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#1
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push vs pull vis a vis rudders
wtf are you talking about? it's awfully early in the day to be so incoherant
from alcohol. Intuitively, most people sense that water "pulled" over a rudder will cause a rudder to change direction of a boat in much the same way as water "pushed" over a rudder does. However, intuition misses some things along the way. [...] end) to port. However, the water drawn over the rudder's port side hits that side and is deflected towards port. Then the rudder would push the boat (after end) to starboard. And equal and opposite reaction. Net, net, the boat does not turn. The pressure on each side of the rudder is equal. Nada. Jox, since you're such an "expert" on Feynman inverse sprinkler problem and how to misapply it to any situation, maybe you can answer a question about it. While it's true that the sprinkler won't turn when water is being sucked in, it's not true that no net force is generated by sucking the water in. In fact, there is a net force generated. It's just not in a direction that will turn the sprinkler. In relation to your discussion about about equal and opposite, net net, no net force, etc., how do you reconcile that with the fact that it's not true for the inverse sprinkler problem? Steve |
#2
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push vs pull vis a vis rudders
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#3
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push vs pull vis a vis rudders
schlackoff, you are using a constrained airflow? know what that means? know
how it is different from unconstrained. get some sleep, schlackoff, and you will feel better by tomorrow afternoonn. wtf are you talking about? it's awfully early in the day to be so incoherant from alcohol. Bzzzt!!! Wrong answer jox. Try again. It's clear you don't understand the sprinkler problem. While you're cogitating on why you're wrong in applying feynman's sprinkler problem to this arena, here's another, simpler question for you: Say you have a wind tunnel with a rudder mounted at the test point. First case is a blower at one end forcing air though the tunnel and past the rudder at 1mph. You turn the rudder at a 45 degree angle to the airflow. Is there a lateral force generated by the rudder? Second case is a blower at the other end of the tunnel but now it's sucking air through the tunnel past the rudder at 1mph. You turn the rudder at a 45 degree angle to the airflow. Is there a lateral force generated by the rudder? Intuitively, most people sense that water "pulled" over a rudder will cause a rudder to change direction of a boat in much the same way as water "pushed" over a rudder does. However, intuition misses some things along the way. [...] end) to port. However, the water drawn over the rudder's port side hits that side and is deflected towards port. Then the rudder would push the boat (after end) to starboard. And equal and opposite reaction. Net, net, the boat does not turn. The pressure on each side of the rudder is equal. Nada. Jox, since you're such an "expert" on Feynman inverse sprinkler problem and how to misapply it to any situation, maybe you can answer a question about it. While it's true that the sprinkler won't turn when water is being sucked in, it's not true that no net force is generated by sucking the water in. In fact, there is a net force generated. It's just not in a direction that will turn the sprinkler. In relation to your discussion about about equal and opposite, net net, no net force, etc., how do you reconcile that with the fact that it's not true for the inverse sprinkler problem? Steve |
#4
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push vs pull vis a vis rudders
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#5
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push vs pull vis a vis rudders
steve, consider just where the air on the "supply side" of the fan blades come
from and consider how that differs from the air on the "demand side". the demand side is more or less a stream that expands. the supply side is more like a hemi-sphere of air (actually, air from the demand side passes back to the supply side as each blade of the fan passes, i.e. tip vortices). Consider, also, that *if* fluid drawn over a rudder by a prop have any effect on the rudder, mariners would all know which direction the stern moved with which rudder position. Even the guys who insist pulled water affects a rudder don't have a clew which way the boat turns. indeed, the "good professor" was reduced to claiming that friction in the rudder bearin made the difference. schlackoff, you are using a constrained airflow? know what that means? know how it is different from unconstrained. Interesting that you think it makes a difference. Ok, try it again but this time with a theoretical infinitely sized wind tunnel, or a physical one large enough that the difference between constrained flow and unconstrained flow is negligable, like a 1 mile diameter wind tunnel and a 1" rudder. In one case the air in an infinite wind tunnel is being pushed at 1mph past the rudder and in the other case it's being drawn past the rudder at 1mph. In both cases, air is flowing past the rudder at 1mph and the rudder is at a 45 degree angle. Does the rudder generate a lateral force in both cases? Steve wtf are you talking about? Bzzzt!!! Wrong answer jox. Try again. It's clear you don't understand the sprinkler problem. While you're cogitating on why you're wrong in applying feynman's sprinkler problem to this arena, here's another, simpler question for you: Say you have a wind tunnel with a rudder mounted at the test point. First case is a blower at one end forcing air though the tunnel and past the rudder at 1mph. You turn the rudder at a 45 degree angle to the airflow. Is there a lateral force generated by the rudder? Second case is a blower at the other end of the tunnel but now it's sucking air through the tunnel past the rudder at 1mph. You turn the rudder at a 45 degree angle to the airflow. Is there a lateral force generated by the rudder? Intuitively, most people sense that water "pulled" over a rudder will cause a rudder to change direction of a boat in much the same way as water "pushed" over a rudder does. However, intuition misses some things along the way. [...] end) to port. However, the water drawn over the rudder's port side hits that side and is deflected towards port. Then the rudder would push the boat (after end) to starboard. And equal and opposite reaction. Net, net, the boat does not turn. The pressure on each side of the rudder is equal. Nada. Jox, since you're such an "expert" on Feynman inverse sprinkler problem and how to misapply it to any situation, maybe you can answer a question about it. While it's true that the sprinkler won't turn when water is being sucked in, it's not true that no net force is generated by sucking the water in. In fact, there is a net force generated. It's just not in a direction that will turn the sprinkler. In relation to your discussion about about equal and opposite, net net, no net force, etc., how do you reconcile that with the fact that it's not true for the inverse sprinkler problem? Steve |
#6
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push vs pull vis a vis rudders
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#7
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push vs pull vis a vis rudders
Consider that it doesn't really matter as long as there is flow of fluid
media over the rudder. but it does, because the rudder and prop are hooked together. If the prop were fixed as to direction, the rudder would turn into it until the movement stopped. Consider the fact that fluid drawn over a rudder by a prop may have an effect on how the stern moves, but one that is much less then prop walk. the "good professor" argued that without friction in the rudder bearings rudder would move. I say it doesn't. plainly, a shot of forward throttle with the rudder turned turns the stern, and all (most?) mariners know in which direction the boat will turn from experience. nobody can remember which direction a boat will turn with a shot of reverse throttle because nobody has seen it. |
#8
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push vs pull vis a vis rudders
Steven Shelikoff wrote: Consider that it doesn't really matter as long as there is flow of fluid media over the rudder. Again, here you're assuming laminar (or at least unidirectional) flow. When inserted into a laminar flow stream, and angled surface, such as a rudder, will certainly be subjected to a force related to the mass of the fluid deflected. Fluid flow on the 'suction' side is nowhere near laminar, and will in fact be totally non-uniform around the rudder. All fluid will be redirected immediately upon clearing the rudder, and the resulting reaction force is parallel to the boats centerline. Consider, also, that *if* fluid drawn over a rudder by a prop have any effect on the rudder, mariners would all know which direction the stern moved with which rudder position. Even the guys who insist pulled water affects a rudder don't have a clew which way the boat turns. indeed, the "good professor" was reduced to claiming that friction in the rudder bearin made the difference. Consider the fact that fluid drawn over a rudder by a prop may have an effect on how the stern moves, It *may* for a brief instant until an equilibrium is reached and the pressure equalizes on both rudder surfaces (remember, water is *not* elastic in the way air is, so you can't create a vacuum in water like you do in air - if you do, you cavitate and dissolve gases come out of solution until the partial pressures equalize and/or until water 'fills in the void' and the gases redissolve). but one that is much less then prop walk. Many orders of magnitude less IME and IMO. Keith Hughes |
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