pugwash
New member
http://www.telegraph.co.uk/science/science-news/9035708/Cambridge-scientist-debunks-flying-myth.html
So how might this affect our understanding of sail trim?
So how might this affect our understanding of sail trim?
Theory of flight debunked
- Thread starter pugwash
- Start date
armchairsailor
Active member
So boats are like bumblebees then?
marklucas
Active member
Journalistic hype
This is not debunking the theory, merely the explanation.
When a journalist with some understanding of science / engineering writes something I will happily eat my hat.
Only last year I changed newspaper after reading; "... the kilogram is the SI unit of weight." AAAAAaaaaaarrrrggggghhhh!
This is not debunking the theory, merely the explanation.
When a journalist with some understanding of science / engineering writes something I will happily eat my hat.
Only last year I changed newspaper after reading; "... the kilogram is the SI unit of weight." AAAAAaaaaaarrrrggggghhhh!
Skysail
Well-known member
I don't think this is new:
see Wikipedia on 'Lift':
"Popular" explanation based on equal transit-time:
"However, equal transit time is not accurate and the fact that this is not generally the case can be readily observed. Although it is true that the air moving over the top of a wing generating lift does move faster, there is no requirement for equal transit time. In fact the air moving over the top of an airfoil generating lift is always moving much faster than the equal transit theory would imply.
The assertion that the air must arrive simultaneously at the trailing edge is sometimes referred to as the "Equal Transit-Time Fallacy".
I used to know more about this subject, and the Kutta Joukowski transformation was taught then.
see Wikipedia on 'Lift':
"Popular" explanation based on equal transit-time:
"However, equal transit time is not accurate and the fact that this is not generally the case can be readily observed. Although it is true that the air moving over the top of a wing generating lift does move faster, there is no requirement for equal transit time. In fact the air moving over the top of an airfoil generating lift is always moving much faster than the equal transit theory would imply.
The assertion that the air must arrive simultaneously at the trailing edge is sometimes referred to as the "Equal Transit-Time Fallacy".
I used to know more about this subject, and the Kutta Joukowski transformation was taught then.
panthablue
New member
The example shown in the video is wrong. A wing shape has a flat bottom surface, and a curved upper surface. It also faces straight into the airflow, not at an angle shown in the video.
Cruiser2B
Active member
What an utter load of rubbish. He fails to account for boundary layer, areas of stagnation, vortices, etc. I think if they showed the area far enough downstream from the airfoil, they'd find the smoke trails would eventually realign.
boomerangben
Well-known member
You're winding us up surely? Or am I misunderstanding you? If what you said was true I'd never be able to land a helicopter and stay there, and aeroplanes would never have to bother pointing at the sky, spilling the drinks. And birds don't have a flat underside of their wings, and sails are also curved on both sides.
Flying Penguin
New member
I suggest you a) look at a few airfoils here: http://en.wikipedia.org/wiki/Airfoil b) look here: http://en.wikipedia.org/wiki/Angle_of_attack
Elemental
Well-known member
Eh? Utter rubbish. http://en.wikipedia.org/wiki/Airfoil
Edit: Oops - too slow replying. Note to self: Refresh page before replying...
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savageseadog
Well-known member
Prof Babinsky proved his theory by filming smoke passing across a wing, with a mirror.
See! It's a smoke and mirrors theory
See! It's a smoke and mirrors theory
jwilson
Well-known member
This is a "scientist" overly keen to get his name in the papers. What is described has been well known as a fallacy for at least 50 years - since they stopped building most aircraft with two or three sets of wings held together with struts and wires.
It also applies to sails. Frank Bethwaite's book 'High Performance Sailing' is probably the best technical description of the actual theory.
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SamSalter
New member
This guy is an aerodynamasist and a sailor.
He wrote this stuff in the '60's and 70's:
http://www.arvelgentry.com/index.html
I did aerodynamics at Manchester in the late 60's and was taught circulation theory and all the other stuff he talks about. It's not new; most people (except people who write sailing books know this!)
This stuff by Arvil Gentry is understandable and gives a good explanation of what is happening to your sails.
sam
He wrote this stuff in the '60's and 70's:
http://www.arvelgentry.com/index.html
I did aerodynamics at Manchester in the late 60's and was taught circulation theory and all the other stuff he talks about. It's not new; most people (except people who write sailing books know this!)
This stuff by Arvil Gentry is understandable and gives a good explanation of what is happening to your sails.
sam
Bosun Higgs
N/A
I doubt it was even an explanation - its obvious even to an arts graduate that there is nothing connecting a molecule that goes above a wing with one that goes below to ensure they both get to the edge at the same time.
Dont understand why that would irritate any more than the use of stupid names like pascal and newton when we had perfectly useable metric units before they all got together in some international meeting and dished out the honours country by country. Have you had a unit of something named after you yet? Indeed the very idea of an SI unit is anathema.
boomerangben
Well-known member
I think you've missed the point - its rather the kg is described as the SI unit of WEIGHT when of course it is the SI unit of MASS
RobbieW
Well-known member
There is a mass of evidence to suggest that this is, indeed, a weighty problem
Edit - too slow!
Edit - too slow!
T
timbartlett
Guest
I've got a book Called Basic Naval Architecture that was first published in 1949, which refers describes the operation of propeller blades based on a theory "first proposed by F W Lanchester in 1907 in his book Aerodynamics"
Do all the ills of the world have to be blamed on dastardly journalists?
Some of us do know the difference between mass and weight. Just as we know the difference between mW and MW, m and M, kb and kB and why you shouldn't write "knots per hour". We know that a kWh means something that a kW/h doesn't, that there's a difference between geostationary and geosynchronous, and that resistance and impedance are different.
As Technical Editor of a magazine, I used to wage an ongoing war against the errant capital, the random slash, and the misleading "simplification". Sometimes I won, sometimes I didn't. There are simply too many hands itching to "correct" things they don't always know much about.
And maybe not quite enough eyes that are able to spot when I've hit <shift>M instead of <alt>M, and produced M instead of µ.
Oh dear.
Do all the ills of the world have to be blamed on dastardly journalists?
Some of us do know the difference between mass and weight. Just as we know the difference between mW and MW, m and M, kb and kB and why you shouldn't write "knots per hour". We know that a kWh means something that a kW/h doesn't, that there's a difference between geostationary and geosynchronous, and that resistance and impedance are different.
As Technical Editor of a magazine, I used to wage an ongoing war against the errant capital, the random slash, and the misleading "simplification". Sometimes I won, sometimes I didn't. There are simply too many hands itching to "correct" things they don't always know much about.
And maybe not quite enough eyes that are able to spot when I've hit <shift>M instead of <alt>M, and produced M instead of µ.
chewi
Active member
This guy is an aerodynamasist and a sailor.
He wrote this stuff in the '60's and 70's:
http://www.arvelgentry.com/index.html
I did aerodynamics at Manchester in the late 60's and was taught circulation theory and all the other stuff he talks about. It's not new; most people (except people who write sailing books know this!)
This stuff by Arvil Gentry is understandable and gives a good explanation of what is happening to your sails.
sam
+1 for Mr Gentry.
I looked up Babinsky, his "revelations" are in print dated 2003, so even this is old news in 2012! Itsonly the Youtube video thats recent.
maxcampbell
New member
Irrelevant
What's this got to do with sailing?
Uffa Fox said, in 1960, that rather than work as an aerofoil:
"... sails are deflectors: [they] turn the wind backward towards the stern and [the] reaction pushes the vessel forward."
He also says, in the same book, that in heavy weather it's best to take seas beam-on.
Do people still believe in Uffa?
What's this got to do with sailing?
Uffa Fox said, in 1960, that rather than work as an aerofoil:
"... sails are deflectors: [they] turn the wind backward towards the stern and [the] reaction pushes the vessel forward."
He also says, in the same book, that in heavy weather it's best to take seas beam-on.
Do people still believe in Uffa?
trapezeartist
New member
Well I had not seen this "new" explanation before. The classical explanation of air speeding up because it has further to travel always sat very uneasily with me, so I'm glad to see a better explanation. As an explanatory video, it would have been better if the wing had not been half-stalled. In talking about "wings", it might also have been better to have shown an asymmetrical wing as is conventional on an aircraft, although most of us here do have two wings as shown dangling out of the bottom of our boats.
