Mast Aft Wing Sails???

Discussion in 'Sailboats' started by mij, Nov 5, 2013.

  1. mij
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    mij Junior Member

    I've decided to start a new thread on this type of rig, so for the sake of completeness I will repeat some of what I posted in the "Aft mast rigs???" thread.

    I should start by stating that all my testing is on a model scale, at this stage on boats less than 1000 mm. I've been building wing sails for 650 mm multihulls for the last year. These wings are constructed from Depron foam, partly because it produces light wings, but also because it is possible to build wing sails quite quickly (2-4 hours per wing, depending on the complexity). I started to build mast aft wing sails following the methods described in a "Delta rig" thread on the rcsailing forum. One of the reasons that I was attracted to them was that I had found it white tricky to set up a conventional wing sail on a model boat, whereas because the mast aft wings simply pivot on swivels on the deck and the mast, the sails are very simple to install. For a monohull there is a lot of rigging to handle the stresses on the mast, however on a multi hull the rigging is very simple.

    I'm not a sail maker, or a fluid dynamics expert, so my efforts have been a bit hit and miss. After some months, I have just started to have some success and I'm starting to see things that can be explored with this rig. When I say "success" I should qualify the statement. Today "success" involved placing last in 3 races and being lapped around a short course twice. This was in very light winds, insufficient for the sail to set nicely. However, when the wind got up the boat seemed to be competitive against very similar boats with conventional rigs. Given the limited development time I think that there is plenty of room for improvement.

    One aspect of this type of sail that I think has potential is the ability to have multiple wings (see attached image) I think that this opens up a range of possibilities, such as constructing an airfoil from multiple individual airfoils, and introducing leading edge elements to improve lift. This is the reason that I have started this thread, as I intend to explore some of these ideas over the coming months.

    Below are links to all my efforts to date (in chronological order), if you have the stamina to look you will see that the initial efforts were not very promising, but they do slowly improve (* indicates videos that I think are worth watching).

    400mm Trimaran
    https://www.youtube.com/watch?v=Nsq43UPAGp0

    650mm Monohull
    https://www.youtube.com/watch?v=NVRlmR_CmyY

    800mm Catamaran
    https://www.youtube.com/watch?v=YdNKDvXhUiw
    https://www.youtube.com/watch?v=xberNtv-pcE
    https://www.youtube.com/watch?v=Gj6oIkA43E8
    https://www.youtube.com/watch?v=BqkIA_WHzTs
    https://www.youtube.com/watch?v=IbBxojGxIa0
    https://www.youtube.com/watch?v=1jzP7Qvy2wI
    https://www.youtube.com/watch?v=Hnj9KxqaOb8
    https://www.youtube.com/watch?v=l_57OXVHMVs *

    650 mm Monohull (Dragon Force)
    https://www.youtube.com/watch?v=Q93UN4Qz0Pw *
    https://www.youtube.com/watch?v=OGOQkSUJ0V0
    https://www.youtube.com/watch?v=oSXtnIXjp1Y *

    To summarise the posts in the previous thread:


    In response to my question regarding why I get weather helm with this boat when I have the sails positioned where I calculate they should be:
    • SukiSolo stated: Forgive me if this sounds naive, but have you accounted for all the extra drag from the spar itself?. It is sufficiently far aft to give a lot of aft drag to the balance. Rigging too may affect it, as it is all effectively aft of the CLR. - No I didn't include this in the calculation, and yes I agree that this would have an effect.

      Nominally a wing is more efficient and I understand the CLR is much closer to the CofE with wing rigs or wingmast rigs. It could be the order of several percent which is significant.
    • Brian Eiland asked :Clarification? You are claiming you get weather-helm with the rigs pictured above....not lee-helm, is that correct? (the vessel has a strong tendency to turn into the wind?) - Yes, definitely Weather helm, although the rigs as they are show are in a balanced position (slight weather helm)
    • Sharpii2 said: I noticed it has a very deep fin keel.

      As the boat heels, the Center of Lateral Area (CLA) shifts to windward, as the Center of Area (CA) of the sails shifts to leeward (as the CA is about halfway up the wing sail(s) and the CLA is about halfway down the fin keel).

      Moving the draggy mast, with its spreaders and rigging further aft only adds to this.

      Calculating a sailboat's balance, based on its rig and hull profile, is always a dicey matter, as it is really a three dimensional problem, not a two dimensional one.

      I once had an instructor avoid me for over a week, as I tried to pin him down on just how far forward I should put the CA on a steel gaff cutter design I was working on.
     

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  2. groper
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    groper Senior Member

    I admire the effort, however one thing i just cant get past is the extra drag associated with a naked mast. With a conventional rig, the drag of the mast itself is largely offset by the sail attached to it - assuming a nice rotating wing masted main of course.

    It will be interesting what sail plan configurations are possible and the potential ease of which they could be implemented in a full size yacht - would be glad to hear more in this regard.
     
  3. mij
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    mij Junior Member

    The "naked" mast is certainly a disadvantage. Something I hope to get to eventually is to have the mast as one of the wings. I think that this will be achievable for a multihull, but may be a bit too difficult for a monohull.

    I will leave it to those who know what they are talking about to speculate on the possibility of implementation at full-scale.
     
  4. Skyak
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    Skyak Senior Member

    One major advantage of wing profiles is that they have large cross sections in which to build the structure needed. I would think that the aft mast could be designed out of any of these configurations. At the very least I would replace the fore stay with a solid compression tube to eliminate the back stay and it's requirements.
     
  5. mij
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    mij Junior Member

    For the sail configurations that I have made to date I agree that they could be built without a mast aft arrangement. However, the sail I'm currently working involves the airfoil comprised of multiple airfoils idea I described above. I reckon that this would be a bit more difficult to implement without a mast aft configuration (diagram attached - black represents booms and mast, colours the cross section of wings and grey the hulls of a cat). Not impossible of course, but you would need a structurally supported mast close the front of the boat.

    (Don't ask how the top of this sail is going to rotate/twist as I haven't worked it out yet).
     

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  6. Skyak
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    Skyak Senior Member

    I would say that mast-aft is not helping you in that configuration. A three element wing will likely be best supported with a compression (or bending) member up the center.

    Slots can be used to delay stall to a higher angle of attack if they are done right- with controlled size and position relative to the next foil. Your three separated high aspect foils shouldn't have much problem with stall and are not in position to help each other -the master boom would have to bend.
     
  7. mij
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    mij Junior Member

    My diagram might not be adequately describing the arrangement. The main boom is attached at the front edge and can swing like a normal boom.

    I thought about having the main boom bend, but opted for having the base of the central foil slide perpendicular to the main boom. I think that this should enable the three foils to assist one another. The interaction would be better if there was more overlap, but I can't see a way of achieving this without losing the ability to tack.
     
  8. Skyak
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    Skyak Senior Member

    If the front of the first foil is fixed, that would be the obvious best (easiest) place for vertical support. The middle would be better if that was the pivot because it could be fatter without damaging aerodynamics.

    Moving the middle foil enables camber the same as an articulating boom at the bottom, but what about the top?

    The foils each have thin film trailing edge don't they? If they do there should be no problem tacking with a mild overlap.

    Does this boat race on an upwind downwind coarse?
     
  9. mij
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    mij Junior Member

    I agree that from and aerodynamic perspective it would be better to incorporate the mast into one of the foils. This would probably be easier to achieve on a “big” boat. The mast aft arrangement I am using allows me to experiment with different configurations fairly easily. I can move the sail positions around without having to move the location of the mast each time. Once I’m happy with a particular arrangement I might try to engineer non-mast aft arrangement. I still wonder if there is something worth considering with respect to the ease of setting up a mast aft wing sail on a larger boat. I imagine that the foil(s) could be winched into position and thus wouldn't require a crane? I also wonder about trying to reduce the drag from the mast by installing a rotating symmetric foil?

    Yes, I’m still thinking about the top.

    The problem is the boom for each individual foil. However, I might be able to shorten these so that there is a section of the trailing edge that protrudes beyond the boom.


    I think that this sail will be a bit too heavy for my RG65 so I’m planning to put it on a cat that is a bit bigger (800 mm). I don’t race this boat, but would like it to perform on a range of courses
     
  10. mij
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    mij Junior Member

    3 element mast aft wing sail

    A bending boom turned out to be easier to construct, and it seems to be light enough for my RG65.

    This sail is going to need some tuning, and I'm not sure it is actually going to work, but I reckon it is a thing of beauty.

    http://www.youtube.com/watch?v=C6s3Ds7CvJE
     

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  11. mij
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    mij Junior Member

  12. mij
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    mij Junior Member

    A canting mast aft wing sail?

    It has occurred to me that it would be quite easy to cant this rig and I'm planning to test it on my rc monohull. I have read several threads on this forum where the pros and cons of canting masts have been discussed, and it seems to me that for a conventional rig the potential advantages and dis advantages of canting probably need to be assessed for each individual boat. However, I do wonder if there are some particular advantages for canting a wing sail on a monohull?

    I've been trying to understand what happens when a wingsail heels. Am I correct in thinking that wing sails are generally designed for their performance in a vertical configuration and that given that they have less flexibility to change shape than a conventional sail that there might be particular advantages for canting a wing sail on a monohull to maintain optimal performance? By the way, I know that there is a a debate on the suitability of wing sails for mono hulls, but for the purposes of this question, please assume that The monohull will have a wing sail and I am trying to optimise its performance. I am only really interested on the aerodynamic aspects of this debate.

    Given that I have only recently joined this forum, if this issue has already been discussed, please just point me in the direction of the thread.
     
  13. mij
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    mij Junior Member

    Found a useful paper. It doesn't answer my question, but I found it helped to better understand the effect of heel angle on the lift and drag associated with the sails of a monohull.
     
  14. Skyak
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    Skyak Senior Member

    MIJ, I am also very interested in the aerodynamic effects of canting wing sails as well as fore/aft tilt. All of the work I have seen for monohulls has been for Bermuda rigs with triangular planform and they are more concerned with drive vs righting. This all makes sense given the focus on one design and common popular sail designs but it doesn't help anyone opening their mind and looking for performance improvements from design innovation.

    What I can tell you from my own experience on a wind surfer is that the fastest orientation of the mast is tilted aft and canted into the wind... and it is significant. There are several reasons this is faster, displacement is reduced which reduces drag, the gap between the bottom of the sail and the board/water is closed reducing induced drag from the bottom of the sail... but I still feel that there is more improvement than these can account for so there must be aerodynamic improvement. My feelings from hands-on the wing, are that on an upright wing the tip looses lift from the wind slipping upward off the end. With the sail tilted back and toward the wind, the angles keep all the wind that hits the leading edge, angling it down into the larger part of the sail. To verify this we could do some experiments with tel-tails near the top of a square or elliptical sail.

    To get quality answers to these questions I was planning to post on the aero/hydro board. I will simplify the question as much as I can because the question is difficult enough without the complications of real hardware and the opinions/bias. It's hard enough to gain understanding from these PHDs without the noise of opinions that wings are a waste on monohulls with their weight and drag.

    My opinion is that wing sails are the greatest advantage to low drag applications. It can be proven mathematically. I would also dispute your statement that wings are less 'flexible' but I have no interest in arguing about it.

    In the meantime I would suggest you look at the postings of 'Tspeer' and 'Miko'. I find their posts to be precise, supported, and accessible/understandable. They both have personal sites with numerous papers and Miko also has a channel on Utube with some wonderful CFD videos.
     

  15. CT 249
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    CT 249 Senior Member

    Re windsurfing rigs and lift effect; as noted in another thread, the top windsurfers try very hard to limit the lifting effect, as noted below from a technique website by a national Formula Windsurfer champ;

    "Now have a look at this photo gallery here; a few photos of some of the top guys in FW going to windward. Notice everyone’s technique is slightly different but most of them have the sail very upright and are very hiked out, getting their body as far from the sail as possible.....
    It is hard to get the sail upright and keep sheeted in at the same time. The two things seem to contradict each other when you try it. Work on getting your body hiked and away from the sail first, as it’s the easiest to correct. When you do, you will most likely be sailing with the rig too far on top of yourself. Once you start to drag the sail on top of you, the lift forces you are generating from the fin begin to decrease, so the second part of your training should be to work on ways of getting the sail more upright whilst still keeping your body hiked out. Here’s some tips to get you started…"

    - See more at: http://www.carbonsugar.com/featured/....xF2w8uup.dpuf

    This is a very common technique; when coached by the Olympic bronze medallist he said the same thing. You can also google "Antoine Albeau speed record" and see pics of the world record holder blasting down a speed trench with the rig very upright. Years ago at the worlds some guys were using very wide booms to keep the rig upright; one was so wide that someone put it inside a doorway and people didn't notice it when they stepped through!

    In an old Gary Hoyt piece about speedsailing that used info from world class windsurfers like Nevin Sayre it was agreed that raking the mast to windward was a very minor benefit, if any at all.

    Early windsurfers like the original Windsurfer (still popular as a racing class in some countries with 45-108 entries at national titles in Australia and Italy) raked the mast to windward a lot when going upwind in big air, but that appears to be because raking to windward reduces rounding up and because of the rig's high drag. Normally people strive to keep the mast as vertical as possible and when the same sailors sail other more modern boats they don't rake the rig as far to windward. Tuft experiments showed that these rigs work best with the lee side flow stalled.

    By the way in some countries there has been a lot of work on the aerodynamics of rigs that are not the normal "pinhead sloop".
     
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