Electronic Foil Control Systems.

[clivee1]

Some thrust bearing/bushings on each side of the board at the pin and some wheels at the top. There is very little friction.

Hi Karl,

Nice to see a picture of your system. What section do you have on the main foil, and are you having any problems with pitching moments or low speed flying and take off.

When I was trying to control the foil in a similar way I found that the pitching moment due to the cambered section would cause the CoL to effectively move aft as the speed increased, increasing the loading on the wand. I even snapped a wand at speed. Quite a crash.

I ended up putting a small tailplane on the main foil to counter the pitching moment.

Although I am now just controlling my rudder foil I can set the angle of my main foil on a string to increase the AoA for take off and up wind.

I believe that I am getting a laminar separation problem at low flying speeds and take off.

I am using an RS600FF main foil, NACA 63412 section. It is not really designed for low Reynolds number operation.

At low speeds I find the boat flying very bow up and feeling draggy, then suddenly (as the flow attaches?) it will flatten and fly properly.

It is posible that at the same Cl and Rn the flapped foils maintain attached flow to the flap and only see flow separation from the last 30%.

It is also possible that a better designed section will produce the required lift without separation, or that there is a different problem.

What is your experience?

Clive.

 

[atypicalguy]

Some thrust bearing/bushings on each side of the board at the pin and some wheels at the top. There is very little friction.

Hi Karl,

Nice to see a picture of your system. What section do you have on the main foil, and are you having any problems with pitching moments or low speed flying and take off.

When I was trying to control the foil in a similar way I found that the pitching moment due to the cambered section would cause the CoL to effectively move aft as the speed increased, increasing the loading on the wand. I even snapped a wand at speed. Quite a crash.

I ended up putting a small tailplane on the main foil to counter the pitching moment.

Although I am now just controlling my rudder foil I can set the angle of my main foil on a string to increase the AoA for take off and up wind.

I believe that I am getting a laminar separation problem at low flying speeds and take off.

I am using an RS600FF main foil, NACA 63412 section. It is not really designed for low Reynolds number operation.

At low speeds I find the boat flying very bow up and feeling draggy, then suddenly (as the flow attaches?) it will flatten and fly properly.

It is posible that at the same Cl and Rn the flapped foils maintain attached flow to the flap and only see flow separation from the last 30%.

It is also possible that a better designed section will produce the required lift without separation, or that there is a different problem.

What is your experience?

Clive.

Hi Clive. That is an E393. It is very cambered and has max lift/drag ratio at a very high Cl, something like 1.4, which is excellent for takeoff and remaining aloft at low speed. Yes the Cl moves quite a lot with AOA but the movement csalculation just goes into the spreadsheet with everything else when you design the foil; this one was a three piece with two Ls and a bottom so once the AOA was set it was pretty much set. Yes the wand needs to be strong but I only see high loads when i pitch down. If the wand bends I add more uni. If the paddle/ski thing sinks I add more surface area; I was using a cross country ski tip until recently which proved adequate upwind but not downwind. It pivots of course to optimise AOA and lift. Basically at high speeds my wand loads are reasonably light, and the wand can generate hellacious power at those speeds, so if everything is robust enough there is no problem. But you have to get rid of any stretch in the actuation line etc and be sure there is zero friction in the line as it is often transiently under quite a lot of load and any friction on shore is amplified. Obviously you want to run in low-drag configuration most of the time, and only have the extra power available for extreme cases (which are not at all uncommon).

Foil drag also plays a role the faster one goes, of course. But that should be offset by the increased lift available from the ski.

Of course none of this will compensate for a foil which has not been designed to function with the center of lift roughly under the pivot at speed. So you just do your math, figure out where the fore/aft center of lift at any AOA is, pick what you think is a good angle of attack to put it in the middle at your "average" running condition, make the foil, and drill a hole in it above that point. If you want to play fancy sweep games that's fine but it seems complicated for proof of concept.

I would caution to make the foil very strong where you drill the hole. Very. Strong. This is pretty easy to do.

I might choose a slightly less cambered section next time, but overall I like it despite the 2D drag penalty as there are other benefits in terms of drag which I believe may outweigh the penalty of a high camber section. These have been outlined elsewhere and I do not wish to rehash them with all the naysayers here on your thread, as you have mentioned them yourself previously here.

We have other ideas on how to change the system to eliminate the moment from the Cl shifting around, but I will only move to them if this pivot system proves untenable, which so far it has not. It is certainly fairly simple to implement.

Performance is much easier to optimize in flat water than in lumps, as with all foiling craft it seems!

Glad to hear you are pressing on - misery loves company!

Karl

 

[clivee1]

Hi Clive. That is an E393. It is very cambered and has max lift/drag ratio at a very high Cl, something like 1.4, which is excellent for take off and remaining aloft at low speed. Karl

Hi Karl,

Are you able to take off at these high Cl without issue? Do you have a set of ordinates for the section I cannot find them on the web.

Clive.

 

[atypicalguy]

Hi Clive. That is an E393. It is very cambered and has max lift/drag ratio at a very high Cl, something like 1.4, which is excellent for take off and remaining aloft at low speed. Karl

Hi Karl,

Are you able to take off at these high Cl without issue? Do you have a set of ordinates for the section I cannot find them on the web.

Clive.

Sure but obviously you want to increase gradually with boatspeed or you will never reach escape velocity...I might go with a slightly less cambered section next time FYI can email you whatever you need for coordinates etc

 

[atypicalguy]

OK, I get that. Now, does the wand need to be any bigger than normal to drive the thing?

Mal what kind of a question is that? My wand is totally normal. Other people's wands are starting to look pretty wimpy though...

 

[Mal Smith]

OK, I get that. Now, does the wand need to be any bigger than normal to drive the thing?

Mal what kind of a question is that? My wand is totally normal. Other people's wands are starting to look pretty wimpy though...

Perhaps I should have phrased that a little differently...

Anyway, I think you have answered my question now in your response to Clive.

 

[Board skiff]

Apologies for reviving an old thread, but does anyone know what became of Clive's electronic wizard? Is it in use, still being developed, or has momemtum slowed?

 

[taobsu]

It is a great thread.

Just wondered with current development of Iphone/IPad, and other GPS/smart phone devices, is the electronc control getting much simple.

iPhone has gyro and accelerometer embedded. Is that possible an Apps with some sensors able to control a foiler Moth?

 

[kprice]

Apologies for reviving an old thread, but does anyone know what became of Clive's electronic wizard? Is it in use, still being developed, or has momemtum slowed?

I had an email from Clive that he is building a standard Moth now.....the large boat with electronic control has been scrapped.

 

[duncan (the other one)]

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...)

A bungy cord stores energy, too.

 

[BalticBandit]

A bungy does not bring extra stored energy ONTO the boat. It only "stores" energy accumulated within the boat. Now I used to have an old mechanical wrist watch that self-wound from the normal movement of the wrist. I wonder if you could build something like that that uses a combo of solar and just the motion of the boat to keep the electronics charged enough. Given the amount of work involved in the flapper though I suspect not

 

[kprice]

It is a great thread.

Just wondered with current development of Iphone/IPad, and other GPS/smart phone devices, is the electronc control getting much simple.

iPhone has gyro and accelerometer embedded. Is that possible an Apps with some sensors able to control a foiler Moth?

In some emails, Clive said the main problem was the actuator to drive the flap on the rudder foil, not the sensors.

He used a large RC servo ( from RC sailing/airplanes) and it would stall out.

 

[Ncik]

the loads are significant

 

[Cruiser]

A bungy does not bring extra stored energy ONTO the boat. It only "stores" energy accumulated within the boat. Now I used to have an old mechanical wrist watch that self-wound from the normal movement of the wrist. I wonder if you could build something like that that uses a combo of solar and just the motion of the boat to keep the electronics charged enough. Given the amount of work involved in the flapper though I suspect not

That's right,

A flexible mast stores energy too.

 

[big_up]

There is a foiling RS boat at WSC in sydney that uses an acuator to adjust flap movement in the main foil.. it is quite interesting, the owner says that the flap response is much better than the old cable system. Hopefully it will line up against the moths soon

 

[kokosir]

Can someone please direct me to the original thread?

 

[Board skiff]

Thanks for the update kprice.

Big_up - do you know whether that is a rotary or linear actuator?

I was thinking that one of these would get you half way there, just need to add a control algorithm and the actuator.

 

[duncan (the other one)]

A bungy does not bring extra stored energy ONTO the boat. It only "stores" energy accumulated within the boat. Now I used to have an old mechanical wrist watch that self-wound from the normal movement of the wrist. I wonder if you could build something like that that uses a combo of solar and just the motion of the boat to keep the electronics charged enough. Given the amount of work involved in the flapper though I suspect not

Please check what I was replying to. A capacitor does not bring stored energy onto the boat, either.

What's to stop me storing energy (via a paddle), then using it for my electronics?

Presumably, the same line in the sand that says I can't store excess energy in a bungee to drive a propeller.

 

[taobsu]

It is a great thread.

Just wondered with current development of Iphone/IPad, and other GPS/smart phone devices, is the electronc control getting much simple.

iPhone has gyro and accelerometer embedded. Is that possible an Apps with some sensors able to control a foiler Moth?

In some emails, Clive said the main problem was the actuator to drive the flap on the rudder foil, not the sensors.

He used a large RC servo ( from RC sailing/airplanes) and it would stall out.

If stall out is due to high load on actuator/servo?

maybe can use cable to control big portion flap, with some preset positions, say take-off, cruising position,

actuator will only control small tip of flap, for fine-toning, that way load could substantially lower then control full flaps

Anyone has tried using Iphone as main control unit+sensor to control foilers and rudder?

I know there are many flight control software (freeware) can be rewrite or port to Iphone as an Apps, as long as gyro and accelerometer in iPhone can reach sensitivities such application demanded.

 

[RobG]

Just wondered with current development of Iphone/IPad, and other GPS/smart phone devices, is the electronc control getting much simple.

iPhone has gyro and accelerometer embedded. Is that possible an Apps with some sensors able to control a foiler Moth?

It's not a matter of computing power, much more a matter of a suitable sensor and power for whatever control is used to adjust the height. I can't tell you how many times I've run aground in a Ross 780 (draws 1.8m) and the depth sounder alarm (set at 3.5m) has gone off a few seconds later. We actually run aground less often when sailing with it turned off.

I expect it's a similar problem for any sensor looking for a boundary layer between media. At a speed differential of say 20kn between Moth and wave, the time to respond is extremely short. The bow to foil distance is perhaps 1.2m which will be covered in about 0.1 seconds.

An additional issue is the momentum of the boat—even if you can make instantaneous adjustments (which a mechanical wand does reasonably well), the boat takes time to respond. So the sensor has to be able to look forward and make adjustments in anticipation of surface level changes—sensing at the strut is too late unless fast, large adjustments can be made to (over) compensate for momentum.

And then there's the power to activate whatever control is used (main foil flap, centreboard AoA, pitch, whatever). The forces involved can be quite high, I hate to guess but likely 3 to 5 kg of compression/tension until some physical limit is reached, which might be some device (say a tether or wingbar) or whatever breaks first (probablly a pushrod or fitting but maybe the wand or flap hinge). So the servo providing the movement probaby needs to be able generate the equivalent of 10kg of force more or less instantaneously over perhaps 20 to 30mm (theres' some units here I'm missing, probably Newton metres).

Note that current mechanical devices work just fine in most conditions, it's only when the breeze gets toward 20kn and whips up 1m chop or more that they start to have problems. Even the best height control in the world isn't going to overcome low sailing ability in those conditions.