A question

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Re: A question

#101  Postby GrahamH » Jan 29, 2016 9:59 pm

Gareth wrote:Thanks romansh. I had a look, and if you read the section called Wing-Pressure Orifices you'll see that they used the same flawed methodology used in the original experiment that I mentioned in the first place i.e using open ended orifices. Have none of these people ever heard of Venturi?

So, yes. That was very useful indeed. Thank you.


So, the only data presented so far you reject. Where is your evidence of three times greater pressure difference under the wing than above it?

Published data from NASA has rather more credibility than mere assertions from an unknown person who just joined a forum.
Why do you think that?
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Re: A question

#102  Postby Gareth » Jan 30, 2016 2:47 pm

Hi BWE. I've got a couple for you.

If you're sold on quantum entanglement there's this: http://www.livescience.com/27920-quantu ... light.html

Otherwise, you might find this more persuasive:-
Researchers on the Opera (Oscillation Project with Emulsion-tRacking Apparatus) experiment recorded the arrival times of ghostly subatomic particles called neutrinos sent from Cern on a 730km journey through the Earth to the Gran Sasso lab.
The trip would take a beam of light 2.4 milliseconds to complete, but after running the experiment for three years and timing the arrival of 15,000 neutrinos, the scientists discovered that the particles arrived at Gran Sasso sixty billionths of a second earlier, with an error margin of plus or minus 10 billionths of a second.
The measurement amounts to the neutrinos travelling faster than the speed of light by a fraction of 20 parts per million. Since the speed of light is 299,792,458 metres per second, the neutrinos were evidently travelling at 299,798,454 metres per second.
https://www.theguardian.com/science/201 ... CMP=twt_gu

The methodology seems quite rigorous. See what you think.
I want to keep this thread about Bernoulli though. I'll send you 2 other things by PM.
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Re: A question

#103  Postby Gareth » Jan 30, 2016 4:31 pm

Where is your evidence of three times greater pressure difference under the wing than above it?

Okay. One more time for GrahamH.

Here is the video's location that I mentioned: https://www.youtube.com/watch?v=3_WgkVQWtno
If you fast forward to 4 min: 00secs and pause it you should be able to observe the smooth laminar flow of the smoke trails under the wing. On the far right of the picture the atmospheric pressure is 1bar (1 x atmospheric pressure) and the smoke trails are evenly spaced, Now look at the smoke trails immediately under the trailing edge of the wing. You will observe that three smoke trails have been compressed into the space that one smoke trail occupies on the far right (about the size of the cursor on your screen)

Now that hasn't been achieved by the smoke trails going faster. Indeed we know that the air below the wing travels slower than the air above it (thousands of references available for this). The air has therefore been compressed to one third of its original volume.
Boyle's Law tells us that if you compress a quantity of gas (e.g. air) to one third of its volume then the pressure of that gas will be increased threefold. The pressure under the trailing edge of the wing must, therefore be 3bar (3 x atmospheric pressure).
Now let's look at the smoke trails above the wing. Here we observe that the smoke trails have dissipated in an area of low pressure due to the steep angle of attack. If that low pressure was actually a total vacuum then the pressure would be zero bar (0 x atmospheric pressure), which is one bar less than atmospheric pressure. It doesn't matter, by the way, whether the vacuum is 1mm thick, 1 metre thick or 100 kilometres thick, the reduction in pressure acting downwards on the wing is still 1 bar.

So the maximum possible (hypothetical) lift generated by the upper wing surface is equal to the force generated by one atmosphere, while, as we have seen, the observed upward force generated by air compression under the wing is equal to three times atmospheric pressure.

I hope I've made that clear. Thanks for your input.
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Re: A question

#104  Postby GrahamH » Jan 30, 2016 4:46 pm

Gareth wrote:On the far right of the picture the atmospheric pressure is 1bar (1 x atmospheric pressure) and the smoke trails are evenly spaced, Now look at the smoke trails immediately under the trailing edge of the wing. You will observe that three smoke trails have been compressed into the space that one smoke trail occupies on the far right (about the size of the cursor on your screen)

Now that hasn't been achieved by the smoke trails going faster. Indeed we know that the air below the wing travels slower than the air above it (thousands of references available for this). The air has therefore been compressed to one third of its original volume.
Boyle's Law tells us that if you compress a quantity of gas (e.g. air) to one third of its volume then the pressure of that gas will be increased threefold. The pressure under the trailing edge of the wing must, therefore be 3bar (3 x atmospheric pressure).


Why do you suppose there is no mention of your method for measuring air pressure on Wikipedia?

Measurement of the dynamic pressure, the static pressure, and (for compressible flow only) the temperature rise in the airflow. The direction of airflow around a model can be determined by tufts of yarn attached to the aerodynamic surfaces. The direction of airflow approaching a surface can be visualized by mounting threads in the airflow ahead of and aft of the test model. Smoke or bubbles of liquid can be introduced into the airflow upstream of the test model, and their path around the model can be photographed (see particle image velocimetry).

Aerodynamic forces on the test model are usually measured with beam balances, connected to the test model with beams,strings, or cables.

The pressure distributions across the test model have historically been measured by drilling many small holes along the airflow path, and using multi-tube manometers to measure the pressure at each hole. Pressure distributions can more conveniently be measured by the use of pressure-sensitive paint, in which higher local pressure is indicated by lowered fluorescence of the paint at that point. Pressure distributions can also be conveniently measured by the use of pressure-sensitive pressure belts, a recent development in which multiple ultra-miniaturized pressure sensor modules are integrated into a flexible strip. The strip is attached to the aerodynamic surface with tape, and it sends signals depicting the pressure distribution along its surface.[1]

Pressure distributions on a test model can also be determined by performing a wake survey, in which either a single pitot tube is used to obtain multiple readings downstream of the test model, or a multiple-tube manometer is mounted downstream and all its readings are taken.
https://en.wikipedia.org/wiki/Wind_tunn ... asurements


Could it be that you just made it up? Or perhaps it's a fact that is being suppressed by a grand conspiracy of NASA et al.

Hmmm. Where did you get that method from?
Why do you think that?
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Re: A question

#105  Postby thaesofereode » Jan 30, 2016 5:04 pm

Gareth wrote:Thank you, Thaesofereode. I was beginning to think this site was only for the first type of skeptic. I've done a little flying, too. Only as far as getting my EP.

I would encourage people to look at the wind tunnel smoke trails in the video. See three smoke trails compressed into the space of one immediately under the wing. Look up atmospheric pressure. Multiply by three. You've reached the same conclusion by sticking a hand out the window. Brilliant.


Just to clarify, none of this was an attempt in any way to gainsay science or the scientific method. Truly only anecdotal on the hand out the window observations. Am perfectly willing to listen to further evidence on this topic, esp. since from the point of view of physics it seems to turn out to be non-intuitive. If in the end what I felt out the window was some kind of "pull" from a vacuum forming behind or above my hand rather than pressure to the lower surface, I'm by all means open to the evidence. Perhaps the highly localized effects of atmospheric pressure perceived by me in my hand-out-the-window experience are completely *relative* yes? Was only saying that I've always been somewhat skeptical of the "vacuum" idea. But am willing to change my mind, as my Mom used to say "in the light of new evidence." If there is something that's measurable (which I cannot imagine there ISN'T) that can shed light on this, and for which I'm equipped to acquire proper understanding, I have no problem learning something new here!

A quick scan of some of the posts tells me that there are disputes about the various measurement systems, equipment, methods, and interpretations of the results. Interesting that we're debating a topic that involves a phenomenon so fundamental to flight, which we've been achieving VERY effectively for many decades now as a practical matter. Would lead one to conclude that we're making full use and advantage of a physical phenomenon that we still don't understand? Then again, we take major advantage of gravity every day, but we're only just barely beginning to understand what that actually is at its very basis, either.
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Re: A question

#106  Postby Macdoc » Jan 30, 2016 9:19 pm

He's ignoring answers already provided ...I'd not waste more electrons on him. :coffee:
You may find this a good read. I did.
http://www.terrycolon.com/1features/fly.html
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Re: A question

#107  Postby BWE » Jan 30, 2016 10:12 pm

Gareth wrote:Hi BWE. I've got a couple for you.

If you're sold on quantum entanglement there's this: http://www.livescience.com/27920-quantu ... light.html

Otherwise, you might find this more persuasive:-
Researchers on the Opera (Oscillation Project with Emulsion-tRacking Apparatus) experiment recorded the arrival times of ghostly subatomic particles called neutrinos sent from Cern on a 730km journey through the Earth to the Gran Sasso lab.
The trip would take a beam of light 2.4 milliseconds to complete, but after running the experiment for three years and timing the arrival of 15,000 neutrinos, the scientists discovered that the particles arrived at Gran Sasso sixty billionths of a second earlier, with an error margin of plus or minus 10 billionths of a second.
The measurement amounts to the neutrinos travelling faster than the speed of light by a fraction of 20 parts per million. Since the speed of light is 299,792,458 metres per second, the neutrinos were evidently travelling at 299,798,454 metres per second.
https://www.theguardian.com/science/201 ... CMP=twt_gu

The methodology seems quite rigorous. See what you think.
I want to keep this thread about Bernoulli though. I'll send you 2 other things by PM.


the neutrino thing was eventually attributed to an electronics error iirc. Will check my messages.
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Re: A question

#108  Postby Calilasseia » Jan 31, 2016 1:28 am

Meanwhile, since aeronautical engineering isn't my strong point, I'll simply point out some elementary errors in the opening post.

Gareth wrote:Some skeptics are proud of being too smart to believe anything at all and will happily argue that black is white. Others just like to tell the devout how dumb they are.

I'm hoping to find some real skeptics on RatSkep -- people who like to think about stuff and reach rational conclusions.
What are my chances?

The reason I ask is because I'd like to enter the Ratskep writing competition on the given topic of a scientific hypothesis that failed. Science-oriented sites usually refuse to post anything that calls into question anything that any scientist ever said about anything (despite the fact that you can't get any two scientists to agree about anything).

Would a person like me be welcome here?


Actually, I wrote a piece for one of those competitions, covering a classic example of a scientific hypothesis that failed. An entire thread devoted to this very topic was launched as a competition here, and you can read it in full here, along with my own entry here.

So the idea that we don't call things into question, is one that fails even an elementary perusal of the data.

As for the idea that you can't get any two scientists to agree about anything, I suspect many in the physics community alone will laugh at that assertion.

Now, I'll return everyone to their scheduled entertainment.
Signature temporarily on hold until I can find a reliable image host ...
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Re: A question

#109  Postby thaesofereode » Jan 31, 2016 3:03 am

No derail intended. And clearly there'll be no consensus there.

By all means return to the original topic.

:popcorn:
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Re: A question

#110  Postby Gareth » Jan 31, 2016 8:09 am

Goodmorning all.

GrahamH first. There is "there is no mention of your method for measuring air pressure on Wikipedia" because it doesn't "measure" pressure, it simply shows that the air is compressed by some ball-park factor. Where I got it from is by using my eyes and looking at the air being compressed.

Next, the modest thaesofereode . Hi. You ask about "If there is something that's measurable" about putting your hand in a windstream and the possibility of there being a vacuum above it. Try this. Suck the back of your hand. You can't create anything close to a vacuum but you'll see the tny blood capillaries in your skin will have burst, forming a "hickey" or "love bite". Now, did you notice anything like that when you stuck your hand out of the window?

And finally, Calilasseia. Good of you to drop in. I had already read your competition piece. Very erudite. I know scientists "call things into question" but you have to admit they don't like it very much when anyone else does. That was my point.

Of course I haven't read everything in science. Perhaps you could remind me of something in science concerning which there is no disagreement among scientists. Lord Kelvin once said "The only thing of which we are certain in science is that ether exists."
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Re: A question

#111  Postby GrahamH » Jan 31, 2016 9:21 am

Gareth wrote:Goodmorning all.

GrahamH first. There is "there is no mention of your method for measuring air pressure on Wikipedia" because it doesn't "measure" pressure, it simply shows that the air is compressed by some ball-park factor. Where I got it from is by using my eyes and looking at the air being compressed.



So you did just make it up and you have no measurements and therefore no evidence for your claim.
Why do you think that?
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Re: A question

#112  Postby Gareth » Jan 31, 2016 10:07 am

I respect your view. How would you explain the compression of the smoke trails if there is no increase in pressure and how do you account for the fact that aeroplanes can fly upside down?
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Re: A question

#113  Postby campermon » Jan 31, 2016 10:27 am

Gareth wrote:I respect your view. How would you explain the compression of the smoke trails if there is no increase in pressure and how do you account for the fact that aeroplanes can fly upside down?


Upside down; nose up, tail down. It's all in the attack angle.

:thumbup:

eta: http://hyperphysics.phy-astr.gsu.edu/hb ... .html#airf
Scarlett and Ironclad wrote:Campermon,...a middle aged, middle class, Guardian reading, dad of four, knackered hippy, woolly jumper wearing wino and science teacher.
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Re: A question

#114  Postby GrahamH » Jan 31, 2016 10:42 am

campermon wrote:

Upside down; nose up, tail down. It's all in the attack angle.

:thumbup:

eta: http://hyperphysics.phy-astr.gsu.edu/hb ... .html#airf


From that page

While the "Bernoulli vs Newton" debate continues, Eastlake's position is that they are really equivalent, just different approaches to the same physical phenonenon.
Why do you think that?
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Re: A question

#115  Postby campermon » Jan 31, 2016 10:53 am

Macdoc wrote:He's ignoring answers already provided ...I'd not waste more electrons on him. :coffee:
You may find this a good read. I did.
http://www.terrycolon.com/1features/fly.html


:thumbup:
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Re: A question

#116  Postby BlackBart » Jan 31, 2016 10:59 am

In otherwords, Gareth has merely exposed a popular misconception rather than any kind of scientific controversy.
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Re: A question

#117  Postby Gareth » Jan 31, 2016 12:38 pm

Thanks Campermon, for the link. Just a couple of points: The Flow lines in the diagram look very different from the real ones in the NASA video. I can't see much in the way of "constricted flow' over the wing in the real one, and, in any case wouldn't constricted flow lines demonstrate compression of air and therefore increased pressure above the wing?

Secondly: "Increasing the angle of attack gives a larger lift from the upward component of pressure on the bottom of the wing." I obviously agree with this and if it is, as he says, a " reaction force to the force exerted downward on the air by the wing," then it must be equal and opposite, so no additional lift is required from the upper surface.

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

It is, as you so rightly point out "all in the angle of attack." I don't really care much what "Eastlake's position" is, though I respect his opinion.

Re: Scarlett and Ironclad's observation, I believe Einstein wore a woolly jumper, as did Feynman. I confess to wearing one myself on occasion. (I wonder what Scarlett and Ironclad's jumpers are made of.) it didn't stop them being pretty damn smart.

Hello. Black Bart. Thank you for that. It enables me to remind readers that the whole reason I'm posting this is to point out the flaw in the methodology used in the 1940's and still in use today in modern fighter aircraft (Thanks to romansh for that link) to measure pressure over and under aerofoils. To remind people, they use tubes connecting holes in the wing to a manometer. If you blow air over the open end of a tube you reduce the pressure in the tube. This is called the Venturi effect and it's how spray guns and perfume atomisers work. This will give a falsely low reading both over and under the wing.

It's my belief that this is the cause of the original misconception and and that pointing it out could bring consensus. (In your dreams, Gareth.)

Black Bart reminds me of students who came in late to my lectures. Bright as a button, but with a bit of catching up to do.

Going for lunch now. Catch you all later.
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Re: A question

#118  Postby BlackBart » Jan 31, 2016 12:48 pm

Gareth wrote:
Black Bart reminds me of students who came in late to my lectures. Bright as a button, but with a bit of catching up to do.


I'm certainly bright as a button, not sure what catching up I have to do though. :coffee:
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Re: A question

#119  Postby GrahamH » Jan 31, 2016 1:23 pm

Who is Gareth and why is he here?

The venturi tube argument looks false because the manometer ports do not project into the airflow. They are covered by the boundary layer.
Low pressure above the wing is demonstrated by condensation over the wing in flight. No venturi tubes there.
Last edited by GrahamH on Jan 31, 2016 2:17 pm, edited 1 time in total.
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Re: A question

#120  Postby Cito di Pense » Jan 31, 2016 1:32 pm

If any of you good lads and lasses are getting bored with circling this drain, perhaps you'd be interested in weighing in on the question of how much of the energy stored by plants is solar energy:

http://www.rationalskepticism.org/evolu ... l#p2365976

It's a subtle point, because all the energy we have available to us (except radiogenic isotopes) we get from the sun. I just think it's glib to say that plants harvest solar energy, by which I assume somebody'd be meaning the photons that fall onto chloroplasts.
Хлопнут без некролога. -- Серге́й Па́влович Королёв

Translation by Elbert Hubbard: Do not take life too seriously. You're not going to get out of it alive.
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