So you’d presume the MVGs on a tuna are there to aid water flow heading into the tail… and not to promote reattachment of flow coming off the rapidly tapering body height in the rear half of the fish? http://www.flmnh.ufl.edu/fish/Gallery/Descript/BluefinTuna/BluefinTuna.html This is kinda important - the vast majority of MVGs are rearward of the leading edge of the foil. They act on flow re-attachment in the draft or rear of the section, where water needs to re-attach. In airplanes, they disrupt flow at the leading edge, so that it is more disturbed coming off the rear of the foil, and separated flow is minimized at steeper angles of attack. http://www.microaero.com/pages/v_howvgswrk.html I kinda think the tuna MVG fins are there to promote re-attachment for water coming off the body, and have little to do with the actions of the rear tail.
Blackstah, I have to agree about with you about the notion that the MVG on the tapering part of the tuna’s body are there to reattach that trailing edge to the water. What seems to be going on to me is a very sensitive steering device along with the MVG affect for the tail – a double function if you will. I thing there is a tremendous amount of multi tasking going on with the fin cominations that cannot be approached effectively on a surfboard. Herb’s supercharger placement seems an attempt at both vortex generation and sloting, which makes perfect sense to me. Mahalo, Rich
For an MVG to work effectively doesn’t it need to disrupt flow on both sides of the foil? All the flight, and the tuna, analogues do this. I look at the superchargers or twinzers and see the smaller fin directing somewhat disrupted flow into the lee side of the fin. As a micro-vortex generator it is not very micro. But improving lift:drag ratios at steep angles of attack is clearly the benefit. It could be that the central fin acts as a canard on tri-fins, making the supercharger benefit less desireable there. It will stall before the outside fin will, and it’s stall will serve to prevent further increases in angle of attack. (I understand a canard is normally in front of a wing, I was just making the analogy that the canard stalls before the main wing, and in doing so rotates the body so the main wing will not stall. And the central rear fin on a TRI has a similar effect).
Mark are you still around with those fins ?
We really would like to get that fired up again.
Thanks Coastal Surf Supplies
1-888-569-7038
Please call us asap
A few years ago i had a 9’2 longboard from Bullock Surfboards in Oceanside. baseball bat shaped similar to a Takayama In the Pink. Key note the tail was a round pin. Anyways the board had 2+1 set up and rode it with a Skip Frye 8.5” fin and two single tab mini fin from a twinzer set up. It rode like magic! Could hold a line really well but also turned like a charm and minimal speed loss too