I have been reading up on the threads on fin design, and the functionality of fins and the different variables (cant, rake, chord length, symmetry, toe-in, foil, etc.), and there is a lot of mentioning of “lift”. How fins create “lift”, how asymmetrical foils create more lift, and how cant and toe-in can effect lift. Lots of references to airplane wings. I understand how asymmetrical foils create lift.
I wanted to clarify what type and direction of lift is being discussed. Is it the lift up the face of the wave, in the direction of the flow of the water on the face? Or is it lift perpendicular to the direction of the fin? or both?
It seems to me that the main function of fins is direction control…duh… fins are there to create more friction in the direction perpendicular to the fin direction, and less friction in the direction parallel to the fin direction… So, the board moves in the direction with the least friction, that is the direction that the leading edge of the fin is facing. (Is friction the correct term?..drag maybe?) Is this also considered “lift”?
Please help me define “lift” as it relates to surfboard fin design… thanks.
I also wanted to say that seems that sometimes people want to refer to the effect of the water moving up the wave and pushing on the side of the fins as lift. But is that really lift?
It seems more like pressure. When you push something it moves.
How’s it going ?
Hopefully some others will chime in but just to get the ball rolling, lift can be in any direction, it doesn’t have to upwards (obvious I know but there it is)
.
Quote:
I have been reading up on the threads on fin design, and the functionality of fins and the different variables (cant, rake, chord length, symmetry, toe-in, foil, etc.), and there is a lot of mentioning of "lift". How fins create "lift", how asymmetrical foils create more lift, and how cant and toe-in can effect lift. Lots of references to airplane wings. I understand how asymmetrical foils create lift.
Standard fluid theory lift refers to a force generated perpendicular to the flow. In surfboard fins it is variously used to mean forces towards the rail, forces perpendicular to the flow, and vertical forces. Sometimes quite ambiguously.
Quote:
It seems to me that the main function of fins is direction control…duh… fins are there to create more friction in the direction perpendicular to the fin direction, and less friction in the direction parallel to the fin direction… So, the board moves in the direction with the least friction, that is the direction that the leading edge of the fin is facing. (Is friction the correct term?..drag maybe?) Is this also considered “lift”?
I don’t know how well this grafts onto the various lift definitions, but I think you can go quite far with this simple intuition. It is a LOT more useful than the idea that fins generate force through assymetric foiling.
obproud–this is my two cents
The fin closest the rail helps stabilize the edgeward hull (railward bottom and rail), pulls the rail into the water (that’s fin lift), so that it stays engaged and tracking (hull planing lift,) and rearward fins help keep the rail fin’s angle of attack more stable so it can do that. All that helps you trim and pump and turn and go vertical.
Blakestah’s last point about your point is on point and most of this has to do with the Newtonian theory of lift…but if you really want to get into “lift” start at NASA: http://www.grc.nasa.gov/…airplane/wrong1.html