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Originally posted by robertfenix
Everyone who says that the wheels are turning twice as fast is mistaken about the "independant" thrust generated by the engine.
To say it again the plane will not take off.
Here is why
Take your converyor and run it at lets say 10ms going to the right (backwards) hold a model plane a car whatever in your hand over the conveyor, now bring it into contact with the conveyor.
The wheels of the plane car etc are turning at 10ms, while you are standing still and holding it over the conveyor.
Now lets say you move the car plane etc forward over the moving conveyor at a rate of 1ms, the wheels therefore are traveling at 11ms and the car/plane etc has moved forward in position (1ms in distance) in regards to its postion from point A to point B.
So by using this scenario you are saying just like a jet engine, independant of the conveyor motion and the rate of the car/plane adds on top of the conveyor rate of motion to get increase of the wheel speed to the point that when the car/plane is moving at the same rate that the wheel speed should be double of the conveyor speed and that the car/plane would be moving forward at the rate of 10ms.
Sounds like this is what you are saying.
BUT the only problem is that by standing next to the conveyor and holding onto the car/plane etc that you are then countering the positional movement of the converyor since YOU are not standing on the conveyor moving along with it, YOU become an equallizing force to the movement of the car/plane etc on the conveyor. So you become a third force which equalizes the force movement of the conveyor allowing the force/movement of the planes engine to then overcome the positional movement of the conveyor. Thus allowing the wheel speed to become increased above the conveyor speed.
BUT in our question the conveyor in fact does not move at a set rate.
So again using the above example standing next to a moving conveyor holding a wheeled, skidded or anyother object over the conveyor then coming in contact with it at say 10ms, you attempt to move the car/plane etc forward at 1ms, the conveyor sensing the increase in velocity of the object over the conveyor equally speeds up to 11ms, thereby increasing the force requried to move the car/plane etc to something higher then 11ms so you apply more force to swing the car/plane etc forward on the conveyor only to have the conveyor equal the force and speed up.
The more force you apply to try and move it forward the more force the conveyor applys in the opposite direction to push it back.
At 20ms you would need to push with 21ms of force to move 1ms at which time the conveyor would then equalize and move at 21ms in the opposite direction. It would become increasingly harder to push forward to move that additional 1ms.
Since there is nothing about the limit to the amount of force either the plane nor the conveyor can generate then it would come down to which failed first. As being the ultimate solution to if the plane would take off or not.
If the plane is trying to push forward with 10,000 force units and the conveyor is pushing back with the equivalent of 10,000 force units then the plane has to make 10,001 just to move forward. It would not move exponetially faster forward since it is alright moving against the equal to 10,000 force units, it would merely travel along the length of the conveyor at the rate of 1ms until it reached the end at which point given the space available it would then start to accelerate at what ever the thrust to weight ratio /mass allowed it to accelerate at. And given enough space remaining would take off like normal.
You could conceivable build a test model by using an electrical torque sensor an arm attached to some sort of car or plane model and moving belt surface that had a speed govenor that you could like to the torque sensor.
As you apply torque on the arm which is connected to the car whatever on the belt attempting to swing it over the surface of the belt as you applied torque the belt would see the new torque amount and speed up the belt to equal the amount of force you are attempting to apply to the car plane etc until both reached ad infinite and something failed.
Since we are dealing with gravity the mass of the plane on the conveyor plus the speed (velocity) at which the conveyor is attempting to the move the plane in a given direction is going to equal a certain amount of force. Since the plane is attempting to overcome this force its engine must also deal with the effects of gravity on the mass and counteract the net force of the conveyor attempting to move it back, As the plane generate more force, so does the conveyor. The wheels have nothing to do with cancelling or adding into the planes favor as the MASS of the plane still exist as is acting ON THE CONVEYOR due to gravity, thus the engine must still overcome the mass of the plane + opposite force.
To solve this question you have to solve using the same term "force" in both cases as the plane model is tricking you by using terminology such as ground speed vs airspeed.
The plane requires X airspeed,
Under normal conditions, therefore the plane must travel forward at a groundspeed of Y
The plane produces Z amount of thrust and the plane weighs A amount in lbs, which gives us a rate of acceleration of R.
If traveling into the wind at a rate of W it is possible for the plane to takeoff at a ground speed on Y-R
As long as Airspeed X and Windspeed R remain constant or increasing then the plane will remain in the air.
So logically speaking then if the conveyor under the plane is moving at a constant rate = to the required groundspeed of the plane to "fly" Y yet in the opposite direction then it would be assumed that the following is true
Groundspeed = Y x 2 required for flight when Ground is 1/Y
BUT in our case Y and 1/Y are always equal
Therefore without the plane moving (which is a requirement of force) at a rate higher then the equal yet opposite rate of the ground then it can not generate enough airspeed to "fly"
Originally posted by robertfenixThe more force you apply to try and move it forward the more force the conveyor applys in the opposite direction to push it back.
Originally posted by Travellar
Originally posted by robertfenixThe more force you apply to try and move it forward the more force the conveyor applys in the opposite direction to push it back.
You had a fairly good grasp of the arguments up to that point. The mistake though, is that th wheels exist for the sole purpose of ensuring the conveyer is unable to effectively or efficiently apply it's motion as force.
Originally posted by robertfenix
Take your converyor and run it at lets say 10ms going to the right (backwards) hold a model plane a car whatever in your hand over the conveyor, now bring it into contact with the conveyor.
Originally posted by maldives01
billybob
thats funny, just looked for you there - that was the page where I said they were calling each other names! And you were one of them! Great stuff! Don't know much about physics, but I'm sure "dill hole" isn't a generally accepted term like "wormhole"
Take care man
Originally posted by veespec
the thrust of the engines would extremerly outweigh the minute rolling friction of the tyres agaist the huge treadmill.
its like getting on a treadmill with rolerblades and using a rope to pull yourself in
thinking that a treadmill of such preportions can be built is silly, that someone would build it is silly and that it could accelerate to the speeds at whcih the rolling friction of the wheels will overtake the thrust of the jet engnes is silly
plane will take off
Originally posted by rat256
reply to post by ShatteredSkies
well... for my first post here, i'm going to wade in... i'm going to go and sit in the yes it will camp... but i'm going to try a small scale experiment with a model aircraft and a treadmill and see what happens... i can't believe no-one else here has a $50 toy plane and a gym membership!
Originally posted by HowardRoark
A plane is standing on a runway that can move (some sort of band conveyer). The plane moves in one direction, while the conveyer moves in the opposite direction. This conveyer has a control system that tracks the plane speed and tunes the speed of the conveyer to be exactly the same (but in the opposite direction). Can the plane take off?"
Originally posted by kilcoo316
Neglecting the wheel speed rating, the aircraft takes off.
In the real world, the tyre speed rating will be lower than 2X the rotation speed - so the tyres will fail and the aircraft will "crash".