Merged DDWFTTW in a “Real” Wind

[ThinAirDesigns]

I still think that talking about wind tends to confuses the issue.

Disagree.

The cart is moving with the wind. You can think of it as a part of the wind.

Only at exactly wind speed is this true.

What's moving, to the cart, is the ground.

What's moving to the cart is *both* the air and the ground. This is true at all speeds other than two -- when zero relative to the ground and zero relative to the air.

The cart uses the moving ground to drive the propeller.

That of course is a matter of perspective of course.

Think of an airplane taking off with the wind. The airplane's propeller doesn't function any differently as the airplane accelerates up to then faster than the "wind." It's the same for the cart.

Yes, there are limits to how fast a propeller can drive a vehicle, and, yes, the thrust of the propeller has to overcome the drag of the vehicle. But, there's nothing significantly different, in regards to how the propeller functions, when the cart is going below, at, or above "wind speed." In all cases, it's providing thrust to accelerate the vehicle.

Extremely correct.

JB

 

[Dr. Keith]

I wonder what the carteers will say if the foam pieces still beat a cart that has successfully advanced on the TM?

I don't think I would be surprised. The BB started off very slow and took quite a bit of time to get from zero to WS. Over any reasonable distance a cart with a jibb could beat it from a standstill. That isn't the point. It isn't a sprinter. It is the top speed that is amazing about the BB, not how quick it is.

Think of a top speed fixed gear bicycle with a front ring the size of a large pizza pan versus a more typical fixed gear bike. The typical bike will win in a race to the end of the block even if the top speed bike can go several times faster, eventually.

One is geared to be quick, the other is geared to be fast. Different concepts.

If you want to know which is fastest you don't race them over a fixed distance from a dead start, you clock them through a trap after they have each had sufficient time to get up to their top speed.

 

[jadebox]

What's moving to the cart is *both* the air and the ground. This is true at all speeds other than two -- when zero relative to the ground and zero relative to the air.

Yes, but I was trying to simplifying things to explain how the cart works.

The "wind" - relative to the ground - isn't important from viewpoint of the the cart. It's the ground moving the wheels that is. The wind speed could be zero, but if the ground were moving backwards relative to the cart, the propeller would spin and the cart would be accelerated. The treadmill test illustrates this.

The cart uses the moving ground to drive the propeller.

That of course is a matter of perspective of course.

The propeller drives the wheels which move the ground?

-- Roger

 

[humber]

I don't think I would be surprised. The BB started off very slow and took quite a bit of time to get from zero to WS. Over any reasonable distance a cart with a jibb could beat it from a standstill. That isn't the point. It isn't a sprinter. It is the top speed that is amazing about the BB, not how quick it is.

Ha Ha Ha.
"it's not a sprinter"
"If only the run were long enough". I told I Ratant that would be an excuse.
The chips are driven by air that has not yet reached the cart, and yet is manages to pass it. The chips will be long gone, as the silly geared cart lags behind.

One is geared to be quick, the other is geared to be fast. Different concepts.
If you want to know which is fastest you don't race them over a fixed distance from a dead start, you clock them through a trap after they have each had sufficient time to get up to their top speed.

Ha ha ha...."Dr" does not understand how gears work, and has folksy notions.

 

[humber]

Oh, you should see the data from the runs that TAD did not let you see. Push...crawl....stop.

 

[Llyricist]

The propeller drives the wheels which move the ground?

-- Roger

No, in the ground frame the power dynamics have to be treated differently, since the ground has no energy in that frame. The shaft power actually comes from the negative work the wheels do on the cart, and the rest of the power comes from slowing the wind down.

 

[Llyricist]

Ha Ha Ha.
"it's not a sprinter"
"If only the run were long enough". I told I Ratant that would be an excuse.
The chips are driven by air that has not yet reached the cart, and yet is manages to pass it. The chips will be long gone, as the silly geared cart lags behind.



Ha ha ha...."Dr" does not understand how gears work, and has folksy notions.

It isn't him that doesn't understand.

 

[humber]

Disagree.

"nobody mention the wind"
How about a wind that reaches 18mph and 40 degrees off ddw during you "record run".

What's moving to the cart is *both* the air and the ground. This is true at all speeds other than two -- when zero relative to the ground and zero relative to the air.

Silly folksy ideas. The road never moves.

The universally accepted definitions of speed and the average speed. Object moving along path P and traveling the distance ∆l during the time interval

∆t = t2 – t1.

The speed v of the object is defined as

v = Lim ∆t → 0 ∆l/∆t = dl/dt

Average speed Vavg overtime T, is defined a time average of v

Definition of the average speed determines the relationship between the travelled distance L (measured along the path ) and the
average speed, Vavg

L = Vavg*T

The average speed over the time T, and the average speed over the distance L are identical.

That of course is a matter of perspective of course.

Einstein from Walmart box room.

 

[CORed]

Ha Ha Ha.
"it's not a sprinter"
"If only the run were long enough". I told I Ratant that would be an excuse.
The chips are driven by air that has not yet reached the cart, and yet is manages to pass it. The chips will be long gone, as the silly geared cart lags behind.



Ha ha ha...."Dr" does not understand how gears work, and has folksy notions.

Clearly, somebody doesn't understand how gears work, but it's not the doctor.

 

[Dr. Keith]

Clearly, somebody doesn't understand how gears work, but it's not the doctor.

I used to wonder what he was getting at, but now I just don't care.

 

[ThinAirDesigns]

Yes, but I was trying to simplifying things to explain how the cart works.

Even what *you* might consider to be a simple explanation much still be correct to be of much value.

The "wind" - relative to the ground - isn't important from viewpoint of the the cart.

Completely wrong. The movement of the air relative to the ground is *exactly what's important* from the viewpoint of the cart -- exploiting that relative movement is the ONLY way the cart can travel DDWFTTW

It's the ground moving the wheels that is

.

Nope - it's *all* important to the cart. You can't say that the pistons are more important that the driveshaft in the family car. Take either one away and you're done. It's a package deal.

The wind speed could be zero, ...

Not relative to the ground it can't be. If that statement were true, a PM machine would have been invented and it wasn't.

The treadmill test illustrates this.

Nope, the treadmill does *not* illustrate a zero wind speed (relative to the ground) scenario. The treadmill demonstrates a zero wind speed relative the the vehicle chassis scenario (and speeds just above and below that).

JB

 

[Llyricist]

"nobody mention the wind"
How about a wind that reaches 18mph and 40 degrees off ddw during you "record run".

Couldn't figure out why the calculated wind speed spiked up to (actually) 19 mph while the CV was accelerating to catch up huh?

And the wind only started getting as much as 40 degrees off DDW 15 seconds after the test period.

Unless of course you couldn't figure out that the wild shifts in calculated wind direction before the CV started moving were due to the random bearings being reported by the GPS while sitting still.

 

[CORed]

I used to wonder what he was getting at, but now I just don't care.

Mostly he just strings together random bits of technical sounding gibberish, sometimes sprinkling in some mathematical or pseudo-mathematical formulas, (in at least once case, the "formula" had no "=" or inequality), then claims it supports his position. Often, if it means anything at all, it actually refutes his position.

 

[Dr. Keith]

Mostly he just strings together random bits of technical sounding gibberish, sometimes sprinkling in some mathematical or pseudo-mathematical formulas, (in at least once case, the "formula" had no "=" or inequality), then claims it supports his position. Often, if it means anything at all, it actually refutes his position.

Yeah, I caught that when discussing the NB balloon. It seemed like he had a single point of confusion and that maybe parsing out that point could lead to progress, but the closer we got to understanding his reasoning the more scattered it became.

So, now I just respond to those who at least fake an interest in understanding. Responding to those with no interest in understanding is just boring.

 

[Subduction Zone]

In the humberverse the only "real" velocities are those measured with respect to the ground. All others are fallacies and only folly can come from their use in his opinion. Just take a look at his last ramble and you will see that this is the case. He can barely understand the concept of relative velocity, in fact he usually gets that wrong, but he can never understand relative distances. All of his distances have to be measured over the Earth. Of course what do you expect from someone who thinks that he can tell difference between a fogged in moving aircraft carrier and a stationary one where the relative wind speeds are identical by jumping?

 

[spork]

Yeah, I caught that when discussing the NB balloon. It seemed like he had a single point of confusion and that maybe parsing out that point could lead to progress, but the closer we got to understanding his reasoning the more scattered it became.

He is fractally wrong. It looks exactly the same at every level of inspection.

 

[windgrins]

Additional Energy from the wind differential question.

I still think that talking about wind tends to confuses the issue. The cart is moving with the wind. You can think of it as a part of the wind. What's moving, to the cart, is the ground. The cart uses the moving ground to drive the propeller.

Think of an airplane taking off with the wind. The airplane's propeller doesn't function any differently as the airplane accelerates up to then faster than the "wind." It's the same for the cart.

Yes, there are limits to how fast a propeller can drive a vehicle, and, yes, the thrust of the propeller has to overcome the drag of the vehicle. But, there's nothing significantly different, in regards to how the propeller functions, when the cart is going below, at, or above "wind speed." In all cases, it's providing thrust to accelerate the vehicle.

-- Roger

Yes, I'm clear on all that. It is obvious though where an aircraft gets its power to turn the prop and not so obvious where the cart gets its power. We say it gets its power from the wheels but there is more to it than this.

The reason the wheels are not slowing the cart and using its KE is that the prop is providing thrust to push on the wheels-more than just is coming back to it through the feedback of the drivetrain. The prop's thrust would quickly diminish to 0 if there was not additional energy being imparted to the prop by the airmass/ground interface. The fact that the cart is being constrained from going forward by the wheel allows the relative wind on the prop to apply this additional force to drive the wheels. If the true wind did not exist, the prop would be producing thrust but slowing until the cart stopped. This additional energy that not only lets the cart continue to run but accelerate it past wind speed is what Ynot is looking for.

 

[windgrins]

You have arrived!

I used to wonder what he was getting at, but now I just don't care.

You have arrived at Wisdom, Dr. Keith!

Regards,

WindGrins

 

[windgrins]

JB is spot on!

Even what *you* might consider to be a simple explanation much still be correct to be of much value.



Completely wrong. The movement of the air relative to the ground is *exactly what's important* from the viewpoint of the cart -- exploiting that relative movement is the ONLY way the cart can travel DDWFTTW


.

Nope - it's *all* important to the cart. You can't say that the pistons are more important that the driveshaft in the family car. Take either one away and you're done. It's a package deal.



Not relative to the ground it can't be. If that statement were true, a PM machine would have been invented and it wasn't.



Nope, the treadmill does *not* illustrate a zero wind speed (relative to the ground) scenario. The treadmill demonstrates a zero wind speed relative the the vehicle chassis scenario (and speeds just above and below that).

JB

JB is spot on! This is what I'm getting at with "where does the energy come from?" for Ynot.

Regards,

WindGrins

 

[Dr. Keith]

He is fractally wrong. It looks exactly the same at every level of inspection.

Perfect description.

No matter where you try to get him to hang his hat it ends up floating off with the wind, only slightly slower.