lift myth debunked

Nebbian - there is no misconception whatsoever. Lift is generated by the difference in pressure - created by the shape of an airfoil. You state we have a misconception without stating what that may be. Whether the plane be upside down or otherwise - the movement of the wing through the air still generates "lift" . That lift - that lift counters the weight of the aircraft versus the force of gravity. Without lift it falls like a brick. When the aircraft goes inverted other things need to be slightly adjusted like aircraft attitude to maintain balanced flight but the lift doesnt change. So if anyone has a misconception then perhaps you do on inverted flight.
Also, I wasnt making any comment on Decrepits initial post re. the speed of air particles over either side of the airfoil - but rather airfoil versus windsurf board fin(hydrofoil).

P.S.Did some checking re. symmetrical airfoils - they will fly, but that is dependant of angle of attack - if the symmetric airfoil has a zero angle of attack - no lift - so they are dependant on a degree of positive angle of attack to create lift.
So the question for me is - a symmetric windsurf fin creating any lift component (because if it is, it will be sideways) - or is it merely acting in its role converting energy from the sail into forward movement, as a keel does??
Sorry Decrepit - didnt mean to change the topic of your thread!!

Thanks Nebbian I remember not long ago i jumped in and said the same things about the lift and faster airflow bernouli's theory and whatnot. You jumped in and corrected me and now i understand it all and it all makes sense.

I belive you directed me to this link > amasci.com/wing/airfoil.html#parts

very helpful indeed.

Glitch, Re the wing twist comment, if both wings are twisted the same then there is nothing stopping one from stalling before the other because they are symmetrical.
Many other factors determine which wing drops first ( if any ) in a stall, and if your quick on the rudder then life doesnt get very interesting.

Symmetrical wings are used on aerobatic aircraft. They get lift by always having a positive angle of attack to get lift. The same goes for the vertical tail on an aircraft to keep it going in a straight line. Whenever the aircraft yaws (goes sideways) one side will get more lift to naturally get it back on track. The same goes for a sailboard fin.
The reason the leading edge is blunt is that it will allow the air to separate more smoothly (have a look at Trev Newmans pic). Sharp leading edges work on high-speed aircraft where the air would compress on a more blunt leading edge. On a low speed airfoil a sharp leading edge will stall quicker & not get as much lift.
Now the even more boring bit about lift. There are 2 types of pressure, dynamic & static. Dynamic pressure is the pressure you can feel such as the wind. Static is the pressure that surrounds an object, like the atmosphere.
An airfoil will get some lift from dynamic pressure with a positive angle of attack. This is Newton's every action there is an opposite reaction theory. This is also the reason a sailboard will plane over the water as it has a positive angle of attack to the water.
As an object moves through a fluid, it will get a negative static pressure; the faster it travels the lower the pressure. You can feel this when you drive with the window open. The wind will blow in at the back of the window to equalize the air being sucked out at the front of the window. As air flows over the curved part of the wing it speeds up and reduces the static pressure to give lift.

Yes maverick there is nothing to stop a wing dropping first with the twist (wash out)being built into a wing, but the stall will be a lot more sedate, and in a lot of aircraft will just mush along in a straight line, although getting closer to the earth, until it gets forward stick pressure.

Correct me if I'm wrong but the further out you stand (i.e. wider the board) the bigger the fin you need to provide the resistance or "lift" to stop the board sliding out from underneath you. (that's technically why the board width and not the sail size determines optimal fin length size although you can successfully use a smaller fin with a smaller sail due to the fact you're in stronger winds providing an equal amount of lift).

Standing right over the fin like a freestyle or wave board and the area (size) of fin can be significantly reduced. Hence a fin will slip when going through a lull because there is no forward drive from the sail and the fin has limited or no lift to counteract the lateral loading your legs are providing through the back of the board.

PS - I'm in Neb's corner.

Thanks for diagrams, I have got it. You are right. Already whole board, sail and fin works as big rudder combination

Still could be room for improvement because at this moment you need to turn whole board to change this angle of attack with not only fin but also board shape having effect.
small tuning at only fin angle still could be beneficial ...at overall performance...
BTW the world "lift" is a bit confusing in such context and more appropriate should be " lateral resistance" as vehicle is in "lifted" of the wind course line but still dropping down of course..
maybe only lifted relativelyto the wind direction.
by analogy we could not say about parachute that is " lifting" a person, just a slowing down drop descent
to be even more confusing I wish to call windsurfer (any sailboat ) trail "negative descent"

muscles?....

Ah ha

Finally we are starting to get somewhere with the terminology so I can start getting my head around it.

Lateral resistance to counteract the rig forces(the sailors part of the rig).

Lift is the force working along the axis of the fin lifting the board out of the water.

True lift of the fin still comes down to water resistance overcoming the mass holding the board down.

We don't sail sideways so therefore flow from front to back of fin is uniform because the foil is symmetrical (excluding the load a heavy footed gumby like myself exerts when cavitate the fin).

So coming back to the lift. 100L board, 7.0m sail, compare the lift between a 32cm fin and a 40cm fin without changing anything. The 40cm is always going to want to lift the board out of the water and the 32 at the same speed will rarely have the board out of the water.

Both these fins have similar thickness's, the chord length on the 40 may be slightly longer but that only increases lateral resistance.

What the difference is, is the surface area of the fin which you can see when looking from the front of the fin which is trying to push it's way through the water.

Water at low speeds offers very little resistance to an object moving through it but as the speed increases so does the water resistance.

So the faster we go the greater the water resistance we have in front of the fin till it overcomes the balancing act which we have with a windsurfer and lifts the board right out of the water and starts the board precariously balancing on the fin making us uncomfortable.

To overcome this excess lift, we...
1) Shift the mast foot forward
2) Drop the boom,
3) Carry more weight
4) Put on a smaller fin

1 through 3 are changing the balance of the board to counteract the lift from the fin. Nº 4 is reducing the lift by reducing the area affected by water resistance.

Now start thinking about the angle of attack of the leading edge and the effect on lift and speed

Barn must be on the toilet.