Wing Sails on Proas!
There is an interesting asymmetry in Mal Smith’s plot of flap angle versus wing angle (post #72). The ‘full power’ curve peaks at a wing angle of 70 degrees rather than the 90 degrees of a beam reach. This effect is probably the result of the pivot being close to the cam and could be reduced by increasing this distance. Given the practical limits to how far this distance can be increased it looks like the effect would need to be factored into a detailed design. The difference between the flap angle at WA = 70 degrees (beam - 20) and at WA = 110 degrees (beam + 20) is about 22%. This will affect the lift of the wing-flap combinations to some extent. The asymmetry could be reversed by placing the pivot on the other side of the cam (i.e. towards the leading edge of the wing).
Perhaps Mal could tell us what the figure for wing angle represents - is 0 degrees when the leading edge of the wing is towards the bow or towards the stern? It would then be possible for individual designers to put the maximum flap condition either ahead or astern of beam reach as they think suitable.
The Worsley cam and flap system gives maximum camber and angle-of-attack on a broad reach and steadily reduces both as the wing comes to a close-hauled orientation.
The heeling component of the wing’s lift is small on a broad reach (as with any sail) and the drive component is large. As the boat gathers speed and the apparent wind swings towards the bow then the camber and AoA (and thus lift) are reduced by the cam and the heeling component (which is a large proportion of the lift when close-hauled) is thus kept within bounds.
Thank you, Peter H.! So the relationship between heading (of the vessel) and wing trim is to reduce heeling forces as you head up from a beam reach. That makes sense!
Is the goal to have the heeling component constant for all courses? Why reduce heeling as you fall off from a beam reach? I thought I saw Saildrone sailing on some pretty deep downwind courses. Why feather on a dead run?
Thanks Mal and Skip for your helpful illustrations.
And welcome Peter Worsley to the forum. Glad to have you!
Best,
Chris
... The results ... show that as I suspected there is not a lot of flap movement in relative terms at small wing angles (i.e. close hauled). This may be ok if, as I did, you configure it to give large maximum flap deflections. If not, you won’t get any decent thrust out of the system when close hauled.
A couple of thoughts. I’m not sure if these are solutions or just work-arounds, but couldn’t you cure the above by: 1) lengthening the tail boom, or 2) increasing the tailplane area, or 3) more carefully aerodynamically balance the main wing, reducing tailplane power requirements, or 4) altering the system so the cam drives a trim tab only, which then drives the tail boom to much greater deflection, or 5) any combination of the above? Point is, there are many adjustments and customizations available within the concept, without making things more complicated and without foregoing its advantages.
Somebody mentioned “user-friendly” as one of Peter’s potential design goals. I won’t put words in his mouth, but perhaps he was thinking instead that when close-hauled, very little wing deflection is wanted for best VMG (hardwings typically have their max L/D at 4-6 degrees AoA), while at a beam reach apparent (broad reach, true), the wing wants to be operating at max Cl, which is closer to 22-25 degrees (for a 1-element hardwing)
If the “working range” or your wing is going to be sort of +/- 16-20 degrees, this is going to be difficult to maintain at optimal with a non-automated system. Hand-holding the cam or hand-setting the tail’s deflection will thus lead to even less optimal average settings of the wing, over time.
Every actual boat (or mechanism) is a compromise; this one doesn’t do the absolute best of every single thing, but it is a remarkably good compromise.
Dave Culp
...... The asymmetry could be reversed by placing the pivot on the other side of the cam (i.e. towards the leading edge of the wing).
Perhaps Mal could tell us what the figure for wing angle represents - is 0 degrees when the leading edge of the wing is towards the bow or towards the stern? It would then be possible for individual designers to put the maximum flap condition either ahead or astern of beam reach as they think suitable.
0 degrees is when the the leading edge of the wing is pointing towards the bow. I had the model set up so that moving the can aft gives forward thrust (as per Peter Worsley’s videos). If you want to reverse this, arrange the flap actuating push rod to cross over so that the flap actuating lever is on the opposite side of the flap.
... The results ... show that as I suspected there is not a lot of flap movement in relative terms at small wing angles (i.e. close hauled). This may be ok if, as I did, you configure it to give large maximum flap deflections. If not, you won’t get any decent thrust out of the system when close hauled.
A couple of thoughts. I’m not sure if these are solutions or just work-arounds, but couldn’t you cure the above by: 1) lengthening the tail boom, or 2) increasing the tailplane area, or 3) more carefully aerodynamically balance the main wing, reducing tailplane power requirements, or 4) altering the system so the cam drives a trim tab only, which then drives the tail boom to much greater deflection, or 5) any combination of the above? Point is, there are many adjustments and customizations available within the concept, without making things more complicated and without foregoing its advantages.
There is probably something you can do with additional cams or by adjusting lever ratios. Ideally you would have a steep curve for the first/last 10 degrees and a flat curve everywhere else.
At he end of the day, it might be cheaper and easier to do it all with electronics (once a system has been developed and is in production). I like the idea that you could have a heel sensor so that you could program the system to fly the ama at a precise and constant heel angle. The big advantage of the tailplane controlled wing is the minimal amount of power required to control it.
There is probably something you can do with additional cams or by adjusting lever ratios. Ideally you would have a steep curve for the first/last 10 degrees and a flat curve everywhere else.
Sure, but that’s precisely what I want to avoid—any additional complication. Moving parts which don’t exist in the first place can never fail. 😉
At he end of the day, it might be cheaper and easier to do it all with electronics (once a system has been developed and is in production). I like the idea that you could have a heel sensor so that you could program the system to fly the ama at a precise and constant heel angle. The big advantage of the tailplane controlled wing is the minimal amount of power required to control it.
Same story regarding electronics. I’m an Old Guy, but still shudder whenever I think electronics and salt water. As recently as 5 years ago on a delivery, a *very* expensive autopilot actuator only a couple of years old failed for salt intrusion—and the spare was frozen as well—in its box. Three of us were left steering a 50’ tri by hand, 2 hrs on and 4 off, for 48 hrs offshore. Worsley’s little device is 100% mechanical, so can be indefinitely repaired with duct tape and bailing wire. I like that.
You could get your heeling sensor using either a pendulum (might consider running it underwater, for damping), or a little flap-type surface follower, like Moths use for setting foiling height. This could be on the centerline, right under the cam so linkages needn’t be very long. There is probably enough oomph in either sensor to bias the Worsley system since, as you point out, it consumes so little energy.
Attached is perhaps the slickest—all mechanical, of course—sheet release I’ve seen. Props to Rob Denney. References only the hight the hull rises, has huge leverage and is dead simple. Small changes could make it auto-resetting, and also with analog rather than its present binary actuation.
BTW, I see that ProaFile’s server migration today seems to have trashed all the attachments on this forum—and the Ed’s email is bouncing as well. Likely it will all be fixed tomorrow, so maybe don’t adjust your television sets just yet. 😉 —-I’ll try to upload the attachment again on Friday; the server won’t let me today—-
Dave Culp
Hey Mal,
Here’s a question for you: The Ed posted a nice pic of SailDrone’s tail plane in this thread, at: http://saildrone.com/index.php/technology This seems to show that it is NOT actuated; but remains at a fixed, zero angle of attack. Only the relatively tiny trim tab/flap actuates, and it’s not larger than maybe 1 sq ft. This does not look, to my eye, as enough power to bias the wingsail, which is about 100 times as large. Do you suppose Richard could be using a flexible stalk between wing and tail? We spoke of it several years ago, but I’d have thought that a flexible empennage would bring to the table more new problems than it solves old ones… Thoughts?
Er, perhaps I’ve solved it; another look at the photo from SailDrone above shows what looks like a pivot pin at the *front* of the empennage, just before it enters the wing’s trailing edge. That would allow the entire tail and empennage to swing as a unit, all controlled by the trim tab. Clever.
Dave Culp
Hey Mal,
Here’s a question for you: The Ed posted a nice pic of SailDrone’s tail plane in this thread, at: http://saildrone.com/index.php/technology This seems to show that it is NOT actuated; but remains at a fixed, zero angle of attack. Only the relatively tiny trim tab/flap actuates, and it’s not larger than maybe 1 sq ft. This does not look, to my eye, as enough power to bias the wingsail, which is about 100 times as large. Do you suppose Richard could be using a flexible stalk between wing and tail? We spoke of it several years ago, but I’d have thought that a flexible empennage would bring to the table more new problems than it solves old ones… Thoughts?
Er, perhaps I’ve solved it; another look at the photo from SailDrone above shows what looks like a pivot pin at the *front* of the empennage, just before it enters the wing’s trailing edge. That would allow the entire tail and empennage to swing as a unit, all controlled by the trim tab. Clever.
Dave Culp
I am in communication with George Seyfang - one of the consultants for the Saildrone project. I will ask him if he knows whether the small trimtab on the tail plane is the only control element, or whether there is other movement taking place in the “stalk”.
I am in communication with George Seyfang - one of the consultants for the Saildrone project. I will ask him if he knows whether the small trimtab on the tail plane is the only control element, or whether there is other movement taking place in the “stalk”.
Thanks Peter, it would be good to know the answer to that.
In answer to Dave, if the trim tab does control the tailplane, the tailplane itself would have to be hinged at or somewhere in behind tailplane leading edge for the thing to work. I suspect (and hope, because it would be very cool) that the tailplane is fixed and that the trimtab is enough to control it. This may be possible if the entire wing is well balanced. We’ll have to wait for an answer from George Seyfang to know for sure.
Same story regarding electronics. I’m an Old Guy, but still shudder whenever I think electronics and salt water. As recently as 5 years ago on a delivery, a *very* expensive autopilot actuator only a couple of years old failed for salt intrusion—and the spare was frozen as well—in its box. Three of us were left steering a 50’ tri by hand, 2 hrs on and 4 off, for 48 hrs offshore. Worsley’s little device is 100% mechanical, so can be indefinitely repaired with duct tape and bailing wire. I like that.
Dave,
I hear you on the electronics. It would require maintenance. In this case however, the control board can be sealed inside the hull, yes I know that the inside of a hull gets damp, but it does improve the chances. The flap actuator can also be inside the hull, although a simple servo up in the wing is an elegant solution. The height sensor can also be mechanically fed back into the hull (no electronics outside). For the height sensor I’m thinking a Moth type wand is probably the simplest.
There are interesting things happening in the electronic control world which make it easy to experiment with control systems e.g. http://www.arduino.cc , which makes it tempting to investigate the possibilities.
Concerning the question of mechanical system versus electronic system.
Ever since the introduction of the Walker Wingsail it has been evident that electronic control can be achieved.
Everything that the mechanical system has, can be done - and more! We also know that systems can be made completely waterproof and very reliable, as demonstrated by the performance of the Saildrone.
But do you want to? when a simpler system exists which can do nearly the same thing?
Typically, you need sensors, a computer that has to be programmed, debugged and tested, servos, batteries, solar panels to complete an electronic system, then there is the cost.
Using wings instead of sails is a big step beyond traditional sailing (which is still the norm nowadays). Using self-trimming wings is an even bigger step. Maybe computer control is a step too far at the moment.
I have tested a radio control link between the operator and the tail control on my boat. It worked well, but somehow it didn’t seem right. I felt it was bringing extra complication to something which could be made simpler. Admittedly, it’s a moot point, but I think it’s more comfortable to go with a mechanical system which uses materials that can be found in your backyard, is simple to understand, and can be repaired and fettled on the hoof, with no electricity involved?
0 degrees is when the the leading edge of the wing is pointing towards the bow. I had the model set up so that moving the can aft gives forward thrust (as per Peter Worsley’s videos). If you want to reverse this, arrange the flap actuating push rod to cross over so that the flap actuating lever is on the opposite side of the flap.
For those who want to investigate the geometry of this the attached image may help.
I suspect (and hope, because it would be very cool) that the tailplane is fixed and that the trimtab is enough to control it. This may be possible if the entire wing is well balanced. We’ll have to wait for an answer from George Seyfang to know for sure.
If the wing and the tail are both fixed relative to each other - does it mean that the trim tab has to provide the whole force to set the angle-of-attack of the combined wing+tail ?
Hey Mal,
Er, perhaps I’ve solved it; another look at the photo from SailDrone above shows what looks like a pivot pin at the *front* of the empennage, just before it enters the wing’s trailing edge. That would allow the entire tail and empennage to swing as a unit, all controlled by the trim tab. Clever.
Dave Culp
I see it as well, there is that sort of a vertical pin, on the pole, right behind the trailing edge of the main wing…
BUT: if the tail can pivot freely around that vertical axis located at the trailing edge of the main element, how is the side force of the tail, created by the trim tab, going to exert a turning moment on the main wing to give it an angle of attack to the wind?
I suspect (and hope, because it would be very cool) that the tailplane is fixed and that the trimtab is enough to control it. This may be possible if the entire wing is well balanced. We’ll have to wait for an answer from George Seyfang to know for sure.
If the wing and the tail are both fixed relative to each other - does it mean that the trim tab has to provide the whole force to set the angle-of-attack of the combined wing+tail ?
Yes. This may seem like a tall ask, but if the trim tab (actually, flap) is given a large deflection, it can cause the tail to generate some significant side force. It can be deflected by up to 90 degees, in which case it would act like a gurney flap.