Sailing downwind faster than the wind

[eyytee]

I didn't spend 10 pages arguing over Dr. Drela's conclusion,

You were not only arguing over but directly against the conclusion of the "MIT-guy".

I was arguing against you and the other 2 stooges convoluted, mubbling, stumbling attempts at explaining physics.

You had problems accepting even obvious facts, like that the propeller blades move in a different direction than the vehicle. It is hard to explain physics to someone with that level of understanding.

 

[spork]

Here's kind of a fun exercise... look at the first few pages of this thread. Notice how consistently origin gets every single aspect completely wrong, but still maintains a completely condescending attitude when talking to the people that not only DO understand this, but have built and tested it, and are now trying to patiently explain it to him.

Within a few pages, you can see that our patience with origin begins to wear thin. I can tell you the precise moment I gave up on him... After failing to understand the scenario I posted (or willfully changing it), he insisted (and still does insist) on arguing about who is interpreting my scenario correctly - despite the fact that I told him we should drop it and concentrate on his scenario. The fact that he simply refused to give me any numbers for his scenario, but instead insists on arguing about something completely unproductive, tells me he'd already figured out he bet on the wrong horse. So this is when he goes from obstinate, condescending, wrongness into full troll mode - rather than simply saying "how about that - I learned something today".

Despite his realization that he got it completely wrong, I have to give him credit for consistency - he's still completely wrong. His claim that we don't understand exactly how this thing works should be transparent to anyone. His claim that this bears no resemblence to the aerodynamics of a sailboat on a broad reach indicates he still doesn't get it, and would prefer to remain ignorant rather than admit ignorance.

And his insistence on refering to the device as a "contraption" rather than a car, cart, vehicle... just shows from the very start what kind of person we're dealing with.

 

[MeteorWayne]

MODERATOR WARNING***

OK folks, enough with the personal sniping from everyone. Discuss the science only

METEOR WAYNE

 

[Couerl]

And his insistence on refering to the device as a "contraption" rather than a car, cart, vehicle... just shows from the very start what kind of person we're dealing with.

What, you mean a skeptic? I rather like skeptics and in contrast detest the hubris of sanctimonious blowhards. :ugeek:

Anyway, your contraption doesn't impress me in the least. :lol:

 

[MeteorWayne]

MODERATOR FINAL WARNING***

OK folks, enough with the personal sniping from everyone. Discuss the science only

METEOR WAYNE

 

[ThinAirDesigns]

Discuss the science only

Would love to:

So, origin -- would you mind explaining the science behind your claim that a towed frictionless vehicle with a generator drawing 1HP from it's rotating axle requires not 1HP to motivate it, but 2HP?

Why is the "other" 1HP required, and where is it being used?

JB

 

[RCP]

I checked, and origins has been posting elsewhere. Apparently he has no further questions, nor intention to participate in this discussion. As it also appears there are no others who question exceeding wind speed going dead downwind, looks like the OP has been fully addressed. Going once, going twice,... :roll:

 

[ThinAirDesigns]

LOL -- well RCP, to be fair to origin, it has in the past sometimes taken him several days to respond to questions that have been asked of him and you only waited a few hours before coming to that conclusion.

I'll give him a bit of time to formulate an answer to the 'where does origin hide the extra 1hp question'.

JB

 

[undidly]

At first I thought this was a joke thread but now I am not sure.
The problem seemed to be that AT wind speed there was no force to spin the propeller.
This is true.
But the wind is still at the same speed relative to the ground.
We don't need to tap the energy from the DIFFERENCE between the wind speed and the vehicle speed.
We need to tap the energy from the DIFFERENCE between the wind speed and the ground speed.
When vehicle speed is the same as the wind speed we can tap the DIFFERENCE between the vehicle speed and
the ground speed by taking energy from the wheel.
This will slow the vehicle.
Put the energy into the windmill.
This will speed up the vehicle by the same amount (if no losses).
However the propeller is now driving against the wind.
Relative to the vehicle (see the video) the wind from the propeller is going backwards.
The wind/ground speed remains in the same direction but drops (locally)because it is opposed by the propeller.
If the wind/ground air speed drops then that means it has less energy.
Where has the energy gone?.
Into the inertia of the vehicle.
If this was a loss less system any energy however small would cause acceleration.
Only losses limit the top speed.

 

[spork]

At first I thought this was a joke thread but now I am not sure.

It's not a joke. This vehicle is real, and it goes DDWFTTW. We've posted plans so you can make your own working model for just a few bucks.... or you're welcome to come witness our next run.

The problem seemed to be that AT wind speed there was no force to spin the propeller.

The wind does not turn the propeller - the wheels do. This is true above, below, and at wind speed - even from a dead start.

We don't need to tap the energy from the DIFFERENCE between the wind speed and the vehicle speed.
We need to tap the energy from the DIFFERENCE between the wind speed and the ground speed.

Exactly right.

When vehicle speed is the same as the wind speed we can tap the DIFFERENCE between the vehicle speed and
the ground speed by taking energy from the wheel.

That's what we do.

This will slow the vehicle.

But it doesn't slow the vehicle because that energy can be used more effectively to create thrust than what it cost us to harvest from the ground. This is only true because we have a true tail-wind - even though we have a relative headwind.

Put the energy into the windmill.
This will speed up the vehicle by the same amount (if no losses).

Nope - it will actually speed it up by more than it would nominally slow it by.

Where has the energy gone?.
Into the inertia of the vehicle.

Once the vehicle reaches a steady state speed above wind speed all the excess energy is going into losses in the system. In other words - heat.

 

[undidly]

To spork.
Since my post it has become obvious to me that a vehicle with a sail ,traveling across the wind and traveling faster than the wind is making use of the DIFFERENCE between the wind speed and the ground (or water )speed.
The vehicle speed in the wind direction is zero .

No one argues with this because it is common to go faster across than with the wind.

Faster down wind than across should not be a big deal,it is just unusual.
Needs a windmill,not a sail.
How important is the gear ratio between the wheel and the propeller?.

 

[origin]

I checked, and origins has been posting elsewhere. Apparently he has no further questions, nor intention to participate in this discussion. As it also appears there are no others who question exceeding wind speed going dead downwind, looks like the OP has been fully addressed. Going once, going twice,... :roll:

Yes I am not participating in the thread it was made clear that my participation was not wanted or welcomed. My posts were characterized as trolling. I put the three caballeros on my ignore list so I wasn't tempted to intrude on their thread. Just passing through....

 

[spork]

Yes I am not participating in the thread it was made clear that my participation was not wanted or welcomed.

On the contrary. You refused to have a responsive discussion about the topic. You simply wanted to argue about whether it was you or I that misinterpreted my scenario. I asked you repeatedly to give me some numbers so we could do the calculations on your scenario. You never even bothered to acknowledge that.

It seems that starting off both wrong and condescending left you nowhere to go.

 

[MeteorWayne]

MODERATOR COMMENT:

Please see my prevous warning.

MW

 

[spork]

MODERATOR COMMENT:

Please see my prevous warning.

MW

If origin insists on mischaracterizing non-technical issues of the thread I will insist on setting the record straight. I'm happy to have you delete the posts on both sides.

 

[alphachapmtl]

This problem is solved in this paperback book:

100 great problems of elementary mathematics: their history and solution
By Heinrich Dörrie, Dover Publications (92. Tacking Under a Headwind p.363)

 

[eyytee]

This problem is solved in this paperback book:

100 great problems of elementary mathematics: their history and solution
By Heinrich Dörrie, Dover Publications (92. Tacking Under a Headwind p.363)

http://books.google.de/books?id=i4SJwNr ... &q&f=false

 

[spork]

This problem is solved in this paperback book:

100 great problems of elementary mathematics: their history and solution
By Heinrich Dörrie, Dover Publications (92. Tacking Under a Headwind p.363)

On the one hand I don't see that the problem of going directly downwind faster than the wind is addressed in the book. On the other hand, the link given doesn't seem to include Page 363.

 

[spork]

Faster down wind than across should not be a big deal,it is just unusual.
Needs a windmill,not a sail.

The rotor must act as a propeller, not a windmill (or turbine). The wheels are turning the prop - not the other way around.

How important is the gear ratio between the wheel and the propeller?.

Very important. For this to act as a DDWFTTW vehicle, the "vehicle speed ratio" (VSR) must be less than 1.0. This is the distance the prop would nominally advance in a single rotation divided by the distance the wheels would advance over the ground in that same single rotation of the prop.

 

[spork]

We finally have the downwind cart more or less completed. New aerodynamic fairings, strengthened transmission, variable pitch prop, logging of GPS and wind speed and direction, and even it's own trailer (finally).

We took it out for some testing yesterday, and had reasonably good luck with the wind conditions. We got about 2.85X wind speed in 12 to 15 mph winds.

Hopefully we'll be making a run for the record in the next few weeks.

We were also invited to give a talk on the topic at the St. Francis Yacht Club next month.

One thing we'd love to find is a small external monitor to put in front of the driver. If anyone has something old to loan or sell cheap, I'd love to hear from you.

 

[undidly]

We finally have the downwind cart more or less completed. New aerodynamic fairings, strengthened transmission, variable pitch prop, logging of GPS and wind speed and direction, and even it's own trailer (finally).

We took it out for some testing yesterday, and had reasonably good luck with the wind conditions. We got about 2.85X wind speed in 12 to 15 mph winds.

Hopefully we'll be making a run for the record in the next few weeks.

We were also invited to give a talk on the topic at the St. Francis Yacht Club next month.

One thing we'd love to find is a small external monitor to put in front of the driver. If anyone has something old to loan or sell cheap, I'd love to hear from you.

I expect that you already know that your vehicle can travel directly into the wind.
Gear down the turbine as much as is needed to drive the wheels AGAINST the wind force on the turbine.
Measure a few speeds.
That will impress the Yacht Club.

 

[RCP]

I expect that you already know that your vehicle can travel directly into the wind.
Gear down the turbine as much as is needed to drive the wheels AGAINST the wind force on the turbine.
Measure a few speeds.
That will impress the Yacht Club.

Do be careful telling spork what he knows, undidly. The metaverse is littered with locked or moderated threads because of people doing this. Better to just ask him.

I think if he did as you suggest-just gearing down Blackbird to function as a turbine-it would work, but not very well. Certainly not as well as the carts set up with turbines in the Aeolus Races, and they have yet to break 70% of wind speed.

 

[undidly]

RCP

Thanks for telling me about Aeolus Races.

I googled this,
""In this first time ever race the participating teams were challenged to drive directly into the wind, without tacking. During the preliminary races, the Stuttgart Ventomobile had already proven to be the most lightweight and most efficient vehicle among the contestants when, with its 130 kg, it succeeded in racing at 64% of the wind speed directly against the wind. From then on it was considered a serious contender for the win.""

Amazing .I was expecting 10 percent.

 

[RCP]

RCP

Thanks for telling me about Aeolus Races.

You're quite welcome undidly. Here's a great site for info on the Aeolus Races, including pics and videos on past events. http://www.windenergyevents.com/

 

[SubductionZone]

The Aeolus Races have been going for a few years at least. There is a reason why spork's BUFC, now Blackbird, got three times the speed of the wind on his first outing and they have not posted the equivalent upwind speed of twice the speed of the wind. In the Aeolus Races there is a severe limit on the size of the rotor. If spork changed his gearing and developed a similar sized rotor as a turbine and not a propeller he would probably have speeds of twice the wind directly upwind. I believe that the area of the disk that the turbines spin through in the Aeolus Races is 4 square meters. spork's cart has an area of over 10 times that.