Quote:
Originally Posted by McGillicuddy
. . . would you suggest more tab area or more breadth of tab? . .
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Hi Gillie,
Lift for a given amount of deflection would be directly proportional to area, so more area would be a plus, regardless of how you get it. The most efficient (highest L/D ratio) airplane wings are high aspect ratio (long with short chord) like a sailplane, and at low Mach numbers air does behave somewhat like water. We used water flow tables at Pratt for that reason to study complex flow patterns in stuff like combustors at Mach numbers of 0.3 and lower. The racing sailboat guys also seem to prefer high aspect ratio keels, so I suspect that they have better L/D ratio. That would indicate that high aspect ratio tabs (wide and short) are probably more efficient, but practical installation considerations are probably more important . . . for instance, if you used a wide tab that straddles the vertical step between panels on a SeaCraft hull, the area near the step is going to see a lot of foam and air, so it won't produce much lift! I'd vote for a narrow and long or square tab that's no wider than the outer panel, which is where it should be mounted.
I agree with Tabman that the large drop fins on the sides of the tabs would definitely improve effectiveness. When water flowing off the transom encounters a deflected tab, it will try to take the path of least resistance, i.e. off to the side and around the tab! The drop fins create a channel to stop that, so should be very effective and they'll also provide additional stiffness to the tabs in the fore and aft direction as well! Denny