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Old 03-03-2006, 04:25 PM
Paradoxic Paradoxic is offline
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Join Date: Mar 2006
Posts: 7
The Plane Will Not Take Off

Quote:
Originally Posted by zut
Second, assuming that the frictional force associated with the wheels will balance the engine thrust is problematical. Clearly, this frictional force is nowhere near the engine thrust when the plane takes off from a concrete runway.
No.

The force generated by the conveyor system itself is what everyone has ignored, and you are still ignoring it.

Clearly, the physics show that the conveyor system itself has to be responsible for a force equal to the thrust of the engines. That's all it takes. If the force of the conveyor system equals the thrust of the engines, the aircraft can go nowhere.

Suppose, for example, you created a conveyor system powered by multiple turbine engines similar to the ones used to power the aircraft?

And the frictional force HAS to be considerable because the physics dictates that the force generated by this turbine-driven conveyor system can not go anywhere else. You must look at this as a closed system and consider the force of the conveyor.

You are making assumptions, and using words like "clearly" and "it's possible", because you are still considering this to be a thought experiment. You have to look at this as a closed system, and consider the force generated by the conveyor system itself.

Quote:
Originally Posted by zut
It's possible that the frictional force increases with increased velocity, but it would have to increase substantially, and this is by no means assured. A more significant force, I would argue, is the force resulting from the rotational acceleration of the wheels (as Cecil mentions).
You are making unwarranted assumptions. Please, don't make me have to take time out to demonstrate the math on this...!

You need to stop treating this as a thought experiment and start looking at this as a closed-system physics equation. You cannot ignore the force generated by the conveyor. The conveyor system must be generating a lot of force to move the belt, and that force must go somewhere, right?

Quote:
Originally Posted by zut
Third, you are clearly correct that the airflow from the engines won't lift the plane, and that bulk flow over the wings is necessary. However, it is certainly possible that if the conveyor were long enough and ran fast enough for a long enough time, air could become entrained with the moving belt, moving fast enough to lift the plane off the belt.
But I reject your assumption. I cannot see any fluid dymanics equation where air can become "entrained" with the moving belt. Even if you look at a speeding car, even at 160mph, you can't "entrain" enough air six feet away from the car to be of sufficient velocity to lift an airplane. Again, please don't make me do the ball-busting math on this...

I know that, as a matter of business, Cecil is supposed to be always right, but in this case, the excuses must stop because the plane cannot take off.

You need to look at this as a closed system, and stop making assumptions about friction and airflow.