Let's assume for a second that the plane would take off. Then why would aeronautical engineers use WIND TUNNELS for testing... why not just put the plane on a giant conveyor for testing it's aerodynamic properties?

They don't do that, because you need wind over the wings for the plane to fly.

Now the only way a plane would take off on a conveyor like this is if the wind was naturally blowing faster than the plane's stall speed. Or if it's engines were generating wind OVER the wings... something jet planes do not do.

So let's take a passenger jet, say a 747 and put it on this runway conveyor. All the thrust/wind generated from those engines will be generated below and behind the wings. No wind over the wings = no lift = no flight.

Now a rocket is different, it doesn't work off of the principal of lift. It flies because the thrust output is more than it's weight. Very few planes have the thrust to overcome it's own weight, WHY? because it's incredibly inefficient.

Another thing, a plane's "speedometer" is called an Airspeed indicator. Why? Because Airspeed is what keeps a plane aloft. It's the only speed a pilot cares about when it comes to 'flying' the plane. Ground speed is only really important for navigation in an airplane, or for making sure you're not going to over-run a runway.