In' my opinion More than 5 degrees in order to swing up into a sharper shunt in light wind. Maneuverability around the dock maybe and when motoring.
On the wobble bar or extra linkage or use of hydraulic to manipulate steering boards. I would say yes especially on the larger craft force go up the bigger you go. I have those square notches attached to my beams that the tiller fits into if I want to let go for duration. In smooth water letting go no problem open ocean with chop it takes a nice size piece of chop to whack the board out of balance it wil slam over and knock you side ways off your seat:) The hydraulic dampener or limiting linkage would insure positive control all the time.
Todd
--- In harryproa@yahoogroups.com.au, Dennis Cox <dec720@...> wrote:
>
> Todd, Rick, or anyone else...
>
> At any normal sailing speeds, I can see you probably don't need much more than
> about 5 degrees of rudder since you can always use the front one to. Would
> there be any situations where more (lots more) might be needed? IOW, does the
> 270 degrees in Rob's design come into play for any other situation besides
> shunting and reversing the rudders?
>
> Thanks,
> Dennis
>
>
> ________________________________
> From: tsstproa <bitme1234@...>
> To: harryproa@yahoogroups.com.au
> Sent: Wed, August 4, 2010 12:21:49 PM
> Subject: [harryproa] Re: Asymmetric Bi-directional Rudders
>
>
> 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
> >
>
