Sailing Foiler Design: Foil Assist and Full Flying

Discussion in 'Hydrodynamics and Aerodynamics' started by Doug Lord, Dec 9, 2011.

  1. Baltic Bandit

    Baltic Bandit Previous Member

    200 hrs is what Nathan put in over 3 weeks Doug. And regardless of how many years of you reading stuff, you have no sailed a Moth, and you have not sailed a foiling cat (the rave is a tri) much less one that uses the "V" foils

    Which means you are hardly in a place to suggest that the stability between the two is the same.

    If they "rivaled" the wand based systems in stability, then it would stand to reason that one of the two best wand foiler sailors in the world would have been able to repeat that stability on the AC 72.

    He was not able to do that. which suggests that the two systems are NOT comparable.

    If you can present us with some FEA/Motion dynamics models that show how this is the case, or some Differntial Equations that show similar magnitudes of control feedback, you might have a case to make.

    But so far I have never ever seen you show any original mathematics to back up your claims. Just math and spreadsheets other people have given you. I suspect you do not even have a STEM based degree , which puts your how "15 years of studying" into the shallow end of the pool.

    You should not call people liars when you cannot back up your claims
     
  2. Baltic Bandit

    Baltic Bandit Previous Member

    They are better, but they are evolutionary, and if you look at a video interview with Nathan, and the "jitter damping" system the OTUSA had on board Its clear that the AC72s had "active control".

    On Groupama, the "active control" is the trimmer.. The trimmer is moving the wing very aggressively to keep a steady state power input (as opposed to seeking to max the power input).. This requires a sailor of high skill.


    And for Doug to start accusing people of Lying when he cannot back up his claims and when the observable facts suggest the contrary - and for the moderator to allow that, well that's a touch much


    And this is not a "revolution" precisely because of your definition. there isn't a major change in direction here, just iterative refinement. Odds are the next C Class event will NOT see J boards but instead the kind of boards you are seeing in the A class. Precisely because of the drag tradeoffs That means this is evolutionary not revvolutionary
     
  3. Boat Design Net Moderator
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    Boat Design Net Moderator Moderator

    If the motivation is to fight with someone or continue with personal attacks/insults, please take the fighting somewhere else and don't use the forums here for this. That's not what the forums here are for. Thanks.
     
  4. tspeer
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    tspeer Senior Member

    This is false. The curved part of the vertical foil produces essentially the same lift as it rises. This is necessary to counter the side force from the sail rig, which does not change as the height changes.

    Because the horizontal lift is constant but the vertical area is reduced as the boat rises, the leeway angle increases. It is the coupling of leeway with heave that is exploited by the L foil to provide vertical static stability.

    The dihedral angle of the horizontal wing is set so that the angle of attack of the wing is reduced as the leeway angle increases. This satisfies the static stability condition that the vertical lift decrease as the heave increases.

    Because the same horizontal lift is produced over a reduced vertical span, the sideways wash in the wake is also greater and the trailing vortices are more intense. This causes a coupling with the horizontal wing that increases the vertical lift, because the horizontal wing acts as a winglet for the vertical part of the foil (and vice versa). The dihedral angle required for vertical stability is greater than what one might expect by looking at the wing alone because it must overcome this wake-coupled influence. The result is there is a range of dihedral angles that provide positive vertical stability and a range of dihedral angles that are destabilizing in heave because of the coupling with the shed vorticity of the vertical part of the foil.

    Although there are times when the foil tip has broached the surface, this is not the normal mechanism for providing heave stability in L foils. The best performance is obtained with the hull just above the wavetops and the wing submerged well below the surface. The leeway-modulated heave stability is still effective in this condition, and the induced drag is minimized.

    Canting the foil inboard has the effect of increasing the dihedral angle of the wing, which enhances the heave stability. The vertical lift is spread over a greater span because the curved part of the foil is oriented to provide more vertical component of the force. This reduces the induced drag due to the vertical force. However, the induced drag of the horizontal force would be increased, so cant is typically used off the wind when the side force from the rig is less and the side force produced by the foils is correspondingly less. The foils still have to support the weight of the boat, so the vertical force is not lessened, but the relative proportions of vertical and horizontal force are changed, making the canted foil better suited to the operating condition. Cant allows the leeway-modulated heave stability to be increased an an acceptable penalty in the induced drag because of the lower side force and the higher speeds, which also reduce induced drag.

    Upwind, the foils are canted to their vertical position to minimize the induced drag from the high side force and reduced speeds. The reduction in horizontal wing dihedral angle with vertical cant impacts the leeway-modulated heave stability, which is why it is much more difficult to achieve stable flight upwind than downwind. The crew had to be more active in trimming the wing and foil to deal with the reduction in natural heave stability, which was very hard on the grinders when flyng upwind.

    Whether canted or upright, the mechanism for providing natural heave stability was still the coupling between heave and leeway, which led to a reduction in vertical lift because of the designed-in coupling between leeway and vertical lift by virtue of the wing dihedral. Reduction in horizontal/vertical-lifting area due to the foil tip broaching the surface was not part of this primary source of heave stability. Allowing the tip to broach the surface had big penalties in terms of induced drag and increased leeway due to insufficient vertical span.
     
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  5. Baltic Bandit

    Baltic Bandit Previous Member

    TSpeer - doesn't canting inboard also allow for creating a symmetric steady state dihedral arrangement (ie symmetry in the dihedral of the foils that makes it easier to have symmetric stability functions?)

    Given that the boards are fixed is it correct to say that the dihedral angle itself changes? I know what you are getting at, but isn't the more accurate way of describing it that with the board more vertical, the dihedral symmetry decreases and that's what makes the mode less stable?
     
  6. Doug Lord
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    Doug Lord Flight Ready

    AC foil design

    ===========================
    Thanks for straightening me out, Tom. I appreciate the help.
    If I understand you correctly, the curved, angled daggerboard portion of the foil does produce a component of vertical lift-but the magnitude of that vertical lift doesn't reduce as the foil lifts out of the water?
     
  7. Baltic Bandit

    Baltic Bandit Previous Member

    No Doug that's not what he's saying. He's saying that's not the controlling factor in the heave control of the dihedral. Rather what's controlling the ride height stability is that as the boat lifts higher out of he water, you get more leeway.

    More leeway generates more spanwise flow and that in turn reduces lift which done right, results in a semi-stable ride. And its one of the reasons your foil design in your MPX is likely to have difficulties with stability
     
  8. Doug Lord
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    Doug Lord Flight Ready

    --------------------
    Wrong. The ama foil on the MPX is not the primary foil for lateral resistance. The daggerboard and the main foil (when developing downforce) take care of lateral resistance. Probably very little to no leeway impact on the ama foil.
     
    Last edited: Dec 27, 2013
  9. Baltic Bandit

    Baltic Bandit Previous Member

    Doug you don't seem to understand the comment. Your ama foils are supposedly dihedrals, but you have massive washout on one side and washin on the other. And regardless of whether they are designed for lateral resistance or not, they are subject to the same lateral flows caused by leeway as they rise out of the water. and the washed-out tips will exacerbate the effect of the differences caused by these flows

    Basically you sketched up the foils without understanding the forces involved
     
  10. Doug Lord
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    Doug Lord Flight Ready

    There is zero washout on my foils.
     
  11. Baltic Bandit

    Baltic Bandit Previous Member

    So then who's foils have you been posting pictures of? cuz the foils you have photos of have a droop tip and washout in that tip.
     
  12. tspeer
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    tspeer Senior Member

    The vertical component from a curved foil would increase as the boat flies higher out of the water. The horizontal component has to remain the same because of the side load from the sail rig. But the foil in the water would be more horizontal, so the ratio of vertical lift to horizontal lift would be increasing.

    Think of an equivalent straight diagonal foil that runs from the tip of the curved foil to the waterline. As the boat rises, that foil becomes more canted. The more it's canted, the more vertical force you get for the same side force.
     
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  13. Doug Lord
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    Doug Lord Flight Ready

    ==========
    Thanks again, Tom. Have a great Christmas!
     
  14. Doug Lord
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    Doug Lord Flight Ready

    Using two uptip foils to foil when leeway is low

    This is an interesting article about some experiments Dario Valenza has carried out with experimental "uptip" foils on an A Cat.
    As I understand it he says that using both uptip mainfoils downwind allows foiling when leeway is very low and in lighter wind. He says, basically, that you then have two "V" foils and the heave stability is gained thru the inboard tip breaching as opposed to leeway coupling as altitude control:
    http://carbonicboats.blogspot.com/
     

  15. Doug Lord
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    Doug Lord Flight Ready

    TNZ type foil

    Based on part of what Tom said and on what Dario says in the blog linked above, it seems evident to me( but I'd like to hear Toms opinion) that if a curved daggerboard + uptip foil was used in an application where leeway played a much smaller role(say on a trimaran with a center daggerboard) that leeway coupling might not be an effective altitude control and that the curved foil might act as a surface piercing foil as well as the inboard foil tip-both providing altitude control by reducing their vertical lifting surfaces as the foil rises?
     

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