Negative drag wind powered car..goes faster than HEAD ON wind

I feel a technical wind turbine discussion is not complete without understanding how the new wind powered cars travel un assisted into a head wind at TWICE the speed of that wind.

Somewhat counter intuitive as born witness by the fact that MIT scientists cant it seems agree on how it works. Well if the boffs cant agree than i won't be taking that route to understanding. But hey I did note that some Airforce aeronautics papers refer to negative drag.....AND that as usual the Victorians were ahead of the game.....Dew Oliver et al.

So what ? well unless its already been discussed on this fab forum..i really wanted to just set the brain matter in motion as I feel that maybe the secrets of wind turbine design can be gleaned from this. With a LOT of lateral thinking and most definitely no Betz or is it jackovsky factors please !!

interesting for sure. i just asked a few coworkers and all agreed it couldnt be done.
then i showed them the video

does the effective wind speed increase as the turbine/car is moving into the headwind?
ie if you have a 20mph head wind and you are moving 10mph into that wind, does the turbine "feel" 30 mph wind?

can the turbine rotate to find wind? what if you want to go a direction other that into wind? Sail perhaps?


here is the companys website: http://www.jobyenergy.com/
seems most of the info is related to high altitude wind power.

good post.

I would say yes...30mph. And thats one of the interesting things because a wind turbines power goes up the square of the turbine diameter and the CUBE !! of the wind speed. That may mean the faster the vehicle travels INTO the wind the more power the vehicle produces. And vice versa.

So if you were to fit a small 4' diameter turbine on a racing car....when it reached 220mph the vehicle would have a boost in power of circa 400hp or 324kw..assuming turbine efficiency of 50%.

Or take an OLD retired jet aircraft like the SR71. IF you attached a tiny weeny 0.5m turbine to it..air break IF you like..how much power at 50% efficiency would you get ? 71154106 watts....thats eh.... 71154kw..which is 71 MILLION WATTS from a tiny 0.5m wind turbine. plus minus 20% if it makes you happy. Not trying to be clever..just interested in turbines.

Question. Could you use a wind turbine as a vehicle brake ? Just saying

I have posted this not as a practical solution but to help us understand how wind turbines really operate

The same effect can happen to sailboats when you have the correct sails and angles. I personally experienced faster than wind travel on a sailboat. (Note: it only happened once, with really good sailor)

Air current to blades causing vacuum by loss of wind current see the wind current seek to fill from behind pushing the wing/tear drop forward in dog chasing its tail.

Peter Mckinlay wrote:Air current to blades causing vacuum by loss of wind current see the wind current seek to fill from behind pushing the wing/tear drop forward in dog chasing its tail.

Like it. Are you saying that if the wind LEAVES the wing tips at a faster speed than it enters the tips...a low pressure area is created in FRONT of the blades and SUCKS the car forward ? I would agree.

BUT is the energy taken from the wind or a result of redirecting the wind and thus introducing new Vectors. Before you laugh...many of the boffs best explanation of the wind car is that its the road that turns the wheels..not the wind...didnt quite get that myself.

Simon Brown wrote: Are you saying that if the wind LEAVES the wing tips at a faster speed than it enters the tips...a low pressure area is created in FRONT of the blades and SUCKS the car forward ? I would agree.

I would agree too. That is why airplane wings, wind turbines are shaped as they are. The faster moving air on the top (for a plane) or front (for a propeller) generates lift which pulls it up or forward.

Good to agree.

Since we started with a wind turbine powered car that travels into a head wind at twice the speed of that wind.....I would now like to suggest that to create in our case a low pressure area..you MAY only have to just change the winds "architecture" for want of a better word. ie from a laminar flow to something else....and in doing so create a low pressure in fron of the turbine. In the same way an aeroplane wing depletes (or not) the laminar air flow

I paid $25 for a used wind surfer and experienced faster than wind travel on my first day (perpendicular to the wind). I stuck with it for six hours and made every muscle sore the next day.

I'm pretty certain that the prop is attached to a chain that's turning the axle. Wind turns the prop, prop turns the wheels. At the end of the video you hear the guy shout, 'chain's broke!' I think this is what he's talking about.

If this is what everyone is saying and I'm grossly misunderstanding you, my apologies.

Charles Tarnard wrote:I'm pretty certain that the prop is attached to a chain that's turning the axle. Wind turns the prop, prop turns the wheels. At the end of the video you hear the guy shout, 'chain's broke!' I think this is what he's talking about.

If this is what everyone is saying and I'm grossly misunderstanding you, my apologies.

Yes correct..chain etc.. Some charge batteries instead. But the point seems to be a lot of people thought it impossible..... and even though it is possible there is much confusion over how it is possible. In this thread we are looking at alternative views.

On a re-read I see where my confusion was. Thanks.

Charles Tarnard wrote:I'm pretty certain that the prop is attached to a chain that's turning the axle. Wind turns the prop, prop turns the wheels. At the end of the video you hear the guy shout, 'chain's broke!'

Yep. I just watched the video, and the first thing I noticed was the vehicle travels at a speed directly proportional to the speed of the turbine blades. This suggested a direct drive. I couldn't see how this was done, but the "chain's broke" comment gave it away.

I don't see a problem with this. That is, it seems clear to me how this works. Ever put your hand outside the window of a moving car? If you put your hand flat against the wind, then you will experience a significant drag. Likewise, putting flat blades on the turbine of this car would cause the incoming wind to force the car in the same direction as the wind. Now, if you pivot your hand such that it is mostly in line with the air flow, then you can generate a combination of (1) less drag, and (2) a force that acts perpendicular to the motion of the air flow. Optimizing this effect with the shape of the wind turbine blades allows for generating work at the turbine shaft, then transferring this work to the wheels. Proper gearing can be used to overcome the combination of reduced drag and rolling resistance to move the car forward.

A little more... the blades interact with the air molecules in two important ways. (1) some air molecules transfer their momentum to the blades causing them to generate a torque on the turbine shaft, and (2) some air molecules do not. Of those that do (1), these air molecules slow down and see their paths diverted. Of those that do (2), these air molecules do not slow down, but they do see their paths diverted. The goal is to maximize the number of air molecules that do (1), and while minimizing the number of air molecules that do (2). This is another way of saying that turbulence at the turbine blades must be minimized as turbulence generates drag, or saying that we desire the blades to interact with those air molecules that actually transfer momentum to generate a torque on the turbine shaft rather than forcing the blades in the same direction as the air flow.

Marcos Buenijo wrote: the blades interact with the air molecules in two important ways. (1) some air molecules transfer their momentum to the blades causing them to generate a torque on the turbine shaft, and (2) some air molecules do not. Of those that do (1), these air molecules slow down and see their paths diverted. Of those that do (2), these air molecules do not slow down, but they do see their paths diverted. The goal is to maximize the number of air molecules that do (1), and while minimizing the number of air molecules that do (2). .

Thank you Marcos !!

I cant disagree !

Maybe Iam clutching at straws but I had this hunch that both air molecules (1) and (2) have also been converted from a lamina flow to a vortex flow..albeit an imperfect one. Under such circumstances the energy lost from air molecule (1) might be less than thought and secondly both air molecules..(1) and (2)..albeit now traveling at different velocities are now more inline with air (and waters) natural tendency....cyclonic.... that of a vortex..thus picking UP velocity and hence energy. As I said earlier..many MORE Vectors are thus introduced..that is to say rotational..translation, centripetal, centrifugal and transverse. (I made that lot up).

Reminding ourselves of some original statements I have now found out that Nasa has a glider..The falco..capable of 13,000 mph. IF that was to deploy a tiny wind turbine of say 0.5m dia....power output would be 46234244187 Watts = 46234 mega watts or 46 Terra watts. Would love somebody to check that. Wouldnt it be a bummer if I was a fact of 100 out and its only 0.46 Terra watts..lol..still not bad for suitcase sided wind turbine..just need the glider eh ? No doubt 46 Terra Watts would be enough to re launch the glider ? Just saying.

Just thinking aloud eh ! and again Thank you everyone

ps. the stubby wings of bees and other insects lift far more weight than can be explained using conventional steady-state aerodynamics principles.Weis-Fogh, a Danish zoologist at the University of Cambridge, used high-speed photography to analyze the exact wing motions of hovering insects and compare them to the insects’ morphological features. From this, he formulated a general theory of insect flight, which included what he called the “clap-and-fling effect.” When insect wings clap together and then peel apart between the up and down strokes, the motion flings air away and creates a low-pressure pocket. Air then rushes back into the pocket, forming a swirling vortex. This vortex creates the force necessary to lift the insect between wing flaps. Similar vortices might be generated by the angle and rotation of the wings, Weis-Fogh posited, providing additional lift.

Here are the records the "Blackbird" land-yacht has set:
http://www.nalsa.org/DownWind.html

It is correct that the turbine is connected to the wheels via a chain and it is the critical component that makes this work.

I built a land-yacht for a senior design project, it was a ton of fun to drive. I plan on making my own combined land-yacht/bike, aka "wike", one day.

Post that has some closer looks the the internals
http://blueplanettimes.com/



This quote helps me visualize how this works

“With a bit of thought it occurred that one could reproduce the aerodynamics and physical constraints of the land-yacht by simply having the sail follow a continuous downwind tack, but wind that tack into a spiral. Two such sails would simply form a propeller. By gearing this propeller to a set of wheels, you could constrain it to follow the same downwind path that the sail of the land-yacht follows, but on a steady downwind tack. So it seemed such a vehicle could in theory be constructed quite simply."

Rick Cavallaro is the guy who came up the idea, John Borton, JB, is the guy who built the original Butt Ugly F'reakn Cart with Rick (before the Black Bird, and the PC that came from asking for corporate and academic grant monies, it was BUFC).

BUFC was built to go: "Directly downwind faster than the wind, n ­ a.k.a. DDWFTTW. An idea that 99 percent of people declare impossible. Ninety-nine percent of the rest can’t figure out how it’s done."

That's a quote from what is probably the best article written, by Rick about their efforts: http://www.wired.com/autopia/2010/08/ddwfttw/all/1

After that effort ended in success they turned their sights on going Direct Upwind Faster Than The Wind, DUWFTTW. JB sorta dropped out and Rick spent much of his time on re-engineering the new props for the new conditions, while a university crew did most of the rest. That effort was also successful, Believe It or Not...

The web sites Rick maintained during the years he was engaged with this effort are gone, but some copies can be found at:
https://web.archive.org/web/20110815000000*/http://www.fasterthanthewind.org/

https://web.archive.org/web/*/http://thinairdesigns.com/

You can also find videos on youtube.

The implications of what Rick and JB did out of their shop are staggering for those who care to think about such things, so good on you Simon for posting this here.

Simon Brown wrote:I feel a technical wind turbine discussion is not complete without understanding how the new wind powered cars travel un assisted into a head wind at TWICE the speed of that wind. ... i really wanted to just set the brain matter in motion as I feel that maybe the secrets of wind turbine design can be gleaned from this.

Here is a very brief summary of an originally rather long thought experiment concerning props written in late 2010 a few months after the Black Bird's successful down wind trials. The underlying concept being of looking at fluid dynamics as the sum of all the actions of all of those incessantly active atoms and molecules that make up a fluid mass. This fundamental property of matter was succinctly described by the great William Crookes in a 1879 lecture on Radiant Matter:

"Gases are now considered to be composed of an almost infinite number of small particles or molecules, which are constantly moving in every direction with velocities of all conceivable magnitudes."

It is this incessant motion which is being referred to when mention is made of potential or kinetic energy; these two terms in actuality only describing a change of view not a change in or of energy. Traditionally potential energy is a reference to a mass at rest relative to its immediate surroundings, ignoring the internal energies of the particles making up the mass. Kinetic energy is simply a reference to the change that occurs when a portion of the internal particles begin to move in unison along a common pathway. Looking at wind from this perspective helps provide a somewhat different view of how air molecules interact with prop surfaces and perhaps how prop designs can be improved - or so it is hoped anyway.

***

Examining Prop Functions: Conventional thought has it that propellers provide thrust by pushing against the surrounding air, that is why they were initially referred to as aerial screws. However, modern props are also airfoils, which gained dominance over air screws when it became apparent that creating lift, the lowering of pressure along the leading surface of the prop, offset a large amount of required pushing power. This occurs because airfoil props, like wings, are actually environmental energy extraction devices that utilize the energy of air molecules to push the airfoil into the lower pressure zone.

However, an airfoil as a prop is a somewhat more tricky proposition than an airfoil as a wing. For meeting air movement straight on with a narrow leading edge seems to be a much more natural function than progressing in the direction of the whole of ones top surface area.

To deal with this somewhat unnatural situation prop blades have many profiles, they can be symmetrical or asymmetrical, they can be varied in width and depth, twisted or straight, tilted or level, etc. It all depends on the specific application the designer is attempting to achieve but a primary goal is to create a stable low pressure zone ahead of the blade while maximizing push.

For instance, on an asymmetrical blade the front surface may be designed to achieve high lift, that is to create a low pressure area over the front of the blade, while smoothly feeding the air to the back surface of the following blade to minimize turbulence. The back surface may be designed to most effectively push the air away from it maximizing thrust into that frontal low pressure zone. However, a symmetrical blade may have the same profile on both surfaces and depend on the blade being tilted on the rotor to provide an angle of attack to generate thrust.

These two separate functions of the leading surface and the back surface are obviously somewhat in conflict, for the faster the back blade thrusts the whole contraption along the more compressed the forward low pressure zone will become, reducing the lift. Is it possible then to split the front surface from the back surface to create non-traditional designs that are more efficient?

Splitting the Prop: As surprising as it may seem, some of the most innovative and effective concepts along these lines were conceived in the early twentieth century.

Henri Coanda: While the Coanda Effect is well known in wing design and other circles today, his propulsion design based on the same concepts never gained acceptance - fated it seems to live on only in an obscure seldom remembered niche in aviation history. His device was powered by a pressurized gas (red arrows) flowing upwards along the axis and exiting through circumferential slots as a high speed flow over the convex shroud, thus creating a low pressure zone on the front surface.



At the same time, air from the front of the device would be admitted as a low speed flow through a central opening and directed to the back surface. This would generate a higher pressure than that existing on the front surface engendering lift, or in this case: forward thrust without revolving blades. History seems silent on whether a functioning device was demonstrated or not. However, the underlying principles are sound.

Fan Wing: A contemporary device which more clearly demonstrates the splitting of functions between front and back surfaces, can be seen in this device which uses what looks like a stretched version of an old push lawn mower reel to create lift on a strange type of wing. It is safe to say this wing has a very non-conventional profile, not to mention blade and rotor configuration.



The elongated blade reel sits in a concave trough 'blown' out at the trailing edge. The revolving blades create a high speed flow over the wing's top surface creating lift, while generating thrust by pushing the air to the back.


Getting Specific: Morph Level One or Getting the Morph Out of Your Basic BUFC

Here we will focus on simply Splitting the Prop while keeping the sail-frame-wheel-airfoil direct drive mechanism.

Before Henri Coanda there was Nikola Tesla and his 1913 patent for 'Fluid Propulsion'. This and the later 'Turbine' patent focused on his Bladeless Disc Turbine designs. It could be used to extract energy from a fluid and function as a motor, or it could impart energy to a fluid and function as a pump / fan. Reminiscent of Henri's design, each disc had a central opening through which fluid entered or exited depending on the mode it was in.

If the primary goal of an airfoil's leading surface is to create a frontal low pressure zone, what better way than to use a spinning centrifugal disc to simply move all of those pesky air molecules laterally out of the way. The disc doesn't even need blades since adhesion works wonderfully well. Set the spinning discs in a tight chamber with circumferential exhaust slots designed to use the Coanda Effect to smooth the exhaust flow over a contoured baffle shroud. Form the stationary back surface of the disc chamber so that it is either flat or perhaps somewhat concave, with the baffle shroud extending somewhat past its edge to create a low turbulence zone. This back surface is now a solid stationary sail surface replacing the prop's former revolving back surfaces.



A one yard diameter disc has a surface area of slightly more than 1,000 sq. inches; lowering the pressure above one surface by just 20 percent creates a differential of nearly 3 psi, or almost 3,000 pounds, 1.5 tons, over the entire disc.

To Summarize: Most winds in our Earth's atmosphere move much slower than the molecules which make up the air comprising the flows. In fact mean molecular speeds of up to 500 meters per second are more than a match for the pushing prowess of any prop that has ever been designed or constructed. Therefore, if the molecules that surround us every second of most of our lives will provide more thrust on their own than the best props ever created, why bother with the prop for thrust? There is no point to it, and a stationary solid base will create more thrust per surface area than any prop ever made, as long as a frontal low pressure zone is maintained. And nothing mechanical maintains a low pressure zone better than a spinning bladeless centrifugal disc.