Steve and Dave Clarks UFO

Discussion in 'Multihulls' started by Doug Lord, Aug 24, 2016.

  1. Doug Lord
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    Doug Lord Flight Ready

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    Many foilers have 80%(or so) of the load on the daggerboard foil(s)- but not for
    "wetted area minimization". For improved pitch control*......

    * coupled with lower foil loading per unit area on the rudder t-foil
     
  2. waynemarlow
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    waynemarlow Senior Member

    So what you are saying then is that it's not hydrodynamically that important to have the dagger board approx. Under the COE of the sail if we are using lifting foils, Isn't that contrary to almost all other modern designed sailing boats and contrary to probably the most advanced small foiler the moth .

    If we can move the foil foward then surely the wider distance between the now equally loaded foils the better for pitch control ?
     
  3. Doug Lord
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    Doug Lord Flight Ready

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    Not ideal for pitch control...... Bill Roberts designed the non-foiling Arc 21 catamaran with the daggerboard ahead of the mast-he called the concept "shared lift". http://aquarius-sail.com/catamarans/arc21/index.html
     
  4. waynemarlow
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    waynemarlow Senior Member

    But that design lasted for about 5 minutes and the rest of the worlds boats carried on as norm which sort of would indicate it was a failure.

    Certainly the boats I've played with the position of the dagger board, to get good balanced rudder feel then the mast rake and by consequence the COE has been critical to the feel.

    These guys are great designers and builders and I will bow to much greater knowledge but just curious to know the reasoning other than the obvious one of being able to lift the blade with the sail on the centre line.
     
  5. Skyak
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    Skyak Senior Member

    Those are not my words. What I said was that dagger placement can be moved and the sizes adjusted when there is value in doing so -and I see two good reasons to do so. Ask Steve or Dave and I suspect they will mention these.

    Main foil location forward is an improvement for pitch as is greater distance between lifting foils. If the dagger foil decreased in size that would be a negative.

    Some other notes -this UFO is not intended to compete in an open development class like moth -it will be one design or nothing so it is free to deviate from absolute optimal placement. Steve and Dave are more than capable of calculating the result and have the credibility with customers to break 'rules'. Also note that the moth dagger is angled forward but the UFO is vertical so the lifting foil location is not so different as the slots in the hulls.

    Doug, if it wasn't clear my comment about wetted surface reduction was for conventional vertical rudders & daggers -when have I ever given foiler advice to beginners?
     
  6. Doug Lord
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    Doug Lord Flight Ready

    Looks to me like the UFO does just what Roberts did: smaller daggerboard with a larger rudder.
     
  7. waynemarlow
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    waynemarlow Senior Member

    Ok but there must be negatives to have a smaller lifting foil at the front or is there ? Doug and Skyak this is a design forum, enlighten us with a bit more depth or are we into an area which you know little as with the rest of us
     
  8. Doug Lord
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    Doug Lord Flight Ready

    The larger foil forward with a trailing rudder foil is probably easier to control. The trailing rudder is set up to automatically develop lift and provide downforce when required.
    I've never designed, built or flown a foiler with less than 75% of the load on the forward main foils. The man that taught me so much, Dr. Sam, was convinced that the "airplane" configuration was the best configuration in terms of control.
    One of the early 4 foil configurations of Icarus had the smaller foils forward and 80% of the load on the larger aft foils.
    At least one Moth was designed with a small "cannard" forward. There's an English cat (C-Fly-see pix below) still under development for ocean foiling that uses small foils forward and larger aft.
    According to Ray Vellingas book several early Moths had between 63 and 75% of the load on the main foil.
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    Just guessing but I don't think the UFO has equal or more load on the rudder than on the main foil*. Steve and Dave made their presentation yesterday or today-check the "Foiling Week" topic in the aero-hydro forum on this site for updates in the days to come. http://www.foilingweek.com/pages/newport-r-i/tfw-forum-2016-newport-program/

    * a rough guestimate is 65%-70% on the main foil, 30-35% on the rudder in the picture above. And because of the small size, crew weight and sail pitching force will affect those figures a lot. And so will the point at which they are measured-before takeoff, at takeoff, or after takeoff. I think right at or just after takeoff is a good point as Dr. Sam did. A trailing rudder foil will gradually reduce vertical lift and begin to pull down at a certain point after takeoff as the boat speeds up and pitches down-automatically on many foilers. This gradually increases the mainfoil loading as well.

    C-Fly:

    [​IMG]
     
  9. Skyak
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    Skyak Senior Member

    Wayne,
    I'm just a state college engineer with one aerodynamics class audited, reasoning his way through the physics. Anyone that can prove the answer likely has a PHD in the subject -and I have seen them on the aero/hydro forum. I can give you my answer with some effort, but I can't or won't defend it.

    My answer -provided on "well you asked..." basis.

    Natural Stability means that when there is an error introduced the system returns to a new acceptable steady state. In the case of pitch stability of two foils, when speed rises, so does lift, but the weight of the boat is constant. To be N stable over speed you want the angle of attack to decline as speed increases and to increase when speed decreases. To do this you want the distance from the center of mass to be closer to the forward foil to give the aft foil a leverage advantage. Similarly for acceleration/deceleration stability, you want the center of mass to be as close to, or even forward of the foil...struggling here... (aft foil lift)*dist to mass>(forward foil lift)* dist to. In terms of natural stability the forward foil is the carrying foil, and the aft is the following foil. Forward foil size is determined by low speed liftoff needs. Aft foil size is determined by the amount of stability needed.

    Of course you can make up for a lack of natural stability with mechanisms, but those have limits and dynamics of their own. The less naturally stable the system is, the greater the loses from control apparatus. The minimum total is when the forward carries nearly all and the aft is only enough to correct stability but lift is always positive. 80/20 would indicate you never need more than 20% in the tail for control.

    Well that's my whack at it. I suggest we go over to the aero/hydro forum for more authoritative answers. There is a guy trying to add foiling to a laser II that needs to know.
     
  10. waynemarlow
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    waynemarlow Senior Member

    Interesting replies guys, thanks. But the foiling side is not really what I'm interested in although you have reinforced what I think is happening ( in a very uneducated way ).

    What I'm really interested in how the sideways loading which is now taken almost entirely by the daggerboard is now distributed to both rudder and daggerboard and what is that effect on say the rudder, many early aircraft tried the equalisation of forces on the lifting components but found that there were other induced problems such as tail planes fluttering and breaking up with high speed .
     
  11. Doug Lord
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    Doug Lord Flight Ready

    Ufo

    Looks to me like about 70% of the sideways load is on the daggerboard. Considering that the rudder has more area I would guess that the response and helm feel would be excellent? Sideways loading is a bit different but not wrong and certainly doesn't appear to me to be able to cause any problems whatsoever in sailing the boat.
     
  12. OzFred
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    OzFred Senior Member

    There are plenty of aircraft with the elevator control forward of the main wing, including current very high performance military aircraft. It's called a canard.

    Likely there are pros and cons to a forward elevator, just as there are for rear elevators. Generally the elevator or smaller wing is not designed to carry any significant load but to provide pitch trim and may produce a downward force just as readily as an upward force. That is changed a bit with a canard, which generally provides lift always.

    I expect the same pros and cons extend to hydrofoils.
     
  13. Doug Lord
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    Doug Lord Flight Ready

    Ufo

    Foiling Week presentation by Steve and Dave:
    http://www.boatdesign.net/forums/hydrodynamics-aerodynamics/foiling-week-50888-3.html#post785855

    Notes:
    1) "canard" foil configuration-wand controls forward foil flap.
    --
    2) takeoff in 8 knots of wind-boat speed after takeoff in that much wind: 15 knots.
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    3) foils upwind but technique driven.
    --
    4) unstayed but very unique rig-no shrouds.
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    5) waterline 8.75', beam 5.6'
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    6) 110lbs (conventional materials mostly)
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    7) price under $8000.
     
  14. Skyak
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    Skyak Senior Member

    Well that is not what your words mean and I already told Doug above that the horizontal can be shifted at the price of wetted surface. The rudder needs a thicker stall tolerant profile and it must be sized larger like 120% to 130% to provide control force. As I have said many times there is no right 'lead' value.

    And Wayne, before you crap on those answering your questions you need to go get some manners.
     

  15. Skyak
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    Skyak Senior Member


    Excellent video. You left out that they confirmed my answers in posts 15 and 20 (19 min) and the design focus is "not to win regattas but to keep flying". Another justification offered for the ~50/50 lift distribution -"more flapless lift". The flaps account for the majority of moth foil drag.

    Not to push the "told you so" too hard Doug but did you note the discussion about weight shift control? The kite board guys pushed pretty hard and Steve stated 'we tried, it doesn't work' and went on to less technical explanation than I gave (you need more degrees of freedom). That Opti will never (well there might be some condition that might exist briefly) foil stable without wand control. It's just not humanly possible.
     
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