Telescopic Wingsail - Why Not?

Yes - it's the concept phase where the design is being designed, and as I said before, I'm looking for for two things: (1) fundamental problems that should lead to the idea being abandoned; and (2) I'm trying to prevent anyone patenting ideas that might block me from selling boats using this kind of sail without having to pay them for using my own ideas.

The diagram shows two front wing sections, a red one sitting inside a black one (if the colours haven't been dinged too much on conversion to jpeg for you to make them out). The base of each section is a plate (or frame) while the top of each section is an external frame through which a higher wing section can pass (except for the top of the highest section and bottom of the lowest section where there's a full plate and external frame in one piece). The controls for the angle of the rear wing are all driven through the external frames at the top of wing sections plus the bottom of the lowest section. Power is tapped from the telescopic power-transmission rod (orange) from cogs inside the bases of sections, and is then transmitted on mechanically to the top of each section at the front end of the wing in the part that doesn't need to accommodate any part of the section above when that telescopes down. (The power-transmission rod would be turned by a gear that goes round the mast which would in turn be rotated by another cog in a fixed location.)

The two vertical cyan things are rods with a thread on them which engage with threads in holes in the base of the red section of wing (at points B and E) - by rotating them (again using power from the rotating orange rod to drive rotation at C and F), the red section can be raised until its base is level with and hidden within the top of the black section (so the parts of its floor shown at points B and E end up at A and D). The telescopic mast and power-transmission rod are both extended by this. If the red section is the top section of wing, its top is a solid plate which has the top of the mast and orange rod locked into it. With multiple wing sections, it's a little more complicated, but I'll get to that later.

The leading edge of these wing segments can be made very strong and rigid because it doesn't have another section telescoping into it. when the red section is raised, the front of its floor (shown at E before it rises) locks firmly into the top of the black section (at D). There is no direct locking equivalent at point A other than vertically because the connection is from floor to floor, but the base of the red section can't move about horizontally once it's up there as it's sitting inside the external frame that's built onto the top of the black section, so it's as good as locked there too. These cyan parts provide most of the resistance against vertical rig collapse. With more wing sections, there is plenty of room for more of these cyan parts to drive the vertical separation between adjacent sections in the same way.

So, we have the basis of a design in which the telescoping (of both wing and mast) and changes in wing angle can all be driven using power transmitted up a single telescopic rod in a fully viable manner. But there is one part that needs further work to demonstrate how it can function. If there are more than two wing sections, raising the middle one with the top one inside it would only pull the top mast section up with it, but we want the second mast section to rise too at that point. The way to achieve this is for the top of each mast section to stick out a little above the one below and to have a collar on it, each with the same width. The only structure adjacent to the tops of untelescoped mast sections is the top plate of the top wing section, so it has to lock onto the collar of the next mast section to be raised each time so as to pull it up (along with any others inside it). Also, when a section is rasied, its base plate locks onto the top of the mast section that it rises up to, and it locks on through that into the mast section inside that once that section of mast has been raised fully. Each time a section starts to rise, a mechanism in the top plate of the top section lets go of the top of one mast section (which isn't to be pulled up any further) and locks onto the next one up instead, and it does this simply by rotating to a different angle.

What I haven't designed yet is the detail as to how all these little controls for locks ate to be operated - anything than needs to be powered to make it move can get power from the orange rod, but there are things that need to be switched. One solution for this is to use electronics, and that's certainly the most practical way. It could be done mechanically too though by having more telescopic control rods, and these would be much less robust than the orange one as they'd be carrying minimal load. The rotation of one rod could be used to select a device to adjust with the rotation of another rod.

"One purpose of building a model is to discover problems with the design, but at this stage you don't even have that so both problems and resolutions are just thought bubbles."

It's possible to explore problems with the design at the concept stage - so far I've been solving a series of design problems relating to testing the concept.

"For example, claiming that it will be able to be installed or removed without a crane..."

I said "a crane" the second time, but I was referring back to an earlier point where I called it "a big crane". If your wing collapses down to a fraction of the height, you can use a much smaller crane, and may be able to do the job using an A frame instead if you have to improvise something out in a remote harbour (and I'm not thinking about AC racing there).

"Guessing that it won't be much more than a solid wing sail is just that, guessing."

If you can see it in your head and compare it with the non-telescoping equivalent, you can see where extra parts actually exist and where fantasy ones that aren't needed don't exist, so you can make reasonable guestimates. If you imagine the red section raised until it's base is within the top structure of the black section, you have something similar to a non-telescopic wing in terms of distribution and density of material - the main visible difference will be small ridges of external structures at the top of each section (which are conveniently aligned in such a way as to cause no drag issues).

"A detailed design will also lead to other estimates, such as construction methods and cost. Those are the easy bits, performance, longevity, convenience, etc. can only be determined once you have a sufficiently detailed design to be confident that it can actually be built and tested."

Can you see anything unconventional there that's hard to cost or design to last? The electronic controls will take a bit of work to design, but that's an inexpensive addition which would cost the same on a small wingsail as a big one, and it could be done through wires (which will coil as sections contract into each other) or by radio transmissions. There are lots of special components to manufacture, but that's normal with any design. The bulk of it is just material on frames, and there's a similar amount of those things on non-telescopic wingsails using the exact same materials. I've replaced hydraulics with mechanical rods which are less costly and can be light. The main difference in weight will be with the mast, but as I've already said, a sail that can reef doesn't need to have as strong a mast supporting it as one that can't, so there's potential for weight savings there rather than gains.

 

I've made progress with one of the other approaches, to the point where it now looks like the best one to try to turn into a reality. It turns out that it is fully possible to attach the top of each wing section to the top of its mast section and also remove the need to transfer power from the bottom to the top of any section as the orange rod can now connect with the tops directly. It also allows the lower mast sections to be wider than the higher wing sections which adds strength lower down. The key to this is to avoid having the mast pass through any of the wing sections (other than the bottom one) so that it is external to them. This means that there are now three sets of wing section which stack inside each other instead of two: the rear ones (not shown in this or the previous diagram), a middle set behind the mast, and a front set ahead of the mast. The way to make this work is to find a way to close the space between the front and mid sections to get smooth airflow across the gaps where the mast is. There's no problem with the bottom section of wing as the front and mid sections are still a single piece with no gap between them, so it's only the higher ones that have gaps to close.

The diagram shows the bottom section in black, the higher section (only one is shown) is in red for the telescoped-down position, and it's shown again in green to show its raised position (with its base plates hidden within the top structure of the black section and locked into them). As before, the vertical dimensions have been squashed in the diagram, so you're looking at a highly stretched section horizontally. The gap is the rectangle with its corners labelled with the letters "a" to "d". We need to close this gap, and there may be many possible ways to do this. The front section could be moved physically aft until it touches the mast, at which point the sides of the mast can serve as part of the wingsail's outer surface (if the mast has a nearly square section rather than circular), while part of the middle section can slide forwards to contact with the edge of the mast from behind. Alternatively, the part sliding from behind can slide right past the side of the mast to connect with the front section, just like sliding a door on a cupboard where one door moves out from behind another to close the opening, although we need to make sure the surface is smooth across the joins to avoid disrupting air flow. This sliding can only take place when a section is fully raised, but as we're not using intermediate positions that is not a problem - just raise the section and close the door.

With the previous concept, the top structure of a section projected out round the side without taking up any space inwards (to avoid getting in the way of other sections telescoping down through that space), but the new concept allows it to have structure right across from side to side around the mast, so it can pick up power from the orange rod there and send it out to the sides from there without getting in the way of telescoping sections.

In the previous version I showed two rods in cyan used for raising and lowering sections - those are over-engineered for the task, of course, but I was merely establishing that there were physically possible solutions. Each could be replaced with a non rotating CF rod and a short halyard. But the need for anything of that kind was caused by the difficulty of accessing the mast for this purpose. With the new version, we can simply have a halyard for each mast section inside the mast, outside the part that's being raised by it, but inside the wider mast section through which it rises, and it's just a matter of winding the halyard up within the top structure of the section below the one being raised, so that's much simpler and more weight is saved. We are getting much closer to the simplicity of the non-telescopic wingsail, and it's clear that the weight difference will be almost entirely caused by using a multi-section mast.

If there's any need for internal bracing in a section that has others telescope down into it, this can be done by having folding flanges which can be held flat against the outside when the interior space is occupied by a lowered section, but can spring out into the inner space when it's empty - I don't know if they're necessary, but it might be the lightest way to provide resistance against the sides of a section being buckled by high pressure on one side and strong vacuum on the other. I can't see much other cause for such internal structure - the soft wingsail in the first video Doug linked to doesn't appear to need any at all.

A forestay's awkward - it may need to attach to or above the top of the top mast section, although on some designs of boat it may be better to use two sets of shrouds instead; one pair running slightly forward and the other slightly aft. I plan to use two wingsails on the hulls of a cat with no head-sails, so I could use four shrouds, two on the same side of each, and a horizontal bar between the two sails at the same height as the shrouds attach, which is at the top of the third section from the bottom. What I'm looking for is lots of power for early flight, but the ability to reef and handle stormy conditions is also essential. This telescopic wingsail should provide both.

 

A few more points just to cover to prevent patent trolls from hindering the design, so if no one feels the need to comment, this will likely be the last post in this thread (copies also lodged elsewhere with a date and stamp time and no ability to edit after the event). The top structures of all sections are the same length to their back end and don't adjust to control the slot size, but just as the "door" parts of panels can slide forwards (the door, incidentally potentially also being useful for getting at the mechanism if a section of wing gets jammed in the raised position), the rear section can slide aft far enough to narrow the slot (and it could be pushed out a little to the side too if that's advantageous, though sideways movement of the rear parts of the leading edge of the wing can also be provided by the joints). The rear wing sections themselves will in their raised positions come completely out of each other to enable twist without any warping of their shape, so they become independent flaps, and if the gaps opening up between them are an issue in any way, they could be blocked by a sheet of fabric from the base which is pulled down into the section below. Some internal support can be supplied for all mid and rear sections to prevent sagging from rectangular to parallelogram shape because the middle is otherwise empty whether the sail is fully up or fully reefed - all it takes is a wire going down from the top leading corner down to a bar across the base near the bottom aft corner, and these will not conflict with each other as the sections telescope together. This may allow the frames to be considerably less substantial as they wouldn't need to resist bending as much, though it's only necessary if the "fabric" used for the sail's surface isn't sufficiently rigid to do that job already.

Edit on 14 Apr: An unstayed rig looks less impossible too now, seeing as it can be so much wider at the base. I'm looking at the possibility of raising mast sections (and everything else that goes up with them) by rotating them from their top and having a thread inside On the inside of the outer section would be a thread the full height (plastic would likely be adequate for most of it), but on the outside of the inside section there would only be two short sections of metal thread covering a few inches at the base and a few more a couple of feet up from there, so, when extended, these would lock each section firmly to metal parts of the one below and make them behave like a single piece instead of allowing a section to slide a little up at one side and down at the other. Whether that can lead to greater strength for the weight I don't know yet, but again I'm seeking to block other people from getting a patent on that.