Sailien construction notes
08 November 2008
First a bit of news from Sailrocket, they plan to book the WSSRC for an official run at the record, starting the 23rd of this month. I wish them all the best and I hope they pull it off.
I've had a request from Van for enough information about my craft so an R/C model can be built. In order to save time I'll be referring to my patent and the drawings it contains. Any of you that have an interest in this, please refer to my post of 17 May 08 "Patents" for instructions on how to access any patent and my patent #. Use my link "Patent Office (search)" it bypasses the first USPTO pages. Also follow my link "Sailien Prototypes" for photos of my early prototypes.
The numbers I'm giving you are approximations of the model shown in the photo and video. The hydrofoils have to be big enough to float the craft, so their size is dependent on the weight of the craft. I made them of foam with a fiberglass skin. The frame is made of three tubes rigidly joined as shown; it is raised at the junction to provide clearance for any waves. The tubes were made of fiberglass that I wrapped around cardboard tubes to form, and then pulled the cardboard out. An easier method would be to use light aluminum tubing, 1" dia. X 0.035" wall, should be more than enough.
Make the main arm 4' (122cm) the smaller arms 2' (61cm) each, the hydrofoils 24" (61cm) span by 18" (46cm) root chord, and the airfoil 5' (152cm) span by 2' (61cm) root chord. If the hydrofoils are too big (float too high) just allow for a little freeboard, as in the photo/video, and cut off the rest. The plan shape for all the foils is a triangle with the tip rounded off. The foil shape for the wing and the two leeward hydrofoils is flat on one side and the arc of a circle on the other. The radius of the arc is 100% of the chord, so for the wing root rib, set your compass to 2' and draw the arc. The windward hydrofoil (anti-drift hydrofoil or keel) is a normal symmetrical foil, so both sides are curved with a rounded leading edge and tapered trailing edge.
The wing was made by making a series of ribs out of foam, the root rib was fiber glassed to strengthen it, but the others were not. The ribs were slipped over a central spar (aluminum tube) and string was attached to the ends of the ribs, forming the wing edges. Fabric was stretched over and glued to the ribs and string. If you make the spar removable, you can collapse the wing down to the thickness of the ribs. The wing is supported by a short vertical mast that attaches where the frame tubes join. The wing must be able to rotate on this mast somewhat in order to position it for each tack.
Now refer to the patent drawings: Fig. 2 shows the general relationship of the foils. Note that the airfoil (#21) and the keel (#29) are parallel (angle 67 and angle 69 are equal). There is no set number of degrees for those angles; it is dependent on the size of the foils and the distance of their separation (frame length). Make your wing and keel mounting points adjustable so you can set the correct angle. Experiment with these adjustments by setting them non parallel and see what happens; you'll find out why I'm so insistent on properly aligning the forces that act on the sailboat. The leeward hydrofoils (#25) are angled so they aim a bit below the tip of the keel. Make that angle adjustable also. Fig. 3 shows the lee foils (#25) set at angle 57. Once again, make the foil mounts adjustable so you can set that angle by experimentation. With too much angle, the trailing foil (of the pair) submerges, and with too little angle, the lead foil submerges. These foil angles control pitch.
For R/C you only need 2 channels; one rotates the wing, the other rotates the keel. I had to modify the servos so they would rotate continuously clockwise or counterclockwise. The servos normally have a stop and limit switch to restrict the rotation to a few degrees. The keel rotates 360 degrees, although you only need about 180 deg. The wing rotates less than 90 deg. but since you will need to gear so the servos can pull the load (as well as slow the motion so you can control it) both servos will be rotating several turns each way.
Another point to be aware of: the resultant on a foil is at about 25% back from the leading edge. This means that the pivot point of the keel ("rudder" post) should be at that position. I didn't understand this at first and both the model and patent (early prototype) show the pivot point in the center. I you put the pivot in the center, at higher velocities the torque on the keel will overpower the servo and you will lose control.
I do not recommend that you try to steer the lee foils. At lower wind velocities you can get away with it, but if those foils provide leeway resistance you will flip the boat at higher wind velocities. This is what happened to Ned Snead's Delta (follow the link "Sailien Prototypes" to find the Delta).
I hope this is enough information to get you going. Let me know how it goes and be sure to ask any questions you may have.
Bob