It’s of theoretical interest to me now Arne, but the quest for high L/D ratio is no for racing but for the ability to carry as little rig area as possible to do the job, and to reduce heeling forces.

I often sailed Poppy with only 5 panels as it gave me close to max hull speed even in moderate winds, and because I was just too lazy to haul up the last two panels. I know you like the extra area as reefing is easy, but I was happy with less area than the standard fore and aft Bermudian area when I could still get 2 knots of speed in 4 knots of breeze and outperform the Bermudian rigged boats with full sail area.

Perhaps I’m just trying to encourage a new drive in rig development which seems to me to have slowed down of late. As you say, “Unless the improvement in the rig can be made very easily, it makes little sense.” I suppose the question that with interest in increased balance, whether a change in rig outline or structure could improve performance or rig handling in any way. I’m still 100% for the KISS approach.

I believe you have taken the Hasler Mcleod rig shape to its top level, but I have never been a fan of the fanned top panels as in my eyes they don’t just simply hang there under gravity. In this respect I prefer the crude simplicity of the van Loan rig, but who is to say what is best? We’ve seen many different rig shapes over the years, but it would be nice to see even more being discussed if at all possible.

More ‘cutting and trying’ would be good.

Cheers, Slieve.

Lots of calories for small gains...

Folks, I can’t help feeling that you are burning calories on small, and woolly improvement factors. Remember, cutting 5% drag in the sail, does not necessarily lead to 5% increase in upwind speed. In a very light wind and low boat speed this cut in drag could be useful, but when approaching hull speed, the resistance-speed curve has become so steep  that there may only be 1-2% gain in speed. For racing, this is fine, if you don’t get any extra handicap penalty, but otherwise, unless the improvement in the rig can be made very easily, it makes little sense.

Group Captain Smith’s experiments with the Insect Flight Theory have been mentioned. Although worth trying, it proved to be a failure. However, Mr Smith had such a high standing because of his military achievements, that nobody dared to oppose to his theory  -  except one: In JRA NL #25, Alan Boswell put things right by showing that the bendy battens in Fenix’s rig was the main contributor to the improved performance. Later, Joddy Chapman came to similar conclusions during his PhD research work.

Paul Schnabel’s experience with his Maxi 77 this summer should open a few eyes.
His sail is a quite ordinary cambered panel sail with (8%? Corrected to 9%) camber, made with the barrel cut method  -  no broadseams or shelf foot. He has also pushed the limits for mast balance  -  and he has been generous with the sail area. 
That big sail area, combined with the moderate camber, has paid off with an impressive performance, both when close-hauled and when running before (SA/disp. is 20-22).

Moreover, by increasing the sail’s mast balance to around 25-26% (corrected to 27%), the CE of the sail has been moved close enough to the centreline to give quite light steering downwind.

As if that was not enough, this setup even lets him raise the sail when going downwind, and reef downwind without needing any downhaul.
These are real improvements, and in my view much more important than theories about keep battens, vortices and the like.

So what should one do to keep a good cruising speed in all directions without making the rig too complicated (wing sail and the like)?

·         First of all, one must be critical when choosing the vessel. Shape and size of keel and rudder must be right.

·         Then, a generous sail area should be fitted (..heard about easy reefing?).

·         Any fixed 3-blade propeller should give way to some sort of folding or feathering propeller.

·         Finally, longer and trimmer vessels just about always pay back with more miles covered. Roger Taylor’s experience with moving up from Mingming 1 to Mingming 2, should be kept in mind.
Long is good.

Cheers,
Arne

PS: As for the shown racing aeroplane below  -  come on! That thing, computer-designed, polished and probably with laminar airflow over much of the wings, is on a different planet. Those thin and small wings surely make the plane terribly fast, but I bet it is also tricky to handle and land. A potential widow maker. This is as far away from the JR philosophy as one can get.

I'm enjoying reading the various posts from some very experienced experimenters with the Junk rig and it prompts me to ask if doing some more tufting experiments wouldn't enhance our knowledge of what's happening with the airflow over the sail.

I wonder if some active sailor could put a few tufts on side of the battens themselves to see if anything can be seen of what's happening with the airflow there, and maybe along the top of the yard itself.

Maybe nothing at all will be seen.  Or maybe the flow of air upwards from the high pressure windward side towards the low pressure side will be demonstrated, while at the same time the tufts contained within the "pocket" of cambered sail between the battens will show the rearward flow of air ("trapped", if you like, by the airflow external to that pocket) on the cambered sail surface itself.

Which might be indicative of the battens acting as "wingfences" of a sort.

And interesting to see what is happening on the leeward side of the sail also.

Also, again purely for curiosity, maybe putting a few long telltales right at the leading edge of Ilvy's "wrong"-facing strongly built luff and shorter ones in a line at several points aft of the leading edge along the cambered portion,  just to see if anything can be seen.

Easy for me to suggest that someone else does the work, I know. :-)

Yours, etc

Dave D.

He at once pointed at the horizontal panels, and his view was that the battens would act as aerodynamic fences, preventing the air from moving spanwise.

- Arne

I agree on this one! Fences is a good word to describe what these batten pockets are acting like. As the camber pockets form on both tacks, there are fences on both tacks. I would speculate that only air from the upper panel would allow for tip vortex generation.

Arne, Slieve, I think that the tip vortex is of way bigger dimension as those longer telltales might be able to indicate. I suggest to have a look at the CFD-image of this NorthSails-Blog. It doesn’t matter if this is a pointy or junky rig, the physics are the same. I derive from this example, that telltales at the leech, of the length Arne used, won’t be able to show the vortex.

Graeme, very descriptive video, thanks for sharing! I grew up below the approach path of Frankfurt Airport. Luckily, our house was too far away, but the villages closer to the airport frequently suffered from the downwash: the tip vortex of those huge jets keep rotating for an incredible amount of time, while slowly moving to earth. They produce wind speeds of gail force and above. If such a vortex got close to a house, the roof goes flying. It happened quite oftenly.

Also, Graeme, thanks for the reminder to read those older magazines/articles. I take that as a well-meant kick from behind to get reading!

However, I feel urged to clear up on the bee flight. It is nothing more than a legend that a bee defies aerodynamics. There was a short time interval (some few months, if I remember correctly) in the first half of the 20^th century, that aerodynamicists were not able to explain why a bee flies. As so often, this was popularized and well maintained by media over decades. In fact, aerodynamics are very well able to easily explain the bees flight. Bees are just using different effects than airplanes do, which was a bit hard to understand at first glance. Bees, as well as many other insects and also some birds, create huge eddies with each wing stroke – intentionally! Those eddies are way more powerful in creating lift than any stationay wing is able to do. Amazing natural evolution! If I resemble that correctly, the only reason why humans don’t use this lift effect is, that we do not know of sufficiently strong materials to carry those loads at a scale of humans, not insects. It might be that the evolution of graphen will be able to change this.

About winglets: Designing winglets is a huge, difficult task! It takes a lot of experiments/simulations, to get a winglet (or any similar wingtip device) right. It has to be tailored to each wing, considering velocity, flight dynamics and behaviour and goes as far as tailoring especially to the flight routes those planes take. It is not just sticking a plate to the end of a wing, because chances are very high that you get it wrong and even increase drag further. With the methods and budget we from the JRA have at hand, I would consider it a most hopeless task. In general, one challenge with fitting winglets/top plates to a sail is how to deal with the widely changing angle of attack of the sail in the upper region. Different states of heeling would only be one of the factors.

That is why I would opt against just simply fitting a plywood winglet. The biggest question would be: how do you ensure that it is parallel to the airflow, with the yard being at some good degree to horizontal (even when heeled)…

I rather took the winglets as an example to understand the effect of the batten pockets/ camber bags. Airflow fence would have been a more catchy word to describe it, I admit. Again: I think we already use winglet-like devices, by putting sewn-in camber in our sails. I would just love to underpin this, my speculations, with experiments/simulations!

I would go so far and speculate that a winglet device on a cambered junk might be of no significant effect, as the airflow is already prevented/ fenced by the batten pockets - which might be the reason for the superb upwind performance.

Slieve, that foto you posted of that fastest airplane shows a different kind of wingtip device: It is not a winglet. I would estimate that the wing is drawn aft to push the wingtip vortex further aft where it hurts less. Also, the very tip of the wing probably is constructed with downwards angle of attack – you generate a bit of negative lift on the edge, to counteract the vortex generation. You deal reduced lift for reduced drag. If done properly, the overall sum is positive.

One more thought concerning the reduction of wingtip vortex: as Graeme mentioned, the elliptical wing (see the famous Spitfire) is optimum to minimize the wingtip vortex - and thus minimizing induced drag - if no further help of wingtip devices is used. However, there is a reason why modern wings are not elliptical: The stall behaviour of the elliptical wing is dangerous. That’s why nowadays you treat optimum lift generation to safer handling characteristics. In the mentioned spitfire, this compromise was achieved by wing twist: the sections close to the fuselage had a higher angle of attack as the outer sections. Therefore, stalling did not appear at once all over the wing – which would be quite deadly – but appeared first at the fuselage and increased towards the wingtips with increasing angle of attack.

As always, speed and lift efficiency are not the only players in the game. We all know that from sailing: there is a lot more to it than just optimizing upwind performance!

However, from all the highly interesting posts here in this thread, one huge point arises to me: As long as we do not understand exactly what is really happening on our sails, or can visualize it, or can put numbers to it, it stays armchair speculations.

What is needed urgently to push development forward, are some proper experiments, or CFD simulations!

An end plate on the yard of, say, 1/8" ply would add negligible weight.

The thing is, that 2-sided yard on my boat might already be acting in a small way as an end plate. Also, the low yard-angle and relatively long yard was from the get-go designed with the view in mind of pushing the vortex up and aft, and it wouldn't surprise me at all if the current set-up is near perfect as it is. It certainly performs well.

If I had the chance I would do some fooling around with a simple end plate just to prove it can be done, but still can't think how any difference in performance (if there is any) could be measured.

PS Slieve - I saw that aeroplane photo before - the opposite planform of the much-vaunted elliptical spitfire wing. Very interesting.

I also note that Edward raced his boat one season with no top panel - ie square top and full-length yard. Any feedback from that configuration? Steve Dawe with his multicoloured split sail has a square top too, and a batten system which requires no running lines. Any of these things are do-able - its just a matter of "does it make a lot of difference?"

(As for the gap below the sail - [probably more potential with this idea than all the other stuff about tip vortices].  What in the old days was called a "water sail". I have often had idle thoughts about having a water sail, permanently attached and carried furled in its own little zipped up compartment under the sail catcher. A very small amount of deck work would have it deployed - simply sheeted fore-and-aft - that would be fun for a bored crew on a fine sunny  day with not too much wind - the hull would then be a bottom end-plate. I bet that would add a margin of difference when fooling around at a junket.)