Cruisingfoiler, -"Aircraft are symmetric in plan view. Lift is balanced around the fuselage. Sailrocket has symmetry in force balance, the single element wing and Bruce foil balance in opposition. So low drag makes sense in these cases. Tacking and shunting sail boats are not symmetric in this opposing or balanced forces sense. "
Drag has nothing to do with symmetry.
Cruisingfoiler, "Lift is counterbalanced by mass to windward on multis and monos alike (and more recently with DSS foils to leeward). Mass righting moment is a constant allowing for mass shifting to windward (or with increased drag penalty with water ballast). Mass has a hydro drag penalty on narrow platforms (i.e. keels) and a parasitic aero drag penalty on wider platforms. Absolute righting moment cannot be scaled with healing moment. So sailing craft carry lots of excess drag baggage already and must depower once lift exceeds righting moment."
You are confusing heeling moment with lift. These are vector forces where direction is important.
Cruisingfoiler, "Blakeley 2 element shows a Cl of 3.5 with a Cd 0.3. The thick single element, Cl of 0.9 Cd of 0.08. Similar ratios."
Let's say that you have an ice boat with a wing sail with a coefficient of lift of 1, Cd of .02 and a lift vector of 80˚ facing directly into the wind, that translates into cos(80) or .17 - .02 = .15 driving force to move the boat forward into the wind.
Your Blakeley foil will have a lift vector around 110˚, sin(20) negative .34 x 3.5 = 1.19 + .3 drag = 1.5 backwards and 2.3 for the heeling moment, can anyone say oops?
Yes, yes if the wind is from behind at around 110 degrees, a wing sail with a flap will accelerate like a rocket from hell and that acceleration will win races. As the boat accelerates the apparent wind will increase and move forward leaving the skipper with two choices, either bearing away to keep the acceleration or eliminating the flaps and sail into the wind. Of course he eliminates the flaps and goes for the best VMG.
That is why the AC cup boats gybe downwind, at each gybe they use the flaps and get a huge acceleration. Then they transition to a no flap wing for low drag and good pointing.
Most of the time though sail boats are sailing upwind and flaps are useless. They probably only went with 'flaps' because of the necessity of wing twist because of the different velocities and angles of the wind, so they got the flaps for free.
A simple, light strong wing will give you most of the benefit of an extremely complex AC wing. Most of the AC wing's advantage is its ability to control the twist. And no, a simple wing will never beat an AC wing in a race, it beats it everywhere else though.
Talador
__._,_.___
Posted by: taladorwood@yahoo.com.au
| Reply via web post | • | Reply to sender | • | Reply to group | • | Start a new topic | • | Messages in this topic (38) |
.