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push vs pull vis a vis rudders
JAXAshby wrote in message ... If you could demonstrate, prove or explain why water speed should be identical along each side of the rudder water speed does not have to be equal or greater or less. This can be a bit confusing because "bernoulli" is often -- though erroneously -- given as the reason sails/wings have "lift". Sails/wings create lift (a force) by altering the momentum of the air passing by. The mechanism creating this lift is a (mean) fluid pressure difference between one side, and the other, of the sail/wing. Any pressure change in a freely flowing fluid will be matched to a change in local fluid speed (barring supersonics, flow breakaway, and the trivial effects of surface viscosity) to conserve energy. This is (presumably) the 'bernouili' bit you claim is often erroneous. Interesting. Do you disagree with the concept of conservation of energy? or do you claim special conditions which make his equations irrelevant? It might be a bit easier to remember that for the rudder to be pushed one way, it (the rudder) must push water the opposite way. If the water is not deflected then there is no force on the rudder. Agree; for the rudder to create yaw, it must deflect water. It must change the momentum of the water. Many ways of saying the same thing. That's where I'm stuck. I see the rudder (prop in reverse, boat static) altering the direction of the water approaching the prop. Now, perhaps it doesn't. Or perhaps there's an opposite effect somewhere else which I haven't yet identified. I'm looking for education here, not stating a flat opinion. JimB |
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