Black graphite Power Surfboard spitfire fins have been called 'Patu' fins because they resemble the Maori war club of that name. This one is laminated paulownia glassed with thick blue Swanndri wool and epoxy resin. The Swanndri wool is equivalent in thickness to about 4 or 5 layers of 6 ounce fibreglass cloth.Here's the wee beastie all polished up with beeswax polish and ready to enter the water:
The 4mm diameter fillet at the base of the fin can be seen here. The most hydrodynamically efficient fillet for a surfboard fin is between 2mm and 5mm in diameter, this can only be acheived if the fin is set into the board rather than glassed on.
The small cutaway at the fin base improves the holding tenacity of the spitfire fin.
Theplanform of the spitfire fins is the most efficient flat plane fin shape in existence
The 'Spitfire' fin is based on the wing of the Spitfire WW2 fighter plane. We were the first to apply these fins to surfboards in 1995, and advertised them as Spitfire fins. Now there is another company ( Revolution surf) doing Spitfire fins, but we were the first by 11 years.The story with the Spitfire fin is that it has the lowest induced drag of any fin or wing planform, essentially this means that it has less tip vorteces and a better lift/drag ratio than other shapes. It is the fastest most efficient flat plane non twisting wing planform possible.It is interesting to note the turning characteristics of the spitfire compared with its rival the Messerschmitt 109. The ME109 with its narrower linearly tapered wing had a tighter turning radius than the spitfire, but the spitfire had a higher turn rate. In other words the spitfire could maintain such a high speed during the turn that it would complete a 360 degree turn before the ME 109 even though it travelled through a larger turning radius. The closest surfboard fin to the ME109 fin is probably the wavegrinder.Another characteristic of this fin other than low drag and its ability to maintain high speed through turns is its benign stall characteristics . When the Spitfire fin starts to stall it does so first near the base of the fin, this makes the onset of the stall predictable and the stall easier to avoid. In comparison the linearly tapering wing like the ME109 or the wavegrinder will give less warning of the impending stall and will basically spin out suddenly and without warning. The spitfire fin does have a higher stall speed though.The characteristics of elliptical planform fins were predicted by the classical lifting-line theory developedby Ludwig Prandtl and published in 1918."The first closed-form solution to be obtained from lifting-line theory showed that in-duced drag could be minimized by using anuntwisted wing of elliptic planform.The classical lifting-line theory developedby Ludwig Prandtl and published in 1918 wasthe first analytical method to satisfactorily pre-dict the performance of a lifting wing. Moreover,until the development of the digital computerin the early 1960s, it was the only analyticaltool available for wing design. Early compar-isons between results predicted from lifting-linetheory and experimental data showed remark-able agreement. Even with modern computa-tional fluid dynamics (CFD) , it is difficult to im-prove on the induced drag predictions derivedfrom lifting-line theory."
http://209.85.173.104/search?q=cache:feNokN7nsukJ:www.aiaa.org/aerospace/images/articleimages/pdf/phillipsjanuary05.pdf+spitfire+wing+drag+theory&hl=en&ct=clnk&cd=1&gl=nzBottom line is that they are a very fast fin, with a high speed turning capability and a high turn rate.Goretex vent:
The 4mm diameter fillet at the base of the fin can be seen here. The most hydrodynamically efficient fillet for a surfboard fin is between 2mm and 5mm in diameter, this can only be acheived if the fin is set into the board rather than glassed on.
The small cutaway at the fin base improves the holding tenacity of the spitfire fin.
Theplanform of the spitfire fins is the most efficient flat plane fin shape in existence
The 'Spitfire' fin is based on the wing of the Spitfire WW2 fighter plane. We were the first to apply these fins to surfboards in 1995, and advertised them as Spitfire fins. Now there is another company ( Revolution surf) doing Spitfire fins, but we were the first by 11 years.The story with the Spitfire fin is that it has the lowest induced drag of any fin or wing planform, essentially this means that it has less tip vorteces and a better lift/drag ratio than other shapes. It is the fastest most efficient flat plane non twisting wing planform possible.It is interesting to note the turning characteristics of the spitfire compared with its rival the Messerschmitt 109. The ME109 with its narrower linearly tapered wing had a tighter turning radius than the spitfire, but the spitfire had a higher turn rate. In other words the spitfire could maintain such a high speed during the turn that it would complete a 360 degree turn before the ME 109 even though it travelled through a larger turning radius. The closest surfboard fin to the ME109 fin is probably the wavegrinder.Another characteristic of this fin other than low drag and its ability to maintain high speed through turns is its benign stall characteristics . When the Spitfire fin starts to stall it does so first near the base of the fin, this makes the onset of the stall predictable and the stall easier to avoid. In comparison the linearly tapering wing like the ME109 or the wavegrinder will give less warning of the impending stall and will basically spin out suddenly and without warning. The spitfire fin does have a higher stall speed though.The characteristics of elliptical planform fins were predicted by the classical lifting-line theory developedby Ludwig Prandtl and published in 1918."The first closed-form solution to be obtained from lifting-line theory showed that in-duced drag could be minimized by using anuntwisted wing of elliptic planform.The classical lifting-line theory developedby Ludwig Prandtl and published in 1918 wasthe first analytical method to satisfactorily pre-dict the performance of a lifting wing. Moreover,until the development of the digital computerin the early 1960s, it was the only analyticaltool available for wing design. Early compar-isons between results predicted from lifting-linetheory and experimental data showed remark-able agreement. Even with modern computa-tional fluid dynamics (CFD) , it is difficult to im-prove on the induced drag predictions derivedfrom lifting-line theory."http://209.85.173.104/search?q=cache:feNokN7nsukJ:www.aiaa.org/aerospace/images/articleimages/pdf/phillipsjanuary05.pdf+spitfire+wing+drag+theory&hl=en&ct=clnk&cd=1&gl=nzBottom line is that they are a very fast fin, with a high speed turning capability and a high turn rate.Goretex vent:
