Rotating adjustable hydrofoils

tspeer · Dec 5, 2013

mij said: ↑

...The idea is to have the foils able to rotate on an axis that is inclined relative to the hull (see attached image). When the foils are vertical they are aligned with the direction of the boat (angle of attack = 0), essentially acting as dagger boards; when they are rotated the angle of attack increases and can be adjusted as required, thus able to act as foils.

Does this idea look feasible? Has it been tried before?...
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It worked for the AC72s. It should work at model scale.

Karl Wittnebel · Dec 6, 2013

high on carbon said: ↑

All of our tooling for foils to date has been built out of pre-preg hi temp carbon resin matrix, to match the final part laminates. This way the coefficient of expansion in the part is matched to the tool, then we don't have laminate pulling off the tool face because it shrank faster than the tool at some point in production. We cook our parts in a 5 atmosphere Autoclave.

Plugs for bits like foils are usually CNC milled from Blue block. Larger parts like hulls are milled from solid MDF, then coated, faired, and tools pulled off of them.

We aim to build 2-12 parts out of most tools, at most. But they are built to high tolerances so we don't have to add a lot of bog after to fair things out smooth.

included here are the super top secret tooling for the wiggle foil and a first version of a part from the tool.

Also shown, a rough bench test of a mechanical system

Also, a physical full size mockup of our deployable slat system. All built from the wing tooling itself, with mechanical systems in place, to see if it all would work (Yep, sure did)

If we mill parts from solid billet, we would organize the matrix and fibre orientation very carefully inside the billet, not just machine any old fibres will nilly and yes there would be wrap layers on the outside for sure, for final fairing and layer bonding etc.
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Nice. Thanks for sharing.

I only mention it because you talked about the cost being significant. Those figures seem fine for production stuff, but for what you are doing I don't get it. I would do unproven concepts in wet layup, cut one-off female tooling, and put it in the autoclave since you have one available.

Exchangeable tips seem sexy, but I'm guessing the next advance will be in controlling the foil.

If you are still in a sharing mood, I am curious about the bending moment at the hull exit and the foil thickness there.

mij · Dec 6, 2013

tspeer said: ↑

It worked for the AC72s. It should work at model scale.
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After some searching I found the image below:

Was the axis around which the foil pivoted at the perforation through the base of the hull?

Baltic Bandit · Dec 6, 2013

Dunno - I think that's the speculation and that makes sense from a load perspective

Karl Wittnebel · Dec 6, 2013

Baltic Bandit said: ↑

Dunno - I think that's the speculation and that makes sense from a load perspective
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The rule prohibited the foil from translating at the hull exit. So yes that was the pivot, more or less, presumably. Some sort of spherical bearing or a gimbal.

tspeer · Dec 7, 2013

mij said: ↑

Was the axis around which the foil pivoted at the perforation through the base of the hull?
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It was somewhat above the bottom of the hull on 17. This was because of the curve of the "elbow" in the foil and the need to retract the foil to within 500 mm of the bottom. There was a sliding seal that moved with the foil to avoid having a big open cavity. The Design Rule required the lower bearing to be fixed, but there was translation of the board & case away from the lower bearing.

Other boats have used a torpedo-like fairing to put the axis at the bottom of the boat for canting keels.

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Rotating adjustable hydrofoils

tspeer Senior Member

Karl Wittnebel Junior Member

mij Junior Member

Baltic Bandit Previous Member

Karl Wittnebel Junior Member

tspeer Senior Member

Any benefit to rotating a non-wing / non-teardrop mast?

Flettner Rotors - Calculating Rotating Skin Friction

rotating mast/fixed boom?