Contest: Going downwind - faster than the wind

[spork]

1) Show Idea Title: Going downwind - faster than the wind.


2) Idea/Myth Description: The myth is that it's not possible to build a vehicle that is powered solely by the wind, yet goes directly downwind, faster than the wind, steady-state.  It's obvious to most people that when a sailboat goes straight downwind it's maximum speed is less than the wind speed.  But is it possible to build a boat (or other vehicle) that could actually go *faster* than the wind speed when going straight downwind?

3) Source of Idea/Myth:
This myth started as a brain-teaser I posted on an R/C heli forum and a kitesurfing forum.  I expected people to say "gee - that's clever", but instead they exclaimed "that's complete nonsense".  This erupted into holy wars and people claiming it would violate all sort of laws of physics.  I later learned I wasn't the first to propose such a thing.  A man named Bauer made such a vehicle (I believe in the early 70's) http://www.dcss.org/bauer_cart.jpg  Also a man by the name of Jack Goodman built and demonstrated a working model much more recently: http://www.youtube.com/watch?v=aJpdWHFqHm0  While you might think this would put an end to the questions, it only fueled the fire more.  Most recently a friend and I built three such vehicles and posted a number of videos on YouTube to answer the critics concerns one-by-one http://www.youtube.com/watch?v=xHsXcHoJu-A  Again, this resulted in little more than attacks and name calling by the critics.  Interestingly, the videos we've posted have amassed over 10,000 hits in only 10 days.


4) Research results of Idea/Myth:
We know this myth is plausible as we've built three such craft, demonstrated them, posted videos on YouTube, posted the list of parts and build guidelines on several forums, and even offered to send our vehicles to the skeptics to test for themselves without our influence.  Again, much of this is covered in our Mythbusters YouTube challenge video: http://www.youtube.com/watch?v=xHsXcHoJu-A    Several analyses have been written and posted (including my own) and I'd be more than happy to provide anything needed.

5) Why this should be considered by the show's producers:
Like "Plane on a Treadmil"  this is just flat out controversial.  We have debated this for thousands of posts over hundreds of pages on many forums.  Emotions run high, and most people will never be swayed from thier religious belief even in the face of solid physical evidence (much the way people continue to debate plane on a treadmill long after the Mythbusters put it to rest).  We have even had endless (ongoing) debates with aerospace engineers, physicists, PhD's, and professors from well known universities such as GA Tech.  We are called hoaxers and charlatans, and told we don't know the first thing about physics if we could possibly believe such a "perpetual motion machine" could ever be built (it is NOT a perpetual motion machine of course - when the wind stops, it stops).

Here is a partial list of some of the forums where this has been discussed, debated, and frankly fought over:

http://www.kiteforum.com/viewtopic.php?t=2328807

http://www.kiteforum.com/viewtopic.php?f=1&t=2329828&st=0&sk=t&sd=a

http://www.hanggliding.org/viewtopic.php?t=5508&postdays=0&postorder=asc&start=0&sid=b481fb9032390532ad808cbf858dc29c

http://www.hanggliding.org/viewtopic.php?t=9340&postdays=0&postorder=asc&start=0

http://forums.sailinganarchy.com/index.php?showtopic=82175

http://forums.sailinganarchy.com/index.php?showtopic=31824&hl=dwfttw

http://community.discovery.com/eve/forums/a/tpc/f/7501919888/m/5081905889/p/1

http://community.discovery.com/eve/forums/a/tpc/f/9701967776/m/4561931559/p/1

http://forum.mythbustersfanclub.com/index.php/topic,12948.0.html

http://www.runryder.com/helicopter/t243488p1/

http://www.runryder.com/helicopter/t251635p1/?highlight=abt

http://ozreport.com/forum/viewtopic.php?t=6546&postdays=0&postorder=asc&start=0

http://forums.randi.org/showthread.php?t=128483

It's easy to find more.  These are just some of the threads we have personally been involved with.

[theSpecialist]

I wonder if comparing this to Plane on a Conveyor Belt is all that wise, spork.  It seemed, at the time, that viewership for such an episode (PoaCB) would have to be unprecedented.  I think, however, it may have turned out that there was really just a core group of devout PoaT fans out there (by virtue of their constant posting and reposting on various sites, made it appear bigger than it actually was) - making the MythBusters episode created to look at Plane on a Conveyor Belt devoted more to a fixed number of cult fanatics rather than having true general-viewership appeal.  I wonder if the show would want to recreate something like that now looking at it in hindsight.  I’m not sure if Mr. Tapster considers PoaCB one of his finest episodes.

Perhaps, since what you are talking about is actually quite fresh, it might be better to simply avoid making any such comparison; allowing Going Downwind to stand on its own merit, rather than getting itself mired down with that connotation.

PS - Just curious - why two threads on this one?

[spork]

You make a good point about the POAT episode.  I assumed it was one of their all time most popular segments - but I may very well be wrong.

PS - Just curious - why two threads on this one?

Good question.  I saw this: "SHOW IDEAS CONTEST SUBMISSION BOARD"  and thought this was some new contest/request.  If this is simply a duplicate (spam) of my other thread the moderators should move or delete one of the two.  It's certainly not my intent to spam this board.

[Cybermortis]

Maybe this thread should be kept here as a full show idea, given the number of links you were able to add and the rather good description of the idea/myth. The original thread would, I think, be better shifted to the breeding ground.

[GregLondon]

It is possible to design a vehicle that can go directly downwind faster than the wind. I wrote up an explanation of how it works using basic high school science. There are rope and pulley drawings, intermeshed gear drawings, and even a short "time lapse" drawing that shows  a vehicle in motion. 

You can read all the details here:

http://www.greglondon.com/tumbleweed/

[ndgeoman]

For this to work I think gravity would need to be involved, ie not a level surface.

[spork]

For this to work I think gravity would need to be involved, ie not a level surface.

Nope. It'll go uphill, downhill, or dead-level.

[spork]

I posted some build videos for anyone that wants to try this at home:

Build video 1 of 3:
http://www.youtube.com/watch?v=T-ArigMKhi4&fmt=18

Build video 2 of 3:
http://www.youtube.com/watch?v=p0rhgop5wEM&fmt=18

Build video 3 of 3:
http://www.youtube.com/watch?v=gSHNqrF93MU&fmt=18

[Wesnex]

At first it seems like perpetual motion for the wheels to push the prop to push the wheels which then push the prop... and get the whole thing going faster than the wind but these facts may help you change your mind.

  1) Windpowered travel faster than the wind in other directions than directly downwind is well known to be possible.
 
  2) Travel at any speed requires less energy directly downwind than any other direction.
 
  3) Kinetic energy keeps things in motion, all that slows them down is friction which is less if going directly downwind.
 
  4) Wind energy is not synonymous with wind speed but increases by the cube of the wind speed. This means that a high enough
      windspeed, the energy available should overcome the cart's friction enough to move it faster than the wind if the cart's design is
      such that it can efficiently collect the wind energy and use it to increase the cart's speed.

The cart is just a machine that causes the propeller blades to travel in a spiral relative to the ground. Now if you understand coarse and fine threads I'll use those terms to compare the pitch of the blades to the spiral of the motion of the blades.  If the blade pitch matches the spiral of motion, the forces in the cart will ballance and the cart cannot use the wind. If the the blade pitch is finer than the spiral of motion, the wind will push the blade forward on the spiral harder than it trys to reverse its spin and it can go faster than the wind if wind energy is higher than cart friction. If the blade pitch is coarser than the spiral of motion, the wind will turn the prop in the opposite direction and it will travel up wind. Faster than wind travel upwind may be possible but is less likely because it involves much greater friction.

To build an advanced version you could make the corseness of the blade's spiral of motion adjustable (via a constantly variable transmission) and the blade pitch adjustable. The challenge would be to keep the blade pitch finer than the spiral of motion for downwind travle and coarser than the spiral of motion for upwind travel.  This adjustable version would be important for very high speed travel because if the spiral of motion is to fine the prop may spin so fast it will explode, but if it is too coarse, the cart will have trouble starting especially carrying a human.

[toga_dan]

http://www.youtube.com/watch?v=k-trDF8Yldc&NR=1
http://www.youtube.com/watch?v=9Yt4zxYuPzI&feature=related

These 2 vids clarify the concept.

Spork, thanks for the how to videos. How about a list of those parts in text? It's a bit cumbersome to extract all that info from 27 min of video.