View Single Post
Old 03-03-2006, 08:32 PM
flight flight is offline
Join Date: Mar 2000
Location: Newport News, VA, USA
Posts: 2,704
Originally Posted by Paradoxic
O.K., then, I guess we agree. Actually, what I am objecting to is your use of the word "clearly". This problem is difficult as a thought problem, and is more obvious when viewed as a closed-system physics equation.

If the plane does not move horizintally, then according to the rest of my analysis, the plane does not take off because the airflow generated by the engines alone is not sufficient to create enough lift with the wings.

Sorry, Cecil.
You have the same problem that everyone else who thinks the plane does not take off has: you are reading the problem differently from the rest of us. To quote an earlier post of mine:
Originally Posted by me with a little tweaking
Most people are coming to correct solution, they just interpret speed differently and diverge from there.

Group 1 (Cecil's flying group) say that when you say speed you are talking relative to a nearby building or a section of ground that is not the treadmill.

Group 2 (the stuck to the groud group) define speed relative to the ground immediately beneath the plane, aka, the moving surface of the treadmill.

Thus, for group 1 there is an increasing backward force on the wheels of the plane as it moves faster relative to a stationary object, but nowhere near enough to stop it from taking off. The wheels are creating friction as if the speed of the plane relative to the ground were 2V.

For group 2 however, the plane has a speed V relative to the surface of the treadmill. The surface of the treadmill has a speed -V relative to a stationary object. Thus (neglecting relativity) the plane has a speed 0 relative to a stationary object. An observer of the plane that has his view of the treadmill obstructed will not notice any motion in the plane. With no motion there is no lift and therefore the plane stays on the ground, whatever V you are talking about.

So, depending on what you define speed relative to, you have two very different problems.
So I ask you, if the speed of the plane is measured relative to a stationary object, and it is that speed that the treadmill mirrors, will the plane take off?

That is the question that Cecil (correctly) answered.