I googled DDWFTTW and still don't get it.

[NoEyeDeer]

Originally Posted by daiquiri

Oh, it's so nice to discover that I didn't get a heck about it till now. Not that I've ever really applied actually, but still...
Thanks for the correction. Apart the wheel-to-prop gear ratio, is the rest of my post correct?

Yes it is.

[Cloxxki]

Basically, if a standardized variometic linked prop/turbine were to be affixed to any car or bike, it could add to top speed. Cumbersome, yes :-)

Headwinds will be the most wanted application (who doesn't hate them?), as placing the turbine right in front of the rider, it would even reduce the rider's own wind drag.

Imagine a typical bike record aerodynamic recumbent cigar. Already quick going into headwinds.
A 1m across prop (and outriggers) could add some serious thrust. Let's say the headwind is 15m/s. Bike also coasting at 15m/s (yes it can, for an hour or better I guestimate).
The 1m prop has a much greater frontal surface than the bike itself. The bike would be merely a small extention behind the prop's core.
Such a setup might come close to reaching 15m/s ground speed, before the rider starts pedaling along. Blackbird is going to do that, I have faith in that team. adding pedal power, 20m/s+ is on the cards.

Oh, and in tailwinds, let's say it could conservatively double the 15m/s of the wind, to go 30m/s. That's still belong the propless top sprinting speed, but well above the one-hour cruise speed. And then the rider decides to "crank it up"...

Performance (terminal speed) greatly comes down to prop size vs. cockpit size. The rest is a matter of optimization within those parameters. You'll see slick small cockpits and huge props/turbines.
I want this on special trains. With wind deflectors all along the track. More weight, but theoretically just one body to displace air. Above the tracks, the wind would always be right over the tracks, thanks to the delfectors. And canalized for greater push, too. And there comes the vehicle which favors tailwinds...
When there's no train for a moments, turbines sit above the tracks to extract lots of the available energy, and feed the grid. Of via capacitor banks, boost the next train's pass. It's self-generated green energy, pump it into the bullit train, why not?

[A.T.]

Originally Posted by Squidly-Diddly

OK, now I'm getting it after remembering my idea I had as a kid to sail 'straight up wind' by connecting at least two sail boats with some sort of scissors so they would tack upwind towards and away from each other, but the frame would be going straight upwind.

That is a good way to think about it. Two boats that can achieve downwind VMG > windspeed can be connected to a single catamaran with two moving parts. The propeller just makes this more compact and practical:

Originally Posted by Squidly-Diddly

I thinking of it as backblast from prop is getting pushed by the wind as it is still slower(groundspeed) than the wind.

That is rather not a good way to think about it. When going faster than wind the vehicle doesn't care if the backblast from prop behind it gets re-accelerated by the rest of the airmass or not. It is getting new, fast moving air from the front and slows it down (relative to the ground) with the propeller.

But during the acceleration phase, around 0.5 - 1.0 windspeed, the re-acceleration of the backblast might be relevant. However, since the vehicle is not enclosed within a pipe you cannot have a buildup of high pressure cushion there.

[TeddyDiver]

Or better to forget the ground alltogether.. think only about two fluids having different velocities.. it's pretty much harvesting energy of the remainder..

[kerosene]

Yeah Teddy that is good way of thinking it. I did the animation above and had also and idea of two parallel wind tunnels with a "cart" that has a prop in one and turbine in another. This would take away the confusion that ground is special.