A question

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Re: A question

#121  Postby Thommo » Jan 31, 2016 2:03 pm

GrahamH wrote:Low pleasure above the wing is demonstrated by condensation over the wing in flight. No venturi tubes there.


I love a good typo. :tehe:
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Re: A question

#122  Postby Gareth » Jan 31, 2016 2:28 pm

GrahamH.
Look again: I wrote: "If you blow air over the open end of a tube you reduce the pressure in the tube." Is there air blowing over the ends of the tubes both over and under the wing? What will that do to the manometer reading?

If there was "condensation over the wing" at 150knots I can't really see how it would stay there for long. Where did you get that?
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Re: A question

#123  Postby GrahamH » Jan 31, 2016 2:54 pm

Gareth wrote:GrahamH.
Look again: I wrote: "If you blow air over the open end of a tube you reduce the pressure in the tube." Is there air blowing over the ends of the tubes both over and under the wing? What will that do to the manometer reading?

If there was "condensation over the wing" at 150knots I can't really see how it would stay there for long. Where did you get that?


I read what you wrote and I pointed out another error that you made.
What you describe is an "atomizer nozzle" (not what is commonly meant by "a venturi")

When a fast gas stream is injected into the atmosphere and across the top of the vertical tube, it is forced to follow a curved path up, over and downward on the other side of the tube. This curved path creates a lower pressure on the inside of the curve at the top of the tube. This curve-caused lower pressure near the tube and the atmospheric pressure further up is the net force causing the curved, velocity-changed path (radial acceleration) shown by Bernoulli's principle.

https://en.wikipedia.org/wiki/Atomizer_nozzle


The manometer ports are flush and do not project into the airflow, so they do not deflect the air. If you disagree then please present evidence, with real data, for your claimed effect.

As for condensation over the wing, Google is your friend.

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Re: A question

#124  Postby GrahamH » Jan 31, 2016 2:59 pm

Does anyone have an issue with NASA on this?

Which camp is correct? How is lift generated?

When a gas flows over an object, or when an object moves through a gas, the molecules of the gas are free to move about the object; they are not closely bound to one another as in a solid. Because the molecules move, there is a velocity associated with the gas. Within the gas, the velocity can have very different values at different places near the object. Bernoulli's equation, which was named for Daniel Bernoulli, relates the pressure in a gas to the local velocity; so as the velocity changes around the object, the pressure changes as well. Adding up (integrating) the pressure variation times the area around the entire body determines the aerodynamic force on the body. The lift is the component of the aerodynamic force which is perpendicular to the original flow direction of the gas. The drag is the component of the aerodynamic force which is parallel to the original flow direction of the gas. Now adding up the velocity variation around the object instead of the pressure variation also determines the aerodynamic force. The integrated velocity variation around the object produces a net turning of the gas flow. From Newton's third law of motion, a turning action of the flow will result in a re-action (aerodynamic force) on the object. So both "Bernoulli" and "Newton" are correct. Integrating the effects of either the pressure or the velocity determines the aerodynamic force on an object. We can use equations developed by each of them to determine the magnitude and direction of the aerodynamic force.

https://www.grc.nasa.gov/www/k-12/airplane/bernnew.html
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Re: A question

#125  Postby Gareth » Jan 31, 2016 4:59 pm

People see what they expect to see.
In the Wiki quote I notice you didn't include the diagram. Look at the diagram. No up and over. Straight. Blowing across the top of the tube at 90 degrees. The principle works. There is no curve. There is no "downward on the other side of the tube. I've done a lot of paint spraying. I know what I'm talking about. The diagram is correct. The text doesn't begin to describe the diagram or the Venturi effect. Doyou think we should believe everything in Wiki?

In the video I saw a plane taking off through thick mist. When the mist hits the front of the wings (and the engines) the mist is concentrated and flies upwards off the leading edge of the wing. There is no side view, so it is not possible to see what is happening along the top of the wing. Let me know if you can find a side view though. That would be interesting. I notice that the condensation stops after a few seconds, yet the lane does not fall to the ground. Curious.

The last quote from NASA doesn't really help, does it? It also mentions Bernoulli. Have I mentioned that the Bernoulli' effect only applies to non-compressible fluids? In any case Bernoulli died a hundred and twenty years before the Wright Brothers' first flight. He had nothing to say about aeroplanes.

I have another quote from another part of the NASA site which lists the Bernoulli theory of lift (vacuum over the wings) as a fallacy. We can't just quote NASA at each other, because it contradicts itself. We really need to think independently, don't you think?
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Re: A question

#126  Postby GrahamH » Jan 31, 2016 5:03 pm

Gareth wrote:People see what they expect to see.


I guess you do.

If you can find any data to back up you claims let's see it.
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Re: A question

#127  Postby Thommo » Jan 31, 2016 5:08 pm

I have to admit I'm struggling to follow this argument against Bernoulli. Bernoulli's law seems to apply to incompressible flows in its simple form, or approximate compressible flows under some circumstances in a more advanced form.

Compared to discussing Boyle's law for a cross section of air (i.e. not fixed volume) which is not held at fixed temperature this seems positively benign, doesn't it? :scratch:

The one thing I'd agree has been successfully debunked would be the two sentences from that one low level explanation on the NASA page "The shape of an airplane's wings is what makes it possible for the airplane to fly. Airplanes' wings are curved on top and flatter on the bottom.", which don't seem to give the right impression at all.
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Re: A question

#128  Postby igorfrankensteen » Jan 31, 2016 5:15 pm

I've run out of patience looking to see if this has been mentioned here already, so I'll just post it, and then let you all carry on and ignore it if you like.

That is, that there is a difference between bad or erroneous science, and poorly executed explanations of good science.

I think I am seeing a lot of complaints about the latter here, being given as proof of the former.

Reality doesn't work that way. What is, is, no matter how erroneously your understanding or description of it is.
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Re: A question

#129  Postby GrahamH » Jan 31, 2016 5:31 pm

I don't get the point of this topic either.
Why do you think that?
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Re: A question

#130  Postby GrahamH » Jan 31, 2016 5:40 pm

Gareth wrote:I have another quote from another part of the NASA site which lists the Bernoulli theory of lift (vacuum over the wings) as a fallacy. We can't just quote NASA at each other, because it contradicts itself. We really need to think independently, don't you think?


If you have a quote from NASA contradicting vacuum above the wrong why haven't you posted it?

Are you equating vacuum above the wing with "the Bernoulli theory of lift "?

NASA wrote:{The upper flow is faster and from Bernoulli's equation the pressure is lower. The difference in pressure across the airfoil produces the lift.} As we have seen in Experiment #1, this part of the theory is correct. In fact, this theory is very appealing because many parts of the theory are correct. In our discussions on pressure-area integration to determine the force on a body immersed in a fluid, we mentioned that if we know the velocity, we can obtain the pressure and determine the force. The problem with the "Equal Transit" theory is that it attempts to provide us with the velocity based on a non-physical assumption as discussed above.
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Re: A question

#131  Postby Macdoc » Jan 31, 2016 5:43 pm

He's just got his baby teeth sunk in a worn out chew toy.... :nono: :coffee:
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Re: A question

#132  Postby campermon » Jan 31, 2016 5:46 pm

Gareth wrote:

Thirdly (and I'm happy to repeat this ad nauseam) the Bernoulli effect applies specifically and exclusively to non-compressible fluids, not gases.



This is incorrect.

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Re: A question

#133  Postby laklak » Jan 31, 2016 5:52 pm

Fluid Dynamics includes gasses.
A man who carries a cat by the tail learns something he can learn in no other way. - Mark Twain
The sky is falling! The sky is falling! - Chicken Little
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Re: A question

#134  Postby Macdoc » Jan 31, 2016 5:54 pm

Yup

BERNOULLI'S PRINCIPLE
Bernoulli's principle, sometimes known as Bernoulli's equation, holds that for fluids in an ideal state, pressure and density are inversely related: in other words, a slow-moving fluid exerts more pressure than a fast-moving fluid.

Since "fluid" in this context applies equally to liquids and gases, the principle has as many applications with regard to airflow as to the flow of liquids

Read more: http://www.scienceclarified.com/everyda ... z3yqR8cVpq
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Re: A question

#135  Postby campermon » Jan 31, 2016 6:44 pm

Macdoc wrote:Yup

BERNOULLI'S PRINCIPLE
Bernoulli's principle, sometimes known as Bernoulli's equation, holds that for fluids in an ideal state, pressure and density are inversely related: in other words, a slow-moving fluid exerts more pressure than a fast-moving fluid.

Since "fluid" in this context applies equally to liquids and gases, the principle has as many applications with regard to airflow as to the flow of liquids

Read more: http://www.scienceclarified.com/everyda ... z3yqR8cVpq


Indeed!

On important fluid dynamical issues: I had a wonderful pint of 'Landlord' today.:

Image

A very nice, and well earned, pint after taking mrsC shopping today.

Currently enjoying a glass of Aussie pinot grigiot while cooking tea.

:cheers:
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Re: A question

#136  Postby BlackBart » Jan 31, 2016 6:55 pm

Yay! Bar's open! :beercheers:
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Re: A question

#137  Postby Gareth » Jan 31, 2016 9:29 pm

Well I've found out what I wanted to know.
I started this thread with the observation that you can't get any two scientists to agree about anything and every contributor has offered a different view/ source/ opinion/ belief/ experience/ conclusion.
If the smoke trails don't lie then the trailing edges (the weakest part) of aircraft wings are under a lot more stress than we thought, but fortunately that's not my problem.
I'm outa here. Thank you all for your input.
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Re: A question

#138  Postby campermon » Jan 31, 2016 9:31 pm

Gareth wrote:Well I've found out what I wanted to know.
I started this thread with the observation that you can't get any two scientists to agree about anything and every contributor has offered a different view/ source/ opinion/ belief/ experience/ conclusion.
If the smoke trails don't lie then the trailing edges (the weakest part) of aircraft wings are under a lot more stress than we thought, but fortunately that's not my problem.
I'm outa here. Thank you all for your input.


The underlined bit is not true.

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Re: A question

#139  Postby Macdoc » Jan 31, 2016 9:33 pm

pathetic hardly covers it... :nono: :coffee:
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Re: A question

#140  Postby BlackBart » Jan 31, 2016 9:39 pm

Macdoc wrote:pathetic hardly covers it... :nono: :coffee:

Welcome to the Internet.
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