re: Can this 747 take off?

Think about this scenario…

You have a small 6” wingspan model plane made of very light balsa wood, and a little propeller. The plane is so light weight that it doesn’t really need that much speed to get airborne. Because of this, the lift off velocity is attainable by the treadmill in your basement.

You set the tread mill to 0 degrees angle and it is flat with no angle relative to normal plane gravity.

Then you set the plane on the treadmill, and turn the treadmill on. The treadmill starts and the plane rides the treadmill right off the back. You realize you need to hold the airplane in place with your hand while the propeller is not spinning or else it will ride off the back of the treadmill, even though it is on wheels. The hot wheel car also rides off the back just like this even though it has wheels.

Since you need to hold the airplane in place to keep it from riding off the back, there is a force being transmitted that you must overcome…. Even though there are wheels.

So you turn the propeller on and the plane starts to creep forward, now you increase tread speed, and the plane slows its forward progress, you increase a bit more, and the plane stops but the propeller is still spinning.

You have balanced the forces.