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Messages - A.T.

1
Science / Re: Direct Down Wind Faster Than The Wind
I was thinking, instead of a treadmill, maybe the cart could run on a round revolving platform like a merry-go-round, Just bend it slightly so it runs in a circle. That would eliminate the problem of the cart running off the end of the treadmill all the time.

Go back to page 1:
http://talkrational.org/index.php/topic,24.msg1863.html#msg1863

2
Science / Re: Direct Down Wind Faster Than The Wind
Inman Harvey, from the University of Sussex, uses DDWFTTW as one example where linear cause-effect reasoning fails.:

http://ensoseminars.com/media/recommended_reading/harvey_circles_submitted.pdf
3
Science / Re: Direct Down Wind Faster Than The Wind
But my post 1575 is not about that, but about how downwind faster than wind and upwind, are just reversed cases of each other, and how you have to reverse power transmission between them.

Here some simple analogies for this:

https://www.youtube.com/watch?v=za_rPKSwiyc

https://www.youtube.com/watch?v=pw_B2MnMqZs


And here John Denker's explanation of it:

https://www.av8n.com/physics/sailing-upwind-downwind.htm
4
Science / Re: Direct Down Wind Faster Than The Wind
I don't think the last two responses followed my point, or got the point I was trying to make regarding the "BOX" on the treadmill.
Yes, you basically describe Galilean Relativity, and how the Cart cannot tell the difference between airmass moving vs. surface moving - only the relative velocities matter. That's the idea behind the controlled treadmill test.

But my post 1575 is not about that, but about how downwind faster than wind and upwind, are just reversed cases of each other, and how you have to reverse power transmission between them.

Here some simple analogies for this:

https://www.youtube.com/watch?v=za_rPKSwiyc

https://www.youtube.com/watch?v=pw_B2MnMqZs
5
Science / Re: Direct Down Wind Faster Than The Wind
How is a cart with a propeller traveling with a 10mph wind 3x the speed of the wind with an apparent headwind of 20mph different from a cart traveling forward into an actual 20mph headwind and utilizing that headwind to go half again faster than the wind?
The difference is obvious:

Downind faster than the wind: airspeed < groundspeed
Upwind: airspeed > groundspeed

For propulsion in steady state, energy conservation demands that you harvest energy at the faster relative speed, and generate propulsion at the slower relative speed.

This is described on page 12 of this solution sheet for a Physics Olympiad test:
http://www.aapt.org/physicsteam/2013/upload/E3-1-7-solutions.pdf

And in more detail in this paper:
http://orbit.dtu.dk/fedora/objects/orbit:55484/datastreams/file_3748519/content
6
Science / Re: Direct Down Wind Faster Than The Wind
lets just say the belt is infinitely long so the cart does not "know" that it wraps around some cylinders.
You don't need an infinite belt. If the cart only interacts with the straight part of the belt, it's irrelevant happens at the rollers.
7
Science / Re: Direct Down Wind Faster Than The Wind
Something like this article for the Society for Industrial and Applied Mathematics will particularly enrage our resident crackpot since he knows it is a thoroughly peer reviewed scenario just as the AAPT was.
BTW, the AAPT solution is still posted, four years after Harold announced they will have to retract and answer for it:
http://www.aapt.org/physicsteam/2013/upload/E3-1-7-solutions.pdf
8
Science / Re: Direct Down Wind Faster Than The Wind
DDWFTTW post by Mark Levi, professor of mathematics at the Pennsylvania State University, writing for the Society for Industrial and Applied Mathematics:

https://sinews.siam.org/Details-Page/downwind-faster-than-the-wind
9
Science / Re: Direct Down Wind Faster Than The Wind
I think this indicates the likelihood that tobermoryphil's (that's a mouthful) idea of the moving wave giving enough slope lift to sustain the albatross is valid.
Flying along the wave crests definitely helps to save energy, but the main energy input comes from dynamic soaring. Especially when making progress against the wind, or downwind, faster than the wind.

10
Science / Re: Direct Down Wind Faster Than The Wind
At indoor model flying meetings, you sometimes get the odd nutcase walking around the room with a sheet of card held at an angle. In front of him is a small, very light, glider, usually made from thin Styrofoam, with a flying speed of 3 or 4 mph. As long as you keep walking and moving the slope through the air, the glider will keep flying. 
An easy experiment to try!

Many videos of this online:

https://www.youtube.com/watch?v=LGZN1-diDjU
11
Science / Re: Direct Down Wind Faster Than The Wind
 Colin "Dynamic soaring in uniform wind" Taylor has made a video:

https://www.youtube.com/watch?v=CdaoiplgyII

He should have spent his time learning some physics instead.

You might still  remember him from a discussion here on TR and this:
https://www.bou.org.uk/dynamic-soaring/
Debunked here:
https://www.bou.org.uk/birds-and-dynamic-soaring/



12
Science / Re: Direct Down Wind Faster Than The Wind
Looks like the Aeolus carts finally went faster than the wind directly upwind:

http://www.windenergyevents.com/uncategorized/danish-team-races-faster-than-head-wind-with-10176/

And it was the DTU, probably the most successful team over the years, which also wrote the paper on DDWFTTW:

http://orbit.dtu.dk/fedora/objects/orbit:55484/datastreams/file_3748519/content
Thanks for the links, A.T.  Too bad (or not?) the H folk are not here to "appreciate" this.

BTW: The winning team optimized their cart on a dynamometer, so Galilean Relativity seems still to work fine:

https://www.youtube.com/watch?v=Sd2I3dr3bL8
13
Science / Re: Direct Down Wind Faster Than The Wind
Looks like the Aeolus carts finally went faster than the wind directly upwind:

http://www.windenergyevents.com/uncategorized/danish-team-races-faster-than-head-wind-with-10176/

And it was the DTU, probably the most successful team over the years, which also wrote the paper on DDWFTTW:

http://orbit.dtu.dk/fedora/objects/orbit:55484/datastreams/file_3748519/content
14
Science / Re: Direct Down Wind Faster Than The Wind
I just received two requests to give talks about the downwind cart 30 minutes apart.  This hasn't come up in years.
Yesterday I visited the physics department in one of the biggest German Universities (Free University of Berlin), during an open house day where they show cool science stuff to the public. One of the demos was this one build to educate their students about DDWFTTW:

https://www.youtube.com/watch?v=2JL_7cx7lnc

They also knew about the Blackbird and noted that it was the most impressive demo of the concept.