Skill's weekend teaser

if the conveyor has a speed of 180mph, and the engines are off, the planes speed is...wait for it... zero.

if the plane's engines are on, its speed is exactly the same as it would be on tarmac.

Look Bramble, I've said it twice already; a plane's wheels are merely there to stop the paint being scratched when it takes off. Stop focussing on the wheels, and what speed they match, it's irrelevant!

I was starting to, but I think I'm almost there with him... definitely the last of the weekend teasers though!

The conveyor belt cancels out any of the thrust forward the plane generates through the turning the wheels and the friction between the surfaces - none. The thrust forward is generated by the engines pulling the plane through the air; each kN of thrust will pull the plane one "air unit" in displacement forward, and the plane will accelerate forward until there are enough "air units" going over the wings to generate the lift necessary to take off.

Exactimondo. The plane is not generating any forward motion through the wheels, or anything connected to the ground; therefore, under frictionless conditions, the conveyor belt cannot affect its forward motion in any way.

Incidentally in reality the friction forces are negligible; the plane must overcome these before it can begin forward motion, but this is the same on tarmac. Since the belt is stationary when the plane is stationary, the plane will take off exactly as it would from the ground.

An interesting spin-off from the result is that you'd need a conveyor belt the same length (i.e. roller to roller) as a runway to get it to work. Right?

Yes, exactly! Well, not the length of a runway, but the length of the runway that's required for a plane to take off; I'm pretty sure the guys at Heathrow leave some slack either side just in case.

Answer the questions as posed and you might find a glimmer of realisation.

If the conveyor is moving backwards (relative to direction plane is facing) at 180mph and that exactly equals the speed of the wheels on the plane, the plane has a realtive groundspeed (relative to ground under conveyor) of 0mph and an airspeed of 0mph.

If you were standing to the side of that conveyor in line with the plane - it would not be moving relative to your position. By your logic, that shouldn't matter and you'd both take off together I presume?

Haha sorry G-man, I knew exactly what you meant