Merged DDWFTTW in a “Real” Wind

[Jack by the hedge]

...A static (relative to the cart), and very thin, cross section of the propeller at (say) top dead centre (looking down), would (thanks to the angle of the blade) show a moving cross section of the blade moving backwards at such a rate that it does not outrun the wind?

Yep. That's how I like to picture it.

 

[Jack by the hedge]

The cart ... is tall, and exploits wind gradients and gusts.

How, exactly?

 

[Jack by the hedge]

[qimg]http://www.internationalskeptics.com/forums/attachment.php?attachmentid=21679&stc=1&d=1301945880[/qimg]

The first of these drawings is irrelevant, as it attempts to describe how part of the mechanism may behave when it is broken. Therefore it tells us nothing useful at all.

The second drawing comes closer to being useful. Consider the red arrow approaching from the right. That is a stream of "headwind" which might bear on the prop blade and cause drag. But note that the prop is turning and moving downwards in that diagram. The point on the surface of the blade which the windstream might come in contact with is constantly retreating, faster than the approaching wind, so the stream of air never reaches it and eventually misses.

Similarly on the back of the blade the suface is constantly retreating, providing a surface which advances slower than the real wind (moving relative to the ground) so that wind can can bear upon it like a sail.

 

[ThinAirDesigns]

The spool was proposed to obviate accusations that the prop could return KE to the cart. It was pointed out to JB that when the cart braked or slowed, the thread would spill off the reel and tangle. The solution being a second ratchet.

Lies of course and documented in writing on the blog, etc.

Neither Spork nor JB, have been willing to say if is operational or not.

Lies of course -- we've always openly said that all ratchets were operational during the record runs and that there was no prop shaft ratchet during the Ivanpah runs.

JB

 

[I Ratant]

...

No engine, I Ratant, so no thrust.

.
I kinda think those round rotating land keels* do the work of a motor.
After all, they are connected to the propellor, which turns when the wheels turn.
It's a not an internal combustion energy generated, but the interaction through friction with the earth due to the initial motion of the cart due to the sail properties of the unmoving propellor get the motion started.
.
*When I was working for ACF Electronics way back when, they'd just completed and abandoned tests on ground effect machines (Air Cushion Vehicle), determining it was simpler to install a rotating land keel at each corner of the craft, and power one or more of those, than lift the whole thing, and then push it around with air ducting.
These things have trouble with going -up- anything, or maintaining a straight course across a slope, which the land-keeled devices could easily accomplish, for much less power installed.
ACVs do make nifty water crossers though.

 

[humber]

How, exactly?

Oh... lots of ways. Tacking boats do not actually operate by the vectors that are used to describe them. If that were true, then all boats would tack at the same speed for any given angle to the wind. It is not velocity, and its not force that determines the top speed, but power.

Boats have a range of lift/drag ratios, but also a level of power demand. Looking at them is not the way to find that out. Viscous drag can produce lift, but the available power level is low, so only boats that have low power demands can make use of that. There are many approaches to the problem, but power is primary.

Two boats may have the same L/D, but one has lower power levels:

[latex] L/D = \sqrt \pi. A.e/Cd, 0[/latex]

Where A is the aspect ratio, ε is the efficiency factor, and CD,0 is the zero-lift drag coefficient. So, L/D will be the same value when A.e = Cd =10, as when A.e =Cd =1, but with a large power difference. The cart needs only a small power level ( it can be pushed to WS), so can run perhaps run on the viscous drag component. Who knows? No data. Nothing.

NALSA were focused on top speed, but that is not issue. DDW is.
When making comparisons with other boats to set the allowable angle, they are comparing apples and pairs. BB is massive and reluctant to start.

"This takes a bit of time and distance, so most of the runs were push-started by JB on foot as allowed in S3."

How many carts are like that? Heavy carts can be tall, but at the expense of acceleration. Skeeters, and other carts are designed to compete. They need to accelerate to win. Give that up, and they may run deeper into the wind. An oil tanker is not a dingy.

"The deepest I have measured (and deepest measurement I am aware of ) is about 25 degrees off DDW (Dan Clapp, 17 mph wind and 70+ mph boat
speed, Lake Champlain 2003)"

Right but at 70+ mph. What angle will get it to 28mph, if it's not in a hurry? Much less than 25 degrees. Lot's of errors like that, but they are difficult to define.

But, the wind measurements are the most egregious error.

"All primary wind speed and direction measurements were made at propeller hub height..Wind speed measurements from the craft itself were not used"

Oh. The prop blades, that are said to drive the cart, can dip into the faster upper wind, unmeasured in speed and direction. There is alwaysa gradient, and the heat makes that more so. Who knows what that is?
The wind rapidly changes direction. Turning wind is accelerating wind, and that is more force than a stable wind. The instruments and sampling rate are too slow to accurately record them.
The wind vane is on an accelerating vehicle, but is designed for fixed use. The results are averaged, and not RMS. That is no good at all. Why bother with the vectors?

There are so many favorable factors, that I ask why is it so slow?

 

[I Ratant]

How, exactly?

.
The air motion closest to the surface is slowed by the surface effect.
It's not usually accounted for, and diminishes but doesn't quite go to zero at the ground.
I've watched ants with their short legs get blown off their feet in the usual Antelope Valley winds...
Model planes are more likely to get affected than the larger full-scales..
As per these diagrams from Andy Lennon's book on model airplane design...
But even those can "arrive" in an "interesting" manner... From Mohave, 1973...

 

[humber]

Lies of course and documented in writing on the blog, etc.

I could find the posts that will contradict that, and the spool was proposed and discussed before the blog was in place. No matter.

Lies of course -- we've always openly said that all ratchets were operational during the record runs and that there was no prop shaft ratchet during the Ivanpah runs.
JB

But you changed then? From not being operational at Ivanpah; fully expected because of the frequent mechanical failures, to operational for the record.

Do tell how the prop can transfer wind energy to the cart.

The wind could only drive the shaft CCW, because prop-wise the ratchet disengages. The only possibilities are the ground driving the wheel (cranky) or the prop and chassis are a sail.

 

[humber]

.
I kinda think those round rotating land keels* do the work of a motor.
After all, they are connected to the propellor, which turns when the wheels turn.
It's a not an internal combustion energy generated, but the interaction through friction with the earth due to the initial motion of the cart due to the sail properties of the unmoving propellor get the motion started.

Gasoline not needed once the friction to the ground kicks in.
Maybe square wheels would be better. More friction. I will ask JB.

.
*When I was working for ACF Electronics way back when, they'd just completed and abandoned tests on ground effect machines (Air Cushion Vehicle), determining it was simpler to install a rotating land keel at each corner of the craft, and power one or more of those, than lift the whole thing, and then push it around with air ducting.
These things have trouble with going -up- anything, or maintaining a straight course across a slope, which the land-keeled devices could easily accomplish, for much less power installed.
ACVs do make nifty water crossers though.

Wheel are good. but have you seen this?
http://www.youtube.com/watch?v=W1czBcnX1Ww
A similar machine in the lab.
http://www.youtube.com/watch?v=e_JBjDzNLFI&feature=related

 

[Jack by the hedge]

Oh... lots of ways.
...
NALSA were focused on top speed, but that is not issue. DDW is.
When making comparisons with other boats to set the allowable angle, they are comparing apples and pairs. BB is massive and reluctant to start.
...

"The deepest I have measured (and deepest measurement I am aware of ) is about 25 degrees off DDW (Dan Clapp, 17 mph wind and 70+ mph boat
speed, Lake Champlain 2003)"

Right but at 70+ mph. What angle will get it to 28mph, if it's not in a hurry? Much less than 25 degrees. Lot's of errors like that, but they are difficult to define.

Google tells me that quote is referring to an ice yacht. And it's the middle of this paragraph: "As outlined below Blackbird meets the requirements of NALSA record category C4. The craft clearly demonstrated the ability to accelerate while sailing dead down wind. Iceboats are also well known for being able to sail deep downwind in high winds. The deepest I have measured (and deepest measurement I am aware of ) is about 25 degrees off DDW (Dan Clapp, 17 mph wind and 70+ mph boat speed, Lake Champlain 2003). In theory a similar iceboat could sustain a speed of 85-90 mph at 15 degrees off DDW in a 30 mph wind (this is well in excess of the wind speed Skeeter Iceboats normally sail in). Blackbird's average angle to DDW through the measurement period in the proposed record run was 5°."

I'm aware that you dispute their method of calculating that 5° figure. Presumably, though, you'd have the same objection to their method of calculating 25° for the ice boat.

But, the wind measurements are the most egregious error.

"All primary wind speed and direction measurements were made at propeller hub height..Wind speed measurements from the craft itself were not used"

Oh. The prop blades, that are said to drive the cart, can dip into the faster upper wind, unmeasured in speed and direction. There is alwaysa gradient, and the heat makes that more so. Who knows what that is?

Not me. I don't know how great the wind gradient is. Let's consider how big it would have to be to magic up a 2.8x windspeed run from a conventional sail: Do you think a metre or so above the hub,windspeed is likely to be 2.8x as high as at the hub?

No. Nor do I.

The wind rapidly changes direction. Turning wind is accelerating wind, and that is more force than a stable wind. The instruments and sampling rate are too slow to accurately record them.

Accelerating wind? Is it accelerating in a useful direction? Are there cleverly-shaped airfoil parts on BB which can exploit these sudden gusts? Can you point them out and briefly explain their operation? Thanks.

 

[Llyricist]

Oh... lots of ways. Tacking boats do not actually operate by the vectors that are used to describe them. If that were true, then all boats would tack at the same speed for any given angle to the wind. It is not velocity, and its not force that determines the top speed, but power.

Boats have a range of lift/drag ratios, but also a level of power demand. Looking at them is not the way to find that out. Viscous drag can produce lift, but the available power level is low, so only boats that have low power demands can make use of that. There are many approaches to the problem, but power is primary.

Two boats may have the same L/D, but one has lower power levels:

[latex] L/D = \sqrt \pi. A.e/Cd, 0[/latex]

Where A is the aspect ratio, ε is the efficiency factor, and CD,0 is the zero-lift drag coefficient. So, L/D will be the same value when A.e = Cd =10, as when A.e =Cd =1, but with a large power difference. The cart needs only a small power level ( it can be pushed to WS), so can run perhaps run on the viscous drag component. Who knows? No data. Nothing.

NALSA were focused on top speed, but that is not issue. DDW is.
When making comparisons with other boats to set the allowable angle, they are comparing apples and pairs. BB is massive and reluctant to start.

"This takes a bit of time and distance, so most of the runs were push-started by JB on foot as allowed in S3."

How many carts are like that? Heavy carts can be tall, but at the expense of acceleration. Skeeters, and other carts are designed to compete. They need to accelerate to win. Give that up, and they may run deeper into the wind. An oil tanker is not a dingy.

"The deepest I have measured (and deepest measurement I am aware of ) is about 25 degrees off DDW (Dan Clapp, 17 mph wind and 70+ mph boat
speed, Lake Champlain 2003)"

Right but at 70+ mph. What angle will get it to 28mph, if it's not in a hurry? Much less than 25 degrees. Lot's of errors like that, but they are difficult to define.

But, the wind measurements are the most egregious error.

"All primary wind speed and direction measurements were made at propeller hub height..Wind speed measurements from the craft itself were not used"

Oh. The prop blades, that are said to drive the cart, can dip into the faster upper wind, unmeasured in speed and direction. There is alwaysa gradient, and the heat makes that more so. Who knows what that is?
The wind rapidly changes direction. Turning wind is accelerating wind, and that is more force than a stable wind. The instruments and sampling rate are too slow to accurately record them.
The wind vane is on an accelerating vehicle, but is designed for fixed use. The results are averaged, and not RMS. That is no good at all. Why bother with the vectors?

There are so many favorable factors, that I ask why is it so slow?

In other words, no, you can't.

FYI, the RMS wind deviation for the entire run from when JB stopped pushing to the end of the test period was 11.58 degrees. And considering that the deviation was negative 91.4% of the time, your whole excuse for using RMS is weak at best. As for the test period, the RMS was 8.83 degrees, still within +/- 10 degrees prescribed in the rules. In fact, the arithmetic mean for the entire run was -9.68 degrees. within the rules again.

Keep making claims in ignorance, please.

 

[humber]

Google tells me that quote is referring to an ice yacht. And it's the middle of this paragraph: "As outlined below Blackbird meets the requirements of NALSA record category C4. The craft clearly demonstrated the ability to accelerate while sailing dead down wind. Iceboats are also well known for being able to sail deep downwind in high winds. The deepest I have measured (and deepest measurement I am aware of ) is about 25 degrees off DDW (Dan Clapp, 17 mph wind and 70+ mph boat speed, Lake Champlain 2003). In theory a similar iceboat could sustain a speed of 85-90 mph at 15 degrees off DDW in a 30 mph wind (this is well in excess of the wind speed Skeeter Iceboats normally sail in). Blackbird's average angle to DDW through the measurement period in the proposed record run was 5°."

I'm aware that you dispute their method of calculating that 5° figure. Presumably, though, you'd have the same objection to their method of calculating 25° for the ice boat.

That speed in the top recorded speed, like Greenbird. If set up, it could travel closer that 25 degrees if the top speed were 30mph.

Not me. I don't know how great the wind gradient is. Let's consider how big it would have to be to magic up a 2.8x windspeed run from a conventional sail: Do you think a metre or so above the hub,windspeed is likely to be 2.8x as high as at the hub?

It could be a lot more. This profile is possible

[latex] \ v_w(h) = v_{10} \cdot \left( \frac {h} {h_{10}} \right)^ a [/latex]

where:

[latex] \ v_w(h) = velocity of the wind at height, h [m/s][/latex]
[latex] \ v_{10} = velocity of the wind at height, h10 = 10 meters [m/s][/latex]
[latex] \ a = Hellman exponent [/latex] = maybe 0.15.

Heat. The open sun adds >400W sg meter.

>ddw is impossible in a steady flow like a wind tunnel. But, wind gusts and tacking make it possible. That is, the first can't be made at all, but the second may be engineered to maximize what is available. That's a big difference, and it was the first case which was, and is, disputed.

No. Nor do I.
Accelerating wind? Is it accelerating in a useful direction?

Yes. F=ma.

Are there cleverly-shaped airfoil parts on BB which can exploit these sudden gusts? Can you point them out and briefly explain their operation? Thanks.

Are you saying faster is not better? I Ratant's sail carts are not that bothered about the angle, so why would that be a problem?

There is also the wind you expect to be there, and the tacking of the cart and towers. After correction to RMS, I would reckon on at least 20 degrees over the run.

 

[Llyricist]

That speed in the top recorded speed, like Greenbird. If set up, it could travel closer that 25 degrees if the top speed were 30mph.


It could be a lot more. This profile is possible

[latex] \ v_w(h) = v_{10} \cdot \left( \frac {h} {h_{10}} \right)^ a [/latex]

where:

[latex] \ v_w(h) = velocity of the wind at height, h [m/s][/latex]
[latex] \ v_{10} = velocity of the wind at height, h10 = 10 meters [m/s][/latex]
[latex] \ a = Hellman exponent [/latex] = maybe 0.15.

Heat. The open sun adds >400W sg meter.

>ddw is impossible in a steady flow like a wind tunnel. But, wind gusts and tacking make it possible. That is, the first can't be made at all, but the second may be engineered to maximize what is available. That's a big difference, and it was the first case which was, and is, disputed.


Yes. F=ma.



Are you saying faster is not better? I Ratant's sail carts are not that bothered about the angle, so why would that be a problem?

There is also the wind you expect to be there, and the tacking of the cart and towers. After correction to RMS, I would reckon on at least 20 degrees over the run.

You reckon wrong.

And you totally missed the point of what Bob Dill wrote. Which was that iceboats would need ridiculously high winds to tack closer to the wind (with downwind vmgs faster than wind speed) than 25 degrees. It has nothing to do with the actual speed of the craft.

 

[I Ratant]

Gasoline not needed once the friction to the ground kicks in.
Maybe square wheels would be better. More friction. I will ask JB.




Wheel are good. but have you seen this? http://www.youtube.com/watch?v=W1czBcnX1Ww.

.
Available at Radio Shack. $9.95 and $14.95.
http://www.radioshack.com/product/index.jsp?productId=3811585
.
But not supported on an aircushion, which limits the slope an ACV could handle.. even with a run at the slope.

 

[jduffy77]

More of what,you say?

The spool was proposed to obviate accusations that the prop could return KE to the cart. It was pointed out to JB that when the cart braked or slowed, the thread would spill off the reel and tangle. The solution being a second ratchet.

Lie/wrong.

It's a fossil from the days when the ground drove the wheels. The new broom of the "distance" argument meant that the ratchet was not a good idea, but was neglected. Neither Spork nor JB, have been willing to say if is operational or not.
But, your objection fails, because a braking cart will slow the drive shaft, and the momentum of the prop will see it spin on the ratchet. All cases where the prop spins faster than the shaft, will disengage the ratchet.

If I can parse the Humberese here you have it exactly backwards, which means I probably parsed it ok.

 

[ThinAirDesigns]

I could find the posts that will contradict that, ... No matter.

Exactly ... "no matter". Because it's a lie and no you can't and no you won't.

JB

 

[I Ratant]

Gasoline not needed once the friction to the ground kicks in.
Maybe square wheels would be better. More friction. I will ask JB.
...

.
Be serious.
There's other ways to move than wheels..

http://www.boreme.com/posting.php?id=28504&page=1
.
But the cart has wheels.
Which when nudged by the sail, seem to work.

 

[humber]

.
Available at Radio Shack. $9.95 and $14.95.
http://www.radioshack.com/product/index.jsp?productId=3811585
.
But not supported on an aircushion, which limits the slope an ACV could handle.. even with a run at the slope.

But ants are diligent, whereas the cart is like a very lazy grasshopper.

 

[humber]

Exactly ... "no matter". Because it's a lie and no you can't and no you won't.
JB

If I could be bothered, I would find the posts where you said otherwise. The spool was in mind around the time I mentioned the wind gradient, and how "building it to the max" may be the way to go.

I also recall motioning the binding, and enormous forces which may develop between the two spools. At that time, the cart moved 8' with each turn of the prop, and for some forgotten reason, Spork calculated the KE of the prop relative to the KE of the cart. Other than that....I do remember the reason for the spool, and Harold mentioning the over-run.

 

[humber]

.
Be serious.
There's other ways to move than wheels..

http://www.boreme.com/posting.php?id=28504&page=1

Looks faked to me. Where is the fencing wire?

But the cart has wheels.
Which when nudged by the sail, seem to work.

Of course. It's a sail. The wheels only seem to work as claimed.