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Old 07-31-2021, 03:18 AM   #131 (permalink)
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A boat can tack alternating to port and starboard, downwind, with an averaged speed parallel to the wind vector, faster than the wind speed.

Now take two boats scissoring back and forth and connect a rope between them that somehow won't get tangled and always stays taught. Connect a 3rd boat, without a sail, to the midpoint of the rope.

Since both sailboats are exceeding the linear wind speed and they're dragging the 3rd boat with them, the 3rd boat must also exceed the linear wind speed in a straight line.

It's like a 2 dimensional projection of the two boats on a steady tack around and along a cylinder, linked solidly together. The midpoint of the connection is not tacking yet since boat boats are on a wind speed + tack, the connection between them must also exceed the wind speed.

Something else to think on is how fast aircraft and the Cheetah "decelerate" air flowing into their engine intakes and nostrils so they can breathe properly.

"Decelerate" is the wrong word even though it's commonly used to describe what's being done. They're really accelerating the air up to close to the velocity of the aircraft or animal right as it flows into the intakes and nostrils.

When a Cheetah bursts up to 70 MPH the shape of its nose must "grab onto" the air in the immediate area and alter its speed so that as it goes into its nostrils the airspeed relative to the notsrils is perhaps 2 MPH. But relative to the outside environment if there is no wind, what the Cheetah's nose is doing is pushing a bit of air up to ~68 MPH. I wonder if anyone has examined the aerodynamics of the nose as a limiter on the cat's top speed duration? Perhaps it can only keep the high relative speed air moving ahead of its nostrils for a few seconds at a time? Could be that the air pressure overcomes the strength of any muscles involved in adjusting nose shape or the stiffness of nasal tissues. Once the pressure distorts the nose from optimal shape, the pressure wave enters the nostrils and the cat suffers a "compressor stall".

Suddenly having the 60+ MPH relative airspeed moving into its nostrils would be analogous to the intake shockwave on a supersonic aircraft falling too far back into the engine intake. (Minus the engine flameouts, flat spins, and crashing.)

Could a Cheetah maintain top speed for longer with a strong tailwind so its nose doesn't have to push the air in front of it as strongly?

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Old 07-31-2021, 11:41 PM   #132 (permalink)
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Quote:
Originally Posted by freebeard View Post
Technically, it is a 'parlor trick' AKA unscalable scientific inquiry.

No way you'll move freight on the Interstate that way.
Ahh, my mistake; upon looking it up, I had the wrong idea in mind of what that phrase meant.

But then... then I guess the response becomes "they weren't claiming in the video that it could be used to move freight". It says right up front that it was built to settle a physics debate, not to be practical.
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Old 08-01-2021, 07:37 PM   #133 (permalink)
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Quote:
Originally Posted by freebeard View Post
Technically, it is a 'parlor trick' AKA unscalable scientific inquiry.

No way you'll move freight on the Interstate that way.
The Interstate, no. There are no conventional sailing freight haulers on the Interstate now either.
But the concept can be applied to ships to allow them to sail in any direction, like straight against the wind and also straight down the wind. Maybe that won't be faster than the wind, but even getting close to wind speed downwind would be an improvement over using traditional sails.

There even does not need to be a physical link between the (air) propeller and the (water) propeller, like there is between the propeller and the wheels of the Blackbird. Each could be connected to a motor/generator and do whatever is best, even if that's drawing from batteries in a wind lull. At other times the principle will work as intended.
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Old 08-01-2021, 07:50 PM   #134 (permalink)
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Point taken.

Quote:
even getting close to wind speed downwind would be an improvement
Not being the son of a sailor, I didn't know this. Hydrodynamic drag?

How does this work?

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Old 08-01-2021, 09:39 PM   #135 (permalink)
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I remember seeing pictures of that car in popular scientific magazines when I was a kid. I couldn't work out how that works back then and I'm not too sure today either.

But it is a hybrid. Maybe the driver helps out by breaking winds too.
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Old 08-05-2021, 06:18 PM   #136 (permalink)
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Often the problem is getting to know why something works.
According to Richard Feynman the problem with that again is in the why part:

Why do magnets repel each other? The answer may surprise you in a different way than you'd imagine.
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Old 08-05-2021, 10:17 PM   #137 (permalink)
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Listening to Feynman is a joy.

It's too bad the interviewer wasn't up to the task. We might have found out why he 'feels' things in the first place. Good insight that a magnet is not dissimilar to his finger not going through the arm of the chair.
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Old 08-06-2021, 04:24 PM   #138 (permalink)
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I stumbled upon another Veritasium video, probably because the Algorithm knows me by now, and I was watching it thinking
Quote:
Nice, but not relevant to the Blackbird thread
And then after 7 minutes, BOOM, there it was!

The Bayes Theorem. It does not provide anything with certainty.
All it can do is shift your level of doubt, and you have to start with some doubt to begin with.
So? Absolutely essential!
Even if Bayes himself did not think so, but what did he know? With certainty?
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Old 10-21-2021, 11:43 AM   #139 (permalink)
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Another scientific principle which seems to defy logic and generates debate over its cause: the Chain Fountain.

Quite funny, and amazing how high it can rise just by the force pushing down on one side of each ball when it gets yanked up on the other side, which if obstructed helps lift the ball itself faster. At least, that's my nutshell version of how it works...

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