That's right, I was explaining to you why you were wrong and Ross was right, so if you want the dummies version....
(edit: all I'm saying is that, if you take direction into account, Ross is correct)
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Merged DDWFTTW in a “Real” Wind
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That's right, I was explaining to you why you were wrong and Ross was right, so if you want the dummies version....
(edit: all I'm saying is that, if you take direction into account, Ross is correct)
I assure you the cart will self-start and there are several videos demonstrating this.Not strictly correct.
It had to be given a push to get it started.[FONT=Verdana, sans-serif][/FONT]
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ynot,
...because a dummy like quarky is never going to get it no matter how dummed down you try to make it because there is a dumming down limit beyond which the explanatory power is inadequate for the task.
I think that's about as good an explanation for dummies as you're going to get.
...because a dummy like quarky is never going to get it no matter how dummed down you try to make it because there is a dumming down limit beyond which the explanatory power is inadequate for the task.
[FONT=Verdana, sans-serif]Given only the wind (directly or indirectly) is the only thing that can constantly increase the cart's velocity (see 1) wouldn't that “something else” HAVE to be part of the cart or something interacting with the cart that is moving slower than the wind?[/FONT]
Yes, how dumb was that!
(Idiot! I was thinking about the actual demonstration I found on youtube when I googled to find out wtf DDFTTW stood for.)
Of course. There must be carts that start without having to be pushed. In fact, given a strong enough wind I guess almost any cart will be able to start without a push.
ynot,
I think that's about as good an explanation for dummies as you're going to get.
...because a dummy like quarky is never going to get it no matter how dummed down you try to make it because there is a dumming down limit beyond which the explanatory power is inadequate for the task.
[FONT=Verdana, sans-serif]Sorry I should have made it clear that I'm using the outdoor cart in a “real” wind in the description. Can you or 69dodge rewrite the explanation to suit this scenario?[/FONT]
If you haven't already seen it have a look at the "speed record" video halfway down the page - http://www.fasterthanthewind.org/
Given you seem to be new to DDWFTTW you might like to also see some equipment I have developed to demonstrate the principle . . .
DDWFTTW demonstrated on an endless moving surface - http://www.youtube.com/watch?v=QTF5kw51H60
DDWFTTW demonstrated in an endless wind tunnel - http://www.youtube.com/watch?v=lOINjCtkL0Y
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So, the wind pushes the cart forward, that forward motion powers the propeller, and the propeller provides additional thrust?
Converting some of the forward motion into rotation of the propeller would slow the cart, but the propeller more than makes up for that?
Converting some of the forward motion into rotation of the propeller would slow the cart, but the propeller more than makes up for that?
Yes to both.
[FONT=Verdana, sans-serif]Essentially the propeller is creating an air mass that is moving slower than the wind when the cart is going faster than the wind and the wind is pushing against that air mass.
[FONT=Verdana, sans-serif]Power/energy from the wind is transferred to the cart via the air mass.[/FONT]
[/FONT]
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Yep, a derailment, but what's new about that? Since receiving that trial data, and what is told me, along with contact with NALSA, has resulted in a change of plan on that score.
But, I wonder what use a vacuum balloon would be? Costly to evacuate etc.
The Hindenburg is perhaps both more interesting and useful, because it managed to gain NB and have breathable air.
The skin of this VB must be able to withstand the compressive force of the air on the outside. That can only be met by tensile force on the inside face.
Bad news, because there are not many materials that have high tensile strength, and even fewer that have both high tensile and compressive strength.
To solve that, the skin would need to be structured to handle the tensile forces, without failing. Like a truss.
Stone is strong in compression, but weak under tension. That is why ancient buildings have limited span. The underside of a lintel is under tension, and a small defect produces a crack that propagates through it, and breaks it.
Finally, someone from MAKE more capable than Charles Platt :
http://www.make-digital.com/make/vol26?pg=58#pg58
http://www.make-digital.com/make/vol26?pg=58#pg58
Subduction Zone
Muse
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Hey!!! That looks suspiciously like the author watched spork's build video.
Rearguard action. Spork likes that. I wonder who that "someone" is.
But I've already answered this with a slight reworking of an explanation by 69Dodge. So why are you asking me a question I've already answered?
Here is is again:
Now, please respond to my answer instead of just posing the silly question again.
What? And you thnk we were NOT talking about the "outdoor cart in a real wind" scenario?
That explantion exactly applies to that scenario and always has.
Please read it again and respond.
Goddamn!
Listen, ynot, you are all over the place now after such a promising start.
The propeller does not "create an air mass". It might, however, cause it to do something. And that air mass is "moving slower" than what? And the cart is moving faster than what wind - the original wind or the moving "air mass"?
I mean dumbing down is one thing, but let's not lapse into incomprehensibility.
It's down to mass. The boat moves in reaction to the water ejected to the rear. F= ma. With steam, m is small so F will be small unless a is large.
But v=at, so to achieve a large acceleration value, the muzzle velocity would need to be very high.
ETA: increasing t, also works. Rocket nozzles are designed to keep the gas "within the rocket" for as long as is possible, so that the heat engine (the fuel) can continue to drive it, before it's gone for good.
Rockets don't push against the air. The motor moves with the rocket, and the mass is accelerated relative to the rocket.
The cart can never go faster than WS, because there is nothing to drive it.
"Upwind" and "downwind' are the results of thinking not of relative motion of the cart and wind, but the cart and ground.
Imagine that you are in some stream of gas in outer space, and traveling at the speed of the medium. From that point, both directions will look "upwind" to you. If you move "left" at 10m/s you, will feel a 10m/s headwind, and the same to the "right".
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ThinAirDesigns
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I disagree.
Every sailboat which can sail faster than the wind says that statement is wrong.
JB
Upwind boats tack, and no direct upwind cart, has managed to exceed 65% of the wind, and that will be the case for ddw.
When you are stationary on the ground, the wind is moving relative to you, and so you feel a headwind, which is exactly the same as if you were traveling at the same speed in still air. The speed of the wind when you are stationary in it, is an offset value, wrt respect the speed of the medium.
In the case of the inter-stellar gas stream, and you are traveling at the speed of that medium, you will not be able to say which way it is flowing.
Moving one way or the other, has the same effect ( same headwind) and takes the same power to move in either direction.
But, you can say which way that is, if you pass over the surface of a planet. Lower a rope to the surface, and that will induce drag. You and the gas, are traveling opposite to the direction of motion that drag produces.
Same with the BB, connection to the ground produces drag the other way, and you can no more power a cart from that to drive it the other way, than the rope can.
ThinAirDesigns
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Listen, ynot, you are all over the place now after such a promising start.
The propeller does not "create an air mass". It might, however, cause it to do something. And that air mass is "moving slower" than what? And the cart is moving faster than what wind - the original wind or the moving "air mass"?
I mean dumbing down is one thing, but let's not lapse into incomprehensibility.
You are correct BillyJoe and Ynot is again wrong.
It's a common misconception that the wind is pushing against the 'exhaust' of the propeller and thus the two "airmasses" are colliding and combining for speed. It's just not true - the interaction between the prop and the air is *exactly* the same as if the propeller were powered and driving the vehicle upwind.
For the above 'colliding airmass when downwind' theory to be true, it would mean that one could study the wake behind the vehicle and determine whether the vehicle was going upwind or downwind - and of course that would be the scientific discovery of the century(s) as it would disprove all of Galilean Relativity.
Think about a swimmer moving downstream -- is the swimmer creating a 'watermass' that is colliding with the 'watermass' of the stream, or is the swimmer merely 'grasping' something that is already moving relative to the shore and 'pulling' on it? (no one needs to point out that "grasping" and "pulling" aren't hydraulic terms -- I attempted there to use simpler, more descriptive but technically incorrect terms)
Of course we know that the swimmer is simply doing what a swimmer does and the swimmer can't tell without seeing the river bottom or shore or some reference which direction the current is going. We could study the wake of the swimmer all we wanted and still not determine whether the swimmer was going up stream or down.
Same with the propeller -- there is no odd or unique interaction between the propeller and the wind under any circumstances. The relationship between the propeller exhaust and the wind is no more unique than the relationship between the wheel and the belt of Lyricist's device he posted just above. On his device the wheel on the belt rolls just like normal -- so is the prop in the moving air.
Ynot knows how to build one - from his attempted descriptions, Ynot clearly does not know how it works. Use his descriptions (and mine) as you see fit.
JB
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I never got the idea behind that misconception. How would the collision of some air-masses somewhere behind the cart accelerate the cart? Of course it is correct that the slowed air in the prop's wake gets re-accelerated again by the following fast airmass. But that doesn't affect the cart which doesn't interact with that air far behind it anymore.
The only situation where that air-cushion-idea makes any sense is somewhere below wind-speed, where the flow trough the propeller switches direction.
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