Moving faster than the wind using only wind power

originally posted by: Phage
Unlike the foil riding, rigid sailed, windjammers that we're going to be seeing in the Americas Cup (scary fast), this is not a terribly efficient system. But it was good enough to win $10k. Perhaps a variable transmission or variable pitch prop could be used to increase efficiency.

If you're talking about the blackbird, it does have a variable pitch prop. When it's just getting started they flatten the prop to give the wind more to push against to help it get moving.

They don't try to exceed wind speed unless wind speeds are in the 8-15 mph range so maybe the transmission works ok in that range, though variable might help. It's somewhat rough construction, so it could use an overall higher build quality too, did you see the vibration in that prop? They were afraid it was going to come apart and hurt somebody like the driver or maybe a bystander.

a reply to: Arbitrageur

If you're talking about the blackbird, it does have a variable pitch prop. When it's just getting started they flatten the prop to give the wind more to push against to help it get moving.

More like making it easier to spin the prop until the wheels are producing more power. If the prop is taking too big of a "bite" it's going to slow the whole rig down. Some aircraft have a hydraulic system referred to as "constant speed propellers". The blade pitch varies to produce the optimal thrust for a given engine RPM.

A fixed-pitch propeller operates at peak performance in only one phase of flight—usually climb, cruise, or something in between. Selecting one requires tradeoffs from the others. Not so with a constant-speed propeller, which utilizes a central hub that connects the individual blades. Inside the hub, oil is used to provide pressure against a cylinder and spring mechanism that either increases or decreases the pitch of each blade.

www.aopa.org...

originally posted by: Bluntone22
a reply to: ChaoticOrder

Sailboat have always gone faster than the wind pushing them.
Why is doing this on land any different than a sailboat?

The Video explains. Watch it.

originally posted by: Arbitrageur

originally posted by: Phage
Unlike the foil riding, rigid sailed, windjammers that we're going to be seeing in the Americas Cup (scary fast), this is not a terribly efficient system. But it was good enough to win $10k. Perhaps a variable transmission or variable pitch prop could be used to increase efficiency.

If you're talking about the blackbird, it does have a variable pitch prop. When it's just getting started they flatten the prop to give the wind more to push against to help it get moving.

They don't try to exceed wind speed unless wind speeds are in the 8-15 mph range so maybe the transmission works ok in that range, though variable might help. It's somewhat rough construction, so it could use an overall higher build quality too, did you see the vibration in that prop? They were afraid it was going to come apart and hurt somebody like the driver or maybe a bystander.

That's what I expected because you need to get the cart to wind speed. The more I think about it the more this shows relativity. let's say you have a 12 MPs tailwind. you can get the cart to 12 MPs no different from a standard sail. Engage the prop to run off wheels you have stored up energy in momentum. And we can take that energy and add it to our wind speed the weight of the vehicle determines the amount of stored energy. meaning eventually the acceleration stops and you will slow down to wind speed.

Once we add the propeller force say it becomes relative on the cart let's say the wind moves 12 meters per sec the wind in front of the prop is 12mps the wind behind the prop is 12 MPs. Now our prop spinning from the wheels let's say we get an extra 2 MPs wind speed on the cart which reduces the speed of the air in front of the cart. 12mps - 2 MPs =10 MPs.This means the wind in front of the cart is now 10 MPs relative to the cart. Behind the prop, we would get 4 MPs to wind speed pushing backward 12mps - 4 MPs =8 MPs (2 to one gear ratio). So relative wind speed behind the cart is now 8 MPs. This shows the cart moves faster than wind speed and stole energy from the wind traveling over the prop.

So now a ground observer what they see is a wind force of 12 MPs pushing the vehicle. I have to admit though the more you think about this the more perplexing it can get a good brain teaser.

originally posted by: Soloprotocol

originally posted by: Bluntone22
a reply to: ChaoticOrder

Sailboat have always gone faster than the wind pushing them.
Why is doing this on land any different than a sailboat?

The Video explains. Watch it.

Not really sailboats are all about vectors the wind hitting the sail sideways. When the wind is at an angle, we have to add vectors representing these velocities. Though now that I think about it yeah the prop is taking advantage of wind vectors. see I told you this is a brain teaser.

a reply to: dragonridr

First, 12 mps is a helluva breeze! It's a sustained windspeed of nearly 27 mph.

Secondly, you haven't factored in the fact that traveling over the ground faster than 12 mps is going to encounter wind resistance in the direction of travel because it is traveling faster than the relative wind. So, the system is going to need to overcome this resistance as well.

Personally, I still think this is some kind of an illusion, and that the physics professor wrongly lost his $10,000 bet (if it was even real). Although, I will admit I am struggling a bit to put my finger on exactly why. At very best I think this whole exercise is a very carefully constructed 'system' which requires such an optimum environment and delicate balance of conditions to demonstrate, for negligible gains, that there is no practical real-world application for what is being demonstrated. Plus, even if all these conditions are met, the vehicle can only travel in one direction...

AH HA!!...I think that may be it! If this vehicle had to travel in a complete circle any gains realized on the downwind leg would be more than canceled out on any upwind leg. The energy input to the system traveling upwind would equal or likely exceed the gains realized in the downwind leg.

a reply to: Arbitrageur

Yes, there are some curious assumptions in the 'plane on the treadmill' question. And, you're correct about it having to do with the function of the treadmill, but you have to look deeper than just that to understand it (and most don't).

The assumption is the plane remains stationary with respect to the ground when the treadmill starts to move. This wouldn't be the case in reality. The Mythbuster's experiment was misleading in that the treadmill didn't begin to move until the aircraft did (therein lies the assumption the plane remains stationary). However, if you look at the same problem from a different perspective where the treadmill starts first, the plane will eventually wind up moving backwards on the treadmill until it provides enough forward thrust to counteract this rearward motion. If the treadmill was allowed to accelerate to the takeoff speed of the aircraft without the plane applying any forward thrust, then the plane would be moving at its takeoff speed in reverse (really BAD for an airplane!). (just for grins let's say the plane's takeoff speed is 100 mph). Now the plane is going to have to accelerate to 100 mph just to remain stationary, but is it really stationary? No, it isn't. And, this is what throws people off. Now 'time' enters into the equation.

Will it still take off? Yes, it will, but it will require more time to take off, and it may cover twice the distance on the treadmill than it would on the ground. The plane will overcome it's rearward motion, but it won't remain stationary there, it will continue to accelerate forward with respect to the ground. Will the plane take off at twice it's normal speed? No, it will still take off at 100 mph relative to air traveling across its wing, but its wheels will be traveling at twice the takeoff speed across the treadmill (which is irrelevant to lift of the wing).

So the harder question in the age-old "airplane on a treadmill" question would be...at what power setting does the airplane remain stationary with respect to the ground? This is a much more difficult question to answer. It's not going to be the takeoff power setting because the plane would take off (eventually). And it's not going to be the 0% power setting because then the plane would move backwards, but it's some setting in between. Some might hazard a 50% power setting, but this isn't necessarily the case either. In order to determine the correct power setting you'd have to know the rolling friction coefficient of the plane's wheels and axles (minus the drag of the airframe moving backwards, until it equalized). In any case, this type of discussion would fully clarify the treadmill's function in the problem.

So yes, some of the details of how the specific treadmill functions are omitted from the initial question. However, why this is relevant goes over many people's heads. I suspect this is the reason the question is banned on the forum you referenced.

originally posted by: Flyingclaydisk
a reply to: Arbitrageur

I think he was referring to the "Airplane on a Treadmill" question, and yes, Mythbusters did test that.

It was "true". The plane did take off, because it wasn't the wheels propelling it, but rather the prop, so the speed across the treadmill was irrelevant, it was the speed over the ground which counted (even though it was 2x the speed of the normal takeoff speed over the treadmill).

Mythbuster also did a episode on blowing your own sail (like with an onboard fan on your sailboat), which is a similar concept. But again, the contraption in the OP has wheels that are connected to the fan, which changes things.

originally posted by: Flyingclaydisk

So the harder question in the age-old "airplane on a treadmill" question would be...at what power setting does the airplane remain stationary with respect to the ground? This is a much more difficult question to answer. It's not going to be the takeoff power setting because the plane would take off (eventually). And it's not going to be the 0% power setting because then the plane would move backwards, but it's some setting in between. Some might hazard a 50% power setting, but this isn't necessarily the case either. In order to determine the correct power setting you'd have to know the rolling friction coefficient of the plane's wheels and axles (minus the drag of the airframe moving backwards, until it equalized). In any case, this type of discussion would fully clarify the treadmill's function in the problem.

I think the assumption is that the wheels move freely. So when the treadmill is moving, the plane would not move backward relative to the ground (non-treadmill ground).

That is, the plane's engine doesn't care what the wheels are doing. The wheels are free to spin independently of the rest of the plane, and they simply spin twice as fast on the treadmill than they normally would on the ground. But, again, if the wheels move freely enough (and the drag of the wheels against the axel is negligible), then the rest of the plane wouldn't care what the wheels are doing.

Here's a good and understandable explanation of how this device can work and not break the laws of physics.

a reply to: Box of Rain

That was a great video, and for a variety of reasons. Some of these reasons may not be readily apparent to some.

First, she did an excellent job putting some of the math and principles behind the system out there in an understandable way.

Second, right up front she said something I've felt since first seeing the OP and the problem. I don't really have a problem with the system creating a vehicle which can travel faster than the apparent wind. That hasn't been my issue with this. My issue has always been...how are the laws of physics not broken by this system? And, as it turns out, they aren't, BUT she doesn't really explain why in her video; she only demonstrates how the system works...when traveling downwind. And, that last part is key (at least for me). Because this system works in the fashion it does, the same system will not work going upwind...at all. So, all of the energy seemingly gained going downwind is more than lost when the vehicle has to be moved upwind. Therein lies the real reason why this concept doesn't defy the laws of physics, not some detailed explanation on how airfoils work and/or thrust and drag vectors.

Thirdly, she acknowledges that her profession is in the wind energy industry, and a quick check of her YT channel confirms this. Consequently, she has a vested interest in not only understanding how this system works, but also wanting concepts like this to work. However, when you look deeper you also see the realities and downfalls of all (to date) of these eco-friendly energy systems; they can never return on their investment. And, the reasons why is what she really explains in the video, although she doesn't couch it that way. Furthermore, this is pretty typical in the wind and solar energy sectors; they paint a far rosier (ironic, that's her name too) picture than the realities of life here on Earth permit. They live in an absolute world where everything is near perfectly efficient all the time, but the harsh realities are that this isn't the case. They construct theoretical models about why things should work, and then construct business cases which support those models, all while ignoring that nature often doesn't play nice in the theoretical world.

Lastly, as I had suspected from the start, this concept is really more just a clever illusion rather than some ground breaking revelation in the energy production, transportation and/or engineering sectors. It's really more just a very controlled experiment, under ideal circumstances, with a decidedly delicate balance of inputs and outputs to solve a very, very, narrowly focused...'dare', really. And that's really kind of what this is, a 'dare', because it's not a 'problem' facing mankind, or the energy industry, or the transportation industry.

Bottom line - There still is...No Free Lunch!

a reply to: Flyingclaydisk

This system will work going up wind if you change the pitch of the props. Although, the speed will be much slower.

originally posted by: Flyingclaydisk
Because this system works in the fashion it does, the same system will not work going upwind...at all. So, all of the energy seemingly gained going downwind is more than lost when the vehicle has to be moved upwind. Therein lies the real reason why this concept doesn't defy the laws of physics, not some detailed explanation on how airfoils work and/or thrust and drag vectors.

originally posted by: graysquirrel
a reply to: Flyingclaydisk

This system will work going up wind if you change the pitch of the props. Although, the speed will be much slower.

What they actually do to make blackbird go upwind is replace the propeller blades with turbine blades, but yes it will work upwind.

FCD I think your energy conservation thoughts are thinking of closed systems which is why you don't want to see more energy out than in. But if you consider heat pumps, you can get more energy out than you put in exactly because it's not a closed system. Part of the energy coming out of a heat pump results from the energy you put in, and part comes from the open environment. The energy conservation laws apply to closed systems, but like a heat pump, the cart is not a closed system. It might even be possible to design blades that could go both downwind and upwind without changing the blades like they do now but the changed blades are likely more efficient. It might also need a fancier transmission than it has now if you want to more easily switch from downwind to upwind travel.

Look up "Autogyro". Practically the same principal, except for the rotor providing lift instead of thrust. I watched all of the videos. That losing Physics professor should take some Engineering classes. One factor that may be involved here is the "Disc Area". It was found that for a helicopter the total lift is a function of the total area of the rotor arc. I can see the same being true for this.

a reply to: Arbitrageur

Hmmm...interesting. I'll have to think about that some more.

Great explanation though.

a reply to: beyondknowledge

You're completely misunderstanding how it works, are you familiar with how sterling engines function, or piezo electric coolers and sensors?

It's all about a difference of energy. With zero wind no it will not ACCELERATE if you push it; it will coast and friction will cancel all forces quickly.

If you were to put a large square sail, yes it could get quite close to wind speed, but it can't exceed windspeed directly downwind because the sail would fold insideout and immediately become its own drag chute. But imagine if you could create something that had a 'visibility' to air resistance from behind, but was essentially invisible to air from the front.

THATS's the propeller, it not only has near zero drag forward, but it creates POSITIVE pressure on it's back side, which also happens to face oncoming wind, so lets say 10mph windspeed, and the prop creates a net effective 5mph worth of thrust, VIOLA, 15mph travel from a 10mph wind.

It's simply working as a moving lever. I grew up sailing so 30seconds into the video last week I knew it was just a matter of recreating the mechanical advantage a sail can create .

If you're familiar with pulley blocks you know you can multiply force either direction for speed, so a double pulley block set can either give you a 3:1 force advantage, or a 3:1 distance/speed multiplication.

When you pull the two pulley blocks apart from each other 10feet, it pulls 30feet of rope.

Imagine for a moment the propeller isnt on the car, a direct rearward wind is going to act on whatever surface area the cars has and still push it as fast as it can until friction and windspeed cancel out. The propeller takes that ground motion and blows it back toward the wind again, EXACTLY like a pulley block multiplier. What's causing the pulley speed doubling is the motion of the pulley block itself.


HIs demonstration of the wood roller accelerating itself faster than it's pusher because of its own gearing; that was a very good demonstration.