Merged DDWFTTW in a “Real” Wind

[Modified]

Tacking allows lift too. DDW doesn't.

Of course it does. The blades of the prop are not moving directly downwind, they are on a continuous tack. Lift due to curved surfaces can be helpful for sailboats and dwfttw carts, but is not strictly necessary. I suspect that the Blackbird could still beat the wind even with flat prop blades.

Many of your arguments in the last few pages are equivalent to saying that a sailboat can not sail upwind.

 

[sol invictus]

Of course it does. The blades of the prop are not moving directly downwind, they are on a continuous tack. Lift due to curved surfaces can be helpful for sailboats and dwfttw carts, but is not strictly necessary. I suspect that the Blackbird could still beat the wind even with flat prop blades.

Many of your arguments in the last few pages are equivalent to saying that a sailboat can not sail upwind.

humber doesn't accept that wine bottles can roll on flat surfaces. I don't think there's much point in discussing propellers with him.

 

[humber]

Of course it does. The blades of the prop are not moving directly downwind, they are on a continuous tack.

That is nonsense. Antediluvian figurative thinking. Like the literal air screw. Primitive. These days, it is CFD. Bernoulli is now a bit naff.

You show me ONE reference from a text book that even mentions the idea of a tacking prop.


A tacking boat follows a different path to ddw. and that is the reason for the lift force. The hub, root, and all other parts of the prop, move in the same direction as the cart. There is no displacement of the prop away from ddw.

Moreover, there is no means by which the prop can drive the wheels to effect, and the electrical model says so.

What you have seen is a very tall cart make use short term gusts and the gradient, while not traveling ddw, and exceed the 10 second mean of the wind. So what.

Lift due to curved surfaces can be helpful for sailboats and dwfttw carts, but is not strictly necessary. I suspect that the Blackbird could still beat the wind even with flat prop blades.
Many of your arguments in the last few pages are equivalent to saying that a sailboat can not sail upwind.

An upwind vehicle never runs out of wind. That is not the case downwind.

You are all making quite different, and contradictory arguments to explain the same phenomenon, and that is die to individual special pleading according to taste.

 

[humber]

humber doesn't accept that wine bottles can roll on flat surfaces. I don't think there's much point in discussing propellers with him.

Lab: The kitchen.
Intruments; haptic and visual
Journal: American Society of Passed-Over Professors.

And you failed the simplest of math, and forgot about the concentric wheels.
That has some interesting effects. Only counter-intuitive if you are ignorant.

Did you do the math? That will tell you why you have rediscovered a canard, thousands of years old.

 

[A.T.]

Actually Ruina's paper was fine. He considers the general problem of extracting energy for propulsion from the velocity difference between two media, and concludes correctly that the achievable velocity is unbounded in both directions, and limited only by efficiency.

If you google for "The Push-Me Pull-You Boat is Better Still" you will find both papers and both reviews in one PDF.

Guanna has taken up that same argument

Yes, Gaunaa et al. have come to the same conclusion as Ruina:

Gaunaa, Mac; Øye, Stig; Mikkelsen, Robert (2009). "Theory and Design of Flow Driven Vehicles Using Rotors for Energy Conversion". Marseille, France: Proceedings EWEC 2009

It is theoretically and practically possible
to build a wind driven car that can go
directly upwind (using a generator/wind
turbine in the air).

It is theoretically possible to build a wind
driven car that can go in the downwind
direction faster than the free stream wind
speed (using a propeller in the air)

There does not exist a definitive upper
limit for vehicles of this kind. As long as
efficiencies are improved, the velocities
will increase unasymptotically

Despite that incredible insight, the real carts don't exceed 65% WS.

Their upwind carts have a size limit on the turbine of 3m².

One has to ask what Spork knows, that Stuttgart University and Delft TU don't know.

Nothing. They all know that with a 20m² turbine you can easily go faster than wind, directly upwind. But they would not be allowed to start in the Aeolus race with it.

 

[Jack by the hedge]

The wind does what? That same headwind which strikes the chassis is drag. Spork has that as an opposing force. It is taken away from the net. That is calculated that way. You want me to believe that if it strikes the prop, it drives the cart.

Do you understand how a propeller drives an aeroplane forwards? You appreciate that despite the craft's high speed through the air, the air presses on the back of the blades, not the front, right?

If there is power input to the drive shaft.

You're heading up a blind alley again. The prop does not push the cart by sending power into the driveshaft. Power in the driveshaft is heading in the opposite direction. The prop pushes the cart directly, through its bearings mounting it to the mast.

Ground power. Medieval. Waiting for Spork to rediscover. Everyone else has missed it. Einstein missed it.

The depth and persistence of your misunderstanding has more than a semblance of wilful ignorance, but I intend to assume it is not.

So the solution is to move the prop so that there is a difference, is that it?

The solution is to turn the prop so that each point of contact with the advancing wind does not move forward faster than the wind.

Drag drives the prop, which drives the cart, which makes the drag which drives the prop...but the ground drives the wheel. Errr...

Still failing to read. The wheels turn the prop, the wind pushes the prop, which pushes the cart, which turns the wheels, which turns the prop some more so that it remains in contact with the pushing wind.

 

[sol invictus]

My intuition would be that going upwind at the speed of the wind is somewhere in between as difficult as going downwind at windspeed and going downwind at twice windspeed. Is that right?

If so, since spork&co went downwind at nearly three times windspeed they should have little difficulty going upwind faster than the wind.

 

[D'rok]

And get this into your head. There is NO TAILWIND above WS. Hence FASTER THAN THE WIND.

Get this into your head. You. Are. Wrong.

Here. Jack explains it better than I can:

Do you understand how a propeller drives an aeroplane forwards? You appreciate that despite the craft's high speed through the air, the air presses on the back of the blades, not the front, right?

You're heading up a blind alley again. The prop does not push the cart by sending power into the driveshaft. Power in the driveshaft is heading in the opposite direction. The prop pushes the cart directly, through its bearings mounting it to the mast.


The solution is to turn the prop so that each point of contact with the advancing wind does not move forward faster than the wind.

Still failing to read. The wheels turn the prop, the wind pushes the prop, which pushes the cart, which turns the wheels, which turns the prop some more so that it remains in contact with the pushing wind.

 

[GlennB]

What you have seen is a very tall cart make use short term gusts and the gradient, while not traveling ddw, and exceed the 10 second mean of the wind. So what.

So what? It means that if the cart were simply acting as a cunning sail then there would need to be a large number of gusts in excess of 2.8x the measured average windspeed. Let's say many* gusts of 30mph for the cart to reach 28pmh groundspeed while measuring an official wind average of 10mph for the run.

Did that happen? Clue: you wouldn't need anemometers to notice such wild variations.

*when I say many I really mean almost entirely, as the cart would also slow during lulls.

 

[Jack by the hedge]

Nice try. You can't drive the wheel while pedaling backwards. The ratchet disengages. Throw away the chain and gears.
As I said, if the prop can drive the cart without driving the wheel, you never needed the chain in the first place.
That leaves you with the ground driving the wheel and then the prop. The ratchet makes it a one way street.

No. You are not pedalling backwards.

Without the chain, the wind would push on the propeller and the cart would probably move a little, but the prop would just spin up in the backwards direction until the wind was not pressing it forward significantly. (I suspect you would not dispute that scenario.)

If you nailed the prop in place to stop it spinning, it would just act like a sail: The cart would be blown forwards up to some fraction of windspeed. (I guess you'd buy that scenario too.)

To make it work as intended, you need the chain, because you need a fixed relationship between the surface of the propeller blade and the ground in order to keep extracting energy from the wind moving relative to the ground when the cart exceeds the windspeed.

The pressure of each stream of air (like your finger pressing on the prop blade) pushes the cart forwards and forces the prop to turn, thereby presenting a fresh portion of the blade to the air (or your finger) which is further back toward the trailing edge of the prop.

 

[humber]

Yes, Gaunaa et al. have come to the same conclusion as Ruina:
Gaunaa, Mac; Øye, Stig; Mikkelsen, Robert (2009). "Theory and Design of Flow Driven Vehicles Using Rotors for Energy Conversion". Marseille, France: Proceedings EWEC 2009

Yep, a sponsored paper. Algebra, where the power calculations do not contain the losses implied by the various "efficiencies" used to derive the force and velocity. None of the carts have even come close to the expectations. "Papers" where all losses are put on a wish list tend to be a bit cranky. All over-unity cranks do it, because there is simply is no other avenue.

Their upwind carts have a size limit on the turbine of 3m².

Yes, otherwise, big props could be used to exploit the gradient. The competitors do not get to choose the wind conditions, or how it is measured.
Otherwise, all may all be open to bias and error.
The upwind record will have as much validity as a used parking ticket.

Nothing. They all know that with a 20m² turbine you can easily go faster than wind, directly upwind. But they would not be allowed to start in the Aeolus race with it.

They know they can catch a fishy like you with that.

 

[Jack by the hedge]

What about my gradient cart?

What indeed?

I saw your drawing of a cart with a propeller, and a chart showing a wind gradient. There might have been some explanatory text which was too small to read at that resolution.

 

[humber]

So what? It means that if the cart were simply acting as a cunning sail then there would need to be a large number of gusts in excess of 2.8x the measured average windspeed. Let's say many* gusts of 30mph for the cart to reach 28pmh groundspeed while measuring an official wind average of 10mph for the run.

Lets say at least 30 degrees off ddw too. RMS during the test run 11 degrees not 4. You will not find a text on meteorology that suggests taking the simple arithmetic mean.
Nothing cunning needed.

Take an extreme example, where the wind blows in a binary fashion
10mph for 1 second, 0mph for 1 second etc. Average 5mph. Peak 10mph
Ride the peaks: 2WS. Easy. The trick is to keep on acclerating.
The peak speed of the cart is 28mph, but the average without the push is 8.5mph. Less than WS. Carteers do not see the significance of that.

Did that happen? Clue: you wouldn't need anemometers to notice such wild variations.

The anemometer is at hub height, and in motion against accelerating air, laughable.

Notice in the Jenkin's video that
1) From rest, the streamer is pointing to the rear, while the vane says tailwind.
2) It sees a real headwind.
3) The vane moves 90 degrees in seconds. All over the shop.

Not ddw, not steady. They were on some kind of group high, not to care about that.

*when I say many I really mean almost entirely, as the cart would also slow during lulls.

That depends only on the rolling losses. The net force to drive the cart is only 35N, so it's low.

 

[Jack by the hedge]

But you have not solved anything. The reason that a sail could never exceed WS, is that it would have to move away from the tailwind. Retreat from the tailwind.
Now you have the prop face moving away from the tailwind.

In this example, the cart needs to exceed WS, the sail does not. If the sail is travelling slower than the cart, it could still be pushed by the wind even if the cart itself exceeds windspeed (until the mast rapidly and inevitably runs out of travel).

If the mast is mechanically coupled to the cart wheels then you have a fixed relationship between the position of the cart on the ground and the position of the sail on the cart (and thereby for any position of the sail relative to the ground there is a corresponding postion of the cart).

Since the wind is moving relative to the ground, it can press on the sail and push the sail forwards (at less than windspeed) and push the cart forward faster than the sail.

 

[humber]

What indeed?

I saw your drawing of a cart with a propeller, and a chart showing a wind gradient. There might have been some explanatory text which was too small to read at that resolution.

You tell me. I can spin you a yarn about how it works. Maybe you won't bite, but if it were on the internet, I could convince perhaps one in ten?
Not now I suppose, but when Spork started, no problem. That's what he does.

If you go for this upwind cart, you're a mug with intent.

 

[Jack by the hedge]

You are all making quite different, and contradictory arguments to explain the same phenomenon

I freely admit I have made no attempt to include any lift effects from the curved prop blades, but as Modified pointed out there is no contradiction.

Did you look at the video D'rok posted? Perhaps it would help if you said exactly where you thought it was mistaken.

 

[Jack by the hedge]

A tacking boat follows a different path to ddw. and that is the reason for the lift force. The hub, root, and all other parts of the prop, move in the same direction as the cart. There is no displacement of the prop away from ddw.

You watched the video where the tacking yacht morphs by stages into a propeller, didn't you? Which stage was wrong?

 

[A.T.]

My intuition would be that going upwind at the speed of the wind is somewhere in between as difficult as going downwind at windspeed and going downwind at twice windspeed. Is that right?

The aerodynamic drag at 1x upwind is like at 3x downwind. But transmission efficiency should be better due to lower speeds. I think they can go faster than 1 x upwind by a clear margin.

 

[humber]

I freely admit I have made no attempt to include any lift effects from the curved prop blades, but as Modified pointed out there is no contradiction.

Did you look at the video D'rok posted? Perhaps it would help if you said exactly where you thought it was mistaken.

It's nonsense. Silly.

 

[humber]

The aerodynamic drag at 1x upwind is like at 3x downwind. But transmission efficiency should be better due to lower speeds. I think they can go faster than 1 x upwind by a clear margin.

"intuition". Fooled by a wine glass.LOL.

If it were only a matter of you mugs, I wouldn't bother.
You could talk and stroke each other as much as you liked.