It sounds like you're onto my evil scheme. The only problem I have yet to solve is that it all grinds to a stop when the wind stops.

I wonder if the speed, either with the wind or against the wind, can be estimated using a formula, based on the power generated by the length of either the turbine or propeller blade. It would seem that the part of the vehicle that "resists" the 'air' in both directions is the carraige ( wheels, frame, mast, etc), and this part would remain the same in cross sectional size, as the length of the propeller or turbine blades changed. The length of the blades would of course, establish the diameter of the circle, through which they sweep, and it seems that it would follow that the cross sectional size of that circle would determine the power being fed into the system.

If the above hypothesis is true, then it would seem that "bigger is better"... that is that the bigger the blade and the smaller the vehicle chassis, the faster the vehicle would go... and that a formula based on the cross section size of the vehicle and the sweep of its blades would express this relationship.

If this were true, then it would seem that the limiting factor to the ultimate speed upwind or downwind, would be based on the weight and strength of the materials used in the construction of the vehicle and its blades... so, the ultimate speed would be just a hair shy of the catastrophic collapse of the contraption.

"Rember the Yellowpages" ... Wear your helmet!

You just need to get you machine into a jet stream then don't you!...

PS my kids use sporks on a regular basis!...

When designing the vehicle I wrote a simulation to compute the acceleration profile and top speed based on a number of inputs - among them: prop/turbine efficiency, drive-train efficiency, rolling resistance, and aero drag. This thing is much more about efficiency than it is about brute force. That being said, you can definitely make a bigger prop or turbine more efficient than a smaller one because you're accelerating a larger amount of air through a smaller delta-V.

Momentum (and therefore thrust) is proportional to Mass x velocity while energy is proportional to Mass x velocity ^2. So it's far more efficient to move a lot of air through a smaller delta-V. That's why helicopters can hover while an airplane of the same weight and horsepower can't.

Using my simulation, I estimated a downwind speed of 3.14X wind speed (being slightly coy), and an upwind speed of 2X wind speed.

Our best downwind runs have been in the 3.5X realm with our official record at 2.8X. Our only upwind tests show us in the region of 2X. So the simulation has been more accurate than I probably would have expected.



So does my wife.

Hey Spork,

Have you still the link to the guy who first designed and built this Gizmo...I think it was in the early days of the last century, or maybe late in the century before 1880 ish maybe?

You posted a picture of it once, and I was thinking it would be cool to compare the stats...

His was huge, and made out of timber as I recall...

Thanks ( props on the effort bye the way--way cool)
Regards
fo

The guy you're probably thinking of is Andrew Bauer. We learned of him not long after I posted the problem here as a brain-teaser. In doing further investigation, we learned that Bauer had not actually thought of the idea, but had learned of it from a student paper written some 20 years earlier.

Bauer built a manned cart to settle a friendly bet between himself and A.M.O. Smith of Douglas Aircraft. Bauer won the bet with that vehicle, but we've learned things since then that suggest he might not have exceeded wind speed. It turns out that he claims to have exceeded wind speed only briefly and by a small amount. Given the placement of his streamer, we've come to see that it is significantly affected both by the induced prop wash in front of the prop and by the wind gradient. Our low streamers turn around significantly earlier than our higher streamers.

That being said, there is no doubt he could have convincingly settled the bet if he had to. He had problems with the chain drive and stopped the experiments when he and his critics were satisfied. He later made models that he demonstrated on a home made treadmill, and they clearly demonstrated DDWFTTW travel. He demonstrated such carts for the engineers at Aerovironment on at least one occasion.

Unfortunately, Bauer was unable to discuss any of this by the time we learned of his efforts, and has since died. We have spoken to his relatives and colleagues however. I sure wish we'd had the chance to meet him.

We have not been able to learn the name of the student that authored the paper that inspired Bauer to build his cart.

What a thorough reply ...

Thank you I'll see if can find that picture...

it was cool looking too...
regards
fo

Here's are some great photos his son sent me...

and...

Nice....

I keep picturing a Black and white shot---Bolar Hats, vests and vintage period clothes...

Looked to be in the Wright era...???

Maybe I'm mistaken? now that would be news...ha ha

Did you ever get your TV spot on Myth Busters?

Thanks, great shots, innovative guys with a wind based hobby, what could be cooler than that?

Best
fo