Zipp's wheel claims: do you believe them?
08-30-07, 07:37 PM
#151
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I have been trying to hold my tongue here, but I just cannot help myself.
The idea of negative drag coefficient violates the first law of thermodynamics. Imagine that your object has a negative drag coefficient and that object is initially stationary in an inertial reference frame in still air. In that scenario there is no kinetic energy anywhere. Now give that object a small push. Mathematically we can say that we give it an infinitesimal push. The object now has a relative air velocity and an aerodynamic force opposite to the direction of that air flow because the drag coefficient is negative. That will cause an acceleration of the object in the direction of the initial push, leading to an even greater relative air velocity, leading to an even higher relative airspeed, etc. The object now is continuously accelerating in the direction of the initial push. The object will move faster and faster all on its own. With such a device we can solve the world's energy problems! We have generated as much kinetic energy that we want out of nothing. Too bad that the first law of thermo does not allow this to happen. Perhaps the Zipp engineers will receive next year's Nobel Prize in Physics as well as untold trillions of dollars if they have patented their device.
This has nothing to do with dimples, or lift, or creative uses of flow by highly clever engineers. Negative drag coefficient violates the 1st law of thermo. It is totally BS.
The idea of negative drag coefficient violates the first law of thermodynamics. Imagine that your object has a negative drag coefficient and that object is initially stationary in an inertial reference frame in still air. In that scenario there is no kinetic energy anywhere. Now give that object a small push. Mathematically we can say that we give it an infinitesimal push. The object now has a relative air velocity and an aerodynamic force opposite to the direction of that air flow because the drag coefficient is negative. That will cause an acceleration of the object in the direction of the initial push, leading to an even greater relative air velocity, leading to an even higher relative airspeed, etc. The object now is continuously accelerating in the direction of the initial push. The object will move faster and faster all on its own. With such a device we can solve the world's energy problems! We have generated as much kinetic energy that we want out of nothing. Too bad that the first law of thermo does not allow this to happen. Perhaps the Zipp engineers will receive next year's Nobel Prize in Physics as well as untold trillions of dollars if they have patented their device.
This has nothing to do with dimples, or lift, or creative uses of flow by highly clever engineers. Negative drag coefficient violates the 1st law of thermo. It is totally BS.
So sailboats can't sail into the wind.
Man, you better tell the sailboat captains that they can't do it, because they think they're doing it right now. I don't want them to cause any universe-eating wormholes or something.
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08-30-07, 07:44 PM
#152
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At no time does a tacking sailboat have a negative drag coefficient.
08-30-07, 08:00 PM
#153
Peloton Shelter Dog
08-30-07, 08:29 PM
#154
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now THAT'S funny! what astounds me isn't the people that don't understand this; it's the ones with no understanding of it but will still try and push their opinions. the only people here with any credibility are the aerodynamics instructors; and since i work in aviation, and have a meager undestanding of this stuff, i'm gonna listen to them, i think. and in reply to VT - if you knew how far off some performance characteristics for airplanes deviate from their planned abilities, a 100-200 gram difference in wheel weight specs wouldn't concern you very much
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-Fyodor Dostoevsky's Grand Inquisitor
'In the end they will lay their freedom at our feet and say to us, "Make us your slaves, but feed us." '
-Fyodor Dostoevsky's Grand Inquisitor
08-30-07, 08:30 PM
#155
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But the sail still has positive force in the direction of travel. So - in the direction of travel of the sail - the only direction of interest - it has negative drag coefficient.
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Last edited by ElJamoquio; 08-30-07 at 09:42 PM.
08-30-07, 09:31 PM
#156
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Wusss wuss wusss wusss wussss
08-30-07, 09:40 PM
#157
Making a kilometer blurry
Well, exaggerated or not, the claims have hit cyclingnews now:
https://www.cyclingnews.com/tech/2007...ts/eurobike072
https://www.cyclingnews.com/tech/2007...ts/eurobike072
08-30-07, 10:20 PM
#158
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I have been trying to hold my tongue here, but I just cannot help myself.
The idea of negative drag coefficient violates the first law of thermodynamics. Imagine that your object has a negative drag coefficient and that object is initially stationary in an inertial reference frame in still air. In that scenario there is no kinetic energy anywhere. Now give that object a small push. Mathematically we can say that we give it an infinitesimal push. The object now has a relative air velocity and an aerodynamic force opposite to the direction of that air flow because the drag coefficient is negative. That will cause an acceleration of the object in the direction of the initial push, leading to an even greater relative air velocity, leading to an even higher relative airspeed, etc. The object now is continuously accelerating in the direction of the initial push. The object will move faster and faster all on its own. With such a device we can solve the world's energy problems! We have generated as much kinetic energy that we want out of nothing. Too bad that the first law of thermo does not allow this to happen. Perhaps the Zipp engineers will receive next year's Nobel Prize in Physics as well as untold trillions of dollars if they have patented their device.
This has nothing to do with dimples, or lift, or creative uses of flow by highly clever engineers. Negative drag coefficient violates the 1st law of thermo. It is totally BS.
The idea of negative drag coefficient violates the first law of thermodynamics. Imagine that your object has a negative drag coefficient and that object is initially stationary in an inertial reference frame in still air. In that scenario there is no kinetic energy anywhere. Now give that object a small push. Mathematically we can say that we give it an infinitesimal push. The object now has a relative air velocity and an aerodynamic force opposite to the direction of that air flow because the drag coefficient is negative. That will cause an acceleration of the object in the direction of the initial push, leading to an even greater relative air velocity, leading to an even higher relative airspeed, etc. The object now is continuously accelerating in the direction of the initial push. The object will move faster and faster all on its own. With such a device we can solve the world's energy problems! We have generated as much kinetic energy that we want out of nothing. Too bad that the first law of thermo does not allow this to happen. Perhaps the Zipp engineers will receive next year's Nobel Prize in Physics as well as untold trillions of dollars if they have patented their device.
This has nothing to do with dimples, or lift, or creative uses of flow by highly clever engineers. Negative drag coefficient violates the 1st law of thermo. It is totally BS.
Now do Part B: Repeat the analysis with a cross wind.
Hint: There's energy in the moving air.
Last edited by gcl8a; 08-30-07 at 10:31 PM.
08-30-07, 10:49 PM
#159
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08-30-07, 11:11 PM
#160
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Not all engineers are created equal...
08-30-07, 11:13 PM
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This thread is fantastic. I want to learn more about fluid mechanics now.
Oh, and enough with the golfball argument. Read the entire thread before posting.
Oh, and enough with the golfball argument. Read the entire thread before posting.
08-30-07, 11:43 PM
#162
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I did
08-31-07, 12:55 AM
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I'll settle this once and for all!!
Someone send me a set of zipps and I'll let you know the results.
PM me.
Someone send me a set of zipps and I'll let you know the results.
PM me.
08-31-07, 01:39 AM
#164
never easier, u go faster
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then you missed the part about other applications being ones other than a golf ball. 
wow, neg. drag but only when you use their tires. Nice! I'm sure some zipp executive got wood when pitched that idea.
zipp marketing reaches new heights... or lows... Anyway, I think I will start looking at the eurobike/interbike like I do superbowl commercials but without the intended funnies.
Hey maybe next year the dimples will have dimples for even more aero silliness. Hmm...maybe I should patent that one.
wow, neg. drag but only when you use their tires. Nice! I'm sure some zipp executive got wood when pitched that idea.
zipp marketing reaches new heights... or lows... Anyway, I think I will start looking at the eurobike/interbike like I do superbowl commercials but without the intended funnies.
Hey maybe next year the dimples will have dimples for even more aero silliness. Hmm...maybe I should patent that one.
08-31-07, 02:33 AM
#165
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08-31-07, 04:31 AM
#166
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In the aeronautics industry, a product often fails to achieve it's planned performance characteristics, or in some cases exceeds expectations. But the specs are always rigidly accurate.
You will never see a product that weighs a significantly different amount than it is spec'd at, or demonstrates other wild variances between the specs and the actual physical measurements, angles, etc.
If a product somehow made it through the line to the testing stage, and the physical characteristics were that far off spec, no engineer in the world would attempt to test theorized performance- they'd laugh and move on to the next product.
Don't scoff at 100-200 grams- remember that when compared to the overall weight of a performance wheelset, that is a substantial percentage of error... unnaceptable in any of the other industries that utilize the technologies the bike industry is pitching people...
Let me put it a different way... everyone here is debating whether or not a sexy bit of engineering works. No one seems to be concerned that the guy selling it has to do the bunny-goes-into-the-hole trick to get his shoe-laces tied in the morning... I'm not limiting my scorn to Zipp, but the entire industry...
Bike Industry: "This beautiful red car features micro-divots on the hood which reduces overall drag by .03 percent and increases fuel savings by .000834 percent."
Man: "That car is black."
Last edited by VT to CA; 08-31-07 at 04:47 AM.
08-31-07, 04:53 AM
#167
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08-31-07, 05:30 AM
#168
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08-31-07, 05:58 AM
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A tacking sailboat can move to windward but, it derives it's power from the wind energy that the skipper did not create. Assuming there is no wind, a rolling bicycle derives it's power only from the skipper, or gravity if going downhill. In any event, a wheel does not add power. It might be able to extract power someway from wind energy under a peculiar set of conditions much the way an airfoil does when the wind is askew but, for normal riding on flat surfaces with no pre-existing wind the wheel does not add energy.
08-31-07, 06:03 AM
#171
Making a kilometer blurry
Reed post #37 here:
Originally Posted by somezippguy
the disc does combine a honeycomb core center with hollow perimeter hoop...no spokes. the shape is the same one we developed in feb at the SD wind tunnel and it does in fact create -80 grams of drag at 15 degrees yaw using the 30-0 test protocole tom talked about. the negative drag window extends from 11-18 degrees and has 30-40 grams lower drag than any flat or lens disc between 0 and 20 degrees. using the 0-30 tunnel protocol it looks even better but experience tells us that protocol yields overly optimistc data.
we also tried doing it with lens center as well as a modified lens with our tire blending geometry and the results were very good wheel only but suffered in a bike..we think from the disc skin being too close to the seatstays.
we also tried doing it with lens center as well as a modified lens with our tire blending geometry and the results were very good wheel only but suffered in a bike..we think from the disc skin being too close to the seatstays.
08-31-07, 06:27 AM
#172
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08-31-07, 06:36 AM
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If everyone is such an expert why aren't they out designing the best wheels? I think everyone should stfu.
You guys crack me up. You spend $1000's of dollars on bike gear and probably couldn't ride a $5 prostitute to her full potential.
You guys crack me up. You spend $1000's of dollars on bike gear and probably couldn't ride a $5 prostitute to her full potential.
Last edited by gabdy; 08-31-07 at 06:41 AM.
08-31-07, 06:50 AM
#174
Making a kilometer blurry
08-31-07, 07:43 AM
#175
Senior Member
I had to stop reading at this point. Go back and read the thread. No one said anything about a negative drag coefficient.