Wind-Powered Car Actually Moves Faster Than Wind Speed

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notsobright
notsobright Solar Expert Posts: 247 ✭✭
in Solar Skeptics, Hype, & Scams Corner #1
intresting..

http://www.popsci.com/cars/article/2010-06/wind-powered-car-looks-odd-answers-tricky-physics-question

I think a retest under strict scrutiny is in order here.
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  • niel
    niel Solar Expert Posts: 10,300 ✭✭✭✭
    #2
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    Re: Wind-Powered Car Actually Moves Faster Than Wind Speed

    pull over that car for exceeding the laws of physics.:p
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  • boB
    boB Solar Expert Posts: 1,030 ✭✭✭✭
    #3
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    Re: Wind-Powered Car Actually Moves Faster Than Wind Speed

    This statement comes across to me sorta like an extraordinary VAWT claim...

    "More pics and then some video once I get on a faster connection."

    boB
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  • russ
    russ Solar Expert Posts: 593 ✭✭
    #4
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    Re: Wind-Powered Car Actually Moves Faster Than Wind Speed

    Maybe they meant how fast the nose flipped up when a gust hit it?

    Partially sponsored by Google though - according to the greens it must be OK!
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  • boB
    boB Solar Expert Posts: 1,030 ✭✭✭✭
    #5
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    Re: Wind-Powered Car Actually Moves Faster Than Wind Speed
    russ wrote: »
    Partially sponsored by Google though - according to the greens it must be OK!

    I noticed that too. Usually that's a good thing. Hmmmm...
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  • dwh
    dwh Solar Expert Posts: 1,341 ✭✭✭
    #6
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    Re: Wind-Powered Car Actually Moves Faster Than Wind Speed

    That would rock if they could do it with a sailboat.
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  • russ
    russ Solar Expert Posts: 593 ✭✭
    #7
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    Re: Wind-Powered Car Actually Moves Faster Than Wind Speed

    Google with the net - very strong

    Google with their green investments - have they had any success yet? I have read of several failures I believe.

    It is just like Khosla - did good in one thing but his efforts in other areas are still mainly in talking.
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  • john p
    john p Solar Expert Posts: 814 ✭✭✭
    #8
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    Re: Wind-Powered Car Actually Moves Faster Than Wind Speed

    Those sail boards that run on wheels along the beach(dont know their corect name) can exceed the wind speed no problem. And that is fact
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  • notsobright
    notsobright Solar Expert Posts: 247 ✭✭
    #9
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    Re: Wind-Powered Car Actually Moves Faster Than Wind Speed

    sailboats allready exceed windspeeds.


    I dont understand how this is faster than the wind speed though since the wheels are gear driven from the prop. it seems that coupled with the rolling resistance would make it impossible. mabey the prop has a flyweel effect that contimues after the winds die down?


    those sailboards on wheels in a race with this would be an intresting competition.
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  • john p
    john p Solar Expert Posts: 814 ✭✭✭
    #10
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    Re: Wind-Powered Car Actually Moves Faster Than Wind Speed

    NOTSOBRIGHT..I dont understand how this is faster than the wind speed though since the wheels are gear driven from the prop. it seems that coupled with the rolling resistance would make it impossible. mabey the prop has a flyweel effect that contimues after the winds die down?What wheels are driven from what prop??? The things have 3 wheels that run free.. the thing it driven by a sail similar to a water going sail board.. Modern land sailors, generally known as "pilots," can go three to four times faster than the wind speed, because of Bernoulli's principle..The world land speed record for a wind powered vehicle was broken on 26 March 2009 by Richard Jenkins in his yacht Greenbird with a speed of 126.1 mph (202.9 km/h).[2] Wind speeds were fluctuating between 30–50 mph (48–80 km/h) at that time.[3][4]
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  • dwh
    dwh Solar Expert Posts: 1,341 ✭✭✭
    #11
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    Re: Wind-Powered Car Actually Moves Faster Than Wind Speed

    A) I'm not a sailor, so I dunno jack about sailboats. That they move faster than the wind is news to me. I'm having a little trouble wrapping my mind around exactly *how* they do that, but I'll look it up and learn something.

    B) The article says, "The wheels turn the car’s propeller, and the prop thrust pushes the car, which turns the wheels, Cavallaro says". Which indicates to me that the wheels aren't just freewheeling - there must be some sort of mechanical interconnect. No?
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  • notsobright
    notsobright Solar Expert Posts: 247 ✭✭
    #12
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    Re: Wind-Powered Car Actually Moves Faster Than Wind Speed
    john p wrote: »
    What wheels are driven from what prop??? The things have 3 wheels that run free.. the thing it driven by a sail similar to a water going sail board.. Modern land sailors, generally known as "pilots," can go three to four times faster than the wind speed, because of Bernoulli's principle..The world land speed record for a wind powered vehicle was broken on 26 March 2009 by Richard Jenkins in his yacht Greenbird with a speed of 126.1 mph (202.9 km/h).[2] Wind speeds were fluctuating between 30–50 mph (48–80 km/h) at that time.


    I wasnt referring to the skatesailers or whatever they are called.

    wow that greenbird is fast!
    dwh wrote: »
    The article says, "The wheels turn the car’s propeller, and the prop thrust pushes the car, which turns the wheels, Cavallaro says". Which indicates to me that the wheels aren't just freewheeling - there must be some sort of mechanical interconnect. No?


    I dont get it but apparantly it only works downhill. I was suprised to see that the axles have off ratchets with the handles cut off fit inside them instead of purpose machined gears. looks somewhat backyard there but seems to work OK
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  • john p
    john p Solar Expert Posts: 814 ✭✭✭
    #13
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    Re: Wind-Powered Car Actually Moves Faster Than Wind Speed

    What I was trying to get across is the FACT a wind powered vehicle can far exceed the speed of the wind.. example speed record 126mph in about 50mph wind Some dont seem to know this, some even stating it breakes the laws of physics.. Obviously that person knows nothing about such things . I was not able to read the original item as cant seem to find it.. it says "not available"
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  • boB
    boB Solar Expert Posts: 1,030 ✭✭✭✭
    #14
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    Re: Wind-Powered Car Actually Moves Faster Than Wind Speed
    dwh wrote: »
    A) I'm not a sailor, so I dunno jack about sailboats. That they move faster than the wind is news to me. I'm having a little trouble wrapping my mind around exactly *how* they do that, but I'll look it up and learn something.

    That's called Tacking, when done in a sailboat. And as I understand it, it is at an angle and against the wind.... back and forth, sideways, Understood using vectors and trigonometry.

    What I don't quite understand here is how they use the wheels and the prop, but I seem to remember that the article did mention something about the wheels and prop being tied together some how. Not enough information.

    boB
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  • niel
    niel Solar Expert Posts: 10,300 ✭✭✭✭
    #15
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    Re: Wind-Powered Car Actually Moves Faster Than Wind Speed
    john p wrote: »
    What I was trying to get across is the FACT a wind powered vehicle can far exceed the speed of the wind.. example speed record 126mph in about 50mph wind Some dont seem to know this, some even stating it breakes the laws of physics.. Obviously that person knows nothing about such things . I was not able to read the original item as cant seem to find it.. it says "not available"

    i wouldn't go that far, but i am with dwh in not understanding how they managed it. how was that principle used to allow the faster speeds? please try to explain rather than be critical.
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  • Cariboocoot
    Cariboocoot Banned Posts: 17,615 ✭✭✭
    #16
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    Re: Wind-Powered Car Actually Moves Faster Than Wind Speed

    A bit of info that might shed some light on the issue (or start another argument!).

    Wind surfers can go faster than wind speed. This is because they aren't just 'blown along' by the wind in the method of the ancient square sail, but rather use the Bernoulli Principle http://en.wikipedia.org/wiki/Bernoulli's_principle to create a pressure difference on either side of the sail. This is the same action which creates lift on an airplane wing, only sideways. The motive force is a function of the difference, rather than just the actual wind speed. It also means they can travel in a direction other than with the wind. This was discovered long ago, and used in sailing with triangular sails to advance beyond simple 'round the Mediterranean' travel.

    As for this car, where does the motive force come from to overcome the inertia and get it moving in the first place? Oh; it only goes down hill? About as good as a soap box racer then. Unless this article is very poorly written, this thing is pure BS. "Wheels turn the propeller which pushes the car which turns the wheels" is totally perpetual motion nonsense. I'd be willing to believe that wind acting on the prop could provide force to the wheels, as this has been done before. Notice how you can't buy such a design today. You won't be buying this thing anytime soon either, and it has nothing to do with oil company conspiracies, okay?

    And I do know a thing or two about which I speak: http://kaleidopsyche.deviantart.com/gallery/#/dohw1f
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  • john p
    john p Solar Expert Posts: 814 ✭✭✭
    #17
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    Re: Wind-Powered Car Actually Moves Faster Than Wind Speed

    Sorry Niel I know absolutely nothing about how you get a vehicle with a sail to go faster than the wind. Never even owned a sailing boat or anything with a sail only owned gas guzzling boats I had never heard of Bernoulli's principle until I read about it trying to find out how. Cariboocoots sems to have as good as an explanation as you likely to get..
    I apologize if I was sounding too critical.. It just anoyed me that there were posts that appeared to say exceeding the speed of the wind wasnt possible .
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  • niel
    niel Solar Expert Posts: 10,300 ✭✭✭✭
    #18
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    Re: Wind-Powered Car Actually Moves Faster Than Wind Speed

    no offense taken as i'm open minded and willing to learn. hey, maybe going faster than the speed of light will be possible with that principle.:confused:
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  • john p
    john p Solar Expert Posts: 814 ✭✭✭
    #19
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    Re: Wind-Powered Car Actually Moves Faster Than Wind Speed

    Not really sure but think there could be a possible physics problem or 2 to solve first.. for one navigation ,that could be a slight problem.another could be putting out the trash can from your space ship each week for removal :confused: If you going faster than speed of light you are going into the future so the can will be emptied before you put it out????????
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  • BB.
    BB. Super Moderators, Administrators Posts: 33,439 admin
    #20
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    Re: Wind-Powered Car Actually Moves Faster Than Wind Speed

    For my two cents--There is no way that a vehicle can exceed the speed of wind when running down-wind. Unless it is down hill or there is some alternative energy involved (battery/motor, pedal power, etc.). Once the vehicle has reached the same speed as the wind, there is no relative energy (difference between wind speed and ground speed) for the vehicle to extract any energy for forward motion).

    For low drag vehicles (wheels, ice, possibly boats/hydroplane, etc.)--With a cross wind (say from 90 degrees right or left)--even if the vehicle matches wind speed--because the wind is a cross wind--there is still a relative wind to the direction of travel that a sail can take advanative of (Bernelle's principle as above) which can still extract some energy from the cross-wind component to continue moving the vehicle forward.

    A modern sailboat can sail within ~22 degrees of the apparent wind (sail somewhat up wind) because of this effect. (apparent wind--remember that if you have wind from 90 degrees--as you move forward faster and faster, the wind appears to be coming more and more from the front--so if you are going very fast, you will hit the 22 degree limit and cannot go any faster--if using a triangular sail).

    I have no useful idea of how the propeller is supposed to work/help here... Helicopters can glide or auto-rotate if they have a complete power failure to a landing--but it is not a very efficient glide (unlike, for example, a sailplane wing).

    -Bill
    Near San Francisco California: 3.5kWatt Grid Tied Solar power system+small backup genset
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  • Dave Angelini
    Dave Angelini Solar Expert Posts: 6,746 ✭✭✭✭✭✭
    #21
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    Re: Wind-Powered Car Actually Moves Faster Than Wind Speed

    Keep in mind there are at least two kinds of sailboats and maybe more since I left the boating world for cash. A displacement hull like most sailboats will basically turn into a submarine if you had too much sail or horsepower. It will never out speed the wind except in the really big boats in low windspeeds.

    A planing hull will skim the waves and just keep going faster, and yes faster than the wind on certain angles to the wind. The Americas Cup is coming up and you will see some of these amazing boats as well as the monohulls!
    "we go where power lines don't" Sierra Nevada mountain area
       htps://offgridsolar1.com/
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  • Photowhit
    Photowhit Solar Expert Posts: 6,003 ✭✭✭✭✭
    #22
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    Re: Wind-Powered Car Actually Moves Faster Than Wind Speed

    I'm an old sailer, so I'll give this a go, with out trying to explain the "Bernoulli Effect"

    While it might seem hard to travel faster than wind if your light enough (have a large profile to weight, think balloon) it's hard not to travel near the speed of the wind.

    A sailboat traveling across the wind doesn't try to go down wind faster than the wind but traveling across the wind the wind 'try's' to get the sailboat to travel as fast as the wind. by traveling across the wind the sailboat never travels faster down wind than the wind, but travels faster point to point.

    I honestly don't understand how this works relative to the car...lol.
    Home system 4000 watt (Evergreen) array standing, with 2 Midnite Classic Lites,  Midnite E-panel, Magnum MS4024, Prosine 1800(now backup) and Exeltech 1100(former backup...lol), 660 ah 24v Forklift battery(now 10 years old). Off grid for 20 years (if I include 8 months on a bicycle).
    - Assorted other systems, pieces and to many panels in the closet to not do more projects.
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  • victor
    victor Registered Users Posts: 13 ✭
    #23
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    Re: Wind-Powered Car Actually Moves Faster Than Wind Speed
    notsobright wrote: »
    intresting..

    http://www.popsci.com/cars/article/2010-06/wind-powered-car-looks-odd-answers-tricky-physics-question

    I think a retest under strict scrutiny is in order here.

    The retest was performed under the strict scrutiny of the North American Land Sailing Association (NALSA):
    http://www.nalsa.org/DownWind.html
    The Blackbird, piloted by Rick Cavallaro sailed "directly downwind" at 27.7 mph in a sustained 10 mph wind, setting a record for ratio of "boat" speed to true wind speed of nearly 2.8.

    blackbirdside500.jpg

    For more information on how it works see the references i this wiki section:
    http://en.wikipedia.org/wiki/Sailing_faster_than_the_wind#Sailing_dead_downwind_faster_than_the_wind

    Especially:
    http://www.boatdesign.net/forums/attachments/propulsion/28167d1231128492-ddwfttw-directly-downwind-faster-than-wind-ddw2.pdf
    http://orbit.dtu.dk/getResource?recordId=241183&objectId=2&versionId=1
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  • jagec
    jagec Solar Expert Posts: 157 ✭✭
    #24
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    Re: Wind-Powered Car Actually Moves Faster Than Wind Speed
    BB. wrote: »
    For my two cents--There is no way that a vehicle can exceed the speed of wind when running down-wind. Unless it is down hill or there is some alternative energy involved (battery/motor, pedal power, etc.). Once the vehicle has reached the same speed as the wind, there is no relative energy (difference between wind speed and ground speed) for the vehicle to extract any energy for forward motion).

    Actually, my understanding was that racers could at times exceed the speed of wind while running down-wind by 'surfing' the waves. Of course, in that case they're extracting energy from both the wind and the waves, and so there's no violation of thermodynamics.
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  • john p
    john p Solar Expert Posts: 814 ✭✭✭
    #25
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    Re: Wind-Powered Car Actually Moves Faster Than Wind Speed

    its got nothing to do with surfing waves or mountain tops its a simple fact ..a vehicle powered by wind only can go faster than the wind.. you all trying to disprove a fact that is well know..ok i dont have a clue how its done but that dont mean its ok for me to try to discredit it.. i dont fully understand how nuclear reactors work either.. but its a fact they do.

    Saturday, March 28, 2009

    Richard Jenkins, an engineer from the United Kingdom, broke a record for the fastest speed attained in a wind-powered land vehicle on Friday.

    Jenkins managed to reach a speed of 126.1 miles per hour (202.9 kilometres per hour) in his Greenbird car along the plains of Nevada's Ivanpah Lake.

    The most basic principle of wind-powered vehicles is harnessing and optimising airflow. Just as airflow over an aircraft’s horizontal wing pushes the aircraft up, the flow of air over The Greenbird’s vertical sail pushes the vehicle forward.

    The Greenbird utilises a combination of technology, usually found on aircraft and Formula One, to achieve staggering efficiency. Made from carbon composites, the vehicle takes huge forces at top speed, being able to transfer up to one ton of side force into the ground.

    The crafts' design achieves staggering efficiency. It enables the land craft to travel at between 3 & 5 times the real wind speed, depending on the surface traction.
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  • BB.
    BB. Super Moderators, Administrators Posts: 33,439 admin
    #26
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    Re: Wind-Powered Car Actually Moves Faster Than Wind Speed

    I agree with "....transfer up to one ton of side force into the ground..." and "...depending on the surface traction." That is a traditional sail/wing with a keel to keep the vessel from sliding sideways (wheels griping ground--same thing).

    These guys are (as I understand) talking about down wind only, no side loads--Although, they allow for some variation in angle of wind as it cannot be controlled as in a laboratory or wind tunnel. Is this small amount of off-angle wind enough to account for the "results"--don't know, but probably not.

    They talked about testing the hypothesis using a endless belt in the lab from one of the linked documents...

    I am trying to figure out how a belt running one direction (backwards) in a still air lab can actually have the the "car" move "forwards".

    Since all motion is relative (moving belt no wind, vs fixed earth and air moving across it in direction of travel)--I am not sure how it can be done...

    If there are any side loads on this vehicle/wheels, then it is not a "pure" downwind speed machine.

    -Bill
    Near San Francisco California: 3.5kWatt Grid Tied Solar power system+small backup genset
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  • victor
    victor Registered Users Posts: 13 ✭
    #27
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    Re: Wind-Powered Car Actually Moves Faster Than Wind Speed
    BB. wrote: »
    Once the vehicle has reached the same speed as the wind, there is no relative energy (difference between wind speed and ground speed)
    As long as there is a true wind (air moves relative to the ground) you always see a velocity difference between air and ground, no matter how fast you move. And if you somehow reduce that difference (slow down the true wind) you are extracting wind energy.
    BB. wrote: »
    If there are any side loads on this vehicle/wheels, then it is not a "pure" downwind speed machine.
    In a real-world experiment you will never go exactly downwind. But it can be shown that the vehicle performs best, when going exactly downwind. And there are no side loads on the wheels then.

    However, even if the center of mass of this vehicle goes exactly downwind, the rotating airfoils are not, because they have a tangential velocity component as well. This animation might help to visualize this:
    http://www.youtube.com/watch?v=UGRFb8yNtBo
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  • BB.
    BB. Super Moderators, Administrators Posts: 33,439 admin
    #28
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    Re: Wind-Powered Car Actually Moves Faster Than Wind Speed

    Victor,

    Are the rotating blades providing thrust or drag when the vehicle is going faster than the wind dead downwind (in steady state conditions--constant vehicle speed and constant wind)?

    -Bill
    Near San Francisco California: 3.5kWatt Grid Tied Solar power system+small backup genset
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  • victor
    victor Registered Users Posts: 13 ✭
    #29
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    Re: Wind-Powered Car Actually Moves Faster Than Wind Speed
    BB. wrote: »
    Are the rotating blades providing thrust or drag when the vehicle is going faster than the wind dead downwind (in steady state conditions--constant vehicle speed and constant wind)?
    There is a simple way to figure that out:

    1) To extract wind energy you have to slow down the true wind

    2) When going directly downwind (no matter at what speed) the only way to achieve (1) is to push the air backwards.

    3) If you push air backwards, it will push you forward (Newtons 3rd law)

    So, the rotor always creates forward thrust: It works as a propeller.
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  • BB.
    BB. Super Moderators, Administrators Posts: 33,439 admin
    #30
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    Re: Wind-Powered Car Actually Moves Faster Than Wind Speed

    So the torque to turn the propeller to provide forward thrust comes from the linkage to the wheels?

    And therefore, the wheels are retarding forward motion?

    -Bill
    Near San Francisco California: 3.5kWatt Grid Tied Solar power system+small backup genset
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  • victor
    victor Registered Users Posts: 13 ✭
    #31
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    Re: Wind-Powered Car Actually Moves Faster Than Wind Speed
    BB. wrote: »
    So the torque to turn the propeller to provide forward thrust comes from the linkage to the wheels?

    And therefore, the wheels are retarding forward motion?

    Yes, the wheels are braking, but the propeller is pushing forward more than they brake.

    In the reference frame of the vehicle, it works like a gear box: A small input force (braking) coming in at high speed (ground speed) is transformed into a larger output force (propeller thrust) going out at a lower speed (air speed)
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