Merged DDWFTTW in a “Real” Wind

[spork]

I'm sure you will come up with a whole lot of nonsense that you and only you think debunks ddwftw, but really makes no sense at all.

Nope - RCP will think he's made some excellent points, and will want to hear our responses to those points. Of course RCP won't be able to actually tell us which points he thinks have merit.

A prop is a rotating airfoil...

That is perhaps the least wrong thing humber has ever said. But it's still wrong.

 

[humber]

Of course it isn't necessary to have string winding onto the reel. Here's a little question for a physics test:
[qimg]http://www.internationalskeptics.com/forums/imagehosting/166124d9614330a322.png[/qimg]
A cotton reel rests on a level surface. The radius of the cotton reel at both ends is b and the radius at its narrowest part is a. A thin strip of cardboard is placed under the centre of the cotton wheel so that it touches it at the narrowest part. Assuming that there is sufficient friction between reel and surface and between reel and cardboard to prevent any slippage, what is the velocity of the cotton reel if the strip of cardboard is moved to the right at velocity v?

A physics test. That usually involves math, so earning the epithet "rocket scientist"
Post the math. I would very much like to see that.

"Assume there is sufficient friction". Well, how about more?
Glue the strip to the reel and then see how far it moves. It will slide, but so what? It would seem that the reel rolls along the strip. Do that in the wind, can you?

You like to say that all things are relative, so the motion of the paper to the reel, must be like the reel to the paper. A "Galilean Transform", would see the driving force moved to the reel. Push the reel with a pencil at the inner reel, and see how much faster than the strip it moves.

 

[humber]

Nope - RCP will think he's made some excellent points, and will want to hear our responses to those points. Of course RCP won't be able to actually tell us which points he thinks have merit.

Conspiracy talk. I am now RP too. Yevgheni is Harold....

That is perhaps the least wrong thing humber has ever said. But it's still wrong.

Sure it is. Rack up the math or references that say that.

 

[CORed]

Conspiracy talk. I am now RP too. Yevgheni is Harold....


Sure it is. Rack up the math or references that say that.

You want math?

a prop is a rotating airfoil

"a" is singular, and implies the number 1.
A prop is actually two or more rotating airfoils (most commonly 2, but more is not unheard of.)

2 != 1.

QED.

Of course, expecting to find a reference book that says every bizarre delusion that humber comes up with is false is not reasonable.

 

[humber]

You want math?
"a" is singular, and implies the number 1.
A prop is actually two or more rotating airfoils (most commonly 2, but more is not unheard of.)

2 != 1.
QED.

You ignored the possibility of a single blade prop, with a mass as a counterweight. Not used in aircraft, but in stirring devices. Pedantry will not led you avoid the remainder.
te heh...
http://en.wikipedia.org/wiki/Single-blade_propeller

Of course, expecting to find a reference book that says every bizarre delusion that humber comes up with is false is not reasonable.

Like the reference I posted which does not support you?

 

[CORed]

You ignored the possibility of a single blade prop, with a mass as a counterweight. Not used in aircraft, but in stirring devices. Pedantry will not led you avoid the remainder.
te heh...
http://en.wikipedia.org/wiki/Single-blade_propeller



Like the reference I posted which does not support you?

Interesting, but your reference doesn't quite seem to match your claim. The propeller you link is in fact used for aircraft, and it does not rotate, but, according to the ariticle teeters (their word, not mine. I assume it means that it oscillates), so it still doesn't qualify as a rotating airfoil, but I will concede that it would be possible to make one that qualifies.

 

[spork]

"a" is singular, and implies the number 1.
A prop is actually two or more rotating airfoils (most commonly 2, but more is not unheard of.)

This is actually why I said that this is the least wrong humber has ever been (but still wrong). The airfoil is simply the cross-sectional shape of the lifting surface. A prop will typically have a wide range of airfoils along each blade. We can say a prop is two spinning blades, wings, lifting surfaces, etc. But it's not accurate to say it's a spinning airfoil.

 

[CORed]

This is actually why I said that this is the least wrong humber has ever been (but still wrong). The airfoil is simply the cross-sectional shape of the lifting surface. A prop will typically have a wide range of airfoils along each blade. We can say a prop is two spinning blades, wings, lifting surfaces, etc. But it's not accurate to say it's a spinning airfoil.

Okay. I thought airfoils was pretty much synonymous with wing, but it looks like I was wrong about that.

 

[humber]

This is actually why I said that this is the least wrong humber has ever been (but still wrong). The airfoil is simply the cross-sectional shape of the lifting surface. A prop will typically have a wide range of airfoils along each blade. We can say a prop is two spinning blades, wings, lifting surfaces, etc. But it's not accurate to say it's a spinning airfoil.

It is. The twist and taper are there to account for the different velocities away from the hub. Generally, but not always, there is a taper to ensure that force is evenly distributed along the length, otherwise there is a bending moment that will produce oscillation and break the prop.

Also, there is effort put into seeing that the effective area of the stream tube on the thrust side, is less that that of the input side. Bernoulli and all that stuff.

 

[Jack by the hedge]

And is the reel gaining on your hand? Then it's accelerating isn't it?

No.

You are confusing a change on closing distance with speed.

You are confusing a difference in velocity with a continuous change of velocity.

 

[spork]

Okay. I thought airfoils was pretty much synonymous with wing, but it looks like I was wrong about that.

Very easy mistake. No shame in being wrong.

It is. The twist and taper are there to account for the different velocities away from the hub. Generally, but not always, there is a taper to ensure that force is evenly distributed along the length, otherwise there is a bending moment that will produce oscillation and break the prop.

But humber doesn't know how to be wrong. He takes this as an opportunity to lecture us on more obvious stuff that he was already wrong about. And NO, the objective is NOT to ensure that the force is evenly distributed along the length. That would make for a very inefficient prop. I'm sure humber will explain it to us shortly.

 

[Jack by the hedge]

Thread is not wind, Chief. It has the properties of a thread.

When an analogy breaks down, it ceases to be an analogy. Sorry if nobody explained that before.

 

[Jack by the hedge]

Inner 3", outer 9" circumference.
Simple rule:
Over
Reel moves 9" (one turn)
Hand moves 9 + 3 = 12" OK

Under
Reel moves 9" (one turn)
Hand moves 9 - 3 = 6" OK

"Half the speed" All good so far.
But, that can only happen if there is enough thread between the reel and the hand to avoid the hand and reel coming in contact. Yes. You can only pull the thread if there is some thread to pull.

Work = F*d, so the same in each case If the hand makes the same movement at the same speed, then yes.
12*F = 6*2F
The under version requires twice the force. Also true.

But F=ma, so acceleration is doubled in the under case. Well it would be, wouldn't it? It has to travel twice as far in the same time, so it has to do everything twice as fast.
Now there is a need to consider time, and not just distance. Wrong. You have already assumed that the movement takes place in the same amount of time. That's why you came up with twice the force. If you could take as long as you like then the force is undefined.

My bits in red.

 

[Jack by the hedge]

Here's a little question for a physics test:
[qimg]http://www.internationalskeptics.com/forums/imagehosting/166124d9614330a322.png[/qimg]
A cotton reel rests on a level surface. The radius of the cotton reel at both ends is b and the radius at its narrowest part is a. A thin strip of cardboard is placed under the centre of the cotton wheel so that it touches it at the narrowest part. Assuming that there is sufficient friction between reel and surface and between reel and cardboard to prevent any slippage, what is the velocity of the cotton reel if the strip of cardboard is moved to the right at velocity v?

A physics test. That usually involves math, so earning the epithet "rocket scientist"
Post the math. I would very much like to see that.

"Assume there is sufficient friction". Well, how about more?
Glue the strip to the reel and then see how far it moves. It will slide, but so what? It would seem that the reel rolls along the strip. Do that in the wind, can you?

You like to say that all things are relative, so the motion of the paper to the reel, must be like the reel to the paper. A "Galilean Transform", would see the driving force moved to the reel. Push the reel with a pencil at the inner reel, and see how much faster than the strip it moves.

Am I the only one imagining a high school examiner trying to mark that answer to the question?

 

[humber]

heh, and if you think Humber is just joking here, at TR jb actually takes the time to paste in my user name on all his quotes of humber's posts, and attributes mine to him. Been doing that for months now. I know this sounds like a 4/1 gag but it's not. And today of all days, the Chief actually managed to get the thread temporarily locked for the first time ever. I only wish I could make up stuff like this! Worth a look for sure.

Like this, where I ask if they knew Steve Smith. I asked many times prior to this one.

(me) #1258069 / #272
More manipulation. NALSA (one official at the trial) Community Centres and now Ames (one engineer). This cart is all about *****. Now, once again JB, had you earlier contact with the author of that email? Has he ever been engaged by you as an aerodynamics consultant?

No.

JB

Smith said he met Spork through flying.

I think we can put the "lying" thing to rest. Already the cart has changed its weight, so that is two down.

 

[humber]

Very easy mistake. No shame in being wrong.

But he is right.

But humber doesn't know how to be wrong. He takes this as an opportunity to lecture us on more obvious stuff that he was already wrong about. And NO, the objective is NOT to ensure that the force is evenly distributed along the length. That would make for a very inefficient prop. I'm sure humber will explain it to us shortly.

Even thrust is same as even force. The stress at the root limits the size of wind turbines. Don't want a lot at the tip. Long lever.
http://www.boeing.com/companyoffices/aboutus/wonder_of_flight/propeller.html

One wiki does not contain the whole story. Lots of different factors,
Fans are usually wider at the tip than the root. Slow props are like that. See Bauer's.

 

[Vega Nova]

Would someone please be kind enough to post an unbiased summation of whats going on in this thread? I notice that it has been a year since first post and there still seems to be an open discussion as to the veracity of the event in question. I gather something cool and science-y was filmed, but the science still hasn't checked out? Please correct me if wrong. Thanks.

 

[I Ratant]

This....

 

[humber]

My bits in red.

As I Ratant said, reels are tricky, and you need to control all of the variables.

One is to ensure that the force is known, or at least the same in each test, otherwise you will be comparing apples and pears, while the slow static case ignore the dynamic effects.
A full reel will be hard to make roll towards the hand - without adequate friction it will slid, but will generally roll away if does not slide.

Two things have changed from the 2:1 reel. The gearing has all but gone, and the mass distribution has changed. A wheel has both linear and angular momentum and so KE for both. The ratio of the two is important.
The angular part depends on the moment, which depends on where the mass is. The same mass as a hoop around the circumference, like a tube, will have a larger moment than if the same mass is near the centre. The velocity is lower near the center. All those things and friction, make for all sorts of behavior, force and acceleration.

But it's easy to see that the average will always be the same as the hand
once acceleration stops, or is averaged out over time.
Take a long runway and pull a reel. If it is going twice the speed as you, it will eventually overtake you. It may pass by at greater than twice the speed, but that is another story, but it will pass by, and then you can't pull it.
You don't want to brake it, so you must let the thread pass through your hand. The reel steams ahead, but slows dues to friction, you catch up with it, and pull it again.
Do that a few times and you will find that the reels is always close by.

 

[CORed]

Would someone please be kind enough to post an unbiased summation of whats going on in this thread? I notice that it has been a year since first post and there still seems to be an open discussion as to the veracity of the event in question. I gather something cool and science-y was filmed, but the science still hasn't checked out? Please correct me if wrong. Thanks.

The people posting here as spork and thinAirDesigns built a wind-powered cart that is capable of going directly downwind, faster than the wind. This has been verified by treadmill tests with miniature performed by them and confirmed by several other posters. A trial was conducted by NALSA (North American Land Sailing Association) that a cart capable of carrying a person achieved 2.7 x windspeed. The science appears to have "checked out". The poster known as humber, who tries to pass himself off as an expert in physics, but makes ridiculous, fundamental errors on nearly every post, asserts otherwise.

The poster known as humber seems to be obsessed with proving that the assertions of the builders of the DDWFTW cart are perpetrating a fraud, but he is remarkably unequipped to do so. Most of the people still participating in the discussion are doing so because humber fails in a remarkably humorous manner.