Hydrofoil boats with downfoce wings

Discussion in 'Boat Design' started by sub_0, May 9, 2015.

  1. sub_0
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    sub_0 Junior Member

    Hy there

    And greetings from Croatia

    So my question goes like this and i please reply to anyone who can help with advice or opinion so big thanks in advance, IS IT POSSIBLE TO combine airfoil shape wing (wich will generate downforce insted of lift i was thinking of just inverting NACA profile) with hydrofoil ( lets assume our hydrofoil is surface piercing dihedral ). So idea is to impose downforce on lifting hydrofoil wich will deny it from breaching the surface for some speed range.Since this looks to me like a simple idea i was wondering why does there are no similar design online , em i missing something .........
     
  2. gonzo
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    gonzo Senior Member

    What are you trying to accomplish? If you want less lift, the angle of attack can be changed. What is the advantage of having more drag?
     
  3. sub_0
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    sub_0 Junior Member

    well there is ofc penalty of drag. I need constant amount of lift let say to lift 200 kg that is 1981 N , and for that at takeoff speed dihedral has wetted surface - lets name it Sto (at take off) , now as speed increases S(wetted area ) reduces until it reaches crittical area at max. speed lets name it Smax .Normaly there is rule of thumb that : vmax=2vto
    (according to Ray Vellinga) and that is rule for system that depend on changing AOA using e.g Shutt strut.However surface piercing can go faster . So wings are there to provide negative lift wich will submerge dihedral more and therefore allow it to reach even higher speeds.So in this system there is no device to change AOA whatsoever .......
     
  4. sub_0
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    sub_0 Junior Member

    let say something similar to CARL-XCH4 aldo i m not sure if it uses this eff i cant find any data on it beside simpler info. when it was built etc. (On picture there are wings and below it dihedral)
     
  5. messabout
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    messabout Senior Member

    Yes you are missing something. The lift of the hydrofoil is controllable by adjusting angle of attack, incorporating adjustable trim tabs, spoilers, or aileron like elements.

    Yes, an inverted wing will generate down force. The degree of down force can be regulated in the same way as on the hydrofoil. An axiom of physics is that anything that creates lift (or force in any direction) also creates drag. A wing is redundant. It is not necessary for the purpose of controlling pitch angle The foil control system already does that.
     
  6. kerosene
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    kerosene Senior Member

    I think his goal is to create a system that is self balancing with locked angle of attack. I as the speed increases to certain point the air wing down force starts acting and keeps to total lifting force constant regardless of speed changes.
    I am might assume wrong.
    And I don't think the system would work. Both forces would grow at squared speed (I think) and there wouldn't be any reason for the airfoil to "catch up" with the hydrofoil.
     
  7. sub_0
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    sub_0 Junior Member

    yes kerosene that is my point , let assume this you have front foil height finder , and rear dihedral so bla bal bal.....at some speed you find your boat at 0 angle of attack flying straight and level right??? -so now dihedral start ascending around front foil until it breaches the surface right??? so this wings are not for pitch control but for as u say kerosene self balancing locked angle of attack .....and i think that with this you my go few mph faster ...
     
  8. sub_0
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    sub_0 Junior Member

    the downforce of wing will not catch up hydrofoil force but it ll slightly submerge dihedral allowing it to go faster ...(thats my theory)
     
  9. sub_0
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    sub_0 Junior Member

    so wings are onlie for increasing max .speed
     
  10. Doug Lord
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    Doug Lord Flight Ready

    Welcome to the forum! I'm going to test a surface piercing T-foil with a center section that is an inverted asymmetric foil: the idea is that as the boat speeds up it pitches down reducing the lift on the foil and allowing the center section to develop down force.
    The point is to replace a wand controlled main foil with a foil having no moving parts. It will be tested on a large model, first as a surface piercing T-foil, then with the inverted asymmetric center section bordered by "fences" :
    More here, starting with post 2024: http://www.boatdesign.net/forums/mu...f-righting-trimaran-test-model-36058-135.html

    Note: the last three pictures show a completed "Batfoil" which is a surface piercing T-foil with experimental intrinsic 15 degree flaps added to each tip to improve low speed takeoff-the flaps rise above the surface as the boat speeds up ,reducing drag. This same foil will be modified to have an inverted asymmetric section to create downforce as the boat speeds up after the initial tests are done. The plan is for the foil to work similarly to a wand equipped foil but with no moving parts.
     

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  11. Doug Lord
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    Doug Lord Flight Ready

    ------------------------
    The Rave, Osprey, Skat and Hobie Trifoiler were all designed to use wand/"feeler" controlled main foils which allowed the foil system to develop all the righting moment for the boats with the crew sitting in the center of the boat. The windward foil would automatically develop downforce. The power of the foils used in this manner was limited only by the structural strength of the boat. These boats were all square to oversquare platforms and that reduced the loading on the mainfoils.
    The Hobie Trifoiler used long "feelers" sticking out in front of the boat on each side to change the lift(downforce) of the main foils. The Rave, Osprey and SKAT used wands to move flaps attached to each main foil to change the amount of lift(or downforce) the foils developed.

    Rave, Osprey, Hobie Trifoiler, 40' SKAT :
     

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  12. sub_0
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    sub_0 Junior Member

    first of all thx Doug and rest of u for advices and help......These are submerged foils that use variable Cl devices some e.g are wands as above and shutt strut (also above 1st row right pic).-correct me if i m wrong ....However i m at this point more interested in surface piercing hydrofoils cuz they are more robust aldo they have disadvanteges ofc (ventilation ,drag etc.) Since "submerged foils are constant area/variable incidence and surface piercer are variable area/constant incidence" - i m quoting mister Tom Speer here -Having that in mind i m having hard time imagining surface piercer with variable incidence device ,em i terribly wrong here???? ...................btw nice idea with that T-foil above so u r in the end planing to get constant amount of lift regardless of speed( beacouse downforce "catches" up with lift and "eats" same portion of it once the lifting area has been reduced due to breaching) .....ventilation could be problem since u have "ventilation sensitive lifting area" let me put it in that way....
     
  13. tspeer
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    tspeer Senior Member

    Yes. One example is the Bruce foil, which can work on either the leeward side, lifting up, or the windward side, lifting down.

    Dr. J. G. Hagedoorn's hinged foil is an improvement on the Bruce foil. It varies its dihedral angle to increase the down force as the boat heels.

    The hapa is a similar concept, with a free-flying/floating foil that rides to windward with a cable to the masthead.
     
  14. Doug Lord
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    Doug Lord Flight Ready

    -------------------------------
    Thanks.The surface piercing T-foils have several potential problems -some of which may be solved in a canting application. They may have more advantages than disadvantages but that remains to be seen. They may or may not be more suitable for model catamaran hydrofoil applications-again, that remains to be determined. The "upside-down asymmetric center section" applied to a surface piercing T-foil was specifically conceived of to replace a wand controlled T-foil acting as a main foil in a bi-foiler configuration on a trimaran. Not sure it would have other applications but it will be fun to play with it-especially on a 20 footer if I get the chance.
     

  15. tspeer
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    tspeer Senior Member

    A variable incidence/variable lift surface piercing foil can be implemented in a variety of ways. All of the methods used to adjust the lift of a fully submerged hydrofoil can be used on surface piercing foils.

    One way is to physically rotate the foil about a horizontal axis, the same way as is done for L foils. One of the first examples of this was the Monitor.

    Perhaps the simplest method of changing the incidence of a surface piercing foil is to rotate the entire boat. A fully submerged aft foil can be used to adjust the pitch trim and thereby affect the angle of attack of the main foil(s). Another way of accomplishing the same thing is to use a surface-piercing canard foil that results in the bow riding at a essentially a constant height. As the boat goes faster and the main foil lifts the boat, the boat pivots about the canard foil and rotates to a more bow-down pitch attitude.

    The HMCS Bras d'Or (FHE 400) used rotating tips to control roll, but the same control surfaces could also be used symmetrically to vary the vertical lift. See attached paper.

    Hinged flaps, such are used by the Moth sailboats, could also be used with surface piercing foils.

    The Savitsky flap (see second attachment) is a flap on an angled surface piercing hydrofoil that also acts as the surface sensor itself. Note that for the flap to work as described, the spring would need to deflect the flap in the negative direction, reducing the lift. As more of the flap is immersed, the negative deflection would be reduced, resulting in a positive change to the lift and raising the boat. The bobweight incorporated into the flap control linkage acts like an accelerometer, while the damper reacts to the rate of change of the flap. So the dynamics of a purely mechanical Savitsky flap control system can be quite sophisticated.
     

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