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Old Nov 14, 2011, 11:38 AM
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The 'Wack, BC, Canada
Joined Oct 2002
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Quote:
Originally Posted by Tim Green View Post
Regarding your accusation that I don't listen - I find your posts vacuous, with lots of words used as a substitute for logic. So, please stop telling everyone I don't listen, because I do. I love logical discussion - but broadsides of useless verbiage aren't useful to me.
Tim, never mind the past exchanges between you and starduster for a moment. He posted a lot of quotes directly from NASA which talks a lot more in detail about what is going on around a wing than the highly basic one you posted in the first link. What about the the information in those links and what they imply with their more detailed explanations of what is going on at the wing itself?

Quote:
Originally Posted by Tim Green View Post
.....Or do we have to look at the "helicopter won't lift if a flat plate is attached to its skids" experiment?

1)Because to me, what NASA's saying, is that the lift is generated at the rotor, which means a chopper with it's downwash blocked should still rise - but it doesn't.

2)There are scientists claiming that lift is both - Newton response to downwash at low speeds, and Bernoulli at high speeds.

3)The chopper experiment intrigues me no end though - and I've yet to see a Bernoulli only, or a turning only, demonstration of lift in a chopper.
OK, by the numbers, although I thought that we dealt with these just fine in the last thread.

1) Until you come to realize that the downwash behind the wing is the after effect of creating the lift and NOT the lift itself you're stuck. What you understand NASA to be saying about the rotor's lift occuring at the rotor is correct and is nothing more or less than we've been saying all along.

2) The airflow at the wing produces a "Yin and Yang" sort of thing with both Newtonian and Burnoullian effects acting at the same time. There is no low to high speed transition between the two. They are locked together with one producing the other and the each supporting the effect of the other. The Bernoullian pressure effects are produced by the way the air reacts to the passing of the airfoil by the Newtonian way that the air is pushed out of the way and around the wing's airfoil. But at the same time it's the Bernoullian pressure effects that hold the air and cause it to follow around the the shape to be thrown down to create the Newtonian downwash effect. So it's like the old "pulling yourself up by the bootstraps" sort of deal. The Newtonian action creates the Bernoullian effect which causes the Newtonian action. You can't separate them however much you want to. As soon as our wing or flat plate or any other object encounters moving air or moves through the air the air moves around the object in a manner which generates both effects at the very same time. .

2A) Only the simplest texts say that the upper and lower airflow meet at the trailing edge. And as you point out those are wrong. This has been known for most of the last 100 years by those that are actually in the field. But it's generally explained poorly by others that write the slimplistic texts that so many folks read. Oddly enough I understand that this simplistic error was actually published in texts used for pilot training for many years and may still be there. Which points out that we don't need to be a scientist to fly a plane.

3) Back to your blocked heli flow. OK, it's blocked because there's a plate attached. But how is this plate different from the ground for a heli that is taking off? Simply it isn't. At the point of liftoff any helicopter's downwash is blocked by the ground. Yet they all lift off. The only difference with the plate is that in that case it's trying to take the "ground" along with it. So why is this? It's NOT because the lift is blocked or the heli would not be able to take off from regular ground. It's because you tied the heli to the "ground". As I said in the last thread, and which you never commented on, if you where to attach the plate to the heli with a force measuring scale you'd see that the lift is still there and that it would be trying to rip the plate off the landing gear of the heli. But you just tied the two together into a locked system. You won't see any lift within that system from the outside. But if you reach into the system and put a force measuring device in the string that holds the plate to the heli you would be able to measure the lift force. The lift is still there, it's just being held down by the pressure effect of the plate. The pressure buildup on the plate is still a totally separate event that is relying solely on the string tieing the plate to the heli to prevent the heli from lifting. Having the plate attached to the heli is also very much the same as my astronaut and toolkit example where the toolkit hooks his foot on the way past. He generated the thrust by throwing the kit but it was negated by the tool kit hooking onto his boot and transferring all the energy back into the astronaut. But that doesn't mean that a reaction didn't occur. The astronaut was moving just fine at the moment the kit left his hand. It was the separate act of hooking his boot that stopped him from from moving. The plate tied to the heli is the same as the kit catching on the boot.
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Last edited by BMatthews; Nov 14, 2011 at 11:45 AM.
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