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

[CassidyNZ]

Originally Posted by cal40john

The next line in italics that you left out of your reply was a quote from your post.

That was stating generally accepted principles of “lift”. Do you disagree with the principle?

I have in other posts said that I’m not an expert on this subject, I too said I’m not about to be become one. If you are/are becoming one, that’s really terrific, you may be able to cut through some of the other rhetoric in this thread with some real facts.

Perhaps you can confirm that by pointing my boat 5 degrees closer to the wind I’m generating lift off the symmetrical keel as opposed to just going in a slightly different direction to overcome leeway or adverse current?

[MicHughV]

Thus far, we have only seen these AC75 boats sail in relatively flat and calm water. Should this change and there is only as much as a 2' chop or other small wave, these may well reach the " bustle" on the NZ boat and cause unnecessary friction. For this reason, the American entry with a relatively flat hull may be the better hull as there would be more clearance under the hull ???

[cal40john]

Originally Posted by CassidyNZ

That was stating generally accepted principles of “lift”. Do you disagree with the principle?

I have in other posts said that I’m not an expert on this subject, I too said I’m not about to be become one. If you are/are becoming one, that’s really terrific, you may be able to cut through some of the other rhetoric in this thread with some real facts.

Perhaps you can confirm that by pointing my boat 5 degrees closer to the wind I’m generating lift off the symmetrical keel as opposed to just going in a slightly different direction to overcome leeway or adverse current?

Why would you believe any arguments I make if you don't believe an aeronautical engineer or a physics prof?

My personal epiphany as to how strong a force lift is, was from working on my upwind skills on a shortboard. The only fin in the water was about a 14" deep 4" chord skeg. I'm leaning out with my foot jammed in the footstrap being pulled hard into it by the sail. All the sudden there is no push back, I'm skimming sideways in the water at around 15 knots. As I crash, I'm thinking it's a long swim home with no skeg since I thought I had to have broken it. Flip the board over and the skeg is still there. Once I had pointed high enough to stall the skeg, I couldn't feel any pressure from pushing the skeg sideways through the water. Whereas when it was producing lift it felt like I was pushing against something solid like railroad tracks. I did this several times that day before I realized what was going on.

Why hasn't someone dinged me for thread drift yet as there's no way the foils on the AC75's are symmetrical?

[jmh2002]

To be honest I'm tired of these inane arguments and thread drifts that is mostly the result of one member posting odd suppositions and then 'inviting comment'.

I'm trying to ignore it.

I have posted plenty of other good, factual, and relevant info for discussion instead.

[jmh2002]

Originally Posted by a64pilot

Is it? If so then I would assume they can trim the amount the leg is deployed...

As mentioned earlier, the Foil Arms are canting.

And the T-foil Wings have adjustable Flaps to create more or less lift, thereby also adjusting the flying height.

Adjusting the flying height naturally causes more or less immersion of the Foil Arm.

You can see that all of the boats have horizontal stripes on the Foil Arms (and on the Rudder too if you look at TNZ) as a visual reference for their flying height.

And AM and Prada also have a Red Line at what I assume is the maximum flying height that still keeps the T-foil Wing sufficiently immersed.

[danstanford]

Not sure what constitutes thread drift on a title like this, but here goes. Was anyone else surprised by how much draft was in the mainsail? I know they need power to get her up on the foils but at those speeds I expected the sails to be much flatter. Am I off track?

[jmh2002]

Yes I kind of agree with you, especially at first glance.

But also these are dual skin mainsails, effectively a 'soft wingsail' and I think that creates the appearance of more draft.

[MicHughV]

I thought the whole point of these forums was to invite open and unfettered discussion on the topic at hand and offer different points of view and not just be the domain of a single individual.

[tp12]

Originally Posted by MicHughV

I thought the whole point of these forums was to invite open and unfettered discussion on the topic at hand and offer different points of view and not just be the domain of a single individual.

Yes, of course. However, there's a point at which we need to move past speculation that's already been explained etc.

[David M]

Just glad they kept fast planing sailboats, which is the most excitement for the most people. Love to see the high technology.

Let's hope the lawsuits stay out of this.

[MicHughV]

...I don't think anyone on this forum knows the inner workings and design brief or goals of any team, so we come here to discuss, share opinions, views, theory's, etc.

...Much has been discussed here and some posters obviously have a very keen interest in these boats and have provided a wealth of information, video's, photo's, technical documents, etc. There is a motherlode of extremely smart people on this thread, but that should not invalidate the opinion or thoughts of another.

...Nonetheless, the reality is that nobody here really knows the thinking or rationale behind the different AC 75 boats.

...Any attempts here to provide a bit of levity or other distraction gets immediately lambasted as being trivial or inconsequential.

...Fact of the matter is that nobody here knows the other person. We are all " faceless" id's on this forum. The AC75 boats are only just beginning to implement their testing program and lots is likely to change, get modified, rectified, etc, between now and then.

...I'm not sure this thread will survive under the current cloud of animosity, which would be a loss to all.

[a64pilot]

Originally Posted by MicHughV

...I'm not sure this thread will survive under the current cloud of animosity, which would be a loss to all.

It will be fine, you see that in all threads, even ones that are pretty cut and dried, things that data has been available for ever. Like batteries or anchors for instance.
There is always speculation, people like me who wonder if it could be this or that, people that don’t have access to the rules etc that explain things, for instance I didn’t even know that they had control of high lift devices and wondered how they controlled lift, speed or pitch came to mind. The bow down attitude for instance, it would be one way to reduce lift by decreasing the foils angle of attack, and would be a good indicator of a boat performing well.
Old school boats I ‘m sure controlled lift by the higher they flew the more foil left the water.

I understand the principles, but have no idea as to how they are applied, I think I’m not the only one.

[wingssail]

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

Fred's Theory of Lift: I know I'm setting myself up for a bunch of ridicule, but I can't help getting into this conversation about lift (and how it affects AC75, to keep it within the spirit of the topic)

I think Arvel has lost the plot so to speak. I've been reading his articles and books since the 70's when some other Boeing engineers (sailors too) introduced them to me. They have never been easy for me to understand.

In this paper, as he has before, he emphasizes the "Thompson's Circulation Theorem" as if it is actually causing flow around an airfoil in the opposite direction of the actual flow. However that is clearly not the case, as tell-tails on the windward side of a sail show. The theorem, in practical application, while mathematically correct, is simply an conceptual explanation of the why the flow on the windward (or bottom) of an airfoil develops higher pressure. There are other explanations for lift, including "deflection" which Avel dismisses in, to me, an incomprehensible way. If deflection does not work as a theory, as he says, then if you sprayed a stream of water at an angle against a flat board, and the board deflected the water, (which it of course does) you would not get any lift (force trying to move the board away from the deflection). But you do (thank you Newton).

Anyhow, any foil, symmetrical or asymmetrical, or even a flat plane, moving through a viscous medium with an angle of incidence, will develop lift. I'm not calling Arvel wrong, of course he is right, it's just that the deflection theory works better for my poor brain. Sailboats with symmetrical keels have an angle of incidence created by the weather vane effect of the pressure of the sails, which is counteracted by the correcting force of the rudder (weather helm).

What about the leeward side of a sail or the top of an airfoil? Certainly there is no deflection going on there. The molecules of the medium which would otherwise find themselves on the leeward (top) of the foil have been displaced (pushed to away). No molecules there! That creates a vacuum. Molecules farther to leeward, or farther above the foil, flow down to fill that vacuum. If the foil has a gentle curve the flow stays attached, but if the angle of incidence is too great they don't flow smoothly, and just a bunch of turbulence occurs (stalling).

Sorry if this next part (as was true of the previous part) is already apparent and well known to all of you. I don't mean to be patronizing. You can skip it, (if you even got this far). And go ahead and fly (pun) at me if you disagree with any of it.

In the AC75's we have a variety of foils: foil arms, foils, rudder, rudder T foil, etc (plus the sails and mast). Foil arms are symmetrical and develop no lift unless the whole boat is angled. The foils themselves are variably asymmetrical depending on the deflection of the foil flaps. On the T-foil on the rudder the angle of incidence of whole T foil may be changed by rocking the rudder forward or aft (rake). The rudder itself can be turned (yaw) to create an angle of incidence in either direction to steer the boat. The force created by the foils can be used to lift the vessel and to resist leeway, by, as A64 notes, banking the foil, which is done by canting the foil arm.

All of these forces must be balanced by inputs from the operators and by clever sizing of the foils. Whomever gets it right will have a faster and more controllable boat.

[wingssail]

Originally Posted by MicHughV

...I don't think anyone on this forum knows the inner workings and design brief or goals of any team, so we come here to discuss, share opinions, views, theory's, etc...

...Nonetheless, the reality is that nobody here really knows the thinking or rationale behind the different AC 75 boats.

Here is a tantalizing bit of pure speculation:

New Zealand and Prada, the Challenger of Record, developed theAC75 rule, (mostly I guess). In it they drew a cross section of the hull shape, shown below. The rule however does not specify that this has to be the shape.

It is interesting to note that the two teams not involved in the formulation used that shape in their hulls, while the two who were involved in formulating the rule used a different shape.

Was that an intentional misdirection?

Further, they have now changed the rule to restrict the allowed modification to the hull, (preventing addition of a bustle to the existing hulls?) Humm?

About not having lawsuits in this round? forgetaboudit.

[jmh2002]

Originally Posted by wingssail

Was that an intentional misdirection?

That's just a basic line drawing remember. Let's give some credit here, the best designers in the world are working on these projects, so nobody is basing their hull shapes on that simple line drawing. Everyone will be considering the actual Rules to the last millimetre.