Merged DDWFTTW in a “Real” Wind

[Llyricist]

Not all speed records go both ways. Records that are supposed to be independent of the wind run both ways to eliminate the wind factor. A record that is for the fastest speed directly downwind can only run downwind by definition. The Greenbird has the land sailing speed record. This record was accomplished on a downwind reach. Again, not both ways since it is a wind dependent record. There are also speed records with kiteboards that are one direction only. I am sure that other posters can think of more.

The direction and speed of the wind was irrelevant to the Greenbird record, in fact, Jenkins actually lost that data by letting the instruments continue to record, and overwrite it.

 

[I Ratant]

I believe they are more efficient although it depends on what you mean. Those are turbines and they have nothing to do with the ddw cart. They are of course limited to less than WS. I believe the record is about .6x WS.

I think the Blackbird's builders plan to crush that record with an upwind vehicle sometime this summer.

.
Upwind traveling wind-powered vehicles work, but I would only give a lot of attention to one that goes both ways, without stopping for a rebuild between directions.

 

[Subduction Zone]

They are not doing a "full rebuild" but there are significant changes. They are building a new rotor since an ideal turbine will have a different shape than an ideal propeller. They will also be changing the drive mechanism. Since previously the propeller was driven by the wheels and now the wheels will be driven by the turbine. He won't be just turning the vehicle around and go from directly downwind to directly upwind.

 

[Llyricist]

I hate to nitpick again, but all they really have to do is create new blades, install them with the opposite and higher pitch, and flip the little levers on the ratchets. Unless of course there is some efficiency advantage in changing the relative RPM as well.

 

[humber]

What is your point? The spool requires traction just as the bb does.

Last word on the reel.

Traction is another problem, but as I have said, the rolling friction works against a car's wheel, just as it does for the reel, but on a car, the torque from the axle drives the wheel in the direction of rotation, whereas in the case of the "under" reel, the thread produces a torque in the direction opposite to rotation. That appears to be paradoxical, because the reel turns CW and to the right.

A reel on a spindle held in the hand will turn CCW, because of the torque produced by pulling the thread, but when on the ground, it turns CW and moves to the right. That is not something that can be seen by observation, nor drawn with simple diagrams because it is not static. But math gives the answer. "Thought experiments" have their limits too.

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Much can be found here, and through links from there.
http://hyperphysics.phy-astr.gsu.edu/hbase/amom.html

This link shows that wheels have linear and angular components.
http://hyperphysics.phy-astr.gsu.edu/hbase/rotwe.html#ro


It's algebra and a basic Newton. I have added some explanation to the original post and diagrams.
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A reel can be rolled towards the hand applying F, but may also turn counter-clockwise (CCW), and roll away from the hand.
Assuming that the force is applied parallel to the floor ( no lifting of the reel), which way will it go?

a = inner radius
b = outer radius
Fd = Friction
F = Applied force
m= reel mass
I = reel moment of inertia
v= linear velocity
w = angular velocity (radians/sec)

This is the significant bit;

1) Linear component:
Net force to the right = F - Fd ( applied force less the drag force)
Acceleration dv/dt = F - Fd/m ( simple application of f=ma)

If the hook is employed, the reel will move at the speed of the hook on that linear force alone, and will roll CW. ( It can slide too, but we will ignore that case)

But, when the thread is used, it generates a CCW torque. It's important to see that the thread produces both linear force (like the hook) and angular force CCW.

2) Angular Component:
Net clockwise (CW) moment = b*Fd - a*F ( net force, geared by the ratio)
Angular Acceleration dw/dt = (b*Fd - a*F/)I ( F=ma for rotating objects)

When a wheel rolls without sliding ( pure rolling) the axle of the reel moves a distance equal to the circumference. So, the linear velocity (the speed the axle moves) and the angular velocity ( the speed it turns) are related by;

3) v = b*w
( That is the no-slip case. Velocity = large radius*rpm w=radians/sec)

The linear and angular accelerations are related as:

dv/dt = b*dw/dt
( relates the linear acceleration (1), to the angular acceleration (2)

The rest is equating forces, which always come in opposing pairs. Perhaps if worked with a= b, it may be clearer.

From a = f/m

(F - Fd)/m = b(b*Fd - a*F)/I

Rearranging to relate Fd in terms of F

Fd( I + mb^2) = F( I + mab)

Fd = F(I + mab)/(I + mb^2)

If the reel moves to the right, then both the linear and angular forces will be positive (to the right). That depends on the friction to the surface and how the force is applied. If pulled slowly, the reel will tend to roll with the hand, but a jerk may send it away.

It's a balance of the inertia of rotation and the friction to the surface, where the angular component is either positive or negative.

There is a third case, where there reel does not roll, but slides, so the angular component is zero. That may happen when the friction is very low. Wheels cannot roll without adequate friction.

The under reel is the worst choice, because it basically opposes itself.

 

[humber]

Would you elaborate on your position re NALSA. They are recognized as the worlds leading authority on land sailing.

By whom?

The two deniers, Harold and Humber, could not sing their praise high enough before the Blackbird's record.

Not really, I did remark that the Greenbird trial had a strong element of chance. That an inferior cart in more favorable winds, could take the prize from Greenbird.
There is some doubt about the claimed accuracy of the GPS. But, I did give them more credit than they deserved, perhaps.
Greenbird trial was based upon established methods and the wind is recorded, but the target is land speed, not multiples of the wind speed. No real time data of the wind is needed,
and they have no experience of that. The Greenbird trial had more official involvement, but the BB had only Bob Dill.

If I had not already satisfied myself that the cart not only could work (but would violate the laws of physics if it did not) before the record run, I would have accepted that it did work on their say so alone.

Boat club, not physicists.

They went far beyond pellets and streamers with their safeguards. They did not ratify a world record on a whim or from reviewing videos.

Pah. The promised "instrument package" was never completed. The wind vane was a forced choice, and so was the CV. Worst case error margin.

I told Spork when he offered to wager me, that I would demand pitot tubes and other mass-less means of wind measurement. Log the data at high speed, and then
give it to a group of Chartered Engineers for analysis. The BB trial was ad-hoc, and contains many technical blunders and failures of experimental design.
The details and rules were kept away from inspection. Served up after the trial.

 

[PhooBar]

ROTFLMFAO!
Oh God... My guts are still sore from laughing.

The main issue here is a really old one.
Theory -vs- Reality.
Some people get all butt-hurt when they find out that something that they 'knew', turned out to be wrong.

A long time ago, some really smart people didn't believe that rockets would work in space. They proved it mathematically.
Oops.

You have to know the difference between de-bunking and de-nial.

If you're really bugged out by the whole idea of DWFTTW, build one of these cart-thingys yourself. The instructions are on the net. How good of a mechanic are you?

Mine worked.


Plus, this humber... fellow, has just got to be in troll heaven.
He probably hasn't had this much attention since he was in diapers.
Ever hear of DNFTT?

Y'all just take a breath for a second and I'll fix it for you.

"It still moves."
Galileo Galilei

Either accept it, (or don't) and go on to what's next.

There now, isn't that all better?

 

[humber]

There were no contradictions provided by the trial evidence. You do not understand the data.

The theoretical support is solid and trivial. You do not understand the physics.

Bluff. I can make a strong case against the instruments, but that is a technical topic. But, the biggest error needs only common sense.

A boat traveling downwind may tack and jibe symmetrically about the path of the direct wind. So, 20 degrees right of that line (+), then 20 degrees left (-) and so forth. A zig-zag path.

A boat following a nominal ddw path, but with the wind moving left and right in the same 20 degree pattern is the GT of the above. The same.

I doubt that many would agree that in the first case, the path was 0 degrees off ddw, just because -20 + 20 = 0.
That is absurd, but that is what NALSA did when they averaged the wind direction. Adding up all the + and - values and dividing. The deviation from ddw,will be much more than published

The correct method is to use RMS.
http://en.wikipedia.org/wiki/Root_mean_square

Symmetrical;
NALSA's method (-20 + 20)/2 = 0

RMS Sgrt ((-20)^2 + (20)^2)/2 = 20.
Equivalent to a constant 20 degrees. That makes sense.

Asymmetrical:
NALSA's method (-10 + 20)/2 = 5

RMS Sgrt ((-10)^2 + (20)^2)/2 = 15.8


That alone is enough to invalidate the record.

 

[humber]

The main issue here is a really old one.
Theory -vs- Reality.
Some people get all butt-hurt when they find out that something that they 'knew', turned out to be wrong.

And you are here to tell us that you are not one of them, but built the a cart, and are defending it.

A long time ago, some really smart people didn't believe that rockets would work in space. They proved it mathematically.
Oops.

The mathematicians are right.

You have to know the difference between de-bunking and de-nial.
If you're really bugged out by the whole idea of DWFTTW, build one of these cart-thingys yourself. The instructions are on the net. How good of a mechanic are you? Mine worked.

Now the empiricists are right.

Anything else?

 

[CORed]

ROTFLMFAO!
Plus, this humber... fellow, has just got to be in troll heaven.
He probably hasn't had this much attention since he was in diapers.
Ever hear of DNFTT?

I know. But humber is a very entertaining troll, or fool (I'm still not sure which). I have never encountered anybody else who can be so wrong, about so many things, in such great detail. It is some of the greatest unintentional (or is it intentional?) comedy I've ever come across.

 

[I Ratant]

Fixed the image in #905 (and earlier)...

 

[spork]

The "record" to me is as pointless as any of the Guinness "records", such as the "world's largest collection of ball-point pens".

Yup. The only point to setting a record was to have a competent and reputable sanctioning body scrutinize the event and take an official stand on it. They did that.

The situation is interesting/amusing, but hardly worth the rancor and acrimony it has aroused.

Worth it to who? It was worth it to us, and no one else was compelled to do anything. People are welcome to comment or not.

The cart can't "violate the laws of physics".
Nothing can.
Misunderstanding the mechanisms of the motion is all that is occurring.

I'm sorry if you're having trouble understanding the mechanism. We can help you with that.

Boeing lost the JSF contract because their vehicle, capable as it may have been, could not perform -all- the tasks the requirements listed, without major configuration changes, while the winner needed nothing extra to fly the envelope.

Unlike the JSF, the downwind cart did accomplish all the requirements and objectives we set.

 

[Llyricist]

Bluff. I can make a strong case against the instruments, but that is a technical topic. But, the biggest error needs only common sense.

A boat traveling downwind may tack and jibe symmetrically about the path of the direct wind. So, 20 degrees right of that line (+), then 20 degrees left (-) and so forth. A zig-zag path.

A boat following a nominal ddw path, but with the wind moving left and right in the same 20 degree pattern is the GT of the above. The same.

I doubt that many would agree that in the first case, the path was 0 degrees off ddw, just because -20 + 20 = 0.
That is absurd, but that is what NALSA did when they averaged the wind direction. Adding up all the + and - values and dividing. The deviation from ddw,will be much more than published

The correct method is to use RMS.
http://en.wikipedia.org/wiki/Root_mean_square

Symmetrical;
NALSA's method (-20 + 20)/2 = 0

RMS Sgrt ((-20)^2 + (20)^2)/2 = 20.
Equivalent to a constant 20 degrees. That makes sense.

Asymmetrical:
NALSA's method (-10 + 20)/2 = 5

RMS Sgrt ((-10)^2 + (20)^2)/2 = 15.8


That alone is enough to invalidate the record.

Even if they should use RMS (and they shouldn't), your "math" is wrong. The RMS value of all the deviation data in the 10 second test period is 8.827. Still within the 10 degrees specified in the rules.

 

[spork]

A free-wheel device which separates the prop from the motor is a better choice.
The prop still windmills, but it's at a zero-slip, zero thrust and low drag condition, relative to having the coupling to the motor.

Wrong. A free-wheeling prop can produce far more drag. That's how a helicopter autorotates. Adding drag to the rotor will not slow your descent.

I hate to nitpick again, but all they really have to do is create new blades, install them with the opposite and higher pitch, and flip the little levers on the ratchets. Unless of course there is some efficiency advantage in changing the relative RPM as well.

If you consider our model carts, the only thing we have to do is put smaller wheels on them.

 

[Llyricist]

If you consider our model carts, the only thing we have to do is put smaller wheels on them.

True, but since you are going for a record, I thought at least changing the twist of the blades would be in order

 

[I Ratant]

Yup. The only point to setting a record was to have a competent and reputable sanctioning body scrutinize the event and take an official stand on it. They did that.



Worth it to who? It was worth it to us, and no one else was compelled to do anything. People are welcome to comment or not.



I'm sorry if you're having trouble understanding the mechanism. We can help you with that.



Unlike the JSF, the downwind cart did accomplish all the requirements and objectives we set.

.
I don't have any problem with understanding the downwind stuff.
I wonder about its utility, being as mentioned, in the same "record class" as the "the world's largest collection of ball-point pens".
The effort spent to achieve the modest result is somewhat disproportionate, to my way of thinking.
That so many people got so hot under the collar is amazing.
It ain't that important!

 

[Jack by the hedge]

The under reel is the worst choice, because it basically opposes itself.

"Worst choice"? That's really very bad engineering, you know.

You can discuss the weaknesses, instabilities or other limitations of the "under reel" configuration as much as you please, but before you write it off you really ought to go back to the beginning and think about the design brief.

The sole purpose of the "under reel" is to provide a trivial demonstration that an object can move faster than the thing which moves it.

It's simple and it works. It meets the criterion. Therefore it is a satisfactory choice.

If you have a better choice then by all means propose it.

 

[Jack by the hedge]

That so many people got so hot under the collar is amazing.
It ain't that important!

Well, no, though it depends on what you mean by important. It's one of those things that inevitably gets argued over until someone actually tries it and settles the matter. I'd liken it to the 19th century argument over whether a galloping horse ever has all four feet off the ground at once.

It's hard to imagine how, but you never know what practical use might be made of the principle in future.

 

[humber]

"Worst choice"? That's really very bad engineering, you know.

It's the one you chose.

You can discuss the weaknesses, instabilities or other limitations of the "under reel" configuration as much as you please, but before you write it off you really ought to go back to the beginning and think about the design brief.

It's a total failure of an idea. Boyish.

The sole purpose of the "under reel" is to provide a trivial demonstration that an object can move faster than the thing which moves it.
It's simple and it works. It meets the criterion. Therefore it is a satisfactory choice.

It's both a theoretical and practical failure. Not at all didactic, but misleading. It does not move faster than the force that is driving it, because that force is applied at the inner reel. Adding string to that does not make it go faster. It's an illusion.
Have you seen those dog leashes that wind into a reel? The dog may run at the same speed, but the distance increases as the leash unwinds. It's that, but the other way.

If you have a better choice then by all means propose it.

Wheels. Like a car. Has a long pedigree.

 

[humber]

Well, no, though it depends on what you mean by important. It's one of those things that inevitably gets argued over until someone actually tries it and settles the matter. I'd liken it to the 19th century argument over whether a galloping horse ever has all four feet off the ground at once.

It's hard to imagine how, but you never know what practical use might be made of the principle in future.

I would say that wasting the time and resources of SJSU and NASA, while promulgating false information is not to be encouraged, especially when the aim is a wind energy project. Otherwise, it would just be annoying.