I found this, have a look. Not unlike the one I’ve been using, which goes unreal by the way. http://www.basiliscus.com/ProaSections/AppendixD/NACA65012.JPG
interesting cross section – looks pretty beefy and the wide point is pretty far back. Might be fun on a big old gun. What kind of board would it be on, and what’s the fin’s template like?
I used it on all my boards, 6’ to 7’2" all modern parabolic roundtails, in-line configuration. I’ll post pics in a couple of months, no access at the moment.
I just found this searching google. Lots of info available, foil cordinates and all.
Hello Wildy, it just occurred to me, did you post under the name of GW on the old swaylocks forum?
I don’t know anything about the science of aircraft foils, but your link reminded me of the model plane I built. It is an “old time stunt” plane designed decades ago. I used to hang around with some aeromodeller enthusiasts on saturdays and I noted that the new stunt planes didn’t look a whole lot different to the old ones so i asked them what made the new ones perform better? the answer was thicker wing foils. Even this ancient design looks thick compared to surfboard fins, but does water require a different foil from air?
Another question, what do you mean about parabolic shapes?
Here’s one man’s opinion of how the the cross sectional view of the foil in Wildy’s original post fits into the fin picture for surfcraft:
It is the type of foil that IMHO is the fastest of them all. The vertical cord is about 45% back off the leading edge. It is the most neutral as a result and does not offer much sensitivity or direction quickness. It’s strictly a high speed foil. This foil, at the request of and with advice of some surfing legends has be used for tow-in single fin application with excellent success (40 ft.+ conditions).
It’s not the kind of thing of one that serves small wave surfing very well or the type of low speeds (under 20 knots) that we find our selves at in 90% of the surf conditions ridden where lift and sensitivity play a bigger roll in center fin performance. The foil in MrJ’s last post is the type of foil that works much better for most all surf condition from my perspective.
Good Surfin’, Rich
MrJ, yep, ex GW. The parabolic I mention was how I made my tail template, just using parabolic curves. The nose blended into the wide point blending into the tail, progressive curve I guess.
Halcyon, I have to agree with you on speed, I’ve never had problems turning it though, fast or slow. Even in small waves I could get drive. I have to admit I haven’t tried a similar foil with thickness forward, the hand-made mould making process was restricting at the time. Too much stuff to try, too little time.
Greg.
so, when you say center fin (in the subject of this note) and that you’ve used it in an in-line setup – are you using a fin like this with a smaller one in front of it? did you try it with side fins as well, or only as a single/inline?
by the way I made (and crashed) dozens of ‘old fashioned’ stunt planes with symmetrical foils in my youth, so these outlines look great to me…
pics of your inline setup and boards would be great Wildy when you get them
if i remember rightly the stunt fliers wanted their airfoils both thicker and wide pt further back for manourverability. My hybrid shapes outline was done with this section of an ellipse. I used the wires that the CL planes fly on to manually slide a pen around two nails on the focii. I found nylon string too stretchy for this job but the control lines perfect.
I know what you mean about balsa wood disentegrating when it hits the ground Keith. I built mine to revive tradition not for longevity.
That’s what’s so great about Swaylocks, there’s always someone with a different twist on how to do it. I love the method, but how did you choose to use this particular section for your template? Any particular theory, or you just liked the way this part of the curve looked?
PS I made many, many wings before I ever made a surfboard… thick ones, thin ones, polyhedral undercambered ones with tip wash-out… Lots of things to try, given enough time…
Quote:
It's not the kind of thing of one that serves small wave surfing very well or the type of low speeds (under 20 knots) that we find our selves at in 90% of the surf conditions ridden where lift and sensitivity play a bigger roll in center fin performance. The foil in MrJ's last post is the type of foil that works much better for most all surf condition from my perspective.
Halcyon,
How do you feel about mixing foils, in general? For example, having the thick point back on the rear fin, and more forward on the side fins.
Keith, I helped an overly qualified engineer with some interesting and varied composite projects, including large radio controlled gliders, modelling and moulding fuselage, hot-wire and vac wings etc. In return he hooked me up with the most efficient low speed hydrofoil he could lay his hands on, and a lot of practical information on dynamics. Very theoretical initially, but once the fins were made and surfed, I can assure you they worked better than expected.
Aviation has so much money tied up in it, that they tend to be very sophisticated. I’m still curious as to how your inline fin setup looks, particularly with this foil involved…in a way the inline makes even more sense to me with such a thick foil, as a forward fin would set up the water flow in advance of the leading edge…
Keith, correct me if I’m wrong, do you invisage the small fin forward? I guess you could, depending on the way you wanted to ride. In modern shortboards I always had the large fin forward, to bring the centre of turning under my feet, stabiliser at the back.
The configurations are wide and varied. It’s personal choice.
I was picturing it the other way, a canard configuration.
hello Keith, looking at an ellipse and playing with a scale drawing using a primitive drawing tool on my puter I believed that the ellipse could produce the accelerating curves that surfboard templates needed. But without a decent drawing tool or plotter, I had to go the manual route and it was really just trial and error to get it to fit closely the curves of the existing board i was trying to smooth out and tweak. You can see that the section naturally yields a squash tail, so i just templated my existing boards rounded pin tail and stuck that on the end.
Wildy next time i should bolt on the parabolic tail which you have used. I remember you approving my targeted asymetric tweaks but even limiting them to the tail area confused my interpretation of the effects.
not enough time and resources to do just one change at a time
Found these NACA profiles in some old trade school notes. platty.http://www.momentoffame.com/snapshots/MomentOfFame/l79637.jpg
