Controlling T Foil

Discussion in 'Boat Design' started by Rockdamned, Oct 4, 2011.

  1. Rockdamned
    Joined: Nov 2010
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    Rockdamned Junior Member

    Hi everybody
    I was searching on the net trying to understand how designers made the t foil control on dinghies, like i14 or kind moth.

    I still can't understand how, onboard, you control the angle of attack, and how it is made...

    We're now designing at my university (La Sapienza - Rome) a skiff, and we were thinking about it...

    Thank you for your help!
    Edoardo
     
  2. daiquiri
    Joined: May 2004
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    daiquiri Engineering and Design

    This is one possibility: http://www.youtube.com/watch?v=yuFwDm8t3IM

    This is the one used on moth foilers: http://sailmagazine.com/racing/learning_to_fly/

    In both cases a skimmer wand is used. It skims on the water surface and translates the flight height into an angular position. A mechanical leverage system then moves a flap on the foil, which controls the lift force and the flight level. In technical or mathematical language, it would be called a P-controller (proportional controller).
     
  3. Doug Lord
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    Doug Lord Flight Ready

    ===================
    Hi, Edorardo! On the I-14, the T-foil rudder is controlled manually by a twist grip on the extension tiller -the foil generates lift "up"(vertically) upwind and "down"( vertically) downwind. The I-14 is not a "full flying foiler"- the foil generates "foil assist" which lifts a portion of the boat upwind and creates downforce aft downwind.
    The Moth uses an altitude control system pioneered by Dr. Sam Bradfield and
    adapted to the Moth by John Ilett. The system relies on a "surface sensor" also called a "wand" that contacts the water and is held against the water by shockcord. When the boat is still supported 100% by buoyancy, the wand is angled way back moving the flap on the main foil down to create max lift. As the boat rises the bottom of the wand moves down and forward until the flap is in its "neutral" position. This neutral position also corresponds to the designed flight altitude of the boat. If the boat starts to rise the wand moves the flap up to decrease lift; if the boat starts to sink the wand moves the flap down to increase lift.
    Both the Moth, Rave and Osprey use a separate manual adjustment of the rudder T-foil that sets the angle of attack of the main foil for the conditions and thereby controls pitch attitude. On the Moth and Osprey this control is on the extension tiller; on the Rave it is mounted to the side of the helmsman.
    ======
    Here is a short video put together by Tom Hayman and Dr. Sam Bradfield illustrating how the wand works. The wand is essentially the same on the Moth, the R Class foiler , Mirabaud and Osprey.
    http://www.youtube.com/watch?v=yuFwDm8t3IM (Just noticed that Slavi posted this as well-sorry)
    ===================
    A Note about Rave , Osprey and Skat: These boats use dual independent wands-that is, there is a wand controlling each main foil located in an ama(hull). The wands are not connected. So these dual independent wands not only control flying height, they also control most of the righting moment for the boat. They are so good at doing this that the only real limit on righting moment for one of these boats is the structural strength of the boat!
    The foils on moths and other monofoilers do not, in and of themselves, generate any righting moment.
    ===================

    ---Dr. Bradfields site: http://sites.google.com/site/hydrosail/HydroSail-Home

    ---Boatdesign.net thread(in "Multihulls") about Bradfields newest foiler the Osprey-1st flight just two weeks ago:

    http://www.boatdesign.net/forums/multihulls/18-osprey-multifoiler-dr-sam-bradfield-25343.html

    --- Mirabaud-Super Foiler- http://www.boatdesign.net/forums/sailboats/mirabaud-super-foiler-2011-a-37699.html
    Note: this boat started out as an 18' skiff and is now over 30' LOA. It uses dual midship (slightly forward of midship) wands connected to a single pushrod on the main foil.
    ===================
    See Bill Beavers Moth Paper below as well as the illustration of the Bieker foil set-up for the I-14:

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



    Pictures: Rave and Osprey foil system showing the planing wand on the Rave and a temporary round wand on the Osprey.
     

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  4. Rockdamned
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    Rockdamned Junior Member

    Thanks guys!!
    Besides the wand, that I think I've understand, I still can't really get the system of the tiller extension.

    I mean, is something mechanical or it has a small rope going straight down the rudder, guess inside it? I mean, maybe the moth has the whole thing already build together so they just "stick" (don't know the term in english) it on the stern, but how about the bigger? I've seen that the i14 (i.e.) has the rudder separated from the tiller (can you understand what I'm trying to say? - I'm sorry for my english). How does it work then?

    Thank you all!!
    Edoardo
     
  5. Jeremy Harris
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    Jeremy Harris Senior Member

    It looks to me as if the tiller has a twisting action to change rudder foil angle of attack and hence boat attitude. Seems to work a little like a motorcycle throttle, twist one way and the bow rises, twist the other and the bow falls, I think.
     
  6. Doug Lord
    Joined: May 2009
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    Doug Lord Flight Ready

    =============
    There are all kinds of ways to rig the rudder control. On some Moths and I-14's the whole rudder is pivoted, on others the foil alone is moved and on still others(Rave and Osprey a flap on the rudder foil is moved). Bradfield does not consider this adjustment something you constantly use-it is more along the lines of set it for the conditions you're in at the moment and then leave it alone. His system on the Osprey consists of two levers, one on each extension tiller connected to the flap pushrod by push-pull cables:

    Pictures,L to R: 1) top of rudder showing cables from each extension tiller, 2) lever mounted on extension tiller for setting flap,
    3) Osprey flying- if you look closely you can see the port wand angled further aft than the starboard wand. Thats because the port foil is developing more lift than the starboard foil. An illustration of the term "dual independent wands". Which is how righting moment is (mostly)generated on this boat.

    click on image:
     

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  7. Rockdamned
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    Rockdamned Junior Member

    Thank you all very much!!! I couldn't imagine I would find all this help and answer :)

    Now I got it...great!!!



    Btw
    Anyone knows about i14 building in Italy?
     
  8. daiquiri
    Joined: May 2004
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    Location: Italy (Garda Lake) and Croatia (Istria)

    daiquiri Engineering and Design

    Very neat, Doug. Thanks.
     

  9. Doug Lord
    Joined: May 2009
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    Location: Cocoa, Florida

    Doug Lord Flight Ready

    =========
    Slavi, thanks to you for the Moth sketch-I hadn't seen that anyplace and it is excellent!
     
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