breaking eggs

breaking eggs

Moth and C-Class wing co-designer Magnus Clarke has stayed pretty quiet on the teething issues experienced by Bora Gulari and the US Air Force down at the Moth Worlds, but with Charlie McKee’s destruction of the second wing, something had to give.  And as usual, Mag puts it all out there so everyone can understand.  Brilliant.  For the whole discussion, check the thread.

No doubt there is still plenty to figure out on that wing, it certainly has moments of brilliance but as noted, it has issues too.

Everyone should keep in mind these things were designed and built in a big hurry. The prototype wing was put together in 8 days at the Object 2 shop with 5 people or so going all out on it. It was mostly pulled out of existing tooling. Subsequently it has all of 10 days of testing on it, which rounds out in the greater scheme of things to about none.

The next 3 wings were built even faster, 3 wings in 10 days by a similar number of people. But they achieved a 30-35% weight savings over wing #1. So again, good job boys to the guys who stayed up late to build those things. They were very well crafted and came out looking very good. Having been built they were promptly stuffed in a container and shipped off to AUS post haste.

From a design perspective we knew going into this project they would not be the optimal wing design by a long stretch. With a D-section leading edge on the front foil, they don’t twist. This means these wings cannot use full camber downwind across the full span of the wing due to gradient effects, so the whole wing is not kicking out the kind of lift per foot of span that say a C-cat wing could.

Next of course are the mechanics. Less hands on board a moth than a C, so what you can tune on the fly is compromised quite a bit. Also we are dealing with a lot of structural scale effects that are affecting how certain components within the wing flex, move and jiggle, this all erodes the performance a bit if it’s not doing what it was designed to.

Reynolds numbers, yes, in a moth they are low, but really not substantially lower than a C-cat in light conditions and we can make C-cat wings work just fine in light conditions. Even in 8 knots TWS the wing should not be dropping below 250,000 on the RE number so we don’t need to call Mr Drela just yet.

As for structure, yes there is also issues to sort out there. We tried working with TPT on this project and for a first go round, I would say it’s been pretty impressive stuff to work with so far but there is a lot of learning to do before we are happy with the whole wing structural package. Again, going into this project we as a team knew there would be structural load conditions well outside what a C-cat wing is designed for, e.g. hitting the water at 25 knots. If you do that in a c-cat, you accept that you have likely blown your wing to bits. In a moth you kind of expect that you are going to do that with some regularity, regardless of skill level it seems. So on balance, the wings in the moths are taking a ton of abuse relative to C-class standards of care and operation.

Also in respect of structure, things do not always work out the way they are planned. Some changes to the drawings were made on the shop floor which might have lead to some potentially not good things in the final build and operation of the wing, I think this was a contributing factor in the demise of the one wing mid-gybe. I don’t really hold the builders responsible for this one because we were all just trying to get the things out the door in record time.

As for the performance of the wing currently? Well to my eye, some 15,000 km away taking periodic reports from Lawn Boy, it’s doing pretty well, all things considered. To imagine that a wing is a panacea that will magically make you jump to light speed is, naive. Currently these things are still very much in the realm of experimental. Issues of usability and how easy it is to step were totally secondary to issues like just getting on the water by the deadline. Learning how to get the most out of it? Well that just takes time, a fair bit. Wings are not easy to sail with, they don’t luff and tell you when they are unhappy, quite the opposite. So to date I am pretty encouraged by their performance. Sure I would have liked to see the wing doing better in the results, but this is still really early days. By C-class standards just getting around the course a couple of times without it blowing up constantly is a very good start. Hanging in in the mid-top of the fleet is very good. Doing all of that with something that is likely 1/2 sq meter smaller than everyone else is really good.

So lets get a few final facts straight before I wander off again:

Bora Gulari wanted to build a wing so he approached Object 2 to do something about it.

Fred Eaton, Magnus Clarke, and Steve Killing designed the wing, based in large part on existing tooling, to help speed up the project. Magnus does the planform shapes and wing sections, Steve is responsible for structures, laminate schedules etc. Fred is the master of the show. We all worked closely with Bora to figure out how it would work and what we might expect. Design was done in a matter of days.

Rossi Milev and Rob Paterson were the lead builders. Bora, George, Chris Rast, and a number of others were involved very closely and tirelessly in the build process of all 4 wings.

One wing was built, tested for a week and a half, ridden very hard and put away wet. The next 3 wings were built based on what was learned in that short timeframe.

The 3 new wings were shipped to Aus and rigged once they got there. They were only intended for Bora and George Peet.

Rob Paterson of Object 2, travelled to AUS to help out the guys in the development, maintenance and optimization of the wings.

After a few days of testing Bora and George were not entirely confident in the wings abilities to help them perform at the worlds, so they chose to go with the soft sail option, they are there to perform as well as possible, not to parade around with a wing on regardless of results. So the choice to not use it, is fair enough.

Charlie McKee chose to step up and use a wing for the event to continue the development of it. For this I personally applaud him.

Again, Rob Paterson is down there keeping the wings fed and watered the way they should be. When it breaks, it’s not Charlie gluing it back together, it’ll be Rob, just like in the C-cats. He is our super capable shore crew who makes sure shit is ready to fly on time, every morning.

So to everyone involved so far in this project, I say: Congratulations, great job so far! Bora, George and the Detroit crew have been great to work with. Steve K and Fredo have been as awesome as ever in bringing the project to fruition, the guys at TPT provided some great product to trial and showed really good support when it was needed. Rossi, as a builder he’s always got your back and his anal tendencies are perfect in a job like this and of course Robbie Paterson, who has tirelessly slaved away at getting these things in the air and going forwards.

Also, good one on the class for allowing it to race. It’s a shame it was such a bun fight going into it, but I am happy to see it able to go and play with the others. I would hope that some sane discussion follows the event on how perhaps wings can continue to develop within the class and hope that there can be a path beaten towards a fair and even standard of measurement for any kind of sail and or rig combo, that suits the classes ethos.