Quote:
Originally Posted by Cole
All these pulley debates remind me of the great physics question:
If you put an airplane on a treadmill that matches the wheel speed of the airplane perfectly so that no forward motion of the plane is achieved, will it take off?
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I've always liked that question. Unfortunately, it's based on fallacious logic. The wheels on an airplane, unlike a wheel-driven vehicle (engine-to-transmission-to-differential-to-axle-to-wheel or similar) are not driven at all; they just idle or "coast" like the wheels on a shopping cart. An airplane-sized treadmill would have no effect on the speed of the aircraft; the aircraft's speed (caution--- oversimplification ahead) is governed by the thrust of the air rearward by the propellor. The aircraft would move forward independent of the speed of the treadmill. As the airspeed increases, the wheels would spin proportionally faster than the treadmill until the airplane would eventually lift off in the same amount of horizontal distance it would have lifted off if the ground beneath it had been stationary; it's airspeed across the wing that determines the lift. Now, if the treadmill/wheel interface creates an appreciable amount of drag, then it would take longer to achieve the required airspeed for take off, but there's no way a treadmill COULD "match the wheel speed... so that no forward motion is achieved" simply because the wheel speed would have no effect (other than friction of the wheel to treadmill interface and bearings) on forward motion. That plane is going forward, no matter what, unless the wheels are being prevented from rotating by brakes or wheel chocks.
Soo... fun question, but faulty premise.
Yeah, there's a bit more to it, but that's the gist of it.
Barry