i see people are still talking this one over. again, the wheels have nothing to do with the plane taking off at all, they are only there so the plane can roll forward and backward. the engine does all the work, and the wheels have no connection to it. So if the plane is at full throttle, even though, it may not be moving forward, it is still using thrust to power itself, and still generating speed, so if the plane needs to be at 60 knots for take off, when it gets there it will take off. a plane could be traveling in a headwind, the same speed as the plane is going, and still lift off, because it has reached that certain speed needed.

 

Ground speed and air speed are what we are really talking about.

An airplane can have a ground speed of zero (hovering in position over a single point) so long as the air speed over the lift surfaces (wings, etc) is sufficient to create lift.

A small Cessna's stall speed is around 60 knots (~70 mph). In other words, if the speed of the air flowing over the lift surfaces goes lower than 70 mph, the plane falls out of the sky.

In other words, if a Cessna is flying at an indicated 70 mph and is flying into a 70 mph headwind, it's ground speed is zero mph, but it's air speed is 70 mph.

 

when a plane takes off the ground ...... at mentioned speed/knots needed to take off ...... it needs solid / unmoveable/ non-moving ground to generate thrust/speed to START to get it moving (the wheels have a part in it with the ground , or else picture the plane on its belly and see what happens without wheels) .... we all can picture this now , right ? it cannot take-off unless it has forward momentum to cause lift under the wings

now if the conveyor & plane are at a standstill ..... then they both start to power-up slowly , gradually ..... eventually not at equal thrust (the conveyor has to go faster to keep the plane still) , thus ; they compensate for each other through the wheels' bearings : the wheels spinning like mad and taking all they can handle before they bust off ..... thus the plane IS standing still ; cause no lift (air under wings) .... In this theory : the jet engines' speed is at full thrust , and , the conveyor's speed is at whatever unlimited/fictional speed (if needed - fictional light speed) to equal/compensate for the jet engines speed in order to prevent the jet engines to garner the upper hand . In order for the plane to take off ; it needs more speed in its engines , than the conveyor .

now to say it would take off ..... or at least start moving forward , then that means that the conveyor (it would have to be a real life one - not fictional one) would reach its max. real-life speed and then the jet engines would start to have the upper hand in speed , and then it would start moving forward


now , to say that the plane can take off from a standstill at full thrust is impossible ..... it needs to accumulate wind lift speed .... accumulate ...... just think that Navy/Marines (F-14) Jets on a carrier , needs a 'catapult' to sling-shot it to take-off speed ; cause its jet engines , by themselves , cannot supply enough thrust by themselves from a standstill .... and that's on a non-moving ground !!! now imagine all the fictionable power in a conveyor to compensate ..... in all of this the conveyor's speed will always be superior to the engines or catapult combined ; to compensate , of course

 

6Pack, you are correct about the wheels, they have a part to play, and that is to roll on the ground, but they in no way affect the speed of the plane, that is the job of the engine. they are not directly connected to each other, in the way a car is. And planes can take off from a stand still, there is a Harrier jet that take off and land vertically, but that jet is not part of this question. Yes, the planes on an aircraft carrier do use a wire to help catapult them, but the carrier is also moving at a certain nautical speed. if there was enough head wind that the plane was going into, it could lift up from a stand still, because of the thrust of the engine, combined with the head wind producing lift under the wings. In the question wind was never mentioned, so you can factor that in, or not.

 

I can't believe this question went on for so long! The thrust of the engine and the wheel speed have little to do with it. Yes, they play a part but have little to do with whether the plane will take off. The ONLY way that the plane is going to take off is if there is airflow over the wings. Since the question says nothing about that, one has to assume there is none. The reason I say the engines and wheel speed have little to do with it is if you think in terms of wind tunnel. There is no engines, no wheel speed. There is ONLY wind over the wings!!!

 

Of course, in a wind tunnel they are testing the aerodynamics of the shape of the plane, and airflow over the wings creates downforce, not lift, which is needed for the plane to fly.

 

Sorry Michael.....airflow over the wings (more specifically, the differential in airflow between the top surface and the bottom surface of the wings) does create the lift necessary for flight. A wind tunnel is an excellent example. The overall aerodynamics of the plane do play into the minimum speed necessary for flight (parasitic drag would increase your stall speed)

Wheels/engine have nothing to do with it....The wheels on a plane have no drive system, they just roll freely. Perfect example of this is a glider. No engine needed for flight, just a tow up to altitude....

The Harrier has VTO capability due to vectored thrust....the engines direct thrust in a downward direction creating "lift" on the airplane's body, however, once airborne, the thrust re-directs out the rear of the plane for regular flight. (Think of it like a Saturn V rocket, no lift surfaces (wings), but becomes airborne due to sheer thrust velocity.)

 

Actually, if air is flowing over the wings, it is creating a downforce with no lift being created because air is not flowing underneath the wings, in order for the lift to be created air has to be flowing both over and under, the way it was stated above is air is flowing OVER the wings, there was no mention of under. Air flowing over the wings only does not create lift only downforce, same idea as on the wing people have on there cars,they are made in such that more air goes over top to pushing the back end down, not lifting. Check out these threads to see what other people have to say about this question:

http://www.airliners.net/discussions...d.main/136068/

http://www.straightdope.com/columns/060203.html

This question has been posed many times, and many people respond, and many people disagree, but the plane will fly. People, go back to original question and read it again. no where in there does it say the plane is stationary, it just says that the conveyor is moving at the same speed as the plane. So the plane can be moving forward, maybe slower thn normal on non-moving ground, but moving forward still, so it can still take off because it is creating lift by pushing air over/under the wings.

 

AH HA !!! The plane is already moving , then slam the thrusters and we have lift ...... but from a standstill as I describe it : no lift cause no drive in wheels compensated by conveyor .....you see the thrusters are already maxed out by the conveyor

much debate cause much unclear in original question ..... I have set my theory clear with all my details imagined ..... my theory stands ..... and now yours

as I said for the REGULAR plane to take off , the conveyor would have to be less powerful than the thrust of the engines , just as a Harrier can over-power a non-moving ground by its sheer power by its downward facing thrusters then gradually towards headwind start going forward

 

Nobody said the plane was already moving, what was said is that it can move forward. let me give another example, but it will probably throw people off. Imagine a car on a dyno, wheels spinning, but going nowhere. thats because the rollers on the dyno are above the ground, essentially holding the wheels off the ground so it can move. take that same dyno, place the rollers at ground level, have the car start to run on the dyno, eventually it will go off of the dyno and fly down the road. the conveyor in this question is the ground, just a piece of flat level ground, that plane will eventually move and be able to lift off the ground. basically, the conveyor is a large flat dyno, at ground level, spinning the opposite direction of the wheels on the plane, the plane will move, it has to because nothing is holding it one place