Merged DDWFTTW in a “Real” Wind

[EHocking]

Theory says that'll happen.

^^^^ This.

Practice says it as well.

JB

^^^^ And This.

 

[EHocking]

Best to hope there are no headwinds. Gusty wind has those.

I can only hope that this was an attempt at humour. Otherwise it's nonsense.

 

[humber]

.
Nope.
Not without some fancy tacking, as with a boat and probably not even then.
No fancy stuff available here.
I would like to get the driven cart to work.
Release both at the same time, and watch the freewheeler accelerate faster, but get caught and passed by the driven cart.
Theory says that'll happen.

Ah, well that remains to be seen. Direct comparison, the freewheeler will win.

ETA: Gusty wind should be avoided. If the carts are blown such that the wheels lift, the geared cart will be much like the prop cart. At a distance, it can be hard to tell which way the prop is turning. The flat base may produce that lift. All forces are small, and that's a problem in general. , Perhaps some audible device could used to indicate the rotor direction, or weight added and then the two compared.

 

[humber]

Practice says it as well.

JB

Nope. No way to make the free-wheeler go backwards, but the geared cart can.

 

[humber]

I can only hope that this was an attempt at humour. Otherwise it's nonsense.

See the Jenkins video. The vane shows a headwind when the camera pans to the vane. Nope, not a tailwind. The direction of motion allows the two to be distinguished.

 

[humber]

And the apparent wind direction, when travelling DDW at a speed <actual windspeed will always be an apparent tailwind.Since we're discussing carts going DDW at a speed <windspeed, yes. The assumption is that the tailwind will be faster than the cart.

Which means you still can't tell a speed change, from a directional change.
Vanes respond to force, and the direction is the result of the sum of the vectors. Both speed and direction.

No. We were comparing a stationary windmill with a windmill moving DDW at a speed < true windspeed. Therefore an apparent tailwind.

Not the same thing. Law of superposition applies to linear systems. The effects are there, but the magnitude changes. When stationary, one is zero.

No. At not time in this discussion were we discussing a self-steering boat. The MECHANISM was alluded to as "something based on this might be used"

Which is still to compare apples and pears, but now by allusion. The proposed "mechanism" removes all the things that makes the other work.
Elementary dynamics. It will wobble.

to steer a cart.And so I have avoided using different scenarios and craft while discussing the steering "problem" (if there is one. You are the one that keeps derailing with irrelevant examples.Blackbird does not utilise a turbine.

When the chain comes of, it turns CCW. It's a turbine, forced by the wheels to turn the other way. That is why it is so ponderously slow. The relative speed of the tailwind is at a maximum when the cart is not moving.
How do things get better, as that tailwind falls? The data says tacking.

This implies that the prop drives the wheels.

Sail drives cart, turns wheels, turns prop. Reduce sail force, and it goes backwards. I have done it, Platt has done it and so have others.

It is the other way around. The wheels drive the prop.No. and No again. The prop on the Blackbird is not a turbine driving the wheels.

It's a sail driving the wheels. The turbine force works against it. Like the cotton reel. Both linear (sail) and angular (turbine) forces. Change the ratio, and the reel goes one way, or the other. So with the cart. I know, it is too bizarre to be true, but it is.

 

[I Ratant]

And of course the whole discussion about trying to find a steering mechanism for the cart may be completely superfluous!

Does it actually need one, or do the carts "self steer" parallel to a prevailing wind anyway?

.
The original version would follow the wind around the buildings, as noted.
The lite version seems to be going straighter in the same location.
Need more wind.
Never thought I'd want -more- wind here!
I'd added a pilot to the lite cart.
He's not afraid to face the oncoming wind!
During one of the runs this afternoon.

 

[Giordano]

I've been lurking at JREF for quite a few years, and I finally uncloaked just to sincerely thank Spork, ThinAirDesigns, CORed, Llyricist, Jack by the Hedge, jduffy77, EHocking, Michael C, and the many other posters for the wonderful insights and education I've received from this thread.

I am a sailor and a scientist, so I began reading this thread with some understanding of downwind tacking and velocity-made-good DW. Nonetheless, the concepts behind a DDWFTTW vehicle remained vague to me, and I had only an imperfect understanding of the relationship between the foils on the prop, the wheels, apparent wind direction, etc. Through the analogies, math, and wonderful animation presented here, I now have an intuitive as well as a theoretical understanding of the physics behind the cart.

The engineering of the cart was elegant, and the patience of all in tirelessly explaining it to others is deeply appreciated! The cart quite clearly works in terms of the physics, and it quite clearly works in real life. And I thank even the doubters on this thread for providing me with a renewed appreciation of Monty Python's "Argument Clinic" and "Black Knight" sketches.

 

[ThinAirDesigns]

Thanks Giordano.

JB

 

[3point14]

About the only way to test it would be to build it and "suck it and see".

NOOOO!!

Don't you understand??

The only way to test it is with reams and reams of excessively complicated, half understood, badly applied mathematics.

If your practical demonstration disagrees with the mathematics then it's reality that's wrong.

 

[Jack by the hedge]

The only way to test it is with reams and reams of excessively complicated, half understood, badly applied mathematics.

Hmm. Reams of text that travel down the page, faster than the scroll function.

You may be on to something.

 

[EHocking]

See the Jenkins video. The vane shows a headwind when the camera pans to the vane. Nope, not a tailwind. The direction of motion allows the two to be distinguished.

None of which has anything to do with the point being discussed and that was your assertion that headwinds are gusty.

But at least progress is being made.... you admit that the Blackbird, as shown in the Jenkins video, travelled DDWFTTW, since it was experiencing a headwind, even though it was travelling DDW.

 

[EHocking]

Which means you still can't tell a speed change, from a directional change.

No. I just means that your reading comprehension is impaired - you are the one mixing up speed and direction.

Nowhere in that paragraph did I indicate that there is any speed or directional change. The statement simply was.

When travelling DDW
Slower than the true windspeed
Apparent wind direction will be a tailwind

Vanes respond to force, and the direction is the result of the sum of the vectors. Both speed and direction.

Or simply, the tail section of a weathervane will always point downwind.

Not the same thing. Law of superposition applies to linear systems. The effects are there, but the magnitude changes. When stationary, one is zero.

If a windmill is stationary it is travelling < windspeed.
We are then comparing it to a moving windmill travelling < windspeed.

In both cases, the windmills will be oriented in the same direction, in the same wind, i.e., a stationary windmill will face north to a northerly wind.
A windmill travelling south in a northerly wind, at a speed less than the wind, will face north.

Which is still to compare apples and pears, but now by allusion.

You really do try hard to misunderstand others' statements, don't you?
The yachting example was merely given a starting point to discuss a possible passive steering system.

The proposed "mechanism" removes all the things that makes the other work. Elementary dynamics. It will wobble.

Ah. Proof by Assertion.

It is said that Aristotle once stated that flies only have 4 legs and that this assertion was repeated in natural history books for some 1000.

We know two things.
1. his assertion was wrong
2. you are no Aristotle.

When the chain comes of, it turns CCW. It's a turbine, forced by the wheels to turn the other way.

No. It is not a turbine. The prop is being driven by the wheels. The prop is not driving the wheels (definition of a turbine).

When the chain comes of it is no longer performing as designed, i.e., the wheels are no longer turning the propshaft.

To quote you from earlier in this post, "Not the same thing" and "comparing apples to pears".

That is why it is so ponderously slow.

All things are relative, but I don't see 27mph downwind in 10mph tailwind to be "ponderously slow".

The relative speed of the tailwind is at a maximum when the cart is not moving.
How do things get better, as that tailwind falls? The data says tacking.

Mere assertion until you present the data that supports this.

Sail drives cart, turns wheels, turns prop.

At last. A correct statement in this post.

Reduce sail force, and it goes backwards. I have done it, Platt has done it and so have others.

Which just goes to show that you/they have not built the cart correctly.

Comparing your failures, due to poor design or construction, with a successfully built DDW craft is not disproof of the success of the properly built craft.

It's a sail driving the wheels. The turbine force works against it. Like the cotton reel. Both linear (sail) and angular (turbine) forces. Change the ratio, and the reel goes one way, or the other. So with the cart. I know, it is too bizarre to be true, but it is.

Just because you can't get it to work is not disproof.

It is the same as asserting that this is a proof.

• I built a steel hulled canoe the other day.
• It sank.
• Proof that fibreglass hulled canoes cannot float.

 

[ThinAirDesigns]

We ran our small carts along a fishing line stretched tight parallel with the wind. We did this of course simply to keep a device with no steering mechanism on a DDW track. Humber of course insisted this was nefarious somehow and that it supported his position (as everything that contradicts him always does).

JB

 

[humber]

I've been lurking at JREF for quite a few years, and I finally uncloaked just to sincerely thank Spork, ThinAirDesigns, CORed, Llyricist, Jack by the Hedge, jduffy77, EHocking, Michael C, and the many other posters for the wonderful insights and education I've received from this thread.

I am a sailor and a scientist, so I began reading this thread with some understanding of downwind tacking and velocity-made-good DW. Nonetheless, the concepts behind a DDWFTTW vehicle remained vague to me, and I had only an imperfect understanding of the relationship between the foils on the prop, the wheels, apparent wind direction, etc. Through the analogies, math, and wonderful animation presented here, I now have an intuitive as well as a theoretical understanding of the physics behind the cart.

The engineering of the cart was elegant, and the patience of all in tirelessly explaining it to others is deeply appreciated! The cart quite clearly works in terms of the physics, and it quite clearly works in real life. And I thank even the doubters on this thread for providing me with a renewed appreciation of Monty Python's "Argument Clinic" and "Black Knight" sketches.

Another first-time poster makes a public service announcement when the cart is in trouble. Happens like clockwork.

 

[Calrid]

Good God this thread is more pernicious than colds in winter.



It's almost an internet meme it's so everywhere.

opcorn:

Though it is an entertaining ride.

 

[humber]

Which means you still can't tell a speed change, from a directional change.
No. I just means that your reading comprehension is impaired - you are the one mixing up speed and direction.

so you say. Apparent wind. Apparent wind.

The headwind was a transient when the cart just passed WS, and it is well known that boats can tack up wind. Such a wind would accelerate the prop, so it would turn on the ratchet, and be of no use to the cart.
But, the point was about your steering, which would fail catastrophically should that happen. Also, should the tailwind deviate from ddw and the cart adjust itself, then any increase in speed of that same wind, would change it again. The idea is a total failure. Assumes its conclusion, misguides the cart, mechanically impractical and a hazard to stability.

 

[Llyricist]

so you say. Apparent wind. Apparent wind.

The headwind was a transient when the cart just passed WS, and it is well known that boats can tack up wind. Such a wind would accelerate the prop, so it would turn on the ratchet, and be of no use to the cart.
But, the point was about your steering, which would fail catastrophically should that happen. Also, should the tailwind deviate from ddw and the cart adjust it itself, then any increase in speed of that same wind, would change it again. The idea is a total failure. Assumes its conclusion, misguides the cart, mechanically impractical and a hazard to stability.

LMAO, he did it again!

 

[humber]

The engineering of the cart was elegant...

No, this one
http://www.youtube.com/watch?v=dOUjGzy04DE&feature=related

 

[humber]

We ran our small carts along a fishing line stretched tight parallel with the wind. We did this of course simply to keep a device with no steering mechanism on a DDW track. Humber of course insisted this was nefarious somehow and that it supported his position (as everything that contradicts him always does).

JB

It was done in such gusty wind, that the carts would have been blown away, unless restrained by the line. According to the whipping of the nearby tree branches the wind speed was around Beaufort 5.
The idea also assumes that wind does not change direction, so is always "parallel to the line" but the trees have another opinion. A bucket suspended on that same line, would probably beat the cart.

I suggested that you employ a simple drag device on the wire to avoid damage to the carts against the stop, but you used a buffer, and the cart broke as expected.

I Ratant's free-wheeler will beat the geared cart, hands down. This time, we have a logical and methodical tester, who controls conditions and responds to remarks. Your cart will fail.

.