America’s Cup - ETNZ launches 1st AC75 (new)

[MicHughV]

...I think a double row of handrails from the bow back to the mast would go a long way to provide some security for the hapless crew member that has to crawl across that open deck to manhandle a code zero...some " decktread" in that area wouldn't hurt either..

[wingssail]

Originally Posted by a64pilot

Now assuming they are asymmetrical foils and I’d bet lunch they are, but if they are with both down the lift from one is cancelled by the other and you just have excess drag.

I think the foils generate lift perpendicular to their span, are symmetrical (both sides the same), and that the windward force to offset leeway is created by the angle of the foil arm (it is not vertical, it is at an angle) presenting the foil to the best point of leverage.

Imagine of you are standing and someone tries to push you over and sideways, you stick your leg out to the side.

With two foils down you would have lift from both, drag from both and no ballast righting moment.

[MicHughV]

...I have to add this salient fact tonight.

New Zealand gets to play England in a semi-final rugby match on Sat 26th in the World Rugby cup currently underway in Japan.

Trust that the players will be focused on rugby and not the AC75 boats.

The Kiwi's have a notable excellent rugby team, but one can't count out the English rugby team out either.

I can't remember the last time I saw an English boat in the America's Cup ?? So surprising to see them give it a go this time around. Who knows....this might be England's year !!

[a64pilot]

Originally Posted by wingssail

I think the foils generate lift perpendicular to their span, are symmetrical (both sides the same), and that the windward force to offset leeway is created by the angle of the foil arm (it is not vertical, it is at an angle) presenting the foil to the best point of leverage.

Imagine of you are standing and someone tries to push you over and sideways, you stick your leg out to the side.

With two foils down you would have lift from both, drag from both and no ballast righting moment.

Understand the foils,
However the legs or struts or whatever they are called function I believe as a keel. The foils lift of course and flying on one will counterbalance the sail trying to heel the boat, but there is still a very significant force trying to push the boat sideways, I believe the struts will provide lift to counter that sideways force, and that is why I’d suspect they are asymmetrical airfoils and may well have what one person called toe in.
On an airplane the angle between the fuselage and the centerline of the airfoil is called the angle of incidence.

Then not to belabor the issue, but in many ways these things are flying machines, as much as sailboats. The rules must specify sails and not double surfaced airfoils I’d guess.
Personally I like sails as opposed to giant model airplane wings, but that would be faster.

Oh and in edit, I’d suspect you would see both foils down during a tack, but only momentarily as they transition from one foil to the other. Although maybe in light winds they would need both to get flying and then raise one?
How fast do they move, is that also regulated?

[wingssail]

Originally Posted by a64pilot

Understand the foils,
However the legs or struts or whatever they are called function I believe as a keel. The foils lift of course and flying on one will counterbalance the sail trying to heel the boat, but there is still a very significant force trying to push the boat sideways, I believe the struts will provide lift to counter that sideways force, and that is why I’d suspect they are asymmetrical airfoils and may well have what one person called toe in.
On an airplane the angle between the fuselage and the centerline of the airfoil is called the angle of incidence.

Then not to belabor the issue, but in many ways these things are flying machines, as much as sailboats. The rules must specify sails and not double surfaced airfoils I’d guess.
Personally I like sails as opposed to giant model airplane wings, but that would be faster.

Oh and in edit, I’d suspect you would see both foils down during a tack, but only momentarily as they transition from one foil to the other. Although maybe in light winds they would need both to get flying and then raise one?
How fast do they move, is that also regulated?

The drawings and photo below show the configuration of the foil arms and the foils. It looks to me like very little of the foil arm will be useful as a keel to resist leeway. The photo shows NZ with about 1mt immersed and it is not vertical. That's why I feel the foil itself provides that "anti leeway" lift. Maybe not. My personal feeling is that they have zero angle of incidence. That too would be in the rule. I have a copy but right now I'm not interested in reading it again.
The hydraulic mechanism is standard, as are the arms, and provided to all teams. In videos they seem to move from retracted to deployed in about 2 seconds, or less.
The mainsails are double surfaced airfoils, only two soft surfaces separated by a hollow place inside and a single leech. They have two luff tapes and two grooves on the back of the mast separated by around 1/3mt (that's a guess, it's in the rule)
I'm not an engineer.

[CassidyNZ]

Originally Posted by a64pilot

Boats keels generate lift based on angle of attack, that is the boat has to be pointed into the wind and not directly in the direction of travel to generate the angle of attack required to generate lift.
It’s not about resisting leeway, it’s about generating lift to cancel out leeway.
This is due to any keel that has an airfoil shape is a fully symmetrical, airfoil or you would have to have two keels, one you used when the wind was to port and the other when the wind was to starboard.

As much as I believe you wish this to be complex, I really also believe you’re over-thinking the keel thing. For a foil/wing/keel to generate “lift” whether horizontal or vertical, it has to be asymmetric. You will know better most that for an aircraft wing to generate lift, it has a flat(ish) bottom and an arced top. I’m not going to belabour the principle of lift - you already know that.

The keel on the great majority of yachts is not asymmetric (as you say). The pointing of a yacht sailing slightly upwind does not resist leeway or create lift. It simply has the boat sailing to an imaginary point above the course that will result in the reaching of the destination despite being “blown” downwind of the course (leeway).

If the foils on the AC75 were to create horizontal “lift” and move the boat to weather, the rudder would need to bring it back on course, thus conflict. Conflicting “lift” = loss of speed, however small. Nobody is going to engineer speed-reducing elements into a racing boat. Going to MicHughV’s two-foils-at-the-same-time, one would generate “lift” to port, the other to starboard. And there will be numerous occasions (tacking, gybing) when AC75’s will have both foils in the water. Surely it is obvious that this would cause loss of speed. Like the toe-in you mentioned - excess toe-in on a car wears out tyres, uses more fuel. No difference.

[Tillsbury]

Originally Posted by MicHughV

...I think a double row of handrails from the bow back to the mast would go a long way to provide some security for the hapless crew member that has to crawl across that open deck to manhandle a code zero...some " decktread" in that area wouldn't hurt either..

Comparing this to the recent AC matches, I'd suspect the thinking is that if you have some kind of sail failure you've lost the race. There's little point carrying extra equipment intended to send a crew member to the bow. Indeed, very often an imperfect tack or gybe was the losing of a race, because of the huge distance you give up by effectively stopping and then having to slowly build up the apparent wind speed and angle you need to get going again. The TNZ "bustle" I believe is a response to this. If they can slightly foul up a gybe but get back on the foils fairly quickly then they are still in the race. I can see races where AM do the same but lose half a leg getting going again, exactly as happened to Oracle In the last final.

[jmh2002]

Originally Posted by Tillsbury

The TNZ "bustle" I believe is a response to this. If they can slightly foul up a gybe but get back on the foils fairly quickly then they are still in the race. I can see races where AM do the same but lose half a leg getting going again, exactly as happened to Oracle In the last final.

Yes this, exactly this, as I have described in detail in earlier posts.

[cal40john]

Originally Posted by CassidyNZ

As much as I believe you wish this to be complex, I really also believe you’re over-thinking the keel thing. For a foil/wing/keel to generate “lift” whether horizontal or vertical, it has to be asymmetric. You will know better most that for an aircraft wing to generate lift, it has a flat(ish) bottom and an arced top. I’m not going to belabour the principle of lift - you already know that.

The keel on the great majority of yachts is not asymmetric (as you say). The pointing of a yacht sailing slightly upwind does not resist leeway or create lift. It simply has the boat sailing to an imaginary point above the course that will result in the reaching of the destination despite being “blown” downwind of the course (leeway).

If the foils on the AC75 were to create horizontal “lift” and move the boat to weather, the rudder would need to bring it back on course, thus conflict. Conflicting “lift” = loss of speed, however small. Nobody is going to engineer speed-reducing elements into a racing boat. Going to MicHughV’s two-foils-at-the-same-time, one would generate “lift” to port, the other to starboard. And there will be numerous occasions (tacking, gybing) when AC75’s will have both foils in the water. Surely it is obvious that this would cause loss of speed. Like the toe-in you mentioned - excess toe-in on a car wears out tyres, uses more fuel. No difference.

How do you explain aerobatic planes flying upside down?

Article by Arvel Gentry Boeing Aerodynamics Research engineer and sailor starting with describing lift developing on a flat plate -

http://www.gentrysailing.com/pdf-the...ns-of-Lift.pdf

[CassidyNZ]

Originally Posted by cal40john

How do you explain aerobatic planes flying upside down?

Article by Arvel Gentry Boeing Aerodynamics Research engineer and sailor starting with describing lift developing on a flat plate -

http://www.gentrysailing.com/pdf-the...ns-of-Lift.pdf

Sorry, wasn’t planning on letting this discussion turn me into a scientist except to say that Mr. Gentry’s work appears to deal with airflow and velocities exceeding 10kn. Perhaps the answer to your question lies in there?

[cal40john]

Originally Posted by CassidyNZ

Sorry, wasn’t planning on letting this discussion turn me into a scientist except to say that Mr. Gentry’s work appears to deal with airflow and velocities exceeding 10kn. Perhaps the answer to your question lies in there?

You stated that you know what is required to produce lift, what do you base
this knowledge on?

For a foil/wing/keel to generate “lift” whether horizontal or vertical, it has to be asymmetric.


From your comments, it's obvious you didn't read the last article, so here's one more direct to the point, an investigation into how different keel geometries affects the lift generated by a keel.

https://www.researchgate.net/publica..._Sailing_Yacht

Section 3.1

All of keel sections must be symmetric since they have to work equally well on both sides. That is the reason a symmetric profile is chosen in the study. Hence, the wing must drift downwind with a leeway angle to produce lift force (Fig.3)

[jmh2002]

As I mentioned earlier, I think this is mostly a red herring that @MicHughV started after seeing some visible spray, and the discussion went off on a tangent unfortunately.

I might be wrong, but there is very little of the vertical Foil Arm and Foil Fairing immersed when the boats are up and flying. As I understand it the T-foil Wing is what is doing most if the work to provide lift, not the Foil Arm.

And it is the T-foil Wing that has the adjustable Flaps.
ie: to adjust the amount of lift being generated...

[jmh2002]

Luna Rossa is up and flying:

https://www.sailweb.co.uk/2019/10/20...f-their-speed/

[a64pilot]

Well something has to be resisting the lateral force, and lift is generated 90 degrees to an airfoil, that is why an airplane is banked to turn, so either the lifting foil is banked or something else is countering the down wind drift.
Normal sailboats with a keel counter it by steering into the wind thereby causing the symmetrical keel to produce lift, whether it has an airfoil section or not.

[jmh2002]

Here is a another article discussing how the AC75 will fly:

https://www.yachtingworld.com/americ...ill-fly-123520

Here are some quotes which mostly cover what I have already posted here earlier.

Originally Posted by www.yachtingworld.com

“The hydrofoils on a Cup boat work exactly as on an aircraft wing: you have the asymmetric flow around the wing or foil, which creates a pressure difference. That then generates a force that’s trying to equalise the difference. The force lifts the plane off the ground – or the boat out of the water, in our case,” explained Ben Ainslie.

Originally Posted by www.yachtingworld.com

“We will have direct control of the flap on the trailing edge of the T-foil,” explained Ainslie. “Moving the flap down will create more lift and more drag, but the lift is good for creating take-off. Moving the flap up to come more in line with the rest of the foil will reduce the lift and drag, which is then good for higher speed. It’s finding that trade-off really.”

Originally Posted by www.yachtingworld.com

“It’s [the AC75] got some form stability from the hull,” said Ainslie, “but after that it’s reliant on the lift from the wings and the foil arm to give the boat the righting moment. We think – we hope – we’ve got a good idea of how this is going to play out and what sort of speed we need to create righting moment and ultimately to take-off.

“Without a lead keel you’ve got to be very, very careful about how you power up the boat, how you create the speed, what angles you sail to create the speed. The simulator has been really critical to developing the techniques, both for the designers and for the sailors,” explains Ainslie.

And here is a close up of the T-foil Wing and Flaps on INEOS Team GB: