|
Re: stolen from another forum
you are adding conditions to the question that are not in the question.
The runway moves in the opposite direction of the plane, at the same speed. Nowhere does it say the runway moves to keep the plane in the exact same spot. That is your mistaken conclusion of what will happen.
A jet plane is able to produce thousands of pounds of thrust. Lets say its an F15, able to generate 30,000 lbs of thrust.
The wheels, with the brakes off, will have a very low coeffecient of friction. So lets start at zero mph.
The plane speeds up to 10mph, putting out 30,000 lbs of thrust. The runway matches this speed in the opposite direction. The wheels are putting maybe 5 or 10 POUNDS of force in the reverse direction due to the runways backward movement.
The resulting net force on the plane is 30,000 pounds forward minus 10 pounds backwards = 29,990 pounds of thrust (force) in the forward direction
and the plane is moving forward with a 10mph airspeed and its wheels are spinning at 20mph. The runway is moving backwards at 10mph (ground speed)
as the plane continues to accelerate (due to the thrust from its engines) the runway speeds up, but the force the spinning wheels apply to the airframe will never match the force of the engines, unless the pilot does something stupid like stand on the brakes.
|