‘Baidarka’ from the Rodntube Paipo forum (who is building several tunnel fins) sent a link to this site belonging to Phillip Carter, who builds aerobatic aircraft using annular wings. Although the aircraft which Phillip builds are powered, and annular wing surfboard fins are not (being more like glider wings) the principles are the same.
As there was considerable scepticism expressed on this forum regarding my claim that annular wing tunnel fins are capable of excellent maneuverability, I thought that this information might be of interest.
Acually we did get a grant a few years ago but there were so many strings attached to it that I am not sure that it helped much. Grants over here are now mainly for ‘Tangata Whenua’ but who knows?
About changing the angle of attack to meet the water flow, if the board is very flexible it does change the angle of the wing. Actually they are tolerant of angle of attack variations if the base is not too long.
Phillip Carter’s radical aerobatic design reminds me of Richard Pearce, the New Zealander who was the first in the world to accomplish powered flight.
The annular wing in this case, just happens to also incorporate horizontal and vertical control surfaces and it seems from a brief overview, that the duct is more about lift than anything else. Also, the duct is in the centre of the plane with the control surfaces at the tail.
Your boards have a fixed duct at the back end of a relatively very long board. Being fixed, means that you cannot change the angle of attack of the annular wing without also moving the entire board. As a result the ability to achieve high angles of attack is severely limited.
So while the duct alone may share similar principles, the application is drastically different and frankly I think you’d make a good politician.
I thought about politics but I am too honest for the job and I made a vow never to wear a tie any more in 1986.
The point I was making was that an annular wing is capable of extreme maneuverability.
I think that you are ‘splitting hairs’ and that the connection between the aeronautical annular wing and the tunnel fin is quite obvious. Try looking at the similarities rather than the differences. There is usually a small depression just behind the left ear, if you tap it sharply three times it should change your settings
Regards, Roy
PS People compare fish and aircraft with boards and fins all the time on this forum. I’m just doing my thing, there’s no need to worry.
Here is a picture of a very maneuverable board with an annular wing. Sorry if you’ve seen it before.
I’m not being negative for the sake of being negative.
Try this on for size, if a sports car can go 180mph and has rubber tyres, then surely a truck that has rubber tyres must also be able to go 180mph.
My point is that the application is vastly different and you’re trying to infer something about the performance of the tunnel fin based on a plane that happens to have an annular wing. Hence the apples and oranges comment.
By the way, I’m certainly not worried about your posts but this is a discussion forum and the perfect place for people to post their opinions and have others discuss and critique those opinions in the hope that we all might learn more.
Now if you had some moveable control surfaces then as Hicksy said, you might be on to something…
Do you have any video of the “very maneuverable board” in action?
Did you get the point that on my flexible boards the control surfaces are already moveable?
An annular wing is just like any fin in the sense that it can be tuned for more or less maneuverability, depending upon what you want. For a maneuverable tunnel the base should be shortened. If the base is shortened enough the fin is so maneuverable that it seems to have no directional inclinations at all. On the other hand, a long based tunnel will be the opposite and is very directional.
Roy
PS You say that I am trying to infer something about the performance of annular wing fins based on the performance of annular wing aircraft. I am not. I have already tested annular wing surfboards on thousands of waves, so I don’t need to prove how they go or infer anything. I was actually providing ‘food for thought’ for those who have no practical experience in the matter. You may take it or leave it, as you please. I really couldn’t give a toss if no one ever rides another tunnel fin ever, I simply enjoy discussing surfboard fins. I am not trying to convert you either, I am just doing my thing.
This is what I was talking about but after drawing it (badly) I thought it could pivot from a semicircular ring attached to the board. It would tilt up and down say 30 degrees and be levelled by the trailing flap.
Is this not a classic case of comparing coconuts with almonds and then calling them Persimmons? Actually I think that you are more deviant than I am. I am struggling to grasp how the board might ride. Certainly it would still give lateral stability but when I imagine the fin pivoting up and down I keep hearing banging noises and I think that you have a warped sense of humour. Perhaps you are a closet member of the Victorian hinged surfboard brigade? It might work though and if you actually build one you have entered outer space and I will send a case of wax your way by way of a humble offering. I would love to see one built.
Yes I have to agree with you, I am more deviant than I’ve ever let on.
Love throwing different ideas around. Attached a better design than Mk1, non knocking model. This fin will stay level no matter where you are on the board. Could even be attached to the board by 2 straight arms from the board. The ultimate noseriding fin!!
Now I’ve just got to reduce some frontal surface area…hmmmmm
Hicksy - I really like the idea but am having problems visualizing how it interacts with rocker as a rider does fore and aft weight shifts to alter angle of attack. I.E. if rider steps back on tail to turn up the face, will the hoop maintain a straight ahead orientation? Will that work against the rider?
Roy, this is the more informative and provoking tone that works well here on Swaylocks. Nice!
John, Cheyne advocates leaving the Starfin free to move up and down with the motion of the board while surfing (ie. don’t bolt it in sometimes). Sounds crazy (and I’ve never tried it with my starfin) but it’s a very interesting concept.
Thanks Rob . .behind the right ear there is a small depression . . I tapped it twice and that made all the difference.
Actually if the wing is completely free to rotate in the vertical plane then the effect of the horizontal control surface would be zilch and I imagine that the fin would be more like a twin (with the horizontal part out of the equation). Probably what Cheyne is doing is allowing the wing some limited movement.
I noticed recently some windsurfers talking about running their fins behind the board on an extension to avoid interference from the bottom of the board. Apparently some high speed sailing craft are doing this with their (conventional vertical) rudders. If a tunnel could be run on the end of a flexible extension then it would do some of what Hicksy is thinking up without the mechanical bits.
…this is an interesting design, but i think like the “arc type fin”, this fin will slide the board in a powerfull wave when you doing a strong carved bottom turn…
The tunnels can sideslip in some cases, but the faster you go the more they hang in. I have only managed to sideslip my ten inch tunnel when going slowly, and it can be fun. A tunnel with a single in front (hybrid) is incredibly powerful, I think that your legs would snap before you ever managed to slide one out.
Thanks Rob . .behind the right ear there is a small depression . . I tapped it twice and that made all the difference.
I noticed recently some windsurfers talking about running their fins behind the board on an extension to avoid interference from the bottom of the board. Apparently some high speed sailing craft are doing this with their (conventional vertical) rudders. If a tunnel could be run on the end of a flexible extension then it would do some of what Hicksy is thinking up without the mechanical bits.
Roy
Funny Roy.
The windsurfer thing is similar to something I sketched up about 6-8 months back (mentionedit privately to Halcyon) where the fin was on an extension that came out of the top of the board so the fin was out of the influence of the board/turbulence. Probably inspired by “Moth” sailboats and too much time on Swaylocks. I threw out the sketch a month ago.
(The Moths have a horizontal foil the same level as the boat bottom and I think it trys to smooth out the turbulent flow off the hull. But as Spindler says lets try to increase lift/thrust rather than focus on decreasing drag. Or both. ???)
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