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

Discussion in 'Multihulls' started by Doug Lord, Dec 28, 2010.

  1. Doug Lord
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    Doug Lord Flight Ready

    ========
    Wrong! If you're going to quote me, do it accurately or don't do it at all. The discussion centered around whether or not the wand springing forward would always cause a crash on a Moth. I said it would and a friend who owns a Mach II explained that the Moth can be set up so the wand won't cause a crash when it does that.
    But I NEVER agreed or said that the Moth system doesn't create downforce- it does but can be set up for a minimum level.

    http://www.boatdesign.net/forums/sailboats/moth-foils-35-9-knots-41-29-mph-11209-106.html post 1584

    =============
    Also see post 1595, where I quote Bill Beaver from his excellent paper on the Moth:
    Although not intuitive, from a sailing perspective flap up
    (shedding lift) is more important than flap down (adding
    lift) because of the dire nature of the crash that comes from
    the inability to shed lift adequately.
     
  2. Doug Lord
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    Doug Lord Flight Ready

    Fire Arrow Foiling System Testing and Development

    Boats like the Rave, Osprey and Hobie Trifoiler (as well as the Whisper and S9*) all have dual ,independent altitude control systems and are designed to utilize downforce from the windward foil to add to righting moment. Most wand systems are adjustable so that downforce can be adjusted from a reduction in lift on the windward foil to full on pulling down of the foil.
    The main foil on the Fire Arrow acts like the windward foil on these boats and can develop downforce when required.

    * Both the designer and one of the US owners confirmed the use of downforce on the S9. The builder of the Whisper confirmed to me that it utilizes dual wand controlled SYMMETRICAL foils with flaps which means it can generate downforce when required. All dual, independent wand controlled multihull foilers are capable of generating downforce when required. The fact that they all use symmetrical foils is a clue: if not for the ability to generate downforce asy foils would be the logical choice. Symmetrical foils are used to facilitate downforce.

    =======================================

    Greg Ketterman on the use of downforce on the Trifoiler:

    HYDROFOIL SAILBOATS IN GENERAL
    "Hydrofoil boats can be categorized into two categories; 1) Incidence controlled hydrofoils* and 2) surface piercing hydrofoils. The difference lies in the way the boat maintains the proper altitude above the water surface. A surface piercing hydrofoil boat maintains proper height by varying the amount of foil submerged. The boat raises up as the speed increases and reduces the amount of foil submerged and therefore the lift. The boat finds equilibrium at the proper altitude. An incidence controlled hydrofoil sailboat has a mechanism that controls the angle of attack of the foil to maintain the proper altitude. It is generally believed that surface piercing is simpler, but incidence control is more efficient. In reality, it is the method that works with fewer problems that is simpler.
    From the beginning it was felt that incidence control was better suited for a sailboat even though most of the existing hydrofoil sailboats were of the surface piercing type. There are many advantages of the incidence controlled foils; however, the most important is what I call the DLA (dynamic leveling affect). This is the increase in righting moment or stability due to the ability of the windward foil to pull down. The DLA has little affect on the low wind performance, but it essentially makes the top speed of the boat limited to the strength of the boat. Conventional boats with a finite amount of righting moment can only extract so much power from the wind, but with the DLA, the righting moment is virtually unlimited.
    Intuitively many people think that the added drag of the windward foil plus the increased induced drag of the leeward foil would offset the gain in righting moment, but calculations show and practice proves otherwise. The dynamic leveling affect not only produces a dramatic increase in top speed, but is also responsible for all the other key features that this stability provides.
    The other major advantage of the incidence controlled foils is they are less affected by the waves and other surface affects. Drag and losses associated with the surface are the major reason incidence controlled foils are more efficient.
    All hydrofoil sailboats have problems with ventilation; however, surface piercing foils have larger problems, because the foils are piercing the surface at a smaller dihedral angle which makes it easier to ventilate."
    ------

    * On the Trifoiler the entire foil was moved to control RM, lift and negative lift hence the term "incidence controlled foils". On the Rave the incidence was generally fixed at +2.5 degrees for the main foils though some owners found a way to decrease the incidence on the windward foil. Lift and negative lift on a Rave foiler is generated by the wand (designed by Dr. Sam Bradfield), a surface sensor(dragging in the water) and attached directly via linkage to a flap on each main foil. The wands are independent just like the trifoiler "incidence controlled" foil sensors.

    ==========================

    Jim Brown article and interview with Dr. Sam Bradfield:
    http://smalltrimarans.com/blog/jim-brown-article-on-sam-bradfields-hydrofoil-trimaran/

    "For very high speed aircraft, and now for hydrofoils, “symmetrical” sections – cambered both top and bottom – (convex/convex) are used by Bradfield and others. When fitted with an articulating aileron or flap, these foils can create lift in either direction, up or down, and so can exert a profound stabilizing influence on a sailing trimaran. Heeling effort in the sails, which would normally depress one side of the craft and elevate the other, is resisted absolutely by the downwind foil lifting up and the upwind foil pulling down. The craft stays dead flat, the mast stays plumb vertical, the usual spilling of wind from heeling is converted instead to thrust, and the power of the sails is fully utilized to propel a craft that is now largely relieved of the age-old drudgery of hull drag."

    [​IMG]
     
  3. David Cooper
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    David Cooper Senior Member

    Look at post #193 from the designer: http://forums.sailinganarchy.com/index.php?showtopic=171408&page=2#entry5275468. He says:-

    "we did not have enough wind to check if we can take advantage of flap downforce, but I can say that this occurs, very often, when the wand does not touch the water we have a inversion of flap, our wand system has an elastic force the flap and slightly reverses the lift, this lowers the bow and the boat does not jump, returns in a horizontal position. S9 wand system has a wheel in the top with which to adjust the range of flap work, so we can choose how much vertical lift and downforce."

    There are clearly some problems with the designer's level of English, so lots of confusion can be generated from many of his comments, but it would take a brave person to bet that that foil with the flap up doesn't generate downforce, the link between the wand mechanism and the flap is clearly designed to pull it up against the pressure of the water, and the designer talks very clearly about downforce. Clearly if the wind and gusts aren't strong, the windward foil will not get to the point where it needs to generate downforce, so the boat will achieve its stability just by that foil reducing lift while the leeward foil increases its lift, but above a certain strength of wind it will reach the point where the windward foil is generating some downforce, though it would be hard to know that you've actually reached that point while sailing. A boat which doesn't generate downforce at that point would start to tip over after the windward foil has gone neutral.

    No, but if asymmetrical foils are that close to symmetrical, are they really capable of preventing a raised flap at the back from deflecting the thrust upwards? It may affect the efficiency a fair bit, but would it reduce available downforce to zero? With gentle flap angles, it doesn't look as if it should stall.

    I don't think he's suggested that they should be generating downforce at times when it's unnecessary to do so - it merely extends the range of windspeeds at which that stability can be maintained. Up to a certain speed, the foils will be behaving identically on two near-identical boats even if one is capable of producing downforce and the other isn't, but as soon as the windspeed is higher than that, the one that can generate downforce will be able to outperform the one that can't (assuming equal crew weight), and at lower speeds than that there will be a range of speeds at which downforce can be generated to compensate for the crew being slow in moving their weight out when a gust hits by generating a little downforce.

    He was basing his beliefs on little clues picked up from the designer's comments, and it's possible that he was reading more into them than he should have. For example, he was told that the rod was linked to the foil, but when you hear that from someone whose English is far from perfect you can't be sure they've chosen the right words - Doug read into it that there was a link capable of pulling up, but it would have been quite possible for the intended meaning to be different. It turns out that there is a link capable of pulling up though, so Doug is, perhaps by luck, right.

    It isn't necessary if the gusts aren't strong enough to need downforce to maintain that stability, but it is necessary if they are strong enough, so who's right and who's wrong? The range in which it's stable is greater if it can produce downforce, so I'd say Doug edges it.

    Some of his comments suggest a poor understanding of some aspects, and that was what led me to doubt him. It is impossible for these adjustments to be made without changes in ride height because the wands would always end up at their original angles otherwise and the foils would do likewise if the height of the hulls over the water didn't change. If the wind goes up and the boat doesn't speed up or rise, it has to lean over a little so that the slightly lower leeward hull can generate extra lift from its foil and the slightly higher windward hull can generate less lift (or more downforce) from its foil: it cannot bring the boat back level and maintain those levels of lift. This will reduce the amount of tilt during gusts substantially though, so it will feel as if the boat's staying plumb upright if you're used to boats that behave differently. If the boat accelerates, it may be a different story: once up to a higher speed, the windward foil can produce more lift than before for the same flap angle, so the ride height may be unchanged, but if the windward hull is also back at its original ride height, the higher speed will either cause it to generate more lift if it's angled for lift at that altitude or more downforce if it's angled for downforce, and that will have different results at different wind speeds, leading to the boat tilting more to leeward or windward through a range of speeds - I can't see how it can automatically self-level the boat perfectly across the range. Again though, it may well be able to keep it fairly level and provide the illusion of being perfectly level for those who aren't looking closely enough.

    Yes, it looks as if he jumps the gun quite a lot, but then again, he does have a habit of asking designers questions through private messages and he may be picking up on things from the replies that he doesn't pass on (or which aren't considered a trusted source if he does pass them on because they've been filtered through him), thereby giving him the confidence to make assertions that look unsound in the full knowledge that he'll be shown to be right in the end.

    Going back to the bit about the S9 not working with the windward foil raised, that could well be the case right through the range in which some lift is still required from the windward foil for the boat to fly, but there will be a windspeed at which it can fly on the leeward foil alone, though you'd lose the advantage of the windward foil generating downforce during gusts to improve stability, so why would you do it? The designer's words were "Only one time . But not fly upwind , and one foil do not support the total load . Better not do this ." The bit about it not flying upwind lead me to read into it that it could fly at other angles. The bit about one foil not supporting the total load could simply mean that at lower speeds it needs both foils lifting to fly. The advice not to try it could simply be because the boat works so much better when using both foils: flying on one foil alone may be fully possible at some angles when there's enough wind, but you'd have to work as hard to keep the boat level as on boats like the FP.

    Thanks for the Rave link - I'd read it long ago but had forgotten about it, and it may explain one thing which has been puzzling me and which also led me to doubt Doug. He talks about a beam being broken on a Rave when it generated too much downforce and I got the impression that he thought this could happen on all the other boats that generate downforce. I wonder if that actually happend on a Rave using manual control rather than a wand. If not, I can't work out how the downforce can keep going up without limit without the force of water on the flap eventually outpowering the bungee on the wand which should apply a weaker and weaker force as the wand goes down: there should be a limit to how much downforce can be applied, and that should prevent you from breaking the boat.
     
  4. waynemarlow
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    waynemarlow Senior Member

    David be a little aware that you just maybe are not taking all things into account and making slight assumptions on why and how both Doug and a foiling boat follows certain paths.

    Doug does have the knack of going down one path and sometimes only one path, which fits into his modus of the time, something we are all guilty of at times, and then pushing that agenda. I have no beef in that, as you suggest, he does seemingly have a lot of time to research and ask questions, which seems to act as a catalyst for a lot of discussion on these sort of forums, certainly I have learnt a lot over the years from issues and ideas he has raised.

    In the S9 discussion you have read and been part of over on SA, most assumed that the foil shape would have been assymetrical due to the efficencies of the assymetric foils giving a wider speed range, only to find that the foil shape is virtually symmetric, would an assymetric shape be better, thats way beyond my pay grade.

    But why did the designer go the symmetric route. There has been huge resources thrown at this subject recently, most of which Bimare would have not been part of, did that influence their decision to stay with the tried and tested route of symmetric foil shapes, was it more down to simplicity and cost of build as much as design. What ever the design seems to work and work well in a relatively simple way. Perhaps for all the research going on into assymetric foils, the old tried and tested KISS route will win through, I guess time will tell.

    But let me ask a question, we know the S9 won't sail well on one main foil and that raises a lot of questions, I can think of a few straight off that blows holes in the theories of negative lift maintaining ride height on such a craft as the S9, but then we look at the very small foils used on the S9 ( which in some ways must nearly be optimal ) and wonder if that foil was just a teensy bit bigger, would it not fly just on one foil alone, but be totally dependant on RM from the mass of the skipper being placed in the right area. Would a compensatory system that gave enough negative flap on the windward side just before the foil broached the surface, be enough to give downforce sufficient to not need a skipper movement.

    Oh the conundrum of a thousand possible combinations of foils and sailing craft. Certainly one thing though, a lot has been learnt with the S9 with its full size model in less than one year, the designers must be collating data and their learning curve can only accelerate away, something the model builders can only hypothesise about.
     
  5. Doug Lord
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    Doug Lord Flight Ready

    Wayne, there is a history of over 40 years of the development of dual wand(and "feeler") based hydrofoil systems using downforce. Dr. Bradfield and Greg Ketterman were pioneers in this area of foiler development. It is obvious, once you study these systems, that the best foil for systems that are expected to develop downforce is symmetrical. They have to lift effectively up and pull down. And the Bradfield systems have to develop downforce when the foil is preset at a + 2.5 degree angle of incidence. Dr.Sam did many years of research on his system and came up with a remarkably effective foiler in the Osprey and 40' SKAT. And while his foil system works very well in stronger winds it is also excellent in light air.
    --
    I was lucky enough to work with Dr. Bradfield one summer and I designed and built the worlds first production RC sailing foiler(F3) the following year.
    We never got a chance to talk about the Fire Arrow but I know he would have thought it was pretty cool.
    That summer I spent with him we talked about things that are just now becoming a topic of conversation among "normal" sailors including his foil system and my idea that when I built the RC model it would have to be able to foil in very light air. He agreed with that and carried thru on the Osprey so that it would foil in light air. He told me personally that with the designed rig the Osprey would take off in 6kts or a bit less. He felt ,as I do, that the key to getting more people involved in foiling is making sure foilers will perform in light air so the customer could expect to foil throughout the wind range.
    Nowadays, the Whisper guys claim their boat will foil in 4 knots of wind, the Quant guys are shooting for a 5 kt takeoff with a foiling keelboat, and Michele says the S9 will foil upwind in 8kts of wind.
    And my 20 year old F3 foils in a 5mph wind as does the much heavier Fire Arrow.

    [​IMG]

    [​IMG]

    [​IMG]
     
  6. Doug Lord
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    Doug Lord Flight Ready

    ==================
    I'm not sure we know that at all. Think about this: I'm relatively sure that you know that at takeoff the the wand is way back and the flap is max down. As the boat speeds up the bottom of the wand moves forward and the flap moves to neutral(neither up or down) which is the design flight altitude.
    But what if the 180 lb crew is on the trap? Then the windward foil has to lift its share of the hulls weight AND the weight of the crew. Also, when the flap is in neutral any imbalance is going to cause the port and stb flaps to move to bring the boat back to level. I'm not sure whether it was a language issue or what but when the boat is flying with the flap in neutral which it does very well it has all kinds of room to move the flaps-not just the small movement shown by Charlie either-look at the vertical fin cutout and there is easily room for the flap to be adjust up. Now, Charlie said it wasn't adjustable and Michele said it was. I'm betting on Michele-and I don't think they have fully explored the range of downforce the boat is capable of.
     
  7. Doug Lord
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    Doug Lord Flight Ready

    Dominion 2-HW--Welbourn-type foils--Experimental

    The model is making progress. I'm posting this here to illustrate a different kind of foil. They are very similar to and inspired by Hugh Welbourns Q23.
    The D2 will be an RC self-righting keelboat. The foils have direct application to multihulls especially the Fire Arrow. The trunks allow the foils to be raked up to 5 degrees and canted 4.5 degrees. The reason for the manual cant is to experiment with sailing at a slightly greater angle of heel to keep the windward foil clear without having to retract it by radio. Once rake is set, it probably won't have to be adjusted again. The last half of the more or less horizontal portion of the foil is twisted from zero degrees to + three degrees in order to help the thing takeoff in light air. As the boat speeds up that portion of the foil will be mostly clear and/or acting as an high aspect planing surface.
    Last page of the build log: http://www.rcgroups.com/forums/showthread.php?t=2434531&page=16

    [​IMG]

    [​IMG]
     
  8. OzFred
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    OzFred Senior Member

    Thanks, I hadn't seen that.

    The picture was just to illustrate that you can't tell if the foil is symmetric or not from a low resolution photo. But you're right, whether the foil is symmetric or not doesn't tell you if it can or can't develop down force in isolation from other factors such as AoA and size and range of flap movement.

    While a Moth foil can generate down force, whether it actually does depends on on how it's set up. A Moth has no use for down force, so the foils aren't set up to generate it (and it's not alone in that).

    Doug tried to argue that Moths nose dive because when the wand goes forward, the flap goes up and generates down force. It took many, many posts and lots of images of Moths sailing with the wand fully forward and hence the flap fully up to convince him otherwise (though only grudgingly).

    Consider this gem:

    "Any wand based multihull foiler with dual ,independent wand systems will be capable of down force. It would be impossible to control altitude , not to mention add RM(when required), without it"

    No one argues with the first part, but "impossible to control altitude … without [down force]" is the kind of illogical and plainly wrong statement that people have been arguing against. It's the extrapolation from "can" to "must" that is plain wrong.

    And that really is all this argument has been about.
     
  9. Doug Lord
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    Doug Lord Flight Ready

    Fire Arrow Foiling System Testing and Development

    oz fred, read what Bill Beaver said about the Moth in the first post above. A wand system, whether on a multifoiler or monofoiler, MUST be capable of "shedding lift" or altitude control would be impossible.
    On a multifoiler, downforce can be a tremendous asset in not only controlling altitude but in creating righting moment.
    Dual, independent, wand systems like those used on the Rave, SKAT, Whisper and the S9 automatically generate righting moment as required as a function of their design flight altitude. Same is true of the Hobie Trifoiler and its incidence controlled foils and "feelers".
    The Fire Arrow main foil does the same thing and more.
     
  10. David Cooper
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    David Cooper Senior Member

    I missed that bit: a clear error which he really ought to own up to: downforce and shedding lift are not the same thing. Posting a clear correction to things like that would go a long way to dissipating the unnecessary hostility he generates against himself. Of course, it works both ways and I didn't see how it all began, so he may have good reason for not correcting things like that. It's a shame though, because I like the people on both sides, and Doug in particular's a great character with unstoppable enthusiasm who inspires people and encourages them to think.
     
  11. Doug Lord
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    Doug Lord Flight Ready

    Flap Up=Downforce!

    David: shedding lift and downforce are IDENTICAL. You couldn't be more offbase than to suggest otherwise! Didn't you read this:

    Also see post 1595(Moth thread), where I quote Bill Beaver from his excellent paper on the Moth:
    Although not intuitive, from a sailing perspective flap up
    (shedding lift)
    is more important than flap down (adding
    lift) because of the dire nature of the crash that comes from
    the inability to shed lift adequately.


    Or did you not understand that FLAP UP=DOWNFORCE everytime! Again, it would be IMPOSSIBLE to control altitude w/o the possibility of downforce(shedding lift)! That is a main principle of wand altitude control. If you could only lift up the boat could never sail straight and level at its design flight altitude in any waves or gusty winds-flight control would be impossible-particularly on a multihull with dual independent wand systems!!!.
    Mach II Moths can have downforce dialed way down but they have active ,twist grip, control of the rudder t-foil. It is physically impossible to use the rudder t-foil in the same way on any foiler with dual,independent wand systems because of the very independence of the two systems! The S9,Whisper, Rave, Osprey, F3, Fire Arrow, Skat and Hobie trifoiler do not have active rudder t-foil control. The Rave and Osprey were available with adjustable rudder t-foils(as an option) but they were only used to make infrequent adjustments similar to what is allowed on the new AC 50's. This adjustment was not needed in normal sailing.
    ====
    Multihull foilers with wand(or "feeler") based altitude control systems:

    1) Rave, Osprey, Skat, F3, S9, Whisper all of which use symmetrical foils with wand controlled flaps and all of which rely on windward foil downforce for extra RM when required.
    -
    2) The main foil on Fire Arrow develops downforce when required and is similar to the windward foil of the other boats but has only a single wand controlled system.
    -
    3) The Hobie Trifoiler uses incidence controlled foils with no flaps. The incidence of the dual, independent systems is controlled by a surface sensor("feeler") sticking out in front of the boat and connected directly to the foil. The foil system produces downforce on the windward foil when required.
     
  12. David Cooper
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    David Cooper Senior Member

    Shedding lift means eliminating lift, not producing downforce. Flap up in the context above means up to level: neutral (zero lift).
     
  13. Doug Lord
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    Doug Lord Flight Ready

    Just nonsense.....
    -------
    I'm probably wasting my time but: I think you are ascribing more to downforce than you should. Downforce says nothing about how much downforce anymore than "lift" describes how much lift. Downforce can be anything from a very small amount less lift to maximum downforce the foil in question is capable of delivering with its flap up. Lift can mean a very small amount of extra lift or all the lift the foil in question can deliver with its flap down.

    Up flap=downforce=shedding lift
     
  14. Munter
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    Munter Amateur

    Doug has always struggled with frames of reference. David's attempts to rationally discuss these issues are admirable but probably bound to fail as all previous attempts have done. In the unlikely event that you are able to help Doug understand where his understanding is incorrect he will either edit his previous posts to conceal his errors ("I want my posts to be the best they can be") or assign his learnings to someone other than the participants in the thread ("my moth friend explained"). No wonder it builds antagonism.

    Again - frames of reference. "Downforce can be anything from a very small amount less lift..."

    Less lift that what? What is the reference point? The rest of the universe appears to work off the direction of force applied to the hull by the foil but Doug defines it as any time the foil produces a small amount less than an undefined figure. Which do you think is the more sensible?
     

  15. Doug Lord
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    Doug Lord Flight Ready

    You know when you take something out of context it might be confusing.
    You said in quoting me out of context:

    "Again - frames of reference. "Downforce can be anything from a very small amount less lift..." "
    --
    When, in fact, the frame of reference was clearly given:

    Downforce can be anything from a very small amount less lift to maximum downforce the foil in question is capable of delivering with its flap up.
     
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