Yes, great format and pacing. Well done. Do hope Ineos pick up the pace, I think Ben was talking of them getting out sailing next week. That'd be great to see. Rob may well be right, simpler and slicker = faster.
I like Rob's theory: it makes sense (in several ways). However Candela, the Swedish foil guys, seems to have mastered the old - Wright Brothers - idea of warping. And in this part of the design space there's an amazing amount of proposals on morphing foils with some even looking practical. Admittedly that is in aero but still ... Love your discussion on this topic BTW. Cheers, Jan
@@MozzySails you’re welcome. Personally I notice that you also possess a rare quality in listening and letting your boys express, that’s why the discussion is elevated further
Just done some calcs to double check and I'm more confident than before. Might be warping the flap for a little fine tune at high speeds but not really required to fly an ac75 through the sped range.
A deeper dive into the (range of) foils and question regarding the use of flaps seems warranted. If the popularity of foiling windsurfers among the ETNZ team has increased, the guy that I would expect to have some knowledge is Alan, the owner of Madloop Windsurfing at Lake Pupuke.
One interesting thing to note about the foil configurations is that the more pitch stable it is (main foils farther back) the lower your maximum lift but the higher you're righting moment because the elevator is pulling down on centerline. To my eye as an aerospace engineering student, the Banana foils look like they're curved in the exact inverse of the deformations from flight loads, being much more curved near the root than the tip. That design makes a lot of sense because it lets you get a longer foil span in the same box and lets you get away with a thinner, lower drag foil. The hull on the ENTZ LEQ12 with the banana foil looks like it generates more planing lift than the other teams hulls, which would help them get up on the foils with less foil area and less flaps. Given how many foiling boats don't have any way to quickly adjust the main foils, flaps are clearly not needed for control if you can get up out of the water without them. They probably don't need fancy composite design twisting either since hydrofoils just don't see gust loading the way aircraft do.
Agree that the foil will propably be straight when loaded, but why do you want to give up on the flaps? Much faster and more precise control. Also decouples the foil forces from other forces related to the pitch of the boat. I guess increasing the chamber of a section by actuating a flap is probably also more efficient than raking the entire section.
@@rafaeltannenberg7403 you're right that a foil with flaps is more efficient than the same cross-section without them, but getting rid of the flap actuator lets you make a thinner section. At aircraft Reynolds numbers like for gliders, they benefit from a few degrees of flap deflection to manage an airfoil with a smaller leading edge radius (smaller stagnation zone). hydrofoils generally don't see nearly as wide an angle of attack range as aircraft, operate at much lower Reynolds number where the AoA range for L/D max is larger, and have to worry about cavitation. A thinner foil section is going to have less drag overall, especially at low Reynolds numbers, and a higher minimum pressure at a given condition, so it can go slightly faster without cavitating.
@@thamiordragonheart8682 Generally agree on that as also stated in my initial comment (not the response to your comment). But I checked the rule and it says you have to have a flap and control systems. So doesn´t sound like you are even allowed to produce a foil without control systems. Maybe you could get away with small systems that only have minimal effect, but it us hard to say to what extent your flap and systems must work. I guess a flap that can´t be tilted at all cannot be counted as a flap.
@@rafaeltannenberg7403 hmm. maybe a flap system that only moves a few degrees would count and still be super thin. Being able to have a few degrees of positive or negative deflection to tune the lift coefficient at a fixed angle of attack would be good for efficiency. Only moving a few degrees to begin with and being made relatively flexible would also probably allow it to work when the foil isn't perfectly straight.
What you described for Emirate on the fixed foil is what the Bureau Vallée IMOCA did to demonstrate the potential gain of adding a plane to control the lift and hull angle on the rudder.
The no flap theory is great! Really good gamesmanship apart from actually checking if a cleaner configuration might actually be better. I'm assuming that the flaps were so strongly implemented as they help solve the problem of liftoff. A boat that can start flying in 5 knots of breeze is going to do very well with boat outright speed over ground and tactical advantages (knock the other boat off its foils and sail away). And a bit of extra drag from the flap will not be decisive if liftoff is earlier - hundreds of metres (early liftoff) vs dropping two tenths of a knot (drag) But on a stronger wind day when flying is not a problem - I see a big advantage for cleaner foils with no flap. So are we seeing a test of a flapless higher wind foil. And they will implement a flapped foil for the light stuff? Which begs the question ... during the cup are teams allowed to change their foil configuration race to race, or rather, day to day?
Rob's theory makes total sense. On a glider the ailerons on the wings are essentially only used for controlling roll of the plane and the elevators at the tail of the plane are used for controlling pitch. Question on Ineos, could they not create some kind of rigid pyramid style gantry between forestay, sidestays and traveller to accomplish the same thing as the tow mast and bypass the mast step altogether? Could even use it to lift the boat in and out of the water so it is considered some kind of crane?
Very interesting theory Rob! Just don´t know if it would be worth it. I think the flap would give far better controlability and allows to decouple the the lift from the foils from the forces generated by the hull. These aero hull forces would obviously change when the boat pitches. Controlling it via the flap most likely also allows faster reactions, more accurate changes and more stable sailing. Controlling the lift with FSI and special lay-ups is only working to a certain extent. I think it usually only allows to reduce the relationsship between boat speed and lift from a quadratic one to a linear one. So the lift still significantly increases with increasing boat speed. And are the LEQ12 foils built from carbon? Just know that the AC75 foils are built from steel and lead to meet the weight requirements. In this case the only option for twisting under load is to offset the centre of pressure from the sheer centre which probalby further reduces the effectivness. The only real benefit I see is that you could get rid of the control systems inside the foil. These are taking up volume inside the foil that causes drag. Getting rid of them would allow to build a smaller foil with less drag I think. What do you think about that?
Good guessing boys, don’t go to the casino any time soon. Your underestimation of the local knowledge that getting the job done pre Christmas drinks shouts and committing to shoveling into a big Christmas dinner and a beer was wonderfully well off. Loving the show looking forward to a humorous retraction next month.
We have certainly seen a lot of morphing foil wings of late. Also, AC72 foils obviously didn't have flaps. They had to rotate the entire daggerboard. A bit apples and oranges, but it has been done in the AC already, so if you can adjust the pitch (be it with just rudder, foil arm position, etc) it can be done. Perhaps it also has a non-swept quarter chord and thus limits the neutral point movement with pitch, making it more predictable and consistent in feedback?
Only problem I see with Robs no flap theory is that I think that the flaps are not so much for ride height but for changing foil shape from low speed high lift to high speed low drag/cavitation.
Great video guys as always. Taking Robs theory as accurate which means the ETNZ foils can be thinner with less drag. Does this also in turn have a positive affect on when cavitation occurs at high speed? As a total layman i would have thought that if you have a thinner, laminar flow type wing with less of a pressure differential between the top and bottom surfaces that would mean cavitation would occur at a higher speed? Any ideas?
Followed Mozzy Sails from the early days, love the tech content and micro breakdown and chat, Robs on it ! keep up the great work⛵💨 the detail reminds me of everyday astronaut 👩🚀
I agree with Rob regarding the flaps. From and aviation background a plane's wing doesn't have pitch control. Lift is controlled with speed and pitch control from the tailplane.
Does the flap on the banana foil need to move along the whole length? or could the flap just warp using composite design near the center where most of the lift is generated?
Remember that changing the trim angle also changes the balance between sails and under water lateral plane arpund the global z axis, while it's probably not desirable.
It is certainly possible to fly those boats without flaps, however, not having flaps will make the high speed pitch adjustments (the now typical bow down high speed foiling) much more difficult, if not limit it altogether, so I heavily doubt that they don't have the flaps. It also seems that whilst under loading the foil might straighten up quite a bit making the hinge much less of a problem, this would also mean the foil can be made thinner, though you can't just fully rely on the foil bending as it might induce the equivalent of undesirable aeroelastic effects
So once the boat is up to speed the issue wouldn't be range of trim but having fine/accurate enough control of that pitch. 0.25 of a degree makes a big difference to total lift from the foil at 40kts! Pitch at take off is controlled by hydrostatics of the hull effectively. As soon as the main part of the hull is clear the boat would naturally trim to the required bow down region.
Love these videos and analysis. Thanks. When the boat is in floating mode but below lift off speed you’d want the angle of attack on the wings to be zero otherwise you’re dragging around a pair of draggy stalling wings.
Like the way collectively you know so much more than the more mainstream commenters around. I don't understand all of your discussions but I understand enough to be able to learn a hell of a lot more from them. And yes, probably correct. The only way you could have a moveable flap with a banana foil would be to use a horizontally stretchable hinge or a flap made of many, many elements. I don't think either are feasible options - for reliability reasons alone - let alone efficacy. So when you have eliminated the impossible, whatever remains, however improbable, must be the truth. Simplicity is key, surely, because the forces on these machines are so great. As Team Emirates NZ has already demonstrated.
I love all the speculations going around. My 2 cents come from kiting, where it seems foils are going bigger and they are becoming much easier to fly year by year. To me, the flaps should bring more control options for complicated powered up maneuvers, but the med will bring 12 knots on a good day. I think the take off point was 11-13 knots of wind for the ac75, so getting that number down is the mission. I just hope they figure it out and have a proper race Will you be doing anything on the ocean race?
I wonder if the foil could be engineered such that the C shape's deflection under load twists the flap upward. On takeoff i assume most of the load is vertical, so you could design under the assumption that a 7t load should have the foil in high lift mode and any load beyond that would be the foil resisting leeway. The foil could use deflection to bend into a less draggy shape at that point.
ETNZ have alot on there plate a land speed record with Horonuku hydrogen fuel case boats and AC40s for teams that have ordered them. I think your right on the foils but I say that they didn't moved on Te Rehutai in the last cup anyway and on Te Rehutai I think we will see her come out of the shed yet with some new toys on of course?
I guess one thing with the large curved foil in terms of peak lift, is while it may not be able to get the same angle of attack as a flapped foil, it is a larger wing than a flapped foil and high aspect ratio foils have less difference between the geometric angle of attack and the actual angle of attack do to reduce up wash ahead of the foil. If we consider aircraft 99% of the lift changes are made by changing the main wing angle of attack with pitch not by changing the chord line with flaps.
Rob's theory makes absolute sense. Simple is better and all of the micro adjustments to foil flaps add drag which can slow you down. The flap fights the directional forces of the main foil to some degree, why not keep the flaps straight and just use the whole foil to change the forces as needed.
Mozzy, would you kindly show us in more detail the pulley arrangement you have on the wall? It looks like something we'd use to trim a set of risers on a paraglider wing.
Thanks Tom. On it as always for all the AC analysis. Parson me, we "recce", only the States does "recon". It's an English vernacular, much as Aluminium has an "I". Brilliant summary and opinion though. Kudos.
Last cup you showed data from Etnz showing how they used the foil as they did the JK which was far quicker . Good theory. Are the wings aloud to move in and out to increase/decrease curvature,eliminating the use of flaps.??
On planes you don't use the flaps to control height you use the elevator. Flaps only used to increase lift at low speed but at the expense of lots of drag.
I guess that's the crux of the question... can an AC75 foil produce enough lift if its mounted with a high AoA so that it doesn't need a flap. One up and foiling flap trim would be much less and potentially ride height just maintained using the rudder elevator.
@@MozzySails I highly doubt they are using the flap once up on the foils as anything away from neutral will be a large increase in drag. Look at the drag curves on most wing sections for various flap angles. But as you say is there enough aoa and lift at that aoa to initially lift the boat out the water at lower speeds.
The problem with the idea that you can just increase the angle of attack of a wing without flaps enough to give lift at slow speed is optimisation. The reason that aircraft have flaps is because any wing big enough to provide slow speed lift cannot be optimised for flight at high speed. That is literally the whole point of flaps. They give you effectively multiple wings with different optimisation. There is no such thing as an all round wing. A wing to get you foil borne early at max AoA will by definition be far draggier than optimal for high speed. Aircraft would love to save all the weight of flap systems if they could, but you don’t see any aircraft without flaps.
@@21142317 theres LOTS of variables and an incredibly complex subject especially on a sailing boat, where you have all these requirements far more than you do out of an aircraft wing. They have some of the best aerodynamics people working for them. It may be that they arent using much flap angle to lift the boat up and are purely using it for height/attitude control due to the large drag penalty that a flap suffers from. They do not seem to be having any difficulty getting up in all but the lightest of breezes where the rig probably simply doesnt have enough power to overcome hull resistance to get to a point of flying.
I liked the kiterace / wing/wind foil analogy. Maybe the most efficient (way to reduce drag and turbulences) way to control a foil flight is with longitudinal weight balance. It would be interesting although for the teams to research & doing testing on that idea applied to AC boats. (But can they have balasts moving forward and aft? I guess not)
'Is it bad that they were late?' No I don't think it is a problem, the key issue INESO face in the final design is to get their computer models to 'line up' with the practical data. They surely have a number of different designs already produced, and are simply wanting to ensure that the models they are using are 'representative', when they get the data, they will be 'more sure' of which design they will build. I like Rob's idea about ETNZs foils, and I think he makes a very solid point. If you can come up with a decent foil and simply use the attitude of the foil arms to adjust for 'best possible' attitude (fore and aft) and the height of the arms to adjust for canting, whilst using the rudder to make smaller adjustments seems the smart way to go. But this all depends if the very variable swell around Barcelona demands greater control over the pitch/lift than the rudder and much heavier arms can allow. Very interesting discussion.
Like the no flaps during flight idea. Would an actuated carbon flexure hinge be in the rules for the flap? Could allow them to crank some more lift on for take off, being a flexure it'd have more angle at the root than the tip which would be beneficial as well.
What if the flaps are “optionally” passive, while usually immobilized into flat plane with the foil? That could be controlled (hydraulic or electrical). The passive action could be used to amplify or suppress lift, if useful.
Would the flaps on a curved foil not be adjusted by extending and retracting the flap? A very tidy version of what large aircraft wings are fitted with, extended for increased lift at take off then retracted for decreased drag during flight.
Great vid guys. I assume the whole idea behind LEQ12s and no tank-testing is to reduce budgets. The INEOS test boat and tow mast attempted to recreate tank testing at large scale - perhaps next time they should allow teams to tank test instead. An electrically powered towing tank is also potentially greener than towing your 40ft model around with a petrol powered tender. Regarding INEOS, if the primary goal of the test boat was to gather real world data with which to train and validate their simulated environments then the current limited time on the water is a major misfire. Meanwhile ETNZ are busy training and validating their tools with masses of data from the AC40, foiling chase boat and the successful land-speed record attempt.
Thanks Nathaniel, I think you're pretty much spot up in your synopsis there. It seems INEOS are not giving up on their tow mast just yet, and in their latest response to the rule committee has suggested new definition for each of the key components... we'll see how far they get with that
From Grant Dalton’s mouth “we expect to have the AC40 back in the water next week” as said at Team NZ base open day on the 6th Dec. Also the new AC 40 should be in there hands before X-mas. All components are on site ready for this new boat.
Hydrofoil design predates the 1950s. Extract from Alexander Bell web site. “HYDROFOIL HISTORY One of the earliest hydrofoil accounts is credited to Thomas Moy, an English engineer who in 1861 installed a set on a boat in the Surrey Canal and noted that when the vessel was towed, it was lifted ‘quite out of the water’. William Meacham explained the principal and described his own experiments in a March 1906 edition of Scientific American magazine. That same year in Italy, Enrico Forlanini is seen racing his hydrofoil craft across Lake Maggiore. Alexander Graham Bell undoubtedly read Meacham’s article. By 1906, Bell was using floats on some tetrahedral kite experiments for trials over water at Beinn Bhreagh.”
Possibility of having the flap mounted to a shaft for torsion control along the length. Piano hinge style. The composite part of the flap would have to be more flexible along its length. Probably couldn’t have the top skin of the foil act as a faired in hinge though
Wonder if with a fixed foil they would ever consider controlling pitch, not with a rudder flap, but with a quick moving internal to the boat pitch mass on tracks. Therefore your pitch would be adjusted much like a traditional foilboard and you would have all the hydrodynamic gains associated with static (non flapped) foils.
If you watch recent videos of the etnz Leq it seems to have a very distinct “dolphining” tendency which almost seems to mimic an underdamped oscillating system.
Regarding Rob's theory: Looking at resent coverage of Luna Rossa sailing/flying my impression is that their boat is highly pitch unstable and there are quick trimm operations necessary to keep flying. I think Rob's theory can only work if there is something about ETNZ boat that makes it inherently more pitch stable.
Totally agree that you control windsurf foil or kitesurf foils without flaps. But you can move a high percentage of the total mass for and aft which you can't in an ac40 or 75. However, I didn't know they are allowed to move the rudder angle of attack during the race or use it to control the pitch of the boat. I thought they control all their lift only with the flaps. Or is this rule with fixed rudder angle back from the ac50 catamaran?
Its not that difficult to move a flap on a bent wing - take a look at a high performance glider. Sealing the hinge line may be a challenge and is definitely required. That's not to say I disagree with Rob! Interesting to see where this all ends up. But what is the advantage of a curved foil over a straight one? Why would you give up the ability to adjust the flap on a trials boat - even if it wasn't used very often why give up that facility. Would also be interesting to know more about why a self tacking jib might be desirable when there is a boat full of people to do the job. Could you also recap on what the AC40s are for?
I think it heard that everyone is using norths for the cup? (might be wrong), is this limiting teams to using the same mast location from the bow, and further the same cut of sails and are they playing with their sail shape which could affect the sheeting angle of the jib?
We need to address this north's point. I also saw that but AM are still very obviously using Quantum (branded) sails. Something interesting going on there.
only problem with robs theory is that windsurf foiling we typically have a huge mass you move to counter the foil movement... i dont see the guys running backwards and forwards to be a option ....
I think Rob 's idea is that the rudder trim will replace weight shift. No idea if that likely to be sufficient, though I will say tail wedges seem to have only a subtle affect.
Is the next step a morph foil that changes form on electric impulse ? What i understand is that when a foil reaches 50kts cavitation becomes a realy big problem. The solution is a different foil form that takes on the cavitation problem but has a big difference in force.. Maybe some ideas for a new topic !
it would be, but the rules wouldn't allow this. Apart from flex under hydro loads, the foil wing can't move, only the flap and flap flexure. The flap can only rotate around a fixed point to, so shape morphing can't really happen in a true sense. However, the teams are allowed many flap segments which join via flexible sections, so maybe they can recreate some elements of a shape morph
Comment on Robs theory: It makes sense for these boats to have a flap to create a better profile for early take off and then slim down the profile when you are up to speed. There might however be some truth in this balancing theory. As for the mechanics of the flap, I think it twists along the span, it might even be fixed at the ends. This will affect the profile the most where the chord is larger giving a more balanced result. Just like a lot of moth foils.
Changing angle of the flaps might for sure create more lift instantly but massibely increase the drag. As we see the boat speeds increase fast as soon as they lift of, I don't think they massivly kick them out to lift by changing the angle of attack. I think the flaps are used to change the general trim.
Although the loads increase with the square of speed so the flap would only work at the highest speeds. I half see the logic behind this argument but it doesn't really make sense at lower speeds when you need most flap down (if you need any flap)
@Robert Gullan Lift increases with the velocity squared, but once the boat flies, where would additional load come from? There's just the mass of the boat and potential acceleration up and down. So you have to control the lift either by pitch or control surfaces. Pitching the entire Wing would greatly increase drag. (Edit: Acceleration remark)
Hmm … probably missed something but, why show what looks like a flap if there is in fact no flap? Misdirection? I will say these discussions are so dense that I need to watch a couple times to get it registered. Love your videos.
Agreed re Ineos campaign. Look behind already. Wish them well but doesn't look good. Wishful thinking is not a strategy for engineering or sporting success.
Maybe in future a similar program could be run of experimentation and optimization with full data sharing to arrive at a standard design that is used in the next iteration by all the teams - the same exact design. Competition is then entirely up to skill of the sailors. The incentive to innovate and not be a “free rider” could be financially engineered into the purchasing of the standard design. Teams that spend less in development would have to spend more in buying the standard design boats. I like the innovation but does the final result in competition depend on who has the largest budget rather than the canniness and skill of crews.
With Ineos, is it a concern that Mercedes have struggled all F1 season with porpoising? I am not so impressed with their design team if they could not predict that or solve that quickly. Too many designers may not help much. PS I know nothing about this subject obviously.
Now we've got a few videos under our belts, I am going to do some more helpful FAQ type videos covering some boats / terminology. First on that list is an explainer of what the different boats are, pros and cons and when we'll see teams using them
I don’t get all of Rob’s comparison to wing foiling. As he said, he’s constantly controlling the foil through the attitude of the board itself. On a larger vessel, that’s got to be done through flaps. So the comparison doesn’t really provide a solution. Still WTF do I know. In the absence of a solution for pivoting a curve maybe that’s it: just don’t. And clear advantages too.
still don´t see any benefit of this approach. Flap is faster, more efficient and more precise. Why would you want to pitch a 20m boat to make continous tiny adjustments when you can do that by just actuating a small flap. Pithcing the boat changes a lot of other forces as well such as the aero hull forces. Plus the rule says you have to have a flap and control system to actuate it.
The benefit would be you can use foil shapes which don't need to account for having a working flap. The pitch changes required at 35kts are in the range of 1 degree or less so almost no effect to the aero forces. Can I see the analysis to show the flap is faster, more efficient and more precise?
Ineos have issues with Mercedes. Mercedes have gone full gas to get back on top in f1, especially for fear of losing multiple years in the wilderness. Ben and co are not getting priority.
Mercedes had to cut heads from the F1 team to get staff compensation under the budget cap. All of the designers for the AC are strictly for the AC as their salaries are no longer counted towards the F1 team.
@@MozzySails agreed. And how many of the red bull team are really working on non f1 projects ie engine programmes, RB hypercar etc etc. Ben will be last in line...which is a shame......but they could keep going as they were.
Not saying it’s totally relevant because it not a curved dihedral but take a look at this as it’s a flapped surface that has no visible hing points ru-vid.com/video/%D0%B2%D0%B8%D0%B4%D0%B5%D0%BE-H31m6Jqw8j0.html
That's the same as some of the flaps we saw in the last AC where the 'hinge' is the composite in the foil surface. I think quite a few moth foils have used this approach also. It's neat! Not sure it would help with the curved shape though
Yea like you say curved flaps would be a challenge but we ride foils without any form of adjustment other than weight shift for kite,wing and surf so it’s not impossible and quite believable that they are running without adjustable flaps
@@MozzySails If you want to adjust a flap in a bended foil the middle bearing must give longitudinal way. This can even be used as single control element to adjust the flap angle. (only possible as long as the foil is curved!!!) But I personally think Rob to be on the right path of thinking: No dynamic flap adjustments.
You can totally fly the boat on pitch with a static foil (no flaps), the movements of flaps or control systems is very slow compared to what you would think, they are monitoring the data at 100hz lets say but that does not mean they are controlled at the speed, we have gone as low as 3deg per second on our systems @mozzysails
