Kiteforum Wiki Recent Changes FAQ How To Gear Useful Tips Safety Rules Schools Shops

 All times are UTC + 1 hour

 Page 25 of 29 [ 281 posts ] Go to page Previous  1 ... 22, 23, 24, 25, 26, 27, 28, 29  Next
 Print view Previous topic | Next topic
Author Message
 Post subject: Re: Downwind Faster Than The Wind - updatePosted: Wed Jun 13, 2012 3:19 pm
 Very Frequent Poster

Joined: Sat Jun 26, 2004 7:41 pm
Posts: 2470
Location: Mtn View, CA (S.F. Bay)
plummet wrote:
can we hook these two machines up in parallel so one is pushing and one is pulling into some form of crazy oscillating perpetual motion machine that powers the whole world with no emmisions?

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.

Top
 Post subject: Re: Downwind Faster Than The Wind - updatePosted: Wed Jun 13, 2012 7:52 pm
 Very Frequent Poster

Joined: Sat Jan 10, 2004 11:53 pm
Posts: 794
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!

Top
 Post subject: Re: Downwind Faster Than The Wind - updatePosted: Wed Jun 13, 2012 9:54 pm
 Very Frequent Poster

Joined: Sat Aug 29, 2009 11:25 pm
Posts: 1561
Location: The Naki
spork wrote:
plummet wrote:
can we hook these two machines up in parallel so one is pushing and one is pulling into some form of crazy oscillating perpetual motion machine that powers the whole world with no emmisions?

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.

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

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

Top
 Post subject: Re: Downwind Faster Than The Wind - updatePosted: Wed Jun 13, 2012 10:49 pm
 Very Frequent Poster

Joined: Sat Jun 26, 2004 7:41 pm
Posts: 2470
Location: Mtn View, CA (S.F. Bay)
tomatkins wrote:
I wonder if the speed, either with the wind or against the wind, can be estimated using a formula...

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.

Plummet wrote:
PS my kids use sporks on a regular basis!...

So does my wife.

Top
 Post subject: Re: Downwind Faster Than The Wind - updatePosted: Thu Jun 14, 2012 1:46 am
 Medium Poster

Joined: Tue Apr 17, 2012 3:27 pm
Posts: 155
Location: The New Old West
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

Top
 Post subject: Re: Downwind Faster Than The Wind - updatePosted: Thu Jun 14, 2012 3:00 am
 Very Frequent Poster

Joined: Sat Jun 26, 2004 7:41 pm
Posts: 2470
Location: Mtn View, CA (S.F. Bay)
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.

Top
 Post subject: Re: Downwind Faster Than The Wind - updatePosted: Thu Jun 14, 2012 3:17 am
 Medium Poster

Joined: Tue Apr 17, 2012 3:27 pm
Posts: 155
Location: The New Old West

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

it was cool looking too...
regards
fo

Top
 Post subject: Re: Downwind Faster Than The Wind - updatePosted: Thu Jun 14, 2012 3:36 am
 Very Frequent Poster

Joined: Sat Jun 26, 2004 7:41 pm
Posts: 2470
Location: Mtn View, CA (S.F. Bay)
Here's are some great photos his son sent me...

 Attachments: Friends helping with wind machine.jpg [ 87.22 KIB | Viewed 223 times ] Conveyor Belt Car.jpg [ 75.41 KIB | Viewed 223 times ] Andy sitting in wind machine.jpg [ 94.19 KIB | Viewed 223 times ]
Top
 Post subject: Re: Downwind Faster Than The Wind - updatePosted: Thu Jun 14, 2012 3:40 am
 Very Frequent Poster

Joined: Sat Jun 26, 2004 7:41 pm
Posts: 2470
Location: Mtn View, CA (S.F. Bay)
and...

 Attachments: Sheraton Hotel Group.jpg [ 84.93 KIB | Viewed 220 times ]
Top
 Post subject: Re: Downwind Faster Than The Wind - updatePosted: Thu Jun 14, 2012 5:37 am
 Medium Poster

Joined: Tue Apr 17, 2012 3:27 pm
Posts: 155
Location: The New Old West
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

Top
 Display posts from previous: All posts1 day7 days2 weeks1 month3 months6 months1 year Sort by AuthorPost timeSubject AscendingDescending
 Page 25 of 29 [ 281 posts ] Go to page Previous  1 ... 22, 23, 24, 25, 26, 27, 28, 29  Next

 All times are UTC + 1 hour

#### Who is online

Users browsing this forum: GregK, knot_moving, pj sofine and 14 guests

 You cannot post new topics in this forumYou cannot reply to topics in this forumYou cannot edit your posts in this forumYou cannot delete your posts in this forumYou cannot post attachments in this forum

Search for:
 Jump to:  Select a forum ------------------ Sports    Kitesurfing    Snow / Land Info    Special Offers    User News    Reviews    Safety    Info    Second Hand    Lost & Found    Events & Demos    Kids Club    New Members    Tricks and Moves    Polls    PDF Files    Weather    Contests    Help Me Board Styles    Kiteracer    Airstyle    Wakestyle    Wave Kite Groups    Board Builders    FKA, RickI column    Women's Forum    Flamer's Paradise Travel    Travel Instructors    Instructor Discussions    Africa       South Africa Instructors    North America       Florida Instructors Europe    Portugal    Spain    Germany    France South America    South America    Argentina Middle East    Israel