The Wind Powered Sail-less Boat

Discussion in 'Boat Design' started by DuncanRox, Oct 20, 2008.

  1. gketterman
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    gketterman New Member

    Dynamic Soaring

    This is way off topic, but you folks have had so much fun debating this issue I guess you will have a lot of fun with this one too. Would you believe a model sailplane that goes 371 mph?

    This video is all about the guy with the record and how obsessed he is with the pursuit; http://www.vimeo.com/2375301

    The sound is the impressive part and this video has the best sound; http://www.youtube.com/watch?v=AQoVBvQacwE&feature=related
     
  2. Guest625101138

    Guest625101138 Previous Member

    Greg
    If you go back to post #226 you will see that Tom Speer has provided a nice little paper on dynamic soaring. Mark Drela and others go on from there to discuss it in some detail.

    Rick W
     
  3. chabrenas
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    chabrenas Mike K-H

    Bet there'll be plenty of people capable of misinterpreting the PDF, and plenty of others who start arguments that don't address its contents.

    You still need to write the words that go with the diagram - i.e. the script for a presentation to an audience - in the same clear-cut manner. Shall we continue fro another 50 pages? :)=? It could be time well spent.
     
  4. Guest625101138

    Guest625101138 Previous Member

  5. PanAmMan
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    PanAmMan Junior Member


    So when you boat is going zero speed relative to the water the water prop generates zero power / lift and therefore provides zero power to the wind prop.

    When the boat is going faster than the water prop it is extracting energy from the bat speed (drag) to push the boat with the wind prop (loss of efficiency).

    the only time this works is in an ultra low drag environment where the relative wind or water over the blade produces (local) wind / water speeds faters than the net relative speed of the boat. These are usually very uncommon (transient) conditions rarely seen even in racing multi hulls and hydrocats. they frequently ccheat by converting intertia into the necissary relative motion for short periods of time. all sailboats do this when they tack. But very very few can maintain that "effect" for more than a few min.

    it is true that very large sails act as a force multiplier which can be converted to a relative speed increase but if it were easy or relaible we would see 14knt oil tankers all over the world... LOL
     
  6. Guest625101138

    Guest625101138 Previous Member

    You should go over to this thread and take up sporks bet if you are confident it does not work:
    http://www.boatdesign.net/forums/propulsion/ddwfttw-directly-downwind-faster-than-wind-25527-10.html

    Rick W
     
  7. ThinAirDesigns
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    ThinAirDesigns Senior Member

    San Jose State University Aero Professor and Stanford Phd Dr. Nikos Mourtos along with a team of students and advisors have taken on a project to construct and document DDWFTTW in a more thorough way than ever before. Their goal is to achieve a documented 2x windspeed DDW.

    Follow their blog at www.fasterthanthewind.org

    Remember that in the blog format the latest posts show up on top. To view the entries from the start, click on the "2009" link on the right (below the list of followers) and scroll to the bottom.

    Enjoy.

    JB
     
  8. Guest625101138

    Guest625101138 Previous Member

  9. spork

    spork Previous Member

    And a couple more clips from the same outting.

    We muted the audio where we were talking specifically about our downwind speeds beyond windspeed because we didn't think it would be responsible to post unofficial numbers without at least discussing with NALSA and our sponsors. More than likely we will wait and post numbers when we have proper instrumentation that is blessed by NALSA.

    Second run: http://www.youtube.com/watch?v=aDzWh9J1dk4&feature=channel
    last run: http://www.youtube.com/watch?v=c5VlX-xEk00&feature=player_embedded
     
  10. Jeremy Harris
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    Jeremy Harris Senior Member

    How can anyone doubt such an incredibly simple bit of physics?

    My guess is that some must have a problem with understanding some really basic principles and manage to confuse velocity, force and power. Anyone who goes back to basic schoolboy physics (think of Newtons Laws and the basic equations governing force, velocity, time and power), works out the power needed for any vehicle to travel at a given velocity and then calculates the practically extractable power in a given swept area of wind at a known velocity can very quickly see that going downwind faster than the wind is perfectly possible and doesn't need any complex experiments to prove.

    There isn't really a issue over the relative wind velocity vs the relative vehicle velocity, provided that you can continue to extract enough power from the wind to meet the vehicle power demand. The only issue is one of being able to extract enough power to overcome the vehicle total resistance.

    Why is something so fundamentally simple causing so much debate? Surely it should have been self-evident from the first instant it was raised?

    Jeremy

    PS: Reminds me of a rather dim acquaintance who came up to me years ago and accused me of speeding in an urban area. His argument was that I had to be going over 30 mph as he was doing 30mph behind me, just to keep up with me in the traffic........................
     
  11. spork

    spork Previous Member

    While I'm inclined to agree with you, I can only tell you that we know of several Physics and Aero PhD's and professors that assure us it's quite impossible. One of whom teaches at my alma mater (GA Tech) sadly enough, another is a nobel prize laureate at Berkeley, and still several others.

    It's surprising just how much even highly educated people will substitute intuition for science - and refuse to hear another thing on the topic.

    ETA: ... and these videos won't change their minds.
     
  12. Jeremy Harris
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    Jeremy Harris Senior Member

    As a scientist I can understand this to some extent. What seriously concerns me is that a significant number of people in my profession have seemingly moved away from the fundamental principles that govern the scientific method and have lost that essential spark of curiosity in the process.

    A colleague of mine and I often have the same conversation regarding this lack of curiosity and willingness to accept unproven statements as fact amongst some of our colleagues. He's fond of quoting this fairly well-known proverb: "The mind is like a parachute, it works best when open" (author unknown).

    I suppose that the opposite of closed thinking and blind acceptance of ideas as fact can be a bit irritating, though. I know that I annoy people by not always accepting things they have shown (to their own satisfaction) to be true, without doing at least some experiments of my own to confirm their findings. My wife sometimes gets infuriated by my need to understand why things happen.......................

    Jeremy
     
  13. spork

    spork Previous Member

    Some of our skeptics prefer the alternative "the mind is like a parachute - use ONLY in an emergency" (and this is NOT an emergency).
     
  14. ThinAirDesigns
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    ThinAirDesigns Senior Member


  15. ThinAirDesigns
    Joined: Dec 2008
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    Location: USA

    ThinAirDesigns Senior Member

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