[RedDevil]

Well, perpetuum mobiles pretend to work without a source of power. they create something out of nothing, like the 53th card in a deck.

The case this thread is about, and all of its examples, do have a power input: the speed difference between two media.

Some people struggle with that concept. Like the thread mill experiment: if there is no wind, nothing can move the car they think.

They fail to grasp that while there's no wind, the tread does move. The propeller can still create a force by turning. That force allows the wheels to drive the shaft that turns the propeller.

As for scientific rigor: notice how Aerohead refers to a lot what I've written but nothing about the equations and calculations, nothing about how the propeller moves the air backwards relative to the car but forwards relative to the ground.

Aha, the circle goes round, perpetuum mobile after all?
Not so fast.
The propeller does not have tu push the air away as fast as the thread runs!
It does move slower than the thread, so it requires less power than the wheels provide when they turn over a greater distance under the same force!

Just like the roller where the top wheel is turning against the movement of the plank, but slower than the wheels that touch the floor.
It is essential that the top roller goes slower than the floor rollers, just like it is essential that the propeller pushes the air away at a lower speed than the wheels turn.

But if that is too difficult to get and making jokes and insulting the people who do get how it works and accusing those who actually built these crafts is up your alley, well... we're done talking then.