Thats exactly what was showed on the flow table when increasing and decreasing AOA. On nasa foil sim with a pointier leading edge it should me you narrow the window from connected flow to separation. That foil you posted looks pretty close to What I came up with in profile anyways. I know its vague my midsection is flatter top and bottom and my leading edge is a little fuller with more tuck on bottom leading edge of foil. Foil has a 10'' chord is 3/4 '' thick 32''long, the part of foil in the water has a 2/1 or less aspect ratio. I didn't map out cordinates for foil just used simulator to see what shape of leading edge would work best for my application at the time. Low stall characteristics minimum drag best flow at 15mph. Wonder how far the profiled shape could be pushed thicker, thinner, higher aspect ratio, winglets , sand paper, etc...
Todd
--- In harryproa@yahoogroups.com.au, "willoughby_rick" <rickwill@...> wrote:
>
> I have taken a look at what should be the best section for an asymmetric bidirectional rudder.
>
> It threw up a few surprises. The best I could come up is a double ended version of a NACA 07 series:
> http://www.rickwill.bigpondhosting.com/Double_End_NACA07.png
>
> At an Re# of 10E6 and aspect ratio of 4 it has an L/D of 27. It has flow separation on the trailing edge at all angle of operation that reduces at higher Re#. But it is no more than 3% of the chord in the normal operating range. The lowest Cd is 0.004.
>
> By comparison a NACA0012 section at same Re# and AR has a best L/D of 17.7. The in-line Cd is actually higher than the asymmetric section at 0.009. One advantage is that it does not have flow separation until about 7 degrees AoA. It would be designed to work at about 4 degrees for nest L/D.
>
> What surprised me is that the large diameter nose actually has better lift, less flow separation and lower minimum Cd than the pointy nose/tail version. The reason becomes apparent when you look at the pressure profile for the respective sections. Notably the 07 series was designed for a flat pressure profile. The NACA 16 series was a development that factored in air compression for higher speed subsonic flight. However not a factor for water although cavitation could need consideration.
>
> This idea has a lot of upside with the one downside of flow separation and possible resulting vibration. There could be some benefit roughing up the nose/tail to help the flow stay attached - could be tested with a strip of sandpaper glued in place down the edges.
>
> Rick
>
