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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 |
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