Help find copy of Fekete article

Discussion in 'Hydrodynamics and Aerodynamics' started by CasparvdBroek, Jan 19, 2018.

  1. CasparvdBroek
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    CasparvdBroek Junior Member

    That is an earlier paper then the one I am looking for, note different titles.

    Still searching ....
     
  2. Doug Halsey
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    Doug Halsey Senior Member

    In your sketch you show 4 separate trim-tabs. Are you intending to have them control the flap deflections, as well as the wing angle of attack?
     
  3. CasparvdBroek
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    CasparvdBroek Junior Member

    The diagram shows two independant self trimming identical wing sections on the same mast. Each section consists of a main and flap in 60:40 ratio, and two tail plains for controlling the angle of attack to the wind. The tail planes are offset so that their support booms do not interfer with the flap, which has the added benefit of reducing the effect of downwash.
    The flap angle to the main will be controlled by a small stepper motor.
     
  4. Dolfiman
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    Dolfiman Senior Member

    In case not yet spotted, there is also these papers from Elkaim and Boyce on same issue :
    http://citeseerx.ist.psu.edu/viewdoc/download?doi=10.1.1.153.6434&rep=rep1&type=pdf
    http://citeseerx.ist.psu.edu/viewdoc/download?doi=10.1.1.115.7863&rep=rep1&type=pdf
    >>> in the references of this second paper, there is the Fekete-Newman paper you search for, so if you contact Prof Elkaim you could got it :
    Gabriel Hugh Elkaim https://users.soe.ucsc.edu/~elkaim/elkaim/Home.html

    Atlantis project :
    Atlantis Project https://users.soe.ucsc.edu/~elkaim/elkaim/Altantis_Project.html
     
  5. CasparvdBroek
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    CasparvdBroek Junior Member

    Y
    Yes interesting reading.....I will contact the Prof
     
  6. tspeer
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    tspeer Senior Member

    I've some experience sailing a landyacht with a tail-controlled wingsail. We experimented with tail control alone, tail control coupled with flap deflection, and fixed tail with manual positioning of the wingsail. The tail control was quite effective, and the yacht could be sailed for extended periods hands-off.

    Your design is obviously heavily influenced by the Harbor Wing configuration. Although I haven't been sailing on the Harbor Wing trimaran, I have been aboard the boat at the dock and discussed the design with Mark Ott.

    I think you should use tail control over servo control of wing angle of attack. The tail control can be done with no sensors, and you have redundant surfaces for fault tolerance. Direct servo control of the upper wing segment will be difficult because you will need to run a torque tube inside the mast to control the wing. Direct control of the lower wing segment can be done from the deck.

    I would also lean toward mechanical control as much as possible because electronics can be unreliable at sea. Mechanical control can also be entirely manual, with no requirement for electrical or hydraulic power. Tail control could be implemented with a linkage that was run up through the mast. We used Morse cables on the landyacht, but that wingsail had stays and did not need to rotate 360 deg. A vertical pushrod with a swivel, aligned with the axis of rotation, could actuate the tail control while still allowing the wing to rotate freely.
     
  7. Rumars
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    Rumars Senior Member

    The article you are searching for does not exist in electronic format so you can not just download it from somewhere. Plus it was published in a scientific journal so somebody had to pay for it. The normal thing to do would be to go to a library and read it there. But no library in New Zeeland holds this journal so far back (yes I checked). So the next thing to do would be to request an international interlibrary loan at your local library.

    Let me make it simple for you. Go to this webpage: subito e.V. - Documents from libraries https://m.subito-doc.de/?lang=en register, and they will deliver by mail a scanned copy within 72 hours. Yes, you will have to pay a fee. Yes I checked, they can deliver, the ETH Zürich Library holds the journal for the specified year.
     
  8. CasparvdBroek
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    CasparvdBroek Junior Member

    Thank you for your input …. I have no direct experience with wingsails so you guidance is particularly appreciated.



    I have given some thought to control mechanisms but remain stuck on whether there is a design advantage in using a tail plane.



    Attaching a tail to the wing adds to the structural complexity and weight of the wingsail. Plus adding to the rotational moments and so reducing responsiveness to control and stability. Both points seem important as 'Fekete' mentions predecessors having problems controlling wingsail oscillations excited by platform roll and pitch.



    Platform motion can be reduced by using hydrofoils or the wingsail could be dynamically mass balanced about the roll and pitch axes, to tightly couple it to the platform, reducing induced motion about the its axis of rotation. I am opting for dynamic balance as I do not wish to sail at the speed needed for hydrofoils.



    I notice from the Harbor Wing photos that they have opted for dual high aspect ratio tail planes and have offset the axis of rotation from the 1/4 chord point. Guessing, this increases the correcting turning moments and therefore its responsiveness to perturbations. But a tail remains a simple proportional controller with no means to overcome dead zone effects (like bearing friction) or allowing for the wingsails current rotational momentum/velocity.



    If I opt for a servo mechanism to set angle of attack, the type of control can be optimized for responsiveness and stability without the penalty of counter lift, drag, weight, and swept area introduced by the tail. Also a control strategy may be found that is able to predict the effects on the apparent wind caused by platform motion. But the wing/flap combination would be required to weathercock when no drive was required, for example at anchor or on a mooring.



    So not just looking for the above article by 'Fekete' but also any data on wingsail experience in a real world sea state.
     
  9. CasparvdBroek
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    CasparvdBroek Junior Member

    Thank you for this. Was all keen until they asked for a signed document giving them rights to my credit card account for unspecified amounts. Will need to think about that, wish it had been a simple PAYPAL transaction.
     
  10. tspeer
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    tspeer Senior Member

    A wingsail needs to be "flown" 100% of the time, since it can't be taken down like a soft sail, and it doesn't luff. An electronic control system becomes safety critical, because failure to control the wingsail can be catastrophic. A tail is a low-cost alternative to the kind of sophisticated control used by the Walker Wingsail.

    A tail is quite effective at gust load alleviation. When a gust hits, the wingsail sheets out by itself and the effect of the gust is greatly reduced compared to the response of a soft sail. A tail can also be good for performance, as it maintains the angle of attack within a very narrow range. The world landsailing speed record was set with a tail-controlled wingsail, showing that it can be a good solution even when performance is critical.

    I think it's very important to mass balance the wingsail and tail, regardless of the kinds of speed you want to hit or how stable the platform is. A wingsail that is free to rotate will be affected by a seaway, and in light winds the pendulum effect of the unbalanced mass may totally overcome the ability of the tail to trim the wingsail.

    Macquarie Innovation is the only wingsail I know that has fluttered, but when it occurs, flutter can totally destroy the wingsail. I have pitchpoled a landyacht backwards when the rotating wing mast fluttered during a tack. A wingsail not only rotates, it also translates sideways due to flexibility in the rigging, hull, or mast. When it accelerates in translation, it will also rotate due to unbalanced mass. If the center of gravity is behind the rotation axis, the rotation due to linear acceleration of the head will be in the unstable direction, and this can lead to flutter. If the center of gravity is ahead of the rotation axis, it will have a stabilizing effect. Because the foot of the wingsail does not translate and the head experiences the most linear motion, it is better to put counterweights up high. If the wingsail has stays, just above the hounds is a good location for a mass balance boom.

    A single tail surface can have a dead zone around zero lift, either due to viscous effects on the tail itself or from being in the wake of the wingsail. The twin tails of Harborwing ensure the tails are out of the wake of the wingsail. They can also be toed in slightly to avoid any dead zone. This makes the wingsail responsive at zero lift when you want the wingsail to stay feathered into the wind.

    The reason Harborwing's wingsail was divided into independent top and bottom panels is because an earlier catamaran prototype experienced difficulties when moored to the dock. Just because a wingsail is feathered so as to produce zero net lift does not mean that it will have no heeling moment. Wind shear acting along the span can induce substantial heeling moments in a feathered wingsail. Their solution was to divide the span into two panels so each could react to the local wind angles. This greatly reduced the heeling moments when the wingsail was feathered.

    The counter lift from a tail does not have to be very large. This depends on how balanced the wingsail is to begin with, and the implementation of the tail volume. Tail volume is the tail planform area times the length of the tail's moment arm. For the same tail volume, you can have a large tail on a short arm, or a small tail on a long arm. Either configuration will produce similar control moments for the same angle of attack disturbance. However, the large tail/short arm approach will have a higher force on the tail. The aerodynamic damping goes up with the square of the tail arm when the tail volume is held constant, so the small tail/long arm approach has much more aerodynamic damping than the large area/short arm configuration. This aerodynamic damping not only makes the wing settle down quickly after a control input, it also helps to smooth out the rotation in turbulence.

    The other thing that is often overlooked is the tail operates in the wake wash from the wing. Although the tail may produce lift in the opposite direction from the wing, the wake wash causes this lift vector to be tilted forward. In other words, it has negative induced drag. What matters is really the combined lift distribution of both the tail and the wing.

    The principal disadvantage of the small area/long tail approach is the volume swept by the tail. The Walker Wingsail used the large surface/short arm approach and was able to keep the tail completely contained within the beam of the trimaran. Harborwing also stays within the confines of its platform.

    If you opt for active electronic control instead of a tail, I recommend you have a temporary tail and mass balance that is attached to the wing when it is moored. This will eliminate the need to have the electronic control active at all times, and protects against failure of the electronics. After all, it is likely the craft will spend more time moored than it will spend sailing.
     
  11. Rumars
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    Rumars Senior Member

    I am not aware of any DD service accepting paypal. Try out another document delivery service, for example the one at MIT. Journal Articles & Conference Proceedings Order Form :: Document Services :: MIT Libraries https://libraries.mit.edu/app/docs/orders/journal
    The british library also holds the paper and has a DD service. Be avare that prices may vary.

    You have to understand that customers using subito usually do not do it for a single article. They are geared toward heavy users with monthly billing. But there also should be a form for individual payment authorizations not only the general one. Or you can use a separate creditcard on wich you transfer funds on demand (like a prepaid or a debit card). Just ask your bank of choice what options they have for you. A separate visa or mastercard debit card should cost nothing and is good online security anyway. If your bank has good online banking then even the hassle of transfering funds is easy.
     
  12. CasparvdBroek
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    CasparvdBroek Junior Member

    Thanks for your input, I used the British Library document service. Paid the monies and 4 days later the Fekete article was in my email.

    No longer searching
     
  13. Rumars
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    Rumars Senior Member

    Glad I could be of assistance. I hope the article helps you.
     
  14. CasparvdBroek
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    CasparvdBroek Junior Member

    During a wind gust , Fin Utne found that the self trimming wingsail on 'Flounder', "turned to a new position with hardly any change in the boat's heeling."

    On the other hand Elkaim on 'Atlantis' was weary of changes in wind speed that could lead to a capsize.

    It would be interesting to understand a mechanism of automatically coping with rapid changes in wind speed and am wondering whether it relates to the drag components contained in the wings turning moments.


    Fekete commented that performance improved considerable when the wing was statically balanced about the pivot axis and also balanced so that the products of inertia about the boats pitch and roll axes with the pivot axis where zero. This seems possible as static balance depends on mass and distance forward of pivot axis whilst products of inertia about axes can be zeroed by selecting suitable vertical position for the balance arm.

    Fekete commented that the wing extension that he later added to the top of the wing was built to achieve static balance locally at all sections of the extension.

    Presumable decoupling wing rotation from platform motion would also then apply to flexing of the wing due to changes in wind speed, as this could be approximated as pitch and roll angular accelerations. Assuming that the pivot, pitch and roll axes intersect.
     

  15. tspeer
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    tspeer Senior Member

    My experience with a tail-controlled wingsail on a landyacht was the tail control was very effective at alleviating the impact of gusts. Which, when you're racing, may not be such a good thing because the yacht also didn't get the immediate acceleration from the gust. The tail reacted to the change in apparent wind angle, sheeting out automatically as the gust hit. The ability of the tail to maintain a constant angle of attack was remarkable. I could set it for just below stall, sail hands-off for a period of time, and when I pulled in on the boom to manually increase the angle of attack a little bit the leech telltales would lift immediately.

    I don't believe drag came into it in any significant degree. When there's an increase in wind strength from a gust, the apparent wind increases in magnitude and shifts aft. This not only increases the force on a fixed sail, it also increases the angle of attack. The angle of attack control from the tail reacts to the shift in the direction of the apparent wind, nullifying the part of the increase in force due to the change in angle of attack. The shift aft in the apparent wind also changes the orientation of the lift vector, pointing it more forward and less to the side. The combined effect of all these influences was to make for only a modest increase in heeling moment when the gust hit.

    I don't think the axes have to intersect. Rotation about a displaced axis is equivalent to rotation about the pivot plus a linear motion of the pivot.

    The flexing of the wing is not the only thing at play, here. The flexing of the platform is also important. An increase in heeling moment results in an increase in tension in the stays and a compression force on the mast. The compression will flex the platform, which loosens the stays. Imagine the pivot staying fixed and the platform flexing upward under the stay tension. This loosening of the windward stays lets the wing tilt to leeward. So there's lateral motion of the head of the wing even if the wing itself were perfectly rigid.
     
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