[MHml] Cat Rudders Toed In?

[Tom Speer]

Glenn Brown wrote:

> ...
>
>For laminar foils, toe-in can also reduce total rudder drag if parallel 
>rudders both run outside the low-drag "bucket" (at an AoA of more than 
>about 3 degrees), and if toe in allows the windward rudder to enter the 
>low-drag bucket.  In this case, toe-in can cause the drag on the 
>less-loaded windward foil to drop more than the drag on the more-loaded 
>leeward foil increases.  However, loading the rudders to such a high 
>angle of attack only pays if you have relatively inefficient forward 
>foils, such as most low aspect ratio centerboards and keels.
>  
>
The NACA 0012 sections he reported aren't laminar flow sections.  
However, it doesn't really take much to be out of the drag bucket of a 
NACA 6-series laminar flow section.  It's actually pretty narrow for a 
symmetrical section because it's centered on zero lift.  With a normal 
amount of leeway, the rudder's most likely operating outside the bucket 
going upwind, and may well be downwind as well, since we sail hot 
courses offwind.

Lift on the windward rudder may also be increasing induced drag, since 
the windward rudder is less deeply immersed than the leeward rudder.  So 
I'm with you - there are a number of possible reasons why a little 
toe-in may be good and it would take a lot of carefull sailing - ie race 
experience - to see the difference.

Cheers,

Tom Speer