![]() I am not saying there is not a place for laminar foils on keels and rudders in certain types of specialized racing sailboats, but it always struck me as a poor choice for most applications. Some of the statements can not possibly be accurate unless they have found a way to suspend the laws of physics. The essay, while interesting, is a rather superficial look at the demands of foils on a sailboat hull, there are a lot of variables not explored in detail. It would take very low wind conditions, and low loads, to take advantage of the drag bucket of the laminar foils narrow drag bucket, even if you could maintain laminar flow (always cleaning and polishing the keel and rudder at each race). If you look at the curves of lift even in the laminar flow plots, at high lift coefficients the 00XX foils are better. Would this be good for a sailboat in varying conditions? the laminar foils are almost ineffective at very high angles of attack, and are are much more prone to stalling at lower angles. But typically the laminar foils when operating in turbulent conditions (high surface roughness), they will have more drag for the same amount of lift, and at very high angle of attack, the laminar foils have much less lift and far more drag. sailboat operate all over the map at different points of sail in terms of required lift coefficent, so it would be difficult to say which is best, type of race and weather conditions would make any choice a gamble. Typically you are designing to a particular lift coefficient, and you pick the best foils for those Rn and Lift conditions. This results is different than often found in aerolab testing, but if you are designing for best L/D, according to this data, there is no reason to use the laminar flow foils at all. Also it shows the best L/D for both laminar and turbulent flow is the 00XX foils in both conditions. Though the 63-series is not as severe, it still show higher drag than the 00XX foil shape. However, there will not be much noticeable difference between 6 and 7 percent, you will notice it if you went to a 12 percent thick one.Ĭlick to expand.that is not exactly what it says, Fig 10 "its entire low drag region is eliminated, and the drag actually exceeds that of more modest foil shapes" (the 00xx foils). One other thing is the thinner section usually has a more abrupt stall, with less warning, than the thicker section. Often much thicker sections are used to keep weight down, the effect just depends on how fast you expect to go, the faster your average speed, the more noticeable the extra drag of the thicker section. So like everything else, it is a trade off. Of course you can always make it strong enough even with a thinner section, but that means more cost, and/or more weight. the only reason to choose the thicker foil section is to make it stiff and strong enough for your chosen materials. You usually choose the thinnest section that you can make strong enough. They will behave very similar but the thinner one will have slightly less drag and yield a very slightly higher Cl max before stall. These are identical foils but one is 7 percent (of chord length) thick, the other is 6 percent thick.
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