Morphing foils concept

Discussion in 'Boat Design' started by SeaSpark, Apr 30, 2006.

  1. SeaSpark
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    SeaSpark -

    The idea of morphing wings has been around for some time in the aircraft design world. One example: http://www.compositesworld.com/hpc/issues/2004/September/554

    Trying to translate the possibilities of a morphing foil to yacht design the following idea arose:

    A boat with just one vertical and horizontal foil. By morphing these foils it should be possible to balance all the forces working on the boat. When dead in the water the boat could "flap" its wings to stay upright.

    I assume the shape of foils (including sail) can be altered in any required direction. In the aircraft industry more than one company is working on the development of wings like this. No human could control this craft, it will have to rely on "sail by wire" technology.

    Imagine someone with no sailing experience at all stepping in something like this
    and sailing away at ..... knots just like he was driving a car.
     

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  2. SailDesign
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    SailDesign Old Phart! Stay upwind..

    SeaSpark,
    If you build a boat like that (if you can...) then you would change the sport forever, and where would that leave us poor elitist snobs who actually understand all the arcane reasons why boats sail?
    Have pity, man!
     
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  3. SeaSpark
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    SeaSpark -

    Changing sports

    Best compliment in my life.

    Why not change the trans-port world also?
     
  4. tspeer
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    tspeer Senior Member

    You may be able to balance forces, but you can't balance the moments in this configuration. For example, a cambered lifting surface like a sail produces not only a lift force but also a moment the spanwise axis - a yawing moment in this case - even when the lift is zero. There's nothing in this configuration to trim out these yawing moments.

    In principle, you can twist the sail and foil so as to cancel the heeling moments while still providing a net lift. The lower portion of the sail is driving, while the upper part of the sail is retarding the boat. The driving portion is larger because the retarding portion has a greater moment arm - more leverage.

    However, the effective span is greatly reduced so that the drag from producing the lift in this manner is very high. It's possible to calculate the optimal span loading for this case so as to produce the minimum drag while still balancing the craft. For example, if one assumes there is zero lift on the rig for the bottom 5% of its height (accounting for the hull and the clearance to the water), the Oswald effiency factor is 0.105. This compares to 1.21 for a rig of the same height and gap, producing the same lift, but with a span loading that is optimized for minimum drag without the heeling moment constraint, or 1.10 for a sail shaped like a sailboard rig. So the lift-induced drag of the proposed concept is an order of magnitude higher, equivalent to a rig that is only 30% as tall. And this is the best you can do without some other means of providing righting moment.

    And although such a rig can be balanced for a given operating condition, the moments are unstable and any change requires constant adjustment of the twist. It requires considerable power to achieve this, even if the computational capability is available to the control system. I doubt the power to actuate this morphing of the rig and foil system has been considered in the design.

    This is a great example of the pretty picture school of design that lacks any understanding of why it's necessary to define the requirements for a specific mission and then engineer all aspects of the craft to meet those requirements.
     
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  5. Doug Lord

    Doug Lord Guest

    Imagination!

    I think the imagination shown by Sea Spark is a great contribution regardless of what " ..school of design " it is alleged to represent.
     
  6. SailDesign
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    SailDesign Old Phart! Stay upwind..

    Doug,
    The problem is that you are right - there is a lot of imagination shown in SeaSpark's pic.
    The problem is that Tom is also right - there are some practical issues that do not yet seem to have been resolved. The word "yet" is the important one there. Let this onje simmer for a while, and it could be interesting. It has been thought of before, nad will doubtless be thought of again, but every new idea is possibly the one that will make it work this time.
    Steve "feeling optimistic today..."
     
  7. Vega
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    Vega Senior Member

    Very small changes in the airfoil of an airplane wing have big effects in lift and drag, therefore the wing they are talking about has only to suffer very small modifications of shape. Not so with a sail, that has to modify its shape a lot.

    Perhaps that is applicable in the shape of masts, in sail racing boats.
     
  8. SeaSpark
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    SeaSpark -

    Morphing hull

    The first application of morphing materials could be in the aft sections of a conventional hull.

    The hull shape could be optimized for upwind/downwind performance or for displacement/planing mode. The last could also work for power boats. Use in masts is more difficult, this is a highly stressed part of a boat.
     
  9. Vega
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    Vega Senior Member

    Hum, the wings of an airplane are also highly stressed parts.

    But I agree with you. There are some areas in the aft section of a hull where small differences in shape can have noticeable results on the control and performance of a sailboat, especially in racing.
     
  10. SeaSpark
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    SeaSpark -

    Sky Ski

    Tom, i am sure you have heard of the Sky Ski www.skyski.com Below you find some pictures from a surfboard by Rush Randle equipped with one.

    Their original application was in water ski's. The "moment in the spanwise axis" is the single largest force on a water ski. The Sky Ski only needs a very small foil to compensate for this moment. Quote of my own: "I assume the shape of foils (including sail) can be altered in any required direction." Perhaps a shape is possible to compensate for the yawing moment. Have to admit many spaghetti like shapes arose when i was thinking about this.

    This idea was presented as a concept. When trying to find new applications for new materials it is important to think out of the box. Many times impossible idea's pop up in this process, these are valuable if you want to come up with something really new.

    Jeroen
     

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  11. SeaSpark
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    SeaSpark -

  12. PI Design
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    PI Design Senior Member

    Sails that flatten themselves as the wind picks up?
     
  13. SeaSpark
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    SeaSpark -

    Shape changing

    Sails could flatten, shrink (reef), bend to windward to provide lift or to the opposite direction to loose some air.

    Same for the underwater foils.

    Know all of this sounds weird, it's a concept.

    When the shape changing is done hydraulically perhaps some forces working on the contraption can be used to generate hydraulic power.

    Btw. Wings (wingroots) are highly stressed parts on planes, flaps (where morphing material already have been applied in experimental models) are less stressed.
     
  14. tspeer
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    tspeer Senior Member

    OK, let's say that material properties are no problem - you can morph into any shape you want, and the material still has comparable stiffness to existing composites. Let's further say that the control system and the associated actuation power are not a problem. But you still have to obey conservation of mass. And you have to satisfy the requirements for dynamic equilibrium and aero/hydrodynamic performance.

    Given the perfect morphing capability, what would you do with the shape of the boat and foils that is different from what you'd do with a fixed shape?

    I haven't seen anyone saying how they would use morphing to actually improve the performance of the boat. Just some vague ideas that morphing in some way might be a good idea in some way.

    The concept that kicked off this thread had no means of maintaining equilibrium - it would fall over in an instant. Morphing might have been used to control twist of the wing, but even if the wing were twisted so as to produce zero heeling moment, its performance would be way less than a conventional rig. And the craft would have fallen over forwards from the drive of the rig. No amount of tinkering with the shape via morphing would have changed the fact that the whole configuration was fundamentally flawed.

    In order for morphing to be useful, you need to have a situation in which the craft has to operate at different conditions, such that optimizing the shape for any one operating point makes it less suitable for the other operating points, driving a fixed shape to be a compromise to cover the whole range. Morphing gives the designer the ability to optimize at each operating point separately instead of having to consider them all collectively.

    A good example of the use of morphing is variable sweep in aircraft. At low speeds, it's important to maximize the span, and there's no wave drag so sweep is not required. At supersonic speeds, the induced drag is small so span is not as important, but sweep is needed to reduce wave drag. Airplanes like the SU-17, F-111, B-1 and TU-22 morph their wings to optimize performance from subsonic to supersonic speeds.

    The Mission Adaptive Wing varied its leading and trailing edge camber to increase maximum lift, center the minimum profile drag at the operating lift coefficient, and to avoid the discontinuities in the surface contour associated with conventional flaps. However, conventional approaches, such as the X-29's discrete variable camber (see fig 3 of NASA TM 100413) does much the same thing using hinged surfaces.

    Sailors already use morphing to optimize performance. That's what vangs/kicking straps, Cunninghams, outhauls and Barber haulers are all about. As well as reefing - morphing into a smaller planform area. If you look inside a dinghy like a Merlin Rocket, most of the spaghetti is all about morphing the rig.

    How about some discussion as to where morphing would be really useful to the designer?
     

  15. Doug Lord

    Doug Lord Guest

    Morphing

    Seems to me one area with potential to benefit from morphing is in creating a sailing hydrofoil foil/foil system that is ideal for the lowest windspeed takeoff possible of a given boat but that could be morphed into an ideal mid range and high speed system.
     
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