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.

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

Mark _australia said...

elmo said...

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

Yeah I reckon too - makes sense

And the high pressure on the leeward side causes lateral lift, eventuallycausing the board to rail up.
Classic overfinned situation

The drag component is obviously important in lifting the tail of the board, but the fin still acts as an airfoil. Consider for example what happens when you spin out, if it was just the resistance that was keeping the board straight why does the board continue to spin out when the fin presents even more surface area to the oncoming stream of water?

There is a reason why I sell gaskets

racerX said...

Mark _australia said...

elmo said...

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

Yeah I reckon too - makes sense

And the high pressure on the leeward side causes lateral lift, eventuallycausing the board to rail up.
Classic overfinned situation

The drag component is obviously important in lifting the tail of the board, but the fin still acts as an airfoil. Consider for example what happens when you spin out, if it was just the resistance that was keeping the board straight why does the board continue to spin out when the fin presents even more surface area to the oncoming stream of water?

Because the fin is an aerofoil operating in a fluid. Once the aerofoil is in a stalled condition, which it is when it's sliding out, it loses almost all lift until such time as a smooth fluid flow is re-established over it's surface.
To do this you have to return the angle of attack to zero, (kick the nose downwind) whereby the flow stream resumes a smooth flow condition, and then you can load it up again.
If you can't re-establish a smooth flow across it then the lift it generates is limited to the small amount it can generate operating in a parachute mode. i.e. turbulent flow.
This is why a bit of weed, jellyfish, or even an air bubble can make the board slide out.
Anything which disrupts a smooth fluid flow will result in the whole aerofoil (fin) stalling and losing almost all lift.
Stalling does not always mean a low fluid speed, although it is more commonly associated with it due to it corresponding with the higher angle of attack needed to generate the required lift at the lower speed.
It can happen at any speed. Even at top speed. The stalled condition simply means the fluid flow is no longer smooth.

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.

fullmoon said...

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.

You have a great point fullmoon. I always thought the flow was even (laminar?) across the whole wing! My ignorance would have been frightening for me if I saw these tufts on a 747!

STOPIT Glitch STOPIT NOW!!!!!!!

Glitch said...

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!

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

eprints.bournemouth.ac.uk/12235/1/Simon_Fagg.pdf

fjdoug said...

I reckon a wing works like a skimboard, expose it to flow at an angle and it gets pushed up.

Exactly correct!! Any pilot knows it's all about angle of attack.

When do you get time to draw things Snags! Your always on the net!
And No, I'm not stalking you.

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.

r2908 said...

KazeRonin said...

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.

this is correct with the wing. its high school stuff really... but why its the leading edge blunt, i understand the fin being blunt for lift, but the wing?? i feel there's alot more to it, is anyone out there an aeronautical engineer ? and can answer this?.. probably not,

Both of you are under a very common misconception about how wings work.

If this misconception were true, then aeroplanes would not be able to fly upside down, which they can do.

Don't worry, you're not alone! There are more people in the world who believe the lie than who know the truth.

Read TrevNewman's post above.