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Well, my theory is by making the foils smaller, they are able to mode their boat for the different wind conditions much more readily.

Heavy winds -> smaller, thinner flaps.

Light winds -> larger, thicker.

With large foils, LR are much more limited in what they can do.

I also think that the sneaky work around with their main sail will mean they can get foil borne with less foil since they are getting substantially more power right down low.

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Just a few interesting bits of the straight-line performances from today: Upwind /Downwind VMGs - race 1: Upwind /Downwind VMGs - race 2: Same story in both races actually.

Thanks to weta27's pics I have created an approximation of NZ's "BFB v2" foil. Main points: Foil area is almost the same, possibly even a smidge larger. Flaps have increased in area as

Is there any interest in a series of technical posts that would illustrate the issues in foil wing section design by starting with the E908 section in this paper and modifying it to make it more suita

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18 minutes ago, Stingray~ said:

Between days, even? Are you sure flaps are not part of measured-in kit before you start the Match? 

Yep. Makes the smaller foils seem a pretty fucking smart idea right?

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1 hour ago, Stingray~ said:

What I’m curious about, is if ETNZ has found some kind of rules loophole that can make the flaps on their ‘30% smaller’ foils behave with efficient and powerful lift even in the light? Hula V2? 

No loophole, NZ just has to use a greater foil AoA, plus greater flap angle, to achieve the same amount of lift.

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47 minutes ago, jaysper said:

Yep. Makes the smaller foils seem a pretty fucking smart idea right?

Haven't heard of any observations of NZ using different size foil flaps, have you seen this?

Considering GB & LR's foils are some 50% larger than NZ, I think some of our sharp eyed observers would have noticed any substantially larger flaps?

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8 minutes ago, MaxHugen said:

No loophole, NZ just has to use a greater foil AoA, plus greater flap angle, to achieve the same amount of lift.

Actually they did exploit the loophole that allows the teams to include the foil faring weight in the overall nine hundred odd kilos as well as the loophole that allows them to have the two flaps connected by a control mechanism that is magically not part of the flaps.

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4 minutes ago, MaxHugen said:

Haven't heard of any observations of NZ using different size foil flaps, have you seen this?

Considering GB & LR's foils are some 50% larger than NZ, I think some of our sharp eyed observers would have noticed any substantially larger flaps?

Haven't seen anything Max but you can get more lift 3 ways. AoA as you mentioned, surface area and profile.

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1 hour ago, jaysper said:

Yep. Makes the smaller foils seem a pretty fucking smart idea right?

This is new to me, too. Where are the rules that specify what can be changed from day to day? I haven't found anything in the class rules, it only lists the max number of components and % of changes. 

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36 minutes ago, erdb said:

This is new to me, too. Where are the rules that specify what can be changed from day to day? I haven't found anything in the class rules, it only lists the max number of components and % of changes. 

Can't remember where I saw it. Might have been one of Mozzy's vids.

If you get into trouble with the MC designing your AC75 accordingly, just send them to me and I'll sort them out for you. 

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3 hours ago, erdb said:

This is new to me, too. Where are the rules that specify what can be changed from day to day? I haven't found anything in the class rules, it only lists the max number of components and % of changes. 

Anything on the measurement certificate cannot be changed without invalidating that measurement certificate, and they I believe have to have the measurement certificate the same across the entire "phase" of competition?

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7 hours ago, JonRowe said:

Anything on the measurement certificate cannot be changed without invalidating that measurement certificate, and they I believe have to have the measurement certificate the same across the entire "phase" of competition?

Yes, I found the rules. It's in the "Match Conditions" document. They have to lock in everything 120 hours before the first race, and everything including flaps need to stay the same for the whole series. 

2020807462_configrules.thumb.JPG.579e3b72ec51e286db3be2c7537470c1.JPG

They have to give a list of replacement parts ahead of time in case of damage, and they can only replace stuff from this list if the MC approves the repair/replacement.

So can't switch flaps day to day, you have to choose the best setup based on your long-term forecast.

Match Conditions (CORD 26).pdf

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On 2/21/2021 at 10:18 PM, uflux said:

More power with less drag. Pretty powerful combination :ph34r:

Going off the time stamps of the footage of ETNZ training after the final race verse LR in the final race. ETNZ were 20 seconds faster during their practice upwind after the final race than LR were on their last upwind of the final race.

Well, it looks like NZ could be competitive than.... Hate for the AC to be too one sided for LR...lol

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10 hours ago, sosoomii said:

Hi Erdb, interesting data as ever.  Are the can’t angles the same on both tacks?

Yeah, I looked at it before. It's hard to tell, because obviously there's some variability in the conditions, and they may sail in a low vs high mode for tactical reasons.

Upwind, port vs starboard:

1885114921_portuwcant.png.2cf0513c5b581a837d790d28a301eba5.png   476609754_sbuwcant.png.23ca206e170d508e138f8994748f2766.png

LR sails with the same cant angle on both tacks. What's interesting here is how LR was much more locked in whereas INEOS was struggling to find balance.

 

2000051653_portuwtwa.png.09cb10b3e5e517ffedcca83faee3582a.png   773124278_sbuwtwa.png.83d9fa4b21a45afb9e0619c47b24932d.png

There is quite a bit of variation for both teams in TWA, but for what it's worth, LR had a tighter average TWA on starboard and INEOS had a tighter TWA on port.

 

Downwind port vs starboard:

515860189_portdwcant.png.bdbd4fe827e45b4abf8dc75434c5240f.png   1545429476_sbdwcant.png.4ec56cfb88842ca0ddd584778ad290e2.png

Downwind, there is 1 deg difference in average cant for LR starboard vs port. Does that make a huge difference? I doubt. INEOS is about the same.

 

 

1149529908_portdwtwa.png.d237af77ec74d91ec958b3b63e5ebd4d.png  1419146304_sbdwtwa.png.aff7bef6d1d9248698c76a7bfd777e3d.png  

Again, hard to tell if there's any real difference in TWA here. LR sailed deeper on port, INEOS sailed deeper on starboard.

To me it seems they are finetuning something that may make some marginal difference in certain conditions. If it made a huge difference, they would have finalized it and had it set up the same way on both sides. Shows a confident team that was thinking ahead for the Cup all along the series. ...or it's just a busted compass. :D:D

 

 

 

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32 minutes ago, uflux said:

These boys are sounding a bit desperate to convince themselves me thinks :rolleyes:

 

I think thir theories are sound, they are things I have thought about boat as well. When I saw Mozzies vid I thought he was making it more than it is.

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2 hours ago, The Advocate said:

I think thir theories are sound, they are things I have thought about boat as well. When I saw Mozzies vid I thought he was making it more than it is.

The apparent wind angle going up-wind at 40 knots is (I'd guess) around 10 degrees.  There's no way that wind is not going to rip down between those fairings and hit the main.  There's plenty of Italian wishful thinking in that video :-)

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1 hour ago, Regular Swimmer said:

The apparent wind angle going up-wind at 40 knots is (I'd guess) around 10 degrees.  There's no way that wind is not going to rip down between those fairings and hit the main.  There's plenty of Italian wishful thinking in that video :-)

Just watched the English version... and I disagree with their conclusions about the venturi effect. When considering the crew pods, and the sail dividing the area between them, this strongly suggests that there would be an acceleration of airflow on the leeward side, and deceleration to windward, resulting in a pressure differential and therefore sail lift.

Being no expert though, I'll side with NZ's design team, and conclude that the extra 3-4 m2 of low down sail area is quite useful!  :rolleyes:

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The hull form itself is not a venturi, but surely the extra part of the sail sheeted towards the side pod is?  The opposite of course is true on the other side, so a high/low pressure differential must also exist in the extra section of mainsail between the pods?

It's almost like tnz created a sail to water endplate, and then worked out how to include the infrastructure and crew within the rules. 

 
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1 hour ago, I ride bikes said:

The hull form itself is not a venturi, but surely the extra part of the sail sheeted towards the side pod is?  The opposite of course is true on the other side, so a high/low pressure differential must also exist in the extra section of mainsail between the pods?

Agree with that.  I think they get very useful "bonus" power in that area.

I see from the plan form that the pods diverge aft, past where the crew are located, which might be to help reduce the trailing hull vortices?

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6 hours ago, uflux said:

These boys are sounding a bit desperate to convince themselves me thinks :rolleyes:

 

Yeah - the Venturi effect (Bernoulli's principle) is diluted by the lower hull being open. Yeah - the angle of attack on the lower part of the sail exploited by the cutout may not be optimized for apparent wind. But shit - surely every little bit counts at this level of extracting/exploring performance?  

Anyway - 7 days until we find out ... :) 

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FWIW... this is my best approximation of the TR and LR hull profiles, taken from pics of their launches. The purple dotted line on TR is where I've estimated the deck profile.

Apologies for the lack of SAAC-approved yellow lines. :)

image.png.1f54225e627842585671834d4e551c85.png

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6 hours ago, MaxHugen said:

FWIW... this is my best approximation of the TR and LR hull profiles, taken from pics of their launches. The purple dotted line on TR is where I've estimated the deck profile.

Apologies for the lack of SAAC-approved yellow lines. :)

image.png.1f54225e627842585671834d4e551c85.png

Thanks for these Max, 

Greens look good, the yellows are for photos :P

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2 minutes ago, 45Roller said:

Thanks for these Max, 

Greens look good, the yellows are for photos :P

Gotcha, I'm still learning the lines.   :rolleyes:

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In which wind conditions there are more benefits from the additional sail area TR gained cleverly exploiting the loophole in the class rules? In light winds there is more power and in strong winds, where power is already too much, there is a gain having less heeling moment. But I can't figure out how much.

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51 minutes ago, strider470 said:

In which wind conditions there are more benefits from the additional sail area TR gained cleverly exploiting the loophole in the class rules? In light winds there is more power and in strong winds, where power is already too much, there is a gain having less heeling moment. But I can't figure out how much.

Very difficult to quantify. 

At the higher wind strengths, we could assume that perhaps only the lower couple of sections of the sail are really providing power. They amount to about 70m2. If we accept an estimate of 3.5m2 extra sail area at deck level, that would be a possible increase of 5% power. But just a slight bit more power would need to be given up at the mid section to compensate... so as a wild guess I suppose you could say an increase of ~4% "bonus" power.

Coupled with NZ's lower drag narrow foils, it's a significant  advantage.

 

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6 minutes ago, kiwin said:

It's not just righting moment. If the COE is lower then the foils can be canted more "out" giving less leeway upwind.

It depends on sea state. In a very calm sea, I think NZ could possibly get to a max of maybe 23-24° - same for LR most likely - with tip surfacing.

However, at least in the ACWS, NZ mostly sailed with 22° foil cant even in fairly flat conditions. This is probably to maintain their -2° bow down pitch to keep the foil at an optimum neutral AoA.

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20 hours ago, uflux said:

These boys are sounding a bit desperate to convince themselves me thinks :rolleyes:

 

I must confess to frequently feeling that these guys kinda just make shit up, I wonder if it might be due to having to explain things in English, but for experienced professionals in the trade, it often feels pretty fluffy...

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20 hours ago, rh3000 said:

I must confess to frequently feeling that these guys kinda just make shit up, I wonder if it might be due to having to explain things in English, but for experienced professionals in the trade, it often feels pretty fluffy...

Yeah I gave up watching them long time ago.

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On 2/26/2021 at 12:59 PM, kiwin said:

It's not just righting moment. If the COE is lower then the foils can be canted more "out" giving less leeway upwind.

 

23 hours ago, MaxHugen said:

It depends on sea state. In a very calm sea, I think NZ could possibly get to a max of maybe 23-24° - same for LR most likely - with tip surfacing.

However, at least in the ACWS, NZ mostly sailed with 22° foil cant even in fairly flat conditions. This is probably to maintain their -2° bow down pitch to keep the foil at an optimum neutral AoA.

There's a lot to gain, and it's because of the complex geometry of the AC75. It's true for every sailboat that if you lower the CoE, you can proportionally increase side force while keeping heeling moment the same. On the AC75, there is an added benefit, because you can cant the foil out further as you lower the CoE of the rig. In turn, it does two things: first, it puts the foil further out from the CG, although this effect is probably minimal (the outside part of the foil may start to come out of the water, plus at those cant angles, you don't gain that much lateral separation anymore). Second, it changes how the lateral and vertical forces are coupled. If you cant the foil out more, you can increase side force more for the same increase in vertical force. Since the vertical force is limited by the weight of the boat and by how much rudder downforce you can/want to use, the higher cant angle allows you to push the boat harder (more lateral force) with less effect on vertical forces and pitch moments.

So far, when I showed graphs I made with my VPP, I only showed solutions where the boat is balanced for maximum speed for a given TWA/TWS.

That gives you a line graph for every TWS like this:

1883173053_Speedpolaronly2.png.fcff9d2c763c70ec34bb8813dec26ca7.png

However, there are a lot more data points where the boat is stable, but it sails slower.

Here is a way to show that. This is for 20kts TWS:

TWS20-speed-cant.png.cc3543c809190a9bb1386a8a129013dc.png

Every dot is the result of a different combination of rudder downforce, cant angle and speed where the boat is foiling in balance. It's color coded, so the hotter the color, the higher the speed for a given TWA.

Here is sail twist and CoE height for the same TWS 20 kts. Notice where the yellow (high speed) dots are:

TWS20-twist.png.88f37a7ff41feee86c7f7e16645ebc65.png  1579161325_TWS20_sailcoe.png.1ae1972f6fe53d1a3f98a9ab366dee63.png

The more negative the twist number, the more twist you have and the lower the CoE. I've limited twist to 15 deg, but the model would love to go further if allowed, especially at reaching angles. Cut outs at the top of the sail and added area at the bottom, does the same thing - lowers the CoE. So I'd say there is quite a bit to gain in the higher wind range. If you look at the speed chart above, there is a 2.5 - 3 kts gain to be had if you can lower the CoE by increasing the twist from 6-7 deg to 15 degree (or lower the Coe by other means).

BTW Max, I forgot how you measure cant angle, but ETNZ sailed upwind mostly with 62 - 66 degree cant in the ACWS.

Race 1, 4, 8, 10 and 12.

1747347881_uwfcant.png.17b913f1092b8357770289f5d262c31a.png397662267_uwfcant.png.e8d6659f7b045c8740db3d02c131889a.png2082375673_uwcant.png.1ddf3807c78e57528ec3393252750e81.png2007453662_uwcant.png.0f03a8b61fe0578c25b983593ca25e6c.png986384506_uwcant.png.e17aa80ddf009e933495d02eed8d76cf.png

You can tell how they were struggling to keep it on foils in the last race in light winds, as they had to use a much lower cant angle (low cant angle means you have more vertical lift for the same lateral force). The other thing to note is that only AM could sail with a higher cant angle than ETNZ. I think these two were in the same design corner in terms of general balance, and AM was on a good track (bat-wing sail included) until they put a huge hole in their boat. Maybe their hull shape wasn't as refined as ETNZ, but in general their design approach was good.

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On 2/25/2021 at 4:27 PM, erdb said:

Yes, I found the rules. It's in the "Match Conditions" document. They have to lock in everything 120 hours before the first race, and everything including flaps need to stay the same for the whole series. 

2020807462_configrules.thumb.JPG.579e3b72ec51e286db3be2c7537470c1.JPG

They have to give a list of replacement parts ahead of time in case of damage, and they can only replace stuff from this list if the MC approves the repair/replacement.

So can't switch flaps day to day, you have to choose the best setup based on your long-term forecast.

Match Conditions (CORD 26).pdf

Thanks for finding this mate :)

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On 2/27/2021 at 5:59 AM, strider470 said:

In which wind conditions there are more benefits from the additional sail area TR gained cleverly exploiting the loophole in the class rules? In light winds there is more power and in strong winds, where power is already too much, there is a gain having less heeling moment. But I can't figure out how much.

Having the extra power down low in high breezes means you can bring the CoE down using the batwing and (maybe?) run the main flatter or smaller jib I think.

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13 minutes ago, jaysper said:

Having the extra power down low in high breezes means you can bring the CoE down using the batwing and (maybe?) run the main flatter or smaller jib I think.

Yes, I was wondering if it is more advantage in high winds or light winds

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3 hours ago, erdb said:

You can tell how they were struggling to keep it on foils in the last race in light winds, as they had to use a much lower cant angle (low cant angle means you have more vertical lift for the same lateral force). The other thing to note is that only AM could sail with a higher cant angle than ETNZ. I think these two were in the same design corner in terms of general balance, and AM was on a good track (bat-wing sail included) until they put a huge hole in their boat. Maybe their hull shape wasn't as refined as ETNZ, but in general their design approach was good.

I think the AM hull design was as refined, they just chose more of the Luna Rosa corner of the design space.  AM had some deficiencies in the boom and rudder controls.

There are a lot of similarities in the goals for NZ and AM, they both are/were going for speed.  NZ hopes that can still maintain speed during the tacking duels.  I think their boom-less main gives them more acceleration during the tacks than AM had and NZ looks to be good in lighter winds.  LR has a high mode that neither UK nor AM could match.  If NZ can match it then they should be fine.  LR has a much better design and control of their main than NZ.  The added sail area fro NZ look very agricultural and can not be very efficient.

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54 minutes ago, The_Alchemist said:

I think the AM hull design was as refined, they just chose more of the Luna Rosa corner of the design space.  AM had some deficiencies in the boom and rudder controls.

There are a lot of similarities in the goals for NZ and AM, they both are/were going for speed.  NZ hopes that can still maintain speed during the tacking duels.  I think their boom-less main gives them more acceleration during the tacks than AM had and NZ looks to be good in lighter winds.  LR has a high mode that neither UK nor AM could match.  If NZ can match it then they should be fine.  LR has a much better design and control of their main than NZ.  The added sail area fro NZ look very agricultural and can not be very efficient.

I agree with the first part. As for LR's high mode - it's an interesing question. The anhedral foils with differential flap settings offer more flexible control of foil forces, and may give them an edge in quickly shifting between high and low modes. On the other hand, they need bigger foils, since the lift is not shared equally by the wing halves. Bigger foil means higher drag, and that may reduce their ability to point high.

I'd be surprised if LR had much better control of their main. Who knows, but I have a feeling GA started to think about this double-skinned main long before anyone else.

The bat-wing main and added sail area on the bottom looks as it does because of the rules. Kind of like IOR bumps. Ugly, but if it gets the max out of the rules, fine.

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7 hours ago, erdb said:

BTW Max, I forgot how you measure cant angle, but ETNZ sailed upwind mostly with 62 - 66 degree cant in the ACWS.

Nice graphs.

To calc the vertical and lateral foil forces, I need the actual foil cant angle, which is foil arm angle - 42°.   So 62-66 arm angle = 20-24° foil cant.

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In an interview some LR team member (don't recall who he was) said that  LR "high mode" is achieved by twisting each flap of each foil with a different angle (and with the sails). My question is: if Te Rehutai really had only one actuator per foil, how could it achieve a similar "high mode" ? 

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Not sure if things are that simple as whatever flap differential exists the net force has to go straight up the foil arm. For sure though a turning moment can be produced at the foil/arm intersection. 

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Thanks to weta27's pics I have created an approximation of NZ's "BFB v2" foil. Main points:

  • Foil area is almost the same, possibly even a smidge larger.
  • Flaps have increased in area as well as meeting at the centreline
  • The bulb mass is narrower (y), taller (z) and longer (x) - it extends further forward
  • Foil anhedral, on average, is about 5°

The 3 images show v1, v2, and then v2 superimposed on v1:

image.png.a65096808973300b73fec7da96de4895.png

image.png.b44a0de448872dfedb388f9891d57f41.png

image.png.077cbe13842647da821c88e5c27c9b3f.png

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11 minutes ago, MaxHugen said:

Thanks to weta27's pics I have created an approximation of NZ's "BFB v2" foil. Main points:

  • Foil area is almost the same, possibly even a smidge larger.
  • Flaps have increased in area as well as meeting at the centreline
  • The bulb mass is narrower (y), taller (z) and longer (x) - it extends further forward
  • Foil anhedral, on average, is about 5°

The 3 images show v1, v2, and then v2 superimposed on v1:

image.png.a65096808973300b73fec7da96de4895.png

image.png.b44a0de448872dfedb388f9891d57f41.png

image.png.077cbe13842647da821c88e5c27c9b3f.png

Thanks for the analysis max, what do you think the benefits are of v2 over V1? 

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3 minutes ago, 45Roller said:

Thanks for the analysis max, what do you think the benefits are of v2 over V1? 

Difficult to say - I remain somewhat puzzled why none of the other teams went with narrower foils. Sure, wider foils may have a stability benefit and be a little more forgiving and less sensitive - but hey this is the AC!   Design pinnacle of sailing boats and all that.

However... the larger flap area means less flap angle is required for the same lift, and there should be  a drag reduction as a result. With the two flaps "joining" each other through whatever mechanism, the flap edge vortices are reduced from four to two, again with a drag reduction.

The modification of the bulb mass shape would - I assume - be attributed to CFD modelling and maybe visual data obtained from cameras.

An obvious question is: why was a small amount of curved anhedral added? The only guess I can come up with is that the foils may be quite thin as well as narrow, so the foils bend under stress. This would make the flap hinge have a tendency to bind. The curve could straighten out under load, relieving hinge stress.

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2 hours ago, MaxHugen said:

Difficult to say - I remain somewhat puzzled why none of the other teams went with narrower foils. Sure, wider foils may have a stability benefit and be a little more forgiving and less sensitive - but hey this is the AC!   Design pinnacle of sailing boats and all that.

However... the larger flap area means less flap angle is required for the same lift, and there should be  a drag reduction as a result. With the two flaps "joining" each other through whatever mechanism, the flap edge vortices are reduced from four to two, again with a drag reduction.

The modification of the bulb mass shape would - I assume - be attributed to CFD modelling and maybe visual data obtained from cameras.

An obvious question is: why was a small amount of curved anhedral added? The only guess I can come up with is that the foils may be quite thin as well as narrow, so the foils bend under stress. This would make the flap hinge have a tendency to bind. The curve could straighten out under load, relieving hinge stress.

Excellent mate, thanks for the clear explanation as always :)

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3 hours ago, MaxHugen said:

Difficult to say - I remain somewhat puzzled why none of the other teams went with narrower foils. Sure, wider foils may have a stability benefit and be a little more forgiving and less sensitive - but hey this is the AC!   Design pinnacle of sailing boats and all that.

However... the larger flap area means less flap angle is required for the same lift, and there should be  a drag reduction as a result. With the two flaps "joining" each other through whatever mechanism, the flap edge vortices are reduced from four to two, again with a drag reduction.

The modification of the bulb mass shape would - I assume - be attributed to CFD modelling and maybe visual data obtained from cameras.

An obvious question is: why was a small amount of curved anhedral added? The only guess I can come up with is that the foils may be quite thin as well as narrow, so the foils bend under stress. This would make the flap hinge have a tendency to bind. The curve could straighten out under load, relieving hinge stress.

What an absolute gem you are Max to patiently explain this stuff for those of us fascinated by the technology but unable to grasp the detail. Much appreciated. Paddy

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1 hour ago, Paddywackery said:

What an absolute gem you are Max to patiently explain this stuff for those of us fascinated by the technology but unable to grasp the detail. Much appreciated. Paddy

Thanks mate. I've learnt heaps from others on this forum myself! :)

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5 hours ago, MaxHugen said:

 

An obvious question is: why was a small amount of curved anhedral added? The only guess I can come up with is that the foils may be quite thin as well as narrow, so the foils bend under stress. This would make the flap hinge have a tendency to bind. The curve could straighten out under load, relieving hinge stress.

I would agree with this, but question the approach. What happens when you want to adjust and aren't loaded enough?

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On 2/28/2021 at 8:21 PM, Zaal said:

In an interview some LR team member (don't recall who he was) said that  LR "high mode" is achieved by twisting each flap of each foil with a different angle (and with the sails). My question is: if Te Rehutai really had only one actuator per foil, how could it achieve a similar "high mode" ? 

I have wondered that. I suspect they twist the flaps to induce a rotational force and then over sheet the main to counter act it. Rudder added as a trim tab effect to balance.

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39 minutes ago, The Advocate said:

I would agree with this, but question the approach. What happens when you want to adjust and aren't loaded enough?

I struggle with that too.

For a start, they have to operate the flap prior to foiling, while the foil is still curved, and this should be difficult.

Best info we have is that the foil is produced from milled steel, but could the flap be manufactured from a carbon composite, so that it can deform and still be operable while the foil is curved? Perhaps something like this is workable whilst at lower stresses.

No matter which way I look at it, the fact that the foil has a slight curvature leaves me with unsatisfactory guesses. :unsure:

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17 minutes ago, MaxHugen said:

I struggle with that too.

For a start, they have to operate the flap prior to foiling, while the foil is still curved, and this should be difficult.

Best info we have is that the foil is produced from milled steel, but could the flap be manufactured from a carbon composite, so that it can deform and still be operable while the foil is curved? Perhaps something like this is workable whilst at lower stresses.

No matter which way I look at it, the fact that the foil has a slight curvature leaves me with unsatisfactory guesses. :unsure:

You aren’t allowed to actively deform a surface, you are allowed to design a surface that deforms.. 

fine margins.

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10 minutes ago, JALhazmat said:

You aren’t allowed to actively deform a surface, you are allowed to design a surface that deforms.. 

fine margins.

True. 

I was thinking about the resultant deformation that would have to occur for a flap forced to angle, despite it's axis of rotation being curved...

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On 2/28/2021 at 7:21 AM, Zaal said:

In an interview some LR team member (don't recall who he was) said that  LR "high mode" is achieved by twisting each flap of each foil with a different angle (and with the sails). My question is: if Te Rehutai really had only one actuator per foil, how could it achieve a similar "high mode" ? 

The direction LR (and INEOS) took is very different from the ETNZ philosophy. AM was kind of in between, but closer to ETNZ. The way I think about the anhedral foils is that imagine a foil with 90 deg anhedral. One wing half completely horizontal, the other completely vertical. With a foil like that, you could completely separate the actions of your flaps. The flap on the vertical wing half would be used to adjust lateral lift (leeway / yaw angle), whereas the flap on the horizontal wing half would be used solely for height / pitch control. If you wanted to go into a high mode, you would only deflect the flap on the vertical wing half while keeping the other flap angle the same => differential flap setting.

Of course a 90 deg anhedral foil would not fit in the class rules, and would probably be very draggy and slow as well, but I think LR's anhedral foils operate in a similar, although more complex way, since the vertical and lateral force components are not completely separated. Still, they have the ability to quickly manipulate the ratio of vertical vs horizontal foil forces with differential flap deflections.

ETNZ don't have this option. They don't have any anhedral (or very little), so even if they deflected the flaps differently, the lift from the two wing halves would point in the same direction. Plus, it seems they can't even deflect them differently, since they only have one actuator. They still have other options to control the vertical-horizontal force ratio. They can change the cant angle (relatively slow, and if you mess with the FCS too much, it may cause problems),and change heel angle - which basically changes the cant angle of the foil.

The advantage of ETNZ's approach is that since the load is symmetric between the two wing halves, they can get away with a smaller foil. On LR, differential flap settings mean one wing half is carrying more than the other, so I assume it has to have a larger surface area as well. Since the foil has to be symmetric, it means both wing halves are larger than if they were carrying equal loads. Furthermore, the asymmetric load on the wing halves probably creates a big vortex behind the foil with higher drag.  Maybe there are structural issues as well. If the sum of foil forces is not lined up with the foil arm, they may need beefier wings and thicker lower foil arm sections to withstand the twisting forces. (Counter argument: what happens when TR sticks the tip of the outside wing out of the water?)

On the other hand, LR can adapt quicker and has more control in maneuvers. If they can tack more efficiently, they may be able to compensate for their lower top speed/vmg. I expect their game plan is to win the start with a more maneuverable boat, then force ETNZ into a tacking duel so TR can never fully gain from its higher top speed. The problem with this plan is that once they fall behind, it's going to be very difficult to get back. 

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7 hours ago, MaxHugen said:

An obvious question is: why was a small amount of curved anhedral added? The only guess I can come up with is that the foils may be quite thin as well as narrow, so the foils bend under stress. This would make the flap hinge have a tendency to bind. The curve could straighten out under load, relieving hinge stress.

I think it would be very risky to design a flap mechanism that relies on having the wings bent under load. My guess is that the flap mechanism works fine with any possible flex angle. However, with the little anhedral added, they can shorten the foil arm and still fit in the class rule-trapezoid. Plus, there may be structural reasons - how to obtain the best shape under load with the least material?

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I have a theory about how ENTZ could be deflecting their foil, even with the anhedral. Instead of putting the axis of rotation parallel to the foils, they could put the axis of rotation as a line between the two foil tips (I attempted to draw this below). This would be more difficult to package, but would allow the flap to deflect freely while also giving them the added benefit of extra foil area in the middle of the foil when the flap is deflected, and eliminating the need to rely on bend as the flap is free to move at all times. This would also still be allowed in the rules, as no part of the flap is changing its axis of rotation as the flap is deflected, and could be accomplished by attaching a hydraulic ram to their little center "control" joining piece between the two flaps. Excuse the crude drawing and bad handwriting, I hope it is clear enough.

Also, this is my first post! I'm an aerospace engineering student and have been racing since I was 11 (9 years now), and I hope to one day be able to work on AC tech and engineering.

Entz foil control.png

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9 minutes ago, erdb said:

I think it would be very risky to design a flap mechanism that relies on having the wings bent under load. My guess is that the flap mechanism works fine with any possible flex angle. However, with the little anhedral added, they can shorten the foil arm and still fit in the class rule-trapezoid. Plus, there may be structural reasons - how to obtain the best shape under load with the least material?

Yes... it's the curvature that is really bugging me.

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4 minutes ago, kai_ said:

I have a theory about how ENTZ could be deflecting their foil, even with the anhedral. Instead of putting the axis of rotation parallel to the foils, they could put the axis of rotation as a line between the two foil tips (I attempted to draw this below). This would be more difficult to package, but would allow the flap to deflect freely while also giving them the added benefit of extra foil area in the middle of the foil when the flap is deflected, and eliminating the need to rely on bend as the flap is free to move at all times. This would also still be allowed in the rules, as no part of the flap is changing its axis of rotation as the flap is deflected, and could be accomplished by attaching a hydraulic ram to their little center "control" joining piece between the two flaps. Excuse the crude drawing and bad handwriting, I hope it is clear enough.

Also, this is my first post! I'm an aerospace engineering student and have been racing since I was 11 (9 years now), and I hope to one day be able to work on AC tech and engineering.

Entz foil control.png

G'day Kai, welcome to the forum.

Interesting idea. Since under the rules they are required to have one flap on each of the two wings of the foil, how could the flaps be hinged inboard - ie at the foil centre line?

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2 minutes ago, MaxHugen said:

G'day Kai, welcome to the forum.

Interesting idea. Since under the rules they are required to have one flap on each of the two wings of the foil, how could the flaps be hinged inboard - ie at the foil centre line?

Not too sure about that one. Perhaps that could be why their little flap joiner is considered a part of the control system, as it could be connected to a linkage in the main wing that allows the middle of the flap to move backward and forward instead of rotating around a fixed point that lies within the wing somewhere, if that is even allowed within the rules. I just though that would be the simplest solution to being able to deflect a curved flap around a straight line.

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43 minutes ago, erdb said:

The direction LR (and INEOS) took is very different from the ETNZ philosophy. AM was kind of in between, but closer to ETNZ. The way I think about the anhedral foils is that imagine a foil with 90 deg anhedral. One wing half completely horizontal, the other completely vertical. With a foil like that, you could completely separate the actions of your flaps. The flap on the vertical wing half would be used to adjust lateral lift (leeway / yaw angle), whereas the flap on the horizontal wing half would be used solely for height / pitch control. If you wanted to go into a high mode, you would only deflect the flap on the vertical wing half while keeping the other flap angle the same => differential flap setting.

Of course a 90 deg anhedral foil would not fit in the class rules, and would probably be very draggy and slow as well, but I think LR's anhedral foils operate in a similar, although more complex way, since the vertical and lateral force components are not completely separated. Still, they have the ability to quickly manipulate the ratio of vertical vs horizontal foil forces with differential flap deflections.

ETNZ don't have this option. They don't have any anhedral (or very little), so even if they deflected the flaps differently, the lift from the two wing halves would point in the same direction. Plus, it seems they can't even deflect them differently, since they only have one actuator. They still have other options to control the vertical-horizontal force ratio. They can change the cant angle (relatively slow, and if you mess with the FCS too much, it may cause problems),and change heel angle - which basically changes the cant angle of the foil.

The advantage of ETNZ's approach is that since the load is symmetric between the two wing halves, they can get away with a smaller foil. On LR, differential flap settings mean one wing half is carrying more than the other, so I assume it has to have a larger surface area as well. Since the foil has to be symmetric, it means both wing halves are larger than if they were carrying equal loads. Furthermore, the asymmetric load on the wing halves probably creates a big vortex behind the foil with higher drag.  Maybe there are structural issues as well. If the sum of foil forces is not lined up with the foil arm, they may need beefier wings and thicker lower foil arm sections to withstand the twisting forces. (Counter argument: what happens when TR sticks the tip of the outside wing out of the water?)

On the other hand, LR can adapt quicker and has more control in maneuvers. If they can tack more efficiently, they may be able to compensate for their lower top speed/vmg. I expect their game plan is to win the start with a more maneuverable boat, then force ETNZ into a tacking duel so TR can never fully gain from its higher top speed. The problem with this plan is that once they fall behind, it's going to be very difficult to get back. 

Thank you, great explanation ! 

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31 minutes ago, kai_ said:

I have a theory about how ENTZ could be deflecting their foil, even with the anhedral. Instead of putting the axis of rotation parallel to the foils, they could put the axis of rotation as a line between the two foil tips (I attempted to draw this below). This would be more difficult to package, but would allow the flap to deflect freely while also giving them the added benefit of extra foil area in the middle of the foil when the flap is deflected, and eliminating the need to rely on bend as the flap is free to move at all times. This would also still be allowed in the rules, as no part of the flap is changing its axis of rotation as the flap is deflected, and could be accomplished by attaching a hydraulic ram to their little center "control" joining piece between the two flaps. Excuse the crude drawing and bad handwriting, I hope it is clear enough.

Also, this is my first post! I'm an aerospace engineering student and have been racing since I was 11 (9 years now), and I hope to one day be able to work on AC tech and engineering.

Entz foil control.png

Welcome mate ! 

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17 minutes ago, kai_ said:

Not too sure about that one. Perhaps that could be why their little flap joiner is considered a part of the control system, as it could be connected to a linkage in the main wing that allows the middle of the flap to move backward and forward instead of rotating around a fixed point that lies within the wing somewhere, if that is even allowed within the rules. I just though that would be the simplest solution to being able to deflect a curved flap around a straight line.

I see your point. Your suggestion could still be used - and stay within the Rules - if considered from the centre line (or the bulb) to the outer end of the foil wing prior to the turned up tip...

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49 minutes ago, kai_ said:

I have a theory about how ENTZ could be deflecting their foil, even with the anhedral. Instead of putting the axis of rotation parallel to the foils, they could put the axis of rotation as a line between the two foil tips (I attempted to draw this below). This would be more difficult to package, but would allow the flap to deflect freely while also giving them the added benefit of extra foil area in the middle of the foil when the flap is deflected, and eliminating the need to rely on bend as the flap is free to move at all times. This would also still be allowed in the rules, as no part of the flap is changing its axis of rotation as the flap is deflected, and could be accomplished by attaching a hydraulic ram to their little center "control" joining piece between the two flaps. Excuse the crude drawing and bad handwriting, I hope it is clear enough.

Also, this is my first post! I'm an aerospace engineering student and have been racing since I was 11 (9 years now), and I hope to one day be able to work on AC tech and engineering.

 

Welcome to the fray @kay_

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43 minutes ago, MaxHugen said:

I see your point. Your suggestion could still be used - and stay within the Rules - if considered from the centre line (or the bulb) to the outer end of the foil wing prior to the turned up tip...

I think I'd need to do some rule reading to see if this would be possible under the rules or not, but I think it would clear up some of the confusion about the interpretation where the join between Emirate's flaps counts as a control system and not as a piece of the flaps themselves.

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4 hours ago, erdb said:

The direction LR (and INEOS) took is very different from the ETNZ philosophy. AM was kind of in between, but closer to ETNZ. The way I think about the anhedral foils is that imagine a foil with 90 deg anhedral. One wing half completely horizontal, the other completely vertical. With a foil like that, you could completely separate the actions of your flaps. The flap on the vertical wing half would be used to adjust lateral lift (leeway / yaw angle), whereas the flap on the horizontal wing half would be used solely for height / pitch control. If you wanted to go into a high mode, you would only deflect the flap on the vertical wing half while keeping the other flap angle the same => differential flap setting.

Of course a 90 deg anhedral foil would not fit in the class rules, and would probably be very draggy and slow as well, but I think LR's anhedral foils operate in a similar, although more complex way, since the vertical and lateral force components are not completely separated. Still, they have the ability to quickly manipulate the ratio of vertical vs horizontal foil forces with differential flap deflections.

ETNZ don't have this option. They don't have any anhedral (or very little), so even if they deflected the flaps differently, the lift from the two wing halves would point in the same direction. Plus, it seems they can't even deflect them differently, since they only have one actuator. They still have other options to control the vertical-horizontal force ratio. They can change the cant angle (relatively slow, and if you mess with the FCS too much, it may cause problems),and change heel angle - which basically changes the cant angle of the foil.

The advantage of ETNZ's approach is that since the load is symmetric between the two wing halves, they can get away with a smaller foil. On LR, differential flap settings mean one wing half is carrying more than the other, so I assume it has to have a larger surface area as well. Since the foil has to be symmetric, it means both wing halves are larger than if they were carrying equal loads. Furthermore, the asymmetric load on the wing halves probably creates a big vortex behind the foil with higher drag.  Maybe there are structural issues as well. If the sum of foil forces is not lined up with the foil arm, they may need beefier wings and thicker lower foil arm sections to withstand the twisting forces. (Counter argument: what happens when TR sticks the tip of the outside wing out of the water?)

On the other hand, LR can adapt quicker and has more control in maneuvers. If they can tack more efficiently, they may be able to compensate for their lower top speed/vmg. I expect their game plan is to win the start with a more maneuverable boat, then force ETNZ into a tacking duel so TR can never fully gain from its higher top speed. The problem with this plan is that once they fall behind, it's going to be very difficult to get back. 

I think your explanation has gone a long way towards explaining why LR appear to be more stable in flight.

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I've done something pretty cool: synchronised video feeds with boat data and GPS tracks. Should keep you guys busy while the racing keeps getting delayed.

P.S. if VirutalEYE people are reading this: Lets see how long it takes for you to copy that, too!

https://ac36.herokuapp.com/map

image.png.ae221c1a91338f79ea478f88c6af1ef3.png

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7 minutes ago, dorox said:

I've done something pretty cool: synchronised video feeds with boat data and GPS tracks. Should keep you guys busy while the racing keeps getting delayed.

P.S. if VirutalEYE people are reading this: Lets see how long it takes for you to copy that, too!

https://ac36.herokuapp.com/map

image.png.ae221c1a91338f79ea478f88c6af1ef3.png

Neat work! Any chance of seeing multiple data graphs?

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Just now, The Advocate said:

Neat work! Any chance of seeing multiple data graphs?

Not at the same time, but you can select any data stream from "statistics" dropbox.

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1 minute ago, The Advocate said:

I have a problem with the centre video not being in sync with the upper and lower.

Try changing the race to a different one and then back. I'm still fixing some issues.

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22 minutes ago, dorox said:

I've done something pretty cool: synchronised video feeds with boat data and GPS tracks. Should keep you guys busy while the racing keeps getting delayed.

P.S. if VirutalEYE people are reading this: Lets see how long it takes for you to copy that, too!

https://ac36.herokuapp.com/map

image.png.ae221c1a91338f79ea478f88c6af1ef3.png

That freaking rocks! Awesome, thank you

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13 minutes ago, dorox said:

Try changing the race to a different one and then back. I'm still fixing some issues.

Copy that, will have another look after work. Great stuff!

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39 minutes ago, dorox said:

I've done something pretty cool: synchronised video feeds with boat data and GPS tracks. Should keep you guys busy while the racing keeps getting delayed.

P.S. if VirutalEYE people are reading this: Lets see how long it takes for you to copy that, too!

https://ac36.herokuapp.com/map

 

Cool indeed, thanks

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The anhedral vs flat discussion was done to death maybe 12 months ago, I've forgotten which thread. There are pros and cons to each design, it's not a case of one is better than the other, it's how the whole package works that matters.

For anhedral, once you cant the foil, biasing the lift to the inboard foil gives more lift to windward, but reduces RM because the centre of lift moves inboard. With a flat foil, you can bias the lift to the outboard wing and get less lift to windward but more RM as the centre of lift move outboard. So it depends on what you have designed the rest of the boat to work with.

The flat foil is inherently more efficient as there is only one lift vector, not two fighting each other. It also might mean a simpler control mechanism, if that's worth anything.

ETNZ's flat foils means it thinks outright speed is the key and it can make up for the loss of VMG from the foil in other areas, such as main sail trickery. LR's anhedral means it thinks VMG is the priority and it can make up for the drag penalty elsewhere, e.g. the minimalist slippery hull shape.

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Mind-bending stuff! Very impressive (Watch right through the gens are towards the end when they discuss the AI)

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5 hours ago, dorox said:

I've done something pretty cool: synchronised video feeds with boat data and GPS tracks. Should keep you guys busy while the racing keeps getting delayed.

P.S. if VirutalEYE people are reading this: Lets see how long it takes for you to copy that, too!

https://ac36.herokuapp.com/map

image.png.ae221c1a91338f79ea478f88c6af1ef3.png

Awesome, thanks!

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The flaps could be mounted so that they don't need to be straight in order to rotate.  It would be really cool though if giving the flaps a slight rotation instantly forced the entire foil to straighten to a span greater than that which would otherwise fit within the box rule.  Either way the intent seems obvious use the difference in loading between sailing and measuring to cause a deflection which allows a longer span more efficient foil.

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6 hours ago, dorox said:

I've done something pretty cool: synchronised video feeds with boat data and GPS tracks. Should keep you guys busy while the racing keeps getting delayed.

P.S. if VirutalEYE people are reading this: Lets see how long it takes for you to copy that, too!

https://ac36.herokuapp.com/map

Hahahaha.... great job @dorox, I can almost hear the VirtualEye team gnashing their teeth!  :D

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