[Public-List] america cup

Wed May 31 08:36:59 PDT 2017

America’s Cup has come a long way from yacht racing…

On 2017-05-31, 11:35 AM, "Public-List on behalf of Mike Meinhold via Public-List" <public-list-bounces at lists.alberg30.org on behalf of public-list at lists.alberg30.org> wrote:

    Jim
     I agree that it's all about trimming foils, and all the helmsman's
    responsibility - but like so much of the America's Cup - that's rule-driven.

    Of course the goal of all the foil geometry, position , and potential
    dynamic control is identical to the Alberg 30's keel and rudder - balance
    hydrodynamic lift and drag against aerodynamic lift and drag with minimal
    drag.  The foils add a much higher vertical component to lift the boat and
    reduce the drag. As you say, when you no longer are using hydrostatic
    balance, you must get pitch balance from the foils also.

    A simpler picture is a pair of horizontal foils that cant with heel, so
    they always lift against gravity, and a a pair of vertical foils that cant
    with heel and leeway, so their lift and drag matches the aerofoiils (sails)
    lift and drag.    L-Foils are a compromise to stay within a certain number
    of moving foils.  The L-Foils use a single foil to get vertical and
    transverse lift.

    The simpler picture allows you to separate the "flying" function from the
    optimal forward-speed function. I think you would ideally have separate
    controls for these two goals.

    The AC 42's can't do this, so helm must also fly!

    I would like to see these boats in some bigger waves and see how they
    control them!

    Mike

    On Wed, May 31, 2017 at 10:11 AM, Jim Mennucci via Public-List <
    public-list at lists.alberg30.org> wrote:

    > Can anyone add to my understanding of how the hydraulically driven
    > hydrofoils work on the Americas cup 42 footers now racing in Bemuda--
    > here's what I think i'm seeing:
    >
    > - In a way its kind a cool--going 30+ knots up and down wind doesn't
    > require much sail trim...hydrofoil trim is another matter.  Talk about
    > changing sail boat racing as we all understand it.  Trophy goes to team
    > that is best at hydrofoil control, in fact hydrofoil control is the only
    > area of boat design the is somewhat left to the syndicates to control on
    > their own. .  Optimizing hydrofoil control maximizes speed.
    >
    > - unlike the 72 footers, the 40 footers will use hand controls i.e., no
    > closed-loop feed-back controls for the hydrofoils--this is what I wonder
    > about?  The hydraulic directional control valves used to pivot the foils
    > use some sort of electrically controlled linear actuator to open and close
    > flow to the hydraulic actuators,  It would be easy to add some feed back
    > control to the electrical part of the valve and if they don't that's good
    > because of the additional skill needed to manually maintain stability
    >
    > - article I read says stored energy (accumulators) are not allowed and the
    > hydraulics must be provided by hand pump--hence they're always pumping
    > (like maniacs) to have fluid under pressure (must be a relief valve to
    > regulate pressure)
    >
    > - the article talks about 3 hydrofoil controls: Cant, lift and pitch are
    > the 3 names used.in the article.
    >        - It sounds like cant angle corresponds to roll which is used to
    > add/control righting moment. Canting the wing off vertical tilts the
    > horizontal part of the wing which should result in some loss in lift making
    > an adjustment to the angle of attack to rebalance the lift--this is where
    > feedback control would be nice but making the helmsmen do the adjustments
    > in a manner that maintains foil stability adds old-fashioned skill to the
    > mix.  Thoughts?   pivoting the hydrofoil outboard adds righting moment
    >        -  lift control would pivot the hydrofoil in the pitch plane to
    > change angle of attack
    >        - pitch control to me is the same as lift except its listed as a
    > separate function.  So I wonder if the dagger board and the rudder foils
    > work in concert to change the pitch of the boat--much like bow and stern
    > planes on a submarine
    > - looks like linear hydraulic actuators are used to control 2 rotational
    > degrees of freedom on the dagger board foils and a single actuator to pitch
    > the rudder foils.
    > - the foil controls are built into the helm wheel and its looks like they
    > run the system open circuit i.e., no feedback control.  They hit buttons
    > built into the helm to open the directional control valves.  So the
    > helmsmen is also the foil trimmer.
    >
    > any insight, thoughts appreciated
    >
    > Jim Mennucci
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