Auto-Flight
This is super exciting, and I love the shared experimentation that makes this forum so compelling.
I’m pumped about the potential for this device, and love the development so far.
Johannes—I very much like the solution of putting the paddle on a spar between the akas. It offers lots of fins adjustment of the AoA. Nice build.
One interesting aspect that hasn’t been addressed is the effect of righting moment on ultimate stability.
My outrigger, when I sit in the vaka, runs out of ultimate stability at very low angles, as the weight of the rig and safety ama take over. So, while the autofilght mechanism does respond to variations in RM by measuring ama lift (the relevant variable) there has to be some minimum threshold of minimum RM (lateral position of cg?) in order to make this whole thing work.
Just one of many boundary conditions….
I’m concerned about the many different variables involved in making this work efficiently on all points of sail in different wind conditions. But I’m also excited to see this super cool technology work.
Forgive me if this has been covered, but what about the drag of the auto flight paddle in conditions where the ama is not flying much/at all. This is a big loss…how to mitigate.
I have no doubt that Dave has thought of this…and much more.
chris
Forgive me if this has been covered, but what about the drag of the auto flight paddle in conditions where the ama is not flying much/at all. This is a big loss…how to mitigate.
It is easy to fold the foil up horizontal between the crossbeams, and sail like a “normal” proa.
Johannes—I very much like the solution of putting the paddle on a spar between the akas. It offers lots of fins adjustment of the AoA. Nice build.
Thanks! This is just a nice aspect of playing with scale models. This solution was just natural when trying to attach the foil to the crossbeams. I can not take credit for this solution. It sort of just jumped at me when trying to find materials and solutions.. When trying to find a solution i often just start with anything, regardless how ridiculous it might seem, and usually a solution just appears. I need to get my hands dirty with sawdust/epoxy/rust/welding slag (hurts like hell)/etc to be creative…
Cheers,
Johannes
As it is now the foil will sheet the sail harder when fully submerged, but once the ama starts flying the foil will loose some of its pull on the sheet, releasing it gradually until the sail is depowered and the ama drops back down. Hopefully i can find a sweet spot somewhere where there is balance and the ama flies at a stable height.
I think I get it now. You have set the foil at a negative angle of attack, so it is working to create more leeway rather than being part of the leeway reduction system?
Mal.
I think I get it now. You have set the foil at a negative angle of attack, so it is working to create more leeway rather than being part of the leeway reduction system?
Johannes…....I am hopefully being positive for once…....
When you try out the various settings and permutations, would you please try your system with the foil set at 45 degrees to windward (ie resting against the side of your ama), the AoA the reverse of what your photo shows (which should give you windward lift and ama lift) then route the mainshheet via somewhere central on the ama and then to the foil.
That way when the ama lifts, there is a chance (hopefully it will be) that the reducing lift on the foil and increased load on the mainsheet will pull the foil towards vertical or even beyond, dumping mainsheet, dumping ama lift as it goes or even switching over to ama pull down in bigger gusts.
I would be grateful if you would try.
Thanks
Rob
I think I get it now. You have set the foil at a negative angle of attack, so it is working to create more leeway rather than being part of the leeway reduction system?
I think there is a potential stability problem with using the sensing foil as a leeway reduction system,, as the leeway will increase when the ama lifts out of the water. This will be a positive feedback loop if the sensing foil is also part of the leeway reduction system.
In my setup the the changes in leeway will make the system more linear. As the foil lifts out of the water the foil will have less lift creating leeway, but the vaka/centerboard will have more leeway - creating negative feedback loop instead.
I am more interested in stability and an as large range of useful linear function of the system as possible.
Once i achieve stable flight i can start playing with added complexities. Right now it is more interesting to achieve flight and maximize synergy and simplicity.
I hope i understand the dynamics of the system right. Now it is midsummer and as a lot of other Swedish people i will try to saturate my central nervous system with C2H5OH, dance around an phallic symbol and sing about small frogs…
Små grodorna små grodorna - Youtube
Cheers,
Johannes
When you try out the various settings and permutations, would you please try your system with the foil set at 45 degrees to windward (ie resting against the side of your ama), the AoA the reverse of what your photo shows (which should give you windward lift and ama lift) then route the mainshheet via somewhere central on the ama and then to the foil.
Yes i will try that, once i get a good stable wind to work with.
I will make a new foil first though. I don´t think the current one is good enough for getting stable flight, as it is sensitive to turbulent water near the surface (waves).
Cheers,
Johannes
Now it is midsummer and as a lot of other Swedish people i will try to saturate my central nervous system with C2H5OH, dance around an phallic symbol and sing about small frogs…
Små grodorna små grodorna - Youtube
Cheers,
Johannes
Johannes,
First of all, how in hell do remember C2H5OH once you are drunk?
And secondly, as a Frenchman (Froggy???), I need explanations on the Frog Dance in the video…
Happy summer!
Laurent
Yes i will try that, once i get a good stable wind to work with.
I will make a new foil first though. I don´t think the current one is good enough for getting stable flight, as it is sensitive to turbulent water near the surface (waves).
As a quick and dirty fix, why not cut a big central hole on the waterline??? That way you have reduced area where waves affect the foil, but still have the width and stability of a wide board at the hinge(s)???
Enjoy your solstice celebrations!!!!
Cheers
Rob
Because leeway remains constant, the load on the sensor blade decreases as the ama rises.
This is precisely what is wanted. The ama rises due to sheet tension, set by the helmsman and allowed by the gadget increasing drive form the sail. As the ama rises, the immersed blade area decreases, blade drive decreases and the blade rotates (it is “preloaded” by the mainsheet). The sheet is eased, the sail is depowered and the ama comes down.
So you rely on the ama coming down before the sensor foil rotates all the way out of the water. That is what I would bet against, because the sensor foil rotates faster than the whole boat.
If you want to prevent that, you need to build a negative feedback mechanism right into the sensor. You can get that by moving the rotation axis to lee and up, but keep the sensor right at the ama (like Rob Denney’s sensor ama, which you linked to), and keep the point where the sheet attaches down, on a line that passes underneath the rotation axis. Then the sheet will pull the sensor (whether foil or ama) to lee and down. Your scheme lets the sensor rotate to lee and up, hence the positive feedback. Down increases immersion and force, hence negative feedback, but only after easing the sheet.
Are you perhaps exploring the potential effects of rotational inertia?
Rotational inertia is part of it, because that is a factor that I expect to prevent the feedback mechanism you describe. The sensor foil will pop out before the boat has time to level out.
Ie: what if the ama comes up and its inertia is such that, even with dumped mainsheet and fully depowered main, angular momentum takes the boat over the top?
No, nothing to do with that.
And secondly, as a Frenchman (Froggy???), I need explanations on the Frog Dance in the video…
I am sorry for going a little off topic, but i have to answer the above quoted question with a link:
Små grodorna - Wikipedia (english)
Now i will build a new foil. (The sound of power tools is really nice when hungover…. )
Cheers,
Johannes
Sorry to have dropped off the thread for a few days; I’ve been on a business trip—was hoping to have more slack time than I did—zero 😉
So you rely on the ama coming down before the sensor foil rotates all the way out of the water. That is what I would bet against, because the sensor foil rotates faster than the whole boat.
The sensor will rotate faster than the ama, but look at the scale; the actuator’s full range of useful motion is 60-90 degrees; the ama’s full range is 5-10 degrees. I don’t think the sensor’s rotation will be an order of magnitude faster than the ama’s.
I feel you are still thinking the sensor/actuator will rotate/not rotate in a binary fashion, always full over. It will not (or should not): As the ama lifts, there is a steadily diminishing force delivered into the system by the actuator. At some point this diminishing force becomes less than the preload due to the mainsheet and the sheet is eased. The angular velocity of the sensor can be much higher than the amas; if so, the mainsheet will be eased earlier and torque on the ama will also reduce earlier. The actuator/sensor is not likely to move particularly fast, however, because the first inch initiates the diminution of the sheet tension, starting the ama back down. You seem to visualize the system reacting in a series of large amplitude jolts—and you may be right. I disagree, and see it as considerably more sedate. If you are correct, your further comments are a good idea. If I am correct they are not needed.
Should the sensor pop out of the water, perhaps because the ama has risen too far, the system will fully extend, completely dumping the sheet. The sensor/actuator might self-park as Johannes describes, which isn’t a good thing in this case, so perhaps arrange the stop in such a way that, as the ama comes down, the tip of the sensor foil becomes immersed without option of parking. Move the stop out of the way and the system can still be parked, dry.
If you want to prevent that, you need to build a negative feedback mechanism right into the sensor. You can get that by moving the rotation axis to lee and up, but keep the sensor right at the ama (like Rob Denney’s sensor ama, which you linked to), and keep the point where the sheet attaches down, on a line that passes underneath the rotation axis. Then the sheet will pull the sensor (whether foil or ama) to lee and down. Your scheme lets the sensor rotate to lee and up, hence the positive feedback. Down increases immersion and force, hence negative feedback, but only after easing the sheet.
So long as we aren’t using the actuator force to bodily lift the ama, therefor enticing us to make it ever-larger and become a lifting hydrofoil, then I’m good with this. Thanks,
Dave
Johannes: I believe the adjustments (to) the sheet needs to keep the ama flying is very minor, and to get a small range, and exact control of the sheet i use a short top of the foil/blade. I can move it up and down very easy, so i hope i can find a good spot on the blade by trail and error. I have to start somewhere.
The above seems to indicate you thought only a small amount of power was needed (Power = force times distance, regardless of “gear ratios”) In a later post you mention you now believe the actuator needs to be quite large, indicating you now think quite a lot of power is needed? Or am I mis-reading? Or are you perhaps being “mislead” by the large reduction in blade force due to light winds?
I note you have the sheet doing a lot of vertical work on the boom, necessitating a larger sheet tension. Perhaps pull the vang really tight (non-stretchy line?) and connect the blade directly to the boom? The angle is not quite as good, but this way the sheet can only create (approximately) horizontal force, all vertical supplied by the vang. –thus less total force needed.
I think the blade should be very high aspect and deep so the variations due to waves is less/negligible. I hope i can test it today, within a couple of hours…
I agree, and offer two points; at scale model size you need to go quite deep to avoid waves. When you scale up this won’t be the case, as the relative sizes of the waves will be much reduced. Second, It’s been my experience with models that all control surfaces need to be much oversized; as you say, to overcome scale friction, simple build methods, and also scaling factor, in foils and sails. Again, hard to visualize what changes will be wanted at full size.
I have tested the autoflight device today. There was not enough wind to fly the ama, but i could see the device working and get a feel for the power, friction and range produced by different speeds, different AoA etc etc… My summary is that it is possible to create a very simple “sheet to tiller” kind of mechanism for autoflight, but it is very sensitive and due to the two different mediums with their very different behavior (different size waves, wave patterns crossing each other, frequent changes in wind speed and wind strength etc) is is not really useful for cruising. I can be wrong about this and i recommend every one else interested in this device to try it out.
I disagree of course, eagerly await further testing in stronger wind. When there’s not enough wind to fly the ama, all the forces are relatively small and making conclusions particularly based on feel, may become a bit dicey
...which leads me to another though about this:
With a much bigger foil with deep immersion, why not make a simple mechanism that adjust the lifting force of the foil in the first place.
Because we then chase the chimera of hydrofoils lifting the ama. If there’s too little wind to fly the ama via heeling moment, there is (likely) too little to do it with active foils—even ignoring the problems of foil drag, range of needed lift and velocity—and matching of same. Seeking to optimize foiling is all but guaranteed to de-optimize the auto-flight and both endeavors may fail—and never be tried again because “that didn’t work.” I believe it is better to limit your variables—severely—and then run different experiments with different aims and mechanical models. You can always combine the two later when both are successful and you can draw reliable conclusions.
With the foil already there, i think there would be less total drag by using the lift to keep the ama flying in the first place, and not increase the sensitivity exponentially by mixing the AoA and lift with a foil and the continuously changing power from the driving foil (sail) in the air.
This is an interesting supposition. Run the numbers first. If the maths bear you out, go for it!
Forgive me if this has been covered, but what about the drag of the auto flight paddle in conditions where the ama is not flying much/at all. This is a big loss…how to mitigate.
Marco hit it—the system just parks horizontally—even perhaps auto-parking, or not, as your complexity/simplicity demons dictate
I think there is a potential stability problem with using the sensing foil as a leeway reduction system, as the leeway will increase when the ama lifts out of the water. This will be a positive feedback loop if the sensing foil is also part of the leeway reduction system.
In my setup the changes in leeway will make the system more linear. As the foil lifts out of the water the foil will have less lift creating leeway, but the vaka/centerboard will have more leeway - creating negative feedback loop instead.
Your logic is good, but makes the assumption that this loop is significant enough to require addressing. Still, better safe than sorry; you can try the other way later as an optimization—and optimization it will be; for every ounce of lift you take from the auto-flight blade the way you have it, you must create an offsetting ounce of side-force from your hull in addition to all sideforce necessary for sailing This adds truly useless drag—twice—and may even require additional dagger or leeboard(s) be clipped onto the vaka. I am also concerned about helm balance as the various opposing forces play out in real sailing
I am more interested in stability and an as large range of useful linear function of the system as possible. Once i achieve stable flight i can start playing with added complexities. Right now it is more interesting to achieve flight and maximize synergy and simplicity.
Agreed.
Dave
I feel you are still thinking the sensor/actuator will rotate/not rotate in a binary fashion, always full over. It will not (or should not): As the ama lifts, there is a steadily diminishing force delivered into the system by the actuator. At some point this diminishing force becomes less than the preload due to the mainsheet and the sheet is eased.
The problem I see is that the feedback to the paddle is sheet load. The paddle will not move until the the force developed by the paddle less than the sheet load, then will not stop moving until the force is again greater than the sheet load. In order to get a good linear response to heeling, the system must be precisely tuned so that the paddle force goes below the sheet load fairly soon after the boat starts to heel. If you don’t and you end up working on just the tip of the paddle, the height of the chop on the water surface will become significant and the paddle will simply release the sheet between wave crests. In practice it will be difficult to tune the system because the force developed by the paddle in dependant on the boat’s velocity and leeway angle, both of which vary greatly dependant on heading, sail configuration (reefing) and trim etc.
Heel angle is only indirectly linked to sheet load, hence a system which controls the sheet load will only indirectly control the heel angle. I advocate a system more like the sensor ama configuration because, if configured correctly, it is independent of the sheet load. The boom angle will vary directly with heel angle regardless of other factors.
Mal.
I advocate a system more like the sensor ama configuration
Forgive me please Mal; the term “sensor ama” has become popular in this thread yet I can’t find a consensus on its definition.
Does the term refer only or mostly to the sensor/actuator device shown by Rob Denney for sheet release?
Does it refer to such a system where the sensor ama is only a sensor, only an actuator, always both sensor and actuator, or any of the above?
Does a “sensor ama” definition include “non-buoyant flapper on bendy wand” style sensors, as on moths?
Does a sensor ama gain its vertical reference via buoyant displacement, lift from a small planing surface, or drag upon a wand trailing in the water? It clearly does not include drive from a foil, but I can’t quite pin down what else it excludes or includes. Can it be a combination of the above; perhaps a buoyant body with a flat bottom, acting in displacement mode then transitioning to planing lift? Or perhaps a high aspect ratio “surface planing” foil, but also able to act completely submerged?
Thanks for the clarification.
Dave
I advocate a system more like the sensor ama configuration
Forgive me please Mal; the term “sensor ama” has become popular in this thread yet I can’t find a consensus on its definition.
Does the term refer only or mostly to the sensor/actuator device shown by Rob Denney for sheet release?
Does it refer to such a system where the sensor ama is only a sensor, only an actuator, always both sensor and actuator, or any of the above?
Does a “sensor ama” definition include “non-buoyant flapper on bendy wand” style sensors, as on moths?
Does a sensor ama gain its vertical reference via buoyant displacement, lift from a small planing surface, or drag upon a wand trailing in the water? It clearly does not include drive from a foil, but I can’t quite pin down what else it excludes or includes. Can it be a combination of the above; perhaps a buoyant body with a flat bottom, acting in displacement mode then transitioning to planing lift? Or perhaps a high aspect ratio “surface planing” foil, but also able to act completely submerged?Thanks for the clarification.
Dave
Dave,
I’m using the term ‘sensor ama configuration’ to refer to any system with a horizontal offset between the hinge point and the sensor at the water surface. However, the important point is that the sensor device should more or less sit on the water surface. It should track the water surface and hence be able to report the distance from the water surface to the underside of the ama. Of your examples above, the last one might not fit the definition, but he others will. I’m not concerned with whether the sensor is also the actuator or not. All that matters is that the position of the sensor should directly affect the angle of attack of the sail.
Note, a trailing wand system will fit the definition while moving in one direction, but when the boat shunts the wand would have to reverse direction, requiring it to be forced underwater, so during a shunt it wouldn’t fit the definition.
One other point is that the sheet load should not significantly affect the position of the sensor. For example, if you directly attach the sheet to a buoyant sensor ama a’ la Rob Denny, the sheet load will tend to sink the sensor (and conversely, lift the actual ama). There needs to be enough reserve in the system so that the sheet load does not force the sensor completely under the water surface.
Mal.