High Performance MPX Foil/Self-righting Trimaran-The Test Model

Well NED he's relying on the critical balance that boats like the Groupama C guys (and the AC boats) had on their J Foils - except

a) he's made them too "open" - which as HighOnCarbon has explained makes for a very unstable foiling config

b) his introduction of the main foil causes a twisting force couple that is only made worse by the ability of the main foil to generate negative lift. Its possible to generate some more RM, but RM is rarely an issue for foilers - stability is.

 

Thank you doug for going to a shorter and non-repetitive format. Might I suggest using more normal sailing and building terms?:

the bottom of the mast is the Mast Butt - because Heel is too easily confused with the lateral cant angle

The insert that goes into the butt of the mast is called a "mast shoe"

things get "reinforced with CF" (or carbon" but "carbonated" means you've spritzed it full of carbon dioxide gas. (carbonated beverages)



One question: why go through the hassle of a rotating wing mast and then throw it away by using a crude hanking system for the mainsail? Seems like a lot of building work (rotating mast, boom noggle, rotating mast step and butt) just to throw it away on a cheapout on the sail attachment.

 

Not sure what you mean to "too open", but as far as the AC cats go:

My understanding is that Oracle basically won because they implemented a computer-automated fly-by-wire foil control system that basically flew the boat the same way highly unstable jet fighters are flown, and that before this system went in they had a lot of trouble getting the thing stable on foils (as did the poor old Kiwis, of course).

Also, a J foil is basically just half a T foil, and T foils are notorious for not having any real depth control on their own (hence wands on Moths, etc). So a J foil without any depth sensing ability (other than breaking out of the surface if it comes to that) doesn't seem like something that is going to provide tolerance of varying loads.

 

MPX Test Model

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If you're going to spend time here you need to read the thread!
1) The ama foil is a hybrid fully submerged AND surface piercing foil similar in concept to the TNZ AC72 foil. That foil used the angle of the daggerboard portion of the foil and the effect of leeway on the "up tip" portion of the "L" to control altitude within a range of speed. If speed changed up or down significantly, then manual control of the angle of incidence was required to select the next "range". This does exactly the same thing except that (hopefuly) the speed range is greater and won't require more than one adjustment of the angle of incidence throughout the speed range. In other words this ama foil will act more like a surface piercing foil with a wide speed range. That means it has automatic altitude control regulated by speed and to a lesser extent leeway.(ps-there is no "washout" to my foil whatsoever)
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2) Again, reading the thread would help! Downforce from the windward foil was pioneered by Ketterman and Bradfield and was integral to the Long Shot
speed record.
When the MPX is sailing the main foil is the windward foil-if downforce is allowed to develop it's because the boat attempts to heel further than the 10 degree angle of heel that the wand is set for, so the wand causes the flap to go up creating down force. As soon as the gust or whatever eases off the the wand moves the flap back to neutral or allows the foil to lift until it reaches the 10 degrees again. Using this kind of foil to create downforce is proven on numerous boats including the Rave, Osprey, Skat and F3 RC model-it works well.
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NO Eye:read the 34th AC thread-Tom Speer 100% debunks the nonsense about "computer control" of the Oracle foil!
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Picture,left-- ama foil-max cant-foil shown with boat at approx. 10 degrees angle of heel, when the boat is heeled to more than 10 degrees there is more of a "V" between the daggerboard portion and the "L" portion of the foil-and therefore for "heave stability from the foil. The running angle of the ama foil is controlled 100% by the interaction of the main foil and rudder foil even with the main foil nominally unloaded:
--Picture, center right- right circle illustrates the nominal area of the daggerboard portion of the foil that acts as a surface piercing foil ,controlling altitude with speed,
left circle illustrates the portion of the "L" section of the foil most likely to be affected by leeway-especialy as the foil gets higher. The leeway effect will tend to reduce lift on this portion of the foil by increasing pressure on the low pressure side of the "L". The effect is not as great on this foil as on TNZ because of subtle differences in the shape including a bit less "up tip" at 10 degrees angle of heel and also because the daggerboard develops lateral resistance as well. Also, helping with altitude control is the loss of lift on the "L" as the tip approaches the surface.
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Illustration, far right-- Left foil= closed- "up tip"(examples-TNZ,Groupama-most stable in heave -longest run time before rake adjust), Center foil-slight "V"( Hydros requires more frequent rake adjustment), Right foil, more "open" no vee or very little. (Oracle is similar but not so open-least stable in heave depending on angle of daggerboard):

 

NED....HighOnCarbon has addressed the issue of "open". IE whether the angle of the dihedral is acute, right or obtuse. The closer it comes to right or obtuse the more "open" it is. The more open it is, the less wasted lift (and hence parasitic drag) it has and the more unstable it is due to leeway flow issues.

The reason Camaas was more successful at foiling is that he went with a more "closed" solution. the Hydros guys were open but they literally were playing the foil in 2 degrees of freedom all the time (like a kite) and had a tough time with consistency even though they were on board to feel the feedback via"seat of pants".

Oracle did not have a "computer"... they and ETNZ started out with more closed foils and then started opening them up as they gained skill and never went beyond 90deg with any consistency

Doug here is coming out of the box with an obtuse angle that has washout in the tip (induces more undesirable leeway flow effects). that is what engineers and designers call "aggressive".

Basically from an engineer's perspective - where you minimize the changes and start from the implementation that is most conservative and use the learnings from that to get you to the next level, Doug's approach is likely to fail. Not necessarily because open foils cannot fly, but because he's simply changing too many things at once and there is no baseline performance to start from

 

That brings me back to what I said about presentation being important if you want people to engage with the content. The thread is, quite frankly, full of so much repetitive boasting and endless regurgitation of the same pictures and badly formatted monster posts that a casual reader will conclude that it's simply not worth wasting their time on the majority of it. This is not being said as a pointless insult. It's just the truth.

Ok, so instead of the complexity of a wand, which at least does things automatically, you have the complexity of requiring manual adjustment of the foil.

I realise the "daggerboard" part of the foil is surface piercing and has some angle to the vertical, and therefore some potential to respond to varying load. What I'm wondering is whether it will have enough response within a reasonable range of speed, heel and height.

Also, as heel increases the vertical lift of the "horizontal" part of the foil decreases, so that's not going to help much. It'll be losing you lift and height right when you want more.

I know windward downforce can be used with foilers and has been used, but whether it will work or not is going to be dependent on the leeward (load-carrying) foil's ability to deal with the extra load, especially bearing in mind that windward downforce limits heel, which limits the angle to the vertical of the surface piercing part of the leeward foil, which limits that foil's ability to respond to varying load. IOW, to make effective use of windward downforce you don't just need a foiler, you need the correct configuration.

Ok, so this model has one wand only, according to you. Presumably said wand has to be running along the centreline of the boat. It's easy to see how it would sense height. Question: without any lateral offset of the sensing tip, how would said wand sense heel?

If you were using the same idea on a windward foil then sure, I can easily see how a wand there would have no problem adjusting for heel, since being so far off the centreline it will have a large response to heel. Not seeing how you expect significant response on a centreline wand though, unless you think the leeward foil wont dig deeper when the load goes up.

You mean that both sections of the foil have more dihedral, not that there is "more V between" them. True, but only the dihedral of the daggerboard portion counts if you are looking for more lift in response to load, since the "L" portion will already be fully submerged, and also since more heel means less vertical lift available from the "L" portion.

But that's just a decreased load situation. None of that deals with the the problem of increased load. Obviously as an end game, if the foil breaks free of the surface it wont lift the boat any higher. What I'm wondering about is things like gust response, where you have an increase in load that has to be dealt with.

Ok, so "open" basically just means "vertical leg and horixontal leg, no significant dihedral anywhere, therefore little ability to respond to changes in depth". IOW, basically what Moths use.

If that's what it means, it would be beneficial for clarity if that is what people said. There's no need to invent new terms for it as the principle of using dihedral to control depth has been around for yonks.

 

Hey, who was the bloke who was lecturing Doug about using normal English to describe normal things?

If you're talking about dihderal, talk about dihedral. Use English, o gentleman who is fond of his mother in totally the wrong way.

In English: he used a foil that had more dihedral, and therefore more response to changes in depth.

In English: they used a foil that had insufficient dihedral, therefore insufficient response to changes in depth, thereby making the effing thing basically uncontrollable.

Ok, so that was a myth then.

Doug wants to totally revolutionise the sailing world. That means evolutionary changes don't appeal to him. Every detail of the boat has to be radical, in the hope that if every radical detail is radically good in practice, the boat as a whole will go down in the annals of history as the greatest thing since beer. As you say, it's a perilous path to tread.

 

MPX Test Model

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Noeye, don't bother to read the thread or the summary-it won't help you.
Sorry I brought it up. Have fun.

 

NoEyeDeer - the "open/closed" terminology comes out of how it was used in the last AC champs by those designers... Blame them.

Yes it is a case of more dihedral by Cammas, less by the AC boats (though iteratively arriving there) and even less by Hydros (which used dynamic trimming) and yet EVEN LESS by our friend Doug here.

Now why Doug keeps injection CO₂ bubbles into his mast tubes and radio box is beyond me.

 

If you have no respect for the man and his RC project why do you linger here? You should find yourself a hobby that does not involve trashing the work of people following their interest. I respectfully ask you to stop this rude intercourse.

 

I don't mind reading the relevant information if you're prepared to link me directly to it. I'm not going searching for a possibly non-existent needle in a very large haystack.

I did read your "summary". It doesn't deal with the points I raised.

 

MPX Test Model-the rig

Ready to go. Before and after pictures of the "shop"* below. That is, before and after the Great Reorganization:
* my living room !

Pictures, L to R: 1-3 Before, 4-6 After---
click-

 

BTW there is a reason for using the "open"/"closed" terminology in place of dihedral that struck me as I was looking at the GroupAma C cat earlier today at the Paris Boat Show

Because their boards are "double Ess" boards, the "J" of the board is not always operating in dihedral mode. As with the AC 72s, with the boards halfway down the "J" is more or less horizontal and the other part of the board is generating lateral resistance 100%.

Then when they lower the board 80% of the way, it goes into symmetric dihedral mode

this is also an area where Doug's boards are going to be challenged: with the tip washout, as the hull heels to leeward, the tip actually increases its vertical lift component rather than decreasing it.

Similarly as the hull rolls to weather the opposite happens. So this is going to make the stability issue more complicated.

 

Doug, I'm curious. How does this relate to the MPX test model? IE isn't this a bit "off topic?

 

Coming up on the last big job-the rig:
1) extend the mast about 10". The extension will be added to the lower end of the mast allowing the wing section to extend to the top. Reinforce for the noggle side panels-see post 698.
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2) cut and set up the gaff which will be used instead of the diagonal batten initially. Gives superior control of a big square head in light air by allowing a functional upper outhaul.
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3) Install the combination noggle/gooseneck/ vang mount. At this point I'm going with the vang instead of the vageller but that could change.
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4) make and rig the main boom and install to noggle/ gooseneck.
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5) setup outside and rig shrouds, Code Zero and jib with adjustable rake. Forestay is integral to both foresails. There will be a separate forestay for reefing.
---a. add bowsprit removably
---b. make Code Zero boom and jib boom
---c. attach long maststep that allows adjustment of mast heel fore and aft and allows rotation of wing mast.
6) Pictures of rig on boat(this coming week?)
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7) Testing!
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1- More on #1 & #3 above- I'm using carbon tubes for the extention epoxied into the wingmast and carbonated and faired as required. The additional section will be 100% sealed. The mast heel will consist of a solid glass insert in the forward most tube with a stainless pin glued in place. A small high strength plastic ball will slide over the stainless pin and support the compression load of the mast while allowing it to rotate easily. The SS pin will fit in any one of
a number of holes drilled in the rectangular aluminum mast step section. The mast heel will be able to be moved approx. 3" forward from the aft most position. This is done to allow for the change in balance as sails are removed in the reefing process.
The noggle/gooseneck will slide on a carbon tube rail glued and carbonated to the aft side of the mast extension. Since, initially I will uses a more or less normal vang, the vang will attach to the bottom of the noggle/gooseneck rail.
The mast extention will be carbonated to reinforce it locally for the loads imparted by the noggle side plates. The sideplates will have adjustable angles relative to the noggle but the default setting will be that the boom will be stopped by the side plates when it is at an angle of about 30 degrees to the centerline of the wing mast. Once set it is 100% automatic from side to side, tack/gybe to tack/gybe.
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2- The next job in assembling the rig is to add the small carbon tubes to the center of the back of the wing mast about every 8" or so using epoxy to bond in place. The micro tubes are big enough to allow a .22" wire to be bent over and still pass thru. This also acts to help the sail luff to fit well even with small inconsistencies. The main is attached by running a wire up the luff and out thru notches cut in the luff to match the tube attachment positions and thru the carbon tube and back into the sail.
The sail notches are big enough to allow the sail luff to move up and down a bit. At this point the main won't be reefable. (See illustration and note below)
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3-More on #2 above: initially the head of the main will be supported by a carbon gaff with an upper outhaul at the "peak" position. This gives tremendous control over the shape of the upper thirdof the sail in a way that is impossible with a diagonal batten. To add camber to a diagonal batten you have to put a compression load on it which makes it increasingly difficult to "pop" from one side to the other. With the gaff and upper outhaul you do anything with the sail with no problems from side to side. And it's a proven system on numerous rc models I have built. But the sail has a diagonal batten pocket so that will be experimented with.
The carbon gaff will rotate like a "normal" gaff and the line supporting the gaff will be able to be adjusted. The outhaul will be adjusted using grommets that slide on the carbon gaff which is a good system with the right grommet.
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4-The main boom will be one or two carbon tubes depending on what I can put together with the appropriate stiffness and weight. If two tubes they wil be glued and wrapped in various places with carbon tow.
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pictures-the sails-(nary a wing in the place-until we test hull#2! ):
click--
Left-main + jib,Center-close up of main head, Right- main plus code zero, Bottom-sketch of an idea that will allow reefable attachment of the luff wire.
Bottom right- mast showing initial 4 degree rake.
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On the RC models I used to build every main was reefable by attaching the sail in such a way that the luff wire remained in close proximity to the round mast. Double sided velcro was used to go around the luff wire at positions where there were notches cut in the sail luff to make room for the velcro. On those boats, the mast was shortened by removing a section for reefing and the main was rolled from the bottom to the reef position and held in place with velcro circles. On the MPX, that system wouldn't work because the airfoil shape of the mast would allow the wire to "slip" around the shape. So I've come up with an idea that may be used down the line: the same small tubes epoxied to the mast will be used but the aft side will be sanded off making the tube "open". Velcro would then be used like it was done on the old boats and would permit the sail to be moved up and down enough to reef it. The open tubes prevent the wire/sail from slipping around the back end of the the wing mast.