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

[JLT]

TL;DR Summary

I was watching Land Yacht racing and wondering why cars, or at least semi-trucks do not use sails? or trains etc. As well as using sails for "wind power", you could also use air brakes, like for semi-trucks driving down hills in Colorado and their brakes often go out with runaway truck ramps etc. - Rather than grinding down brake pads, add "airbrakes" - like flaps on airplane wings?

Land Yacht racing has been around for awhile -
https://en.wikipedia.org/wiki/Land_sailing
a few people still trying it out


The question, is has anyone seen ideas of sail-boating applied to semi-trucks, trains, even cars to improve energy efficiency?

Another application - has anyone seen air-drag used to slow down trains or semi-trucks? For airplanes, there are flaps on the wings that help slow it down - could the same idea be used for semi's and trains? I-70 in Colorado semi's often lose their brakes, have to use the runaway truck ramps etc. For a long hill, seems like it might be worth it to just throw out a parachute or use a sail to help keep the truck slowed down?

I've googled a bit, have not found examples of the above ideas - if anyone knows of places it has been used, or explains why it has not been used? Thanks!

 

[anorlunda]

The question, is has anyone seen ideas of sail-boating applied to semi-trucks, trains, even cars to improve energy efficiency?

There may be many reasons, but one is that most highway bridges allow only 14 feet clearance, and the trucks barely fit underneath as it is.

Another thing that sailors learn is that you can't go directly into the wind. and you shouldn't go directly away from the wind. Therefore, sailing doesn't work well on narrow rivers where you have no control of the direction. Ditto for land yachts on highways. There is not much room to tack in a 12 foot wide lane.

 

[Vanadium 50]

why cars, or at least semi-trucks do not use sails?

 

[JLT]

View attachment 279415

Haha - it could be retractable. Just seems like there is something that could be done with all that free energy:

 

[Vanadium 50]

Just seems like there is something that could be done with all that free energy:

Just seems like you have a solution in search of a problem.

 

[phinds]

Haha - it could be retractable. Just seems like there is something that could be done with all that free energy:

And do you think that car and truck manufacturers have never thought of such a thing? You think maybe they DID think of it and had good reasons for rejecting it. I've seen several already just in this thread.

 

[Baluncore]

Traffic usually flows at a fixed speed. That is almost impossible to achieve with sails on a fixed course.

For a few months I experimented with a sail on my bicycle, but it did not get much use because I could usually ride faster than the wind, and half the time it was a head wind.

As a land yacht pilot I sailed in car parks and along little used roads between wide beaches. Sailing on roads was mentally demanding because I needed to be aware of other traffic, while lifting a wheel high to lower the mast when passing under the power lines. I also needed to obey the speed limit which was rarely possible without brakes. Like a bicycle, I did not need a license on the road.

 

[JLT]

There may be many reasons, but one is that most highway bridges allow only 14 feet clearance, and the trucks barely fit underneath as it is.

Another thing that sailors learn is that you can't go directly into the wind. and you shouldn't go directly away from the wind. Therefore, sailing doesn't work well on narrow rivers where you have no control of the direction. Ditto for land yachts on highways. There is not much room to tack in a 12 foot wide lane.

Ok - so how about using wind to help with brakes?

 

[hutchphd]

Do you want to repack the drogue chute at each stoplight?

 

[JLT]

Traffic usually flows at a fixed speed. That is almost impossible to achieve with sails on a fixed course.

For a few months I experimented with a sail on my bicycle, but it did not get much use because I could usually ride faster than the wind, and half the time it was a head wind.

As a land yacht pilot I sailed in car parks and along little used roads between wide beaches. Sailing on roads was mentally demanding because I needed to be aware of other traffic, while lifting a wheel high to lower the mast when passing under the power lines. I also needed to obey the speed limit which was rarely possible without brakes. Like a bicycle, I did not need a license on the road.

Really neat to get a reply from someone who has experimented with it! How difficult would it be to automate it? Self-driving / self-adjusting sail?

 

[Baluncore]

How difficult would it be to automate it? Self-driving / self-adjusting sail?

I expect it would be close to impossible for the road. It would be possible offshore with a reliable collision avoidance system.

 

[JLT]

Do you want to repack the drogue chute at each stoplight?

I was thinking more highway miles / use on semi's and trains than in the city. Googling for sailboats, did not find anything more recent than:

 

[anorlunda]

How difficult would it be to automate it? Self-driving / self-adjusting sail?

I suggest that you make one, then test it, then post your results here for us to see.

 

[Dullard]

Also: In my experience, any time 2 sailboats are heading in the same general direction, it becomes a race. That would make I-95 an even more dangerous place.

 

[russ_watters]

Haha - it could be retractable. Just seems like there is something that could be done with all that free energy:

What I see in that video is a problem, not free energy. Do you think adding a sail will make that truck more or less stable?

 

[russ_watters]

Traffic usually flows at a fixed speed. That is almost impossible to achieve with sails on a fixed course.

This would be motor sailing.

 

[Baluncore]

This would be motor sailing.

Yes. It could be very relaxing if no one else wanted to use the same roadway and you did not have a delivery deadline to meet.

 

[DaveE]

I suggest that you make one, then test it, then post your results here for us to see.

But first, take a sailing class on a nearby lake or such. It will be both educational and fun.

 

[Stormer]

Another application - has anyone seen air-drag used to slow down trains or semi-trucks? For airplanes, there are flaps on the wings that help slow it down - could the same idea be used for semi's and trains? I-70 in Colorado semi's often lose their brakes, have to use the runaway truck ramps etc. For a long hill, seems like it might be worth it to just throw out a parachute or use a sail to help keep the truck slowed down?

Engine breaking is used for that. Especially on big semi trucks that even has restriction valves in their exhaust to increase the engine breaking. But you should use engine braking on normal cars for long downhills too, not just ride the brakes until they start boiling the brake fluid, or the discs start glowing red hot... At last here in Norway there is traffic signs before long downhills that tell you to select a low gear.

 

[Lnewqban]

Ok - so how about using wind to help with brakes?

The drag force will be proportional to the square of the speed of the truck; therefore, the braking effect would rapidly decrease as the truck slows down.
In order to have a practical use in long downhills, the speed of the truck would need to be high enough.

The natural drag of the profile and surface of the truck inmediately starts slowing it down as soon as the throttle is closed by the driver.
Deteriorating the aerodynamics with some deploying scoop or flap would add some braking effect, but again, the effectiveness will not last up to a full stop.

 

[256bits]

Ok - so how about using wind to help with brakes?

Most likely that picture is from a 'stuck' brake causing overheating of the assembly while the truck is travelling.
A system with braking flaps wouldn't help with such a mechanical failure.
Same thing for trains. If a brake will not release, it overheats and can cause brush fires along untrimmed railway, and train derailment in the end. When a train, or truck needs to stop abruptly, brute force is needed with the available brakes and not a soft slowing down. Other times removing engine power and coasting is employed prior to a full stop or change in speed.

 

[russ_watters]

Yes. It could be very relaxing if no one else wanted to use the same roadway and you did not have a delivery deadline to meet.

No, what I mean is that with motor sailing you aren't at the mercy of the wind. You go whatever speed you want, and the sail just reduces the load on the motor.

 

[russ_watters]

Ok - so how about using wind to help with brakes?

Yeah, that's already a thing:

 

[chemisttree]

Can you imagine having a vehicle deploy a parachute in front of you? That would cause a lot of road rage!

 

[anorlunda]

Can you imagine having a vehicle deploy a parachute in front of you? That would cause a lot of road rage!

I've often wondered what I could do (other than risky brake checking) to discourage tailgaters. You just provided a great idea; and also fun.

 

[chemisttree]

It would give bumper stickers a new meaning. Imagine having the face of a <insert hated politician> deployed in front of you 20 feet wide! Oh the humanity!

 

[cmb]

Summary:: I was watching Land Yacht racing and wondering why cars, or at least semi-trucks do not use sails? or trains etc. As well as using sails for "wind power", you could also use air brakes, like for semi-trucks driving down hills in Colorado and their brakes often go out with runaway truck ramps etc. - Rather than grinding down brake pads, add "airbrakes" - like flaps on airplane wings?

Land Yacht racing has been around for awhile -
https://en.wikipedia.org/wiki/Land_sailing
a few people still trying it out


The question, is has anyone seen ideas of sail-boating applied to semi-trucks, trains, even cars to improve energy efficiency?

Another application - has anyone seen air-drag used to slow down trains or semi-trucks? For airplanes, there are flaps on the wings that help slow it down - could the same idea be used for semi's and trains? I-70 in Colorado semi's often lose their brakes, have to use the runaway truck ramps etc. For a long hill, seems like it might be worth it to just throw out a parachute or use a sail to help keep the truck slowed down?

I've googled a bit, have not found examples of the above ideas - if anyone knows of places it has been used, or explains why it has not been used? Thanks!

Sure. Go grab yourself some free energy.

However ...

for most of the time most traffic wants to move faster than the air mass they are moving through ... (and that's not even mentioning that the air mass might be at a negative velocity to the desired magnitude!)

... errr ... surprised no-one's mentioned that yet!

Cars and trucks do definitely benefit from the prevailing winds. On one particularly windy day I had to recharge my car twice on a trip I could do with a tail wind with no charge stops at all.

Probably less noticeable in dead-dinosaur powered cars. But definitely an effect.

 

[The Bill]

for most of the time most traffic wants to move faster than the air mass they are moving through ... (and that's not even mentioning that the air mass might be at a negative velocity to the desired magnitude!)

... errr ... surprised no-one's mentioned that yet!

Perhaps surprisingly, that isn't a deal breaker in and of itself. See the Blackbird land yacht built in 2010, which could go faster than the wind both downwind and upwind. That's nowhere near practical for road travel, of course. But I do find it to be a fascinating demonstration.

 

[anorlunda]

for most of the time most traffic wants to move faster than the air mass they are moving through
... errr ... surprised no-one's mentioned that yet!

Sorry, that is a popular myth. Sailboats and sailing iceboats go faster than the wind all the time. Just watch this week's news about America's Cup racing in NZ. Those sailboats go up to 50 mph in a 15 mph wind.

 

[Klystron]

FTR while not sails, some car designs include flaps, fairings and adjustable wings to improve performance.
Air Dams, Splitters, Spoilers and Wings - NASA Speed News Magazine

 

[cmb]

Sorry, that is a popular myth. Sailboats and sailing iceboats go faster than the wind all the time. Just watch this week's news about America's Cup racing in NZ. Those sailboats go up to 50 mph in a 15 mph wind.

I'm aware of these possibilities, however, only in a very specific direction to the wind. Roads tend not to line themselves up with the direction of the prevailing winds, as it happens!

At sea/on a beach, one can select the direction arbitrarily. The issue about being on roads is that they tend to constrain you along a particular heading.

 

[Kenwstr]

Sorry, that is a popular myth. Sailboats and sailing iceboats go faster than the wind all the time. Just watch this week's news about America's Cup racing in NZ. Those sailboats go up to 50 mph in a 15 mph wind.

Um as a sailor with decades experience and placements in both state and national titles, I assure you that you are mistaken, entertainment commentary is not accurate to reality. It is only very high performance boat designs that can sail faster than the wind and even then, only on certain headings. Efficient sail boats can not sail closer to the true wind than about 40 degrees due to their lift/drag efficiency. It looks like they sail closer than this because of the addition of their speed vector and the true wind vector. I am not aware of any sail boat that can exceed wind speed when sailing up wind. In fact, this is the slowest point of sailing as only a small fraction of the sails reaction is driving the boat forward while most of it is trying to tip the boat over.

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

Efficient, faster than wind sailboats tack downwind. So that their speed vector plus true wind vector produce an apparent wind directions change to the front quarter of the boat. They are sailing so fast that the angle between true and apparent wind is greater than 90 deg. Boats that are efficient enough to achieve this and more are known a apparent wind boats and they can indeed sail faster than the wind across or at a downwind angle but they certainly cannot sail faster than the wind in any random direction and no sailing boat can sail between about -40 to +40 degrees against the wind, we all have to tack upwind.

Add the fact that many roads go through cuttings, corridors through tall forests, buildings, tunnels etc which all block and channel the wind and considering the speed vector of cars changing apparent wind to almost always be practically directly ahead, there are almost no situations in which a sail could be employed effectively on a car or truck. Then of course, there is the considerable hazard that a mast on a car presents both for road safety and infrastructure.

I suppose, some of these crucial terms will be unfamiliar, but I have far too limited space to fully explain the physics of sailing. Look them up if you wish to understand these points.

 

[anorlunda]

I suppose, some of these crucial terms will be unfamiliar, but I have far too limited space to fully explain the physics of sailing. Look them up if you wish to understand these points.

See post #2 in this thread.

 

[sandy stone]

no sailing boat can sail between about -40 to +40 degrees against the wind, we all have to tack upwind.

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.

 

[cmb]

Tacking on the highway is frowned on, incidentally, so moving ever more from the original question.

I did see some design for one of those directionless vertically rotating sails. But, again, it is not merely getting the direction right on the road but also the speed. I suggest sails deliver poorly on both dimensions of one's vehicle's 'desired' velocity vector.

Hint; even canal boats don't use sails ... answer why not for canal boats and probably a similar answer for use on roads.

 

[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.