Foiler Design

What section are you using? Are the cordinates on uiuc database, I can plug it in to solidworks and give you the moment of inertia. is it a solid section?

 

Thanks Mal.

That's basically what the estimated moments do - they integrate the thickness chordwise and come up with a figure for the area and the total amount of area displaced from the neutral axis. I'm no calculus guru though.

Apparently, the moments only go so far with composites, though, which do not have uniform strength in all directions. I was just looking to calculate the stress at the surface to be sure I wasn't completely out of the ballpark, but apparently that isn't a reliable indicator of when or how things fail necessarily.

For the wave loads, I will probably have a decent number on how many G's I pull in the near future, as I am going to put some gear on the boat and go sailing.

But in the end I'll do what you describe. I know 14 rudder lifting foils are right at the limit, and I think they are more highly loaded than a Moth, so I'll go a tad thinner and wider and hope it isn't too much and that it holds an angle of attack reasonably well. Should be fun.

Best,
karl

 

I purchased a seat of DesignFlow for $195. It provides the critical coefficients and geometry factors for thousands of foils, and it is easy to use.

-Doran

 

Manual Altitude Control

I have long advocated at least experimenting with manual altitude control on a bi-foiler and now-finally- some results from somebody( besides myself, David Lugg/Alan Smith) who has recently tried manual control on the largest bi-foiler on the planet-Mirabaud. I hope this inspires others to consider experimenting with manual control as well. I'm posting the entire e-mail with permission:

Hy Doug

No waves no problem - if manual control then it is certainly for sailing in waves - not for being faster but for being able to fly (so overall faster also)

The problem with the wand control is that it is a static system - the wand reacts (sometimes very odly and also false eg depending on wave length)

Manual control (very much as stearing) allows to anticipate ! (a good helmsmen is fast because he anticipates just the minimum amount of stearing)

So manual cotrol allows to fly in conditions where the wand does not work anymore

Manual control could also be replaced by some electronic system properly programmed....but that is onother story

Our project this winter is to build a manual control system on each wing (bicycle cables) which allow to override the wand from a hiking position

Probable range of use : Downwind sailing in wind over 18 kn (waves bigger than 60 cm)

Regards

Thomas

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The first bi-foiler to use manual altitude control was David Luggs boat,an I-14, and it used a system whereby the twist grip on the extension tiller was used to move the flap on the aft foil. My boat was next-though with very limited time and the twist grips on dual extension tillers controlled the main foil flap. This same system with push pull cables replaced by push rods is being used on my new boat. Mirabaud is using "bicycle cables" connected to the main foil flap....

 

I suspect manual foil control on a boat as big as Mirabaud might require less cat-like reflexes than a foiler Moth.

I posted some notes on PID control theory and practise in post #967 of thread http://www.boatdesign.net/forums/sailboats/moth-foils-30-31-knots-34-86-mph-11209-65.html#post331350

I think that a combination of manual and automatic foil control based on PID control theory (to the extent it can be applied) might have some promise for ease of control, speed and stable flight in heavy weather. It should be possible to do this without the added complexity of an electronic system.

 

Thanks, Terry. The interesting thing about Mirabaud is that, apparently, the new system will allow the crew to switch back and forth between wand and manual control at will....
Mirabauds manual control system will certainly be easier to implement than on a singlehanded bi-foiler since they have the extra labor to devote to it whereas on the Moth it's in the hands of the skipper.
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I'm not sure I understand PID theory-could you elaborate on it in an example
that I might understand? I appreciate the effort....

 

Recently, I've been thinking that it might be possible to devise a semi surface piercing foil, basically a flapped T-foil with long surface piercing winglets at say 45 degrees. The idea being that the winglets would control the ride height, but coarse control for the prevailing conditions would be provided by manual input. This compromise solution may be slightly more efficient than a fully surface piercing foil, but not as difficult to control as a fully manual T-foil.

 

Doug, about a month ago I had expressed you (through PMs) my thoughts about the possibility that wand control system (being essentially a proportional control) might enter into crisis at a certain wave conditions. You said that it is not the case and that is very stable, but it appears from the lasts posts (#859) here that maybe some problems really can happen.
Could you please tell me what is the actual situation and what are the limits of the system, because I was thinking about using something similar for a thing I have in my head... In case I have misunderstood the sense of your last post, I truly apologize.

 

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Daiquiri, I remember that conversation-it was in regard to the altitude control system on the F3 RC foiler. The wand system on that boat never caused any anomalies whatsoever in roll or pitch and that is pretty much true of a correctly set up RAVE full size foiler. The worst case on the F3 is when waves start to hit the bottom of the main hull and the boat starts to slow down. But even in those conditions wand response was accurate and worked well.
Many wand systems used on monofoilers like the Moth and Mirabaud have experienced problems in big, short period waves. What has happened on Moths is that the wand comes clear of the water then springs forward(pulled by a shock cord used to keep it "against" the waters surface) raising the back end of the flap which causes an immediate crash. The Moth flies proportionately much higher than the RAVE or F3 so tends not to bottom out
but it seems that perhaps the wand length may be too short in some conditions. Some boats use adjustable length wands. Mothies I have talked to say that problem is not happening as much anymore-but if you look at the video on "Moth on Foils" you'll see crashes caused by this very thing. It can be eliminated by design-it is not a charateristic of a monofoiler. Hope that helps.

 

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Mal, I designed this foil to experiment with a very small flap(12%) and to use the "winglets" in exactly the way you propose. Don't have enough experience with this foil yet to say too much but in three hours foiling with manual altitude control the foils appeared very docile-not a single crash or broach of the surface. More relatively soon,I hope.

 

I would anticipate problems with uncontrolled ventilation along more of the foil than you might desire if you took the t-foil + angled tips route. Each time a tip breaches the surface air might get sucked down the low pressure side, potentially across the t section also. I'm not sure it is sensible to combine the two foil approaches.

 

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You're right it could happen-but it could be dealt with just as Hydroptere and other surface piercers have dealt with it-with a fence or fences. I also think Jon Howes approach is a viable alternative for a stable foil system that does not require an altitude control system at all.
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I think what both these foil approaches show is an attempt to make foiling user friendly at what may be some cost in top end speed but with no loss of the ability to take off in the lightest wind if that is what is the focus of the design as well as more docile control.

Jons foil:

 

So, the Tomohawk foil equipped boat has been around for just about 1 year now, after huge fanfare from Ovington, et. al. My questions, then, are how many have been sold... and where's the evidence that they really touched on something significant for the consumer at the entry level of foiling?

Go ahead, dig it up... I'll wait for the announced revelation in small craft foiling that was purported back in March of '09.

 

Doug,

That is sort of what I had in mind, but I envisaged that the "winglets" would be proportionally at least twice the length of those shown in your photo. I think your implementation would require a larger degree of manual input than I would like. For a combined foil system like this the degree of flap control required would be a function of span.horizontal/span.total. The best ratio would vary depending on the design objective.

I will be interested to hear more progress reports on your foil system. Do you have any photo's of the foil in action?

Munter,

Regarding ventilation of surface piercing foils, this is always an issue. There there are plenty of working examples of surface piercing systems (Hydroptere is one example) which suggests that it's not a deal breaker, but it is a factor that must be considered during the design process.

 

No action photos now but that will change soon, I hope. You might want to try your idea on an rc foiler-the foil performance scales remarkably well except that ventilation is not as likely on designs that would ventilate easily at full scale. Good Luck!
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Hydroptere,Scat, the Hobie Trifoiler and others were tested as rc models.....
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PS- for anyone interested in the details of making manual control work it should be apparent that some way to get control input from the skipper(or crew) to the mainfoil flap will be required. In the past some sort of cable or push rod system has had to be devised and on a single hander that can take some routing and be a little complicated. There may now be an order of magnitude simpler way to do this based on a new wireless technology that has been introduced for small boats. The system-about $300 to 500US- appears to be an almost perfect solution to manual hydrofoil control while eliminating all pushrods, cables and bellcranks. Anyone interested can PM me for the details as I know them now-lots more research,experimentation and testing to do but seems to have great potential.