Quote:
Originally posted by MattyX:
OK. one more try. Kind of the opposite scenario posted by XPLORx4. Can we agree that one effect of the conveyor is to double the rotating speed of the wheels?

Imagine an aircraft on a long runway wtih a tailwind (FYI- a tailwind is counter-productive to the attainment of lift) of say, 120 knots. Exactly the airspeed needed by the aircraft to lift off. The aircraft begins takeoff roll, with the wind. The wheels spin faster and faster. The plane reaches 120 knots of groundspeed, and has reached zero airspeed. The aircraft continues to accelerate and reaches 180 knots groundspeed, which is 60 knots airspeed. The wheels are spinning at 180 knots now. The aircraft then reaches airspeed of 120 knots, which is 240 knots groundspeed, 240 knots of wheelspin. Lift can be achieved at 120 knots airspeed, and the plane takes off.

Those numbers in review:
At rest on the approach end:
Airspeed -120 [negative 120 knots]
Groundspeed 0
wheelspin 0

starting takeoff roll:
Airspeed 0
Groundspeed +120
wheelspin +120

Halfway to achieving lift:
Airspeed 60
groundspeed +180
wheelspin +180

at liftoff:
airspeed +120
groundspeed +240
wheelspin (before liftoff) +240

Now shouldn't the plane stay on the ground according to the "not-flyers'" logic?
See, this is what I'm saying. Your argument rides on a tailwind of fixed velocity. In the scenario, the conveyor moves faster and faster as engine thrust is increased, so the speed relative to the surrounding air remains zero.