the myth being, "that the flow the particles on both sides of the foil, that arrive together at the leading edge leave together at the trailing edge http://www.newscientist.com/blogs/nstv/2012/01/physics-in-a-minute-how-wings-really-create-lift.html
Not unless you're going dead downwind.
A symmetrical foil with no angle of attack will produce no lift. If you want to resist the sideways force of the sail, fin lift is needed, so is an angle of attack. Same goes for the sail.
That's old news... I think it been clearly understood since the early part of the last century. Its just that many text books erroneously over simply what actually happens.
Also the airflow does not actually split at the leading edge either. Some of the airllow that would have flowed under the airfoil actually flows over the top of the foil. You can see that in the video in the area between the leading edge and the leading stagnation point. So not only is there a downwash from the trailing edge but there is an upwash as the air approaches the foil.
Apparently for tappered airfoils like sails this upwash increases as you reach the tip of the foil, this is one of the reasons why you need some sail twist to maintain an optimum angle of attack.
This is the best explanation that I found for all this stuff.
www.av8n.com/how/htm/airfoils.html
Methunks there is some Confucius with the term "lift" when applied to a wing and a windsurfing fin.
With my back yard physics (I use a hammer I'll hurt myself) A fin generates lift because the faster it travels through water the more solid the water appears, the fin moves in the direction of least resistance which is upwards
I think some people don't understand what foil lift refers to.
Foil lift is in a direction at 90deg to the foil, not necessarily upwards.
There is only one thing we can do, write a letter to Mythbusters and lets get this sorted because it has always confused me, I will get onto it tonight.
Any time that a foil is generating lift (with a low pressure on the top and a high pressure underneath) there is a reverse flow at the trailing edge as the high pressure tries to equalize with the low. The closer to a stall the more pronounced the reverse flow is. Because of this there is no way the two flows could reach each other uniformly.
Many years ago we did an experiment to settle an argument on what actually happens to the airflow when it stalls. The 1st picture shows the wing as it starts to increase the angle of attack. With the tufts on the tailing edge flowing opposite way and the 2nd in the stalled condition. For anyone interested the 3rd photo is the tail when the aircraft is stalled (that is why the stick shakes). I don't have any good pics when in level flight but there was always a reverse in the airflow.
Thank god they dont have tufts on comercial aircraft. I found those pics extremely disturbing.
Or mabey they could just glue them down?[}:)]
Skydiving never really appealed to me until now.
Brilliant images Glitch they have really helped me understand more about what is happeing with flkow. . Why is the uneven flow more pronounced towards the fuselage?
Wings are deliberately built with a twist on most aircraft so that the wing will stall close to the fuselage 1st while the outer section will still have some lift. This reduces the chance of one wing stalling before the other. When that happens life can get exciting!
STOPIT Glitch STOPIT NOW!!!!!!!
The folks on the mythbuster forum have enlightened me about something called 'Equal Transit Fallacy' so the myth has indeed been debunked
www.grc.nasa.gov/WWW/K-12/airplane/wrong1.html
www.grc.nasa.gov/WWW/k-12/airplane/wrong2.html
www.grc.nasa.gov/WWW/k-12/airplane/wrong3.html
I am never getting on airplane ever again if no one knows how the f@$k they work, although these dudes seem to have an idea:
www.grc.nasa.gov/WWW/k-12/airplane/bernnew.html
Don't confuse wings in air which are at 20 degree plus stall angles and fins that operate at 1-3 degrees in water.
If you look at the classic airfoil shape of the wing of an aircraft in cross section - they arent symmetrical - the bottom surface is flatter, and the top surface more rounded - meaning that a higher pressure is created under the wing, during flight, than over it - thus creating "lift". However if you look at a fin of a windsurfer - it is a symmetrical foil - in cross section - both sides are the same. Movement of a foil/airfoil through water is no different than air - the only thing that changes is density.
What puzzles me is that - as our windsurfer fins are symmetrical, they will both create an equal pressure on both sides as speed increases through water - so the definition of "lift" that we use re. our windsurfer fins is I believe a misnomer.
If you put two symmetrical airfoils of appropriate size on an aircraft, as wings - it wouldnt fly, as the pressure on both side of the airfoil would be the same - no lift!
My thought are, that the equal pressure generated over the symmetrical foil (windsurf fin), might translate into an upward force that helps unstick the board from the drag that we have at pre planing speeds - my two bobs worth.