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spork

We've discussed a wind powered vehicle that goes directly downwind faster than the wind on this forum - and as I recall, there were plenty of non-believers.

I'm trying to get the Mythbusters to do a segment on this (and prove or disprove it for all). But I don't have anyone on that forum pointing out the reasons it should not work. Anyone willing to have the other side of the debate there?

JDyer · Posted: Sun Oct 12, 2008 7:40 am Post subject:

nope.
I was a non believer but from the last go around you proved to me that it could be done (in theory). I'm just waiting till you get off your ass and build one for proof of concept.

I like the mythbusters show but remember that ratings is all that matters and to the general public, DWFTTW is not ratings material.

spork · Posted: Sun Oct 12, 2008 8:38 am Post subject:

BubbleBoy · 2 thumbs up Joined: 31 Jan 2008 Posts: 2217

I've heard that POAT was one their (if not the) highest rated shows.

I think the segment can be made very interesting. The thread on the mythbusters site is one of the most popular ever.

JB

spork · Posted: Sun Oct 12, 2008 10:26 am Post subject:

SeeMarkFly

SeeMarkFly

BubbleBoy · 2 thumbs up Joined: 31 Jan 2008 Posts: 2217

SeeMarkFly:
>What would be wrong with this statement.....
>If your device could go downwind faster than the speed
>of the wind.... then it SHOULD also be able to move when
>there was no wind at all.

The only thing wrong with that statement is that it's false.

When there is no wind at all relative to the surface, there is no relative motion to exploit between two mediums. As long as there *is* relative motion, there is the potential for energy to be removed.

To put it another way, when you're on the cart going the same speed as the wind, an onboard observer could easily say "there is no wind ... it's a calm day". However, when they looked down at the pavement, they would say "but that road is sure as heck whizzing by". It's all a matter of frame of reference ... which medium is moving and which is not? But no matter which frame you choose, something is whizzing by.

If DWFTTW defied the laws of physics, and were inherently over unity, ordinary sailing vessels could not outrun their power sources. Additionally, ice boats, land yachts and even top of the line racing sailboats regularly achieve VMG (velocity made good) greater than the velocity of the wind.

JB

BubbleBoy · 2 thumbs up Joined: 31 Jan 2008 Posts: 2217

SeeMarkFly:
>Anything faster than the wind would be
>working into a headwind.

Yes it would ... wind powered craft work into headwinds all the time.

>So I can only assume that you are talking about an
>over-unity device. (something that makes more
>energy than it uses)

Nope -- it's a user of energy, not a producer. The energy comes from the wind. If the wind stops blowing (relative to the ground), the cart stops moving.

JB

SeeMarkFly · Posted: Sun Oct 12, 2008 12:32 pm Post subject:

SeeMarkFly · Posted: Sun Oct 12, 2008 1:09 pm Post subject:

dayhead · Posted: Sun Oct 12, 2008 4:09 pm Post subject:

Mythbusters is designed to entertain those with no education or experience in physics and mechanics.

The last time I bothered to watch they did a test to see if a pick-up truck would get better gas mileage with the tailgate lowered or up.

They rented two "identical" trucks and wasted a lot of time and fuel to prove something that my brother and I proved in about 15 or 20 minutes by simply coasting down a hill twice, once with it up and once with it down.

Yes, the truck has less air resistance with it down.

But I'm sure the TV viewing public found their test more entertaining than they would have found ours.

But I can't watch their show because I get hoarse screaming at them.

AP · Posted: Sun Oct 12, 2008 5:11 pm Post subject:

Please don't flame me if I am wrong. I am a SNAG. Rolling Eyes

I still haven't got the understanding of how a wind powered vehicle can start its roll from zero, go directly downwind eventually exceeding the wind velocity. Excluding friction I can only see a groundspeed equalling the wind speed. Then I thought of using a wing/sail, like a yacht, at just the correct AoA to displace its airflow thereby adding drive as a component from the resultant lift. But in reality this should be very difficult since an AoA greater than about 15 degrees creates stall.

Maybe if you travel obliquely to the wind and build up velocity so the ground speed vector exceeds the downwind air speed vector by a good margin and then turn the craft directly downwind the momentum should have the craft traveling for a time downwind and parallel to the wind direction in excess of wind veolcity. But this is not sustainable, eventually the craft will slow down to and below wind.

Please explain. Me no understand. Sad

Wingspan34 · Posted: Sun Oct 12, 2008 6:21 pm Post subject:

AP · Posted: Sun Oct 12, 2008 6:28 pm Post subject:

SNAG: Sensitive new-age guy.

Sensitive New Age Guys Home
D: A term used to describe a man who listens to his partner, is sensitive to her (or his) concerns, and gives them lots of 'space'.
It was a good way for a man to describe himself if he wanted to get laid in the mid 1980s. It no longer is.
See
Political Correctness

cheer

BubbleBoy · 2 thumbs up Joined: 31 Jan 2008 Posts: 2217

BubbleBoy · 2 thumbs up Joined: 31 Jan 2008 Posts: 2217

BubbleBoy · 2 thumbs up Joined: 31 Jan 2008 Posts: 2217

AP · Posted: Sun Oct 12, 2008 6:45 pm Post subject:

OK I think I follow you BB.
And the average downwind speed of the ice boat is faster than the steady 15mph southery wind.
Say the straight line course is 15mi the ice boat in tacking with the wind completes the course in under an hour.

spork

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