High Performance MPX Foil/Self-righting Trimaran-The Test Model

Discussion in 'Multihulls' started by Doug Lord, Dec 28, 2010.

  1. Doug Lord
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    Doug Lord Flight Ready

    MPX Testing and Development

    I've seen the main foil lift the main hull of this boat and my first model foiler used the Bradfield system foil configuration and a similar(but different) wand set-up to Dr. Sams on the Rave. The cool thing about the wand + flap is that the geometry of the foil changes automatically to maximum lift to get the boat out of the of water then goes into "neutral reserve" to keep the boat at a set flight altitude.
    It's brilliantly simple and works really well.
    So Friday I was trying to figure out how I could get a foil based on UptiP geometry to behave like a wand equipped foil but with no moving parts, no leeway and very low speed. The idea is to have maximum lift to get to flight altitude and then have the flap drag disappear. I came up with the i-flap which is simply a portion of the ama foil modified to include a 15 degree flap. I got so excited by the potential of this I started Saturday to modify both ama foils to be ready for Thursdays Test session.
    The basic concept is to add an integral molded-in large flap* to the relatively horizontal portion of the ama UptiP foil. If it works on the model it would be likely the scaled up version would work as well-at least be worth a test. No application on UptiP foils used as a single main foil on a catamaran.
    The way I think it may work is to create maximum lift at very low speeds so that the ama would lift as early as possible reducing drag and helping to build speed to get the main hull flying.
    As it lifts(see sketch below), portions of the tip break the surface and lift from the i-flap replaced by "normal" foil lift. On the first examples the flap portion of the foil may be reduced in area by cutting along a hinge line and then cutting fore and aft slits to allow the individual segments to bend which would reduce the drag from the segment deployed as a flap but retain the lift area. If it is determined that lift area can also be reduced without removing any early takeoff advantage then the segments can simply be removed. This is such an easy way to experiment-- any changes required are a piece of cake-including going back to "normal".
    *integral flap = i-flap
    Again,the idea is to reduce the speed at which the ama foil will lift in order to increase boat speed, resulting in an earlier takeoff of the main hull. The problem in designing an ama foil that doesn't have(or need) rake adjustment is in working out the speed so that the ama foil takes off early but doesn't have too much lift when the boat is going fast.
    The i-flap may work in much the same way a wand + T-foil works, but with no moving parts-we'll see.
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    See posts 1327 and 1328 for the modifications made to one of the ama UptiP foils and the reasoning behind it.
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    Pictures: 1) rough sketch of the concept showing how flap portion will emerge above the waterline, giving a similar performance to a foil equipped with a wand except that the i-flap has no moving parts. Also, leeway coupling is not necessary for this to work, 2) port ama foil roughed in,3) Starboard ama foil tip view 4) starboard ama foil roughed in:
    click-
     

    Attached Files:

  2. Rosebud

    Rosebud Previous Member

    redreuben,

    The modification suggests that the builder realizes that there is an inherent design problem with the current set-up. Unfortunately, it appears that he is attempting a solution to the problem that is more consistent with "L" foils, as he appears to be disregarding the known relationship that exists between the chord widths of the downward, and upward components of "V" foils.

    Therefore, for the builder to solve the issue of insufficient lift, he needs to increase the chord widths of both downward and upward components (as well as the transitional curve).

    By increasing the chord width of only the upward pointing portion of the "V" foil, he is creating a dynamic pressure instability between the two lifting surfaces. Additionally, each component of the "V" foil will have different stall speeds/characteristics, which will cause additional dynamic instability.

    Regards,

    -Rosebud
    *Bladerider Moth
    *Foiling A-Cat (not class legal)
     
  3. R.Finn
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    R.Finn Junior Member

    In this case, how is your design an improvement on the basic AC 72 platform? Seems like early take off was a goal of your design. Also, do you believe the AC 72 would be a better design with a central lifting foil?
     
  4. Doug Lord
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    Doug Lord Flight Ready

    MPX Testing and Development

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    This boat is intended to be an improvement on "normal" trimaran design. Without the mainfoil neither the model or full size version would be capable of flying the main hull in light air. That's why you don't see any small tri's with substantially oversquare platforms: an oversquare platform w/o foils on the main hull would likely be dangerous and certainly not fast(unless the foils were on the amas like Hydroptere). And that's why this concept has the potential to produce a fast boat that's easy to sail and will fly the main hull in light air: the oversquare platform gives it the power to carry a large sail area and the foils give it the pitch and roll stability to handle it. This concept has zero application to a catamaran platform, in my opinion(it requires an oversquare platform), but a cat(Happy Feet) was built with a bifoiler arrangement designed so that the foils could move side to side.
    I've lost track of what the final verdict was on it's performance. The one advantage it shares with the Fire Arrow(to a small extent) is that the wand controlled mainfoil would hold an angle of heel, producing downforce when required. Unfortunately, it probably wasn't wide enough for downforce to work real well-but I don't know for sure.

    "Happy Feet"--pictures from Arnie Duckworth
     

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    Last edited: Jul 19, 2014
  5. Rosebud

    Rosebud Previous Member

    Mr. Lord,

    Regarding #1 and #2 below:
    #1 There is a difference between a "discussion" and an "explanation". Just because you state your "explanation" of events does not mean that it was "discussed in detail" as you suggest!!!

    #2 This statement is completely untrue. I currently have in my stable 5 RC multihulls, 3 foiling and 2 traditional. I regularly take my boats out in winds far exceeding those in your video, and have stuffed the bows many, many times without pitchpolling. I will say that the heavier the model, the more likely the recovery, as my prototype model is quite heavy (7.9kg), and recovers more often than not.

    No matter how you try to spin it, it is clear to anybody who watches the video of your 2nd test sail that EVERY TIME the main hull flies, the nose comes up and the boat stalls out uncontrollably.

    I am confident that you will get many of these issues sorted out. However, with the lack of buoyancy in the aft portion of your floats, I believe that this model will not achieve stable flight for any sustained distance.


    Regards,

    -Rosebud

     
  6. Doug Lord
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    Doug Lord Flight Ready

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    Man, that is just nonsense!
     
  7. R.Finn
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    R.Finn Junior Member

    Can you clarify what part of Rosebud's statements are nonsense? A lot was said.
     
  8. Doug Lord
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    Doug Lord Flight Ready

    -------
    Sure: the part I quoted.
     
  9. R.Finn
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    R.Finn Junior Member

    "Additionally, each component of the "V" foil will have different stall speeds/characteristics"

    So this has no merit based on your updated design?
     
  10. Doug Lord
    Joined: May 2009
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    Doug Lord Flight Ready

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    No merit at all-almost very single airplane wing is designed with "washout" a change in the angle of incidence of the wing root to the tip where the tip has a lower angle of incidence in order to allow the inboard portions of the wing to stall first-to minimize the chances of the plane rolling over in a stall. In other words, the stall characteristics of the wing are different inboard and outboard and change along the span.
    When my foil is right the i-flap portion will only be significantly immersed at takeoff. Initially it is large to allow me to get the size right testing it-I'm guessing it will trim out similarly to the sketch above.
    An UptiP foil already has differences along the span from the more vertical portion that develops some lateral resistance along with a little vertical lift to the more horizontal portion of the foil. Raking such a board changes the angle of incidence, primarily, on the more horizontal part of the foil which is different than the angle of incidence of the more vertical portion of the foil. To change the angle of incidence of the more vertical portion of the foil it has to be twisted( the leading edge moved port or stb with respect to the trailing edge)-and that doesn't change the AOI of the more horizontal part.

    see the experimental foil from Dario Valenza below. Rendering by Dario Valenza. :
    --Be sure to click on this image and look very closely at the junction between the vertical and horizontal elements of the foil-
     

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  11. Doug Lord
    Joined: May 2009
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    Doug Lord Flight Ready

    MPX Testing and Development

    ------------------
    I presume you meant buoyancy. If so, how would buoyancy in the aft portion of the floats affect stable flight on hydrofoils?
     
  12. Doug Lord
    Joined: May 2009
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    Doug Lord Flight Ready

    MPX Testing and Development

    This is the Exocet 19 trimaran, by Perspective Design currently under construction in France. It is slightly similar to the Fire Arrow in that both designs use UptiP foils on the amas. But the Exocet also uses a rudder t-foil on each ama. The Exocet 19 is the only full size trimaran to use UptiP foils on the amas-but it sure won't be the last-UptiP foils are a natural for use on trimarans. Should be real fast once the main hull is flying:

    Picture from the Perspective Design Website:
     

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  13. oldsailor7
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    oldsailor7 Senior Member

    As a full size foiling Tri that Exocet really looks the goods. :cool:
     
  14. Doug Lord
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    Doug Lord Flight Ready

    It sure does!
     

  15. Doug Lord
    Joined: May 2009
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    Location: Melbourne, Florida

    Doug Lord Flight Ready

    MPX Testing and Development

    This is the last major fill-sanding and minor fills left.(left picture)
    UPDATE: 7/20/14- picture of the finished and primed foils:

    click-
     

    Attached Files:

    Last edited: Jul 20, 2014
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