Slip Wand for foiler height and roll control

[Skyak]

Doug, That's a rather complicated vector force diagram for veal heel. It breaks some forces into components but not others and includes insignificant forces (mast weight) while neglecting significant ones like hull wind drag. A much simpler diagram results when you make one very accurate assumption -veal heel is primarily a tactic to cut foil drag by zeroing out the lift of the vertical of the T foil (the reality is a small negative lift on the vertical for stability and respect for consequence). The horizontal foil is larger than optimal for speed because it is important to get the hull out of the water as soon as possible. At speed the horizonatal has plenty of lift to both counter leeway and support the weight of the craft. With this realization the vector diagram gets very simple. The force of the keel goes straight up the center of the boat, The sail force is normal to the sail (aerodynamics give a very accurate position) and adding the rest of the boat only moves it slightly lower. The weight of the crew is the only known vector, straight down, but the sum of the moments about any point being zero and choosing the center of lift of the keel we have one equation and one unknown. Of course this is just one condition, but it is the 'fastest' and I would say that it defines the design when combined with the low speed liftoff requirement. I call this the skyak theorem for simple foiling monohulls.

 

[Doug Lord]

There are a lot of things going on . You can't ignore the substantial RM developed due to Veal Heel but including wind drag in this diagram would be out of place(other than sail force).Beaver covers wind drag at length in his paper and it turned out to be much higher than most people had assumed-which is why the fairings Gulari used recently were so important.
The horizontal mainfoil (when the boat is level) is not larger than optimal on any Moth or other bi-foiler I have seen-where did you come up with that? To "get out of the water" faster the whole boat can be pitched up- assuming the wind is strong enough to overcome the momentary extra drag during takeoff-and made up for by the quick takeoff.
Other elements include vertical lift from the rig.
This idea of lift to weather in excess of the lateral resistance requirement due to wind force on the sail is probably difficult to achieve because the boat, as it is eased into Veal Heel, will attempt to find equilibrium between the sail force and the components of lift from the foils. Exceeding that equilibrium(which is automatic) would require adjusting the flap on the main foil as well as adjusting the AOI of the rudder t-foil. Just adjusting the rudder t-foil(with the twist grip) would not allow the boat to move sideways toward the wind as claimed by some-and would be high drag.

 

[Skyak]

Doug, That's a rather complicated vector force diagram for veal heel. It breaks some forces into components but not others and includes insignificant forces (mast weight) while neglecting significant ones like hull wind drag. A much simpler diagram results when you make one very accurate assumption -veal heel is primarily a tactic to cut foil drag by zeroing out the lift of the vertical of the T foil (the reality is a small negative lift on the vertical for stability and respect for consequence). The horizontal foil is larger than optimal for speed because it is important to get the hull out of the water as soon as possible. At speed the horizonatal has plenty of lift to both counter leeway and support the weight of the craft. With this realization the vector diagram gets very simple. The force of the keel goes straight up the center of the boat, The sail force is normal to the sail (aerodynamics give a very accurate position) and adding the rest of the boat only moves it slightly lower. The weight of the crew is the only known vector, straight down, but the sum of the moments about any point being zero and choosing the center of lift of the keel we have one equation and one unknown. Of course this is just one condition, but it is the 'fastest' and I would say that it defines the design when combined with the low speed liftoff requirement. I call this the skyak theorem for simple foiling monohulls.

Note I am intentionally being pompous here. Feel free attack my assertion but don't bother getting all emotional about it. I am sure that others involved earlier realized this long ago and there may be value in the elaborate detail needed to win a competitive class. But for privateers like myself, the OP and the majority of readers on this board getting the 2D solution to fit on a napkin is critical. It allows us to quickly size components and move on to 3D and velocity prediction.

About the validity of the assumptions, I am sure the keel force will be questioned but it is easy to measure -if you look at the force on the dagger board case during VH sailing you will find that horizontal lift is nominally small and negative. The bigger inaccuracy is likely in the sail -I suspect the force of a sail healed to windward moves down the mast but I have nothing to quantify this. I have been searching for aerodynamics of sails healed to windward with one end terminating against a horizontal but I have not found anything but doing the CFD which is a long way from the napkin calculation I need for an excel or mathcad model.

 

[Skyak]

There are a lot of things going on . You can't ignore the substantial RM developed due to Veal Heel but including wind drag in this diagram would be out of place(other than sail force).Beaver covers wind drag at length in his paper and it turned out to be much higher than most people had assumed-which is why the fairings Gulari used recently were so important.
The horizontal mainfoil (when the boat is level) is not larger than optimal on any Moth or other bi-foiler I have seen-where did you come up with that? To "get out of the water" faster the whole boat can be pitched up- assuming the wind is strong enough to overcome the momentary extra drag during takeoff-and made up for by the quick takeoff.
Other elements include vertical lift from the rig.
This idea of lift to weather in excess of the lateral resistance requirement due to wind force on the sail is probably difficult to achieve because the boat, as it is eased into Veal Heel, will attempt to find equilibrium between the sail force and the components of lift from the foils. Exceeding that equilibrium(which is automatic) would require adjusting the flap on the main foil as well as adjusting the AOI of the rudder t-foil. Just adjusting the rudder t-foil(with the twist grip) would not allow the boat to move sideways toward the wind as claimed by some-and would be high drag.

Doug,
by 'wind drag' on the boat I meant the leeward force of the wind on everything that is not the sail can be estimated and the vector added to the larger sail vector. The sum will be slightly larger and lower but not very far off normal to the sail.

About foil size 'larger than optimal' I mean that there is much more plan area than needed to support the weight of the craft at the high speed it is traveling in VH.

Note all my discussion here is 2D which we need to size things before we move on the 3D.

 

[ozandy]

Cheers Doug.
I've read some of that material before as background...I did a lot of Googling!
Will check the rest.
I was going to go for 4 surface peircing foils for the practicality...all could be swept back which is good for launching and makes dealing with the inevitable collisions easier. It was the success of the moths bi-foiler arrangement and the stability issues discussed earlier (trike vs bike handling) that settled me on the bifoiler arrangement.

One of the studies I read talked about the importance of aerodynamics and the fact that it becomes most relevant over 15 knots or so. One thing I'm keen to avoid is the "Audi TT" factor where at a certain speed the bad aerodynamics causes abrupt stability issues (in the TTs case the nice looking rear end became a lift generating device...not a good idea when cornering at high speed!)

I want to build mine to be not draggy and have a little bit of lift in the right places. The wings will be sheathed so they are small auto-stable foil with COG such that any forces will be kind to me and assist the boats stability rather than work against it.

One of the more "out there" ideas I have relates to dynamic soaring, which is extracting energy from sheer. The "back-side" gliders extract energy each time they go through the sheer layer. Albatros also dynamic soar but use the sheer generated by waves.
http://www.youtube.com/watch?v=uMX2wCJga8g
Now sailing is basically dynamic soaring but with wings in two mediums and the sheer is the water's surface. Could you transition from fast foiling, to ground effect skimming whilst heeling into the wind thus doing a "steady state" albatros energy extraction? L/D ratios would need to be very good on all wings, we are talking at least high performance HG...30:1. I imagine a high performance kite would be needed to get enough sheer. I'll do some maths at some stage to see how much energy is available and see just how crazy this is.
A rough calc is here: http://douglasturner.tripod.com/id27.htm
A wing with 25:1 glide ratio, with a sheer delta of 30 knots can get to 224Mph!

BTW. Made good progress over the weekend: Amma mouts are now fixed and lugs made, wand and bow mount done but not fitted, horns, and control rods done (need ball-joints and final pinnage...got to minimise slop). Rudder box fitted and fitted to rudder blade. Nearly ready to mount main foils and start tweaking controls.

 

[Baltic Bandit]

Note I am intentionally being pompous here. Feel free attack my assertion but don't bother getting all emotional about it. I am sure that others involved earlier realized this long ago and there may be value in the elaborate detail needed to win a competitive class. But for privateers like myself, the OP and the majority of readers on this board getting the 2D solution to fit on a napkin is critical. It allows us to quickly size components and move on to 3D and velocity prediction.

About the validity of the assumptions, I am sure the keel force will be questioned but it is easy to measure -if you look at the force on the dagger board case during VH sailing you will find that horizontal lift is nominally small and negative. The bigger inaccuracy is likely in the sail -I suspect the force of a sail healed to windward moves down the mast but I have nothing to quantify this. I have been searching for aerodynamics of sails healed to windward with one end terminating against a horizontal but I have not found anything but doing the CFD which is a long way from the napkin calculation I need for an excel or mathcad model.

Skyak you are spot on here. Doug's analysis is not only overly complex but it also is actually wrong. His "Righting arm" is basically a rule of thumb" approach that doesn't actually look at how force couples work

In an actual force diagram what all these component forces are - are actually "force couples" that induce a rotational moment around the Center of Lateral Resistance in the vertical domain.

so assuming the boat isn't flipping over, what you have is force couple for each component force with a radius of the couple being theoretically the integral of the weight/force over dRadius. In practice you can basically take the average weight of the component as operating at 1/2 the full radius of the component.

And you can also essentially average the total weight distribution of the components and integrate that in to a single large force couple.

The big error Doug makes is in armwaving where the rotational pivot of the force couples are. The actual location in a flying moth is fairly complicated but one place it absolutely is NOT is at the center of the horizontal foil.

in a classic keel boat its on the rotational axis of the hull as it heels.

But in a foiler - it is somewhere above the surface of the water since the surface of the water is always contributing some amount of lateral resistance to windward, and thus the basic force couple is between the lateral component of the sail lift and the lateral component of the foil lift. And the axis will be between them based on the relative magnitudes of the forces involved.

But I suspect Doug lacks any formal engineering training in this analysis so he's not really aware of where he is going wrong

 

[Baltic Bandit]

Cheers Doug.
I've read some of that material before as background...I did a lot of Googling!
Will check the rest.
I was going to go for 4 surface peircing foils for the practicality...all could be swept back which is good for launching and makes dealing with the inevitable collisions easier. It was the success of the moths bi-foiler arrangement and the stability issues discussed earlier (trike vs bike handling) that settled me on the bifoiler arrangement.

One of the studies I read talked about the importance of aerodynamics and the fact that it becomes most relevant over 15 knots or so. One thing I'm keen to avoid is the "Audi TT" factor where at a certain speed the bad aerodynamics causes abrupt stability issues (in the TTs case the nice looking rear end became a lift generating device...not a good idea when cornering at high speed!)

I want to build mine to be not draggy and have a little bit of lift in the right places. The wings will be sheathed so they are small auto-stable foil with COG such that any forces will be kind to me and assist the boats stability rather than work against it.

One of the more "out there" ideas I have relates to dynamic soaring, which is extracting energy from sheer. The "back-side" gliders extract energy each time they go through the sheer layer. Albatros also dynamic soar but use the sheer generated by waves.
http://www.youtube.com/watch?v=uMX2wCJga8g
Now sailing is basically dynamic soaring but with wings in two mediums and the sheer is the water's surface. Could you transition from fast foiling, to ground effect skimming whilst heeling into the wind thus doing a "steady state" albatros energy extraction? L/D ratios would need to be very good on all wings, we are talking at least high performance HG...30:1. I imagine a high performance kite would be needed to get enough sheer. I'll do some maths at some stage to see how much energy is available and see just how crazy this is.
A rough calc is here: http://douglasturner.tripod.com/id27.htm
A wing with 25:1 glide ratio, with a sheer delta of 30 knots can get to 224Mph!

BTW. Made good progress over the weekend: Amma mouts are now fixed and lugs made, wand and bow mount done but not fitted, horns, and control rods done (need ball-joints and final pinnage...got to minimise slop). Rudder box fitted and fitted to rudder blade. Nearly ready to mount main foils and start tweaking controls.

Aero drag has affect at any wind speed. For CARS it becomes the dominant resistive force (vs rolling resistance) at roughly 15mph (13 knots AWS). Now the thing to realize is that if you are sailing upwind in 10 knots of breeze - as soon as you break 6 knots of boat speed you have hit that 15mph.

Secondly, for a foiling moth, the aerodrag becomes the dominant resistive force probably the moment the hull flies so aero is far more important here. That said - get the thing foiling first - and worry about Aero afterwards. Stable flight iis going to be the hard part.


Ground effect is something different, though some of the top mothies have been talking about and experimenting with adding lifting shapes to their trampolines - the idea being that particularly with the notion of "veel heel" you could have some battens inside the tramp so that the side without the driver has a lifting airfoil shape and thus contributes to RM.

but again - foiling is hard enough, get your boat foiling first.

 

[P Flados]

BTW. Made good progress over the weekend: Amma mouts are now fixed and lugs made, wand and bow mount done but not fitted, horns, and control rods done (need ball-joints and final pinnage...got to minimise slop). Rudder box fitted and fitted to rudder blade. Nearly ready to mount main foils and start tweaking controls.

Your discussions of theory are interesting, but I concur with BB on the need to focus on making it all work to achieve stable foiling.

I also want to encourage you on what appears to be faster than typical progress. I try to think in the world of theory, but until I put at least a portion of that thinking into something out in the water, I know it really does not mean much. It looks like you are on track for a tryout sooner rather than later

 

[Baltic Bandit]

This idea of lift to weather in excess of the lateral resistance requirement due to wind force on the sail is probably difficult to achieve because the boat, as it is eased into Veal Heel, will attempt to find equilibrium between the sail force and the components of lift from the foils. .

I do have to comment directly on this particular piece of idiocy in the context of PFlados' point about actual on water experiments.

Its quite clear from this that

• Doug has not had a conversation with an active mothie
• Doug has not sailed on the water anywhere near a Moth
• Doug has not sailed on the water anywhere near a Moth in a boat that is in the same speed ballpark as a Moth to compare leeway tracks
• Doug does not understand how balanced force vectors work or that boats don't have desires to "find" anything. Instead these are designed vector balances

Now its true that Veal Heel was not originally designed in - though now it is. Nor was it the result of folks trying to "neutralize the lift/drag of the vertical foil". Rather it was discovered because in a tippy unstable skiff, one of the techniques for improved stability is to do what windsurfers do - rake the rig to weather. This works because even if the air shuts off 100% (which it never really does) you still have the lateral resistance of the sail to give you time to get your weight shifted into the boat. Whereas the opposite: when the boat is heeled to leeward and a puff hits - you have no such "safety net".


Also I suspect, that once Rohan learned to sail stably, he tried what most skiffies will try in any dinghy: namely heeling to weather to reduce rudder loads as a way of improving speed. And in the moth not only does it reduce rudder loads AND vertical strut loads, but it also generates negative leeway

 

[Skyak]

Skyak you are spot on here. Doug's analysis is not only overly complex but it also is actually wrong. His "Righting arm" is basically a rule of thumb" approach that doesn't actually look at how force couples work

In an actual force diagram what all these component forces are - are actually "force couples" that induce a rotational moment around the Center of Lateral Resistance in the vertical domain.

so assuming the boat isn't flipping over, what you have is force couple for each component force with a radius of the couple being theoretically the integral of the weight/force over dRadius. In practice you can basically take the average weight of the component as operating at 1/2 the full radius of the component.

And you can also essentially average the total weight distribution of the components and integrate that in to a single large force couple.

The big error Doug makes is in armwaving where the rotational pivot of the force couples are. The actual location in a flying moth is fairly complicated but one place it absolutely is NOT is at the center of the horizontal foil.

in a classic keel boat its on the rotational axis of the hull as it heels.

But in a foiler - it is somewhere above the surface of the water since the surface of the water is always contributing some amount of lateral resistance to windward, and thus the basic force couple is between the lateral component of the sail lift and the lateral component of the foil lift. And the axis will be between them based on the relative magnitudes of the forces involved.

But I suspect Doug lacks any formal engineering training in this analysis so he's not really aware of where he is going wrong

I try to keep the conversation constructive but I also never miss a chance to point out the forest to tree counters. I am glad he posted the diagram because correcting/simplifying it in my mind helped me reach some insights. I got the zero to negative leeway from your comments BB and the lift and drag minimization from T. Speer's papers. Now I can make a model and do some digital prototypes. Getting the 2D down to one equation one unknown is great because I still have two more equations to error check.

I haven't forgotten about your solidworks. I have a student edition. The reason I would need your license would be if I was doing CAD work for money which I am not at present. Then there are maintenance fees and other alternatives to consider (a friend has an up to date seat).

About "neutralize the lift/drag of the vertical foil", if the sailor is not doing it ie he has heeled past to negative leeway for stability/recovery he is sacrificing speed. More vertical boat heel with an eased sheet would be faster but closer to the edge. If he goes over the edge he has to depower to recover. I am pretty sure we had this argument on another thread, but you were making the opposite point about windsurfers being faster upright.

Oz,
I don't understand your wand dynamics, but if your wands are free to rotate port/starboard it will tend to decrease stability -the low side wand will tend to slip to the high side measuring high not low. Fixed wide placement will add maximum righting stability.

About dynamic soaring, I am not sure what you are getting at but there are lots of vertical wind gradients you can sail in and out of. Your foiler is low drag as boats go but drag is still too large relative to mass to use dynamic soaring with momentum. The most interesting thing about dynamic soaring is that it is a very complex behavior that relatively unintelligent creatures learn based on experience.

 

[ozandy]

I put all the bits on the scales over the weekend:
Rudder and box: 3.4, Main foil, 3.4, front hull 6.3, rear hull 10.5, ammas both 4.1, sail 6.6, mast 2.3. All up 40.7 Kg.
I'd expect to add another 5-10Kg before completed, which brings me to around 50Kg sailing weight. I expected a bit more but this is in the ballpark.
I probably should have put a bit more beef in the front section as it has to deal with the main foils and the mast loads. As with the main foils...we will see.
Ball joints are in the mail so hopefully I'll have the entire control system completed this weekend.
BTW. Skyak. There is only one wand with two axis of movement. The tip of the wand has a small keel and planing surface so it tracks...pics will make it all clear.
As for a wide stance: This is a dynamic stability system, not static stability. Like a bike it requires significant forward speed for it to work at all. Putting training wheels on a bike will not stabilise it at speed nor allow it to turn at faster speeds. At some stage the tricycle static stability will be overwhelmed by forces, whereas a bike can react smoothly to forces by leaning more...up to a point.
The DS stuff is just blue sky thinking. I've managed to do a few albatross passes with my discus launch glider (F3K) and it is lots of fun. The theoretical amount of speed you can extract from sheer is pretty amazing! Above 50-60 knots or so (IMHO) you really need to be flying for any sort of comfort or safety...even foils get gnarly with the need for supercavitating sections. Crashes are deadly at these speeds. So when there is plenty of aerodynamic lift, sheer to extract energy from, why not use the air for what it is good for at those speeds? Probably completly impractical for the same reasons that groud effect craft are (too many compromises) but I cannot imagine a better way to go faster with wind.
I reckon all birds have an instinctive understanding of flight. I often watch seagulls dynamic soar in the turbulence around the skyscrapers in the city, and galahs seem to love playing in willy willys and rough air. Swifts also appear to dynamic soar more often than not (hard to tell though). Different form of "intelligence" I guess.

 

[Baltic Bandit]

About "neutralize the lift/drag of the vertical foil", if the sailor is not doing it ie he has heeled past to negative leeway for stability/recovery he is sacrificing speed. More vertical boat heel with an eased sheet would be faster but closer to the edge. If he goes over the edge he has to depower to recover. I am pretty sure we had this argument on another thread, but you were making the opposite point about windsurfers being faster upright.

.

Well windsurfers are running a steady state (relatively vertical foil, so the don't get any VMG benefit from additional heel. That's the diff with Moths- with negative leeway, the question is whether the lift to weather exceeds the drag. And I'd suggest that it almost necessarily does. After all your sails generate more driving force lift than drag, even though they are generating both.

now of course a lot depends on exactly where in the drag bucket you are, what the drag bucket looks like etc.

But I've watched moths heeled to weather just climb away from moths sailing flatter - this is as we sat downwind of the start waiting for our sequence to begin. its quite amazng.

 

[ozandy]

I think the dynamics of a full foiler are a little different from a traditional vertical centerboard. I guess I see the main foil as not needing the vertical part at all except for structural reasons, but the back-end is a different story.
I'd love to know just how much load the vertical part (the daggerboard bit) of the Moth front foil is taking and what AOA it is running at at full speed. I suspect a very small AOA and that almost all sail countering forces are being handled by the horizontal blade rather than the vertical.
Also once heeling the rudder blade almost acts as an elevator...and this is one dynamic I'm not quite sure how it will feed into stability. Normally a bit of weatherhelm is a good idea: safer and it makes the rudder "fly" to windward instead of fighting the centerboard: How does the Veal Heeling affect this? When heeled to Leeward the rudder force countering weatherhelm is a lifting force, when heeled to windward it is the opposite...the rudder blade is trying to fly slightly downward. This may be fine, after all the Moths handle it, but I'd like to know whether the fast Moths trim for lots of weatherhelm, just a tad, or even Leehelm. There is also the issue of rudder foil trim...where veal heel will make "up" trim steer a bit to windward and "down" trim will create a bias to Leeward.
One thing is for sure, there is always a cost to making a craft stable and if one tries to cheat you end up paying more. You can build a tailless aircraft, but there is a good reason why high performance sailplane designs all converge on one rudder and one stabiliser as far back from a high aspect wing as possible and a COG at approximatly 1/4 of lifting surface chord. Autostable wings work, as do tailless designs using sweep, as do canards, but not as well.
So what is the best stable layout for a foiler? I'm starting with a similar layout for similar reasons: asymetrical main foil with roll coupled to slip, symmetrical tail foil with vertical stabiliser/rudder. I am confident, with the Moths showing the way, the height control is quite doable. The slip roll coupling is the main issue.
Cheers Pflados: I made sure this would get wet fairly soon before posting anything...we are in crank country here: we still see "Newton vs Bernoulli" arguments on how wings work so words are pretty useless tools when mental axioms are different and the scenario is complex. It is tricky turing dynamic 4d ideas into words...in a few weeks footage will do the job much better (whether it is positive or negative!)

 

[tspeer]

...The change I am adding is to have 2 flaps on the main foil with each one controlled individually according to the amount of side slip detected by the wand, which has a keeled paddle on the tip to keep it tracking straight even when heeled. The wand will be allowed to rotate about 20 degrees to the left and right whilst also doing the 90 degrees forward-backward movement with 45 degrees the designed trim height angle. The two flaps have +/- 4 degrees, are full span and are about 1/3 chord.

If the wand is deflected to windward then the flaps will try to roll the boat to windward and visa-versa, the idea being to tune it to maintain balance between the sail force and the weight of the boat....

I don't think your basic question has been addressed in the discussion. What you're trying to do is feed back leeway angle to rolling moment, in addition to feeding back height to vertical lift. You're looking at the steady-state trim of the boat, but I think you need to be considering other time-scales in the dynamics.

In the steady state, when the boat is heeled to windward, there is not necessarily any rolling moment required from the foil. The crew weight offsets the heeling moment from the rig, and the leeway is zero so the lift from the foils is directed up the strut and there's no rolling moment from the foils about the centerline of the boat. The flap deflection would be equal on both sides of the foil for this case, and the rolling moment would be zero. You need to consider the dynamics of the boat about this equlibrium condition.

When a gust hits or the sail is trimmed in a bit, there will be an increase in side force and an increase in leeway. There will also be an increase in heeling moment. Leeway feedback would apply a rolling moment to oppose the change in heeling moment. How much leeway develops for a given side force will depend on how high the boat is flying. If it is flying high, more leeway will be experienced and there will be more rolling moment. Is this what you want to have happen? If not, you could change the gearing in the leeway feedback such that the gain between the wand and differential flap deflection is reduced when the boat is flying high, thus compensating for the increased leeway such that the product of the gain times leeway is approximately constant as the flying height varies. You might be able to get this effect by how you arrange the yaw axis of the wand - it wouldn't have to be vertical, for example.

Another factor to consider is the longitudinal position of the wand and the leeway at that location vs the leeway at the center of gravity or the foil. When you're turning, the bow of the boat will be moving sideways, generating a local leeway angle there that is different from the leeway further back. this will couple yaw rate with rolling moment through your feedback system. It's common practice to mount the wand forward so as to generate phase lead with respect to the oncoming waves. This allows the foil to increase its lift before the crest reaches the middle of the hull. However, the coupling between yaw rate and leeway at the wand's location will mean that your feedback will cause the boat to roll to the outside of a rapid turn. This is probably an undesirable situation.

If the wand were mounted at the stern, the coupling would be reversed in sign, rolling the boat to the inside of a rapid turn. But then the heave response would be reacting the the wave that just passed, instead of the wave that is approaching. So you might want to consider two separate wands - one at the bow for heave and one at the stern for leeway. This would let you optimize the design and linkages for each purpose. Another option might be to mechanically add a linkage from the tiller to couple rudder movement to differential flap movement. The effect would be similar to a really deep rudder that has a very low center of effort, producing both a yawing moment and a rolling moment. This might overcome the leeway feedback in a turn, while leaving the leeway feedback to operate as desired in straight-line sailing.

There are fast dynamics vs slow dynamics to consider. Do you want the boat to react to short, quick changes in leeway, or to longer term adjustments?

Then there's the performance aspect. Heeling to windward makes sense when flying high, because you can reduce the wetted area of the strut and without leeway, there's no induced drag penalty from reduced span to counter the side force. This presupposes the horizontal foil is sized to provide both the vertical lift and the side force. Providing the side force from the horizontal foil isn't difficult if it only takes a 15 deg heel angle to provide the necessary side force. You get 26% of the weight in side force for less than a 4% increase in lift on the horizontal wing, which sounds like a pretty good tradeoff. But the optimum leeway angle may not be zero.

If you carried some side force on the strut, the optimum lift distribution on the wing will be discontinuous. It will have a step change in lift at the strut so as to maintain a constant downwash along the span, even in the presence of the wake from the strut. Your differential flap deflection could help in getting just the right amount of lift on each half of the foil. By spreading the vertical lift and side force over the span of both the foil and the strut, it may be possible to reduce the induced drag below what would be experienced with lifting with just the wing alone. This might make it worth the wetted area of the strut and change your optimum flying height and heel angle.

You may want to have a manual input to the differential flap deflection so the pilot can set the trim split between the flaps and then use body weight to balance the boat with the resultant rolling moment.

 

[ozandy]

Hi Tom,
You clearly understand the system and have addressed most of the issues that have been on my mind! Your summary of the dynamics is pretty much exactly what I have in mind.
The wand will indeed reduce the slip/roll coupling as it flies higher. It does this because as the height angle of the wand approaches 90 degrees the slip angle is more vertical (arms rotate up and down rather than forwards/backwards) and so will reduce smoothly from the maximum at the slow speed position to zero at 90 degrees. The effective height range will be about 80 degrees so the authority never quite reaches zero. I have also mounted the slip arm at an offset to the height pivot so that the roll inputs will be down biassed...this creates "differential" alieron deflection so there is a tad more on the downside than the upside. Similar to Ackerman compensation in steering. It seems safer to roll down than up when heeled.
There is also the torque generated: Without 100% stiffness in the struts the the flap down side will generate more drag then the up side and twist the struts...thankfully this torsion is in the correct direction to help steer to foil in the desired direction rather than fight the roll. Too much flex will vibrate, change AOAs and do other nasty things so this is not designed in...I'm just glad it turns out to be benign rather than an issue.
Your leeway picture is spot on I reckon. I too came to the conclusion that whilst a height wand belongs at the bow, the slip wand should probably be at the stern. Until I get a hydraulic system organised this is just a bit too complex!
You are also correct that a hard turn may produce the wrong correction. I spent quite a few hours working on that one...leaning to outside of turn would be bad. I am hoping that minimal vertical foilage up front and the foiling mode will prevent this: ie at speed any rudder deflection will slip the entire boat for long enough for the correct roll to be initiated. As it is not pivoting around a vertical dagger I have some hope that this will work similarly to how a plane with no ailerons will roll via dihedral when the tail at the back starts the slip...it does not rotate around the COG because at flying speeds the forward momentum is way larger than the rotation momentum that the rudder can generate. At slow speeds the roll authority will be minimal anyway, which is what the ammas are for. Powered tests should sort it out.
The rudder feedback idea I rejected as it would probably not handle sail forces well...all the boats I have sailed have quite variable forces on the rudder depending on wind variability and the point of sailing and a direct rudder to roll would be unworkable. A small corrective factor may be useful though (another one for the hydraulic system)...
The fast/slow dynamics will have to be tuned via the geometry first, then possibly with some damping...I imagine it will be a bit like suspension tuning. I'll start with gearing similar to the Moths and add a bit of mass to the wand tip. For now the focus is on building it without too much slop (build tight, then lubricate).
I have two struts for the main foil, but this is only to make up for my building methods and to make deployment on the water possible, but you could easily build a single centerboard and run the two control rods down it. As you say, any side loads on the support struts will do horrible things to the efficiency of the main foil, so ideally it will settle on a slip free orientation...which may or may not be with exactly equal flap deflection.
I will probably add a manual override for exactly the reason you say: it may enable an optimum weight/lean/flap setting depending on conditions. Could be fun too!
Thanks very much for the ideas. It is nice to see my own concerns and solutions fed back from an independant authoritative source.