Foiler Design

[Chris Ostlind]

Originally Posted by sailor2

Just a guess, but how about computer power allowing...

Yes, I agree it might be very much connected to the computer and also to seat of the pants trial and error methods.

The computer part; it was probably all about the incredible access to worldwide, near-instantaneous, communication and information, well before it was about using the available technical tools, such as parametric CAE and CFD software when running on an affordable and powerful platform.

[sailor2]

Originally Posted by bistros

Evolution, not revolution.

Exactly, therefore the time frame I meant was not 5...10 years but rather anything up to 30 years.
What kind of foil design was possible by computers 30 years ago and by whom and at what cost ? Was there any method to make real foils matching those of theory predicts at any reasonable cost 30 years ago. You may reduce time frame from that, but 5 is way too little. I don't buy that some average person could have just done a succesful foiling moth 20 years ago.

[bistros]

Originally Posted by sailor2

Exactly, therefore the time frame I meant was not 5...10 years but rather anything up to 30 years.
What kind of foil design was possible by computers 30 years ago and by whom and at what cost ? Was there any method to make real foils matching those of theory predicts at any reasonable cost 30 years ago. You may reduce time frame from that, but 5 is way too little. I don't buy that some average person could have just done a succesful foiling moth 20 years ago.

The Moth as a development class has used the historically most successful technology development method - mirroring the academic model where experimenters publish their thesis and results for others to build upon, rather than the commercial model where advances are hidden behind patents and secrecy. When you can start your project with complete knowledge of what other's have done before, you can very quickly progress - far faster than if everyone hides their cards.

I would suspect Chris' postulate that communication is a factor is dead on - add that to more people communicating and you have effectively created a clustered development environment, sharing the same database.

There is no way the same progress is possible in a closed development environment where information is withheld and not shared.

Originally Posted by chabrenas

If you folks consider this off-topic, I'll start a new thread...

I grew up watching early foil development (including the Hook Hydrofin), and I have crossed the English Channel on a hydrofoil ferry, but I was out of the loop long before the 1990s when the Moths took a big leap forward by becoming foilborne.

What was the enabling technology that kicked this off? I'm sure that the number of people playing with them speeded up knowledge about efficiency, control and stability, both at transition speeds and at top speed, but was it materials technology - in the foils and/or the mast & sails - that made the sudden surge possible? If not, what was it?

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I think the answer is all of the above. The first Moth was sailed on just two foils(and a wand alititude control system) in 1999 and the first two person bi-foiler(an I14 by David Lugg and Alan Smith) was sailed within months of that. I think a huge amount of credit for the increase in interest in foiling is due to the rules of the Moth class and its early pioneers Brett Burvil,Andy Paterson, Ian Ward, John Ilett and Rohan Veal. But Veal and Ilett PROVED that the technology was really fast and I believe that they are the heroes of the foiler REVOLUTION going on now.
There is no question that the surface has barely been scratched in the potential applications of two foil technology: applications to larger monofoilers and multifoilers are just a matter of time. And new variations of three-foil easy to sail multifoilers like Dr.Sam Bradfields new Osprey and new developments from Greg Ketterman and others are coming up.
In fact ,it was Ketterman and Bradfield that pioneered production foilers way before the Moth. A refinement of the wand system developed by Bradfield is now used on almost every bi-foiler from the Moth to the RS600FF to the flying 18's and the 26' Mirabaud! This is an exciting era where foiler development is begining to
get the attention it deserves.

Originally Posted by Karl Wittnebel

Well, it's good to know someone with some actual training in this field doesn't think I'm completely mad.

I think my foil section maxes out at Cl of 1.4 or so, where it has optimal L/D.

People tend to ignore real-life features like hinge gaps, what the vertical strut intersection looks like with a flap eating up 30% of the chord (ugly), how much easier it is to build a strong foil intersection without a flap, how much less hassle it is to not have to cut the trailing part of a wing off and reattach it somehow, how nice it is to not have to put little bellcranks and rod tubes through the foils for flap control, etc. Getting rid of the hinge also gives much more design control over planform, section thickness, sweep and anhedral than a flap permits.

IIRC, drag varies with square of section thickness, and building an 8 or 10% section that will hang is much easier without a flap sinking your battleship. So far I have not done it, but it's only a matter of time before we push the materials to their logical limits, and flapless is stronger - probably not much, as it is so thin back there, but still.

Regarding the foil size, my foil is about the same area as the flapped foils currently being used. I think I could go a bit smaller actually, but it feels pretty good in takeoff the way it is.

On bending issues, cutting the last 30% of the foil off doesn't improve spanwise stiffness any, and the foil is much more sensitive to bending with a hinge, which will bind if the foil bends too much. Practically we are running aspect ratios of around 9 on mainfoils, so not as extreme as decavitator, mainly because the tips hit the surface if span is increased too much.

I just cannot believe my flapless foil with a nice intersection fairing has more drag at just about any lift coefficient than a similarly-sized foil with a flap on it. Newer flaps are hinged at the lower surface, which is better in my experience, having done some experimentation on the water. But still there is a gap somewhere. And that nasty wedge cut from the foot of the vertical, which must induce some cavitation at speed.

Mechanically, active control of the entire foil is also complex, which is presumably why there aren't more boats with a stabilator-type setup.

Functionally, on a not so obvious level, having a boat that can and does get itself down out of the sky pronto when you need it to can be a huge advantage offwind, and a tilting foil seems to have far more authority and less drag than a flapped foil in this mode, say Cl zero, where the flapped foil's flap is way up high and not looking very much like an airfoil at all. In fact the tilting foil has more authority than one can use at times, but that is an easier problem to solve than too little authority

The last point I will make is that my foil routinely recovers from ventilation before the hull hits the water, which is something that never happens with a flapped foil, period. I did not anticipate this behavior, but I am not complaining.

==========================
Karl, how does your altitude control system work?

Check this video out-particularly toward the end-a planing foil control surface is shown. Also shows "jumps"(done for the FUN of it)-fairly lame compared to what we'll be seeing on monofoilers before long! Video posted by Paul on Dinghy Anarchy:
http://www.youtube.com/watch?v=-VyOZVtOWoI&NR=1

[alans]

Breakthrough
There is an old adage in aircraft design “ stability then control and then performance”. Wind the clock back a decade or more and their were many sailors around the world persisting with surface piercing foils because the provided stability in height control as a result of their area decreasing as a function of height out of the water. All attempts to use fully submerged had failed the “stability” test. When I started work, about 10 years ago, with David Lugg in Perth to foil his International 14 possibly Ian Ward in Sydney had solved the problem but we where unaware of Ian’s success until several years later. I convinced David that some form of height control loop was necessary to achieve height stability with fully submerged foils. We considered a “wand” type control but reasoned that it would not be accepted under the international 14 rule and successfully went to man in the loop control via an elevator on the rudder foil. The elevator was controlled by the helmsman by twisting the tiller extension. David designed the mechanism to do this. This had the added advantage that the main foil was a fixed foil (no flap).
At the same time John Illet was developing the “wand” main foil flap combination for his Moth’s, essentially independent of David’s building and testing although Bret Burvill was working with both David and John at the time. It was this work by John that perfected the stability and height control method to achieve what is virtually used universally on Moths today.

Materials technology design of foil sections and math modeling have contributed considerably since then.

For the record the first computer modeling of yacht stability was a masters thesis at Cranfield University UK in 1967 submitted by Alan Smith

[Karl Wittnebel]

Originally Posted by Doug Lord

==========================
Karl, how does your altitude control system work?

At the moment I'd give it a gentleman's "C". But like most crude things it is fairly easy to improve; I never sail the same boat twice these days.

[chabrenas]

You're talking about carbon fibre as if it were old technology. Maybe - but when did it become easy for amateurs to use it? That required mass acess to both the raw materials and the skill to use them.

There appear to be plenty of carbon foils out there now, which makes it easy to experiment with new shapes, but metal still seems to be around. Can anyone tell me the pros and cons of using carbon vs metals that an amateur can work with? (e.g. machining out of a titanium block is not an option)

[bistros]

Originally Posted by chabrenas

You're talking about carbon fibre as if it were old technology. Maybe - but when did it become easy for amateurs to use it? That required mass acess to both the raw materials and the skill to use them.

There appear to be plenty of carbon foils out there now, which makes it easy to experiment with new shapes, but metal still seems to be around. Can anyone tell me the pros and cons of using carbon vs metals that an amateur can work with? (e.g. machining out of a titanium block is not an option)

The skill is out there and amateurs are building better and better carbon parts. The Cherub class is now mostly carbon homebuilds on foam core. Go to the UK Cherub class site for some really good tutorials. I've used Phil's Foils / Competition Composites to CNC cut foil cores for me that were subsequently finished and skinned. There is a lot of folks out there that have done their own cores from foam using glider wing hot wire technique.

Higher end homebuilders are doing vacuum bagging of Nomex & Klegecell cores. Wind Apparent (who infrequently posts here) and more often on Sailing Anarchy has built a low buck garage oven for curing epoxy/fom core build. Phil Stevo has blogged extensively on home build foam core.

The SwiftSolo site is full of carbon part fabrication.

Very few people use metal - weight being an obvious reason. Creating the dies for aluminum extrusion of foils is a big cost as well.

Originally Posted by Karl Wittnebel

At the moment I'd give it a gentleman's "C". But like most crude things it is fairly easy to improve; I never sail the same boat twice these days.

============
Karl, I'm interested in how your system works mechanically. Is it wand controlled? I think I understood you to say that your daggerboard and main foil are one piece-is that correct?

[chabrenas]

The Cherub class is now mostly carbon homebuilds on foam core. Go to the UK Cherub class site for some really good tutorials

Thanks. Think I'll apply to change my user name on this fabulous forum to RipVanWinkle. Over 40 years ago I owned and helped to design & build the first UK Cherub to the full restricted class rules - until then, the class was deliberately limited to Spencer MK IIs with the idea that this, and one licenced builder, would help get it started. Must try to get a look at a modern one when I go to UK in a month or two...

[Karl Wittnebel]

Originally Posted by chabrenas

Thanks. Think I'll apply to change my user name on this fabulous forum to RipVanWinkle. Over 40 years ago I owned and helped to design & build the first UK Cherub to the full restricted class rules - until then, the class was deliberately limited to Spencer MK IIs with the idea that this, and one licenced builder, would help get it started. Must try to get a look at a modern one when I go to UK in a month or two...

Yes, the topic deserves its own thread.

[Tinman85]

On the topic of foil design the majority of current sail boat foil designs are variations of straight wing design. The use of swept wings has been around the aircraft industry for some time now. I know some of the advantages of swept wings in aircraft come at high speeds where air starts to become compressable.
-Do some of the advantages of either forward swept wings or backward sept wings transfer to water bound hydrofoils?
-Has anyone else been looking into swept wing designs for hydrofoils?

Darryl Barrett, the designer of the Aussie Alpha Omega 14 Cat, has. Here is a rudder foil picture and he is using the same sweep on the main foils of a new foiler he is developing: