Electronic Foil Control Systems.

[dougculnane 0]

For another thread but this is very worthy of its own. So I started it.

[PorVida 8]

Well aside from the typical hype to which we are exposed around the world of foiling boats, especially those of the type such as the Moth, this development of the electronically controlled foil system by Clive Everest is a breath of fresh air.

 

I hope to hear more about it, its further development and how it will fit into the existing boat classes (or not) in the future.

 

Chris Ostlind

Lunada Design

www.lunadadesign.com

[dougculnane 0]

Electronics are banned from the Moth and I think all (ISAF classes) so it is just a side show. However I feel that it has such great potential to increase the control of the boats it will be hard to ignore.

 

Electronics have the ability to know if the boat is going up or down and how fast. The present systems just know how high it is now. The cost of such systems is potentially high but the complexity of them is nothing compared to the electronics in everyone's car, video, lift, wrist watch, fridge or electronic toothbrush.

 

As Clive indicated you can adjust the parameters on the water... So you have the chance to select the right configuration parameters, for chop, flat water, learner, sport mode etc... like your car.

 

Clive what are your thoughts about the future of such systems? Do you think they have a place in the sailing world and will this involve new classes or modificatins to the rules of old classes?

[Doug Lord 1,219]

Clive, very interesting design and congratulations on some terrific development work.

I'm most interested in your opinion of the various altitude sensors that could be used in this application-ultrasound ,micro radar etc.

Thanks for having the guts, courage and determination to make such a trmendous contribution to foiler development!

[Kevin Schultz 1]

Clive, very interesting design and congratulations on some terrific development work.

I'm most interested in your opinion of the various altitude sensors that could be used in this application-ultrasound ,micro radar etc.

Thanks for having the guts, courage and determination to make such a trmendous contribution to foiler development!

 

Over thinking it, go with a 3 axis accelerometer and a contact switch. You know when you are on the surface, integrate the acceleration twice and you have height off the water. It should be a lot less expensive than either other option, plus you won't have to filter out the waves.

 

Interested to see what his solution was.

[kprice 1]

Electronics are banned from the Moth and I think all (ISAF classes) so it is just a side show. However I feel that it has such great potential to increase the control of the boats it will be hard to ignore.

 

Electronics have the ability to know if the boat is going up or down and how fast. The present systems just know how high it is now. The cost of such systems is potentially high but the complexity of them is nothing compared to the electronics in everyone's car, video, lift, wrist watch, fridge or electronic toothbrush.

 

As Clive indicated you can adjust the parameters on the water... So you have the chance to select the right configuration parameters, for chop, flat water, learner, sport mode etc... like your car.

 

Clive what are your thoughts about the future of such systems? Do you think they have a place in the sailing world and will this involve new classes or modificatins to the rules of old classes?

 

Electronics are banned but what about fluidic logic?

 

http://en.wikipedia.org/wiki/Fluidics

[BalticBandit 7]

Electronics are banned but what about fluidic logic?

 

http://en.wikipedia.org/wiki/Fluidics

The problem with fluidics is that you still need a hefty power system of some sort to drive the flap itself.

 

Note BTW, while Clive has done something very cool, 5 hours of sailing time is rather minimal for sorting out durability and other issues. Remember that at a major regattae, you can crank out 5 hrs of sailing time in one day. And a control system that lasts but a week isn't going to cut it.

 

BTW, an accelerometer won't really give you accurate readings since you aren't accounting for the hysteresis in the system from the foils. What you really want are are LED (low power) distance sensors, with which you can sense

• Wavetop distance
  
• Waveface slope
  
• Ride height above surface
  
• velocity of approaching waveface
  

[kprice 1]

in the other thread BB said

 

"That said, I don't see that the electronic control system in place is doing anything that could not be mirrored through a mechanical linkage. In essence the electronic system provides an easier means of controlling damping rates"

 

Clive mentioned two other sensors besides the wand so he can get

 

1. height by the wand

2. pitch attitude by the gyro

3. acceleration from the accelerometer (duh!)

 

and close the loops around each to keep height at a target, minimize pitch changes, counter unwanted acceleration, etc.

 

More information should mean better control.

 

It seems one advantage of the electronic control is the ability to accept more inputs about the system.

 

A mechanical system could use two wands (fore and aft) to get pitch and height, some dashpots to filter out the (chop) noise, etc. but it would be more complex to implement....but more fun for someone still a MechE.

 

KP

 

If anyone has an idea on integral control by mechanical linkage, let me know.

All I can think of is tanks filling up, there must be something more clever.

[atypicalguy 0]

Note BTW, while Clive has done something very cool, 5 hours of sailing time is rather minimal for sorting out durability and other issues. Remember that at a major regattae, you can crank out 5 hrs of sailing time in one day. And a control system that lasts but a week isn't going to cut it.

 

 

 

Note that while Wilbur and Orville have done something very cool, 26 seconds of flying time is rather minimal for sorting out durability and other issues...

 

If Clive's achievement were really so meager, surely you would have surpassed it by now...or are you holding out on us Baltic?

[BalticBandit 7]

Note that while Wilbur and Orville have done something very cool, 26 seconds of flying time is rather minimal for sorting out durability and other issues...

 

If Clive's achievement were really so meager, surely you would have surpassed it by now...or are you holding out on us Baltic?

Nope not at all. As I acknowledged in the other thread, I'm just an engineer who started as a MechE and then went on to electronics and software and am still in the process of saving pennies for a foiler.

 

I was primarily trying to forestall claims by HWMNBN that electronic controls are now a proven, race-ready technology. I fully expect that dramatic refinements can be achieved, but there's quite a bit of work ahead on proving it out. Meanwhile mechanical controls are race proven.

 

Where I could see electronic controls first making inroads is in the straightline Velocitek challenges where RRS and class regs on electronics don't apply.

[k_kirk 0]

I think there is room for wiggle here. The current rules read :

 

52 MANUAL POWER

A boat’s standing rigging, running rigging, spars and movable hull

appendages shall be adjusted and operated only by manual power.

 

hull appendages are defined here ( wont let me cut and paste) http://www.sailing.org/technical/ERS2005-2008.pdf page 12, but is basically anything that effects: stability, leeway, steerage, directional stability, motion damping, trim and displacement.

 

So in other words, unless you move your flap yourself you are in violation of the rules anyways. I am sure I'll get myself into hot water over this but I think all modern foiling moths using a wand to drive the flap are effectively in violation of the rule. So case in point, lets violate a little more and see what happens.

 

Personally I like the mechanical wand system and the issues that come with it. IMHO, mothing would not be as much fun if fly-by-wire was to take care of all stability issues and all we had to do was to be there. However, the geek in me wants to see this happen just for the sense of achievement.

 

My goal is to find a way to package an electronic solution for < USD500 and make it a plug & play add-on which can be installed over an existing standard Moth configuration with minimal modification. One can then sail legal in the competition and sail electronically assisted for a blast occasionally.

[the_skiff_devil 0]

We've already been through the rule 52 shenanigans when foils were first brought into mothing - the forward motion of the boat that moves the wand and drives the flap is interpreted as 'manual power' ie. it's not a stored energy device, so the existing mechanical wand devices clear the rule.

 

Electronics OTOH require stored energy of some description (unless it's run by solar or wind power and even then I suspect that the device would need to have no capacitance in the circuit as a capacitor is technically a means of storing energy...) and hence does violate R52. For that matter most of the modern canting keel maxis also violate R52 as they all use engine power to cant the keel... how do they get around it?

 

It's cool to see that someone's gotten out there and put into practice something that has been quietly talked about among the moth population for a little while; there was talk a while ago of simply using a wireless rotary detector attached to the wand in lieu of the existing mechanical rods and cables, with a small wireless servo installed in the head of the centreboard (and perhaps even the rudder), which would reduce the complexity of rigging a moth a little bit... make launching a matter of just plugging in the foils and going.

[clivee1 0]

To try and answer some of questions from both treads:

 

Thanks for all the positive comments.

 

I see what I have done as been very much the first step. Even on my boat there is a lot to be done to improve and refine the system. I have only just started.

 

At this stage I just want a cool boat that is fun and practical to sail and able join in races at a local club level. I do not have the time and no longer the inclination to put in the hours to compete in a formal class, and I get as much of a buzz from the development as the sailing. The restricted time means that my rate of ongoing development will not be that fast.

 

I do have ideas for the future to develop it for a foiling cruising tri, but that is many years away.

 

I think that many fast boats; foiling, multis and monohulls could be made to perform better with active pitch control.

 

If classes were to allow it I think that the cost would be similar to an auto helm product for obvious reasons. It need not be that expensive, however there are still people who choose to use self steering systems based on mechanical wands vanes levers etc.

 

I am not sure how the rules would stand if it was wind powered but this would be adding cost because of the rule.

 

I am not doing this as a commercial project. There are more effect ways to earn a living.

 

The electronics allows a more sophisticated and flexible control system to be implemented more rapidly than could be done with a mechanical system.

 

There are many ways to measure height. The wand is simple and cheap. You can also see what it is doing. At the moment I am getting occasional major wobbles whose origin is yet to be determined. If an IR or ultrasonic system were used it would take some development to be confident that its output was correct. Both have the ability to generate false readings in a number of ways. If anyone can point me in the direction of suitable devices I would certainly be interested but I see it as a very neat secondary development.

 

Do you know if the LED systems will reliably pick up a transparent water surface? The level of reflection could vary a lot.

 

Using accelerometers for height measurement is not practical. The measured vertical acceleration has to be compensated for changes in pitch and heel and these have to be separated from forward and some lateral acceleration. Small errors and offsets grow rapidly in the double integration to produce significant errors. I am trying to use a vertical accelerometer to work out whether inputs from the wand are due to chop/ motor boat wash etc or due to changes in height. At the moment I have not made the double integration stable over the few seconds that this needs.

 

Even if the electronics fully sorts the control of the flying it will not make these boats trivial to sail. They have no static stability they are very fast with a lot of sail and a lot of righting moment. At best they will still be as extreme to sail as any high performance dingy out there.

 

I agree with Ian Wards ideas from a few months ago that it would be great to see the Moth class get rid of many of its rules banning wig tip foils, multihulls, sailboards, electronics etc and see just how fast an 11’ dinghy could be.

 

If anyone else out there building 1 off foilers is interested in adding electronic control and sharing resources let me know.

 

 

 

Clive.

[k_kirk 0]

We've already been through the rule 52 shenanigans when foils were first brought into mothing - the forward motion of the boat that moves the wand and drives the flap is interpreted as 'manual power' ie. it's not a stored energy device, so the existing mechanical wand devices clear the rule.

 

Electronics OTOH require stored energy of some description (unless it's run by solar or wind power and even then I suspect that the device would need to have no capacitance in the circuit as a capacitor is technically a means of storing energy...) and hence does violate R52. For that matter most of the modern canting keel maxis also violate R52 as they all use engine power to cant the keel... how do they get around it?

 

The bungee chord stores energy but lets let it pass... Actually if you think about it even hoisting your sail up by pulling the halyard on any sailboat is a form of storing energy. Anyways. We all know our little voice will not change rule 52 so lets get on with it and experiment for the sake of "out of class" fun & development. Thanks for your input.

[k_kirk 0]

If anyone else out there building 1 off foilers is interested in adding electronic control and sharing resources let me know.

 

Clive, count me in. PM on the way for offline collaboration. Cheers & thanks

[Sailingkid 3]

We've already been through the rule 52 shenanigans when foils were first brought into mothing - the forward motion of the boat that moves the wand and drives the flap is interpreted as 'manual power' ie. it's not a stored energy device, so the existing mechanical wand devices clear the rule.

 

Electronics OTOH require stored energy of some description (unless it's run by solar or wind power and even then I suspect that the device would need to have no capacitance in the circuit as a capacitor is technically a means of storing energy...) and hence does violate R52. For that matter most of the modern canting keel maxis also violate R52 as they all use engine power to cant the keel... how do they get around it?

 

It's cool to see that someone's gotten out there and put into practice something that has been quietly talked about among the moth population for a little while; there was talk a while ago of simply using a wireless rotary detector attached to the wand in lieu of the existing mechanical rods and cables, with a small wireless servo installed in the head of the centreboard (and perhaps even the rudder), which would reduce the complexity of rigging a moth a little bit... make launching a matter of just plugging in the foils and going.

Couldn't you mount a little generator between the foils like the 747s have for when they lose power, because when your not moving your not going to need much electricity, and its not stored power because your using wind power to generate it, and your wont have to lugg one of those heavy batteries around. It would have to be dectachable so that you wouldn't need a massive trolley. Also you wouldn't be limited be battery life, in case you have to launch at like 8am, then get postponed for like 8 hours. See rendering.

[grooveman 0]

Couldn't you mount a little generator between the foils like the 747s have for when they lose power, because when your not moving your not going to need much electricity, and its not stored power because your using wind power to generate it, and your wont have to lugg one of those heavy batteries around. It would have to be dectachable so that you wouldn't need a massive trolley. Also you wouldn't be limited be battery life, in case you have to launch at like 8am, then get postponed for like 8 hours. See rendering.

 

Couldn't the moth foiler guys just wake up and make their own class rules? electronic control, bigger sail, slightly longer hull? why continue along the same limited rule path as the lowrider moths when you are so obviously in a different plane of design and performance?

[BalticBandit 7]

Do you know if the LED systems will reliably pick up a transparent water surface? The level of reflection could vary a lot.

depends on the tuning of the system. All air/water boundary layers reflect. What matters is the frequency selected and the gain in the system. I would think a bigger issue would be signal swamping from the sun. but clearly things like Laser rangefinders have solved this.

 

As for using a wand to measure height - don't you have some error caused by waves vs steady state?

[clivee1 0]

My next step is to use a vertical accelerometer to detect short term height changes and the wand to provide long term reference.

This is not as easy as it sounds. changes in pitch, heel forward and lateral acceleration affect the vertical acceleration reading. The double integration rapidly generates significant errors.

Will the LEDs be confused by water on the lens?

My preferred method of non contact height measurement is to look at the capacitance between an area on the bottom of the hull and the water.

 

Clive.

[BalticBandit 7]

My next step is to use a vertical accelerometer to detect short term height changes and the wand to provide long term reference.

This is not as easy as it sounds. changes in pitch, heel forward and lateral acceleration affect the vertical acceleration reading. The double integration rapidly generates significant errors.

have you considered looking at the various 3D "air mouse" products? They have done much of the work disambiguating this into inputs that convert to USB data.

Will the LEDs be confused by water on the lens?

 

I honestly don't know. I suspect it would depend on the way the lens system is designed.

My preferred method of non contact height measurement is to look at the capacitance between an area on the bottom of the hull and the water.

 

Clive.

DAMN that's clever! I really really like that.

[Doug Lord 1,219]

Clive ,if you haven't already you might be interested in looking at this:

 

United States Patent 3704442

 

 

"Abstract:

A method for detecting the relative position of a gaseous-liquid interface with respect to a datum point and an apparatus embodying the same for use in hydrofoil height sensors. A transmitter situated on the watercraft's hull directs an ultrasonic signal at the water surface. A portion of that signal is transmitted through the surface and refracted thereby to an ultrasonic receiver preferably situated on the hydrofoil. Evaluation of the transmission time of the ultrasonic signal from the transmitter to the receiver yields significant information concerning the relative position of the water surface with respect to either the hull or the hydrofoil. Factors for successful implementation of this technique are discussed in detail, and reference is made to a specific embodiment of a detector for transmission times. "

[Christian 72]

My next step is to use a vertical accelerometer to detect short term height changes and the wand to provide long term reference.

This is not as easy as it sounds. changes in pitch, heel forward and lateral acceleration affect the vertical acceleration reading. The double integration rapidly generates significant errors.

Will the LEDs be confused by water on the lens?

My preferred method of non contact height measurement is to look at the capacitance between an area on the bottom of the hull and the water.

 

Clive.

 

Sounds like worth while checking out. You might find, though, that the capacitance is going to be highly affected by the relative humidity and the amount of spray in the air between hull and water - and in the case of spray it will probably also be affected by the salinity of the spray. It may be a minor influence - I don't know.

[the_skiff_devil 0]

Couldn't you mount a little generator between the foils like the 747s have for when they lose power, because when your not moving your not going to need much electricity, and its not stored power because your using wind power to generate it, and your wont have to lugg one of those heavy batteries around. It would have to be dectachable so that you wouldn't need a massive trolley. Also you wouldn't be limited be battery life, in case you have to launch at like 8am, then get postponed for like 8 hours. See rendering.

 

Nice rendering kid

 

Good enough an idea kid but a small masthead wind generator or a solar panel would be better simply because it's out of the way of the free flow around the foils... rudder vent is bad enough without a prop out in front of it curling the flow up before it hits the rudder!

 

Re: Bungee storing energy... well, in that case every shock-cord take up on every dinghy on earth causes them to fail rule 52 since they use the stored energy of the shock-cord to clean up the boat which assists in reducing the cleanup work the skipper has to do, allowing the skipper to concentrate on driving the boat harder and improving speed. I won't even start on spring-loaded cam cleats... Yeah, we'll let those slip.

 

Chris Miller had a good idea with the resistance of a metal strip being used to detect the water level - I think that if a metal strip were used to sense for an average flying height and a bow-mounted wand to detect waves were combined it would give a pretty reasonable pitch controlling system... but I'm not sure if it'd be enough to overcome the natural lag from the foils. Basically, it'd need to be fast enough to predict a wave coming or leaving by a couple of tenths of a second abd have the main foil adjusted to suit before the wave encounters the foil... while electronics are good enough to do that I don't think there are lightweight servos that are quite up to the job of constantly moving the flap for a long period of time.

[Sailingkid 3]

Thanks! Since you liked them so much , heres another one using ur idea, and my idea, using the sail as a solar panel.

[BalticBandit 7]

Clive ,if you haven't already you might be interested in looking at this:

 

United States Patent 3704442

 

 

"Abstract:

A method for detecting the relative position of a gaseous-liquid interface with respect to a datum point and an apparatus embodying the same for use in hydrofoil height sensors. A transmitter situated on the watercraft's hull directs an ultrasonic signal at the water surface. A portion of that signal is transmitted through the surface and refracted thereby to an ultrasonic receiver preferably situated on the hydrofoil. Evaluation of the transmission time of the ultrasonic signal from the transmitter to the receiver yields significant information concerning the relative position of the water surface with respect to either the hull or the hydrofoil. Factors for successful implementation of this technique are discussed in detail, and reference is made to a specific embodiment of a detector for transmission times. "

Not a valid patent as it fails the "prior art" test. I read your patents Doug, you fluffed the "prior art" part and therefore jeopardized the validity of the patents themselves. I assume that you wrote them yourself without consulting a real patent atty. Too bad. A good one might have made you some money.

 

 

Couldn't you mount a little generator between the foils like the 747s have for when they lose power, because when your not moving your not going to need much electricity

 

This would generate drag and turbulence. So that means you would have to tow it aft of the stern to preclude it being a ventilation inducer (remember just the wand itself can induce ventilation) And it generates a fair amount of drag. Lastly in a crash, the last thing I want is a spinning prop at the end of a fairly heavy metal can (the generator) whiplashing at me from behind the boat.

 

Note the Solar panel sail (setting aside the weight issues), is not "action of the wind and water" As for shock cords. I suspect that if you had bungees attached to the boom that allowed you to pump the main based on stored energy, you would fail 52, though the arguement could be made that the energy put into the bungee comes from the "natural action of the wind and water". the gotcha on electronic systems is that the energy is coming from a pregenerated form (except for SailingKids taffrail generator idea)

 

 

Nice thinking though - out of the box.

 

 

I suspect it would be simpler to hvae a separate "EC" class at big regattaes with tinkerers sailing the ECs starting with everyone else, but getting scored separately. You'd want to start them with everyone else just so that you can start to get a feel for how they are doing compared to manual control boats.

[Sailingkid 3]

Don't finns have thick bungee going from the bow to the end of the boom then back up to the mast then back to the bow to help pull the boom out to assist pumping?

[Doug Lord 1,219]

Clive, I have a couple of questions: if I understand your system correctly your wand operates a pot sending a signal to your electronics. Does that mean that the sometimes rapid wand movement (that on a "normal" foiler would also move the flap up and down rapidly) is not transmitted to the rudder foil flap? In other words the rudder foil flap would not move as rapidly as the wand-is that correct?

Do you think a future version of your system would benefit from simultaneous control of both the main foil and rudder foil?

[Doug Lord 1,219]

For those interested in Clive Everest's electronic foil control system here is some of the amazing background of the man himself by Andy Rice in 2004:

=====================

Clive Everest has also been inspired to draw the lines for his own foiling machine. Best known as the designer of successful singlehanded classes, the RS600 trapeze boat and the RS300 hiking dinghy, Everest is an unreformed speed junkie. He has raced International 14s, 18-foot Skiffs and most recently an A-Class catamaran. He also has a history in Moths, including designing the world championship-winning Moth of the early 90s and finishing second in his own right as a sailor. He was also part of a pioneering group who experimented with foiling over a decade ago. “I was involved with Moths when we were experimenting with a tri-foil arrangement, but then the class banned it,” he says. “These days at 13 stone I’m too heavy to campaign a Moth competitively; you’ve got to be about 10 stone and I think the weights might come down even further with the foils. But I was totally inspired by what Rohan Veal was doing so I decided to design my own boat, with no rules or restrictions to worry about.”

 

 

 

His own RS300 design, itself a derivative of the Moth, has proven fast and easily driven in light winds so Everest took this as the basis of his new foiler. “The only time the hull’s going to be in the water is in light winds, so the RS300 seemed like a good place to start.” Because Everest only expects to be sitting on the water in conditions of 7 knots or less, he has had the top 150mm of freeboard chopped off the RS300 hull to save weight, and has commissioned Richard Woof of RMW Marine boatbuilders to construct the hull of carbon.

 

 

 

To this hull Everest is attaching carbon trapezing racks for added leverage. The rudder and rudder box are standard 49er equipment, with the addition of a T-foil wing to the base of the rudder. The rig consists of a carbon mast and fully-battened Mylar sail. So far, the basic configuration differs very little from the Rohan Veal Moth, but where it differs is in Everest’s approach to the foil arrangement. “I have adopted a tri-foil arrangement similar to what you see on a commercial passenger-carrying hydrofoil ferry,” explains Everest. “We experimented with this set-up on the Moths 10 or 15 years ago but because the class banned it, Rohan has had to go for his more complex T-foil arrangement.”

 

 

 

Unlike the T-foil system, Everest’s tri-foil configuration has no moving parts and there is less tweaking and calibration involved as a result. The hull is supported on two carbon foils, one from each trapeze rack, angled at approximately 45 degrees underneath the centre of the hull, with the T-foil rudder providing a small element of lift at the transom. It will run closer to the surface and will provide a more stable ride than the high-flying Moth of Rohan Veal. It may look a little less spectacular but should prove equally fast, if not faster, with anticipated speeds of up to 25 knots. “I wanted something simple and maintenance free. I’ve got a young family and limited time to go sailing, so the tri-foil will just let me get on with the fun part,” explains Everest, who plans to club race his foiler during the summer in Chichester Harbour. “The aim is to give the fast twin-trapeze boats like the International 14s a good run for their money.”

 

 

 

Everest’s Achilles heel is going to be in the sub-foiling conditions when all that hydrofoil becomes added drag, but he has given himself a big rig and big foils to promote early foiling, at the expense of reduced top speed. And unlike the Moth, he has the added turbo of a small gennaker which he will hoist downwind in light to moderate conditions. “Because of the amount of apparent wind, the sail is very flat - more like a Code Zero than a gennaker. But once the wind is above a Force 3 to 4 I expect to be generating enough power around the course with just the mainsail.”

[Cheesy 0]

Hi Clive, if you don’t mind elaborating a bit more could you give us/me an idea of how you are using the gyro and accelerometer inputs.

On the height input a few years ago while I was at varsity there was a group developing thin film devices for measuring boundary layer thickness, it may be possible to use several devices like this on the foil strut to give incremental height steps, I’m guessing that by using the accelerometer and gyro you aren’t actually using the wand to control any pitching etc, just a heavily filtered input for the height control?

[clivee1 0]

The inputs to my electronics are the wand, A solid state gyro mounted in the pitch plane which measures the rate of pitch rotation, an accelerometer mounted in the pitch plane that will respond to changes in pitch and acceleration of the boat. This is used to provide a low frequency reference to the gyro. as it is safe to assume that the long term acceleration of the boat is zero, and a vertical accelerometer.

I have 2 nested control loops. I drive the rudder foil servo to try and achieve a target pitch based on the pitch measurement that comes from a hardware integration of the gyro out put and the pitch plane accelerometer, and the rate of change of pitch that comes directly from the gyro.

The target pitch is set by the height control loop as a function of the measured height from the wand and a software integration of the height.

I want to use the vertical accelerometer to measure the vertical velocity and acceleration to provide phase advance to the height control loop. I also want to double integrate the acceleration to generate a second height reading that will allow me to separate the vertical motion of the boat from the contours of the waves.

My initial attempts to do this have not worked as small changes in heel and pitch change the measured vertical acceleration and the double integration rapidly produces significant height errors. Whilst I can correct for the error due to pitch I need to measure heel to compensate for that, This is my next step.

Both control loops have non linear gain functions so that when running close to target setup they do not respond significantly to small deviations however the responce gets much more agressive if the boat is seriously out of shape.

Regarding the question as to whether a second servo on the main foil flap would be beneficial:

Undoubtedly the height control could be improved and in no way would it be diminished. However in the horizontal plane we do not need a rudder and a centreboard trim tab to steer our boats so why should we in the vertical plane.

Also it would duplicate a relatively expensive and vulnerable part of the system.

Most importantly however: I found last year sailing with a mechanical system that I seemed to be hitting a hard wall regarding max speed. Contrary to all the text books the drag appears to be going up far faster than V^2.

I have an unsubstantiated theory that around 18Kts we are starting to see true cavitation around unfair parts of the structure and that the size of the cavitation bubbles grows rapidly causing the rapid increase in drag.

I hope someone more qualified will comment.

By fixing the main foil flap and removing the push rod cut out I have the opportunity to make a significantly cleaner structure.

I must reiterate that I feel that I have made the first step and do not for one second want to think that I am any were near what will be achieved.

I liked the analogy of the Wright brothers 26S flight.

 

Clive.

[atypicalguy 0]

Most importantly however: I found last year sailing with a mechanical system that I seemed to be hitting a hard wall regarding max speed. Contrary to all the text books the drag appears to be going up far faster than V^2.

I have an unsubstantiated theory that around 18Kts we are starting to see true cavitation around unfair parts of the structure and that the size of the cavitation bubbles grows rapidly causing the rapid increase in drag.

I hope someone more qualified will comment.

By fixing the main foil flap and removing the push rod cut out I have the opportunity to make a significantly cleaner structure.

I must reiterate that I feel that I have made the first step and do not for one second want to think that I am any were near what will be achieved.

I liked the analogy of the Wright brothers 26S flight.

 

Clive.

 

The Wright Bros. patent was actually on a control system - many had flown before them, but no one had sustained it because they could not control the flight.

 

I have a similar speed-limited sensation on my moth, though I am not sure what the ultimate cause is. Getting rid of flaps is certainly a step in a good direction.

 

Pitching the rig seems a slow way to fly, but perhaps the impact is negligible at speed.

 

In terms of drag that second vertical strut must be adding significantly; surely with a bit more material in the foil this could be eliminated?

[SimonN 281]

Clive

 

Thanks for posting. As always, the stuff you do is very thought provoking!

 

For me, the biggest thing you raise is not actually the electronics but this

 

I found last year sailing with a mechanical system that I seemed to be hitting a hard wall regarding max speed. Contrary to all the text books the drag appears to be going up far faster than V^2.

I have an unsubstantiated theory that around 18Kts we are starting to see true cavitation around unfair parts of the structure and that the size of the cavitation bubbles grows rapidly causing the rapid increase in drag.

I hope someone more qualified will comment.

While I might not be qualified, never mind more qualified, I would make the following observations. It has struck me that the top speed of Moths hasn't improved for the last (I think) 3 years. Some have put this down to inaccurate measring of that speed but if we look at the data and ignore the tails, I think that we do observe some sort of barrier. At the same time, the speed around the course has improved dramatically. I am prepared to accept that the textbooks are right, in no small part because those same text books are used to design large aicraft and they seem to work! Whether your theory is right s to what is acusing the problem I don't know, but I suspect that this is where the next big breakthrough will come from.

[JimC 671]

to help pull the boom out to assist pumping?

Mainly to avoid having to push the boom out by hand running square I believe.

[BalticBandit 7]

Undoubtedly the height control could be improved and in no way would it be diminished. However in the horizontal plane we do not need a rudder and a centreboard trim tab to steer our boats so why should we in the vertical plane.

Also it would duplicate a relatively expensive and vulnerable part of the system.

I think the latter arguement is the stronger one. The horizontal plane analogy isn't as strong as in the horizontal plane we are primarily concerned with attack angle of the airfoil and are using the rudder to control AoA rather than trying to control lateral translation.

 

but the strongest arguement I think is

 

By fixing the main foil flap and removing the push rod cut out I have the opportunity to make a significantly cleaner structure.

 

Seems to me then that if you were able to fly the whole foil (ala modern airplane Stabilizers) you would be able to have a clean structure AND have that control. But then you need more power, which argues for the approach you are using.

[BalticBandit 7]

Most importantly however: I found last year sailing with a mechanical system that I seemed to be hitting a hard wall regarding max speed. Contrary to all the text books the drag appears to be going up far faster than V^2.

I have an unsubstantiated theory that around 18Kts we are starting to see true cavitation around unfair parts of the structure and that the size of the cavitation bubbles grows rapidly causing the rapid increase in drag.

I hope someone more qualified will comment.

By fixing the main foil flap and removing the push rod cut out I have the opportunity to make a significantly cleaner structure.

I must reiterate that I feel that I have made the first step and do not for one second want to think that I am any were near what will be achieved.

I liked the analogy of the Wright brothers 26S flight.

 

Clive.

 

Over in Sailing Anarchy forum someone just posted the announcement of a new breakthrough in fluid dynamics modelling

 

http://www.dailytech.com/article.aspx?newsid=13067 is the link to the story behind it. Potentially has dramatic impacts on foiling blades

[Sailingkid 3]

Mainly to avoid having to push the boom out by hand running square I believe.

Cool now i know why they have it!

[clivee1 0]

I have managed to get afloat again after a month of poor weather and other commitments.

Key change this time has been the addition of a data logging capability and the ability to send the servo to max to generate a disturbance to evaluate the control.

This data should allow me to now start optimizing the control.

First impressions are that the servo is responding far too much to chop but not actually managing to control the height that well.

I need to separate chop from height changes without adding a lag to the control loop.

The GPS logged 10 NM of sailing during an hour afloat with top speed of 17.1kts I did not push the speed as the control looked like it would become unstable at higher speeds.

 

[Cheesy 0]

would it be possible (or even feasable) to use a double differential of the vertical acceleration to calculate the change in height and then use the wand input peiodicly to define a start value for of the system ?

 

alternativly would a low pass filter be enough to eliminate most of the problem?

[clivee1 0]

I think that a double integration of the vertical acceleration with a slow (~5 seconds) convergence to the wand reading is what I will try next.

I think that simple filtering of the wand will reduce the control potential.

My previous experiments with a vertical accelerometer showed that I will need to compensate for pitch and heel.

My other thoughts were to use pitch and speed measurements to predict the rate of rise and an estimated height and steer this to converge with the actual wand reading.

[BalticBandit 7]

I have managed to get afloat again after a month of poor weather and other commitments.

Key change this time has been the addition of a data logging capability and the ability to send the servo to max to generate a disturbance to evaluate the control.

This data should allow me to now start optimizing the control.

First impressions are that the servo is responding far too much to chop but not actually managing to control the height that well.

I need to separate chop from height changes without adding a lag to the control loop.

The GPS logged 10 NM of sailing during an hour afloat with top speed of 17.1kts I did not push the speed as the control looked like it would become unstable at higher speeds.

 

Trying to read the data plot and wondering if I'm getting it right.

 

Servo drives to Max UP, followed by a rapid flap move to almost the opposite extreme and then slowly with chop driven oscilations stabilizes

 

Nose pitches up, and then slowly comes back down

 

All the time the ride hight is dropping slowly and then gently comes back up?

 

 

 

Or am I misreading the data?

[clivee1 0]

The servo drives to max lifting the transom and causing the bow to pitch down, A button on the tiller extension starts the data log and drives the servo to max.

Remember that the servo is exclusively driving the rudder foil.

The gyro shows max rate of rotation at ~0.4 seconds.

The bow drops from ~3.5 degrees bow up to 1 degree bow down at 0.6 seconds, and then recovers to ~7.5 degrees bow up.

The height drops from ~800mm to ~300mm and then starts to recover.

The servo drive shows a lot of high frequency movement induced by chop effecting the height reading, and the phase advance software in the control system.

[Munter 0]

Great post Clive. The ability to capture and analyse data should help refine the system far faster than is possible with current techniques. I wonder if the top moth designers have considered some form of data capture to help them develop mechnical systems? I think it would be a great advantage to really know what is happening with the control surfaces rather than just incidentally observing them while sailing.

[atypicalguy 0]

Great post Clive. The ability to capture and analyse data should help refine the system far faster than is possible with current techniques. I wonder if the top moth designers have considered some form of data capture to help them develop mechnical systems? I think it would be a great advantage to really know what is happening with the control surfaces rather than just incidentally observing them while sailing.

 

Yes I could use an accelerometer about now to get a handle on pitch, even if it were not linked to the control system in any way (mine is all mechanical). It's interesting that Clive's boat recovers to 7.5 degrees bow up - that is a lot of bow up to deal with.

[clivee1 0]

I got to sail again this weekend with a vertical accelerometer added to the electronics so that short term height measurements could be derived from the vertical accelerations and only tied to the wand over a couple of seconds. This is to allow the control to ignore chop but respond quickly to real changes in flying height.

 

Previous tests had shown that a vertical accelerometer would need compensation for pitch and heel.

 

12' of heel gives a height error of 430mm after just 2 seconds, so I added heel measurement using a horizontal transverse accelerometer.

 

The boat flew well in light conditions and I managed to complete a club race and finish well ahead of the rest of the fast handicap (not asymmetric) fleet.

 

The height control felt that it would become unstable at higher speeds. The top speed I recorded on the GPS was 17kts.

 

Subsequent review of the data log showed significant fluctuations in the inertially measured height at 1 – 2 Hz frequency that had no correlation to the height as measured by the wand.

 

I had expected the inertially measured height to be flat with higher frequency fluctuations on the wand measurement as it bounced over the chop.

 

I think that changes in coarse as I steer for balance are causing lateral accelerations that are giving false heel readings and consequently feeding through to the vertical acceleration.

 

The 1 -2 Hz frequency is consistent with the rate at which one steers for balance and adjusts the main sheet.

 

Running through the numbers at 15kts and 12' of heel a 12' change in course over 2 seconds will produce a height error of 400mm. This will become more significant as the speed increases.

 

I think that for the vertical accelerometer to work so that I can fly smoothly through chop, I need heel compensation and that this will require a roll axis gyro as well as a transverse accelerometer so that heel can be separated from course changes.

 

 

 

Clive

[Major Tom 390]

I got to sail again this weekend with a vertical accelerometer added to the electronics so that short term height measurements could be derived from the vertical accelerations and only tied to the wand over a couple of seconds. This is to allow the control to ignore chop but respond quickly to real changes in flying height.

 

Previous tests had shown that a vertical accelerometer would need compensation for pitch and heel.

 

12' of heel gives a height error of 430mm after just 2 seconds, so I added heel measurement using a horizontal transverse accelerometer.

 

The boat flew well in light conditions and I managed to complete a club race and finish well ahead of the rest of the fast handicap (not asymmetric) fleet.

 

The height control felt that it would become unstable at higher speeds. The top speed I recorded on the GPS was 17kts.

 

Subsequent review of the data log showed significant fluctuations in the inertially measured height at 1 – 2 Hz frequency that had no correlation to the height as measured by the wand.

 

I had expected the inertially measured height to be flat with higher frequency fluctuations on the wand measurement as it bounced over the chop.

 

I think that changes in coarse as I steer for balance are causing lateral accelerations that are giving false heel readings and consequently feeding through to the vertical acceleration.

 

The 1 -2 Hz frequency is consistent with the rate at which one steers for balance and adjusts the main sheet.

 

Running through the numbers at 15kts and 12' of heel a 12' change in course over 2 seconds will produce a height error of 400mm. This will become more significant as the speed increases.

 

I think that for the vertical accelerometer to work so that I can fly smoothly through chop, I need heel compensation and that this will require a roll axis gyro as well as a transverse accelerometer so that heel can be separated from course changes.

 

 

 

Clive

 

 

Reading through all this it looks as we may have under estimated how ahead of it's time a bow mounted wand is!

[atypicalguy 0]

I got to sail again this weekend with a vertical accelerometer added to the electronics so that short term height measurements could be derived from the vertical accelerations and only tied to the wand over a couple of seconds. This is to allow the control to ignore chop but respond quickly to real changes in flying height.

 

Previous tests had shown that a vertical accelerometer would need compensation for pitch and heel.

 

12' of heel gives a height error of 430mm after just 2 seconds, so I added heel measurement using a horizontal transverse accelerometer.

 

The boat flew well in light conditions and I managed to complete a club race and finish well ahead of the rest of the fast handicap (not asymmetric) fleet.

 

The height control felt that it would become unstable at higher speeds. The top speed I recorded on the GPS was 17kts.

 

Subsequent review of the data log showed significant fluctuations in the inertially measured height at 1 – 2 Hz frequency that had no correlation to the height as measured by the wand.

 

I had expected the inertially measured height to be flat with higher frequency fluctuations on the wand measurement as it bounced over the chop.

 

I think that changes in coarse as I steer for balance are causing lateral accelerations that are giving false heel readings and consequently feeding through to the vertical acceleration.

 

The 1 -2 Hz frequency is consistent with the rate at which one steers for balance and adjusts the main sheet.

 

Running through the numbers at 15kts and 12' of heel a 12' change in course over 2 seconds will produce a height error of 400mm. This will become more significant as the speed increases.

 

I think that for the vertical accelerometer to work so that I can fly smoothly through chop, I need heel compensation and that this will require a roll axis gyro as well as a transverse accelerometer so that heel can be separated from course changes.

 

 

 

Clive

 

who sells gyros like that and how much do they cost?

[SimonN 281]

Clive

 

Thanks for the update on a really inetersting project. I can understand why you are doing it and it is certainly an interesting challenge. However, do you think that you are going to end up with something that is actually significantly enough better than the current wand systems? Or is part of the purpose of the project the actual technical challenge itself.

[clivee1 0]

who sells gyros like that and how much do they cost?

 

 

Analog devices:

 

~£50 1 off.

 

The device is 7mm x 7mm x 3mm

ADXRS300_gyro.pdf

[clivee1 0]

Clive

 

Thanks for the update on a really inetersting project. I can understand why you are doing it and it is certainly an interesting challenge. However, do you think that you are going to end up with something that is actually significantly enough better than the current wand systems? Or is part of the purpose of the project the actual technical challenge itself.

 

 

 

I think that ultimately it could significantly out perform a mechanical system.

I do not know if I will single-handedly manage to get that far, and the technical challenge is in itself worth while.

 

 

Key advantages are:

 

It allows significant fairing as there is no moving parts on the main foil.

It can be more intelligent during and before take off.

it can provide controlled damping. A simple proportional system will be prone to oscillations.

It can provide a reactive pitch torque to counter gusts. At the moment Moths steer some pretty wild courses downwind to maintain control.

It can separate ride height changes from chop.

It can optimize itself for upwind / downwind / marginal / full on conditions.

 

In all similar applications electronic solutions have ultimately become better and cheaper than the mechanical alternative.

 

Clive

[Basiliscus 411]

The inputs to my electronics are the wand, A solid state gyro mounted in the pitch plane which measures the rate of pitch rotation, an accelerometer mounted in the pitch plane that will respond to changes in pitch and acceleration of the boat. This is used to provide a low frequency reference to the gyro. as it is safe to assume that the long term acceleration of the boat is zero, and a vertical accelerometer.

It would be best to use the accelerometer for high-frequency height control and use the wand for low-frequency height control. The accelerometer will be subject to bias, scale factor, and alignment errors that will result in unbounded (ie, very, very large) errors if the acceleration is integrated to get vertical velocity and height. However feeding back wand position to the height estimate will stabilize the estimate against these errors. At the same time, the accelerometer will respond faster to a change in height than will the wand, making it most suitable for adding lead to the height control.

 

I have 2 nested control loops. I drive the rudder foil servo to try and achieve a target pitch based on the pitch measurement that comes from a hardware integration of the gyro out put and the pitch plane accelerometer, and the rate of change of pitch that comes directly from the gyro.

The target pitch is set by the height control loop as a function of the measured height from the wand and a software integration of the height.

I want to use the vertical accelerometer to measure the vertical velocity and acceleration to provide phase advance to the height control loop. I also want to double integrate the acceleration to generate a second height reading that will allow me to separate the vertical motion of the boat from the contours of the waves.

My initial attempts to do this have not worked as small changes in heel and pitch change the measured vertical acceleration and the double integration rapidly produces significant height errors. Whilst I can correct for the error due to pitch I need to measure heel to compensate for that, This is my next step.

Both control loops have non linear gain functions so that when running close to target setup they do not respond significantly to small deviations however the responce gets much more agressive if the boat is seriously out of shape.

 

I suggest three nested loops. The inner most loop would use acceleration feedback. The middle loop would use pitch rate feedback, and the outer loop would use wand feedback. Each loop should command a rate of change in the controlled variable proportional to the error in the controlled variable. For example, the controlled variable for the outermost loop is height. The difference between the desired height and the height measured by the wand is the height error. The outer loop should multiply the height erorr by a gain to calculate a vertical velocity command. The next loop would then respond to the vertical velocity command. The vertical velocity loop would compute the vertical velocity error, then multiply the vertical velocity erorr by a gain to form a vertical acceleration command. The innermost loop would use the acceleration feedback to form the acceleration error. The vertical acceleration control would then be comanded by a gain times the acceleration error. Unfortunately, this approach would be best suited to direct lift control from a main flap than by control by the tail, but the principle would still be the same. Form the erorr, use the error to comand the rate of change.

 

Pitch attitude corresponds to height rate because at a constant speed the flightpath angle is proportional to the vertical velocity divided by the speed. So both the pitch rate gyro and the accelerometer are somewhat related to the second derivative of the height. But there is a difference because the lift on the foil is also dependent on the angle of attack, which is affected by the pitch attitude.

 

Another way to go would be to use two nested loops, with the outer loop being a height loop, as above. The inner loop would be a combination of accelerometer and pitch rate gyro feedback to form the controlled variable.

 

What you really need is a dynamic model that allows you to express the relationship between the motion of the boat and the values measured by each of the sensors, and the effectiveness of your control surface. Then you can estimate the quantities you want to control and determine how to move the surface. Check out NACA TR-918.

 

Regarding the question as to whether a second servo on the main foil flap would be beneficial:

Undoubtedly the height control could be improved and in no way would it be diminished. However in the horizontal plane we do not need a rudder and a centreboard trim tab to steer our boats so why should we in the vertical plane.

 

If you were trying to achieve precise positioning in the horizontal plane, you'd want direct side force control then, too.

 

There are really two coupled modes to the boat's motion you're trying to control - a pitch mode and a heave mode. With one control, you can only get at one mode by the way in which it is coupled to the other mode. With two controls, you can control each mode directly. And with the additional control you can satisfy an additional objective, such as minimizing drag.

 

The control of height using tail control will always have a lag compared to controlling height with the main foil flap. The reason is to change height, you need to change the vertical velocity, and to change the vertical velocity you need to change the vertical acceleration by changing the lift on the foil. If you have a flap on the foil, when you change the flap deflection, you change the lift and create an immediate change to the vertical acceleration. If you change the lift through the changing the pitch attitude of the boat to control the angle of attack of the foil, then you first have to generate a pitch acceleration to generate a pitch rate to generate a change in pitch attitude. Only once the pitch attitude changes do you change the lift on the foil and change the vertical acceleration and start to affect the height.

 

But it's worse than that. With tail control, as opposed to a canard, the tail has to drop to increase the angle of attack. So the boat actually has to descend slightly before it can start to rise. This has significant implications for the stability of control loops.

 

It's simply not possible to get as tight a height control using only the rudder foil compared to controlling only the main foil flap. The lags in the height response to pitch control mean that the boat will go unstable if the height control is cranked up too high.

 

However, height control using the flap is also subject to serious limitations. The flap only has limited authority. The lift on the foil is a function not only of angle of attack but of speed. Since the lift has to equal the weight, as the speed increases, the flap has to be deflected to offset the increase in lift due to speed. Eventually the flap will be fully saturated just trying to maintain the trim of the boat, and even before then, any deflection for trim takes away from the authority available to counter dynamic disturbances. Tail control doesn't have quite as much limitation in this regard. There's not much difference in angle of attack required to climb or descend at a constant angle, so once the pitch attitude is set, the tail control can return to near its trim value as the height changes. So over the long term, the tail can be much more powerful than the flap.

 

The combination of characteristics means the flap and tail controls can be used in complementary ways. The flap can null out high-frequency disturbances from small waves and the tail can adjust the pitch trim so that over the long term the flap deflection returns to neutral. This maximizes the flap's effectiveness for dynamic ride control, and the steady state flap deflection can correspond to the optimum angle for minimizing foil profile drag.

 

Most importantly however: I found last year sailing with a mechanical system that I seemed to be hitting a hard wall regarding max speed. Contrary to all the text books the drag appears to be going up far faster than V^2.

 

Pitch control is very important for hydrofoil peformance, especially if you are using surface piercing foils or if the flap doesn't span the full width of the forward foil. At constant lift, the induced drag should decrease with the square of the speed - this is the whole point of using hydrofoils at high speed. But if the effective span shrinks with speed, the induced drag can actually go up. Pitch control can be important for flying lower and increasing the effective span to reduce induced drag more than the increase in parasite drag due to extra wetted area.

 

I have an unsubstantiated theory that around 18Kts we are starting to see true cavitation around unfair parts of the structure and that the size of the cavitation bubbles grows rapidly causing the rapid increase in drag.

 

That's quite possible. At areas where the local flow velocity is increased due to interference, you can get cavitation at 18 kt. You can also start to get cavitation if you have sharp pressure peak, such as at a corner.

[aus_stevo 2]

That's quite possible. At areas where the local flow velocity is increased due to interference, you can get cavitation at 18 kt. You can also start to get cavitation if you have sharp pressure peak, such as at a corner.

is this why bladerider , mach2 and the new fastacraft foils all have the bulbous fairing at the t-joint junction? rather than just for structure

[ferrero 0]

Clive, very interesting design and congratulations on some terrific development work.

I'm most interested in your opinion of the various altitude sensors that could be used in this application-ultrasound ,micro radar etc.

Thanks for having the guts, courage and determination to make such a trmendous contribution to foiler development!

 

Over thinking it, go with a 3 axis accelerometer and a contact switch. You know when you are on the surface, integrate the acceleration twice and you have height off the water. It should be a lot less expensive than either other option, plus you won't have to filter out the waves.

 

Interested to see what his solution was.

 

You don't get the accuracy from an accelerometer unless you spend 10 grand pluss on the unit and have some very fancy filters. Integrating the output twice would basically give you garbage.

[ferrero 0]

We've already been through the rule 52 shenanigans when foils were first brought into mothing - the forward motion of the boat that moves the wand and drives the flap is interpreted as 'manual power' ie. it's not a stored energy device, so the existing mechanical wand devices clear the rule.

 

Electronics OTOH require stored energy of some description (unless it's run by solar or wind power and even then I suspect that the device would need to have no capacitance in the circuit as a capacitor is technically a means of storing energy...) and hence does violate R52. For that matter most of the modern canting keel maxis also violate R52 as they all use engine power to cant the keel... how do they get around it?

 

If it is just stored energy that is the problem does that mean you are'nt allowed shock chord?! How about having a wind up power system with little crank arm you wind up before you get to the start? Same deal as stretching a bit of elastic, you are just using the energy in a cleverer way.

[the_skiff_devil 0]

We've been through the rule 52 issue already. Everyone uses shock cord, so it'd be very hard for someone to protest on 52 for it.

[Kenny Dumas 211]

How 'bout some really small pressure sensors on the back of the foil (to avoid the Bernoulli pressures) to sense depth / elevation?

http://www.pmctransducers.com/tranducers.html

Gotta be some really cheap ones out there from the automotive world. Figure ~1.5 psi at 3 ft. depth with typical 1% accuracy and easy to use since they're just resistor bridge strain gages with a DC output. Should be fast enough, just depends on the DAC.

[atypicalguy 0]

That's quite possible. At areas where the local flow velocity is increased due to interference, you can get cavitation at 18 kt. You can also start to get cavitation if you have sharp pressure peak, such as at a corner.

is this why bladerider , mach2 and the new fastacraft foils all have the bulbous fairing at the t-joint junction? rather than just for structure

 

I have no insider knowledge Astevo but I think they have them because they are all two part foils and there isn't enough depth to make the connection robust otherwise. You need more depth/material locally at the T and a bulbous fairing is the simplest way to achieve that. And it is a proven design now.

 

But if you build single piece foils I'd say one is better off without it.

[Mal Smith 28]

That's quite possible. At areas where the local flow velocity is increased due to interference, you can get cavitation at 18 kt. You can also start to get cavitation if you have sharp pressure peak, such as at a corner.

is this why bladerider , mach2 and the new fastacraft foils all have the bulbous fairing at the t-joint junction? rather than just for structure

 

I have no insider knowledge Astevo but I think they have them because they are all two part foils and there isn't enough depth to make the connection robust otherwise. You need more depth/material locally at the T and a bulbous fairing is the simplest way to achieve that. And it is a proven design now.

 

But if you build single piece foils I'd say one is better off without it.

 

It may have only been done on moths for structural reasons, but bulbs have been used to control cavitaion at the foil root e.g on the Boeing Jetfoil (there is a paper on it somewhere). So maybe it serves both purposes.

[ferrero 0]

That's quite possible. At areas where the local flow velocity is increased due to interference, you can get cavitation at 18 kt. You can also start to get cavitation if you have sharp pressure peak, such as at a corner.

is this why bladerider , mach2 and the new fastacraft foils all have the bulbous fairing at the t-joint junction? rather than just for structure

 

I have no insider knowledge Astevo but I think they have them because they are all two part foils and there isn't enough depth to make the connection robust otherwise. You need more depth/material locally at the T and a bulbous fairing is the simplest way to achieve that. And it is a proven design now.

 

But if you build single piece foils I'd say one is better off without it.

 

It may have only been done on moths for structural reasons, but bulbs have been used to control cavitaion at the foil root e.g on the Boeing Jetfoil (there is a paper on it somewhere). So maybe it serves both purposes.

 

The cavitation number on flow over a moth foil is too low for cavitation to be an issue. You are talking around 40 knots before it is an issue. The bulb helps structure but can also help reduce junction drag if you do it right.

[ebnelson 4]

The inputs to my electronics are the wand, A solid state gyro mounted in the pitch plane which measures the rate of pitch rotation, an accelerometer mounted in the pitch plane that will respond to changes in pitch and acceleration of the boat. This is used to provide a low frequency reference to the gyro. as it is safe to assume that the long term acceleration of the boat is zero, and a vertical accelerometer.

It would be best to use the accelerometer for high-frequency height control and use the wand for low-frequency height control. The accelerometer will be subject to bias, scale factor, and alignment errors that will result in unbounded (ie, very, very large) errors if the acceleration is integrated to get vertical velocity and height. However feeding back wand position to the height estimate will stabilize the estimate against these errors. At the same time, the accelerometer will respond faster to a change in height than will the wand, making it most suitable for adding lead to the height control.

 

I have 2 nested control loops. I drive the rudder foil servo to try and achieve a target pitch based on the pitch measurement that comes from a hardware integration of the gyro out put and the pitch plane accelerometer, and the rate of change of pitch that comes directly from the gyro.

The target pitch is set by the height control loop as a function of the measured height from the wand and a software integration of the height.

I want to use the vertical accelerometer to measure the vertical velocity and acceleration to provide phase advance to the height control loop. I also want to double integrate the acceleration to generate a second height reading that will allow me to separate the vertical motion of the boat from the contours of the waves.

My initial attempts to do this have not worked as small changes in heel and pitch change the measured vertical acceleration and the double integration rapidly produces significant height errors. Whilst I can correct for the error due to pitch I need to measure heel to compensate for that, This is my next step.

Both control loops have non linear gain functions so that when running close to target setup they do not respond significantly to small deviations however the responce gets much more agressive if the boat is seriously out of shape.

 

I suggest three nested loops. The inner most loop would use acceleration feedback. The middle loop would use pitch rate feedback, and the outer loop would use wand feedback. Each loop should command a rate of change in the controlled variable proportional to the error in the controlled variable. For example, the controlled variable for the outermost loop is height. The difference between the desired height and the height measured by the wand is the height error. The outer loop should multiply the height erorr by a gain to calculate a vertical velocity command. The next loop would then respond to the vertical velocity command. The vertical velocity loop would compute the vertical velocity error, then multiply the vertical velocity erorr by a gain to form a vertical acceleration command. The innermost loop would use the acceleration feedback to form the acceleration error. The vertical acceleration control would then be comanded by a gain times the acceleration error. Unfortunately, this approach would be best suited to direct lift control from a main flap than by control by the tail, but the principle would still be the same. Form the erorr, use the error to comand the rate of change.

 

Pitch attitude corresponds to height rate because at a constant speed the flightpath angle is proportional to the vertical velocity divided by the speed. So both the pitch rate gyro and the accelerometer are somewhat related to the second derivative of the height. But there is a difference because the lift on the foil is also dependent on the angle of attack, which is affected by the pitch attitude.

 

Another way to go would be to use two nested loops, with the outer loop being a height loop, as above. The inner loop would be a combination of accelerometer and pitch rate gyro feedback to form the controlled variable.

 

What you really need is a dynamic model that allows you to express the relationship between the motion of the boat and the values measured by each of the sensors, and the effectiveness of your control surface. Then you can estimate the quantities you want to control and determine how to move the surface. Check out NACA TR-918.

 

Regarding the question as to whether a second servo on the main foil flap would be beneficial:

Undoubtedly the height control could be improved and in no way would it be diminished. However in the horizontal plane we do not need a rudder and a centreboard trim tab to steer our boats so why should we in the vertical plane.

 

If you were trying to achieve precise positioning in the horizontal plane, you'd want direct side force control then, too.

 

There are really two coupled modes to the boat's motion you're trying to control - a pitch mode and a heave mode. With one control, you can only get at one mode by the way in which it is coupled to the other mode. With two controls, you can control each mode directly. And with the additional control you can satisfy an additional objective, such as minimizing drag.

 

The control of height using tail control will always have a lag compared to controlling height with the main foil flap. The reason is to change height, you need to change the vertical velocity, and to change the vertical velocity you need to change the vertical acceleration by changing the lift on the foil. If you have a flap on the foil, when you change the flap deflection, you change the lift and create an immediate change to the vertical acceleration. If you change the lift through the changing the pitch attitude of the boat to control the angle of attack of the foil, then you first have to generate a pitch acceleration to generate a pitch rate to generate a change in pitch attitude. Only once the pitch attitude changes do you change the lift on the foil and change the vertical acceleration and start to affect the height.

 

But it's worse than that. With tail control, as opposed to a canard, the tail has to drop to increase the angle of attack. So the boat actually has to descend slightly before it can start to rise. This has significant implications for the stability of control loops.

 

It's simply not possible to get as tight a height control using only the rudder foil compared to controlling only the main foil flap. The lags in the height response to pitch control mean that the boat will go unstable if the height control is cranked up too high.

 

However, height control using the flap is also subject to serious limitations. The flap only has limited authority. The lift on the foil is a function not only of angle of attack but of speed. Since the lift has to equal the weight, as the speed increases, the flap has to be deflected to offset the increase in lift due to speed. Eventually the flap will be fully saturated just trying to maintain the trim of the boat, and even before then, any deflection for trim takes away from the authority available to counter dynamic disturbances. Tail control doesn't have quite as much limitation in this regard. There's not much difference in angle of attack required to climb or descend at a constant angle, so once the pitch attitude is set, the tail control can return to near its trim value as the height changes. So over the long term, the tail can be much more powerful than the flap.

 

The combination of characteristics means the flap and tail controls can be used in complementary ways. The flap can null out high-frequency disturbances from small waves and the tail can adjust the pitch trim so that over the long term the flap deflection returns to neutral. This maximizes the flap's effectiveness for dynamic ride control, and the steady state flap deflection can correspond to the optimum angle for minimizing foil profile drag.

 

Most importantly however: I found last year sailing with a mechanical system that I seemed to be hitting a hard wall regarding max speed. Contrary to all the text books the drag appears to be going up far faster than V^2.

 

Pitch control is very important for hydrofoil peformance, especially if you are using surface piercing foils or if the flap doesn't span the full width of the forward foil. At constant lift, the induced drag should decrease with the square of the speed - this is the whole point of using hydrofoils at high speed. But if the effective span shrinks with speed, the induced drag can actually go up. Pitch control can be important for flying lower and increasing the effective span to reduce induced drag more than the increase in parasite drag due to extra wetted area.

 

I have an unsubstantiated theory that around 18Kts we are starting to see true cavitation around unfair parts of the structure and that the size of the cavitation bubbles grows rapidly causing the rapid increase in drag.

 

That's quite possible. At areas where the local flow velocity is increased due to interference, you can get cavitation at 18 kt. You can also start to get cavitation if you have sharp pressure peak, such as at a corner.

 

 

How about using something like a capacitive fuel gauge for measuring ride height like aircraft use, http://www.airstuff.com/fuelmon.html#section1 The sensor tube could be fed down the dagger board and is long enough for the entire length of the blade, I think. If the inside of the dagger board filled and drained quickly enough with height changes then height could be sensed without too much delay. This in pair with the accelerometer and gyro seems tunable at first glance.

[clivee1 0]

It would be best to use the accelerometer for high-frequency height control and use the wand for low-frequency height control. The accelerometer will be subject to bias, scale factor, and alignment errors that will result in unbounded (ie, very, very large) errors if the acceleration is integrated to get vertical velocity and height. However feeding back wand position to the height estimate will stabilize the estimate against these errors. At the same time, the accelerometer will respond faster to a change in height than will the wand, making it most suitable for adding lead to the height control.

 

 

This is what I do. I do not amplify the accelerometer input to provide a phase advance, but do use the vertical velocity in the height control loop to achieve the same thing through a controlled gain setting.

Attached pic show data log from moment of instability, and a full 18kt crash. At the moment I have the height coupled to the wand quite tightly (0.5 sec) but this still filters a significant amount of chop that would feed through to the servo.

Scalling:

Height (mm)

Vvel (mm/S)

Vacc (mm/S/S)

The height trace follows the wand with no phase lag, but with reduced chop.

As my confidence grows I am sure that I will be able to further decouple and fly in inertial space.

[clivee1 0]

What you really need is a dynamic model that allows you to express the relationship between the motion of the boat and the values measured by each of the sensors, and the effectiveness of your control surface. Then you can estimate the quantities you want to control and determine how to move the surface. Check out NACA TR-918.

 

I have a model using an electrical analogue and a spice simulation package however at this scale

verifying and developing the model can make the project bigger not smaller.

[clivee1 0]

If you were trying to achieve precise positioning in the horizontal plane, you'd want direct side force control then, too.

 

There are really two coupled modes to the boat's motion you're trying to control - a pitch mode and a heave mode. With one control, you can only get at one mode by the way in which it is coupled to the other mode. With two controls, you can control each mode directly. And with the additional control you can satisfy an additional objective, such as minimizing drag.

 

The control of height using tail control will always have a lag compared to controlling height with the main foil flap. The reason is to change height, you need to change the vertical velocity, and to change the vertical velocity you need to change the vertical acceleration by changing the lift on the foil. If you have a flap on the foil, when you change the flap deflection, you change the lift and create an immediate change to the vertical acceleration. If you change the lift through the changing the pitch attitude of the boat to control the angle of attack of the foil, then you first have to generate a pitch acceleration to generate a pitch rate to generate a change in pitch attitude. Only once the pitch attitude changes do you change the lift on the foil and change the vertical acceleration and start to affect the height.

 

But it's worse than that. With tail control, as opposed to a canard, the tail has to drop to increase the angle of attack. So the boat actually has to descend slightly before it can start to rise. This has significant implications for the stability of control loops.

 

It's simply not possible to get as tight a height control using only the rudder foil compared to controlling only the main foil flap. The lags in the height response to pitch control mean that the boat will go unstable if the height control is cranked up too high.

 

However, height control using the flap is also subject to serious limitations. The flap only has limited authority. The lift on the foil is a function not only of angle of attack but of speed. Since the lift has to equal the weight, as the speed increases, the flap has to be deflected to offset the increase in lift due to speed. Eventually the flap will be fully saturated just trying to maintain the trim of the boat, and even before then, any deflection for trim takes away from the authority available to counter dynamic disturbances. Tail control doesn't have quite as much limitation in this regard. There's not much difference in angle of attack required to climb or descend at a constant angle, so once the pitch attitude is set, the tail control can return to near its trim value as the height changes. So over the long term, the tail can be much more powerful than the flap.

 

The combination of characteristics means the flap and tail controls can be used in complementary ways. The flap can null out high-frequency disturbances from small waves and the tail can adjust the pitch trim so that over the long term the flap deflection returns to neutral. This maximizes the flap's effectiveness for dynamic ride control, and the steady state flap deflection can correspond to the optimum angle for minimizing foil profile drag.

 

Most importantly however: I found last year sailing with a mechanical system that I seemed to be hitting a hard wall regarding max speed. Contrary to all the text books the drag appears to be going up far faster than V^2.

 

Pitch control is very important for hydrofoil peformance, especially if you are using surface piercing foils or if the flap doesn't span the full width of the forward foil. At constant lift, the induced drag should decrease with the square of the speed - this is the whole point of using hydrofoils at high speed. But if the effective span shrinks with speed, the induced drag can actually go up. Pitch control can be important for flying lower and increasing the effective span to reduce induced drag more than the increase in parasite drag due to extra wetted area.

 

Whilst tail control has inferior height control it has superior pitch control and the biggest disturbances seen by a dinghy foiler are pitch disturbances due to the height of the rig above the CoG and the foils.

To meet my objective of a boat that can be easily flown in a wide range of conditions with a system that can be scaled to a larger craft, it may be necessary to control both foils.

[atypicalguy 0]

If you were trying to achieve precise positioning in the horizontal plane, you'd want direct side force control then, too.

 

There are really two coupled modes to the boat's motion you're trying to control - a pitch mode and a heave mode. With one control, you can only get at one mode by the way in which it is coupled to the other mode. With two controls, you can control each mode directly. And with the additional control you can satisfy an additional objective, such as minimizing drag.

 

The control of height using tail control will always have a lag compared to controlling height with the main foil flap. The reason is to change height, you need to change the vertical velocity, and to change the vertical velocity you need to change the vertical acceleration by changing the lift on the foil. If you have a flap on the foil, when you change the flap deflection, you change the lift and create an immediate change to the vertical acceleration. If you change the lift through the changing the pitch attitude of the boat to control the angle of attack of the foil, then you first have to generate a pitch acceleration to generate a pitch rate to generate a change in pitch attitude. Only once the pitch attitude changes do you change the lift on the foil and change the vertical acceleration and start to affect the height.

 

But it's worse than that. With tail control, as opposed to a canard, the tail has to drop to increase the angle of attack. So the boat actually has to descend slightly before it can start to rise. This has significant implications for the stability of control loops.

 

It's simply not possible to get as tight a height control using only the rudder foil compared to controlling only the main foil flap. The lags in the height response to pitch control mean that the boat will go unstable if the height control is cranked up too high.

 

However, height control using the flap is also subject to serious limitations. The flap only has limited authority. The lift on the foil is a function not only of angle of attack but of speed. Since the lift has to equal the weight, as the speed increases, the flap has to be deflected to offset the increase in lift due to speed. Eventually the flap will be fully saturated just trying to maintain the trim of the boat, and even before then, any deflection for trim takes away from the authority available to counter dynamic disturbances. Tail control doesn't have quite as much limitation in this regard. There's not much difference in angle of attack required to climb or descend at a constant angle, so once the pitch attitude is set, the tail control can return to near its trim value as the height changes. So over the long term, the tail can be much more powerful than the flap.

 

The combination of characteristics means the flap and tail controls can be used in complementary ways. The flap can null out high-frequency disturbances from small waves and the tail can adjust the pitch trim so that over the long term the flap deflection returns to neutral. This maximizes the flap's effectiveness for dynamic ride control, and the steady state flap deflection can correspond to the optimum angle for minimizing foil profile drag.

 

Most importantly however: I found last year sailing with a mechanical system that I seemed to be hitting a hard wall regarding max speed. Contrary to all the text books the drag appears to be going up far faster than V^2.

 

Pitch control is very important for hydrofoil peformance, especially if you are using surface piercing foils or if the flap doesn't span the full width of the forward foil. At constant lift, the induced drag should decrease with the square of the speed - this is the whole point of using hydrofoils at high speed. But if the effective span shrinks with speed, the induced drag can actually go up. Pitch control can be important for flying lower and increasing the effective span to reduce induced drag more than the increase in parasite drag due to extra wetted area.

 

Whilst tail control has inferior height control it has superior pitch control and the biggest disturbances seen by a dinghy foiler are pitch disturbances due to the height of the rig above the CoG and the foils.

To meet my objective of a boat that can be easily flown in a wide range of conditions with a system that can be scaled to a larger craft, it may be necessary to control both foils.

 

I agree with Clive. Even with a pivoting daggerboard I spend a lot of time managing pitch-induced phenomena.

[Doug Lord 1,219]

Sketch by Tom Speer from boatdesign.net-I'm using a system similar to this to further explore manual control:

[BalticBandit 7]

Sketch by Tom Speer from boatdesign.net-I'm using a system similar to this to further explore manual control:

 

No one cares.

[atypicalguy 0]

If you were trying to achieve precise positioning in the horizontal plane, you'd want direct side force control then, too.

 

There are really two coupled modes to the boat's motion you're trying to control - a pitch mode and a heave mode. With one control, you can only get at one mode by the way in which it is coupled to the other mode. With two controls, you can control each mode directly. And with the additional control you can satisfy an additional objective, such as minimizing drag.

 

The control of height using tail control will always have a lag compared to controlling height with the main foil flap. The reason is to change height, you need to change the vertical velocity, and to change the vertical velocity you need to change the vertical acceleration by changing the lift on the foil. If you have a flap on the foil, when you change the flap deflection, you change the lift and create an immediate change to the vertical acceleration. If you change the lift through the changing the pitch attitude of the boat to control the angle of attack of the foil, then you first have to generate a pitch acceleration to generate a pitch rate to generate a change in pitch attitude. Only once the pitch attitude changes do you change the lift on the foil and change the vertical acceleration and start to affect the height.

 

But it's worse than that. With tail control, as opposed to a canard, the tail has to drop to increase the angle of attack. So the boat actually has to descend slightly before it can start to rise. This has significant implications for the stability of control loops.

 

It's simply not possible to get as tight a height control using only the rudder foil compared to controlling only the main foil flap. The lags in the height response to pitch control mean that the boat will go unstable if the height control is cranked up too high.

 

However, height control using the flap is also subject to serious limitations. The flap only has limited authority. The lift on the foil is a function not only of angle of attack but of speed. Since the lift has to equal the weight, as the speed increases, the flap has to be deflected to offset the increase in lift due to speed. Eventually the flap will be fully saturated just trying to maintain the trim of the boat, and even before then, any deflection for trim takes away from the authority available to counter dynamic disturbances. Tail control doesn't have quite as much limitation in this regard. There's not much difference in angle of attack required to climb or descend at a constant angle, so once the pitch attitude is set, the tail control can return to near its trim value as the height changes. So over the long term, the tail can be much more powerful than the flap.

 

The combination of characteristics means the flap and tail controls can be used in complementary ways. The flap can null out high-frequency disturbances from small waves and the tail can adjust the pitch trim so that over the long term the flap deflection returns to neutral. This maximizes the flap's effectiveness for dynamic ride control, and the steady state flap deflection can correspond to the optimum angle for minimizing foil profile drag.

 

Most importantly however: I found last year sailing with a mechanical system that I seemed to be hitting a hard wall regarding max speed. Contrary to all the text books the drag appears to be going up far faster than V^2.

 

Pitch control is very important for hydrofoil peformance, especially if you are using surface piercing foils or if the flap doesn't span the full width of the forward foil. At constant lift, the induced drag should decrease with the square of the speed - this is the whole point of using hydrofoils at high speed. But if the effective span shrinks with speed, the induced drag can actually go up. Pitch control can be important for flying lower and increasing the effective span to reduce induced drag more than the increase in parasite drag due to extra wetted area.

 

Whilst tail control has inferior height control it has superior pitch control and the biggest disturbances seen by a dinghy foiler are pitch disturbances due to the height of the rig above the CoG and the foils.

To meet my objective of a boat that can be easily flown in a wide range of conditions with a system that can be scaled to a larger craft, it may be necessary to control both foils.

 

I agree with Clive. Even with a pivoting daggerboard I spend a lot of time managing pitch-induced phenomena.

 

OK I reserve the right to disagree with myself. If my mainfoil flies like a stabilator it has just as much control over pitch as the rudder would, and even more really, because it just parks the nose of the boat a certain distance from the water (ideally). That in turn sets the AOA on the rudder, which is really just along for the ride. Tempting to call it a canard setup but in the end that terminology is just so many angels dancing on the head of a pin. Or was that 'angles'?

[The Black Pearl 0]

Angels dancing on the head of a pin, that's just what it feels like when it all goes right......

[bgulari 7]

If you were trying to achieve precise positioning in the horizontal plane, you'd want direct side force control then, too.

 

There are really two coupled modes to the boat's motion you're trying to control - a pitch mode and a heave mode. With one control, you can only get at one mode by the way in which it is coupled to the other mode. With two controls, you can control each mode directly. And with the additional control you can satisfy an additional objective, such as minimizing drag.

 

The control of height using tail control will always have a lag compared to controlling height with the main foil flap. The reason is to change height, you need to change the vertical velocity, and to change the vertical velocity you need to change the vertical acceleration by changing the lift on the foil. If you have a flap on the foil, when you change the flap deflection, you change the lift and create an immediate change to the vertical acceleration. If you change the lift through the changing the pitch attitude of the boat to control the angle of attack of the foil, then you first have to generate a pitch acceleration to generate a pitch rate to generate a change in pitch attitude. Only once the pitch attitude changes do you change the lift on the foil and change the vertical acceleration and start to affect the height.

 

But it's worse than that. With tail control, as opposed to a canard, the tail has to drop to increase the angle of attack. So the boat actually has to descend slightly before it can start to rise. This has significant implications for the stability of control loops.

 

It's simply not possible to get as tight a height control using only the rudder foil compared to controlling only the main foil flap. The lags in the height response to pitch control mean that the boat will go unstable if the height control is cranked up too high.

 

However, height control using the flap is also subject to serious limitations. The flap only has limited authority. The lift on the foil is a function not only of angle of attack but of speed. Since the lift has to equal the weight, as the speed increases, the flap has to be deflected to offset the increase in lift due to speed. Eventually the flap will be fully saturated just trying to maintain the trim of the boat, and even before then, any deflection for trim takes away from the authority available to counter dynamic disturbances. Tail control doesn't have quite as much limitation in this regard. There's not much difference in angle of attack required to climb or descend at a constant angle, so once the pitch attitude is set, the tail control can return to near its trim value as the height changes. So over the long term, the tail can be much more powerful than the flap.

 

The combination of characteristics means the flap and tail controls can be used in complementary ways. The flap can null out high-frequency disturbances from small waves and the tail can adjust the pitch trim so that over the long term the flap deflection returns to neutral. This maximizes the flap's effectiveness for dynamic ride control, and the steady state flap deflection can correspond to the optimum angle for minimizing foil profile drag.

 

Most importantly however: I found last year sailing with a mechanical system that I seemed to be hitting a hard wall regarding max speed. Contrary to all the text books the drag appears to be going up far faster than V^2.

 

Pitch control is very important for hydrofoil peformance, especially if you are using surface piercing foils or if the flap doesn't span the full width of the forward foil. At constant lift, the induced drag should decrease with the square of the speed - this is the whole point of using hydrofoils at high speed. But if the effective span shrinks with speed, the induced drag can actually go up. Pitch control can be important for flying lower and increasing the effective span to reduce induced drag more than the increase in parasite drag due to extra wetted area.

 

Whilst tail control has inferior height control it has superior pitch control and the biggest disturbances seen by a dinghy foiler are pitch disturbances due to the height of the rig above the CoG and the foils.

To meet my objective of a boat that can be easily flown in a wide range of conditions with a system that can be scaled to a larger craft, it may be necessary to control both foils.

 

I agree with Clive. Even with a pivoting daggerboard I spend a lot of time managing pitch-induced phenomena.

 

OK I reserve the right to disagree with myself. If my mainfoil flies like a stabilator it has just as much control over pitch as the rudder would, and even more really, because it just parks the nose of the boat a certain distance from the water (ideally). That in turn sets the AOA on the rudder, which is really just along for the ride. Tempting to call it a canard setup but in the end that terminology is just so many angels dancing on the head of a pin. Or was that 'angles'?

 

 

careful douggie will call you insane

[atypicalguy 0]

If you were trying to achieve precise positioning in the horizontal plane, you'd want direct side force control then, too.

 

There are really two coupled modes to the boat's motion you're trying to control - a pitch mode and a heave mode. With one control, you can only get at one mode by the way in which it is coupled to the other mode. With two controls, you can control each mode directly. And with the additional control you can satisfy an additional objective, such as minimizing drag.

 

The control of height using tail control will always have a lag compared to controlling height with the main foil flap. The reason is to change height, you need to change the vertical velocity, and to change the vertical velocity you need to change the vertical acceleration by changing the lift on the foil. If you have a flap on the foil, when you change the flap deflection, you change the lift and create an immediate change to the vertical acceleration. If you change the lift through the changing the pitch attitude of the boat to control the angle of attack of the foil, then you first have to generate a pitch acceleration to generate a pitch rate to generate a change in pitch attitude. Only once the pitch attitude changes do you change the lift on the foil and change the vertical acceleration and start to affect the height.

 

But it's worse than that. With tail control, as opposed to a canard, the tail has to drop to increase the angle of attack. So the boat actually has to descend slightly before it can start to rise. This has significant implications for the stability of control loops.

 

It's simply not possible to get as tight a height control using only the rudder foil compared to controlling only the main foil flap. The lags in the height response to pitch control mean that the boat will go unstable if the height control is cranked up too high.

 

However, height control using the flap is also subject to serious limitations. The flap only has limited authority. The lift on the foil is a function not only of angle of attack but of speed. Since the lift has to equal the weight, as the speed increases, the flap has to be deflected to offset the increase in lift due to speed. Eventually the flap will be fully saturated just trying to maintain the trim of the boat, and even before then, any deflection for trim takes away from the authority available to counter dynamic disturbances. Tail control doesn't have quite as much limitation in this regard. There's not much difference in angle of attack required to climb or descend at a constant angle, so once the pitch attitude is set, the tail control can return to near its trim value as the height changes. So over the long term, the tail can be much more powerful than the flap.

 

The combination of characteristics means the flap and tail controls can be used in complementary ways. The flap can null out high-frequency disturbances from small waves and the tail can adjust the pitch trim so that over the long term the flap deflection returns to neutral. This maximizes the flap's effectiveness for dynamic ride control, and the steady state flap deflection can correspond to the optimum angle for minimizing foil profile drag.

 

Most importantly however: I found last year sailing with a mechanical system that I seemed to be hitting a hard wall regarding max speed. Contrary to all the text books the drag appears to be going up far faster than V^2.

 

Pitch control is very important for hydrofoil peformance, especially if you are using surface piercing foils or if the flap doesn't span the full width of the forward foil. At constant lift, the induced drag should decrease with the square of the speed - this is the whole point of using hydrofoils at high speed. But if the effective span shrinks with speed, the induced drag can actually go up. Pitch control can be important for flying lower and increasing the effective span to reduce induced drag more than the increase in parasite drag due to extra wetted area.

 

Whilst tail control has inferior height control it has superior pitch control and the biggest disturbances seen by a dinghy foiler are pitch disturbances due to the height of the rig above the CoG and the foils.

To meet my objective of a boat that can be easily flown in a wide range of conditions with a system that can be scaled to a larger craft, it may be necessary to control both foils.

 

I agree with Clive. Even with a pivoting daggerboard I spend a lot of time managing pitch-induced phenomena.

 

OK I reserve the right to disagree with myself. If my mainfoil flies like a stabilator it has just as much control over pitch as the rudder would, and even more really, because it just parks the nose of the boat a certain distance from the water (ideally). That in turn sets the AOA on the rudder, which is really just along for the ride. Tempting to call it a canard setup but in the end that terminology is just so many angels dancing on the head of a pin. Or was that 'angles'?

 

 

careful douggie will call you insane

 

I thought he didn't give compliments? How are rudders coming?

[Phil S 159]

"Pitch control is very important for hydrofoil peformance, especially if you are using surface piercing foils or if the flap doesn't span the full width of the forward foil. At constant lift, the induced drag should decrease with the square of the speed - this is the whole point of using hydrofoils at high speed. But if the effective span shrinks with speed, the induced drag can actually go up. Pitch control can be important for flying lower and increasing the effective span to reduce induced drag more than the increase in parasite drag due to extra wetted area."

 

Disagree.

In my last 4 years of racing foil moths I think all my crashes were due to either"

Excess height due to friction, lag or poor settings in wand/flap linkage, or

wave troughs deeper than centreboard length enabling main foil to aerate when I did not manage to steer around them, or

Poor roll control in manoevres like gybes, or

Bad sailing.

 

Pitch stability is very well controlled by the aft foil without any adjustment, just as it is in a well trimmed aeroplane. Variations in rig drive are adequately managed by an efficient wand/flap mechanical system. In fact rear foils are getting smaller without detriment to pitch control.

 

Suggest that development of this hybrid, and moth illegal control system should take into account what is really happenning in the competitive end of the moth fleet, and not just a few brief encounters either on the water or via the www.

Bladerider has proven that simple but efficient mechanical systems which are easilly managed by saiors without necessarilly full understanding, make for more sucesful foiling sailors and a wider market appeal. Complex electonic systems with associated maintenace issues are not needed.

[Doug Lord 1,219]

Complex electonic systems with associated maintenace issues are not needed.

===============

Typical Philism. Who is to define what is needed? You have said that manual control is not only not needed but won't work. Only thing is a working manual system would likely beat a wand(and IS legal in the Moth Class). There are many extraordinary developments that may increase speed, make it easier to foil or both and God help us if they weren't tried because they weren't legal in the Moth Class. Go Clive!

[Phil S 159]

Doug,

I have done maybe 500 hours of foil sailing in the last 5 years, designed built and tried many different foils and systems, configurations and arrangements. All done in a competitive competition environment where success can be measured and failures made obvious for what they are. I do not win much but I am prepared to learn from others who do better than me.

 

Doug, just what have you done to make you such an expert?

 

(Do not bother answering me direct as I will have you back on ignore.)

[Doug Lord 1,219]

Doug,

I have done maybe 500 hours of foil sailing in the last 5 years, designed built and tried many different foils and systems, configurations and arrangements. All done in a competitive competition environment where success can be measured and failures made obvious for what they are. I do not win much but I am prepared to learn from others who do better than me.

 

Doug, just what have you done to make you such an expert?

 

(Do not bother answering me direct as I will have you back on ignore.)

======================

And you've been very,very wrong in your past expert predictions about large foilers and now about manual control and electronic developments. I don't need to be an expert to see what you've said with your own words and that has been proven wrong by numerous experimenters.

Thats not to say you aren't a Great Man; you are. Just wrong about some important aspects of foiler development.

[the_skiff_devil 0]

GTFO troll.

 

You advocate manual control of foils. This is about electronic automated foil control as an alternative to mechanical systems. Big difference.

 

You have no expertise on this topic. Come back when someone could give a fornicating rodent's rectum about what you have to say.

[SimonN 281]

And you've been very,very wrong in your past expert predictions about large foilers and now about manual control and electronic developments. I don't need to be an expert to see what you've said with your own words and that has been proven wrong by numerous experimenters.

Thats not to say you aren't a Great Man; you are. Just wrong about some important aspects of foiler development.

And you, who has no track record of building multiple succesful foilers, including designing and building your own foils, claims to be always right! Actions speak louder than words and while you try your ideas on this forum, Phil tries them on the water. And while Phil might occasionally be wrong (and usually he admits when that has happened), how often can you prove you are right? The answer is simple. You cannot prove you are right because you are not out there sailing foilers you have developed and you aren't actually trying your ideas for real. They are all still sitting in a workshop, although that seems a grand term to describe what appears to be little mnore than a garage used for storage.

[atypicalguy 0]

Disagree.

In my last 4 years of racing foil moths I think all my crashes were due to either"

Excess height due to friction, lag or poor settings in wand/flap linkage, or

wave troughs deeper than centreboard length enabling main foil to aerate when I did not manage to steer around them, or

Poor roll control in manoevres like gybes, or

Bad sailing.

 

Pitch stability is very well controlled by the aft foil without any adjustment, just as it is in a well trimmed aeroplane. Variations in rig drive are adequately managed by an efficient wand/flap mechanical system. In fact rear foils are getting smaller without detriment to pitch control.

 

Phil I think if you actually measured the variation in pitch on your boat as it is foiling you would find there are rather large variations, particularly offwind overtaking waves, which contribute to the boat's excess height and crash. But it is only a guess as I have no accelerometers or gyros either.

[Phil S 159]

Karl,

Some automated pitch respose only when boat tries to follow surface of large rolling waves. If they are big enough then the boat can follow down troughs and up to the peaks, but mostly they are smaller.

 

Dilemma for control system and skipper is to distinguish between those small enough to ignore, (ie shallower trough to median less than foil depth below design ride level), and those waves which are deeper but too short to allow the wand and rudder foil to retrim pitch and follow the contour. Then if the skipper does not take action the foil can break surface and the boat will crash. What we do to adjust pitch in this case is move weight, sail lower by strategic trimming bow down with rudder foil, or heal and steer to use the vertical rudder as pitch control. Mostly we try to steer around the big holes we can see ahead of the boat.

 

It all happens very quickly, at 20 knots a moth does three boat lengths a second, if the mid size dilemma waves are about 0.5m deep they are probably about a boat length peak to peak, so we are passing 3 waves a second at that speed which is too fast for wand or skipper reaction, so avoiding the troughs or going slower and lower are the safer options.

 

I do not see how the elecronic sysyem can decide whether or not to change pitch based on the trough depth just ahead of the boat. If it reacts to pitch changes it might be contradicting the boats desire to follow a big safe rolling wave or reacting against the skippers intention to heal and track down a hole he can not steer around.

 

It is crasy to think any control system whether mechanical or electronic will be able to change the pitch of the boat to steer up and down 0.5m waves at a frequency of 3 per second or more. The loads and forces needed to move the total boat mass up and down this distance at those frequencies are just too much for the foil structures and the skipper's stomach.

[atypicalguy 0]

Karl,

Some automated pitch respose only when boat tries to follow surface of large rolling waves. If they are big enough then the boat can follow down troughs and up to the peaks, but mostly they are smaller.

 

There is a great photo of Scott from Garda bearing off at a windward mark with his bow waaay up in the air...I think there is something about the cyclical flow of water in a wave which provides more lift as the mainfoil approaches the crest, either that or the boat pitches up enough in climbing over the wave that the wand/flap cannot scrub enough lift to bring it back down quickly.

 

It is crasy to think any control system whether mechanical or electronic will be able to change the pitch of the boat to steer up and down 0.5m waves at a frequency of 3 per second or more. The loads and forces needed to move the total boat mass up and down this distance at those frequencies are just too much for the foil structures and the skipper's stomach.

 

Well there's a lot in that statement.

 

In short, you don't have to change the pitch of the boat to accomplish that - you only need to change the pitch of the foil. I do pretty well overtaking waves sailing really fast. It's when I slow down to gybe that the problems appear!

 

You are right about the skipper's stomach or more accurately the skipper's inner ear - it is really hard to gybe a boat that is bouncing up and down all over the place several times per second! Very rodeo-esque, but the bull weighs only 70 lb and the landing is much softer!

 

My control system does pretty much what you describe as crazy Phil. Really it is not that far fetched. The materials are plenty strong enough to handle it. I have my share of problems but the behavior you describe is readily achievable.

[aus_stevo 2]

My control system does pretty much what you describe as crazy Phil. Really it is not that far fetched. The materials are plenty strong enough to handle it. I have my share of problems but the behavior you describe is readily achievable.

is it faster?

[atypicalguy 0]

My control system does pretty much what you describe as crazy Phil. Really it is not that far fetched. The materials are plenty strong enough to handle it. I have my share of problems but the behavior you describe is readily achievable.

is it faster?

 

I lose speed in the maneuvers, as it takes me a bit longer to get foiling again. This loss is amplified in marginal foiling conditions. So for now it is hard to see how I would keep up around a course. Gybing is also giving me fits in the lumps, for complicated reasons. But in a straight line it seems more slippery than my old flapped mainfoil - it just goes faster and faster where the other one seemed to hit a limit. So for now I continue to wear my rose colored glasses.

 

Honestly it is hard to see any of these technical developments making large enough speed differences to make up for one bad tack at the pointy end of the fleet. I mean, if you could go two knots faster around the course it would be significant, but that would be pretty hard to achieve I think.

[Phil S 159]

Karl,

I know you have an all moving foil working but somewhere along the bloggoshere I missed the details on how it works. Wardi had one where the foil pivoted on the bottom of the centreboard but I understand you swing the whole T foil from with in the CB case. Can you please give us an outline on what moves and where the pivots are along with how the wand provides the power to make the moves?

Phil S

[atypicalguy 0]

Karl,

I know you have an all moving foil working but somewhere along the bloggoshere I missed the details on how it works. Wardi had one where the foil pivoted on the bottom of the centreboard but I understand you swing the whole T foil from with in the CB case. Can you please give us an outline on what moves and where the pivots are along with how the wand provides the power to make the moves?

Phil S

 

Steel pin at the hull exit, wand pulls aft on the top of the foil. Some bearings in the appropriate places.

[Mal Smith 28]

Karl,

I know you have an all moving foil working but somewhere along the bloggoshere I missed the details on how it works. Wardi had one where the foil pivoted on the bottom of the centreboard but I understand you swing the whole T foil from with in the CB case. Can you please give us an outline on what moves and where the pivots are along with how the wand provides the power to make the moves?

Phil S

 

Steel pin at the hull exit, wand pulls aft on the top of the foil. Some bearings in the appropriate places.

 

Got some photo's, or is it secret? I can't imagine how you can get the power to control that without a very large wand with some sort of paddle on the end. And I imagine that the location of the pin might be critical.