Keen_Ed
Well-Known Member
Motion of the cart is DDW. Motion of the prop blade is in a spiral as described. The fact that you're even asking that question shows a fairly basic misunderstanding of what's going on.
Last edited:
Downwind Faster than the Wind - Successful Run by manned cart
- Thread starter Pierrome
- Start date
Motion of the cart is DDW. Motion of the prop blade is in a spiral as described. The fact that you're even asking that question shows a fairly basic misunderstanding of what's going on.
shaunksb
Well-Known Member
Are you not listening or not watching? It doesn't matter if he is holding onto the cart with his hand or a piece of string the results are the same - its what happens when he lets go thats important.
The fact that you're even asking that question shows a fairly basic misunderstanding of REALITY.
RAI
Well-Known Member
Are the blades of a propeller aerofoils? Is a sail an aerofoil? Does airflow around an aerofoil produce forces on it? Why is a propeller different from an sail in this respect?
RAI
Well-Known Member
Poppycock
shaunksb
Well-Known Member
Ooohhhhh......................tou che
cliffordpope
Well-Known Member
I was sceptical, but was persuaded by the clip showing the lego model and the ruler.
After that, converting the ruler to wind power was just a detail.
Let's have an argument about Ram water pumps. Can they really pump water higher than the level of the dam ?
After that, converting the ruler to wind power was just a detail.
Let's have an argument about Ram water pumps. Can they really pump water higher than the level of the dam ?
shaunksb
Well-Known Member
The church of scientology is going to have a field day if it ever finds this place!
Keen_Ed
Well-Known Member
Strings are in tension from the force driving the cart forward. Remove the strings, and the cart will move forward. Oh, I forgot. You don't believe in Newton's first law. There's this magic extra drag which is conjured up from somewhere which slows the cart down.
How's your Quiddich team doing?
H
halfway
Guest
tobermoryphil: You are my hero. Practical and an investigator.
"and will be developing a forward thrust component FROM THE TAILWIND via the apparent wind passing over it."
Assuming the wall did not win in your attack, I assume your head can also see that this prop does not "suck" or "blow".
Just in front of the prop, the air has no change from the ambient conditions. It has no "knowledge" of the cart about to arrive.
Just behind the prop, the wind is still going the same basic direction but slower and has a rotational component.
On the way through it gave up energy to the aerofoil. Therefore there is no blowing or sucking CAUSED by the prop. It therefore does not work as a prop in traditional terms of moving air from the "suck" side to the "blow" side.
It is actually a "synchroturbine". Or in our world a "sail".
This is confirmed by Oracle. The wind in front of Oracle has no alteration, and has no knowledge that it is just going to be hit by a huge aerofoil. The air behind is slightly bent and has less speed in the direction of the original wind.
This is also confirmed by the land yacht video. Look at the streamer in front. It is approximately reflecting the streamers around the prop.
However, If you look at the treadmill you will see that while it is tethered, the air in front of the prop is altered from the steady state. To be a correct analogy, of the moving situation, the air in front should be completely still. But the circulation caused by the fan is rotating the air around the prop. So the treadmill can not be an analogy of the real moving cart situation.
By accepting the "sail" explanation the prop is not working in any way that is reflected by the "proofs" given by Mark Drela or any of his supporters. The wind power is certainly not relative to the road either. Also there is no proof that can rely on a reference point alteration. Since no alteration can suddenly make a concept work. A proof must work for all reference point choices simultaneously.
So the proofs supplied when I first saw the original thread are poppycock, and anyone that believed at that point, based on those proofs, is a "false believer". They were as much incorrect as the ones that still do not believe it is possible. False beliefs based on incorrect proofs are as serious in our daily life as those that do not believe. These are the basis of all the bad politics used in the UK today. We have been conditioned that any "expert" with a theory means that it must be true.
Blind belief of "experts" is the downfall of our society and the whole problem about the forum's banned subject. Also why the government has brainwashed the public into many untrue situations, all they need is a nerdy looking expert and the believers just flock to the demonstrations, or rush to war. The best proof of this is the "Coal is bad" argument that ignores the fact that most new gas is extracted from wells with up to 87% CO2 content. Natural gas is the most un-natural fuel in the world. Please wake up and stop believing these experts.
As the false proofs are retracted it will be the false believers that will need to apologise, and the non-believers will have a chance to accept the reality. The non-believers do not need to apologise to anyone, as their common sense easily saw the failures of the incorrect proofs and put them off accepting the concept. They made no mistakes, unlike the false believers.
"and will be developing a forward thrust component FROM THE TAILWIND via the apparent wind passing over it."
Assuming the wall did not win in your attack, I assume your head can also see that this prop does not "suck" or "blow".
Just in front of the prop, the air has no change from the ambient conditions. It has no "knowledge" of the cart about to arrive.
Just behind the prop, the wind is still going the same basic direction but slower and has a rotational component.
On the way through it gave up energy to the aerofoil. Therefore there is no blowing or sucking CAUSED by the prop. It therefore does not work as a prop in traditional terms of moving air from the "suck" side to the "blow" side.
It is actually a "synchroturbine". Or in our world a "sail".
This is confirmed by Oracle. The wind in front of Oracle has no alteration, and has no knowledge that it is just going to be hit by a huge aerofoil. The air behind is slightly bent and has less speed in the direction of the original wind.
This is also confirmed by the land yacht video. Look at the streamer in front. It is approximately reflecting the streamers around the prop.
However, If you look at the treadmill you will see that while it is tethered, the air in front of the prop is altered from the steady state. To be a correct analogy, of the moving situation, the air in front should be completely still. But the circulation caused by the fan is rotating the air around the prop. So the treadmill can not be an analogy of the real moving cart situation.
By accepting the "sail" explanation the prop is not working in any way that is reflected by the "proofs" given by Mark Drela or any of his supporters. The wind power is certainly not relative to the road either. Also there is no proof that can rely on a reference point alteration. Since no alteration can suddenly make a concept work. A proof must work for all reference point choices simultaneously.
So the proofs supplied when I first saw the original thread are poppycock, and anyone that believed at that point, based on those proofs, is a "false believer". They were as much incorrect as the ones that still do not believe it is possible. False beliefs based on incorrect proofs are as serious in our daily life as those that do not believe. These are the basis of all the bad politics used in the UK today. We have been conditioned that any "expert" with a theory means that it must be true.
Blind belief of "experts" is the downfall of our society and the whole problem about the forum's banned subject. Also why the government has brainwashed the public into many untrue situations, all they need is a nerdy looking expert and the believers just flock to the demonstrations, or rush to war. The best proof of this is the "Coal is bad" argument that ignores the fact that most new gas is extracted from wells with up to 87% CO2 content. Natural gas is the most un-natural fuel in the world. Please wake up and stop believing these experts.
As the false proofs are retracted it will be the false believers that will need to apologise, and the non-believers will have a chance to accept the reality. The non-believers do not need to apologise to anyone, as their common sense easily saw the failures of the incorrect proofs and put them off accepting the concept. They made no mistakes, unlike the false believers.
Bosun Higgs
N/A
Excellent Geeky - I too am a scientist ( physicist) albeit one that hasnt used much more than a facility with numbers since coming down some 45 years ago. So could you please put the detailed physics on here so I can understand why it works as it seems to do. My initial reaction was that it was defying conservation of energy ( impossible) so I am missing something somewhere. I still cant see how the machine can be taking energy out of what is relative to itself, stationary air.
snowleopard
Well-Known Member
Round, like a circle in a spiral
Like a wheel within a wheel.
Never ending or beginning,
On an ever spinning wheel
Pierrome
Well-Known Member
There is a limit to the number of times you can say the same thing.
Of course you can't take energy out of stationary air.
You take energy out of the moving ground. Before, you said you couldn't do this (I don't see why).
So therefore presumably, when you're riding your bike downwind at 10mph and the wind also happens to be 10mph you can't get any energy out of the bikes dynamo to power your lights.
mikemonty
Well-Known Member
And thus you have benchmarked your own level.
There is no more a limit to the number of times one can say something than there is to the number of times one can be wrong.
...OK - can't resist it...
two scenarios (because you didn't outline your problem well enough):
Bike pedalled downwind = no apparent wind and power comes from err.. LEGS!
However not as much power needed as in still air because air drag eliminated.
Bike freewheeling downwind = gradually slowing down or speeding up to point where input from tailwind is sufficient to balance dynamo plus rolling resistance.
Pierrome
Well-Known Member
MM
You don't understand what this is about. This is a reply to Bosun Higgs, who claimed that it was "impossible" to obtain energy from a moving road when the air is still, (and he's a physicist!) this proves it is.
You haven't won a point here, you just misunderstood what the point is.
It's all perfectly correct what you say. But your thinking doesn't go far enough.
In the example of the bike, the energy is just being used to provide light.
But in the downwind cart the energy is being fed into the air. It's not just "drag" as you suggest, it's a transfer of energy. This transfer of energy allows the cart to progress through the air which is the effective medium that it is in (cart static - air static).
Now, before you say "how can the wheels provide more thrust than the drag they create" - which you inevitably will, we have the example of the upwind windmill boat that can progress through the water AGAINST the wind that powers it, and in that case the windmill clearly provides more thrust than the drag it creates, thus proving it is possible.
There are many examples on here of people not reading carefully what is said to them and not thinking through carefully! Try not to be one of them!
snowleopard
Well-Known Member
OK, this has dragged on long enough so it's time to reveal how the demonstrations were staged.
The treadmill one was easy. You will notice they are all very tight shots of the treadmill. That's because the large fan had to be kept out of shot to the left of the picture.
The unmanned outdoor cart was a clever one. It was actually geared to move upwind but the video was run backwards.
And for the manned cart the film was simply run at double speed and the sound track dubbed in afterwards.
The various wind direction telltales are easily rigged using rigid 'threads'.
So – no hidden motors on the carts, no hidden strings pulling them. The videos were unedited and showed exactly what happened – just not quite in the same way as they appear.
APRIL FOOL
The treadmill one was easy. You will notice they are all very tight shots of the treadmill. That's because the large fan had to be kept out of shot to the left of the picture.
The unmanned outdoor cart was a clever one. It was actually geared to move upwind but the video was run backwards.
And for the manned cart the film was simply run at double speed and the sound track dubbed in afterwards.
The various wind direction telltales are easily rigged using rigid 'threads'.
So – no hidden motors on the carts, no hidden strings pulling them. The videos were unedited and showed exactly what happened – just not quite in the same way as they appear.
APRIL FOOL
RAI
Well-Known Member
Dang! And I thought they did it by pulling the desert forwards. Didn't you notice all those trucks on the highway? They were actually parked.
A.T.
Member
This is by Mark Drela from MIT:
http://www.boatdesign.net/forums/at...w-directly-downwind-faster-than-wind-ddw2.pdf
http://www.boatdesign.net/forums/at...w-directly-downwind-faster-than-wind-ddwe.pdf
Drela said:
It takes energy from the relative motion of air & ground, reducing their velocity difference. It basically leverages one against the other:
It is symmetrical to going directly upwind, with a turbine cart or a turbine boat:
In less abstract terms it is a "space saving" method of tacking downwind with a VMG greater than windspeed. This is how sail vehicles do it:
In the case of the propeller cart the propeller blades are tacking on a helical path. Just like the sail they are mechanically constrained to move indirectly downwind, even if the vehicle itself moves directly downwind:
Tommyrot
Well-Known Member
I did a similar thing with a fixed-wheel bike.
After learning to peddle it backwards I could engage the dynamo and produce a small black hole.
After learning to peddle it backwards I could engage the dynamo and produce a small black hole.
mikemonty
Well-Known Member
Pierrome,
Your reply contains the same elements of trollerie that Ubers do.
First - the difficult frame of reference - an insistence on using the air as a frame of reference and taking energy from the road - Dont do that! Why would you do that? the only reason I can think of why you should is to try to warp your understanding into your observations.
The road is static, the wind and cart are moving and energy is obtained from the air/propellor interaction.
Next the misrepresentation - I didn't suggest "drag" and "transfer of energy" were mutually exclusive terms.
Next the inexplicable leap(s) of logic - from the bicycle downwind to the cart, unless the cyclist has no legs, a propellor on top of his head and a shaft running down his spine and out his ... other end, there is little to be "proven" from the analogy.
And the Straw Man - You set the question "how can the wheels provide more thrust than the drag they create?" - referred to the upwind windmill boat - then you then presented this as some form of proof.
Of What? that the easy principle of the upwind scenario works!
I have no problem with the energy from the wind, real or apparent - being sufficient to get get purchase on the water (or ground if a cart) and cranking it upwind - its just gearing.
That does NOT equate to the downwind scenario working.
Finally, the sting - the accusation that I misunderstood, or have not read carefully, your post. As far as it goes I thik I have understood perfectly.
What you do NOT offer is a logical, comprehensible, feasible explanation of the apparent phenomenon where the cart is POWERING downwind through the air and therefore must lose energy to air drag and (in your theory) gain it from the ground.
The fact that the wheel WILL be dragging does not imply any transfer of energy from the ground, do not confuse force and energy. At the point of contact wheel to ground there is no motion and therefore no work done - no "transfer of energy" at that point.
To do what you want it to do it was asserted that the "drive wheel" must be physically driven.
If you lifted the drive wheel off the ground it would require a source of power in order to provide any drive to the propellor. In what circumstance does the ground become a motor?
In fact the cart is the motor (the stator to the wheels "rotor") and the drive to the wheel provided by force applied to, and movement of, the cart.
So explain please,
And in your reply please keep the ground as your frame of reference.
Actually I should put you out of your misery.
Lets go back to the ORACLE (boat, not Greek seer) as it is a system that we accept works and is easier to think through.
The boat is going down (true) wind at a diagonal, apparent wind is forward and to one side of the boat.
Apparent wind produces a force on the sails roughly perpendicular to the sail. So that force will be pushing sideways and forwards with respect to the boat.
That force is transferred to the keel, again at the same angle sideways and forwards with respect to the boat.
The sideways component is lost, as far as the boat is concerned but the "boats forwards" component of the force is what will propel the boat.
The downwind vector component of the motion that that force results in is what we are interested in. It is what MIGHT make the boat go with a VMG greater than true windspeed if a whole list of criteria are met - not least of all that the nett downwind force after taking away all losses is sufficient to power it to high apparent windspeeds.
But crucial to all this is the understanding that the interface between vehicle and fixed frame of reference (water or ground) is no more than this. The FORCE of the wind is being APPLIED to the frame of reference unopposed -resulting in MOVEMENT.
The same principle applies to the cart with the prop blade(s) as sails. The sail/blade is still going diagonally down the wind, except this time the force is being tranmitted to the wheel, not the keel
The wheel is no more being driven by the ground than the boat is by the water. No energy is being transferred from water to boat or ground to wheel, other than by frictional losses.
Two conceptual problems arise:
One is in the transition between startup and steady-state.
At rest one of two things could happen:
The prop drives the cart up (true)wind
The wind drives the cart down (true)wind
For the cart to drive the wheel to drive the prop - at startup the force (torque) generated by the wind on the prop and transmitted to the wheel has to be lower than the aero drag of the cart.
If the torque generated by the prop is too high it will drive the cart upwind.
Assuming the prop generated torque/force-at-the-wheel is lower than the carts air drag, it starts off downwind. The torque produced by the prop (and drag at the DRIVEN wheel) will decrease as it gets closer to windspeed.
As it passes windspeed the apparent wind starts to take over and starts to DRIVE the wheel(s).
The limit is reached when the drag on prop blades and cart equals mechanical losses or the prop is over-pitched.
The other conceptual problem is in how the boat/cart "knows" that there is a true component to the wind - why can't it simply keep on sailing/carting if the true wind dies?
Try it - do the vector diagram - as you decrease the true wind, the apparent moves to the point where it is "on the nose". In irons for the boat and neutral or reverse pitching the prop on the cart - no more power and the vehicle stops
Energy IS being transferred - but I got through the whole thing without having to refer to it once (except in rebuttal)
So there - I arrived at the conclusion required by the more excitable correspondents but for different reasons.
Some might suggest that this is sophistry - but if one has to tie oneself in knots (air as frame of reference) and use false assumptions (driving/driven wheels) about what is happening then one is just as wrong as the next man.
To any who have used the correct reasoning, and/or I have repeated in some way, I apologise. If I appear to have lumped you in, it is not my intention, but I'm not going back over all the correspondence especially after I said a few posts back that I was not interested any more!
Bosun Higgs
N/A
Cant take heat energy from the road. Cant take chemical energy from it either. Tarmac isnt magnetis. The road doesnt go any lower so no potential energy loss. So your postulation must be that the vehicle takes energy from the road which will show itself ( so small as to be unmeasureable in practise) as a slowing of the rotation of the earth. In which case of course, the gadget would only work in one direction
Not really. I can repeat the question as long as you post a nonsensical answer.
Can someone who has scientific training please answer my question?