Slip Wand for foiler height and roll control

I had sensed your views as the thread developed.

FYI, it is great to see another builder / thinker trying to leverage off of experience and/or knowledge of aircraft stuff to try to push forward ideas in the world of small single handed sailboat foiling. The moth performance is incredible with the right sailor, but it also obvious that the moth is not the only solution. The more we share ideas and help each other, the more we improve the chances for finding a few other good (or at least useful) configurations .

Recently I did make it to the water with a much less ambitious little project (very low dollar small proa), but so far it has been mostly a case of trying to stomp out really basic bugs to enable more serious focus on experimentation later. When it gets warm again, I am hoping to move on to fun stuff like stable foiling (preferably with a potential for efficient passive altitude control). I also want try out a functional "reversible camber" wing, but this is on the back burner for now.

 

Thanks for the support.
I am concerned that I may be taking on a bit much complexity and ideally I'd start with a modern Moth, but the build process itself is so much fun I don't mind if all I get from this is a bruised ego and some learnings.
I got interested in foiling when I saw a design in an old 70s Popular Mechanics...I was about 10 at the time so this idea has been brewing for 30 years or so!
I think aircraft are a reasonable starting point for designing the dynamics of a foiler...although I reckon without extensive sailing experience I'd have little chance of success. Plenty of devils in the details!

What are the main bugs you have found in the proa project?

 

The initial goal was to demonstrate that you can come up with fast shunting foiler configuration with:

• Almost all weight (rig, rudders, platform, crew) at or near a windward main hull that is just big enough to support the required 90% all up boat weight at rest.
• Cross beams that are very long, very low air drag, very strong and not high dollar (carbon tow on hollow wood core seems to be a success at this point )
• A very slender (4.25" OD thinwall pvc for now) ama that is longer than the main hull (14' vs 10' for now) for pitch stability with simple straight reversible surface piercing foils near each end.

Lots of bugs including:

• Basic shunting proa rudder nightmares
  - how big (1st and 2nd tries did not work, defaulted to my very old and very heavy Hobie 14 plastic ones)
  - Where to put them (location 2 seems to work)
  - Can I only have only one wet or do I need 2 in the water
  - How to mount with required rotation angles (version 3 seems ok for now) and have kick up or cassette to allow only one wet if desired.
  - With 2 in the water, do I try to use one at a time or two at a time.
  - How to get them balanced with the rig and the ama foils when running
  - How to not totally stall them when attempting to tack / shunt / jibe.
• Rig (old beat up sunfish sail at this point) handling issues.
• I have been trying to using a tacking approach with a fast mode (main hull windward) and a "just get back to the other side of the pond" mode (ama windward). This would let me manually set my ama foils for one direction sailing during testing. Success with this approach has been very mixed.

My last sail had things just sorted out enough to get the expected ama foil surging and ventilation issues that will require experimentation to overcome. Ama foil AOA and angle (30° was used initially) are both big variables. Need to be able to adjust as required during testing. Configuration change to allow angle adjustment is in progress.

 

Sounds like a fun project.
Amazing how simple concepts always get complex really quickly when you try to make them work.
I was lucky enough to have a sail in a traditional Micronesian proa in the Marshall Islands recently. We had 4 on board this 14 foot thing with a seemingly crude rig and I was amazed how fast it was! These things show how a non planing hull can beat "boat speed" by using very slim hulls. The process of "shunting" by walking the mast from one end to the other was fascinating...I guess it works on the ocean where you only have to tack every few hours. The steering was also...unlikely as it was just a paddle tied by rope to the middle of the proa. They would let it go and it just floats to the other end when shunting, during which they basically steer with the mast. Amazing boats. I can see why folks like them.
http://www.chineblog.com/wptest/wp/wp-content/uploads/Imports/currace.jpg
Trying to make shunting work with a traditional rig is pretty tricky so I can see why you are tacking. Dealing with two rudders sounds very tricky!
I switched from surface piercing foils when I realized the fiberglass ones I built were just too flexy to work. The AOA would not be controllable enough without lower aspect ratio, thicker section, and better materials. Add in the issues of ventilation/cavitation variable AOA due to slip and heel, the eventual need to bend them...the wand for height control started seeming like an easier option!
I think you never really know the trade-offs and what works until you hit the water...and if the thing is for fun then all you need is safety and you can deal with some quirks. I *almost* bought a Moth...but building is fun and wading out with a capsized boat doesn't appeal. You get to pick your quirks when you build.

 

I've been thinking about the issue Tom raised about the slip wand creating the wrong roll response in hard turns. The following little model explains it a bit better.

Assume 5 m/s forward speed.
Assume boat rotates around center of mass (COM)
Assume 18 degrees/sec rotation (90 degree turn in 5 secs)
Wand is 1m ahead of COM. (it is actually a bit closer, and moves but I'll be conservative)
In that position 18 degrees/sec imparts about 0.3 m/s to the wrong side of the wand.
To do this the boat must rotate and there will be some slip (it is not on rails), the amount of slip required to counter the .3 m/s from rotation at 5 m/s is about 3.4 degrees.
So to stop the slip wand from rolling the wrong way due to throwing the bow to the side, the boat must slip a bit. It actually must slip past that point so as to impart a roll and establish a carving turn rather than a quick topple and crash!
I reckon 3.4 degrees is realistic enough, and if it is an issue I should be able to move the wand back to the COG and reduce the required slip. Whether I can tune it to be responsive yet stable is the real test.

 

90 degrees in 5 seconds is slow. remember the "bad turn" is typically going to be one that is slightly out of control - and you don't want to make it worse. If you look at Fybes and Facks from moths, those are side to side in under 3 seconds. So double your turn rotation speed.

So 0.6 m/s

but I don't get how in a carving turn there needs to be a lot of slip. Lets say I'm Fybing from STB to Port. So I start out flat ( cuz in maneuvers you want to be flat so mast momentum doest screw with you)

bow now moves right to left at 0.6m/sec. this is the same as though I was going in a straight line and the boat started making 0.6m/sec leeway. which you would counter by rolling to weather - which in this case means heeling to Stb.

but since I'm rotating anti-clockwise, heeling to stb means heeling to the outside of the turn. Seems bad to me

 

BB: Yep, the adverse roll effect of a sharp turn has been concerning me. I concur with Tom that the slip sensor should probably be behind the main foil, not in front.
What gave me some cause for optimism is two things:
1) At 18 degrees/sec the 3.4 degrees slip is achieved within about 1/4 sec...if the correct amount of roll is applied to balance within a second or so the turn can be increased, when that is balanced it can then be increased more...etc. 18 degrees per sec would only be the starting point.
2) The rudder is applying the slip from a position below the COM and will tend to impart some roll in the correct direction. I was hoping this would negate the incorrect feedback from rotation.

Now having said all that it still concerned me and I thought about how to get the slip detection behind the foils while leaving the height wand out front where it should be.
(I have fond memories of gybing a Sailfish on high wind days...ended up in the drink more often than not! Resorted to granny turns at times too.)

At first I considered two additional wands trailing the struts. These would be slip only and be "slaved" to the height wand by disconnecting the front arm from the wand so it rotates freely but still feeds in height. This would involve 2 arms, pivots, vanes and 4 more ball-joints.
Then I came up with a more elegant approach:
Apologies for the quality of the pics.
A vane is attached to the bottom surface of the main foil.
Slip will make the vane rotate to the left and right. The triangular attachement to the flaps turns this vane deflaction into differential flap deflection.
The arm attachment to the wand is now free to rotate and the arm itself moves as purely height control now. Because the mixing still occurs on this pivot there will still be some damping of the roll inputs as height increases.
I'll trim this system with shears initially: start with a big vane and trim until oscillations stop.

If I had a single strut with a single height control rod I could do the mixing much simpler by moving the the slip vane up and down whilst allowing it to rotate left/right. (Anyone got a spare Moth foil I can cut up? )

This also leads me to a much simpler height control system where a leading strut, surface peircing from below could be mounted to the top of the foil so that slip vane is deflected for height control based on the front wand and the slip/roll is then added by the vane. This height control strut would only need to be a tad longer than flying height so would be less bulky too.
Forward leaning struts are an issue, but removing 6 pivots and 4 ball-joints from a control scheme has got to be a good thing!
I'll stick with the current height control for now, but it is such a simple build that I'll have it as an option on testing day.
I've decided I'll need a rudder gantry too.

Other progress over weekend: Amma mounts bored out and ammas now fit nicely, added amma lugs to rear hull. A pin through a lug on each hull and the amma lower strut will hold it all together. Mounted main foil and set initial angle...will need to beef up this area. Finished height control and freed up front arm so it is slaved to height. Also pinned wand so it no longer rotates.