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Lift over foils
On Thu, 1 Apr 2004 10:33:19 +0100, "JimB"
wrote: I'm not proposing that the air 'has to catch up'. I'm just saying that if it loses pressure, it's got to gain speed (or disperse energy in some other way). ================================== Let's try for an intuitive approach using a flat plate (your hand, for example). Imagine sticking your hand out the window of a moving car and "flying" it through the air as most of us have probably done as a kid until our parents yelled at us. If you hand is more or less parallel to the ground, you have wind resistance (drag), but no lift. Tilt you hand slightly upwards and now the wind strikes the bottom of your palm and forces it upwards (lift). The reason lift is created is that your hand is deflecting molecules of air downwards (change in momentum), and the resultant force is upwards. It's simple Newtonian mechanics. |
#2
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Lift over foils
On Thu, 01 Apr 2004 23:25:21 -0500, Wayne.B
wrote: On Thu, 1 Apr 2004 10:33:19 +0100, "JimB" wrote: I'm not proposing that the air 'has to catch up'. I'm just saying that if it loses pressure, it's got to gain speed (or disperse energy in some other way). ================================== Let's try for an intuitive approach using a flat plate (your hand, for example). Imagine sticking your hand out the window of a moving car and "flying" it through the air as most of us have probably done as a kid until our parents yelled at us. If you hand is more or less parallel to the ground, you have wind resistance (drag), but no lift. Tilt you hand slightly upwards and now the wind strikes the bottom of your palm and forces it upwards (lift). The reason lift is created is that your hand is deflecting molecules of air downwards (change in momentum), and the resultant force is upwards. It's simple Newtonian mechanics. Nothing wrong with this explanation, as far as it goes. [Except possibly the idea that aerodynamics is 'simple Newtonian dynamics'. :-) ] But to answer the question, "Why does 2/3 of the lift come from the upper surface?" you might need to continue with some suggestion that the faster flow over and above the upper surface meeting the slower flow under and below the lower surface effectively turns the flow downwards which provides that change of velocity which with the air mass flow, provides the Newtonian mass rate times acceleration called the ' momentum change' - is the lifting force Brian W |
#3
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Lift over foils
"Why does 2/3 of the lift come from the
upper surface?" it doesn't. 100% comes from the difference between the bottom and the top. obviously, the bottom is greater when the foil has lift. |
#4
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Lift over foils
JAXAshby wrote in message ... "Why does 2/3 of the lift come from the upper surface?" it doesn't. Decades of aerodynamicists believe it does, based on the the evidence of thousands of surface pressure measurements by a variety of different methods, in flight and in wind tunnels. They've designed aircraft and their structures, then flown them, then tested them, based on this knowledge. Jax, I'm beginning to believe you come from a different planet. 100% comes from the difference between the bottom and the top. I'll go along with that self evident truth obviously, the bottom is greater when the foil has lift. Sure, the bottom has greater pressure than the top. You've just said that. But your phrasing was designed to mislead people into thinking that you'd said the 'bottom' contributed more lift than the 'top' contributed. And I can't believe that's what you meant. JimB |
#5
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Lift over foils
JAXAshby wrote in message ... "Why does 2/3 of the lift come from the upper surface?" it doesn't. Decades of aerodynamicists believe it does, based on the the evidence of thousands of surface pressure measurements by a variety of different methods, in flight and in wind tunnels. They've designed aircraft and their structures, then flown them, then tested them, based on this knowledge. Jax, I'm beginning to believe you come from a different planet. 100% comes from the difference between the bottom and the top. I'll go along with that self evident truth obviously, the bottom is greater when the foil has lift. Sure, the bottom has greater pressure than the top. You've just said that. But your phrasing was designed to mislead people into thinking that you'd said the 'bottom' contributed more lift than the 'top' contributed. And I can't believe that's what you meant. JimB |
#6
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Lift over foils
the faster flow over and above the upper surface meeting the slower
flow under and below the lower surface effectively turns the flow downwards which provides that change of velocity which with the air mass flow, provides the Newtonian mass rate times acceleration called the ' momentum change' - is the lifting force nah. that's barroom talk after the three beer. It won't design any airfoils at all. |
#7
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Lift over foils
JAXAshby wrote in message ... the faster flow over and above the upper surface meeting the slower flow under and below the lower surface effectively turns the flow downwards which provides that change of velocity which with the air mass flow, provides the Newtonian mass rate times acceleration called the ' momentum change' - is the lifting force nah. that's barroom talk after the three beer. It won't design any airfoils at all. So, you don't agree that a change in momentum [of air] is needed to create a [lift] force? This seems to confirm that you live in a different universe from the rest of us, Jax . JimB |
#8
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Lift over foils
JAXAshby wrote in message ... the faster flow over and above the upper surface meeting the slower flow under and below the lower surface effectively turns the flow downwards which provides that change of velocity which with the air mass flow, provides the Newtonian mass rate times acceleration called the ' momentum change' - is the lifting force nah. that's barroom talk after the three beer. It won't design any airfoils at all. So, you don't agree that a change in momentum [of air] is needed to create a [lift] force? This seems to confirm that you live in a different universe from the rest of us, Jax . JimB |
#9
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Lift over foils
"Why does 2/3 of the lift come from the
upper surface?" it doesn't. 100% comes from the difference between the bottom and the top. obviously, the bottom is greater when the foil has lift. |
#10
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Lift over foils
the faster flow over and above the upper surface meeting the slower
flow under and below the lower surface effectively turns the flow downwards which provides that change of velocity which with the air mass flow, provides the Newtonian mass rate times acceleration called the ' momentum change' - is the lifting force nah. that's barroom talk after the three beer. It won't design any airfoils at all. |
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