Mike
I have a couple of ideas for a tail plane. They both involve the tail plane being supported off an arm coming from the convex face of the wing. The tail plane would be a non-cambered section. At this stage I expect the choice of it being pivoted independently of the arm or fixed to the arm will depend on intended use. For mooring you would want it rigid to the arm and the arm also parked and looked to the wing in the zero lift point for the wing.
The section selection will alter the ratio of Cd at zero lift to the maximum Cl when sailing. Ratios of the order of 30 to 1 are possible. I expect this would be better than a typical mast with standing rigging. Remember that when moored the boat will be head to wind so the resistance to pitching moment is probably higher than the rolling moment. Lets say you designed sails to take 20kts without reefing. Then you should safely handle force from (30)^0.5 or about 5 times, say 100kts, with the boat moored. You need to make absolutely certain that the rig is free to weather vane - so reliable bearings.
I have never known anyone who relaxes when their boat is on a mooring. It is one reason why I do not want that headache again.
From my brief look, a section around 20% thick with 11% camber seemed to give a good ratio of maximum lift to minimum drag at zero lift. This also works OK in reverse if you were worried about flipping it through the wind.
My view is that a wing with tail plane would be inherently stable in quite severe winds. There would be buffeting as you get in an airplane but this will depend on how disturbed the oncoming air is. Airplanes operate at much higher speeds than you are contemplating. Even gliders that have what might be considered fragile wings move faster than the speeds you have mentioned.
I am interested enough to do a test with a rigid wing later in the year with a couple of old pedal boat hulls to play with different methods of control. I would like to try it out in strong northerlies when the dinghy fleet cannot stay upright.
This video shows my prop boat test in very light wind:
I initially took this boat out in 70kph winds with gusts to 90kph. I rolled it when trying to turn. The prop is only 2.2m diameter and blades 100mm chord but the swept area is much larger than blade area. It is amazing the difference in load between prop turning and not turning. The big spider wheel you can see for controlling the angle was an addition after the first outing. It enable me to feather the prop very easily. So I could depower. When I capsized it I only had a lever arm and I could not get enough angle to stop the prop from rotating - I had to put my head too close to the blades that were moving at incredible speed. The tip speed ratio is about 7 to 1 so of the order of 500kph wizzing past my face. Enough power to make froth at the prop and just sit there ventilating.
Point is there is a huge difference between the maximum lift force a wing can generate and the drag it experiences when there is no lift being produced. The prop is a bit different because it has a bigger gain in apparent wind at the tips. On the other hand an easily driven proa also has a significant gain in apparent wind.
I guess overall this discussion is pointing out the merit of sail efficiency and what it means for pointing ability over just having lots of sail area. Downwind the proa readily runs away from the wind so there is not a great advantage in having lots of sail there. The one range where sail area gives an advantage is when reaching free where the heeling moment is low but you are still making apparent wind - say in the range 100 to 140 degrees true. Of course if you are after light air performance you need more rig area.
Rick
On 08/06/2011, at 11:49 AM, Mike Crawford wrote:
<<The best wing profile from a performance perspective is cambered as Todd has. To get benefit from this it needs to flip through the wind per your observation>>
I definitely get why the camber is effective at generating lift, why the wing can be a lot smaller than the equivalent sail, why the apparent wind will be an even bigger benefit/effect, and why all this can combine to make the momentary broadside position during shunts a minor issue or non-issue. Comparing a perfectly-cambered rigid wing to any normal sail is to compare apples to oranges.
For a coastal speed demon, as Todd defines it, this is a very simple and efficient rig for a certain window of wind speeds. And man, can it shunt quickly...
However, I'm going for a rig that will let me enjoy four knots of wind, work at sixty knots (whether through reefing or shaping), and then be able to ride
out a hurricane as good as or better than a bare tapered cylinder.
Even in our home harbor, there have been times we've gotten nor'easters that were much more powerful than predicted, and I've watched our moored boats ride out thirty to fifty-knot winds for two days. I definitely want my next boat to be able to do the same thing without my having to worry about it.
This is where a cambered bidirectional wing appears to come up short. I can't yet envision a wing that works in four knots being safe over forty knots, or being able to hang out in true neutral for long periods of time, whether at sea or on the hook.
However, that doesn't mean it can't be done. I'd *love* to be able to shunt as quickly as Todd's rig can shunt while still being safe throughout a huge wind range. It's possible that I just need to learn more.
<<The only way I see to make a rigid wing work
reliably is with a tail plane or flap. >>
Thus far, I agree. I don't see another way of allowing the wing to tend itself, particularly in neutral, for any significant length of time.
Two sets of questions:
1) Staying in Neutral. I understand how a flap could default to neutral when the sheets are released, and stay that way for minutes or even days (you'd surely want to lock in in neutral if intentionally leaving it unattended for any length of time).
But what about a wing with a tail plane? Would the tail plane be in conjunction with a symmetric foil with a single leading edge, a wing with a single leading edge that has camber induced by a flap, or a cambered bidirectional wing?
I'd love the auto-adjustment ability of a tail plane with a bidirectional wing, but would definitely worry about the entire
system falling apart if the tail were to get damaged. It's probably a very low probability of failure, but still the potential for a single point of failure. Though I suppose you could make both the tail and its control system really beefy. Would the tail have to be switched from one side to another on each shunt?
2) Windage. Could any of the above wings end up providing the same or less windage as the bare pole? I know that many foil shapes will do this, but I don't know if that's true for a foil that's long enough to be a sail.
<<If you are after a real easy to handle rig then maybe a Flettner rotor would be of interest>>
Those rotors are awesome! I've only seen them on larger test craft so far, not on smaller sailboats. Neat.
Alas, I may have to go with a more traditional rig on the next boat.
:-)
- Mike