Merged DDWFTTW in a “Real” Wind

[humber]

The questions below ONLY relate to DIRECTLY DOWNWIND travel.
The explanations I have been giving have been in the form of anecdotes in an attempt to simplify. I agree that some of the things I have said have been totally wrong and I never intended to present myself as an faultless authority on the subject.

I’m disappointed that the two threads have been merged and I’m not sure if I want to continue in this repulsive atmosphere of argument and insult. Thanks to those that took part in the “Dummies“ thread with a positive and sociable attitude.

Merging is a practical option for moderation, I suppose. I had little hope of keeping the topic to the cart in the wind, anyway.
There are many cart supporters, including its constructors, who have shown that they have little interest in physics, or have any history of experimentation. For them, the cart is a matter of personal aggrandizement.

1. The cart is ONLY powered by the wind.

All else is not only outside the scope of the claim, but will be nescient
Wheel power, ground power etc.

1. Wind can't DIRECTLY transfer power to anything that is moving faster than the wind.

ddw, that is correct. No moving component can move slower than the cart, while maintaining an average velocity of the cart. That applies to a propeller too. The axis and center of mass of the prop, move at the speed of the cart.
Force acts through the center of mass. Another way to see it, is that KE can only be transferred from the more energetic state, to the lower energetic state. ( like heat)

Given that the cart and wind are at the same velocity when at WS, it must be the faster cart that has the higher KE, regardless of relative mass of cart and wind (or WS could not be reached in the first place). That means the cart loses KE to the air, and not the other way around.

3. When the cart is moving faster than the wind there MUST be some part of the cart or something that interacts with the cart that is moving slower than the wind so the wind can transfer power to it

Same as above really. There is simply no means of transferring energy from the air to the cart when above WS.

 

[spork]

Is the car test is equivalent to a change in wind speed propagating through the air?

Yes, I believe it is by definition. We take a parcel of air and accelerate it. Whether a car size chunk of air would be accelerated in just the same way in nature is another question.

I'm floundering a bit here.

I'm in need of someone telling me that ddwfttw is not do-able, even hypothetically, without this prop; these wheels; these gear ratios:

Please!

Jb; spork; humber; I ratant?

Am I this wrong?

Sorry quarky - I miss big pieces of this thread. Please feel free to PM me if you have questions I'm failing to answer.

 

[humber]

Yes, I believe it is by definition. We take a parcel of air and accelerate it. Whether a car size chunk of air would be accelerated in just the same way in nature is another question.

Within the confines of a vehicle? Like with doors and windscreens that may make a difference? A pressure wave reflecting for example? Sound, like pressure transients, travels about 1 foot in 1ms (.001s), Spork.

 

[A.T.]

A rocket motor is most effective when its exit pressure matches the ambient pressue.

Yes, you said that already and I asked more specific questions about the meaning of "most effective" here. What is compared here? Which parameters are free/fixed? The way I understand it is: For a certain fixed ambient pressure the most efficient motor is the one that matches exit and ambient pressure. That however says nothing about how efficiencies at different ambient pressure compare.

But, generally, a rocket's efficiency is better in the atmosphere than in space because the nozzle can be designed to match the exit pressure to the atmospheric pressure.

I don't think you can make that general statement. The fact that in the atmosphere you can achieve an optimum, while in vacuum you can't, does not mean that the efficiency in vacuum is worse. The efficiency at optimum for vacuum can be different than the efficiency at optimum for atmosphere.

 

[quarky]

There are alternative ways. In the old thread there are some suggestions for possible non-prop ddwfttw vehicles, for instance:

http://www.internationalskeptics.com/forums/showpost.php?p=4191830&postcount=41
http://www.internationalskeptics.com/forums/showpost.php?p=4195040&postcount=136
http://www.internationalskeptics.com/forums/showpost.php?p=4216082&postcount=833
http://www.internationalskeptics.com/forums/showpost.php?p=4217307&postcount=892
http://www.internationalskeptics.com/forums/showpost.php?p=4221704&postcount=987

All these ideas have something in common:

- First construct a vehicle where a part of the vehicle is always moving forward slower than the vehicle as a whole. This isn't hard: if you consider just a simple wheel rolling along the ground, there are points on the wheel moving forward faster than the centre of the wheel (any point above the centre) and points moving slower (any point below the centre).
- Then make sure that the wind is always blowing on a part that moves slower than the vehicle as a whole. This is where you need to be more ingenious.

To my knowledge nobody has yet constructed a non-propeller ddwfttw vehicle that actually goes faster than the wind, but there's nothing that says it's theoretically impossible.

You're a gem. Much thanks.

 

[recursive prophet]

Here’s some recent videos from I Ratant. Just click on his user name there to see the others. I’m pretty sure he posted what the gear ratio was on that cart but I don’t recall it. Anyone? Thought the foam popcorn was an interesting way to show ws. Too bad we didn’t get to see something similar at El Mirage. http://www.youtube.com/watch?v=zqW6BFCypoA

To my knowledge nobody has yet constructed a non-propeller ddwfttw vehicle that actually goes faster than the wind, but there's nothing that says it's theoretically impossible.

Wait…what!? Perhaps I’m just having another senior moment lapse in the synapse, but I could have sworn quite a few here were saying Humber’s claim to have built a cart that could go up a treadmill without a prop would re-write the laws of physics. Have to look at the TR archives again. Still want to find the picture I’m positive is there of Humber’s cart which all the regulars here repeatedly promised would never exist. Not you of course, Michael. You’ve sort of become the patron saint of DDWFTTW.

One question for you, that I’ve asked before on this thread. Why is it that unlike most wind powered craft, BB does not benefit from the wind changing direction and hitting it at more of a angle. I recall posts on this claiming that the prop(?) already saw the wind at various angles in its rotation and that it was set up to to maximize the tacking effect going ddw.

What humber has repeatedly failed to realize is that there has been no change in the explanation of how the ddwfttw cart works. The explanations are equivalent, and differ only in frame of reference.

Boy I wish I could get the hang or RFs. They're so very useful in debate.

@ynot: I also wish these threads hadn't been merged, but suspect it was inevitable despite being a very different discussion. Sort of like the original thread was from TVOCP that was split off from it. Thanks for trying anyway. The mods giveth, and taketh away I guess. It will now be difficult to sort out the how versus if discussions, especially given the high traffic level.

 

[Llyricist]

One question for you, that I’ve asked before on this thread. Why is it that unlike most wind powered craft, BB does not benefit from the wind changing direction and hitting it at more of a angle. I recall posts on this claiming that the prop(?) already saw the wind at various angles in its rotation and that it was set up to to maximize the tacking effect going ddw.

When directly downwind the propeller blades will have the same angle of attack all the way around their arcs. But when off DDW the upper and lower sideways arcs of their travel will have higher and lower angles of attack than when they are traveling upwards or downwards at the sides. And that will cause the lift they produce to be less than optimum during those periods. Less lift, less thrust, lower performance.

The Data shows that the performance is affected a lot more by wind speed than direction, so the first half of the double run makes it difficult to separate the causes of the differences in performance while the wind varied between DDW and 20 degrees off. But the second half of the run has a long period where the deviation from DDW was varying between 20 and as much as 50 degrees, and the decrease in performance was stark and obvious.

 

[Subduction Zone]

Yes, RP, the ability to use frames of reference correctly is a very powerful tool in physics. For example the whole science of using wind tunnels is based on the idea of the equivalence of the wind tunnel to flying at speed. humber is the sort that would argue that the wind tunnel is not a "true wind" if it would suit his cause.

 

[Modified]

Wait…what!? Perhaps I’m just having another senior moment lapse in the synapse, but I could have sworn quite a few here were saying Humber’s claim to have built a cart that could go up a treadmill without a prop would re-write the laws of physics.

Humber claims such a cart that is not wind powered, and that such a thing is possible without extracting energy from the wind, or anything else. His claim is that an unpowered cart can go downwind at wind speed, only he doesn't realize it because he doesn't understand reference frame equivalence.

 

[recursive prophet]

<snip>But the second half of the run has a long period where the deviation from DDW was varying between 20 and as much as 50 degrees, and the decrease in performance was stark and obvious.

HOw can you be so certain of cause and effect here? We are talking about very short periods of time. Braking effect? KE stored in the prop? Gradient effects? Might we not have a ways to go in sorting it all out? Did Orville and Wilbur understand everything about aerodynamics?

For example the whole science of using wind tunnels is based on the idea of the equivalence of the wind tunnel to flying at speed. humber is the sort that would argue that the wind tunnel is not a "true wind" if it would suit his cause.

So there are no differences between a wind tunnel and true wind? Remember I told you about my aero-pal who built his own test-lab for solar energy collectors and shot down experts from all over the country on all the flaws he had found in their testing procedures? The one who assured me ddw... was definitely doable? Well he has also told me existing wind tunnels have many serious problems. He did not in any way imply they didn't serve a very useful purpose, but that they are far from perfect.

 

[spork]

Remember I told you about my aero-pal who built his own test-lab for solar energy collectors and shot down experts from all over the country on all the flaws he had found in their testing procedures?

It's so rarely worth responding to an RCP post, but yes, I remember that well. The guy is an idiot.

The one who assured me ddw... was definitely doable?

Even a broken clock is right twice a day. Look at ynot. He finally convinced himself that DDWFTTW works despite his best efforts, but he doesn't have a clue why.

 

[Llyricist]

HOw can you be so certain of cause and effect here? We are talking about very short periods of time. Braking effect? KE stored in the prop? Gradient effects? Might we not have a ways to go in sorting it all out? Did Orville and Wilbur understand everything about aerodynamics?

30 to 60 seconds are not such short periods of time, and those are the periods that are available for comparison between 0-20 and 20-40.

Operator braking effects show up quite obviously in the graphed data as sudden large changes in acceleration that are not related to wind direction or speed changes.

KE stored in the prop is a non issue, the cart would only slow down running on the prop's KE.

Gradient effects are a non issue, only in the humberverse could the gradient be significant between 15 and 23 feet.

 

[Subduction Zone]

RP, yes there are limitations to a wind tunnel. And there are limitations to the treadmill test too. Knowing what the limitations of a tool are necessary to be able to use it. For example, I am a bit more educated on radiometric dating methods. When debating with creationists you very often run into them saying something like "C14 dating does not work" and then they bring up some cases where it does not work and they try to apply that to all cases. The thing is that anyone familiar with C14 would not use it in the named cases because they know it does not work there. Just because there are limitations to wind tunnels, or the treadmill, does not mean you throw those tools away. The treadmill only tests how the cart reacts right around wind speed. It does not tell you if it will self start. It does not tell you how many multiples of the wind that particular cart can achieve. All it tells you is if that cart can go faster than the wind if it starts out at the speed of the wind. But since that is the critical point for many it is the one point that you definitely want to test.

 

[ThinAirDesigns]

Gradient effects are a non issue, only in the humberverse could the gradient be significant between 15 and 23 feet.

And in the real world, the gradient is greater from 7 to 15ft (the lower half of the rotor area) than it is from 15ft to 23ft.

JB

 

[ThinAirDesigns]

The questions below ONLY relate to DIRECTLY DOWNWIND travel.

And still wrong.

JB

 

[Llyricist]

And in the real world, the gradient is greater from 7 to 15ft (the lower half of the rotor area) than it is from 15ft to 23ft.

JB

Yeah, I have to shake my head in wonder every time humber posts a graphic of the gradient curve and then goes on to say the opposite of what it clearly shows.

But then, he does the same thing with every graphic he didn't make himself.

 

[ynot]

And still wrong.

JB

Why is this wrong?

The cart is ONLY powered by the wind.

 

[ThinAirDesigns]

Yeah, I have to shake my head in wonder every time humber posts a graphic of the gradient curve and then goes on to say the opposite of what it clearly shows.

But then, he does the same thing with every graphic he didn't make himself.

Yeah, it's so wrong on so many levels. The BB has no mechanism to take advantage of gradients and the gradients are such that measuring wind speed at the hub level (as NALSA required) is actually measuring *higher* than needed to measure the average wind velocity of the prop area.

Keeps RCP all excited though -- humber's got that going for him.

JB

 

[ThinAirDesigns]

Why is this wrong?

The cart is ONLY powered by the wind.

Nope, what it's 'powered' by is frame dependent -- it can also be powered ONLY by the ground if analyized in a frame moving the speed of the wind.

JB

 

[spork]

And in the real world, the gradient is greater from 7 to 15ft (the lower half of the rotor area) than it is from 15ft to 23ft.

Not to mention the fact that we put a tell-tale well above the highest point of the prop and made it point straight aft while going DDW.

Nope, what it's 'powered' by is frame dependent -- it can also be powered ONLY by the ground if analyized in a frame moving the speed of the wind.

To be fair JB, Ynot doesn't understand the basics of how this works. It's not reasonable to expect him to understand this.