First off, there is absolutely no difference between a treadmill and a conveyor belt. A treadmill is a conveyor belt specifically designed for humans to run on to exercise. In this case, the words are interchangeable, so no more complaining about that.
Second, the plane takes off. That's been described. A lot. In detail.
Now to address some specific posts:
Originally posted by: LTC8K6
So are you saying the belt has zero effect on the plane? Zero, Nada, Nil?
No, it's not actually zero.
It is effectively zero for purposes of the myth.
You can try to hold back a car from driving away by attaching it with a thin string to a sturdy post.
The string does exert a force to keep the car from moving and we can measure that force. That force exists, but it's effectively zero because the car will easily break the string and accelerate away normally.
This isn't a great example because a string tied to a post is acting as an anchor, and you'd break the string as you pulled away in either the plane or the car, because both generate enough forward thrust to break the string. The plane does not "break" the conveyor belt; the conveyor belt is not acting as an anchor, nor as a significant counter to the primary thrust of the plane (which comes from the plane's engine acting on the air).
Seeing as how the plane's primary thrust is the engine moving the air, a conveyor belt will have little effect. A car's primary thrust comes from its engine turning the wheels pushing it along the ground, which a conveyor belt WILL effect. A better analogy to the plane on a conveyor belt is a car in a wind tunnel. If you set up a giant fan pushing wind at a speed of 25 mph in front of a car, would the car be pushed backwards at that speed? No. Would the car have to do more than 25 mph to move forward? No. The car's primary thrust is not based in air, it is based along the ground.
So it seems to me that anyone who thinks the plane won't take off is also of the frame of mind that it is impossible to drive in a stiff breeze.
Originally posted by: Ns1
Originally posted by: FoBoT
not drag, you mean lift
it'll have lift as it accelerates normally
the engine pushes on the air, not on the ground
doesn't that depend what kinda plane they're using? I guess I'll find out in a few hours.
No. Every plane engine pushes air. If a plane gained velocity by spinning its wheels, it could take off... but what would happen when it started to lose velocity (air will exert friction on the plane, slowing it down)? The wheels would have nothing to spin on to generate more speed and the plane would come back down. Then you'd have to get up to speed again to take off. If this were how planes flew, they'd have to have bounce pads all over the place for planes to regain speed. But a plane's engines don't work that way. They push air horizontally which moves the plane forward to generate air movement over the wings. The engines themselves do not move air over the wings any more than they spin the tires.
An analogy I read in the last thread which helped me visualize this better is to imagine something we're more familiar with than jumbo jets. Imagine a toy plane, like an RC car version of a plane. It has wheels which spin freely. Imagine putting this toy plane on a treadmill. You turn the treadmill on, you up the speed, and you hold the plane in place. Does it get harder to hold the plane still as the treadmill goes faster? Not really. I mean, it's not like at 2 mph everything is hunky dory, but if you get it up to 15 mph, you've really got to lean into the plane to hold it in place. This is what the wheels on a plane exist for; they free spin to match whatever speed the plane happens to be at relative to the ground it is on.
Now imagine yourself pushing this plane forward. Doesn't take much effort, does it. Push the plane up the treadmill. Now turn the treadmill off and push the plane up it again. Not really much of a change in how much effort it takes. The thrust is not coming from the wheels, so the treadmill does effectively nothing to counter the thrust. Regardless of how fast you make that treadmill spin, you will still be able to push this toy plane up it.
In the real world, the thrust of a plane does not come from the wheels. No matter how fast you get that treadmill, it is doing effectively nothing to counter the thrust generated by the plane's engines on the air. The plane will still move forward, and because it is moving forward, air is moving across the wings (which is the sole consideration in whether or not a plane will take off). The plane will take off.
Oh, and to everyone who thinks that the treadmill could effectively spin fast enough to keep the plane from moving because it does have some friction with the plane, this is not really fair. At the speed the treadmill would need to move to generate the friction on the wheels to completely counter the forward thrust of the plane's engines, the wheels would burst, and the plane would fall onto its undercarriage, which would exhibit much more friction than the wheels, and since the treadmill was still moving, the plane would be hurled backwards along the treadmill. But that's not the myth, and it never has been. You can reword it in lots of different ways to make the plane not take off, but as the myth originally stands, the plane takes off.