Auto-Flight
I am sorry for the lack of progress the last couple of days. I am waiting for the paint to dry on my 70 cm long new foil. I made it huge so can cut it down to a good size after testing it. It is a totally unscientific foilshape made with a beltsander. 700 mm long, 7 mm thick and 55 mm wide (a piece of plywood i had laying around). A very simple ogive section.
No pics today.
I hope i can test-sail it tomorrow.
Cheers,
Johannes
First off, I want to say that there are many possible solutions to any challenge. It is less important that any experimenter use “my” solution than it is that he/she/they experiment with any viable solution. I believe that auto-flight in multihulls has far-reaching ramifications for both speed and comfort, and via the “beneficial spiral,” on structural loading, thus weight, cost and enjoyment of our boats.
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.
I have considered most of these at one time or another. Most will work, some will work well. I made a couple of early design choices in order to narrow the field:
1) I wanted the actuator to take energy from the lift side of the fluid dynamics of the boat, not the drag side. Moth-type sensors, ama sensors and wands dragging in the water are all pure drag devices. This does not make them “bad” or even ineffective, it only means that the control device will impede the forward movement of the boat more (10X more, if a foil has a 10:1 L/D, for instance. Multiply that again by 2, since a drag-type sensor can only move through something less than 90 degrees, while a lift-type sensor can approach 180 degrees)
2) I wanted to combine sensor and actuator in a single piece if possible, simply for reduced parts count, cost and robustness
Do you agree with either restriction? Within their constraints, can you suggest a better device than auto-flight? Don’t get me wrong, I’d be very happy to be proven wrong, so long as the superior gadget were similarly efficient and/or simple
All that matters is that the position of the sensor should directly affect the angle of attack of the sail.
We need two things; we need to sense the approximate water surface and we need to extract sufficient power to alter the angle of attack of the sail. A further reason I didn’t choose devices fitting your definition of sensor ama is that these often follow the water surface precisely, thus need attenuation to avoid reacting to small waves. Yes, they can be made narrow, even tapered (as the auto-flight blade is), or they can have flexible, even shock-absorber devices in their linkages, but the fact remains they require attenuation. This introduces an entirely new set of problems requiring careful matching of materials’ physical abilities, calibration and tweaking—of relatively small and fragile parts. I thought—still do—that a narrow, tapered sensor carried near vertical on or near the ama is a good compromise, and also that such a profile shape might make an effective actuator at the same time. (BTW, the “near vertical” aspect only needs to be approximate. Tilting away from vertical—yielding horizontal offset—isn’t precluded)
Long way around to say it’s not as simple as referencing only the position of the sensor; the actuator must move in order to extract power efficiently, so if we limit ourselves a sensor/actuator combination, its position must vary over time without losing track of the ama’s position. You suggest referencing heel angle which is fine, but the ama’s vertical distance from the water—without knowledge of the angle of heel, even the rate of change of that angle, is all that is necessary to achieve both position AND efficient power generation. The Auto-Flight gadget, surely, is only one of any number of similarly simple solutions.
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.
This is important I agree, but only if the forces available are small. A powerful actuator need never be overcome by the sheet, and a sensor which cannot be driven under by its nature is not difficult to design. On the other side of the coin, designing sheet loads to be small opens additional sensor-types to be considered for sensor/actuator combinations, and allows the entire system to be smaller, requiring less power.
Dave
On the other side of the coin, designing sheet loads to be small opens additional sensor-types to be considered for sensor/actuator combinations, and allows the entire system to be smaller, requiring less power.
And that is why I like the idea of using a heel sensor in combination with a tail controlled wing.
For any system where the sensor is also the actuator, directly controlling the sheet, the actuating force must be derived from the motion of the vessel through the water and will translate into additional drag. If the actuating force can be derived from some other source, the actuator can be smaller and less draggy.
On the other hand, a tail controlled wing comes with it’s own inefficiencies, but if you had decided to use a tail controlled wing for some other reason, adding an auto flight system comes with little additional drag cost.
Mal.
And that is why I like the idea of using a heel sensor in combination with a tail controlled wing.
For any system where the sensor is also the actuator, directly controlling the sheet, the actuating force must be derived from the motion of the vessel through the water and will translate into additional drag. If the actuating force can be derived from some other source, the actuator can be smaller and less draggy.
On the other hand, a tail controlled wing comes with it’s own inefficiencies, but if you had decided to use a tail controlled wing for some other reason, adding an auto flight system comes with little additional drag cost.
Mal.
I agree with you, Mal, but there’s only us chickens out there—all power consumed aboard a sailing vessel eventually comes from wind over wings. Any auto-control therefore must result in some minute amount of increased drag and consequent reduced speed of the yacht. There are no other sources.
I’ve said many times that optimization is worthwhile, but at the same time, I wouldn’t want to leave the impression that controls such as auto-flight are limited to any narrow cross-section of boat types or rig choices.
I’d note that, for the 70+ years that windvane self-steering has been used in everything from the most casual of cruising to flat out open-ocean racing, the drag of actuators’ power-draw is not cited as a significant impediment—anywhere I can find at least. In point of fact, I’d argue the opposite, that an auto-flight mechanism, as you have said yourself, serves the dual purpose of maximizing average rig thrust over time, as well as reducing several sources of drag directly, without the exhausting input—and unavoidable sub-optimal performance—of hand-controlling the boat. I’m confident the increased average performance of Auto-Flight far outweighs the additional drag—all the more so as one optimizes the system.
I would value input from you regarding alternative systems. They should be comprehensive; ie: not simply sensors or simply actuators, or “magic happens here” black boxes, but complete systems. Your conservatism nicely compliments my “Let’s go try this!” progressiveness. Together I’ve a feeling we could do great things. 😉
Dave
Hey Johannes, how is your auto-flight mechanism coming along? Are you still working on the device for your model? I’m dying to hear about your progress! 😊
Cheers,
Marco
No progress on the autoflight device. We have been out sailing in our Marieholm 26 monohull (similar to the Folkboat and International Folkboat), so there has been no time to experiment with my proa models.
I will post more once i have tried it.
Cheer,
Johannes
I have tested this auto-flight device a couple of times, but without any real success.
I have never achieved stable flight. I think there is to much friction in the system and there is to much drag in my very simple and crude sensing foil.
I can achieve short stable flight without the foil immersed, but the wind has to be very even and stable.
With the foil immersed it needs more wind or a steeper angle towards the wind to lift the ama, but once flying it just keeps lifting the foil out of the water and then capsizing the proa.
I do think it is possible to get a stable flight, but the system needs better foils, less friction and a better range. It seems very sensitive to waves, so the sensing foil needs to be very deeply immersed, which gives more drag, and a more exposed and weaker foil.
I will not work on this device any more at the moment, even though i like the idea.
Cheers,
Johannes
With the foil immersed it needs more wind or a steeper angle towards the wind to lift the ama, but once flying it just keeps lifting the foil out of the water and then capsizing the proa.
Johannes,
I am probably wrong and appreciate that there are frictional issues etc, but if the new set up is the same as the photo you posted originally (apart from a new foil), it looks like in the photo that the sheet goes directly to the foil.
Shouldn’t it go to the foil somehow via a suitably placed turning block on the ama first. Otherwise mainsheet tension is always going to hold or pull the foil further into uplift (canted to windward) mode and not pull it to downlift (canted to leeward) mode to provide the travel and sheet release?
And it looks like the lines and shock cord you have used to stablise the foil, countering mainsheet pull need to be reversed, so that there is additional tension on the foil trying to keep it to uplift mode, countering the sheet tension pulling it to downlift mode.
Hope this makes sense…..Thanks for all your efforts in any case.
Rob