Some homework for Paul
Regarding luff webbing, winglets and battens, and the "bad tack"...
The above does not apply to Paul, it applies to me. Paul, your exploration of theory (and your beautiful diagrams) IN ADDITION TO your out-on-the-water gaining experience, is an inspiration.
Paul wrote: "But wait, what I saw right in front of me, were already winglets. Winglets not located at the wingtip, but spread all over the sail. It was the battens in their batten pockets, which force the air horizontally along the panel, limiting any vertical airflow (which creates the tip vortex)."
This perked my interest. At the present moment I am doing some “homework” : critically studying all of the early newsletters and magazines. I am overwhelmed by the amount of thinking and debate which was taking place, and debated so hotly, despite the snail-like pace of the pre-internet and pre-forum era.
These were early days in the development of ideas we now take for granted, people were only starting to come to grips with the various ways in which camber can be given to a junk sail and the advantages which might ensue from it – keep this in mind as background to what follows.
In 1989 (long standing members will know all this) a talk was given by Group Captain “Bunny” Smith (DFC and Bar, OBE, CBE) and I mention his “gongs” so as to clarify that he was not some sort of over-imaginative “flake” – he had a seriously respectable war-time record as an aviator and leader – perhaps in the same league as Blondie Hasler. He must have been a real character – at the age of 70 he took up junk rig sailing and declared “I am jolly well going to find out how this rig works and I haven’t got long” !
The Newsletter published an article - an introduction to Bunny Smith’s “I.F.T.” (Insect Flight Theory) as applied to the junk rig. He was interested in low speed aerodynamics and had done considerable testing on his 26’ Saddler Fenix – investigating such possibilities as battens attached to both sides of the sail to create vortices, (“turbulators”) and also something along the lines you seem to be suggesting, he refers to these double battens as “keep battens”.
In addition, he utilised quilting of the sail which we see on some of the photographs of traditional Chinese junks (always a mystery to me). These are all details visible in insect wings, an inspiration to him due to the fact that a bee can carry 50% of its weight aloft, and in a number of ways defy conventional aerodynamic theory. As it happens, he was also experimenting with bendy battens, carefully designed and built to provide camber in the way we want it to be – but his main focus was on his theory, that turbulent airflow is able to re-attach itself more quickly than laminar flow, and the benefit thereof.
(He also had his answer to your question as to why the mast, on one tack, does not seem to degrade the lift generated by the sail – the mast is buried in that bubble of turbulent air, which re-attaches itself further down the foil before exiting.)
Needless to say, much discussion was generated. He also had something to say on planform, and the induction of camber from the controlled twist of fanned panels. Unfortunately, so many things were going on at the same time, that it would be difficult today to analyse which particular innovation led to the improved windward performance he was able to demonstrate. (The camber from his bendy battens, as much as anything else, it seems most likely to me).
He was convinced that the interrupted and re-attached flow of air over the sail (as he saw on the wings of insects) was of great benefit. I wonder what he would have made of your offset luff webbings, given that your sail seems to perform so well. (Rather than try to criticise your sail-making, (the luff issue which seems incompatible with aerodynamic efficiency) I suspect he would have looked instead for a reason why this quirk seems to work so well! Something to ponder. [The Schnabel Luff Turbulator. Don't fix it if it works ! ])
Smith was happy to disregard aerodynamic theory if it did not seem to fit the results he was getting (nothing wrong with that). It seems he was in good company.
Smith was greatly offended by a fluid dynamics PhD student who was researching at the time and reporting back to the JRA (Joddy Chapman). Chapman's reports did not support Smith’s findings. Smith wanted him off the payroll (JRA funds). It seemed to more or less come to a head in Newsletter number 34 in which Chapman published a detailed academic paper which, among other things, was a serious reply to Smith – though it did not “take the wind out of his sails”. If you have not already read that report of Chapman's, I believe you would be interested to do so.
Bunny Smith died less than a year later. His Insect Flight Theory still appears from time to time but he is probably now remembered more for the “Fenix” planform, an ancestor along with the planform of Reddish, of some of the fanned sails we still see today.
Bunny Smith's 26' Saddler, Fenix, with his trademark "wu liu" (56) on the sail.
If you have the time to ponder, may I suggest you download JRA Newsletter 24 which outlines his theory, and also 25 and 26. Number 34 which is Chapman’s paper – and you might like also to read Robin Bains’ obituary to Smith in issue 37.
Finally, you may also find interesting a short Forum discussion on Smith which took place in 2011 – just 10 posts, each one excellent and worth reading – here https://junkrigassociation.org/technical_forum/484001
Apologies Paul, if you have read all this, and to longstanding members who were there at the time. Those of us who were not, ought to know a little of the history.