Down wind, faster than the wind.

Thought of another approach to understanding the phenomena while repairing a hole in the fence. If there was good wind within a 3hr drive I'd be sailing.

Imagine there's one of these devices going downwind at 12 m/sec in a 10 m/sec wind.

From the devices perspective it has a 2 m/sec headwind which it has to accelerate rearwards.

If the prop has an "effective" radius of 1 metre and a blade pitch of 20 degrees in 1 rev, when freewheeling, it will go forwards

2 pi Sin 20 = 2.148 metres.

So in a 2 m/sec relative airstream it will freewheel at 0.93 Hz

If it spins faster it will generate an angle of attack throw air backwards with a lift to drag ratio appropriate to a propellor.

Let's guess that 1.2 Hz is fast enough and that the lift to drag ratio is 10:1

(This would all be subject to tuning in a real device but just trying to see why it could work at this stage)

And then lets guess that the prop has blades of a size and number that under the above conditions the blades generate 10 Newtons of lift (~1 kg)

From the props frame of reference 10 cos 20 Newtons of this lift is in the forward direction and 10 sin 20 of the lift is in the lateral direction, opposing rotation of the prop shaft.

Of the 1 newton of drag 1 cos 20 opposes shaft rotation and 1 sin 20 opposes the forward thrust.

Total forward thrust = 10 cos 20 - 1 sin 20 = 9.05 Newtons.

Torque on the shaft = 1metre * ( 10 sin 20 + 1 cos 20) = 4.359 Nm

Power to turn fan = Torque X angular velocity

= 4.359 X 2 pi X 1.2 = 32 watts

But this 9.05 of thrust can be applied to the wheels via the ground speed of 12 m/sec

Power into wheels and gearbox = force times velocity

Power input = 12 X 9.05 = 108 watts

So you've got 108 watts to put in the gearbox and only need 32 watts to turn the fan - there's a lot of drag, ( gearbox, windage of the chassis, rolling resistance) we've neglected but it's not surprising that it goes and will even have a bit of power left over to climb a hill.

So basically the power to drive the fan in a 2m/sec headwind is less than the power that can be obtained from the thrust by running wheels against the fast moving ground below.

I think the key is the magic of a lift to drag ratio. We have accepted it in traditional sailing,
but don't we baulk when we see the same principal used differently.

This first video was subject of much discussion a couple of years ago on www.ozreport.com (which is a hang gliding forum). In the end I think it turned out to be a fake. I'll try and dig out a link for it.

In the end you cannot get away from the fact that this is a perpetual motion machine and therefore a breach of the laws of physics. If it really worked you should be able to remove the wind and it would continue moving (once moving it is running directly into the apparent wind so the wind is ceasing to provide it thrust). If it worked the world energy crisis is solved.

Yeah, so maybe one day we will get energy for free out of the wind, wouldn't that be nice... ow... we are doing that already? Right!

Good one, but the obvious difference is that you cannot build a motor/turbine on a permanent magnetic force only (but yes, people have claimed that also), but you can build a motor/turbine on wind energy.

And this is even more obvious if you use the rough calcs in my previous post. It's a linear sort of thing so all the ratios can scale if you fiddle with the numbers. You can use knots instead of m/sec it's all proportional.

To generate the same thrust in a 12 knot head wind you have to spin that prop 6 times faster than in a 2 knot headwind. The power required to spin the prop is thus 6 times as great. ie using the sample figures - 192 watts. But the wheels at 12 knots only supply - thru the gearbox - the same 108 watts - It's not going to keep going.

You can also fiddle with the figures to find the ratio of ground speed to wind speed when the power required to turn the fan equals that generated by the wheels. At about twice windspeed the power figures are a pretty close match - ( A lot of drag has been skimmed over so that is optimistic for a real device) To improve the ratio of ground speed to windspeed you need to use a fan with a better lift to drag than 10:1. It all gets down to lift to drag again.

It's never claimed to be a perpetual motion machine, and it will stop if there is no input force. The laws of physics are unbroken, but you do need to bend your mind a bit!

The non-intuitive part is that the device isn't using the wind to 'waft it along' once it reaches wind speed. In the same way that a windsurfer can travel at more than the wind speed across the wind, the propellor is able to travel at an angle to the apparent wind (as seen by the chassis).

Think of the apparent wind relative to the spinning propellor blades, don't get distracted by the apparent wind seen by the chassis.. they're not nearly the same thing.

If, by travelling faster than the wind, we windsurfers are "extracting more energy from the wind than the wind is theoretically able to impart", does that make us perpetual motion machines, and mean that the wind is really irrelevant once we get going?

You do realise that $1,000k is more than $100k? You only need $10k to take on Spork's 10:1 bet..

I'm sure this will run and run...but here goes.

A wind surfer on a reach is a false analogy. On a board we are using the sail to deflect the wind and create a force with a forward vector. When crossing the wind our boardspeed makes little difference to the lateral force our sail experience (so the force on the sail remains roughly constant irrespective of board speed - a gross simplification but will do for now). This allows us to accelerate beyond the wind speed. The geometry of this situation starts to change quite markedly as we turn directly downwind. Here the faster we travel the less force our sail experiences.

Perhaps I can find another way of explaining why the machine in the video doesn't work. A propellor turning in one direction will only push air one way. Equally wind moving through a prop will only turn it in one direction. In the case in the video the prop is first driven by the wind. This wind is coming from the back of the vehicle. As ground speed exceeds wind speed the wind direction seen by the prop reverses (it now appears to the vehicle to be coming from the front). The wind should now be slowing the prop and therefore slowing the vehicle. It is absolutely no different to running directly down wind on your windsurfing board, as board speed approaches wind speed the force on the sail approaches zero. If board speed exceeds wind speed (say in a lull) then the sail is now slowing the board. This is why running downwind is so different to a reach as far as your ability to exceed wind speed goes.

I suppose it doesn't get away from the fact that I can't tell $1,000 from $1,000k!!!

The prop isn't driven by the wind during start up. As soon as the device moves forward the wheels drive the prop in the opposite direction that the wind would like to turn it.

So during start up the prop is stalled , it's just drag that inches the device forward. But once it gets enough forward speed the prop goes aerodynamic and it's away. The wheels drive the prop in the opposite direction that the initial tail wind wants to turn it.

You missed it again..

Think of one of those great big huge wind turbines. Now, attach a smoke cannister to the end of each blade and let it spin. The smoke will trace spirals, (not three straight trails) which suggest that while the turbine tower sees a 'headwind', the blades are seeing something a little different as they rotate.

We're not dealing with any kind of 'air catching' device like a sail, spinnaker or shopping bag.. it's a spinning propellor.

In effect, the rotating propellor is able to use the difference in wind vector due to it's rotation to still see a lateral component to the wind. Despite the fact that the device is moving dead downwind, or slightly into a headwind, the blades are still able to push against the equivalent of a slight crosswind on a windsurfing sail. Certainly, as the device goes faster into the new head wind, the lateral component is decreased, and you'd either have to change the pitch, or preferably the speed of rotation to compensate up to the point where the drag on the rest of the system prevents any further increase in speed. To an extent the increase in speed is automatic via the gearing.

If your brain works this way, replace the propellor blades with windsurfers, and consider the angle that the wind will hit them as they spin. (awkward I know seeing as the board will be providing the power, not the sail, but it may help get your mind around it!)

Maybe we can convince 'Landyacht' to build a big one to run on the salt flats!

Hi all.

I'm JB and I'm the guy you see in the treadmill videos posted here. My partner and I have built and tested several of these carts in various situations.

It's not perpetual motion. It's not a hoax. Is simply and basic and long utilized sailing principles packaged in a untintuitive way.

The prop is simply two sails on a broad reach while the chassis goes DDW.

The treadmill set at 10mph in a still air room is the exact equivalent of going straight downwind at 10mph with 10mph wind blowing.

Our best device (so far) will beat the wind with as little wind as 2.7mph on the level and at our highest treadmill setting (10mph) will climb a 4.4 degree slope.

Someone previously said they would give $1,000 for a working model and commercial rights -- sold! Actually, we've posted the parts list many places (can here if people wish) and you can build one for ~50 US.

It truly is a novelty with no new technology and no real value other than creating a unreal amount of hubbub on the internet. We had no idea it would cause this stir.

Happy to answer questions if there are any.

JB

DL .......WHATS BROUGHT THIS ON ........HAVE THE BATTERIES RUN OUT ON YOUR AVATOR PICTURE

Like a flying fishing out of water ? traveling down wind ? motion less in time ?

I CARNT PLAY my heads hurting

Select to expand quote

[quote
Or from a bipartisan's perspective you could say the device is extracting energy from the velocity discontinuity between the two mediums.

Yeah, thats what I thought too, the old velocity discontinuity trick between the mediums...

I was tempted by the forecast too, then put off by the big dark clouds, but its quiet as a mouse now, no rain, no wind.

As you saw in the photo of the boat on the canal you need quite a big blade set up . the thought of that wizzing over your head is scary. Ive no doubt it would work tho, as a land yacht the only advantage I could see would be the ability to go directly upwind. I suspect a regular landyacht would be faster.
there could even be some rotation effects similar to helicopters that need to be considered.
But yes It could be done. so many ideas, only 1 life[}:)]

The Goodman video is most definitely not a fake. It was however the subject of much debate. JB and I were naive enough to think we could answer all the skeptic's concerns by building our own cart and performing our tests in controlled conditions. This is why we chose to use a treadmill in a closed room. No worries about wind direction, wind gusts, downhill, etc. We thought this would put the issue to bed - not fan the flames.



Actually, we got away from that fact quite easily by convincing the laws of physics that it's a simple wind powered machine - nothing to see here - move along...



That would be a great machine indeed. But it certainly isn't what ours does. Ours has the very unfortunate property that it coasts to a stop when the wind stops.

If anyone wants to try this at home you should check out the build videos I posted last night:


Build video 1 of 3:


Build video 2 of 3:


Build video 3 of 3:




How about if I ship you a working model? Will that get me the $1,000K (or the $1000 or whatever)? I can send one tomorrow. We can talk about sharing the Aus rights.

Gradient works against us - just as it does for windsurfers. The less gradient we have the better our cart performs.