DDWFTTW - Directly Downwind Faster Than The Wind

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

  1. spork

    spork Previous Member

    Yes, the system efficiency requirements start to become pretty ludicrous at 3X to 4X wind speed.

    The excess power graph for upwind and downwind are offset but otherwise perfectly symmetric. The upwind cart has the disadvantage that aero drag is quite significant (as it's moving through the wind faster than it is over the ground). It also has the disadvantage of the Betz limit since it operates as a turbing, while the downwind vehicle uses a prop.
     
  2. Dave Gudeman
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    Dave Gudeman Senior Member

    I recently read a book on air power in World War I (written during World War I). It is startling how quickly air power advanced from the first flight in 1903. I'm not sure if you would call it "common use", but by the beginning of the war in 1914, there were already hundreds of aircraft in private use, and more than that owned by the militaries of England, Germany, and France.

    There is also an interesting chapter on the English sea-plane program.
     
  3. Guest625101138

    Guest625101138 Previous Member

    It is possible to beat the Betz limit using a venturi.

    My first thoughts are that a moving turbine will also beat the Betz limit but I have not sat down and worked through it.

    The big advantage of the windward cart is that you get better flow regimes with small blades at the scale suitable for a single person vehicle. The benefit of this may not be as significant at large scale using large blades but it is not something I have considered.

    What are Joby spending their money on?

    Rick W
     
  4. Guest625101138

    Guest625101138 Previous Member

    By common use I mean available for the masses. I guess the thought of passenger flight was on the agenda by the mid 1930s.

    I think the likes of Benz were doing their thing with cars in the 1880s and 1890s. It was Henry in the teens who made them for the masses.

    Think of any invention (discovery) and see if the 30 year rule applies. TV as I recall was 1925 (at least in the west) and by the 1950s they were hitting homes.

    Rick W
     
  5. backyardbil
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    backyardbil Junior Member

    Like the ideas of Leonardo Da Vinci are still "curiosities" such as aircraft, parachutes, ball bearings and others I guess!
     
  6. Guest625101138

    Guest625101138 Previous Member

    These are Ideas not discoveries - not the linkage that makes them work.

    Dick Tracy had the wrist communicator. Get Smart had the shoe phone. The idea is not enough. These needed the enabling technology of large scale integration to become reality.

    There are ideas about invisibility - remember the Invisible Man. There is technology to achieve this but I do not think anyone is actually doing it yet. There is an idea for warp speed but no one has discovered how to do it. I think Da Vinci did make some discoveries but I am not versed enough on his work to know what actually got developed. He was certainly an ideas man and no doubt of impressive talent but many of his ideas needed enabling technological discoveries to become workable. I dare say cavemen watched birds with some jealousy so the thought of flight as an idea goes back a long way. Wright brothers had sufficient command of all the essential technologies lined up to demonstrate it.

    Rick W
     
  7. backyardbil
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    backyardbil Junior Member

    Yes, but you said "ideas" - now youre changing it to "linkages" and "discoveries" -
    So you admit then you did not mean just ideas.
    You need to think about what you are saying before you say it to avoid confusion.
     
  8. powerabout
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    powerabout Senior Member

    There was a guy in the UK and NZ that had flying machines before the Wright Bros.
    >>http://www.destination.co.nz/temuka/pearse.asp<<
    The UK guy died before his mods got the thing flying ( a replicate was built and flown) and the Kiwi went un noticed?
    IBM couldn't see the use for a PC..so they effectively handed it to a guy who didnt invent anything and he became the richest guy on the planet?
     
  9. Guest625101138

    Guest625101138 Previous Member

    If you go back to the original statement you will see I stated discovery. I admit to being loose with the terminology and used ideas interchangeably with the word discovery. I thought you had been following the thread and not just replying to that particular post.

    Rick W
     
  10. backyardbil
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    backyardbil Junior Member

    That's exactly my point about "building bricks in a wall" There was indeed someone as you describe (Sir George Cayley) who made gliding flights, I think many years before the Wrights, then there was Lillianthal in Germany and Percy Pilcher in England, and indeed the Wrights themselves made quite a few gliding flights before 1901, and yet the "dawn" of flight is usually dated from when the Wrights made a 12 second flight - I guess that was because this was the first time they used a motor. The whole thing was a development process but the media often give the idea to the public that someone thought it up and it worked straight away. Actually, the Wrights went down the wrong path and the most significant development was in France by Bleriot and others. (but that's another story).
    History shows that even the most imaginative inventors can never predict the final outcome of their inventions, which often exceed even their wildest dreams!
     
  11. spork

    spork Previous Member

    At the risk of taking us further off topic, can you share that story?
     
  12. ThinAirDesigns
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    ThinAirDesigns Senior Member

    While you are correct that the large version will not sway many skeptics, there is one very significant difference between this and the many smaller versions that have been demonstrated -- the outdoor demonstrations with the large version are able to be much better documented.

    Turbulence low to the ground is a real problem for wind measurement and for streamer behavior. The reason we went so large and so tall is that now we can measure the wind at the prop hub (~14ft) with much much more convincing consistency. A streamer at 1ft off the ground (our small cart) or even 3ft (Goodman cart) is subject to a ton more boundry layer chaos.

    Additionally, a small unmanned version would not have been eligible for NALSA record recognition and ratification. Having an outside organization whose business is such and whose motives are harder to question, instrument, monitor and collect the data will sway some skeptics merely on credibility alone.

    JB
     
  13. backyardbil
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    backyardbil Junior Member

    Way off topic definately. But this is what I meant.
    I don't want to put down the Wrights achievements, they were great developers and they had the right approach of testing, observing, testing again and gradualling refining things until they achieved their objectives.
    However, at least a couple of things they came up with did not point the right way to go. The first was the fact that they used a canard configuration for their planes, and although canards have been used successfully later, they did not point the way to go at that time. The second was wing-warping, which they patented, but was soon superseded by the more simpler and probably more crude to them, ailerons. Development soon passed to the French, and the Bleriot monoplanes were the first aircraft configured in the way which has become the norm - ie tractor engine up front, fuselage and two-wheel undercarriage. One of these crossed the English channel in 1909. Don't really want to go any further off topic on a boat forum!
     
  14. ThinAirDesigns
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    ThinAirDesigns Senior Member


    I hardly think you could go more off topic than a wheeled vehicle driven by a propeller on dry pavement. :D

    JB
     

  15. SamSam
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    SamSam Senior Member

    In post #140, reference is made to another forum http://talkrational.org/showthread.php?p=610758#post610758 where Spork offers 10 to 1, in favor of doubters, whether this is possible or not. I'll put $20 on that. I still say it won't work.

    The reason I (and possibly others) quit arguing the question and posting to the thread a long time ago was not because, as Rick W stated (more or less), that "we" had realized we were wrong and were too sheepish to admit it, but that "we" realized there was no reason to try and argue with the believers. Now that a machine has been made, perhaps you will be proven right and then you can strut and crow about it all you want, and deservedly so.

    In post #139 in the above mentioned forum, reference is made to the Brennan torpedo http://en.wikipedia.org/wiki/Brennan_torpedo and a claim is made that that clearly proves the concept and shows how DDWFTTW craft operate. It doesn't do that at all. It does show how a steam powered winch can pull a wire one way and that that same steam powered energy can propel something the other way. Much has been made of the small cart on the treadmill proving the concept, but again, it only proves that a small cart powered by a comparatively massive electric treadmill motor can go faster than the treadmill.

    Even though they both have propellers, both machines are only examples of gearing, neither uses the available wind as the motivating power. The large cart will have to be driven by the wind, and seems to me it will have to be a turbine and propeller at the same time to accomplish your goals. The propeller will have to capture the power from the wind and in turn has to power the same propeller to bite into the wind to pull it forward. That is more than perpetual motion, that is one step beyond. The problem being to me, once the speed of the wind is equaled, there is no more wind and so there is no more power to drive the wheels over the ground to gain an advantage through gearing to make it go faster.

    You may refer to us unbelievers as "flat earthers", but you also admit there are an awful lot of aerodynamicists and physicists in the same boat.

    Aside from that, I am glad you have made the large cart to test the theory in actual conditions that will approach a reasonable conclusion. I am sure you have enjoyed making the thing almost as much as proving the point, I often find making the tool to make the product much more interesting than making the product. I believe the journey can be better than the arrival. The only concern I have is that it is necessarily fragile, and that it will be damaged before things have been conclusively settled. I honestly would not mind at all to lose this bet, and honestly wish you good luck.
     
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