Allright, here's one i came across. I know the answer, but i just want to see where this goes, it's been quite the source of debate on another forum i frequent.

there is a jet aircraft sitting on top of a gaint treadmill the same size as a standard runway. as the plane powers up and starts moving, the treadmill exactly matches the speed in the opposite direction at all times.
quesion:
under full power, can the jet take off?

Justin

I'd say yes, but I'm not an engineer and have no idea, so that's just a guess.

no, because its not the speed the wheels are traveling but the airspeed overthe wings that causes the lift. Unless of course there was a strong headwind

It could take off. The jet engines just have to overcome the relatively small amount of additional friction at the wheels brought on by the treadmill.

Of course not, silly rabbit. The jet's wings need air resistance to provide lift for the jet, and since it is stationary in the atmosphere, it won't go anywhere.

I agree with Snocat to a degree, but there is the factor of relative windspeed because of the treadmill. The movement of the floor will create some relative windspeed for the jet, and while it is much less than the relative windspeed of the jet under full flight, it might be enough to lift the plane a bit. And if the plane gets off the ground at all, its "full power" is going to take over, and push it farther and faster.

Asuming the landing gear can sustain the tiwce the rotational speed of a standard takeoff. The wheels do not propel the aircraft, the thrust from the jet engine does. The plane would need to be in a wind tunnel to be incapable of takeoff.

there is no way you could put it on such treadmill, how on earth would the plane make the treadmill turn, it is not powered through the friction of the ground

good question though

it would take off. Linear motion of the runway would likely have little effect on the motion of the plane because the engines pull it through the air, and not along the ground. the wheels are free to spin however they want to.

imagine if you walk at the airport in the opposite direction as a human conveyor belt, but in the opposite direction, but you're only walking beside it, and not over it: if you drag your suitcase along the oppisite moving conveyor, it will only slow you down minimally. the force to move the suticase comes from you, on stationary, non moving ground. the ground moving parallel to your movement beneath the suitcase has little to do with its motin

This can be a trick question.
I assume by the statement that the jet aircraft doesn't move and is in a static state, yet the engines are 100% power. Using that assumption, a typical jet aircraft will not be capable of lifting off.
Now, if all the mumbo-jumbo (friction, external forces, etc) you people mention was to directly affect the jet, e.c. the jet is not static but the treadmill does match the relative airspeed, then a typical jet might be able to get enough to hop up, but not sustain a complete liftoff.

One must also take into account which type of jet is being used. A B737 jet ( well jet-fan) is far different from a L45 or a Bombardier Challenger, and even more different than a VLJ or even a Falcon 10 or 20. Placement of the engines, relative takeoff speed, and takeoff roll distance can all affect this problem.

I say, from experience of being in both jumbo and business jets, and from flying business jets, the chance of this happening is very slim.

Now, lets try this!

Obviously, since my jet is a Harrier (sp)

I say yes, it will take off.

Normal situation: The engines suck and blow enough air to pull the jet foward along the ground. The wheels have no power of their own. When the air is moving over the wings quickly enough, it causes lift and the plane takes off.

This situation: It's the same thing, except that "pull the jet foward along the ground" is replaced by "causes the conveyor to move backwards." It doesn't matter if it's a jet moving along a stationary ground or the ground is moving below a stationary jet. All that matters in the takeoff is the speed of the jet relative to the air.

yes the speed relative to the air is what matters, but if the plane is stationary to the ground. Which it is, the treadmill is moving under it in exactly the same speed as the wheels are moving just in reverse. Then the plane will never move foward, so it will never pick up the speed realtive to the wind it needs to take off.

Think of it this way. If you are at Wal-Mart and put a toy car on a conveor belt you could easily move it in the opposite direction of the belt's motion, since the wheels are free-moving. If the jet was like a car and needed to get moving by turning its wheels it would not take off. However, it gets going by thrust. The wheels on the jet would just turn twice as fast as normal but it would still take off...the motion is accomplished by thrust, not by the wheels providing forward motion.

but according to the problem if the wheels spin twice as fast then the convever belt spins twice as fast thus negating all foward movement.