Rotating adjustable hydrofoils

Unstable foiling demonstrated..

 

Doug, Taking on more than I can realistically achieve is my speciality.

Thanks for the advice everyone. I'm confident that I have the best advised rc foiling boat project in history: a foil test system mostly designed by tspeer, with foil selection by high on carbon, Doug Lord and Baltic Bandit. Now I just have to build it. By the way, I promise not to hold any of you responsible for the mast aft wing.

 

Sorry, I left out the tooling as tooling in a RC model isn't that high... with tooling I suspect you approached closer to $30k. Even with "3D printing" for small gadgets the quotes I consistently get from design houses is north of $30k for a mold that can do a production run of around 100-300

Now a fair amount of that is designer cost and amortization of the investment the designers have in printers, workstations and high end design software but I would expect your mold tooling to be around $12k min. You aren't engaged in the cheap end of the sport.

Mij, what HoC says is spot on.

 

Yes, I've reread the post several times, best description of the effect of different factors for J and L foils that I have come across.

 

Mij, thanks, you are too kind.

We spent the summer working our way through the foiling issue(s) on our program, with not as much success as we might have hoped. for a number of reasons. One thing I can tell you is that failure was punished with physical beatings for the crew / design guy. Sadly it got to the point where despite our enthusiasm, we were becoming gun shy about foiling by the end of the summer, right when we needed to be full on. It was a tough mental block to overcome every day on the water.

So I learned the effects of the L, the J etc, the hard way. I spent a huge amount of time, time that should have been spent on my business, working out how the leeway effects worked. So much so I wrote my own VPP of sorts to work out all the forces at play in the different configurations. It built on one I already had, which has the whole boat modelled, the wing, simulated by Tom Speer's vortex lifting line program, and all the foils on the boat. It's a sprawling Excel program with tons of macro's to step through dynamic reactions and forces. It's total spaghetti code, that could not be ported to anyone else's machine. It draws on multiple data bases for different foil behaviours, and is salted with a number of corrections that were learned empirically on the water.

We did not have the benefit of $100M to play with, nor vast design teams with many computers chugging away day and night, just me chugging away, mostly at night.

It took a while to be able to simulate what was happening in static conditions, E.g. sailing perfection, where nothing is changing on the boat. It took a lot more to be able to simulate anything approaching real dynamics on the boat, 1 foil, 2 rudders in the water, varying crew pitch trim, varying sail forces. Now change everything as the boat accelerates a few knots, and it all gets crazy.

Sadly I learned a lot, but too late to be able to catch up to our competitors in time, given the lead time on building the bits and pieces.

That having been said, I can now see different systems and very quickly understand their pro's and cons, down to little details. Like the radius in the elbow of a foil. The larger the radius, the more quickly it reduces the benefits of the leeway effect.

I'm glad what we learned on our team can be of value to others. One day, when I have some time, I'll try to write a paper to explain what we learned, and what we also know we had to work on.

In practical terms, we made big steps, and we know the next steps we would have to take to get in step with other teams.

Sorry if I digress, I just know I will not be able to post for a while again, I came up for some air and will have to deep dive again on work.

BB: we spent a bucket load on tooling, then built quite a few parts from it, independent port and starboard wiggle foils. towards the end of the season we cut the tooling and put it back together, to be able to build foils with different angles, twice in two weeks, at great expense to Fredo. the progressive steps most certainly helped to achieve more stable foiling. As late as 5 days before racing started, we were drawing trunks for canting foils and determining if we could pull it off in time for racing, it was that important.

When we got to England we quickly realized the other guys were using solid carbon foils. We know now that the go forward would almost certainly be fabricating solid carbon billets for strut and wing, indpependently, and then machining them t the desired shape, and bonding the elbows with steel or titanium. Far more cost effective that molding two halves of a foil, particularly when you want to keep stepping through different shapes all season.

 

Physical beatings for failure ultimately looked like this...
Seven deep stitches later, I got back on the water two days later.

 

The crash that caused said injury...This is what happens, frequently, when you have a vertical strut while trying to rely on a j-foil to fly stable. Had we been heeling more and had an adjustable foil angle (AOA) from the wire, we could have managed the rapid acceleration that was precipitated by a puff with a 40% increase in wind speed, we went from about 21 knots, to 26 knots, very quickly. The boat started to fly higher, to the point that we were lift with almost no foil in the water, you skip sidewise as described, roll in to windward and stuffed the windward bow.

Photo credits, Meredith Block.

 

Cool info on the tooling. You know how to contact me. I think I know how to get you fairly inexpensive access to "compute time" for your excel spreadsheet as is - so when you are ready for more bruising, contact me, I'll be happy to help. And since these days I'm based in Paris, I might be available to lend a hand on the ground in Geneva (apologies MiJ for the slight digression)

 

HoC: no need to apologise, it is a great story, you should certainly write it up some time. Like you I'm about to immerse myself in work for a while. The reason for starting this, and related, threads was to line some ideas up for when I re-surface. Thanks again for the advice.

BB: No problem, it is the diversions that make these threads interesting.

 

Seems like machining from billet doesn't get you the nice long surface fibers on the outside to hold the package together. I suppose you could sheath it in cloth afterward. Not quite sure why you feel that is cheaper than one off Mdf molds; the carbide gets expensive in solid carbon.

Look me up if you ever get to LA.

 

Ps I think you guys are getting far too carried away with tooling quality if you are paying that much. Molds like that can be knocked together fairly cheaply for prototype/ low volume stuff.

 

This is LittleAC cup stuff. you are on the hairy edge of tolerances. MDF molds won't cut it. you will end up with foils that require too much hand fairing and don't work out well as a result.

What you are missing is that most of their prototyping is being done via computer simulation (hence the VPP program HoC talked about as well as the) as well as other mockups

If you go to the C Class Championships thread in Sailing Anarchy - you can see HoC (where he posts as Blunted) show off some of how they mocked up controls and such before actually implementing them.


essentially these folks are building IndyCar racers. You are suggesting that they put a piston into an IndyCar engine that was sand cast in a backyard and filed to shape by hand....

 

For real.

 

All of our tooling for foils to date has been built out of pre-preg hi temp carbon resin matrix, to match the final part laminates. This way the coefficient of expansion in the part is matched to the tool, then we don't have laminate pulling off the tool face because it shrank faster than the tool at some point in production. We cook our parts in a 5 atmosphere Autoclave.

Plugs for bits like foils are usually CNC milled from Blue block. Larger parts like hulls are milled from solid MDF, then coated, faired, and tools pulled off of them.

We aim to build 2-12 parts out of most tools, at most. But they are built to high tolerances so we don't have to add a lot of bog after to fair things out smooth.

included here are the super top secret tooling for the wiggle foil and a first version of a part from the tool.

Also shown, a rough bench test of a mechanical system

Also, a physical full size mockup of our deployable slat system. All built from the wing tooling itself, with mechanical systems in place, to see if it all would work (Yep, sure did)

If we mill parts from solid billet, we would organize the matrix and fibre orientation very carefully inside the billet, not just machine any old fibres will nilly and yes there would be wrap layers on the outside for sure, for final fairing and layer bonding etc.

 

some mockups from another larger project of note.

The one on the water actually survived out there in the middle of the harbor for a matter of weeks, and that included a storm that hit the City killing a few people with Tornado activity. The other one was for working out mechanical means of installing a rather large wing, on a boat, while it was on the water. In both cases we ended up doing it this way for the most part.

Rough stuff like this can help a lot, before you get committed to big actions