Slip Wand for foiler height and roll control

[philSweet]

Doug Lord and Baltic Bandit have a thing going for months on Dinghy Anarchy and this forum.

And I for one wish BB would leave it over there.

 

[ozandy]

Skyak: Please don't tell me there is another spat going on!
All I've done so far on the 3d printer is the wand tip, the wand front dual pivot (proto until I get the brass ball joints to screw in and tweak details), the strut horns and mocked up a rudder trim device...which I cannot use as I will need to fabricate in stronger materials.
Overall length is 2.8M...it may extend if I need a rudder gantry.
Ballpark weight is fairly high as I used the "brick outhouse" approach when in doubt. I also foam filled all hulls to make un-sinkable. Probably about 50-60Kg.
Main foil is about 1.6M wide and approx 4000cm*cm...it is swept and tapered. I cannot recall the real numbers here at work...the foil was one of the first builds. I wanted it to be easy takeoff rather than maximum speed as befits a fun machine. I am worried that glass fiber will not be strong enough and even with two supports it may fail...I'm sourcing CF cloth and have the makings of a vac-bag setup underway but will not invest more $ until this one gets wet.
The two wand system is another backup plan worth trying...but I'm not quite ready to "forget about" an idea that has occupied my mind for so long. I'll just cop it if it turns out to be unworkable and admit to being silly!
I still cannot help thinking that leeway when flying on flat foils heeled to windward is a tad different to leeway when planing with a vertical foil and weight shift stability. It is worth checking out at least. In science a failed experiment is often as useful as a "successful" one. I'll most definitely be adding some manual override: easy and potentially very fun.

 

[Baltic Bandit]

well if you are heeled to windward, you should be getting enough lift that you will make negative leeway. That's what the Moths all do.

Yeh if your blade is just FG, there's a high chance of failure even with CF, homebuilt foils have a habit of failing at the T joint.

 

[Baltic Bandit]

Phil, I suggest that you direct your comment at the poster who initiated the name calling in this forum

 

[ozandy]

BB. Negative leeway may indeed be a factor that makes the slip wand unworkable. The slip wand may prevent it, making decent pointing impossible. I don't want a total dog upwind!
I am assuming there will be a balance point where the wand stops moving around and settles on fairly equal flap settings (ie. the centerline), but the balance point may be with a little bit of upwind slip, leading to a slight un-equal flap setting at equilibrium, which would be fine so long as they are in the right direction to increase stability. What would not be fine is if the system starts oscillating or gets into a more unstable state as a result of the slip sensing.
As leeway leads to leaning to windward, negative leeway would lead to a leeward moment, which reduces the negative leeway and allows for leeway again. I'm hoping this feedback can be tuned to be stable, and even efficient
Wave noise makes it more vital that the sensor feedback and balance dynamics do not tend to any positive feedback or oscillation.
Although these little thought experiments are somwhat flawed and subject to error, I've got to the point where I have to try it!

One reason I used two support struts is to spread the load, and I added a little CF in the tension zones, used epoxy instead of polyester and then added another layer, and another. I have heavily gusseted the compression regions. Without pre-preg or vac-bag I cannot guarentee decent structural integrity though (bulk aint strength!).
The rear one I'm not so concerned about as this was made with 2 commercially made daggerboards I had lying around (been thinking about foils for a few years now!). The weak point is still the T join but I used enough CF cloth and epoxy on the join to be fairly confident. The rudder blade is also a point of potential failure but it is pretty chunky and should not have to support as much torsion as a non foiler would, but probably more compression which solid wood core can deal with OK.

 

[Baltic Bandit]

Well over in DA and MA there are some folks who have examples of foils that they've built that failed under load. Hence why I recommend you go there to talk to folks

Hopefully your dual struts will be enough

 

[ozandy]

Will do BB. Have already perused the archives but if/when this one fails I'll be looking to build another more robustly.
The guys that build dynamic soaring RC gliders (468Mph!) build amazingly strong CF wings with foam cores. My next foil will probably use this technique but with hardwood core and in a single piece. With vac-bagging you can get some pretty good foils but I would like to know how they align the layout: how many layers, what orientation, etc.
One thing I will never do again is a non-vac-bagged foil using GF...way too time consuming and not accurate enough.

 

[Baltic Bandit]

Their loadings are much much much lighter remember that as you go down in size, material properties go up in strength by order square in any axis of freedom

You might consider post curing it with heat even now. read up on it at West System

 

[ozandy]

Size wise they are similar or larger...but even at theose speeds I agree the loadings are lower...mind you at Mach 0.8 and with the ballast they use the loads are not trivial! They are not floaty soarers.
I'll have a look at the West Systems site...I had considered heat cure too complex for my garage...certainly no room for autoclave, but I'll have a read.
Found this site: http://www.playwithcarbon.com They appear to have all the goodies.
As with many construction techniques there are many, many variations on "vac-bagging" I have found...which is why I'll check out the boat building forums and try and find someone with hands on experience.

I've also been looking at the Moth asn forums on foils...excellent resource!

 

[Baltic Bandit]

you don't need an autoclave. Just a box built out of Home Depot Pink Styro blocks that you can fit your foils into.

 

[ozandy]

I'll definitely have to read up on it. Are heat cure resins really that much better than a slow cure epoxy? What sort of temps are we talking? Does the vacbag, peelply and such have to be heat resistant?

 

[Baltic Bandit]

even slow cured epoxy gains strength if post cured. Read up on it. You don't have to heat cure it in the mold. in fact there are often reasons not to.

you heat cure in mold if you are using pre-preg. Which btw is something you might consider since pre-preg gives you much better laminate and wetout control

 

[ozandy]

In that case, the way summer is looking I may just be able to leave it in the garage for a few hours after it comes out of the bag!

 

[Jim Caldwell]

The sailplanes he is referring to are flying in a circle at almost 500 mph. I believe they were reporting in excess of 40 G's. Go to rcgroups.com and turn the sound up, you won't believe sound they make. They call it "shredding the air".

 

[Doug Lord]

Cheers guys.
Alas, I have not sailed a foiler and was hoping to get some feedback from those that have. I guess the guys that sail them have no reason to hang around design forums though. Bummer. I realise that it is far easier to theorise than build. Having theorised and half-built many small aircraft (it gets scary dangerous *very* easily!), the move to a foiling boat is actually not too bad in terms of "what if I stuff it up?". Embaressment I can handle better then broken limbs!
Also having actively skydived for many years I realise that "expertise" is quite different in the sky as compared to around the bar. Similar in competition sailing.
Although I realise that full roll control is probably out of reach I want to see if some sort of slip/roll coupling is useful.

As to what I'm building...well pics are worth a thousand words.
All the main bits are now there, I just have to sort out a few details like the mast mount, rigging, steering, rudder trim, etc. Having a 3d printer makes engineering small parts pretty easy, and ABS dipped in polyurathane resin is amazingly strong! (a little bit of CF or GF helps too).
I will not be abandoning the idea just yet as it will kill me to get this far and not give it a go. The wand system is pretty cheap and easy to test out...and I'll revert to a simpler system if needed.

BTW. Rudder box will be mounted conventionally on the transom (may build a gantry), amma mounts are just sitting there, not attached. The "wings" will be sheathed to make a decent aero shape. The main foil will actually pivot from its mounting point forwards, it is not in its real pos. The main hull is in 2 parts that snap together like a large rowboat...it should fit in my car.
Yes, she is tiny, but so am I.
Failure to try is real failure...stuffups I expect and have learned to enjoy. I have learned so much fom building this baby that even if I end up with an unusual fishing platform with an outboard on the back it will not be a waste of time.
I'll post an update when she gets wet in a few weeks.

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ozandy, there are a number of excellent resources on this forum. Look thru the Aerodynamics and Hydrodynamics forum as well as these:

UPDATES, 1/11/14:
1) See the pdf included below by Bill Beaver-it is one of the most comprehensive studies of the Moth yet done and explains exactly what "Veal Heel" is. Also much info on foils.
2) Consideration of leeway is very important in foiler design-here are two reasons why:
a) http://www.boatdesign.net/forums/hy.../effect-leeway-lift-drag-hydrofoil-37398.html particularly posts 6,8, 9
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b) Magnus Clarke's description of how the "L" + curved foil works on the AC 72-and the prominent role played by leeway:
http://www.boatdesign.net/forums/multihulls/little-americas-cup-uk-2013-a-37972-10.html post 137
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From 1/10/14:

1) Moth on foils(with the current top recorded speed of the Moth in its name)-there are comments from the inventors of bi-foiler Moths-John Illet and Ian Ward plus from many others in the largest Moth thread on the internet. Ilett also pioneered the bow wand after getting enthused about the wands used on Dr. Sam Bradfields boats. I believe there are some early posts from Rohan Veal: http://www.boatdesign.net/forums/sailboats/moth-foils-32-2-knots-37-03-mph-11209.html

2) Foiler Design-started by Tom Speer as a design discussion on small monohull foilers. Lots of tidbits from him and many others experienced in sailing hydrofoil development: http://www.boatdesign.net/forums/sailboats/foiler-design-2447.html

3) Hydrodynamics and Aerodynamics Forum: http://www.boatdesign.net/forums/hydrodynamics-aerodynamics/
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Illustrations-both show Veal Heel-one might be clearer than the other-the picture version is from the paper included below: