Split Thread The validity of classical physics (split from: DWFTTW)

[spork]

...comparing them with my own experiences (ALSO R/C models! Plus I'm a professional pilot, ex-skydiver, glider pilot, sailor...

Sounds like we share a lot of the same interests. I'm a very casual SEL and glider pilot, as well as hang gliding, paragliding, kitesurfing, a little outdoor skydiving, and a lot of indoor skydiving. Never tried a land-yacht, but I envy you. Sounds like a blast.

Here's one for Humber- the current R/C model speed record is around 300kph.

I thought a new record was recently set at something like 371 MILES/hour - no?

 

[spork]

Here's one at 357 mph. I thought they recently hit 371, but I could well be wrong.

http://www.youtube.com/watch?v=Vi0hrjqU15I

 

[RossFW]

I thought a new record was recently set at something like 371 MILES/hour - no?

Yep, I stand corrected (note to Humber, that's what you do when you are WRONG!!)

 

[humber]

There's a world of difference between a skeptic and an A-hole. I've always welcomed sceptics. Frankly I have little interest in talking about the performance curves with people that already understand this thing.

Quite, yes.

Mark F. may be a sceptic..

Not of member of the set, 'Those who are Skeptics and A-holes'

I suspect humber may actually believe that.

A member of the set, 'Those who are Skeptics and A-holes'

All good stuff. My argument lies in ruins

 

[spork]

Here we go - this is the one I was thinking of: http://vimeo.com/2375301

 

[humber]

Yep, I stand corrected (note to Humber, that's what you do when you are WRONG!!)

Sailplanes are not wind borne objects in a steady flow. They are aircraft.

Do you understand the concept of wave energy? Do you think that wind gusts make be like water waves? All sorts of things can go faster than the medium, if they exploit waves. Including oil tankers and whales.

Now, please show me the wave generator this is cunningly built into the treadmill.

ETA:
I made a pulse jet model. Do I win?

 

[spork]

I know the topic is humber abuse, but I have to say... 371 mph with an R/C sailplane is incredible. Better than 1/2 the speed of sound with no engine in maybe a 20-25 mph wind? That puts them into the region of compressible flow. You pretty much ignore that in everything I've ever flown (R/C or otherwise). To put it in perspective, I was flying a friend's ultralight motor glider yesterday with a top speed of 65 mph and stall around 25 mph!

I made a pulse jet model

No you didn't

 

[RossFW]

Yes I understand wave energy.

Dynamic soaring has nothing to do with it.

It involves utilising the potential energy of the difference in velocity of two mediums (sound familiar?), in this case, both of them air but with a velocity gradient.You fly the aircraft into a differnt airstream which is slower than the aircrafts current speed (therefore into a headwind) which inceases the aircrafts airspeed. You then reverse the direction of the aircrafts flight and fly it back into the original, slower airstream, thus AGAIN giving an increased headwind. This is repeated with the aircraft gaining energy with each reversal.

So here we have two air streams moving in the same dirrection, but at different velocities. Because there is a RELATIVE difference, it is an energy source that can be exploited.

If I recreated this in still air by providing a second stream using a powerful fan, I could do the same thing. Much like using a treadmill to provide a REALATIVE airflow.

Now, if your Pulse jet had a top speed of 100MPH True Air Speed and you flew it into a 100MPH wind, what would its ground speed be?

 

[spork]

If I recreated this in still air by providing a second stream using a powerful fan, I could do the same thing. Much like using a treadmill to provide a REALATIVE airflow.

The treadmill is DENIED! (sorry I couldn't resist - I must be feeling a little humber).

Now, if your Pulse jet had a top speed of 100MPH True Air Speed and you flew it into a 100MPH wind, what would its ground speed be?

Oooh - ooh, I know this one! The question is moot. humber never even had a pulse jet model.

 

[Clive]

<snip>

I couldn't really get anything useful from the first part of your post humber. The scenario we were talking about is me standing on the belt, with the belt moving so that I feel wind against my back. You said (at least twice) the laminar flow in that case moves from my toe to heel. I said before, and I say again, that what you stated earlier was not correct. Do you accept now that you were wrong?

At the very least, a flow from toe to heel (as you said would be seen) would mean the air in that particular region (down very close to the belt) is moving in the same direction and faster than the belt (w.r.t. the ground). Why on earth would it do that? That would require the air which was not moving initially to be accelerated to match the belt speed and then further accelerated to go faster than the belt.

Try this:
If when fixed to the belt, you actually "jump", you are magically suspended but a real body. What happens?
You continue in the direction of the belt until your kinetic energy is expended against the air. In the direction of the belt (road).
Do that in the real wind. You are accelerated to some speed less than the wind, (not windspeed!) in the direction of the wind, not the road per se.

Putting aside the "not windspeed!" and the suggestion that kinetic energy is the best way of thinking about this, fine. So what? In both cases, if I look down at the surface I have just jumped off, I will see it moving in the same direction relative to me ("backwards"). This is because I'm now being accelerated by net horizontal force which brings my velocity closer to that of the surrounding air mass. The net force acting on my body is due the relative difference in velocity between me and the air mass I am in. If there was no net force acting on me in the horizontal direction, then due to Newton's first law my velocity would not change. As it is, I will be accelerated, and the direction of the acceleration is the same (relative to the ground/belt) in both cases. If I start facing "downwind" in both cases, then the ground/belt starts to moves backwards ("toe to heel") as I jump up because I will be accelerated in the direction of the "wind", meaning my velocity increases in the direction I am facing. That happens to be "downwind", so no real surprises there! I jump up so my feet are no longer holding me to the ground, some "humber magic" allows me to float above the surface indefinitely, and the wind accelerates me in the direction it flows past me. That all sounds fine to me.

This has consequences, that allow the cart to sit on the belt doing nothing.
KE can show that too.

This has been said before but I'll say it again. Kinetic Energy is calculated using velocity. Velocity is measured relative to our chosen ("close enough to inertial") frame of reference. I can choose a frame of reference (at rest w.r.t. to ground/belt) that had my initial velocity as zero. I jump up and am magically held up somehow (as per your description) so any kinetic energy I gained by jumping up is now converted to gravitational potential energy and perhaps some other forms. I have no kinetic energy to be "expended against the air". In fact in this frame of reference I gain kinetic energy as I am accelerated.

I don't think I was following the parent thread when the main topic was your idea of how kinetic energy can somehow be used to explain the cart's behaviour. But feel free to summarise that idea again if you can, or else provide a link to a relevant earlier post(s).

When will you respond to my earlier (#516) "five stages" post? There's no treadmill in that at all in the early stages, and when one is eventually introduced then it is always operating in a "real wind". Presumably that will mean we won't need to debate the direction of laminar flows there at all. Surely that's got to be a good thing?!

 

[H'ethetheth]

Yes, H'ethetheth. The profiles are the same. The average velocity of the real drag porfile is opposite to the cart. Look at the arrows.

In real downwind, the wind near the road interface lags the real wind, but the average is still downwind, in the direction of the cart.

At the surface the average is in the direction of the cart, yes, but not when viewed from the cart. This is true for both situations. An observer on the cart sees the same type of boundary layer. A boundary layer between the air that is travelling with him and the ground that is passing by from front to back.

Not so on the belt.

And that's where you're wrong. Viewed from the cart, the conditions are the same (for a sufficiently large treadmill).

So how can the laminar flow move opposite to the supposed tailwind?

Just like on the street, the wind at the surface moves slower than the bulk of the air. If we choose a vantage point moving with the wind, we will see air moving opposite to us at the surface.

That is a clue as to what is really happening.

You say things like this with so much confidence, and yet it is clear that there are at least two major things you do not grasp. It would help if you would stop thinking of choosing reference frames as some kind of voodoo magic that can be used to obtain any desired outcome. It isn't. It's a very precisely defined and very useful tool for analysing this type of problem.

 

[John Freestone]

You could try addressing the matter directly. The floor is open.

Allow me. I get 4 as well.

 

[John Freestone]

Let's have a round of applause for humber! He got something right. Welcome to our universe!

Oh dear, I spoke too soon.
He's in a Hi-roof boxcar. It's not a tiny hop, it's a Michael Jordan quality basket-dunking vertical leap, and he nearly manages to touch the ceiling of the boxcar. Inside height of the boxcar is 13 feet. He's a short guy, and so he stays off the floor for (hang on...) 1.8 seconds (somebody feel free to check my math on that one). We can make a taller custom boxcar if you like, and give him a trampoline. He's still going to land on the chalk mark.

Make a chalk mark on the belt. Jump. Check your wind directions again.

Give him everything he needs to build hot air balloon so he can take off in the - to hell with it - 1300 foot high boxcar and hang suspended over the chalk mark in the still air inside it. Oh, but he'd better be quick and land again before the gravitational frame dragging kicks in.

 

[CORed]

If quick = No loss of KE.

Now, you were saying?

If he's not quick, where does the KE go?

I think we're back to the idea that in the Humberverse, anything moving relative to "the ground" experiences "drag", even inside a full enclosed boxcar.

 

[huh34]

Since humber made a clear statement and a question, I'll just exercise my fingers a bit. (I'm quite fustrated with my present work assingment, you see.)

To make the model complete, moving with the belt must be the equivalent of being stationary in the real world, with the wind to his back.

Yes, moving with the belt must be equivalent of being stationary in the real world. You must compare _being still_ in real wind and _movin with belt_ in treadmill. Being still in real wind must NOT be equivalent with being still above the belt. And moving in real wind must NOT be equivalent with moving above the belt (same speed ofcourse). Agreed?

Realwind:
Wind from the back, with the laminar wind flowing from heel to toe. Like the wind. Correct?

Yes, being still in real wind.

Now, become an imaginary observer, which way does the flow move?
From heel to toe. It passes from heel to toe, like the wind.

Yes, the imagynary obeserver continues being still in real wind.

Treadmill:
Wind to the back, with laminar wind flowing from heel to toe. Correct?

Yes, moving with the belt.

Now, become an imaginary observer.
Which way does the laminar flow go?
From toe to heel. It passes from heel to toe like the belt (road), not the wind.

No, the imaginary obeserver must continue moving with the belt. In your realworld example, becoming imaginary does not change observers velocity. In your treadmill example, becoming imaginary changes observers velocity. That is the fallacy.

Here is your mistake. Your imagynary observer suddenly stops, it is no more moving with the belt, and therefore the situation is no more equivalent with real world.

If the observer is not moving, the wind passes from toe to heel.
If the obeserver is moving with the belt, the wind passes from heel to toe.
The latter is the situation that should be and is equivalent with real wind.

Which part do you not agree with?

I hope I made it clear, but feel feel to ask for a line number or something.

Two separate "winds" that are only "correct" in two limiting cases. When fixed to the belt, or at "windspeed". At other velocites, the ratio will change.

The treadmill and real wind are identical in any practical sence at all possible speeds. It is true though, that the treadmill can be used to model ONLY the situation, were the cart is already going at windspeed or just a bit over or under it. Nobody claims otherwise.

 

[mender]

Maybe, Mender. I have read his paper, but not yet the power part, but I think that he is taking some liberties. But that is not the point. You can see that it is treated as an engineering problem. A few equations and some estimated factors. There is no equivalency as such. The text does say "ground power" but that is it. The rest is simply the differential velocity of the wind over the ground, as I expect.

The treadmill supports other notions, that are not in Dela's ideas.


That works both ways. It takes effort.


Can't agree with that. If you agree with him, yes, otherwise you are dismissed. Skeptics are not all alike. Some just say "can't work" just because they think so. They are useless, Mark boing-boing included.



Yes, Mender. Nobody gets abuse from me as first strike. Some not at all. That is not the point. The treadmill is wrong. The cart is the cart. It's a propeller and wheels. An entirely conventional engineering problem.

I never "misunderstood" any of the ideas. The "eureka" moment, is the time that you abandon what you have learned, to be transported back 400 years.

You have to agree, that if it is equivalent, then it should pass all the tests, from any "frame". They are inconsistent. It is internally inconsistent. Behavior when fixed to the belt, is not the same as when at windspeed.
Test are difficult, because it cannot support them. All failures result in motion back with belt. It has no valid intermediate states. It cannot be shown to move from belt speed to windspeed, nor any state in between. Only "windspeed"

You misunderstand how the cart works, and have refused to contemplate scenarios that others have posted that could possibly help you. The essence of how the cart works is by using the relative speed difference between the air mass and the ground. Wind outside provides that. A treadmill inside provides that. The cart can't tell the difference and when the amount of energy present in that relative speed difference is sufficient, the prop cart develops enough thrust to go faster than a sail powered cart. Put a sail powered cart beside a prop cart on a treadmill and you'll see the difference.

A few tests with your own cart on a treadmill like I've recently completed would show you exactly what happens in the intermediate steps. Before the relative speed difference between the air mass and the ground gets to a certain level (indicating the energy available), the cart moves slower than a sail powered cart. As the speed difference (and energy available) increases, there is a point where the cart moves over the ground or belt at the same speed as the speed difference between the air mass and the ground. When the relative speed difference is increased again, the cart goes faster than that speed difference. It's really quite simple, but you have to do more than say "it doesn't work". A good start would be to ask how it works.

It's not rocket science but it does require that you be willing to learn. So far, you've resisted all attempts to help you learn. Being open minded doesn't mean that you're gullible, it means that you can consider other ways of thinking. Of all the people that have joined conversations about this cart, I'd have to say that you're the most closed-minded I've seen.

 

[Dan O.]

The treadmill and real wind are identical in any practical sence at all possible speeds. It is true though, that the treadmill can be used to model ONLY the situation, were the cart is already going at windspeed or just a bit over or under it. Nobody claims otherwise.

The treadmill is in fact used to model in the specific case that most deniers (including humber) say that the cart will fail: the transition point where the cart goes from moving slower than the wind to exactly as fast as the wind to faster than the wind. The cart on the treadmill shows that it can quite easily cross this transition. By attaching a horizontal tether to the cart we can directly measure the excess force that is used to accelerate the untethered cart to beyond wind speed. The same force can be indirectly measured by inclining the treadmill and seeing that the cart can maintain it's position against the force of gravity pulling it down the slope.

Humber cannot see any of this because he keeps getting his vectors reversed. Is this some form of physical dyslexia that affects his perception?

 

[Tunny]

Give him everything he needs to build hot air balloon so he can take off in the - to hell with it - 1300 foot high boxcar and hang suspended over the chalk mark in the still air inside it. Oh, but he'd better be quick and land again before the gravitational frame dragging kicks in.

Nonsense! A hot air balloon could never reach train speed! The drag from the air in the enclosed car would keep it pinned to the rear of the coach! Also, you forget that the KE at 1300 feet is vastly different from that at ground level! And there's a laminar boundary flow of air along the floor of the car that would obscure the chalk line. You need to account for these in your computations. Your question is meaningless...

Tunny
Channeling my inner Humber...

 

[humber]

Uote

Yes I understand wave energy.

Dynamic soaring has nothing to do with it.

It involves utilising the potential energy of the difference in velocity of two mediums (sound familiar?), in this case, both of them air but with a velocity gradient.You fly the aircraft into a differnt airstream which is slower than the aircrafts current speed (therefore into a headwind) which inceases the aircrafts airspeed. You then reverse the direction of the aircrafts flight and fly it back into the original, slower airstream, thus AGAIN giving an increased headwind. This is repeated with the aircraft gaining energy with each reversal.

Yes it does. Define a wave.
OK then, do you understand the concept of homogeneous flow?

So here we have two air streams moving in the same dirrection, but at different velocities. Because there is a RELATIVE difference, it is an energy source that can be exploited.

Like between air and ground, for example. So, make the air a homogeneous flow of constant velocity.
Seriously RossFW, you have given me several examples of such things. It seems that engineers have long exploited this idea. Brunel built a ship that used rotating cylinders in the air rather than a propellor. Do you think that with this "relative" stuff, the you have discovered a hidden secret of the universe?

If I recreated this in still air by providing a second stream using a powerful fan, I could do the same thing. Much like using a treadmill to provide a REALATIVE airflow.

Now, if your Pulse jet had a top speed of 100MPH True Air Speed and you flew it into a 100MPH wind, what would its ground speed be?

I say it again. Why do you insist that this has any relevance?

 

[humber]

The treadmill is DENIED! (sorry I couldn't resist - I must be feeling a little humber).



Oooh - ooh, I know this one! The question is moot. humber never even had a pulse jet model.

Of course, nobody can do what is inconceivable to you, Spork, but you do produce the inconceivable.