quote:

ORIGINAL: Jr. Mechanic

For all the non believers, do this since you are right in front of a computer and these things should not be hard to find. Take a piece of paper, set it on the desk, then get a round pen or pencil that can roll, set it on the left side of the paper. Begin to pull the paper to your left slowly, then push the pencil any speed you want. That is the exact same principle as a real plane. 

Thrust acts accordingly to Newtons Third Law of Motion - every action has an equal and opposite reaction. In the case of an aircraft, the reaction of the engines is that of forward motion, against whatever medium it is stationary. But the ground the aircraft is sitting on in this case is NOT stationary, its providing an exactly CANCELLING force pushing the aircraft back.

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ORIGINAL: GrApHite03

I think i see what your getting at with your pencil explaination, but it is quite confusing.

Maybe a better explainations is this that i found.

QUOTE:  http://txfx.net/2005/12/08/airplane-on-a-conveyor-belt/

Their argument is this, to quote one poster:

Thrust acts accordingly to Newtons Third Law of Motion - every action has an equal and opposite reaction. In the case of an aircraft, the reaction of the engines is that of forward motion, against whatever medium it is stationary. But the ground the aircraft is sitting on in this case is NOT stationary, its providing an exactly CANCELLING force pushing the aircraft back.

The problem here, of course, is that the poster (and Neal) cannot disengage themselves from seeing the airplane as a car. The difference between a car and a grounded airplane is that a car uses its wheels to propel itself forward, and an airplane moves itself forward by moving air. They assume that the runway moving backwards would move the plane backwards. This is what would happen with a car (that is in gear), so why not for an airplane? Well, because an airplane’s wheels are free rolling. There is obviously some friction, so there would be some small backwards force, but it would be infinitely small as compared to the forward thrust of the airplane.
 
You can test this with a piece of paper and a matchbox car (which has free rolling wheels like an airplane… or like a car in neutral.) Place the paper on a table, and place the matchbox car on the paper. Take your hand, and hold the car still with a lightly placed finger on top of the car. At this point you are providing no forward thrust, and the “conveyor belt” is not moving. The car remains stationary. Now, continuing to hold the airplane with a lightly placed finger, and start to pull the paper out from under the car, in the backwards direction. According to Neal’s logic, the car should push back on your finger with the same force that you are exerting on the paper… but this is not what will happen. You will find that your lightly placed finger is not stressed to any noticeable extent. The paper will slide out, and the wheels will spin, but the car will not be propelled backwards. The reason for this is is that the rotation of the wheels is not related to the movement of the matchbox car except by the very small friction component of the axle, which your lightly placed finger can easily control.
 
So now we have established that movement of the surface beneath a free wheeling object does not exert a noticeable force on the object. Next, we’ll see what happens when the object is trying to move forward. Attach a string to the matchbox car. Place the car at one end of the paper, and use the string to start pulling the car forward with a steady force. As the car moves forward, start pulling the paper out from under the car, backwards. Do you feel increased resistance as you pull the string? Of course not. The wheels are free rolling! Spinning the wheels does not make the object move!

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ORIGINAL: pghsebring


NOW, if they increase the engine thrust to a point it is more forceful than the belt in the opposite direction, and the aircraft is able to gain enough speed, then yes, it can take off.  That would be the equivalent of me running faster than my treadmill and going off the front.

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ORIGINAL: pghsebring

Wait - so let me get this straight.  They are going to have the airplane powered up, headed in one direction.  Underneath they are going to have the belt going in the opposite direction at the EXACT same speed?

The plane will not take off.  The only thing that matters is the speed of the wings cutting through air.  If its sitting still on a conveyor, the plane can't take off.

The opposite of this would be to put a plane in a wind tunnel, and make the wind go thorugh the tunnel, but not have the engines on or allow the plane to go forward - it will take flight in the tunnel with sufficient wind speed, because the air passing the wings is what matters.

NOW, if they increase the engine thrust to a point it is more forceful than the belt in the opposite direction, and the aircraft is able to gain enough speed, then yes, it can take off.  That would be the equivalent of me running faster than my treadmill and going off the front.

So, are they setting the treadmill speed the same as the speed of the engine going forward?

FYI, some planes can fly with as little as 38mph of wind...i'll be more amazed if they can find a treadmill that big that goes 38 mph in the opposite direction.

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ORIGINAL: truckin151

But thats not the way they are going to test it. They are going to put a small prop plane on a large tarp and pull it in one direction via truck while the plane is facing in the other direction, the pilot is ONLY going to give the plane enough forward motion to counter-act the friction of the tarp and the wheels to remain in the same spot. The plane will not take off.

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ORIGINAL: Nofrag

quote:

ORIGINAL: pghsebring


NOW, if they increase the engine thrust to a point it is more forceful than the belt in the opposite direction, and the aircraft is able to gain enough speed, then yes, it can take off.  That would be the equivalent of me running faster than my treadmill and going off the front.

Common misconception infact.  See, you could not do that, because your legs have a maximum speed.... Airplane wheels do not.  Get over the thought that wheels govern the speed of an airplane, wheels are merely baerings, and save for spinning them to some amazing speed at which they will overheat and seize or putting a block infront of them, nothing can be done beneith the wheels that could possibly stop forward motion of the airplane.

Very simple principle, look closely, examine each of the following words.....  BECAUSE THE MOVEMENT OF THE AIRPLANE IS NOT GOVERNED BY THE GROUND, FORWARD MOTION IS GUARANTEED, FORWARD MOTION ENABLES AIR MOVEMENT OVER THE WINGS, AIR MOVENT OVER THE WINGS ENABLES LIFT.

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ORIGINAL: truckin151

But thats not the way they are going to test it. They are going to put a small prop plane on a large tarp and pull it in one direction via truck while the plane is facing in the other direction, the pilot is ONLY going to give the plane enough forward motion to counter-act the friction of the tarp and the wheels to remain in the same spot. The plane will not take off.

quote:

ORIGINAL: batman13
i liked the first clinton,
he shot from below the belt.....