Vampire Cat with Canted T-foils

Discussion in 'Multihulls' started by Doug Lord, Sep 4, 2014.

  1. Doug Lord
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    Doug Lord Flight Ready

    This is a modified Masrtom M20. Unfortunately, the forum doesn't support docx format so I can't post the info. if you're interested e-mail me and I'll send the file.
    The boat uses canted T-foils with a wand altitude control system. The boat sails on only one main foil with the windward foil retracted. You would not want to be sitting behind the retracted foil when you capsize!
    http://www.wyc.org.uk/news/the_vampire_flies

    click-Note retracted windward foil:
     

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  2. Skyak
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    Skyak Senior Member

    Interesting. I would like to see tacks and gybes flopping those foils around.
     
  3. Doug Lord
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    Doug Lord Flight Ready

    I just don't like that arrangement-the poor crew in a pitchpole and pivoting that foil will be a nightmare. UNLESS this is just a prototype to test the concept. Maybe after they're satisfied they'll build a boat with canted trunks. Then the foil system would be no more hassle then the UptiP foil system-and, perhaps better?
     

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  4. Moggy
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    Moggy Senior Member

    Try save as PDF.

    If it is not native, there is a plugin for Word 2007, Libre Office does it native, Adobe has a tool...

    http://www.adobe.com/au/products/acrobat/pdf-to-word-doc-converter.html

    ... and there are a number of utilities like Nitro PDF that set up a "PDF Printer" to which you can print anything to make a PDF.

    It is a good thing to have, better than posting the various doc formats.
     
  5. Doug Lord
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    Doug Lord Flight Ready

    Thanks-I'll look into it!
     
  6. Skyak
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    Skyak Senior Member

    The foils would still present a sharp edge in front of the crew with trunks and the wand input would be much messier in a daggerboard arrangement. This swinging arangement might be an improvement if it swung much more than 180 degrees (low and flat) or less than 180 (out to the side). The shift from one foil to the other might not be so bad. The scary part is the big swing down until it is locked and this might not be as bad as it looks if you could control the tabs and 'fly' it into position. This might be automatable -not to be confused with foolproof. The forces and potential impact of a flying gybe would snap the foil like a twig. At any rate it would be VERY interesting to see how they tack and gybe this boat.

    The other interesting point would be the performance comparison of this T-foil cat to the highly developed uptip foil boats. The T-foil should have a small but significant drag advantage theoretically. And then there are the messy hydrodynamics of the surface that the T-foil can distance itself from. This boat might even adjust the cant of the foil based on conditions. The losses at the surface are proportional to the lift of the vertical foil so if the horizontal resists all the leeway those losses will be cut. In my estimation the potential gains are sufficient to justify 'fixes' to many problems. Keep an eye on this one.
     
  7. Doug Lord
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    Doug Lord Flight Ready

    Skyak, I don't think the T-foil has less drag than an UptiP foil-both carrying the same load. Greg Ketterman pointed that out in a paper illustrating the pressures on each side of the foils. A "normal" T-foil has a low pressure/high pressure intersection on the lee side of the lee foil whereas the UptiP foil(or Ketterman's inward pointing "L" foil) has the same pressure on each side. Now, the canted T-foil is another story-a friend is working on the Vampire project and he's convinced that the canted T-foils are less draggy then UptiP foils.
    --
    Wands can be done fairly simply with any daggerboard but Bradfields arrangement is, by far, the simplest. The wand axle on the Osprey is attached directly to the board:
    click--
     

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  8. AlexanderSahlin
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    AlexanderSahlin Junior Member

    The present canted T-foils is exactly the foil-configuration I would choose with a catamaran as platform!

    1) If you compare with a L-foil in the trunk, you will get up to 50% higher righting moment, because the L-foil has the inclined total hydrodynamic force inside the hull, while the canted T-foil has the resultant hydrodynamic force outside the hull.
    2) With an appropriate canting angle (about 30°) the hydrodynamic force will produce much less bending moments on the components than for a similar L-foil. This allows for thinner foils with higher AR.
    3) With the same appropriate canting angle the hydrodynamic force on the surface-piercing strut will be small, so ventilation can be avoided even without ventilation-fences. (Ventilation is a serious problem if you try to get lift from a surface-piercing foil at the present speed.) The port/starboard pressure difference on the strut near the lifting foil will also be small. Interference drag at the T-intersection can be minimised if the lifting foil is displaced some half chord-length forwards relative the strut. See e.g, the T-foil of the Mach-2 Moth.

    With a M-20 as platform you can choose a take-off speed about twice that for the Moth, and the M-20 will reach that speed in very light wind. Therefore, this concept has a huge speed-potential!
     
  9. rwatson
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    rwatson Senior Member

    Good pics Doug. I finally got an idea of what this 'wand' business is all about. Just as conformation, confirm for me that as the wand angle decreases ( hull rises out of the water ), the attack angle of the adjustable lifting surface is reduced to prevent 'popping out' of the water. ?
     
  10. Doug Lord
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    Doug Lord Flight Ready

    Exactly. The wand is set up so that at flap neutral, the boat is at its designed flight altitude.
     
  11. groper
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    groper Senior Member

    Remember the interview with Martin Fischer when asked about the t foil rudders on Jessica rabbit? His response tells a clear story and affirms Alexanders comment above, the choice is predominately a structural one. The center strut t foil has half the cantilever supported span of an equivalent L foil and so can be made thinner for the same design loads. Stability isn't an issue with wands which seems the main reason for using up tip foils... the up tip foil for the Americas cup was simply a product of the rules, not necessarily the best approach if there were no rules at all...
     
  12. Doug Lord
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    Doug Lord Flight Ready

    The UptiP foil is the first hydrofoil ever developed that is capable of intrinsic altitude control as a single main foil with no wands or moving parts. Thats why it's such a breakthru in foil design and why it's used on the GC32 and Flying Phantom*. Those guys could have chosen any foil system but chose uptip foils because of the single main foil/3 foil configuration with automatic altitude control.
    Alan Smith, who worked with Kevin Elway on the Vampire, is totally convinced that the canted, wand controlled T-foil is faster than an uptip foil-but it isn't simpler. And for AC boats it presents a problem rule wise.

    * and why it's such an ideal foil for a trimaran ama. Picture below is my large test model using UptiP foils on the amas-they have required zero adjustment under sail while maintaining the ama's altitude above the water very closely even with different speeds and loading:
    click-
     

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    Last edited: Oct 9, 2014
  13. oldsailor7
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    oldsailor7 Senior Member

    Thats a great pic Doug, and shows the effectiveness of the foils very clearly.
    That said, the twist in the Mainsail is just 'orrible :eek:.
    I see this on so many boats I sail on and see in sailing pics.
    The bottom part of the sail is producing more side force than propulsion, and the top isn't working at all.
    So many boats have their mainsheet tackle located at one point, or on a very short outhaul track. Admitted not every boat can have a wide circular sheet traveller track. But there are other ways to arrange the down-haul / out-haul system so that the boom can be let out and the mainsheet hardened to get the leech of the main vertical and the tell tails streaming.
    The same applies to the Jib, which on windward headings is pulled in too close at the clew and too loose at the top. Easing the sheet and vanging the clew outboard is often worth a couple of knots. Just MHO. :)
     
    Last edited: Oct 9, 2014
  14. Doug Lord
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    Doug Lord Flight Ready

    Paddy, I moved a copy of your post and my response to the Fire Arrow thread so not to hijack this thread. Thanks for your comments!
     

  15. groper
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    groper Senior Member

    Tell me something I don't already know...

    One thing I've noticed with you doug, is that you never consider structural design along with your hydrodynamic design. This is understandable because with small models, the structural requirements are very minimal, just about any material with an average modulus can be used in these very small craft. This all changes as things get bigger, very quickly, the modulus requirement from the material increases and there's only a few choices of material that can be used to make a highly loaded foil without increasing the thickness of the foil so it doesn't end up with high drag. Fwiw, using carbon fiber in your models is a waste of money. Eglass could be used just as effectively provided you choose the correct fabric. In larger boats, there's little choice other than carbon, as nothing has the stiffness and strength to weight density in order to create a foil strong enough, stiff enough, and thin enough, to give the best performance possible.

    What I'm saying is, there is a balancing act happening with large boat foil design, structural considerations weighed up against hydrodynamic efficiency. The bending moments on a T foil is vastly less than an L foil which is a very important consideration.

    And just because the aforementioned boats are using uptip foils, doesn't mean they are the bee all and end all. This is very early days, and it would surprise me if the foils on the fastest boats 10years from now we're not a totally different configuration- such as active automatic electronic control. It's a natural progression that has happened in all other indusries, aerospace, automotive, you name, they all have active automatic electronic control... I actually find it bizarre it hasn't happened in a huge mainstream way in boats yet...
     
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