Wing sail for an A Class Cat

Discussion in 'Multihulls' started by DSmith, Dec 1, 2004.

  1. DSmith
    Joined: Dec 2004
    Posts: 53
    Likes: 2, Points: 0, Legacy Rep: 12
    Location: Sydney

    DSmith Junior Member

    No, I didn't. I was getting a little ahead of myself when asking this question. I was putting my A Class Cat on foils and was considering the virtues of a solid rig.

    I have spent the time since simply tying to get the cat foiling. It has towed successfully but in its first full sailing trial, we had some breakages.

    As it is now winter Down Under, I am concentrating on writing a VPP for the foiling cat. The VPP is just about finished (I hope) and as it is starting to warm up again, I will be back with the A Class soon.

    Cogito's twist mechanism is basically a structural tube up the guts of the front element which is connected to the foward section at the hounds. The wing is then twisted by pulling the base of the forward section relative to an arm off the tube. It doesn't twist above the hounds.

    From memory, Marchaj's main concern was laminar seperation due to low Reynold's number effects. Cogito seems to have enough power to lift a hull to windward in 5 knots plus suggesting it might not be as big an issue as he thought.

    I think that single element split flaps have died a death after the last Little Americas Cup.
     
  2. Rolf Nilsen
    Joined: Jul 2006
    Posts: 24
    Likes: 0, Points: 1, Legacy Rep: 10
    Location: tack

    Rolf Nilsen Junior Member

    Thanks for replying, and the information about Cogitos twist mechanism.

    Good luck with your A, hope you get around to playing with a wing when the platform foils cleanly. It seems like the land/ice sailors are the ones most active on wing development for the time beeing..
     
  3. DSmith
    Joined: Dec 2004
    Posts: 53
    Likes: 2, Points: 0, Legacy Rep: 12
    Location: Sydney

    DSmith Junior Member

    The VPP appears to be saying that the extra weight of the solid wing counteracts the benefit of the superior aero performance of the solid wing. I want to run the VPP on an equivalant C class to see whether the balance is tipped back in the solid wing's favour.

    Dave
     
  4. frosh
    Joined: Jan 2005
    Posts: 621
    Likes: 14, Points: 0, Legacy Rep: 44
    Location: AUSTRALIA

    frosh Senior Member

    There is no such thing as free lunch!

    Inevitably there is always a price to pay for a seeming performance enhancement. The weight differential between a soft sail rig and a rigid wing is a smaller percentage increase on a C Cat than A Cat. If you get real lucky, the price is only in $ terms. :)
     
  5. Rolf Nilsen
    Joined: Jul 2006
    Posts: 24
    Likes: 0, Points: 1, Legacy Rep: 10
    Location: tack

    Rolf Nilsen Junior Member

    Percentage vise, I suppose the increase in weight is pretty large on a light platform like the A when swapping the soft sail rig to a rigid wing. It would be interesting to know the result if you ran a i.e. 40% wingmast+soft sail trough your VPP (if it can handle it).

    There was an 18square with a rigid wing which was very hard to beat in its day. But I think platform weight was the double of an A.
    http://www.geocities.com/mec_coleman/magazinecover.jpg
     
  6. L. Hutchins
    Joined: Aug 2006
    Posts: 6
    Likes: 0, Points: 0, Legacy Rep: 10
    Location: Canada

    L. Hutchins Junior Member

    Has anyone attempted a solid sail for an A-Cat yet? I am very interested.It seems that the small size of the boat and rig may make this a viable option. I would love to hear about any ongoing projects.

    Leigh
     
  7. Erwan
    Joined: Oct 2005
    Posts: 393
    Likes: 18, Points: 18, Legacy Rep: 97
    Location: France

    Erwan Senior Member

    A Cat Wingsail

    Hi Everybody,

    It was a great pleasure to discover your very interesting discussion about this project.
    I sailed 15 years A cat, and it has been a dream to achieve such a project.
    In 1996 I met Martin Fischer at the world championship, he holds a Ph in fluid mechanics and at this time he had already studied a similar project.

    According to Mr Fischer's research I found much later on the web, I investigate myself the global drag of a A Cat winward with just enough wind to fly a hull full trapeze (about 4.5 knts true wind speed).
    So we have the righting moment, the wind speed, the boat speed= a proxy from Tornado polar) the average angle of incidence (22°), and we found that the required lift coefficient which matches real life condition is around 1.2 for a an aerodynamic force of 650Newtons+. A proxy of wave drag is interpolated from a serie 64 David Taylor Bassin model, wetted area and its friction drag calculated with a I???? Coefficient, and so on.
    I founded a 160N ewton total drag with 90 N from aerodynamic drag and 70 from Hydrodynamic drag. And as the lift Coef was above 1 the Induced drag accounted for more than 60% of the aerodynamic drag.

    A multi elements airfoil would be perfect for high lift downwind, but now, downwind, A cat sail "Wild Thing" in order to create apparent wind and therefore the issue is also to deal with aero drag.
    That is why I decided to investigate a single element wing section with morphing capabilities . I think that Eppler 61 is enough for hight lift downwind & lower reynolds (maximum camber) and I try to find a very low drag wing section, which could be "consistent" with the Eppler 61 for good performance (low drag) upwind with high Reynolds. I guess a symetric Eppler wing section with similar thickness will do it ??

    First I aim to achieve a real size wing section on the ground, and find by trial an error the mecanism which allow to change from one section to another.

    It is still a project...of course, I am not very confident about my analysis I am not engineer neither that is why I am on this forum
     
  8. petereng
    Joined: Jan 2008
    Posts: 581
    Likes: 21, Points: 28, Legacy Rep: 252
    Location: Gold Coast Australia

    petereng Senior Member

    I realise that this is an old thread but is a rigid wing on an A Legal? Could they say you have two masts? Will they be concerned with two seperate elements? Do they consider the front element a mast and the rear a sail? I'm designing a small triamaran at the moment and would like to use a rig that complied with the A class rules as I have a couple of friends that sail that class. They are interested in a wing if legal and If I can do it. I see no problem doing it but has anyone done this legally or has had a favorable interpretation thats its legal?

    Cheers Peter Schwarzel
     
  9. Corley
    Joined: Oct 2009
    Posts: 3,770
    Likes: 189, Points: 63, Legacy Rep: 826
    Location: Melbourne, Australia

    Corley epoxy coated

    There are precedent's Ben Hall was allowed to race his A class catamaran with his rigid wing. The chief problem seems to be the extra weight aloft which caused more pitching and the relative fragility and difficulty of transporting the wing.

    http://www.youtube.com/watch?v=cCAoJrKsiw4
     

  10. petereng
    Joined: Jan 2008
    Posts: 581
    Likes: 21, Points: 28, Legacy Rep: 252
    Location: Gold Coast Australia

    petereng Senior Member

    Thanks Corley, I know about Bens wing. Mine will be a light first panel with a soft sail second panel. So it should be lighter then a C Class type construction and easier to transport. Until the wings are easy to transport and be more robust they won't get popular. But thats what development is about. I'll have to find a measurer and check out the interpretation. Cheers Peter s
     
Loading...
Forum posts represent the experience, opinion, and view of individual users. Boat Design Net does not necessarily endorse nor share the view of each individual post.
When making potentially dangerous or financial decisions, always employ and consult appropriate professionals. Your circumstances or experience may be different.