Land Yachts -- Why don't cars and trucks also use sails?

[DaveC426913]

Tacking on the highway is frowned on...

It sure is. I once tacked on a highway - a boat highway - and the 300 passenger party boat coming up behind me was not amused.

We got so close the passengers on the bow rail could have dropped a penny and hit me on the head.

(I'm very lucky I wasn't fined for sailing in an 'all vessels must be under power' channel.)

 

[pyroartist]

This problem has been well thought out in the past:

 

[ardnog]

I am not aware of any sail boat that can exceed wind speed when sailing up wind.

No sailing boat can sail directly downwind faster than the wind.

There is a land yacht called Blackbird that does both of these. How it works that the wind drives a rotor, and the rotor drives the wheels directly via a mechanical linkage. Technically this is still powered by only wind, and does not use stored mechanical or electrical power, and is therefore a sail, though traditionalists might not accept it.

https://en.wikipedia.org/wiki/Blackbird_(land_yacht)

I don't see any reason such a mechanism won't work on a boat, but the engineering challenge of implementation is of course much harder.

 

[cmb]

" No sailing boat can sail directly downwind faster than the wind. "

There is a land yacht called Blackbird that does both of these.

You might want to think about that a bit more and consider motion through a body of air, independently of the ground it is traveling on.

What is possible is that a very small cross wind can be utilised to provide the tractive force directly downwind. But ultimately the vehicle would have to travel with some degree of cross wind and never 'directly' downwind.

Just consider what forces (assuming the rolling wheels and surface are 'perfect' and non-lossy) one is trying to overcome by pushing a vehicle along at speed? It's the air resistance, of course. If one can generate more power from the air resistance than the power that this air resistance generates, hey, maybe we can invent a perpetual motion machine there using a wind tunnel and some clever engineering.

 

[ardnog]

You might want to think about that a bit more and consider motion through a body of air, independently of the ground it is traveling on.

What is possible is that a very small cross wind can be utilised to provide the tractive force directly downwind. But ultimately the vehicle would have to travel with some degree of cross wind and never 'directly' downwind.

Just consider what forces (assuming the rolling wheels and surface are 'perfect' and non-lossy) one is trying to overcome by pushing a vehicle along at speed? It's the air resistance, of course. If one can generate more power from the air resistance than the power that this air resistance generates, hey, maybe we can invent a perpetual motion machine there using a wind tunnel and some clever engineering.

Think about what a gearbox does.

No disrespect intended, but you're claiming the wikipedia entry for the Blackbird land yacht is wrong. Are you absolutely sure?

 

[cmb]

Think about what a gearbox does.

No disrespect intended, but you're claiming the wikipedia entry for the Blackbird land yacht is wrong. Are you absolutely sure?

I have to think so.

From whence does the gearbox derive its input power if not from the wind when traveling into wind? If it can generate more power from the wind it is driving through to push it through that air, then it is a perpetual motion machine.

I simply cannot see how this can be done without SOME crosswind.

 

[russ_watters]

I have to think so.

From whence does the gearbox derive its input power if not from the wind when traveling into wind? If it can generate more power from the wind it is driving through to push it through that air, then it is a perpetual motion machine.

I simply cannot see how this can be done without SOME crosswind.

This is a topic we've discussed before on PF. It's a surprising result, but it's true. The key is that the relative wind drives the wheels. When sailing dwftw, the relative wind is opposite the direction of motion (making them hard to start). A neat little trick.

 

[cmb]

This is a topic we've discussed before on PF. It's a surprising result, but it's true. The key is that the relative wind drives the wheels. When sailing dwftw, the relative wind is opposite the direction of motion (making them hard to start). A neat little trick.

What does 'drive the wheels' mean? What are the wheels driving against?

 

[russ_watters]

What does 'drive the wheels' mean? What are the wheels driving against?

There is a transmission system. The turbine drives the wheels, the wheels drive the vehicle across the ground.

 

[Baluncore]

The propeller drives the wheels, the wheels drive the vehicle across the ground.

The technical term for the wind driven rotor is actually turbine.
Turbine blades differ from propeller blades in that, for an asymmetrical airfoil section, the twist along the blade is reversed.

 

[russ_watters]

The technical term for the wind driven rotor is actually turbine.

Yes, corrected.

 

[cmb]

There is a transmission system. The turbine drives the wheels, the wheels drive the vehicle across the ground.

Yes, yes, of course! What I mean is 'driving against what?'. What 'force' is it driving against that it has to overcome?

 

[russ_watters]

Yes, yes, of course! What I mean is 'driving against what?'. What 'force' is it driving against that it has to overcome?

Drag and rolling resistance.

I suspect you have a point you're getting at but I'm not really up for heading down a quiz rabbit hole. Please make it, but also please read up on dwfttw first so you don't inadvertently step in the hole.

 

[cmb]

Drag and rolling resistance.

I suspect you have a point you're getting at but I'm not really up for heading down a quiz rabbit hole. Please make it, but also please read up on dwftw first so you don't inadvertently step in the hole.

OK, sure, I call this out as BS.

The power generated driving 'directly' into headwind cannot overcome the power needed to drive directly into headwind.

I emphasise 'directly'.

It just cannot be done.

I am surprised this is not stamped on, on a site like this.

The photograph shown on the wiki page shows a cross wind. It is not 'directly' into headwind.

I would not want to stab at a guess of how much cross wind is needed, it might indeed be very little. Close enough perhaps that a wet finger in the air says 'yep' he's going into headwind.

But just please explain to me, in basic physics, how a vehicle that is within a body of air can gain energy from the air it is pushing through?

Seriously? I mean, next we will have propeller aircraft that can 'generate' power by speeding up! The propeller at the front can become a generator!

If I am wrong then it's because I need to see some extraordinary evidence for this extraordinary claim, and I haven't.

 

[Baluncore]

The power generated driving 'directly' into headwind cannot overcome the power needed to drive directly into headwind.

Yes it can, because the turbine rotates due to airfoil lift, but there is also the perpendicular airfoil drag component that must be overcome. In order to rotate the turbine, the lift must be perpendicular to the wind direction.

If the turbine blade lift to drag ratio is greater than unity, then the lift perpendicular to the wind will overcome the drag component into the wind.

 

[russ_watters]

OK, sure, I call this out as BS...

Ok, well, it's not, and you really should read-up on it and try to learn how it works, then ask specific questions about the parts you don't understand. The search term on PF is "dwfttw" (the second "t" is sometimes omitted) and of course there's plenty you can get from a google search as well. I don't think this is the right thread for a starting-from-scratch walkthrough of the concept (and one should always try to brush up before jumping into it anyway).

 

[ardnog]

I would say "very few sailing boats". For instance, the Etchells 22 website claims a 70 degree tacking angle, and I'm pretty sure the AC70 boats could do even better.

Very rough calculation: AC 75 are claimed to be 4x faster than the wind. Inverse tan (1/4) is 14 degrees, for the effective wind the boat is sailing into.

 

[Klystron]

If made light enough, the instrumentation package for Blackbird mentioned in the article could measure lift throughout the test run; perhaps strain gauges associated with the lower chassis and each wheel?

There should be some ground effect from the wind motion under the chassis and horizontal parts of the fairings coupled, as @Baluncore states, with substantial lift from the turbine assembly. As lift and drag vary with forward motion and turbine rotation, not to mention variations in wind direction, I wonder how the operators stabilize and steer the vehicle?

I suppose the turbine spin produces some minor gyroscopic stability but have not thought this through. Would like to see some data from a model in a 'ground effect' wind tunnel with horizontal steel plates simulating the Earth such as the 12' at NASA Ames. Models usually remain rigidly mounted throughout the test; so, are not free to tip over.

Unable to roller skate or skateboard as a child, I mounted skate wheels on wooden boards with different sails to excellent effect on windy days sans rider. I experimented with propellers from powered gliders replacing the sails and one vertical turbine without success as a land vehicle. Guess the blade pitch was incorrect.

 

[Baluncore]

There should be some ground effect from the wind motion under the chassis and horizontal parts of the fairings coupled, as @Baluncore states, with substantial lift from the turbine assembly. As lift and drag vary with forward motion and turbine rotation, not to mention variations in wind direction, I wonder how the operators stabilize and steer the vehicle?

The vehicle appears to be steered by the front wheel, probably by both feet on rudder bar pedals.

The azimuth of the turbine will also be controlled, probably with the right hand, maybe using a hand wheel. The turbine has only two blades so it will not be gyroscopically difficult to change the turbine azimuth.

The lift I referred to is that of the turbine blade airfoil profile. The rotating blades are moving across the wind direction, driven by blade lift. Only the smaller drag component is in the wind direction.

 

[cmb]

Ok, well, it's not, and you really should read-up on it and try to learn how it works, then ask specific questions about the parts you don't understand. The search term on PF is "dwfttw" (the second "t" is sometimes omitted) and of course there's plenty you can get from a google search as well. I don't think this is the right thread for a starting-from-scratch walkthrough of the concept (and one should always try to brush up before jumping into it anyway).

So, why don't we have aircraft with self-propelling propellers? Instead of drive to the ground they can go through a gearbox to a second pushing propeller at the back that runs quicker than the front one?

It's like someone saying you can go read up on cold fusion if you don't believe it. All very convincing. Whole conventions run by established scientists on the subject.

Extraordinary claims .. etc ...

 

[cmb]

Yes it can, because the turbine rotates due to airfoil lift, but there is also the perpendicular airfoil drag component that must be overcome. In order to rotate the turbine, the lift must be perpendicular to the wind direction.

If the turbine blade lift to drag ratio is greater than unity, then the lift perpendicular to the wind will overcome the drag component into the wind.

I'd like to see some accurately recorded data showing such an experiment.

I can see a photo on wiki but it appears to show a small cross-wind to the vehicle being tested.

 

[ardnog]

Comparisons to cold fusion are very unfair. Cold fusion is not supported by current physics, and attempts to reproduce it don't work. On the other hand, plans for these land carts are available (there is a detailed building guide on the inventor of Blackbird's youtube), others have built them, and physicists can explain how they work, if you ask nicely and don't call them (and by implication also the land yacht racing judges) crackpots.

 

[cmb]

Comparisons to cold fusion are very unfair. Cold fusion is not supported by current physics, and attempts to reproduce it don't work. On the other hand, plans for these land carts are available (there is a detailed building guide on the inventor of Blackbird's youtube), others have built them, and physicists can explain how they work, if you ask nicely and don't call them (and by implication also the land yacht racing judges) crackpots.

OK, but I have asked nicely why no-one's made an airplane propeller along the same principles.

 

[Baluncore]

OK, but I have asked nicely why no-one's made an airplane propeller along the same principles.

That is simply because you don't understand the principles. Your fixation with the ridiculous precludes a rational approach.

Given a source of energy, birds and insects can fly through the air, while fish can swim in water. Neither of those can extract energy from the one stationary fluid in which they are totally immersed.

The requirement to extract energy is that there is a solid reference, the ground and one moving fluid, such as water or air, or that there are two separate fluids with a differential velocity, such as the wind blowing over water.

 

[Klystron]

The physics of fluids fascinates and strains understanding perhaps because we live immersed in air and originally evolved in and require water. One must remain skeptical yet open to new concepts.

This thread concerns land yachts but consider how a helicopter rises and flies under rapidly rotating rotors with pitch controlled by the pilot. In the event of engine failure the same rotors can be tilted to auto-gyro and safely land a heavy un-aerodynamic vehicle. Tilt-rotor and ducted-fan aircraft often appear to defy gravity and common sense translating from vertical to horizontal flight regimes to hover like hummingbirds. These latter examples require significant energy expenditure but hint at the potential of unaided flight.

I had read about Bauer and similar experimental land vehicles but using an adjustable turbine-prop in place of sails leaves me with much food for thought.

 

[cjl]

There is a transmission system. The turbine drives the wheels, the wheels drive the vehicle across the ground.

Worth noting that the prop on Blackbird only acts as a turbine when the vehicle is in its upwind configuration. When set up to go downwind, it is acting as a propeller, and the driving force is coming from the wheels.

When going upwind, the turbine harvests energy from the air and uses it to drive the wheels. When going downwind, the wheels harvest energy from the ground, and use it to drive the propeller. In both cases, the reason this works is because the vehicle has a higher relative speed compared to where it is extracting energy than where it is expending it for propulsion.

 

[cjl]

So, why don't we have aircraft with self-propelling propellers? Instead of drive to the ground they can go through a gearbox to a second pushing propeller at the back that runs quicker than the front one?

It's like someone saying you can go read up on cold fusion if you don't believe it. All very convincing. Whole conventions run by established scientists on the subject.

Extraordinary claims .. etc ...

The fundamental principle that makes Blackbird work is that the vehicle's speed relative to the ground is different than its speed relative to the air. As a result, it can extract power from one and use it to propel itself against the other. This obviously doesn't work for an aircraft. This is also why the Blackbird only works when there's wind.

 

[cmb]

I see this as a 'large body' problem

If there is a cross-wind, it can be quite small, a body can be constructed to cause the air to scatter from the side and redirected to behind. If the efficiency of that process is high then momentum from the air in the opposite direction of body travel will provide a source of power for the body to continue along its path.

I remain hesitant on a conclusion. One might consider a vehicle braked and stationary, putting wind power into some batteries. That could be done. One can then imagine (wind not changing) the vehicle then sets off under battery power.

In principle, the energy can be gained when stationary, I see no big difference if it in motion providing the traction force is higher than the wind loading, and the mechanical power used directly rather than via a storage medium.

... I will have to consider further ... I still would regard this as a case of momentum via redirection of air, as I can see the cross wind in the photo. I'd like to see real data with calibrated vane anemometers to show direction of travel versus speed, etc..

 

[ardnog]

Drela's maths paper is quite accessible, and shows the equations for propulsion without a crosswind.

If you mean the photo in wiki, I don't see how you can see crosswind in that. Trace the perspective lines and look at the shadows. It's inexact enough that you wouldn't be able to tell if there was a slight crosswind or not - nor do I understand why this is a productive activity.

Examining the mathematics would be a better use of time.

 

[cjl]

I see this as a 'large body' problem

If there is a cross-wind, it can be quite small, a body can be constructed to cause the air to scatter from the side and redirected to behind. If the efficiency of that process is high then momentum from the air in the opposite direction of body travel will provide a source of power for the body to continue along its path.

Yes, but it's very obvious that's not what the Blackbird is designed to do. We have methods of very efficiently curving a slight crosswind component to the rearward, and that is a large sail or airfoil. What you're describing is exactly what a high performance sailcraft (be it an ice boat, catamaran, or land sailer) does. However, the blackbird has no large sail, and has no method by which a large sail could be controlled anyways (since to achieve optimal performance you would need to be able to rotate one around a vertical axis).

It seems odd to say that, somehow, purely by accident, the builders of the blackbird accidentally made its superstructure such an efficient sail as to make a VMG of over double windspeed directly downwind based only on a small unintentional crosswind component, rather than that the designed mechanism works as intended.