monkey13, on Jan 29 2008, 18:05, said:
Well I can't sleep and I've been thinking about this again. Damn it!
My theory is the plane will not take-off, regardless of if it can move down the conveyor. Here's why.
There's been a lot of talk about the wheels having no effect. This is impossible. For the wheels to have no effect the wheel bearings holding the weight of the plane would need to be entirely frictionless (impossible). The force required to compress the wheels as they rotate would have to be nil (impossible). Another way to think of it is; If the plane had these magic wheels and was in a vacuum (i.e no air resistance) the plane would move with any forward force applied to it (e.g. a small child could push it along with one hand) Another way to think of it is that the wheels behave the same regardless of if the plane is there or not. Ridiculous.There is a resistance which is why the engines have to be revved to get the pane moving when taxiing.
The next thing I was thinking about is; If the plane's engines were turned off and the conveyor belt it's on accelerated would the plane remain still? The answer is no. The forces, as mentioned above, that act through the wheels would still act moving the plane backwards. Therefore a force is required just to keep the plane in the same place. Meaning that more force is required to accelerate the plane on the conveyor than on the ground. Regardless of if the plane can move along the conveyor.
Now the question is; Does the plane have enough extra power to overcome these additional forces and move along the conveyor to reach take-off speed?
I'm going with no.
The friction force isn't so huge that it can counteract any other force that is applied. Since friction is independent of speed or acceleration, it doesn't matter if the conveyor belt is going at 1 m/s or 100 m/s (assuming the wheels are built to withstand it. Certainly that isn't part of the question). Therefore, the plane is just trying to overcome the wheel's friction, which it always does normally. Static friction is greater than normal friction, so once the wheels are able to spin, they will keep on spinning until some other force makes it stop.
Even a person can pull a plane: http://www.ananova.c...sm_2672263.html
. It doesn't require a massive amount of force to do so.