Downwind Faster than the Wind - Successful Run by manned cart

[PaulJS]

In simple terms...

Having started off as a disbeliever, then seeing the desert trials, and then revealing myself as not being the brightest spark on the bonfire by falling for SnowLeopards April Fool explanation, here's how I now understand it:-

At standstill the propellor, together with the lightweight chassis only has the force of the wind acting to push it.
If there is enough wind the chassis will start moving forward, and the wheels will start to rotate the propellor counter to the direction in which the wind is trying to turn it, even at low rotational speed this will give slightly more resistance to the wind so the cart will go faster.
Eventually when the cart is moving at wind speed the propellor will be giving thrust relative to the wind pushing the cart and the cart will accelerate to a speed faster than the following wind until a balance is reached where the propellors thrust and the following wind thrust is balanced by friction and apparent wind resistance to the cart chassis.

Writing this down I still feel as though I'm being wound up - (probably like the elastic band on the cart's propellor )

 

[mikemonty]

It is never "wrong" to use a different reference frame. And in this specific case, clinging to the idea that ground or water define an ideal or preferred reference frame is very counter productive for the understanding. It is exactly what gives the deniers the wrong idea, that you cannot extract energy from the true wind, when you are at rest relative to the air.

I disagree.
And very shortly I'm going to get in my car and pull the universe round until my home appears.

 

[snowleopard]

At standstill the propellor, together with the lightweight chassis only has the force of the wind acting to push it.
If there is enough wind the chassis will start moving forward, and the wheels will start to rotate the propellor counter to the direction in which the wind is trying to turn it, even at low rotational speed this will give slightly more resistance to the wind so the cart will go faster.
Eventually when the cart is moving at wind speed the propellor will be giving thrust relative to the wind pushing the cart and the cart will accelerate to a speed faster than the following wind until a balance is reached where the propellors thrust and the following wind thrust is balanced by friction and apparent wind resistance to the cart chassis.

A good summary. Your user name is very appropriate. Been to Damascus lately

 

[snowleopard]

I disagree.
And very shortly I'm going to get in my car and pull the universe round until my home appears.

You can of course do that but the acceleration imparted by a 2000kg car to the Earth (mass 6 x 10^24 kg) might be a little hard to measure.

 

[mikemonty]

You can of course do that but the acceleration imparted by a 2000kg car to the Earth (mass 6 x 10^24 kg) might be a little hard to measure.

Oh gosh no! No longer than usual! You see, my frame of reference is going to be the car.
The fact that this automatically and for no good reason (by my frame of reference) requires the universe to pivot round the centre of the Earth is of no consequence - one frame of reference is as good as the next - right?

In fact I'll take a piston head as an anchor for a frame of reference - now going home involves the universe bouncing up and down 33 times a second as it rotates round an arbitrary point as my home makes its way to me.

 

[A.T.]

It is never "wrong" to use a different reference frame. And in this specific case, clinging to the idea that ground or water define an ideal or preferred reference frame is very counter productive for the understanding. It is exactly what gives the deniers the wrong idea, that you cannot extract energy from the true wind, when you are at rest relative to the air.

I disagree.

With what exactly? With physical laws like equivalence of inertial reference frames and relativity of motion/rest? Or with the wrong idea of the deniers?

one frame of reference is as good as the next - right?

This only applies to inertial reference frames. If you car accelerates it's frame is not equivalent to the Earth's reference frame. But with constant true wind the frames of ground and air are equivalent.

 

[mikemonty]

With what exactly? With physical laws like equivalence of inertial reference frames and relativity of motion/rest? Or with the wrong idea of the deniers?


This only applies to inertial reference frames. If you car accelerates it's frame is not equivalent to the Earth's reference frame. But with constant true wind the frames of ground and air are equivalent.

Whoa!
Suddenly we are making the distinction between inertial frames and spatial frames!
And your points are based on - Oh look, inertial frames!
And my points were based on... Heavens! spatial frames!

Now WHERE did inertial frames come into it? - Oh yes - when you wanted to score a point!

 

[Tommyrot]

Having started off as a disbeliever, then seeing the desert trials, and then revealing myself as not being the brightest spark on the bonfire by falling for SnowLeopards April Fool explanation, here's how I now understand it:-

At standstill the propellor, together with the lightweight chassis only has the force of the wind acting to push it.
If there is enough wind the chassis will start moving forward, and the wheels will start to rotate the propellor counter to the direction in which the wind is trying to turn it, even at low rotational speed this will give slightly more resistance to the wind so the cart will go faster.
Eventually when the cart is moving at wind speed the propellor will be giving thrust relative to the wind pushing the cart and the cart will accelerate to a speed faster than the following wind until a balance is reached where the propellors thrust and the following wind thrust is balanced by friction and apparent wind resistance to the cart chassis.

Writing this down I still feel as though I'm being wound up - (probably like the elastic band on the cart's propellor )

Welcome in Paul. As far as I can see, the team building it sees it, and Andrew Bauer saw it, that's exactly how it works.

We'll just have to let these folk with planet sized brains carry on now.

 

[Baggywrinkle]

Shearing forces ....

What you are doing whether sailing in water or on land is exploiting the difference in relative speed of the two media you are connected to. Boats have a keel in the water and a sail in the air and they exploit the relative speeds of the two media to move relative to one of them.

In a boat it is possible to sail faster than the wind, I doubt anyone will argue against this. How does this happen? Because the force you can generate with your sail and keel is great enought to evercome the drag of your vessel through the water and wind to such an extent that you can move across the water faster than the wind can move across the water (not in the same direction but this is a limitation of a sailing boat not the physics of exploiting the energy present at the boundary of the two media)

In this contraption at first it just creates static drag in the wind and as the bicycle wheels have little rolling resistance the cart starts to move. As it moves, the prop turns the wrong way and actively tries to prevent the wind from getting through the prop (maintaining high pressure on the windward side of the prop) so the cart moves a little faster and the cycle repeats as the cart slowly accelerates. When the pressure generated by the prop (due to the movement over the ground), and the pressure from the wind are reduced to zero by the forward movement of the cart then it has reached it's terminal velocity. As the prop is acting against the following wind, it is possible to maintain pressure behind the prop even if the apparent wind is zero (i.e. the cart is travelling at windspeed).

Perhaps

 

[A.T.]

Whoa! Suddenly we are making the distinction between inertial frames and spatial frames!

No. The distinction in physics is between inertial reference frames and non-inertial (accelerated) reference frames:
http://en.wikipedia.org/wiki/Inertial_frame_of_reference
http://en.wikipedia.org/wiki/Non-inertial_reference_frame

And your points are based on - Oh look, inertial frames!
And my points were based on... Heavens! spatial frames!

What do you mean by "spatial frames"? I never heard that term in the context of reference frames.

Now WHERE did inertial frames come into it? -

Assuming a constant wind, both ground & air define inertial reference frames.

 

[Blueboatman]

The pub beckons but afore I go, I have just had an idea as to how you could fake that without actually faking it, ''technically''
Sorry folks.

So, until I see a 2 mile run continuously and some clear pics of the inside of that soap box, I shall remain in a state of suspended belief.

Clever though, one way or t'other.

 

[A.T.]

The pub beckons but afore I go, I have just had an idea as to how you could fake that without actually faking it, ''technically''

I'm sure there a many ways to cheat here, but there is no real need to cheat. The calculations I linked here are based on realistic propeller and friction parameters, and show that it is easy to achieve with a wheeled vehicle on land.

So, until I see a 2 mile run continuously and some clear pics of the inside of that soap box

The space they had was limited. Here they reached the end of the lake after going above wind speed for 1:30min:
http://www.youtube.com/watch?v=aDzWh9J1dk4#t=3m10s

But if you think they run on stored momentum, here some points to consider:

- The prop cannot store much of it, as it is made out of light foam: http://www.youtube.com/watch?v=Od9tV5d2uao

- The wheels have ratchet hubs which prevent the prop from driving the wheels.

- Given the simple & open design, any type of flywheel would have been easily detected by the many land sailors taking part in the NALSA-regatta, during which these tests were made: http://www.talkrational.org/attachment.php?attachmentid=1800&stc=1&d=1270227874

 

[snowleopard]

Well this one seems to have died a natural death but the debate still goes on elsewhere.

It's still going pretty strong with a few remaining sceptics on boatdesign.net with 200+ posts but the granddaddy of them all is talkrational.com with over 2000 and one of the sceptics still calling everyone, including the constructors of the manned cart, f*ckwits.

 

[snowleopard]

Well this one seems to have died a natural death but the debate still goes on elsewhere.

It's still going pretty strong with a few remaining sceptics on boatdesign.net with 200+ posts but the granddaddy of them all is talkrational.com with over 2000 and one of the sceptics still calling everyone, including the constructors of the manned cart, f*ckwits.

 

[Tommyrot]

Amazing how many are still convinced that the prop is driving the wheels, despite the ratchet hubs....

 

[snowleopard]

Correction - I've just realised that Talkrational closes the tread every time it hits 2500 posts and starts a new one. It's now running somewhere over 32,000 posts and the same sceptics are still saying (well yelling really) the same insults.

 

[Blueboatman]

Re AT

OK I missed the ratchet hubs bit..My thinking was that all the time the vehicle is accelerating up to the true wind speed, some of the energy 'captured' by the prop could indeed be used to increase the momentum of a flywheel or other energy storage device, and then, briefly, once the vehicle is at or very nearly at actual wind speed, the stored energy can then be fed back into the drive train and used, briefly, to exceed true wind speed.

Thanks for the links. It is indeed fascinating. Time to dust off my elementary calculus. This is going to HURT.

 

[spork]

Howdy folks. JB and I are the guys that built the BUFC that ran in Ivanpah. We're now making improvements in preparation for making an official NALSA run (North American Land Sailing Association). We're currently working with NALSA to develop a new category for this type of craft. Hopefully we'll have made some official runs in the coming weeks.

In the meantime, I'm delighted to see the interest here. I notice this crowd seems brighter (and far more civil) than we find on a number of the other forums.

But I also noticed in another thread you have a poll in which most people seemed to think it was a hoax or other confusion. Is that still the case I wonder. I'd be happy to help explain what we've done, how it works, and generally make our tests and methods as transparent as possible.

 

[ThinAirDesigns]

Hello all. Cool thread with a lot of folks who have a pretty good grip on the physics involved in what we call the BUFC (Big Ugly Cart).

I'm JB and I'm one of the two primary designers and builders of the vehicle you see in the videos (both large and small).

Just as a note, of the people who have posted their own descriptions of the physics involved, "Halfway" and "MikeMonty" seem to be mired in wrongness the deepest.

If anyone has any questions for me, fire away. Rick and I just finished a couple good days working on upgrades to the machine. I moved the primary brake system from a lever on the left to a foot pedal on the left to allow the left hand to run the soon to be installed 'in flight' variable pitch system.

We won't get the VP system in place this week though as we have to have the BUFC operational this weekend for a film crew from the Discovery Channel who will arrive this weekend. Also, look for an upcoming article in "Sail Magazine".

Best wishes.

JB

 

[spork]

...the granddaddy of them all is talkrational.com with over 2000 and one of the sceptics still calling everyone, including the constructors of the manned cart, f*ckwits.

Howdy all. I'm one of the two f*ckwits that built the BUFC seen in the Ivanpah videos (and the small carts seen in most of the treadmill videos). It seems that many of you have this pretty well sorted out. This crowd seems both sharper and far more civil than most we've encountered on the web.

For those that doubt DDWFTTW - I invite you to come by and see it. You're more than welcome to see it operate if you come to one of our tests or hopefully soon our official NALSA record attempt. Also, I'm happy to describe how it works. Others here have already done a good job, but we've found that different explanations work for different people.

Also - it's a brainteaser. It's supposed to seem intuitively all wrong. For me that's how it originally started. I posed it as a brainteaser and simply assumed people would think it was a clever approach to going DDW when I revealed the answer. I had no idea it would ever erupt into something of this scale. We then learned that others had already done it (Bauer back in the 1960's), but had not documented it very well. He hope and plan to document our efforts and results so that anyone could reproduce them.