DDWFTTW - Directly Downwind Faster Than The Wind

Discussion in 'Propulsion' started by Guest625101138, Jan 4, 2009.

  1. A.T.
    Joined: Feb 2010
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    A.T. Junior Member

    It is interesting to see where people get stuck on this counter-intuitive stuff, and how they eventually overcome the block. This gives you new ways to understand it yourself.

    Recently someone on a wiki page was absolutely convinced, that even downwind-VMG > wind-speed with a sail-craft is impossible. When he finally got it, he explained what explanation changed his mind. I made an animation based on it:



    Apparently for some people the above works much better than the wedge analogy I used so far:



    I may adapt the new explanation to DDWFTTW.
     
  2. spork

    spork Previous Member

    I wonder if a video of a pair of scissors would be compelling. Maybe a pair of scissors trying to cut something hard that's sliding as you try to cut(?)
     
  3. sirclicksalot
    Joined: Jun 2010
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    sirclicksalot Junior Member

    These videos are fantastic.

    I have one more suggestion to eliminate the jumps at transitions between each reference frame segment and instead make them smooth and seamless. To do that you need three surface-boat objects:

    Start with the air-at-rest frame. As the first surface moves down and the first boat moves up and to the right, a second surface-boat object drifts into place from below-left i.e. stern of new boat moves to left edge of air dotted line. When it reaches there, ...

    Switch to surface-at-rest frame; first surface-boat object fades. As the air moves up and the boat moves up and right along the surface line, a third boat object drifts into place from the lower left of a third surface line above and to the left of the second surface line. When the stern of the boat reaches the air line, ....

    Switch to boat/sail-at-rest frame; second surface-boat object fades. Air moves left and down; surface moves left and more down.

    Draw Ground symbols attached to the fixed object for each segment e.g.

    Code:
       |
     __|__
    //////
    
    Alternate sequences are possible and may be better; Surface, Air, Boat might work but you would need two air & boat objects (for the Surface to Ground transition the first air moves up and fades as a second air comes in from below along with the second boat) but then air is too low for the Air to Boat transition. Anyway, I leave it in your capable hands.
     
  4. A.T.
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    A.T. Junior Member

    I don't really want them seamless. It could be more confusing than helpful. I made a DDWFTTW-version now:



    And here the downwind VMG version with force vectors at the end:

     
    Last edited: Jul 3, 2010
  5. kerosene
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    kerosene Senior Member

    Isn't that a little cheap shot. I think bringing up PMs always stinks unsportsmanlike.

    This has reduced to retarded name calling and while I applaud Spork's and ThinAirDesign's achievements I do wonder how is it that you guys can have web-debates with guys who agree with you.

    Yes its silly for Rick to say there is no difference between theory and engineering. yet he has helped a lot of people here, and like you gone out to test his ideas of small powered boats and keeps working on them despite the nay sayers (Wouldn't be so surprised if the said PMs came from this camp).

    Cheers and good luck for the NALSA tests.



    you might know me as coalburner form the other forums btw.
     
  6. spork

    spork Previous Member

    I guess that's a matter of opinion. I really don't care for Rick's continued condescending and innaccurate statements about me. I didn't post a PM from Rick afterall. What's wrong with passing along something told to me?

    Agreeing with me regarding DDWFTTW doesn't automatically make you good and right in everything, just as disagreeing with me on this topic doesn't make you automatically wrong about everything. Wouldn't that be a little silly and childish?

    Oh - I guess since he's helped a lot of people here I should agree with his ridiculous statements and welcome his condescending attitude.
     
  7. ThinAirDesigns
    Joined: Dec 2008
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    ThinAirDesigns Senior Member

    Yeah, like everyone who agrees on DDWFTTW agrees on everything. :rolleyes:

    I'm glad he has helped a lot of people here -- that's very nice of him. That doesn't give him license to make silly statements without being corrected -- that's just a silly statement on your part (now corrected).

    JB
     
  8. A.T.
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    A.T. Junior Member

    I think this whole argument was a semantic one. By "theory" Rick W. apparently means a "numerical investigation based on real world parameters" while others mean "physics".
     
  9. spork

    spork Previous Member

    I disagree. It would be easy enough to go back and review the statements made - but is there any point?
     
  10. ThinAirDesigns
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    ThinAirDesigns Senior Member

    Two days of NALSA testing complete. ~16-18 speed runs in ~12-13 distinct passes -- wind was lengthwise the lake on the first day giving us room run throught 2 sequential 'traps' on one pass.

    Data shows every run well over 2x. Most runs over 2.5x. Best runs above 3x. We won't know details of which runs qualify against NALSA rules until they go through the large amount of data and figure out which runs are best documented. There is a fairly comprehensive list of requirements to be met for a run to be NALSA valid and I'm certain that some runs will be disqualified if all the sensor info was not to their liking (wind switching direction too much during the run, etc).

    There are reams of data for them to go through from more than 20 separate sensors (multiple gps, wind direction and wind speed sensors) on the vehicle itself, chase vehicle and lakebed, plus multiple video cameras. It will take some time for them to go through it all once they get home.

    To say the least we are quite confident that a record well over 2x will be ratified by the NALSA BOD.

    On the project blog (www.FasterThanTheWind.org) Pictures, video and more information to follow as we recover from the long days and long drive home.

    A special thanks to the NALSA officials who put in so much time, effort and money (they wouldn't let us pay for their travel expenses) to make this happen. Thanks also to the NALSA BOD who saw something interesting in this crazy little project.

    JB
     
  11. Zilver
    Joined: Nov 2007
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    Zilver Junior Member

    Congratulations !

    Could you (and Spork) now please go picking your fights somewhere else ?
    Thanks in advance,

    Hans
     
  12. spork

    spork Previous Member

    We aren't picking fights here. We're here to discuss the topic and answer questions. But we're not here to take **** from people either. Thanks for your understanding - now leave.
     
  13. Windmaster
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    Windmaster Senior Member

    It seems from this that some are against advancing human knowledge! Seemingly they would prefer to wallow in ignorance rather than learn the truth.
     
  14. ThinAirDesigns
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    ThinAirDesigns Senior Member

    Going through the data from the 18 recording sensors that were used for the test it's becoming more and more likely that NALSA has the data to ratify a record of more than 3x the speed of the wind -- perhaps as high as ~3.5x.

    JB
     

  15. Munter
    Joined: Jul 2007
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    Munter Amateur

    Congratulations - an impressive and well documented exercise.
     
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