"BDS" wrote:

Maybe he's not so smart after all :)
Maybe not, but smart enough to see this one.

On a calm day you can run and feel a wind on your face because you are
moving across the ground as well as through the air. But, if you run on a
treadmill there will be no wind because you are not moving through the air -
the air is calm so it has no relative motion with respect to the ground.
Neither do you when you run on a treadmill.
True. Irrelevant, but true.

Assume the airplane is on the conveyor and there is a 10 kt headwind, and
assume we need 60 kts for takeoff. The only way to generate the additional
50 kts of airspeed is by moving across the ground at 50 kts.
Right so far.

If the
airplane is standing still
Hold that thought...
because the conveyor is moving backwards at the
same speed that the airplane is moving across the ground at
Skip back up to see what speed you say the airplane is moving across
the ground. Then go back to the original question and figure out what
speed the conveyor must be moving when the airplane is not moving.


If the conveyor keeps the airplane standing still relative to the ground,
then it cannot take off.
Yeah, but the original statement of the problem made no such claim.


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