Lasted edited by Andrew Munsey, updated on June 14, 2016 at 9:09 pm.
Page first featured December 7, 2008
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Is it possible to build a device in which the forward motion turns a wheel that turns a propeller which provides enough wind propulsion to accelerate the device forward? Physics and common sense would say: "absolutely not." Yet some investigators appear to have accomplished just this.
Take a look at some of the videos below, and if you don't believe it, build one, and report your results. If this really works, it would make a great toy.
The most astonishing video is the one showing a treadmill set on an incline, yet the gizmo is proceeding up the treadmill against gravity, propelled by the fan which is propelled by the forward motion of the gizmo on the treadmill.
The effect seems to work better at higher speeds than lower speeds (probably due to the cubed relationship between increased wind speed versus increased power).
aka: DWFTTW and DDWFTTW
Dec. 4, 2008, 4:30 pm Mountain update by Congress:Founder:Sterling D. Allan, CEO of
: I just got off the phone with Spork33, the person featured in several of the videos below.
: He is convinced that existing laws of aerodynamics can explain this phenomena, and he is in process of composing a scientific paper for publication in a refereed journal that will detail the mechanics involved.
: Bear in mind that you will not be able to just plop this on a flat surface such as a gym floor, give it a good push, and it take off accelerating. The device on the treadmill is analogous to a cart going along with a tail wind of the same speed, and the mechanism makes it go faster than the tail wind.
: He said he has been assembling about 20 of these to ship out to a few people (primarily skeptics) from various forums who have asked to replicate the effect. He said that in doing several at once, the parts run around $40.00 USD. He asks another $5.00 for shipping. So at this juncture he's only doing it on a limited basis for scientific advancement. At that price, he's not willing to make very many.
: Until the thing is mass produced, it will be fairly expensive. We () are in discussion with him about entering into an agreement to build and ship kits with adequate mark-up to make it worth our while, e.g. $80 retail. If you are interested (customer side or business side), please send an email to [mailto:email@example.com?subject=DDWFTTW%20interest DDWFTTW.firstname.lastname@example.org].
: Because the gadget won't accelerate across a flat surface but will only move forward on a treadmill, the number of people wanting one will probably be fairly low, and the practical aspects perhaps lower yet.
: It certainly is a scientific curiosity. Perhaps the principles underlying it may eventually spur some significant aerodynamic advancements in efficiency.
Downwind Faster than the Wind (DWFTTW) Myth Challenge - A submission for the Mythbusters video challenge (YouTube November 15, 2008)
Other Overview Documents
Down wind faster than wind - PDF - radio-controlled wind car. (Catalyst Jan. 2006)
On November 24, 2008, the following statement was published as part of an introduction to this subject at DonkeyPuss's Wonderful World of Technology, where they built a replica of the principle that gave positive proof:
"Over a year ago there was an article in Make magazine by Charles Platt inspired by a YouTube video [below] of a propeller-driven cart that allegedly could go down wind faster than the wind that was pushing it…. Everyone’s first instinct is to think “free energy”, or “perpetual motion machine”. I was convinced that this was not the case, and that the cart could work. I had seen a similar cart presented by Paul MacReady, founder of Aerovironment."
http://makezine.com/11/windpower/ - The Little Cart That Couldn't Wind-powered vehicle claims look like hot air.
Here's the video of the cart built by Jack Goodman that spurred the debate:
DWFTTW - Sailing directly downwind faster than the wind - No it is NOT impossible! (YouTube November 30, 2007)
: "A demonstration that you can make a vehicle that is powered solely by the wind, that will go downwind, faster than the wind. It's just easier to put it on a treadmill than to find a perfectly straight road that's perfectly aligned with a perfectly steady wind." - spork33 ~Nov. 5, 2008
Direct Downwind Faster Than The Wind #4 (DDWFTTW) - [Takes wheel off shaft to show it go off the back of the treadmill. Shows device climbing treadmill, going uphill repeatedly after being pushed back.] (YouTube November 9, 2008)
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Direct Downwind Faster Than The Wind #3 (DDWFTTW) - [Outside in wind inside on treadmill.] (YouTube November 9, 2008)
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Direct Downwind Faster Than The Wind #2 (DDWFTTW) - JB shamelessly stole MarkC's design and had to try it for himself. This really does make a slick little cart that nicely shows that it is possible to make a simple wind powered vehicle that goes downwind faster than the wind. (YouTube November 8, 2008)
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Direct Downwind Faster Than The Wind #5 (DDWFTTW) - This video shows our DDWFTTW cart, and demonstrates that stored kinetic energy is not the explanation for how it advances on a treadmill, or even climbs an inclined treadmill. (YouTube November 10, 2008)
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Direct Downwind Faster Than The Wind #6 (DDWFTTW) - A simple demonstration of our DWFTTW cart running unassisted for as long as we could managed to keep it on the treadmill [about a minute and a half]. (YouTube November 11, 2008)
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Direct Downwind Faster Than The Wind #7 (DDWFTTW) - In this video we show that the DWFTTW cart is not being affected by any external fans or other devices. This video is in response to critics concerns. (YouTube November 12, 2008)
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DWFTTW Self-Start - This is being posted in response to folks that have asked if the cart can self start in a tailwind. (YouTube November 23, 2008)
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This is our little homemade cart that demonstrates it's possible to make a wind powered vehicle that goes directly downwind faster than the wind. (YouTube November 5, 2008)
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DDWFTTW - Prop or Turbine
This video was made to address a common misconception about whether the wheels provide the torque that turns the prop or the prop (working as a turbine) provides the torque that turns the wheels. I very much look forward to the creative claims on various forums explaining how this video is a hoax. (YouTube March 11, 2009)
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Directly Down Wind Faster Than The Wind Treadmill Test 2008-11-22, Part 1 - Part 1 of the treadmill test of my own version of the Jack Goodman cart. (YouTube November 24, 2008)
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Directly Down Wind Faster Than The Wind Treadmill Test 2008-11-22, Part 2 - Part 2 of the treadmill test of my own version of the Jack Goodman cart. (YouTube November 24, 2008)
(Source: RTFA.com Dec. 2, 2008)
Here is the parts list, compliments of Spork33 (the creator of the video above):
4.15 Century Tail Gear Set Hawk (Tower LXMJX7)
6.95 Century Tail Gearbox Hawk Pro (Tower LXLKD0)
2.00 5×13x4 Revolution (2 front prop shaft bearings) (Avid 695-RSZ)
3.00 5×11x4 Revolution (2 axle bearings & 1 rear prop-shaft bearing) (Avid MR115-RSZZ)
21.00 Prop GWS 15×7.5 Propeller (6 for $21.00) (Tower LXHHZ1)
1.75 GWS 3.00? Wheels (2 for $1.75) (Tower LXHHZ8)
7.00 5mm x 40? Carbon tube for prop shaft and axle (AeroMicro)
4.00 4mm x 40? Carbon tube (40? for $4.00) (AeroMicro)
2 pieces at 2? used for axle step-down
3.20 3mm x 40? Carbon tube (40? for $4.00) (AeroMicro)
2 pieces at 2? used for axle step-down
9.99 0.08? Music wire (2 pieces at 2? used for axle (Tower LXWV01) step down)@ 9.99 for 15 pieces at 36? each
9.69 1.25? of 0.063? Music wire for rear axle (Tower LXWV00)@ 9.69 for 15 pieces at 36? each
2.00 3/8? soft aluminum tube (24?) from plumbing dept at OSH
2.99 Dubro 2? Micro Lite wheels 2 for $2.99 (Tower: LXAZC6)
1.00 Nuts and bolts to hold aluminum tube to gearbox
1.00 HDPE Bearing block to support rear prop-shaft bearing (Tap Plastics)
Total: $79.72 Plus Tax & shipping (but you’ll have lots of leftovers)
5mm drill bit and some standard sized bits
Metric Allen wrenches
OSH: Orchard Supply Hardware
Include, if possible:
overview description / abstract
parts used (if different from above)
Quoting from Directly Down Wind Faster Than The Wind (DDWFTTW)
:"The treadmill test is scientifically sufficient to prove that, once at wind speed, the cart can exceed it. If a cart is going down a road at x miles an hour in x mile-per-hour winds, then the wind speed relative to the cart is zero and the ground speed relative to the cart is x. Thus the cart on the treadmill at x miles per hour is exactly the same situation. If the cart can move up the treadmill, or add tension to an anchor rope, as is the case in our tests, then that means that there is positive net thrust, that is, the thrust exceeds the friction and thus the cart can accelerate. The treadmill cannot simulate what happens after that (the relative wind goes from zero to against the cart) or before (when the wind is going faster than the cart). However, the first point is inconsequential, because we are not looking for the terminal velocity, just knowing that it is greater than wind speed. As for the second point, there are numerous ways to get the cart to wind speed if its own drag is not enough: imagine, for example, a set of hinged sales that open flat like a book when the wind blows from the aft and close into a “double flag” when the wind blows from the front.
:One way to analyze this from an energy point of view goes as follows: imagine the cart has just reached wind speed let’s call this state 1. At some short time later, the cart is at state 2. Between the two states 1 and 2, the cart’s kinetic energy change is and this energy change must come from the work done by the cart by any external forces over some distance covered in this time. The two forces acting on the cart are the thrust of the propeller and the overall resistance (friction, propeller turning drag, other losses) . So our equation reads [http://projects.m-qp-m.us/donkeypuss/wp-content/plugins/latexrender/pictures/f67479678be09e89573f8c34d306f4aa_3.5pt.gif
:If the speed at station 2 is larger than that at station 1 (meaning the cart has accelerated past wind speed), then the quantity on the right side must be positive. That is, http://projects.m-qp-m.us/donkeypuss/wp-content/plugins/latexrender/pictures/49eabcd21f2002eacdbaee843ea71e26_2.49998pt.gif.
:Part of the resistance comes from the propeller itself. It is essentially a rotating wing, so it has lift and drag, and the two can be related by the lift to drag ratio, which depends on a number of factors, but to some extent can be considered a design choice. If we call the ratio then our expression becomes where is the propeller drag force, and are all the other losses combined. This inequality can be simplified to yield [http://projects.m-qp-m.us/donkeypuss/wp-content/plugins/latexrender/pictures/4feb800b0ba2880cc3b92d38b9defa9a_4.44841pt.gif
:Note that if our losses are small relative to our drag, the lift to drag ratio need only be greater than 1—an easy task. Either the losses must be minimized (good bearings, low rolling friction, etc.) or the drag on the propeller must be increased. As bad as that sounds, what this really says is “or the propeller must be made bigger”, or “the propeller must be made to generate more thrust”, keeping a constant lift to drag ratio, of course."
ScienceBlogs (Dec. 3, 2008)
BoingBoing (Dec. 1, 2008)
OverUnity.com (Dec. 7, 2008)
Energetic Forum (Dec. 8, 2008)