A 3d printed 9" Gull Wing surfboard fin
The Eppler 168 foil is a curvaceous and powerful foil.
Super light with a honeycomb core, 9" at present but smaller ones in the works. Check out a gull wing
surfboard fin or any other Bumpy leading edge foil fin here please pick one up and give it a whirl!
They'll fit standard FU single fin boxes.
The humpback whale bumps will reduce flow to the tip and the associated induced drag. We've made the BLEF (Bumpy leading edge foil) more regular in it's sinusoidal curve than the whale has them. These bumps increase the angle of attack capability, while increasing lift and reducing drag. The difference can be felt by the rider as a marked improvement in control with a 'drag free' feeling.
Eppler Foil
Professor Richard Eppler at the University of Stuttgart, Germany, devised a mathematical model of the two-dimensional viscous flow around airfoils. His program was painstakingly written in Fortran77, a machine language now obsolete. This led to a series of beautiful shapes not even visualised by other foil manufactureres. Eppler foils are reputed to be better in higher lift conditions than others.
Foil is E168, structure 3D printed honeycomb cored polycarbonate,
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| Whale wing BLEF by Roy Stuart |
Bumpy Leading Edge Foils (BLEF)
Q: Roy, would you mind explaining to us non engineer types what the bumpy leading edge in the fin achieves?
A:The short answer is that it a) increases the angle of attack which the fin can handle by 40%, so the fin can do tighter turns without stalling b) reduces drag by 32% and c) increases lift by 8%( more drive) compared to a fin of the same planshape with a smooth leading edge.
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| BLEF even at a low speed manages waterflow into a pattern of aligned vorteces |
The bumps induce vortices which inject momentum into the flow. Circular motion has a powerful momentum in liquid (and gas). This means that it keeps swirling once it is set in motion, effectively keeping the flow attached to the surface of the fin and delaying the stall to much higher angles of attack.
The BLEF also manages turbulence by preventing water flowing up the leading edge towards the tip and then making a drag inducing tip vortex as it spills off the tip. This is a well observed phenomenon in regular smooth fins.
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| Like a creature from the deep |
The leading edge is not sharp like a serrated knife as some think. The bumps are softly rounded more like knuckles:
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| E168 has a soft leading edge and a curvaceous, almost hollow trailing edge |
Looks real nice at 9.0"
ReplyDeleteAs production continues several sizes will serve.
A small one at about 4.75" would be good on three fin boards.
Traditional single fin boards would do well with a series between
7 and 8 inches with quarter inch depth differences.
All this down the road as supply and demand dictates
Stay Stoked, Rich.
Hi Rich, w e've been making our Spitfire single fins in half inch increments from 6.5" to 9" and can now go up to 10" so we'll offer the same size range in the Gull Wing once it's been tested. There's a fellow here in NZ who makes Thruster fins to a similar Gull Wing template and swears by them so I imagine that you are correct about thruster fin versions. Thanks for commenting. Roy
ReplyDeleteDude! That's going to be the best fin EVER!
ReplyDelete