Can Plane Take Off

No, the plane is moving through the air. The belt is meaningless, its only there to confuse you.

Zuuljin said:

No, the plane is moving through the air. The belt is meaningless, its only there to confuse you.

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Summarily, yes, this is the case.

I might suggest this as an exam question for whatever physics class ends up covering the dynamics brought about by potential differences in pressures.

I"m pretty sure that advanced mechanics will cover this. This is an awesome thought experiment

If the conveyor is moving in the opposite direction at the same speed, how exactly is the plane moving relative to the air?

Perhaps I"m just missing something but I"m envisioning it as something like a person walking up/down an escalator the wrong way: they are still and never move up or down.

potam said:

If the conveyor is moving in the opposite direction at the same speed, how exactly is the plane moving relative to the air?

Perhaps I"m just missing something but I"m envisioning it as something like a person walking up/down an escalator the wrong way: they are still and never move up or down.

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It"s more like someone running on a barrel in water. They"re not moving horizontally because the barrel turns beneath them, but they are perpetually falling, thus the challenge in staying on the barrel. Thus, vertical motion with no horizontal motion. Then again, this analogy falls short when you start talking about the forces involved.


Aye, the key is in understanding that the forces involved do not rely on the ground at all.

Explanation #3: Pretend theres a toy car tied to a string, and its on a treadmill. Now make the treadmill run so that the cars wheels are moving along the treadmill, but since your holding it there with a string, its not moving relative to you. Now give the string a pull (thrust through air) and the car moves! As far as the wheels are concerned, they just spin faster, but have no bearing whatsoever on you pulling the string (engine thrust). That make sense?

Zuuljin said:

Explanation #3: Pretend theres a toy car tied to a string, and its on a treadmill. Now make the treadmill run so that the cars wheels are moving along the treadmill, but since your holding it there with a string, its not moving relative to you. Now give the string a pull (thrust through air) and the car moves! As far as the wheels are concerned, they just spin faster, but have no bearing whatsoever on you pulling the string, or the engine thrust. That make sense?

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If the string is attached to the top of the car, and not the front, yes.

brekk said:

No, running on a barrel of water is about keeping your balance, and using the friction of the barrel rolling to counteract falling over.

This isn"t a case of friction but rather the actual application of the force.

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Aye, you"re right. I was just trying to think quickly of an example of vertical movement with no horizontal movement. The barrel really is a bad example.

For those still having trouble visualizing why the plane takes off... A glance at this web site should helphttp://www.bluewaterair.com/index.htmSimply stated the purpose of the wheels during take-off is to minimize friction. Replace the wheels and conveyor belt with an amphibian plane and a body of water. Or forget the water and just imagine the plane on the conveyor belt having no wheels- you just lube up the bottom of the plane and it"ll slide right along no matter how fast the ground is moving under it.

Also don"t make the problem more complicated than it is. If there is any reasonable situation where you can answer the question as "Yes, a plane can take off in those conditions" then the answer is yes. You don"t need to define how much angular momentum the bearings need to withstand or how much heat the material must endure, etc.

What"s not making sense to me is the application of the bourneli effect. If the plane is stationary in location as the thrust builds there still is no increased movement in air flowing over the wings. I"m definetly very uneducated in this field so I"m not too confident in what I"m perceiving in all of this, but unless you have a plane with a 1:1 thrust to weight ration like a beefed up biplane you aren"t going to lift off.

And if you are concerned with a successful takeoff, I don"t think you"ll find that trying to get a plane from 0mph (relative to a stationary object near the plane) to 100mph+ to maintain airspeed and keep it aloft.

Astaire said:

What"s not making sense to me is the application of the bourneli effect. If the plane is stationary in location as the thrust builds there still is no increased movement in air flowing over the wings. I"m definetly very uneducated in this field so I"m not too confident in what I"m perceiving in all of this, but unless you have a plane with a 1:1 thrust to weight ration like a beefed up biplane you aren"t going to lift off.

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The only way to understand this is through the simple acceptance of Newton"s Third Law, which can be proven pretty easily.


When you set down an object on a table, gravity is pulling down on it, right? Well, why doesn"t it just pass straight through the table, and hit the ground?

At the molecular level and lower, there are huge gaps between the stuff that makes up both the object and the table. It"s concievable that the molecules of each could just pass right by eachother, as the object falls through.

The reason that it doesn"t is Newton"s Third Law. The table is pushing back on the object with just as much force as the object is pushing on the table, thus keeping it from falling through. The reactive force on a surface is called a normal force.


Likewise, the plane isn"t pushing on the air, so much as the air is pushing back on the plane. Thus, the air has its own thrust over the wings.

But the plane IS moving through the air, AND its moving relative to the ground. The plane moves from point A to point B regardless of the fact that there is a belt underneath. Like was said above, picture a plane taking off on water, with the water running the opposite directino of the plane taking off. It doesnt matter! When the thrusters start to move air around, it pulls (or pushes, depends on how you look at it) the plane untill its traveling fast enough for liftoff.

If the plane were standing still relative to the ground, there is no way it could take off, as the air is not moving past it to give it any lift.

i"m no rocket scientist, but are the jet engines enough to over come the initial resistance of the sheer weight of the plane? like that"s why the plane needs space to take off, so the engines push at 250 miles an hour or whatever, propelling the plane along the ground allowing the wings do do their magic of different pressures above and below the wing. so the engines are pushing like a motherfucker, but the wings aren"t doing anything.

i don"t now, i"d like to see it on mythbusters

brekk said:

0_o?

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For the vertical acceleration Otherwise, the car on the treadmill would only model horizontal thrust

Zuuljin said:

But the plane IS moving through the air, AND its moving relative to the ground. The plane moves from point A to point B regardless of the fact that there is a belt underneath. Like was said above, picture a plane taking off on water, with the water running the opposite directino of the plane taking off. It doesnt matter! When the thrusters start to move air around, it pulls (or pushes, depends on how you look at it) the plane untill its traveling fast enough for liftoff.

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Also, even if the plane does not move an inch horizontally until it takes off, it will take off. To demonstrate why the air is moving over the wings without the plane actually moving, place a sheet of notebook paper on the back side of a fan. Actual horizontal velocity has nothing to do with the lifting force, from what I understand.

Of course, I haven"t studied the math for all of this yet, and if physics has taught me anything thus far, it"s that the math always yields a few surprises.

I agree, though. Mythbusters seems focused on things that people generally believe to be one way that really is false another way or true for a different reason. For them to say that this wouldn"t work well for the show because it can be explained with basic physical principles makes no sense, because 90% of what they do can be explained using basic physical principles.

I could see this being a problem for their budget, but this could easily be simulated with a scaled down variation. There are scaled down turbine engines out there too, so they could make it a perfect scaled down model if they really wanted to put the effort into it.

Is the original question asking in real, technical terms? Like the unpowered wheel shit, was that considered? Or was the original thinking more like a car with wings? I dunno, my head hurts.

GaliemVaelant said:

For the vertical acceleration Otherwise, the car on the treadmill would only model horizontal thrust


Also, even if the plane does not move an inch horizontally until it takes off, it will take off. To demonstrate why the air is moving over the wings without the movement, place a sheet of notebook paper on the back side of a fan.

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And if its a jet liner? And not a propeller plane? That doesnt work. What exactly would happen in your scenario? Once the plane is no longer on the ground, is it hovering? Does it suddenly shoot forward at 250 mph? The plane has to be moving to be in flight. Thats why you dont see prop planes hovering around, beause the force of the propeller alone is not enough to make it fly. In this scenario the plane is infact moving relative to the ground. Again, the belt has NOTHING to do with anything in terms of the plane taking off. It does not alter its speed in any way.

You guys are making this way to hard. =P

Everyone who voted no is a damn retard.

The general argument for flight seems to be that the plane *would* be moving forward regardless of the conveyor belt. Since the wheels spin freely it wouldn"t matter how fast the belt moved, the plane would still move forward until liftoff.

That"s what I"m having trouble with. Seems to me the question implies that the plane is at a stand still but the thrusters are going full blast.