in response to one of mine, both at Talk:Lift (force)#Upwash:
causing the particle to finish where it started. - This conflicts with the fact that the particles that the wing passes under end up displaced from the particles that the wing passes over.
I agree with you. When I wrote my comment about particles finishing where they started I was obviously thinking about a sphere (or a cylinder). Non-rotating spheres and cylinders don't generate lift so particles finish where they started. The same is true with an airfoil generating zero lift. When an airfoil is generating lift there is cleavage of the flow and, as described by the Kutta condition, the flow over the top of the airfoil moves very fast and never returns to its starting position. (Maybe the flow under the lower surface of the airfoil moves a little too slow and also never returns to its starting position. I need to think about that one.)
I have noticed that a number of contributors to Talk:Lift (force), including you, are inclined to add a new comment right in the middle of some other User's text. (Your comment on 1 March, described in the para above, is an example.) As a result it becomes almost impossible for readers to determine who wrote what because part of each User's text becomes separated from his signature block. I would appreciate it if you always add your comments immediately after someone else's signature block, rather than in the middle of someone else's text. Many thanks! Best regards. Dolphin51 ( talk) 23:51, 17 March 2009 (UTC)
Hi Jeffareid. I archived the talk page of "Lift (force)", because of its length (137 kB). Unfortunately that also moved your contribution of April 7 to the Upwash section there. I will try to create the streamline plot you requested (but cannot promise whether I will succeed and when). Shall we discuss here? Or create an "Upwash (cont'd)" section at the talk page of "Lift (force)", at the moment that may be needed? Further, the WikiProject "Fluid dynamics" has been revived as a task force, see WP:FDTF. If you like to join in, you can do so there. Best regards, Crowsnest ( talk) 18:19, 10 April 2009 (UTC)
(unindent) Why do you expect the streamlines to become vertical lines far from the airfoil? Comment: also note the streamline spacing increases with distance to the airfoil, so the velocities and other effects reduce with distance from the airfoil. The airfoil only significantly disturbs the fluid in its neighbourhood. -- Crowsnest ( talk) 09:48, 14 April 2009 (UTC)
I like the other one and animation, since they show the displacement of the air by the passage of the airfoil (Darwin drift). The schematic one is a bit too "schematic", in my opinion, see the velocity vectors in the top-right picture above. -- Crowsnest ( talk) 15:49, 29 April 2009 (UTC)
Hi Jeff,
I responded in two places to comments/questions you posed at the following location:
http://en.wikipedia.org/wiki/Talk:Bernoulli%27s_principle
Today is my first day ever to post on wikipedia, so I'm not sure how to include the pointers to the comments or if it's even necessary. I know I can put something inside pairs of square brackets, but not sure what should go in there. Anyway, I suppose you will sort it out.
-Kim
Kimaaron ( talk) 06:22, 9 September 2009 (UTC)