Thanks for the paper reference. That is the one that I have been looking at for wing masts, but it is not clear to me how relevant it is to the soft wing sail. The leeward side of this sail is only wing shaped right at the "bulkheads" and collapses ww in between, so the whole efficient has to be way less. From re-reading the article, it does seem that even JavaFoil won't help much in prediction, because it is based on a constant cross-section, since it only works in 2D. With the varying cross-section between the "bulkheads", there could be all sorts of complex behavior, and it might not all be good. I guess we are going to have to wait on more data from the few people who build them.
I believe this paper has the information you want:
This is the model used for David Tyler's swing-wing sails (although he uses a slightly different foil section, I can't imagine that the difference would be significant in these soft wing sails).
On Mon, May 30, 2011 at 12:10 AM, Gardner Pomper <gardner@networknow.org> wrote:Mike,
I thought that I had seen you post a message that you were going to try out JavaFoil. Did I remember that right? It would seem that is what this discussion needs; some actual numbers comparing the lift of a softwing sail in this configuration to a "normal" sail. From looking at the photos, it would seem it would be worth approximating the shape as a solid wing, with a thickness of half the frame.And I wish you would stop being so darn reasonable.. I had ruled this sail out a year ago and now you have me seriously considering it again! <grin>- Gardner
On Thu, May 26, 2011 at 9:45 AM, Mike Crawford <mcrawf@nuomo.com> wrote:Micha,
I also like the use of multiple sheets to deal with twist. That should cut down on excessive twist without the huge stresses on sheets and sail cloth that you'd see in a normal high-aspect high-roach main without a backstay.
Sometimes I debate adding the rotating boom as you suggest. It's a bit more complexity and expense, but it should make tacking and shunting easier from the cockpit, and also provides a nice fixed place to drop the sail while reefing or stowing.
That said, I stand corrected on the junk's suitability for a schooner rig. Never having seen a schooner junk up close, I had assumed that the sheets had to be lead as far aft as they are on Fercot's Tiki. That angle may be ideal for reducing sheet loads and wishbone/batten stresses (or maybe not), but it looks like the ideal is not necessary. Also, Fercot ends up combining his his multiple sheets into just two per sail, so it's not as complex as it might seem at first glance. You could even combine those two into one, perhaps at the expense of having to use a winch more often.
After reading Rudolph's update on the origin of the rig, I browsed across these photos of Badger (junk schooner) and Tystie (swing-wing schooner):
https://picasaweb.google.com/108735432675049110317/Badger#5518116655093321266
https://picasaweb.google.com/108735432675049110317/Tystie#5519151842438542050
Neither one has the sheets on the forward sail lead past the aft mast.
So, maybe a schooner could indeed work, particularly with the extra step of that rotating boom.
Imagine the speed of two wings, combined with the lower heeling moment of wings and lower COE of a schooner...
Maybe it's not perfect. But what excites me is that it's something I could try, and perhaps fine-tune, without a huge R&D and equipment budget. The allure of a better airfoil definite has its draw.
Personally, though, I'd have to go with a higher-aspect shape that looks more like an efficient wing. Tystie and Pha might work well, but the sail profiles challenge my notion of a pretty boat.
- Mike
Micha Niskin wrote:I like how the swing-wing deals with twist in the leech (the "chinese" sheeting arrangement). The omer wingsail seems more complicated. I was thinking that you could adapt the swing-wing for use on a proa, and still keep the chinese sheeting arrangement. This is the configuration I imagined: Unstayed, round-section mast, wing sail as in Mr. Tyler's Tystie. The mess of chinese sheets would be led to the outboard end of a boom under the sail. This boom would have jaws or a gooseneck at the inboard end and be free to rotate independently from the sail. Thus, I think you'd be able to set the chinese sheets relative to this lower boom, and then have your mainsheet that you'd use to adjust the angle of the whole sail rigged to this boom and run to the cockpit. When shunting you'd be able to leave the complicated web of chinese sheets fixed relative to the boom, and use the simpler, conventional, secondary mainsheets to get the sail over to the other tack.
On Wed, May 25, 2011 at 2:17 PM, bjarthur123 <bjarthur123@yahoo.com> wrote:
thanks for the info. i'll book mark it. seems similar to omer's wing sail:
http://www.omerwingsail.com/
ben