Re: DWFTTW


"Woody Brison" <woody_brison@xxxxxxxxx> wrote in message news:1173965845.707049.79350@xxxxxxxxxxxxxxxxxxxxxxxxxxxxxxx
On Mar 15, 3:37 am, "Androcles" <Engin...@xxxxxxxxxxxxxxxxxxxxxx>
wrote:
"Woody Brison" <woody_bri...@xxxxxxxxx> wrote in messagenews:1173931508.872792.312220@xxxxxxxxxxxxxxxxxxxxxxxxxxxxxxx
On Mar 12, 3:15 pm, "Androcles" <Engin...@xxxxxxxxxxxxxxxxxxxxxx>
wrote:
"Woody Brison" <woody_bri...@xxxxxxxxx> wrote in messagenews:1173736930.236273.74210@xxxxxxxxxxxxxxxxxxxxxxxxxxxxxx
An interesting demo of sailing downwind faster than the wind (DWFTTW)

<http://www.youtube.com/watch?v=aJpdWHFqHm0> ?

1 house per 21 seconds.
That's three houses a minute, 180 houses an hour.
I'd hope the mailman could do better on foot.
Given that the rag-flag drooped, where is the evidence for your
claim that it was faster than the wind?

A marathon is 26.22 miles. The current world record is
2 hours 4' 55" = 2.082 hours. That's 12.6 mph. If you
claim your mailman can do better than that *carrying a sack
of mail*, your skepticism over a little machine on wheels
going 13 mph seems odd.

http://upload.wikimedia.org/wikipedia/commons/thumb/a/a4/Hurricane_Ka...

Your odd notion of 13 mph being faster than the wind is a lot odd.
Obviously a chase car with a camera aboard was used, what
it didn't show was the tow truck and the nylon fishing line.

We are not all as gullible as you, odd bod.

Link didn't work...

Not my problem.



A fishing line was my first impression, too, but after
writing equations of motion, it seems to me that the
leverage to make this work does exist in the system. Jack
Goodman wrote a paper describing the vehicle

<http://www.ayrs.org/DWFTTW_from_Catalyst_N23_Jan_2006.pdf>

Wood

The propeller will act as an energy storage device, pushing the vehicle
when the wind drops and absorbing energy when wind speed is greater
than vehicle speed (gusts), both speeds being measured relative to the
ground. However, the vehicle will not exceed *mean* velocity of the
wind relative to the *wind*.

If you'd ever done any sailing you'd know that you don't feel
wind in your hair because you are moving with the air mass.
The propeller is simply a sail, if Goodman really wants to prove
the vehicle exceeds wind speed he'll need to mount an anemometer on it.
(Or run it in a wind tunnel.)
http://www.pfmt.org/standman/images/anameter1.gif

If Goodman's vehicle exceeds wind speed the anemometer will run
backwards. If the vehicle runs at exactly wind speed the anemometer
will stop. Any forward motion and the vehicle is travelling at less
than wind speed. The rag-flag is a crude anemometer but is
clearly perturbed by the turbulence from the propeller. Doubtless
Goodman chose a windy day for his run, and we all know
wind gusts, particularly around buildings. Chicago is called the
"Windy City" because wind is channelled into the artificial canyons
formed by the tall buildings.

Turbulence:
http://www.af.mil/shared/media/photodb/photos/060516-F-9712C-956.JPG

All motion is relative.
http://www.androcles01.pwp.blueyonder.co.uk/PoR/PoR.htm

Incidentally, this vehicle goes against the wind simply by gearing
the vertical shaft to the wheels:
http://home.comcast.net/~awatkins42/zephyr.html

Add a differential and it will turn without dragging.
http://www.androcles01.pwp.blueyonder.co.uk/Differential.gif

However, they are neither efficient or stable, you couldn't
run one on a public road.
Nature also has propellers in the form of the sycamore seed.
http://www.newscientist.com/blog/technology/uploaded_images/sycamore_seed-789909.jpg

These spin as they descend from trees and are carried on the wind
for miles.


.

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