Rotating adjustable hydrofoils

Mij, Doug's playing semantic games - feel free to look to the content instead.

obviously you can go with both foils in the water and you might consider that to get initial fore/aft balance sorted.

But more foil means more surface area means more drag. The C class guys were running only one J foil in the water (with heeling and with board cant an L foil becomes a J foil hence the semantic games Doug is worried about)

and theoretically this can be stable with just one rudder in as well - as you are essentially in the same configuration as a low wing dihedral airplane - but the second rudder gives you a bit more lateral stability

 

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I say it that way because of an article I read by Pete Melvin and Gino Morrelli
where they state ,unequivocally, that they came up with the TNZ foil(and the three foil configuraton,single main foil) while working for that syndicate.

From: http://www.cupinfo.com/en/americas-cup-pete-melvin-foils-multihulls-13146.php see parts one and two
“At Team New Zealand, we developed a new type of foil that allows you to keep your height above the water more or less steady. No one had been able to do that before, at least not on a course-racing boat that was not going downwind. "

 

No Doug, I mean with EVERY single thing you speak about you feel compelled to say who it was you think invented it, I am not talking specifically about TNZ or any other thing, it is a broad strokes thing, EVERY "innovation" you speak to, you HAVE to say who you think "invented it", every time you speak about it.

I used TNZ as an example, you do the same every time you speak to something that might have been by Bradfiled, Ketterman, TNZ, or the martians.

Why is that?

 

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Simple: to give credit where credit is due(or overdue). To help people understand the details of the history of foil(foiling) development.
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Does that help? Or better yet: satisfactorily answer your question?

 

Every single post though?

I like to drive a fast car, I even like to enjoy their design details from time to time, doesn't mean I need to know the genesis of every design element of it every time its mentioned.

Would it not be easier to simply start a thread which is JUST the history of foils and related matters, then simply put a link to that in your various signatures, instead of peppering every post with historic details?

Just a thought....

 

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I think, when communicating with the diverse groups of people at the distances you say I am, it's probably better to give the credit thats due in the context of the specific reply-just to make it crystal clear.
That reminds me ,I started this thread for just such a purpose but haven't updated it in a while-wanted to get the MPX sailing first.....
http://www.boatdesign.net/forums/hy...ler-design-foil-assist-full-flying-40894.html

 

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mij-I apologize for my part in the 6 post thread hijack-we probably should have done it in PMs. Sorry.....

 

Doug - just stop please

 

BTW Mij - any suggestions you see from High On Carbon - take them. He really knows his stuff.

 

Guys, I really appreciate your advice and willingness to take the time to consider and respond to my ill informed questions and crazy ideas, but I might raise a flag and declare my threads a demiliterised zone.

So, I seem to have a few options. Doug, I agree that for a rc boat that T-foils and the Bradford system makes the most sense, but I'm stubborn and keen to try the rotating foil approach. Assuming that I use this approach I can see that using Baltic Bandit's two foil suggestion probably provides the best performance both up wind and down wind (given that I'm realistically not going to be able to foil up wind). The question that I'm still not sure about is the type of downwind foil to use. I like the idea of having some inclination in the axis of rotation to give some ability to make adjustments to the angle of attack, but the point High on Carbon makes regarding the asymmetry being built into J-foils is good. For some foil options this inclination won't be required and may be counter productive.

So my question is, what foil type would provide the most stable foiling downwind (other than T-foils) with limited ability to respond, and of the options which would benefit from the rotating foil approach?

 

Unless you have very well instrumented onboard controls, I suspect you will never sort out the rotating foil bit. There's just too much stuff changing at once. The basic engineering principle is "change only one thing at a time"

Now obviously when deploying a whole new system you cant quite do that, but you can start with a baseline and get it as good as you can incrementally statically, and then and only then add dynamic controls.

Its like one of the best non-pros in J-24s told me about how he tells new folks to the class to come up the learning curve:

1) don't start by trying to point high and go fast. Instead, first try to go through the water at the same speed as the top guys.

2) when you have figure out how to do that, THEN and ONLY THEN try to come up 2-3 degrees and regain that speed. Rinse and repeat.

Because that way, you know how to 'change gears' and later can do things more dynamically but only after you've set a baseline.

On downwind foils, I'd suggest you first start out with what would be most stable. And that's a J-foil ala the GroupAma C class.

once you have that sorted, then you can start "straightening the L" which will change your stability but also give you more speed. But building new foils for a model is at most a weekends work. not the $10k+ that it costs for something like a C class boat

 

Mij,

do you want to achieve full foiling, or just high lift fraction sailing, or "foil assist" as DL calls it? it's a big step between the two modes.

An L or J foil will do fine for controllable foiling down hill. The difference between L and J is quite small. What's important is how acute the angle is between the wing and the strut, the strut being the vertical part, the wing being the horizontlish part of the foil.

Groupama C had about a 67 degree angle between the two, this is a very stable foiling set up. BUT, it's only stable if the whole foil is canted inboard 15-25 degrees, I measure this by how far off of vertical the strut is by the way

So upwind their strut would be perhaps -10 degrees from vertical, putting the wing closer to horizontal. downhill the strut angle would be say +20 degrees, putting the wing up at almost a 45degree angle relative to the water plane.

The more acute the angle, the more parasitic drag you will have upwind but the more stable it will be in heave (up and down motion due to changes in sail forces and boat speed).

With a more OPEN foil angle, the more slippery will be the boat, but also the less heave stable. so it will go faster than the same boat with a more acute angle foil, but it may crash a lot more often.

The canted straight foil is simply the logical extension of the most OPEN foil, and angle between the strut and the wing is simply zero.

The more open the foil, the more you trade away the "leeway effect".

another very important factor is that when the strut is near vertical, you also mitigate the leeway effect quite a bit on the foil system, so it's ability to tune itself and adjust ride height automatically is compromised quite a bit. It's more likely you will go up, up, up, and then sideways very fast, roll into windward, and then crash down, rinse wash repeat.

In the AC you can chart a clear path or progression for all the teams as they move through the development cycle. They all start with a horizontal wing and a vertical strut, it's a sensible response to the two vectors you want, but it ends in tears pretty quickly (up-up-up-sideways, down repeat).

Then they all cant the foils a fair bit. It takes longer to fly, but the whole crew thanks you for the reduction in the daily ration of contusions, scrapes, bumps and **** in their pants.

If they were smart (Not like us, we were not smart in this regard) they make a more acute angle, and reap the benefit of a pretty stable ride.

As they get more clever, they open up the angle a bit, generally landing near 90 degrees. Now they are going quickly, but it's tricky to control well, ride height is on a feather edge and has to be closely coordinated with the wing trimmer.

In the C-class event this year, you can see three examples, and I think Groupama who won, is the most analogous to model boats, in that there are not nearly enough hands to go around to trim all the bits required for successful flight. So they went with a safe package, and had consistent stable flight.

hydros has a more squirrely package, had higher top speeds, and had the most spectacular crashes.

We on Fill your hands, had an insufficiently refined package, and had to heel the boat a fair bit to achieve stability in flight, all because we were locked into a vertical strut.

Some things to think about there.

 

try more than twice that, per foil, net of tooling...

 

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Magnus, do you think a beginer in rc foiling should tackle an ac type system rather than "traditional" surface piercing foils? He doesn't want a wand based system and the RM that comes with it but the complexity and sailing control requirements of a hybrid AC foil seems a bit much to me-what do you think?

PS- for anyone interested Magnus has written a great article about the technical details of the LAC in the January issue of Seahorse magazine....

 

An example of the angle I was talking about