How about: is it possible for a wind powered vehicle to "sail" directly downwind faster than the wind is blowing?
No
Is it going down a hill?
Is it on a conveyor by any chance? If so, then probably yes
Are really strong magnets involved?
all things are possible if you believe
If the wind is gusting then technically yes but if it is steady wind on flat ground then no.
Yes, simply attach a large funnel to the vehicle to collect the wind and direct it at the sail
Yes. The wind can slow down, but wind powered vehicle will continue at a faster speed. Unless it's not on wheels.
It's possible for a vehicle to travel faster than the wind. Not directly in the direction of the wind, but the filled sail acts like a wing and generates 'lift' the magnitude of this force is what governs the speed of the vehicle. (of course other bits as well)
Some clarification:
the vehicle is moving in exactly the same direction as the wind.
the wind is blowing at a constant speed, and doesn't ever slow down or stop.
it's on flat ground with no conveyor belts, magnets or any other external forces.
Then no. Sails work most effectively in lift. is this a theoretical question or a problem that needs solving?
Has it got any booster rockets ?
No booster rockets, the only force involved is due to the wind (and a bit of friction).
Yes. 2.8 times faster than the prevailing wind.
http://boingboing.net/2010/11/05/downwind-faster-than-2.html
Yes. 2.8 times faster than the prevailing wind.
http://boingboing.net/2010/11/05/downwind-faster-than-2.html
My guess is that going 2.8 times faster than the wind has everything to do with the fishing rod strapped to the front of the car..
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yes - its all about apparent wind
seriously!!
Wind car sponsored by Joby
Trick question? The "wind" is from cows farts and is caputured in a big tank and used to power two jet engines?
Instinctively I would have said no, but after reading [url] http://dwfttw.blogspot.com/ [/url], I'd say yes.
Actually reading the OP's question again, I would say no, as he uses the term 'sail', which a wheel driven prop isn't, by any conventional definition of 'sail'
So the OP needs to define more clearly what 'sail' means.
I think you need to read the question again again. Not only did I use quotes round the word "sail", it's also being used as a verb. I don't suppose the propulsion device used on the latest US Americas Cup yacht is what most people would call a sail - does that mean the yacht wasn't sailing? I'd argue that by any conventional definition of the word that vehicle is sailing, as it's using energy from the wind to move.
Surprised how long it took anybody to google!
Now having established what did happen, does anybody on here understand how it works?
Or explain this:
does anybody on here understand how it works?
It works on [i]exactly[/i] the same principle as a propeller on a plane or boat does ? The only difference being that it is powered by wind, as opposed to being powered by internal combustion/steam.
I guess you could have a huge "wind farm" type turbine on a ship which drives a ships propeller to the same effect. You could also have the turbine drive an electrical generator which powers the propeller (or wheels)
You're suggesting the prop is powered directly by the wind? How does that explain the treadmill video where there is no wind?
That Joby wind vehicle has so many jokes going for it, I don't know where to start
AFAIK the faster than wind vehicle uses the tailwind to turn the prop that is linked to the wheels by a very clever and very strong gearbox. As the vehicle accelerates the forwards rotation force of the wheels overtakes the roation force of the wind driven propeller and this starts to turn the propeller via the same gearbox, making the car go faster, I think there's a flywheel effect in there too...Its not a perpetual motion machine as it uses an external force. It cant sustain this acceleration and it will slow down after a short while.
How does that explain the treadmill video where there is no wind?
You mean the air wasn't stationary.......it was travelling at the same speed as the treadmill ?
Because that's the only way I can figure out how there would be "no wind".
In the same way, there wouldn't be any "wind" if I opened my car window at say 30mph, if the wind/air outside was travelling at the same speed and in the same direction.
I'm not ure what the point of the OP question was. Further i would question if wind-powered was sufficient for a definition of sailing. I've not had a close look, but it looks like the turbines are still acting in lift. Clearly the car is not being blown downstream. I can see how the car would accelerate with a tail wind, but once the car approaches the speed of the wind, the power generated would be so small that i imagine it would have trouble reaching wind speed and further, accelerating beyond it. of course once faster than the wind the turbine can be powered by the now headwind. It's the transition which I'm struggling with.
In the treadmill, it looks like the treadmill is driving the fan, which in this case is acting as a prop, rather than a turbine
It cant sustain this acceleration and it will slow down after a short while.
Nope - it can keep going as long as it likes.
I can see how the car would accelerate with a tail wind, but once the car approaches the speed of the wind, the power generated would be so small that i imagine it would have trouble reaching wind speed and further, accelerating beyond it. of course once faster than the wind the turbine can be powered by the now headwind. It's the transition which I'm struggling with.
Check out this vid, no trouble at all with the transition which it accelerates smoothly through! See from about 1:20 if you can't be bothered watching the whole thing.
In the treadmill, it looks like the treadmill is driving the fan, which in this case is acting as a prop, rather than a turbine
You're almost there - what do you think the relevance of the treadmill video is, and do you understand the concept of inertial reference frames? http://en.wikipedia.org/wiki/Galilean_invariance
Not entirely sure what you are trying to lead me to with those questions.
I'm familiar with the idea of reference frames, though I'm not sure how they explain my underlying concern about how the car can accelerate past the 'no wind' situation, without an external motive force, be in stored inertial, or other.
I can see how the treadmill replicates the 'no wind' with velocity situation. But there is external power too.
It would then seem that once the car is going faster than the wind, it will continue to accelerate unaided 'until the wheels fall off and burn'.
Not that the idea of external / stored power is problematic. Clearly on a still day all you would need to do is push the car and off you go.
I don't care what you all say, I want on of those cars!
On a day like today I could be at work in MINUTES!! (and with no emissions). Why can I not buy one in the shops?
Yes it's possible, but you need a non-fixed sail to do it (kite). With a fixed sail I don't think the combination of apparent wind and real wind vectors would ever be possible to achieve >1.
And I'm slightly confused by that second vid, unless my eyes are deceiving me the prop is turning the wrong way to start with - with the blades in the orientation they are they should be turning the opposite way, at least according to just about every experiment I've tried with props in the wind!
The wee carts in the treadmill video above (and the full-size one, which is exactly the same thing) are very cool and they can run "faster than the wind", but it's not a perpetual motion machine, they can only go a wee bit faster than the wind is blowing.
The propeller on them is just that - a propeller. It's NOT a turbine - the fan is being driven by the wheels, not the other way around.
I have my doubts about whether they could theoretically accelerate from a standing start, but in reality I think they probably could - just the wind acting on the (stationary) fan and the vehicle body would be enough to get them started.
That video has to be a fake.
Anything travelling downwind without gusts, cannot go faster then the wind is blowing.
Crosswind is an entirely different matter, and the speed depends on the overall lift/drag ratio of the machine.
That video must be a fake. The prop is acting as a propellor (look at the blade angles), so could only be driven round if geared to the wheels of the machine which itself is getting blown slowly downwind because of it's parasitic drag.
Sounds like a hopeless case to me, and then to keep on accelerating even further after the apparent wind reverses is impossible.
Actually, thinking further. By utilizing the wind gradient, something like this might just be possible. The wind at the top of the blade arc is faster than the wind at the bottom because of it's friction with the ground. I haven't got my head fully round the implications in this example, but I am sure there are some useful ones!
If there are other model flyers out there who have done any "dynamic soaring" in a wind gradient you will know what I mean.
I was kinda sceptical of the claims initially, but am coming round to thinking that it probably does work, although I am still waiting to hear a satisfactory explanation of why it works...
What I have gleaned so far is this:-
The wheels drive the prop, there is a ratchet mechanism that stops the prop driving the wheels.
This is not some kind of free energy machine, and it won't move when there is no wind.
Apparently this effect has been known about since the '60s.
At standstill, the wind pushes against the whole car, prop included, and this is enough to get the car moving slowly, at this point the prop is turning very slowly, and not really acting as a prop at all. The wind still keeps the same pressue on the car though, so it continues to accelerate slowly.
As the speed of the car increases, the prop will turn faster and faster, until at some point the prop will start to provide forward 'lift'... at this point the car should start accelerating faster. I'd guess the limiting factor in how fast it can accelerate here would be the losses due to machanical friction in the drive train and aero drag, both by the buggy and the prop.
Now, the problem I have is working out how it still takes energy from the wind while travelling faster than the wind... I can't quite see the mechanism for how this happens... and it's bugging me!
What's the tide/current doing?
Nothing.. it's a land vehicle.
My thought is this: Consider the craft equalling the windspeed measured (for example) at the altitude of the prop hub. The top of the blade arc will still be in a small tailwind, whilst the bottom will be experiencing a small headwind. (There is no wind at zero altitude because of friction, and there will be something in between at the bottom of the arc).
So with the vehicle at "windspeed" (at the arc centre), the bottom of the arc is in a headwind and the blade down there will be driven by the forward movement of the vehicle, the top is still experiencing enough tailwind for the blade there to be able to drive the car a little faster than the wind speed.
So energy is gained from the wind gradient and the rotating "sail" effectively mixes the slow moving air near the surface with the faster moving air up high. This mixing increases entropy (ie mixing of the wind gradient) and thus extracts the energy from the wind gradient itself.
Similar principles allow an non-powered aircaft (ie a glider) to remain airborne indefinitely by flying repeatedly across a wind gradient boundary. This is easy to prove and fun to do if you are a model aircraft flyer.
I think this might allow it to propel itself very slightly faster then the wind.
It's the only way I can think it could ever work.
Why are the top and bottom of the arcs in headwind and tailwind?
Above all else, I cant' see how the pressure balance equations work out if the car is moving forward in headwind
@charlieMungus. Air is viscous, and friction will always mean the bits of air at ground level won't be moving at all, whilst high up you have the greatest windspeed. Naturally in between the wind varies with height. It does this most over the first few metres.
Sea birds such as the Albatross and to a lesser extent even seagulls use this wind gradient all the time to soar the turbulence.
here is a video (happens to be me) flying a model aircraft on the lee-side) (ie the back) of a hill. All the air is going downwards and the model has no engine. - yet it's quite possible to fly the model indefinitely in circles. This model happens to be quite inefficient, it's not very good and is loosing energy all the time. So where has this come from? it's come from causing mixing of the two horizontally moving airmasses.
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If you imagine the model is in fact the rotating blades of the air-car thing, then those blades will be driven round and can extract energy from the CHANGE in the windspeed - not the actual windspeed per se.
.Air is viscous, and friction will always mean the bits of air at ground level won't be moving at all, whilst high up you have the greatest windspeed
Ok, so you mean boundary layer effects? Forgot about them.