Directly Down Life Faster Than The Life

The following was edited on 19 April 2011 to replace a post published on 10 April 2009. The original was harsher and caused offence. I deleted it, but was asked to repost it, so here it is in edited form. I hope it causes no further offence, but if it does, hey, you can’t please all the people all of the time, and they really have to get over themselves.

Since posting it originally, DDWFTTW has progressed substantially. I dropped in from time to time, but haven’t kept up with it. There’s been a ride-on version called Blackbird that set the benchmark world record at nearly three times windspeed. I understand the pissing match continues. There’s a really good troll called humber, and few can resist a really good troll.


My goodness, how time flies when you’re having fun. What is it, half a year since I posted here? What was my blog about before?

It was going to be all about philosophy, especially my conversion (or awakening) from buddhism into the light of reason. Then I just got bored with the sound of my own typing, and the next thing I knew I was reading about a strange little brainteaser on the JREF forum (and everywhere else, apparently), the question of whether it’s possible to build a vehicle that goes directly downwind faster than the wind (DDWFTTW) powered only by the wind, “steady state” (which means not just as a passing burst, but settled at that speed).

There is so much to this, which I’ve been immersed in since at least December, both as a physical phenomenon and a social one, that it’s really hard to know where to begin.

I learned a lot in these few months. I learned how a little cart with wheels and a propeller can go directly downwind faster than the wind. I think…

…because I also learned how wrong I can be about such things. Even now, I’m not sure, and keep thinking I’ve spotted a flaw. I spent the first few weeks very sceptical about it, and even got to the point of saying that I’d eat my hat if it was true, but the last few months I’ve been 99-point-something percent convinced that it’s not only true, but has been demonstrated both outside and on a treadmill. (They let me off with the hat thing.)

The “treadmill tests” have been a big part of the debate, and it was something of a revelation – or a rediscovery – to learn about equivalent frames of reference in mechanics, how useful they are, and how philosophically interesting. Velocity, as we kept insisting to the nay-sayers, is relative: hence, a cart being blown by a steady wind over the ground is entirely equivalent in its local conditions (i.e. for a Directly Downwind cart running there) to a treadmill belt going backwards under the still air of a room. Thus, if we put such a device on a treadmill and it moves forward in still air, that is equivalent to it moving across a piece of land outside blown by a steady wind. It’s also a little easier to do the tests, and to guarantee that this is a steady wind (if you close the doors and windows and don’t wave things about too much).

Writing the above, I’m well aware that many people will laugh at the idea, or just read blankly wondering what on earth I’m talking about. How can still air have anything to do with a steady wind? How can a cart going forward in it prove that it would go faster than the wind outside? Well, answers to that are plastered all over the net, but in brief, it is so for all such situations where the relative velocities between the parts remain the same: you can shift all of the velocities numerically one way or the other, so that a moving wind becomes still (in this case) as long as the “road” is now shifted in its velocity also, by the same amount. The different “zero velocities” are called inertial frames of reference, and we’ve known that they are equivalent for several hundred years, with no exception having been found ever. These things are so long and fully established that they are considered basic laws.

Complications exist. With a treadmill, there are some things one can observe that don’t occur if you literally translate the motion to an outside scene. On the ground, the ground continues to stretch out as far as the eye can see, and is a globe and comes back around the backside. If you translate the treadmill with a cart on it back to a piece of earth, you’d have to construct a smaller stationary piece of earth with the cart on, and great areas on all sides moving forward. But such differences as exist are ones of scale – they have the potential to alter the result, and must be studied, IMHO, and shown to be negligible, rather than just ignored, but in this case they do seem to be utterly negligible.

As with many brainteasers, once you see it, it’s easy to keep seeing it, and your earlier objections fall away. However, I’ve never come across something for which my personal mental objections kept rising and rising, each time being shown to be unreasonable. As I say, I still have the occasional doubt.

The social side of it has been immensely interesting as well, almost more so than the physics. There are two guys, one of whom goes by the username of spork (and at youtube, spork33), and his mate, “ThinAirDesigns”, or “JB” as he signs his posts, who are heavily into this and promoting the idea in dozens of forums, building carts, testing them and posting the video, teaching the physics, arguing with nay-sayers and trolls, and one wonders how they manage to hold down their jobs (and, apparently, go flying or paragliding at the weekends, too).

I have recently fallen out pretty badly with spork. Our relationship was stormy from the start. I was a bit naive to expect that I could blather on about the machine from a position of relative ignorance and be heard with endless patience. There were some misunderstandings, and I think I pissed the guys off particularly by raising objections again after announcing that I understood it. I have the feeling it seemed like I was being deliberately awkward, and spork seemed to react as though he felt betrayed. I was genuinely just working through my questions, but I might have put them rather forcefully, as positive opinions rather than questions. I found spork and JB – and still do – highly defensive, but they were under attack by a constant stream of sceptical newcomers and hardened trolls.

I had a final fight with spork over his insults on the forum (towards others, in fact, not me). These may have been in response to earlier insults from the other, but were to my mind beyond the pale. I reported one of his posts to the mods and things went from bad to worse.

Someone I have made a better friendship with is Recursive Prophet. This was a little surprising as well, because he did strike me as an unlikely friend at first. I didn’t trust him. He was too complimentary about everyone, and then occasionally seemed to stick the knife in about something, or seemed not to respond to answers to questions he’d asked, just repeating them. He got a lot of things wrong, especially his analysis of “humber”, the uber-troll of the whole downwind debate. But he – “RP” – turned out to be a genuinely nice guy. As with most of us, his biting remarks were in response to being rubbed up the wrong way by others.

This is a big lesson – one that a lot of people are learning through internet discussion – the way we go around with a mental picture of ourselves all squeaky clean and wonderful, only ever being a bit short with someone who deserves it, after much provocation. Unfortunately, we’re all doing much the same. Some are a little more patient and forgiving and “relativistic” in their outlook than others, and they tend to recognise that ubiquitous human problem and sometimes manage to apply it to themselves (I’m thinking of my good self here, obviously, tee-hee), while others have no idea how different our perspectives are, just believe that things are correct however we see them and if anyone disagrees, they’re obviously wrong.

Spork, for instance, said that he never gave insults that weren’t in response to an insult by the other. I tried to suggest that the other might also see it the same way from their side, that our little niggles and irritations can grow gradually, each adding to the severity of the response, always thinking that they are giving a reasonable and measured reply, or perhaps trying to warn the other off – a sort of “I have caught on to the fact that you’re getting at me and if you don’t stop, you’ll get more of this incredible wit” – while the other reads that as “your last warning is ignored, and I insult you further”.

Anyway, I decided to write here not to slate spork or talk about the physics of downwind travel, but just to celebrate my new friendship with Recursive Prophet. RP is quite sarcastic about the spork-JB program now as he exits from it [er, what, again? – he’s still there! – ed.] and I’m pretty sure that he’s seen on the forums as a troll and a troublemaker, talking shit and being aggressive. Some of that criticism may be deserved, but he’s a relativist; for the most part he recognises that our beliefs and views are separate from us, and thus he expects people not to feel any resentment about his disagreement. Within the scientific/engineering community this is often poorly appreciated: facts are highly prized, and facts are facts, not opinions, so if there’s a disagreement someone is right and someone else is wrong.

The difference between “that’s a stupid statement” and “you’re stupid” – which is the watershed on a lot of forums – goes deeper than just a handy distinction for separating dispute from insult. One example that came up is “liar” and “a lie”. JB – I think it was – argued that if someone has clearly been shown to have told a lie, then they are by definition a liar, so calling someone a liar should be an exception to the no-insults rule.

But to someone who understands a bit more about relative viewpoints, or just has a little deeper understanding of psychology and philosophy, this argument doesn’t stand up to scrutiny. Firstly, whether something is established as true is a doubtful proposition (due to the self-referential quality of language, if nothing else), and secondly, it is generally considered unlikely that any human being has not lied at some point, so by the definition we’re all liars.

Logically, this doesn’t mean it’s an offence to point it out, but it’s a bit like saying to someone that they are “nuclear waste” (as opposed to “stardust”), or “somewhat evolved slime” (rather than “a human being with a brain that is an example of the most complex entity in nature”). Clearly, calling someone a liar has meanings of greater social significance than saying that the statement they just made was untrue.

Similarly, some were angry when RP called spork a “fundamentalist”, and a few posted to say that the word had very offensive connotations, but RP posted a standard definition of the word, from which it was clear that belief in the tenets of classical mechanics, or of science, without any doubt, could be a kind of fundamentalism. Again, it could be said that it had greater social significance than the definition, like “liar” does, or one can observe the accuracy or otherwise of the meaning that the speaker intends to convey, and if it is not known, ask more to find it out.

One can take offence with a semi-conscious image in mind of a suicide bomber, or one can try to learn what another human being is trying to get over. Understanding what the other is trying to get over has to come before working out whether we agree or not; deciding how to respond should then come even later. What too many of us do too much of the time is react to communication at an autonomic level: a word triggers a gut reaction as it filters through the unreflective lizard brain we all still have below the grey matter.

Of course, in the world of science, it is often argued that the facts are pure and simple, established beyond doubt, and all that relativistic nonsense should be kept in its social context. The next minute, the same people might argue that they’re not fundamentalists in outlook, because science is about holding theories reasonably tentatively, being ready to doubt them and overturn them in the light of more empirical evidence or powerful theory. There is a healthy balance of these things, which I feel does defeat many of RP’s arguments for relativity (where they apply to laws of physics). On the other hand, too many scientists push the boundaries of the absolutism of science, or they fail to appreciate the postmodern insights into language that make such statements as “I’ll find the quote where you said it”, or “I know exactly what you’re saying and it’s just plain wrong” childish extravagances or denial.

A perfect example happened in my last few days’ involvement, when I tried to help spork and another poster, “asymptotic freedom”, to recognise that they were misunderstanding each other in their discussion. Spork said there was no misunderstanding, but AF acknowledged it as a “mis-communication”.

If anyone was paying attention through these months (for some, years) of debate, it would be clear by now that we often take a simple statement or question as though its meaning is totally unambiguous – “does a balloon track the wind?” for instance – only to discover that each of us may assume different bounds and relevant conditions, and we might set off arguing about the answer and not realise we’re discussing two different things. One way to try to avoid that is to establish the correct meaning at the beginning, but some details may only come to us as we investigate the question, and if we’re already pissed off we’ll not be free to discover them with equanimity. We get too invested in having the right answer already, and our discussion with others, instead of being a mutual discovery, becomes a fight. Science, of course, is full of it.

The “pissing match”, as spork called it, of DDWFTTW was amazing fun at times and brought out some people’s best humour. I’m sure everyone learned a few things, and a lot of people learned a lot of things.

I nearly got to the point of wanting to study mechanics at university or something, although I’ve backed off from that since. I know I can’t get my head round maths problems quite the way I used to, and there are other things that interest me more.

As an ex-therapist I’m aware that I often have unconscious motives for the things I do, and I suspect that all this involvement in a physics problem was to give me a break from my own pressing personal problems, and I think I’ve come out of the other side now, clearer of the answers to those life questions. I was taken down-life faster than the life, while my unconscious sorted out the mess that I was only making worse by worrying about it.

As Spring springs, I’m gearing up for getting a new motorcycle [yep] and starting work on getting a book published, which is almost finished in draft form [nope]. I also intend (when I’ve got a new laptop to replace my desktop machine[yep]) to use the space freed up in the study for recording my music [nope], something I’ve neglected for years[yep]. I hope to blog a bit more frequently[nope] and on a wider range of subjects in future[nope].

In the meantime, one of my new pleasures these days is listening to RP’s voice mail most mornings – it’s like my own personal Letter from America – and sending mine to him. It’s down to his enthusiasm for that medium that I got into it. Thanks, RP.

It was weird at first, but I quite enjoy it now. Talking in a 2-way conversation on Google Talk is slightly more difficult at the moment, because I haven’t got used to the dropout that happens as each of us tries to talk – I guess it’s just one channel – and because he talks most of the time 😉 but voice mail is a revelation. Being able to talk to someone is quicker than typing emails, even for a fairly quick touch-typist like myself. Like an email, each participant can pay attention to it when they have time – also an important consideration when there’s about 8 hours between us, me in the UK and him on the “left coast” of the US. It’s one of the best forms of therapy, and has some interesting features in common with traditional forms of therapy. You’re talking to the other, knowing that they will listen (and, if it’s a good friend, understand and be sympathetic), but they don’t keep interrupting with “helpful suggestions”.

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17 Responses to Directly Down Life Faster Than The Life

  1. numnm says:

    LOL at RP bigging himself up in a faux blog.

  2. lettersquash says:

    😀 He sure is one helluvaguy.

  3. the ghost says:

    Here it is 2011 and there still is no evidence the ddwfttw cart works. Forget the treadmill: That is a rotating frame of reference and no galiliean transform is valid from that frame. try to find an inertial frame 9moving in uniform motion ) where the treadmill belt is not rotating! (you can’t) so the transform is bullshit. take away the treadmill and there is nothing at all to support the claim. humber was/is right all along and spork is the troll.

  4. lettersquash says:

    The belt “rotates” (at least at each end of the treadmill), but it’s not a rotating frame of reference.

    For any mechanical system you can construct any number of intertial frames (“moving in uniform motion”, if you like, but it doesn’t really make any sense – the whole point of an inertial frame is that it is considered at rest). You could choose the room, the bottom of the treadmill as it returns, a passing vehicle (not accelerating), etc, etc.

    Hence, considering the steady velocity at which the top of the belt is moving as zero makes that a perfectly acceptable inertial frame, which is the one used to prove DDWFTTW.

    Here it is 2011 too, BTW. 😉

  5. lettersquash says:

    Hi Harold?

  6. Donald Telfer says:

    Downhill Faster than the Wind has a website.

    I could only find two “videos” on the website. The first video runs 39 seconds, consist of about 5 shots cut together, & looks more like some 1970-ish Super 8 cine film transferred via a telecine machine to video. It shows a cart moving, in what in different shots look like an airfield, a carpark, and then a sportsground.

    But it does not show the “Blackbird” model. It shows something that looks like a backyard garage job.

    The second video I have not watched (yet, on this computer), it could be a video of parts being made or assembled. I get the feeling it is not going to show a field test.

    There are no diagrams of the transmission design on the website.

    So I am wondering where the videos are that they are posting, or which videos are they ? There are plenty of still photographs.

    Are there no videos of it in action uploaded onto their website, and if not, why not ?

    I suggest that if it can go faster then the wind downwind then maybe people should ask themselves can it continue to accelerate, 3 times faster, 4 times faster, 10 times faster ?

    If one of the sponsors is Google, there should be plenty of video of this, maybe it is on YouTube, does Google own YouTube ?

    Is this some kind of advertising prank ?

  7. Donald Telfer says:

    I have now found that there are five or six other videos on the website – I found them by re-tracing my search back up the webpage, they are on the right a couple of scrolling pages down from the top. So I am now waiting… for some video called The “Money Shot” to download and run.

    I am still waiting a couple of minutes later, and it is redirecting to a YouTube video with an associated name David Glover.

    A minute or so more, and it is nearly ready, but according to the title it is going to be an Opposing the WInd video. Drat. It runs 23 seconds, and seems to have hung at the 13th second, somewhat appropriately. The prototype in this shot appears to be a different model of the cart. But at least they have a small flag fluttering in the breeze, what I would call a telltale if this was a yacht.

    Maybe between one and five of the other five remaining videos, is/are the downwind ones ?

  8. Donald Telfer says:

    A few hours later, with nothing going on at the museum here now, I have not looked at the remaining five videos yet.


    For example:

    If the wind was blowing south at 10 mph, and Blackbird was facing south, the 10 mph wind would exert some force against the windmill blades, irrespective of the pitch (or feathering) of the blades, and the shaft/axle carrying the blades should rotate. Assume the wheels are indeed connected to some nebulous “transmission” connected to the blades. The contraption would begin to accelerate from 0 mph, southwards, and the wheels would turn. As the cart increased in velocity, the pressure exerted by the wind against the blades would decrease as the cart´s velocity increased, because if the cart reached say 4 mph, then the wind would only be pushing against the blades at 6 mph, the acceleration would diminish, and the velocity would stabilise at a finite value, something less than 10 mph.

    You should ignore the claim from the inventors that the wheels make the blades rotate, the wheels simply don´t make the blades rotate (unless the vehicle is pushed by someone, or there is an engine connected to the wheels). The only two agencies that make the wheels rotate are either the “normal” (i.e. opposing, as the word is used in physics) reaction of the wheels against the ground (when someone else is pushing the vehicle) or torque from the wind twisting the blades conducted to the wheels via the transmission.

    If the gear train was such that rotation of the wheels forward made the blades turn in reverse (compared with the previous paragraph) then the cart would need to have someone pushing it – or the blades would need to have the magical property that they could create/generate matter in the form of air (as they would in effect be pumping a lot of air the wrong way in the wind, the “lot of air” that they would need to be using presumably cannot be created out of nothing.)

    I hope I am not wrong.

  9. Donald Telfer says:

    Before anyone teststhis for themselves, I would like to point out that there is no need to build a large cart 15 feet long or so, you can instead do it easily and relatively cheaply with a small model, say something about a foot long.

    Hey, why didn´t they think of that ?

    Remember not to put your foot in your mouth, though.

  10. lettersquash says:

    Oooh, fresh meat! 😉 – Hi Donald, and thanks for your interest. I’m sure you are wrong, unfortunately, but it sounds to me like you’ll get this without too much trouble. You sound like you have some sailing background, and of course I know you have physics. I’m sorry, I haven’t been keeping up with their various websites or the project itself lately – the net is stuffed with DDWFTTW diagrams, maths and videos, but it’s a bit scattered as I remember.

    “You should ignore the claim from the inventors that the wheels make the blades rotate, the wheels simply don´t make the blades rotate (unless the vehicle is pushed by someone, or there is an engine connected to the wheels). The only two agencies that make the wheels rotate are either the “normal” (i.e. opposing, as the word is used in physics) reaction of the wheels against the ground (when someone else is pushing the vehicle) or torque from the wind twisting the blades conducted to the wheels via the transmission.” – bearing in mind that English descriptions don’t quite explain actual mechanics too well, there is another force that can push the cart, the wind, and yes, the normal force (or braking force, or whatever you want to call it) is what is driving the prop – note – against the wind. First thing to get is that this isn’t a turbine.

    Imagine that instead of someone or an engine pushing the cart, the wind is. Imagine that the prop has a very short pitch (i.e. almost perpendicular to the wind direction). Now, there’s a force on the blades that is transfered via the chassis to the wheels, pushing it down the road. In the extreme, imagine the prop at zero pitch or fixed with a brake – the wind blows it forward, just like it blows a cardboard box down the road. So it is forced to roll forward, if it has enough rolling resistance at the tyres, yeah? And that rolling forces the prop to turn, creating thrust, blowing wind against the oncoming wind. That’s not reducing the wind pressure as the cart gains speed, it’s increasing it. It’s about getting the pitch right so that you make this bluff wind-resistance force of the machine (translated into thrust) overcome the tendency of it to turbine (which it is ‘trying’ to do, and it is thus ‘trying’ to drive the cart upwind).

    I’m a bit busy at the moment, but I’ll dig out some more for you later if you like. To be going on with, if you’re still doubting it, here’s a little puzzler – imagine you have a bike wheel on the ground with the axle east-west (kept upright by someone, or two fixed to an axle if you prefer). Imagine you apply a force to the wheel southwards, but at a point directly below the axle somewhere (say, half way down towards the tyre). Imagine that as the wheel turns, you keep applying the force always at that point below the axle.
    1. Which direction does the bike wheel move?
    2. How fast does it move compared to the point at which force is applied?

  11. Donald Telfer says:

    Thanks for your explanation.

    I would like to see any videos, the computer I am using can play video but it is an old computer with a shortage of RAM, shortage of both chip RAM and virtual memory, which is being continually encroached upon by “Shockwave Flash Player” – I suspect. But I cannot get rid of it (installed by someone else, and I do not have the privileges (?) to remove it.)

    To answer your two questions (if I understand what you describe in words), I think:

    1: The centre of the bike wheel moves southwards. The tyre at the top is instantaneously moving south on the cusp of turning down. The tyre at 9 o´clock is moving slightly south of directly downwards. The tyre at the bottom (on the ground) is momentarily stationary. The tyre at 3 o´clock is moving slightly south of upwards.

    2. The centre of the wheel is stationary relative to the point at which force is being applied. All the points around the tyre are moving in a kind of eccentric ellipse or oval relative to the point at which the force is being applied. (To a standing observer the motion of individual points around the tyre would look something like a spring that had been over-stretched, or like a coiled garden hose pulled open in a particular way)

    Good hunch, I have some sailing experience, I spend 9 to 11 months each year living on a replica of an early 19th century small wooden sailing ship. The museum is the Rødvig Ship Motor Museum, where I am a volunteer custodian. We have at least four working exhibits here of feathering propellers (for forward and reverse changeover via propellers instead gearboxes).

    We have the rotor/fan from a turbine at the museum too. I think I have not confused anything here with a turbine.

    I also (I think) have not neglected that wind can push the vehicle, I may not have explained myself clearly ?

    I was thinking :
    if the wind is 10 mph southwards,
    and the vehicle has accelerated to 7 mph southwards,
    the air ahead (south) of the blades is moving southwards from the surface of the blades at 3 mph,
    for the blades to be giving any push I think there needs to be some other air (out of thin air ?) for them to push.

    I also think…, it could be considered what happens underwater, you get cavitation, when the propeller rotation exceeds the water supply you get bubbles (a vacuum) the propeller loses mechanical efficiency, chopping through a vacuum will not move a ship. (I may be wrong here, maybe the cavitation is on the wrong side of the boat propeller ?)

  12. lettersquash says:

    Hi Donald

    “1: The centre of the bike wheel moves southwards.”
    – Correct – you’re doing better than I did on first try!

    “2. The centre of the wheel is stationary relative to the point at which force is being applied. All the points around the tyre are moving in a kind of eccentric ellipse or oval relative to the point at which the force is being applied. […]”
    – Correct, but the directions aren’t quite the point I wanted you to consider. The point where the the force is applied is momentarily moving southwards (as are all points in a vertical line from the centre to the tyre, except, as you say, the very bottom, which is momentarily stationary). The question relates to how fast the wheel (i.e. the centre, or, if you want to think of it this way – the vehicle) will move, steady state, compared to the point at which the force is applied. The latter is a bit tricky to think about, because it’s never the same point on the physical wheel, but theoretically we can think of it as a very tiny … hey, what the heck – fin – being hit by, er, let’s say air molecules!

    I don’t think spork (Rick C) or his partner in crime would say they were the inventors, by the way. They know of at least one much earlier craft built by a certain Bauer that probably beat windspeed, and Bauer also analysed the mathematics of it. He built a sit-on vehicle, like a primitive Blackbird, but you’re right, of course, you can have a very small version. They tested it on a treadmill.

    I, on the other hand, might just possibly the inventor of something called the watercartwheel, which is basically a pair of coupled wheels rolling along on a flat surface, with a paddle-wheel inset at a shorter radius between them. This is placed over a long, raised trough of flowing water, so that the bottom of the paddles sit in the water. This replicates in principle the bike wheel idea above, so we can ask (ignoring frictional losses) what speed the watercartwheel should accelerate up to if placed over a trough of water flowing at v, assuming the water touches the paddles at half the radius of the road wheels…or any other radius if you’re ready to generalise the question. There’s a really amazing surprise when one does.

    “I was thinking :
    if the wind is 10 mph southwards,
    and the vehicle has accelerated to 7 mph southwards,
    the air ahead (south) of the blades is moving southwards from the surface of the blades at 3 mph,
    for the blades to be giving any push I think there needs to be some other air (out of thin air ?) for them to push.”

    Your numbers are right, but not the last bit. The problem is partly due to English descriptions again – it’s the same air. Perhaps I can make it clearer by pointing out that the prop is “slowing down the air”, rather than “pushing it backwards” (and I imagine you’ll know that these are the same thing depending on which frame of reference you choose). At below windspeed, as per your example, the wind is still overtaking the cart, but, since it is forced to rotate and create rearward thrust (via the gearing, from the wheels’ rolling resistance, and ultimately from being pushed along by the wind) it is slowing the wind (relative to the ground), and thus extracting energy from it. Above windspeed, it is of course overtaking the air, but it’s still slowing it down relative to the ground. The air isn’t going backwards in that frame – just a little less than the 10 mph of the free stream. In the cart frame, it is going backwards, obviously.

    This is the bottom line of the explanation: the cart does not gain energy from the relative motion of the air and itself, or from the relative motion of itself and the ground, but the relative velocity of the air and the ground.

    To answer an earlier question – there is theoretically no limit, but of course there are increasing losses due to friction in the real world.

    Cavitation is a feature of water screws because it’s made of air bubbles. It doesn’t apply in air (unless you get to the sorts of energies where it’s time to call a nuclear physicist because we’ve created a plasma or something!).

  13. Donald Telfer says:

    Thanks, I mostly understand what you have written, although I might have temporarily originally misunderstood the significance of the part in your previous message about the pitch of the blades being fine tuned at some acute angle to the wind direction, and if I now understand what you meant originally there, I may have now newly misunderstood the relationship between the blades and the distance from the centre of the wheels to the place below the axis of the wheel (which I anticipated was going to have something to do with ratios and leverage, but perhaps it doesn´t).

    Also I have newly learnt something about cavitation today which I did not know before, as there is an article in German, but not in English (?) on c(K)avitation on Wikipedia. I was wrong to write the bubbles are a vacuum, according to WIkipedia they are water vapour (!). And as your reply points out, cavitation only occurs in liquids, not in gases (I guess because gases are more stretchy/squashy than liquids).

    I should be on a faster healthier computer at a library for an hour or so tomorrow so I can look for, find and watch whatever I may find by way of videos, and/or diagrams.

    You should build a watercartwheel, even just a model, if you haven´t already, I would like to see a picture of it. Maybe you should patent it first though.

    Danmark currently has a slight relativity issue on the TV stations, the equipment for the digital programme guides thinks it is an hour ahead here of the true local time.

  14. lettersquash says:

    The pitch of the prop is important, and the way DDWFTTW works is often described as being about leverage. The bike wheel, watercartwheel or wine glass are useful simpler models of the main principle. I’m not surprised that I may have confused you. I tend to get carried away and give loads of information at once.

    I have wondered about building a watercartwheel, but it’s a lot of work just to demonstrate a principle that’s already been demonstrated. But maybe I’ll get round to it sometime, as I’ve had a recent brainwave about how to do it fairly simply. I’ll be sure to post a video and give you a shout if I do.

    Since I got off track a bit last time, I’ll briefly say what I should have said before. The answer to question 2 is “Twice”. The centre of the bike wheel is moving twice as fast as a point half way between it and the ground, which is where we’re applying the force.

    What does that mean? Well, if I’ve given you enough of a picture of the watercartwheel – it is just a way of getting the force to stay at that point below the axle (by making it some paddles) while the wheel is free to roll. So if we imagine the wheel could be accelerated up to waterspeed and analyse the situation at that velocity, since the axle is going along at the same velocity as the water, (say, Vw), the paddle at the bottom, in the water, is going Vw/2. Hence, the water is applying force to the upstream side, and it must still be accelerating. It will only stop providing a positive force accelerating the watercartwheel when the latter is moving downstream at 2*Vw.

    In the ideal (no friction), we can even move the paddles out further towards the ground, and the multiple increases towards infinity!

    Now, what they’ve done is a bit like transformers in the film – they turn the paddles into a prop geared to the wheels. There is a direct correlation in the physics. Just as the lowest paddle of the watercartwheel is always going slower than the axle, every point on the blades of the prop of the DDWFTTW cart is going slower than the cart in the direction of travel. That causes the cart to continue to accelerate beyond windspeed. The faster it goes, the faster the prop spins, and so the more those points on the prop blades (the component of their motion parallel to travel) are going slower than the vehicle.

    Ultimately, the reason the cart can go faster than the wind is because it keeps part of it going slower than the wind – the part that’s being pushed.

    I hope you get a faster computer – there are some great videos out there! But I expect you would enjoy some of the maths analysis, which is right over my head. I’ll keep looking for stuff with smallish file sizes for you.

  15. Donald Telfer says:

    Thanks for your further explanation, and your time. My guess for the numerical answer was 2, but I did not write that because it was a guess, and I was not sure I understood the context of the question, (whether Q1 and Q2 were both solely concerned with “Blackbird”, or whether Q1 was solely about Blackbird and Q2 was a mix of Blackbird and watercartwheel, or something else again). I also was afraid of being wrong. Consequently I did not want to put an answer in writing that I was not sure about and which could later be used to argue for something I did not accept.

    * I started thinking about kinetic energy in the wind, versus kinetic energy of Blackbird. But leave that for a couple of paragraphs. *

    I need to point out that the mathematics I learnt at university over 30 years ago is now mostly just a passive memory. I would not pass the same examinations now if I was asked the same problems as back then. I would like to re-activate my ability in maths though. This is part of the 30 year cycles in my life, which I did not plan that way, it just seems to keep on recurring.

    ** Something similar (to the maths memories) applies to physics, a lot of the university physics is now a passive memory, and in some cases I have unlearned it. (i.e. For some examination questions, if I re-learned physics I could probably again give the correct orthodox answer on paper, but in the case of quantum theory I would now be of the opinion that the answer should be: Mu.) **

    There is a line of thought running between paragraph * and paragraph **.

    There is a kind of water pump. I saw it perhaps 20 years ago, but only on TV, I thought it would be very good for native villages on the sides of hills or mountains. I have not seen inside it. I assume it uses the kinetic energy of a larger amount of water flowing downwards through a pipe to pump a smaller amount of water uphill. So for example you might have a water source at a waterfall where water falls 1 metre. My wife Matagofie was from just such a village, at the foot of a volcano, it had water coming out of the ground, which was lava, at springs and small waterfalls, quite a lot of water in one of the springs, about 20 cubic metres per minute. You can use the potential energy of the upstream water converted into kinetic energy as it drops through a pipe to operate the pump which pushes a smaller amount of water up to a head height of say 3 metres. That water at 3 metres is stored in a tank also at about 3 metres from which pipes lead to the houses in the village, with taps at the ends of the pipes at about ½ metre. It does not need electricity or an internal combustion engine. The overall effect is that (a fraction of the ) water appears to be going uphill, which is counter-intuitive.

    There is a corollary (?) in quantum physics: tunnel diodes etc. Sub-atomic particles can escape from holes without having enough energy to escape from the holes. They are said to “tunnel” out of the holes. Modern physics models this as something which happens at random (I think). Or at least it has particles escaping during radio-active decay as being something that happens at random, but at an overall predictable rate when you have a huge number of atoms decaying at random. But the randomness in the model suggests to me that we do not correctly understand yet what is going on, and hence the model may be (or I think, or Einstein thought) incorrect. They need a new model, and start over again.

  16. Donald Telfer says:

    I am using a computer at the library at Store Heddinge (80km south of Copenhagen), & this computer is working at normal speed, I have been to find and watch about 7 videos via links on their faster-than-the-wind website to Youtube.

    At least one of the videos shows the vehicle accelerating very slowly from zero, picking up speed, reaching windspeed, and passing windspeed, apparently, as far as I can tell. It then has the brakes applied and slows down to a stop.

    There is evidently only slight wind resistance in the body + blades of the vehicle, hence the slow acceleration, whereas a ship on the other hand might weigh 10 tonnes, for which it has about 120 square metres of sailcloth and charges around like an excited horse if there is a strong wind, but does not go faster downwind.

    They might find a better test bed in Australia, on Lake Eyre (when it is dry/empty), because it is bigger, and because I think it possible the wind at Lake Eyre might be less likely to change direction during test runs (as they seem to encounter at El Mirage, I don´t know if that name El Mirage is some kind of in-joke ?)

    I came across some other vehicles on Youtube, which look rather more stylish:

    They happen to conduct their races in Danmark.

    The two videos I saw at the museum a day or so ago appear to be what I thought they were: some archival footage of another person decades ago (seemingly Super 8 cine) – who may have died since then, and in the other case some video of the parts of the vehicle.

  17. lettersquash says:

    He-he, I was wondering whether it was possible to embed a video or photos on comments and thought maybe not, so thanks for showing me you just type in the URL! Those are upwind carts, where the ‘fan’ is acting as a turbine to drive the wheels forward, although you can run an upwind cart as a faster-than-the-wind downwind cart just by reversing the gearing. Interestingly, either vehicle should operate roughly the same way whichever end you point into the wind!

    By the way, in English it’s actually “Denmark”. But that’s one more word than the sum total of my Danish!

    You sound much more cautious in guessing answers than I am, but that’s not a bad thing.

    The water pump is brilliant. I’ve not heard of that.

    Quantum Physics – I just say mu, or “I haven’t got a clue”. I’m a poet. Don’t I just know it?

    “Thanks for your further explanation, and your time.” – you’re very welcome. I’m enjoying talking about this again. Unfortunately, I have seriously confused you with my analogies, I think. The two questions were just about the thought experiment of the bike wheel (I say thought experiment, but it’s not difficult to do…and I actually had to do it to learn that Rick was right).

    On the other hand, that then does apply very directly also to the watercartwheel (wcw). If you try to push a bike wheel half way down the lower spokes, you’re in trouble, because as soon as it rolls away from you, you’re no longer pushing directly under the axle. The wcw just replaces one paddle with the next as it turns. But I’m not sure I’ve described the wcw clearly enough anyway. I don’t have a drawing to hand, but here’s one of the insane discussion threads on the subject, with not only a diagram but an animation. If you see Sarah Bellum or John Freestone mentioned, they’re both me.

    And then that principle also applies to the wind cart – obviously, that’s why I’m telling you about the wheel versions!

    I was chucking a lot of ideas your way because people ‘get’ DDWFTTW from different angles. And yes, I expect your maths and physics might be a bit rusty and isn’t a PhD in aerodynamics, but I’m sure it’s a big help having that as a background when you find some of the mathematical analyses.

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