Found some good stuff in SA archives,
'Steve Clark', on 18 Nov 2010 - 12:48, said:
I try to answer questions. Please understand that while I have been doing this for a long time, I do not have reams of data comparing one wing section with another and confirmation that the on the water performance validates the predictions. We just haven't had the time, money and inclination to work that hard. We are pretty smart and we take what we feel are logical steps, but we simply don't have an "optimal" solution. We have "what we have done" and "what works".
1) What has proven to be the most effective section shape used for the main wing? Is it a standard NACA section? If so, # please?
The current #1 elements have been reverse designed using XFOIL or other proprietary foil design software. This has lead to foil shapes that are blunter than the standard 000 NACA series. Cogito's #1 element is 19% section. So is the X wing. Magnus Clark reduced the thickness of the Canadian wings based on a study he did using XFOIL. He has not shared this with me, but from what
I HAVE seen, I am not convinced that he is right and am not scampering around the change my wing shapes. A NACA 0018 WILL NOT BE A BAD CHOICE. It is close enough, but
increasing the LE radius makes the wings a bit more stall tolerant, you can do this yourself or you can wait and plot out the nose sections on the plans.
2) Should the rear flap be of the same section shape? If not, which section has proven most effective in that role? Is it a standard NACA section? If so, # please?
The trailing edge flap is not the same section. I have used NACA 630A10 and NACA0009 sections. Tom Spear makes an argument for NACA 0012 sections. There are quite a few practical compromises in the flaps and I think any of these sections is fine. The thinner sections will provide a smooth leeward side at a lower flap angle.
3) Should the main wing and rear flap be 50/50 area wise? Or should it favor greater area in the main wing? If so, what percentage would be the optimal split?
Current wings are pretty much 60-40 splits. We have the #2 at about 20% of #1 as well. The placement of the pivots along the fore and aft axis of the wing determines the lateral displacement of the flaps at various flap angles. This is a fairly complex compromise.
4) Is there an accepted method for the control systems? If so, are there articles/drawings/photos on the web detailing the principals and execution there of (links please)?
I have DXF or PDF file of what has become the standard control system. This was invented by Dave Hubbard 490 years ago and developed over 10 wings or so by the Patient Lady Team. I believe thay wings are only as satisfactory as their control systems. This is the only one I can say is dead nuts reliable. Send me PM and I will send you the file. Specify format please.
5) Since rigid wings are more efficient, can the total sail area be reduced to achieve equal or greater performance over a soft sail on all points of sail? If so by what percentage can it be reduced?
In theory, but most of the design work has been done to provide more power for equal area. I actually look at it the othr way: since wings can be so much cleaner and can be depowered more effectively than soft rigs and sails, how much could their area be increased? Can this increase make light sails unnecessary? My current best guess is about 25%.
5) What is the optimum aspect ratio?
Wings are not subject to the same constraints that sails are. They can be taller and narrower, however the vertical CG of the vessel and thus the stability of the vessel is effected by the rig height. You have the competing values of center of effort height and aspect ratio at play as well, so this is a hard answer to give. C Class wings have been about 40' tall for 300 square feet.
6) How low can the aspect ratio be pushed before there is an appreciable drop off in performance?.
In catamaran sailing there is a big performance increase associated with flying a hull. So being short doesn't pay until it is blowing pretty hard.
7) Is there a proven optimum side profile shape? Some variation of quasi-eliptical. What we have done is some form of taper. It is usually simplified for ease of construction.
8) What has proven to be the best method of inducing twist into a rigid wing sail? BMW Orical AC tri appear to have 9 seperate adjustable sections on the rear flap, Is there a way to mimic this on a smaller scale and be mechanically controled for twist? The Oracle wing controls were losely based on the Patient Lady system. PM and get the drawing.
Also Bille, this is for you,http://www.tspeer.com/RigidRigs/50flap/S901fa20.htm
My wingsail build is progressing, making some errors in the building of the ribs, but each one is better. Im on #4, quit vacuum bagging after #2, hand layup with wax paper is providing a smoother build believe it or not.
The leading edge of the 1st element was built using a jig, which really is a simple curved section about 3 ft in length. I lay up a 3 ft section at a time and then epoxy them together. The 12ft section is around 4#'s, and is quite strong. Its not really structural per se as I will have a mast thruogh the ribs that wil provide the structure.
more to come...