Would the plane take off?

[zaqwert6]

It was a pretty hard answer to grasp, even when explained and it took several examples for me to fully "get" it.

/Then again, I could be slow.

Well there are 2 issues here and I don't mean any real disrespect but....

1) Inbility to grasp the fact that airplanes don't use thier wheels to accelerate/go forward...should be obvious to anyone who has seen a plane fly without it's wheels touching hte ground.

B) Inability to 'read' a link posted 3/4 pages ago containing the complete thorey, example and practical explaination.

I won't pretend to know why either of , or apparently both of those two would be.

[SlartyBartFast]

re-read my post slowly...

Rethink your position slowly....

the first method is the speed of the wheels. the speed of the wheels will be increased by the belt rotating.

But it's one to one. THe belt MATCHES the wheel rotation.

if the linear speed of the wheels exactly matches that of the belt, the wheels CANNOT move forward and thus the plane cannot move forward.

Hold a hot wheels car on a belt sander. Rapidly increase the speed of the belt. At what point does the belt stop you from being able to mover the car forward? NEVER.

note i did NOT say RPM of the wheels at takeoff speed. i said the actual linear speed of the wheels in the experiment.

Your missing the very basic concept. Belt speed is irrelevant. No matter what the belt does, the plane will take off at normal take off speed, in the normal length of runway. Jus the wheels will be doing twice the RPM.

The belt cannot slow or stop the plane.

the second method is the belt spins at the speed of the plane in a normal takeoff. this results in the wheels rotating at about twice their normal rate.

Which is the same as the first. Please tell me how it can't be.

the third method is the belt speed adjusts to match the actual forward speed of the plane, as compared to the ground. the friction from the belt will slow the plane down somewhat, although not much, so it wont be exactly the same. it will be close to method 2... ehh, maybe i should have just not mentioned it. although it is a different interpretation of the question, they all are valid interpretations.

WHAT THE HOOBY is different between the "actual" forward speed, linear speed calculated through RPM, and speed at normal take off?

[slade]

Rethink your position slowly....



But it's one to one. THe belt MATCHES the wheel rotation.



Hold a hot wheels car on a belt sander. Rapidly increase the speed of the belt. At what point does the belt stop you from being able to mover the car forward? NEVER.



Your missing the very basic concept. Belt speed is irrelevant. No matter what the belt does, the plane will take off at normal take off speed, in the normal length of runway. Jus the wheels will be doing twice the RPM.

The belt cannot slow or stop the plane.



Which is the same as the first. Please tell me how it can't be.



WHAT THE %&^*$ is different between the "actual" forward speed, linear speed calculated through RPM, and speed at normal take off?

*slaps forehead*
gah!

re-read my post again. you obviously missed something. your hotwheels and belt sander idea is completely irrelevant to what i said. the belt sander runs at a constant RPM. its speed is NOT ADJUSTABLE.

first lets state that if the belt starts moving while the plane is off, the plane will certainly move backward due to friction through the wheels.

let me rephrase this. you know what linear speed is, right? its the speed of the outer edge of a wheel. its a function of the RPM and diameter of the wheel. on a belt, the linear speed is the speed of any point on the belt. now, in this way of interpreting the question, the linear speed of the belt matches that of the wheel, as long as the plane is on the ground and not airborne. think of them as interlocked gears. if they match speed one cannot move faster than the other. because of the incredible force when the engines of the jet start, the plane will be pulled forward... but the sensors will pick up the rotation of the wheels, and attempt to match the belt speed to it, so the belt will begin turning... and that turning will cause the wheels to turn faster. the sensors will pick up that higher RPM and speed up the belt... which will cause the wheels to rotate faster. the plane will be slowed down because of the friction from the wheels, but not substantially, so the belt speed will essentially increase rapidly, to the point where the wheels break, and the plane will crash. the system will attempt to keep the plane from moving forward by negating the force of the jet through the RPM of the wheels, but since the friction is neglidgeable compared to the force of the engines, the belt will rapidly increase in speed. This is of course assuming the belt is powered in a manner that can support a plane, but still turn at an incredibly high RPM... im not sure which id hate to fund more, the engineers or the power bill.

i realize that post is sort of confusing, but my logic is not flawed.

think back to your belt sander theory. if you hold the car on the belt sander, the wheels spin at the same speed as the belt. but if you move the car forward, the speed of the wheels will increase slightly compared to the speed of the belt, and what im saying is the belt will speed up attempting to match that speed... but in speeding up, the wheels will speed up to match the belt PLUS the speed you are pushing it forward. the ultimate goal of the setup is to cancel the force you put on the car (or plane) through friction through the interface (wheels and belt). this of course cannot happen perfectly, but if you set it up this way with a very powerful belt system, it will result as i predicted.

as i explained, the second method is the speed in a normal takeoff and the third is the actual speed. i shouldnt have mentioned the third, since it is basically the second with the minimal difference that will come from friction through the belt/wheels. almost everyone is interpreting the question as method 1 or 2. ignore 3, forget i mentioned it.

[Shives]

OK, been thinking about this a while...

The only 2 facts everyone seems to agree on are...

1) Air needs to move across the wings to provide lift.
2) The jet engines don't provide lift or air flow over the wings.

People are pointing out that the tires and conveyor belt act like a frictionless surface. So, the engines should "slide" he plane along despite what the wheels are doing. Other people think the conveyor belt will hold the plane back.
The big problem I see in the discussion is that people want to leave some parts "real world" while other parts "ideal".
I looked at it sort of upside down. The treadmill starts moving. If the planes wheels were frictionless, they would start turning, and the plane thanks to inertia, would stay still. The wheels aren't frictionless, so the plane would start to move, in this case backwards. Now, say the pilot starts to feel this backwards movement and powers up the engines giving it a little forward thrust. The plane is not moving anywhere in relation to the air around the wings. If the conveyor belt speeds up, the pilot will also have to increase thrust to stay stationary. However, he will still be just keeping up w/ the backwards movement the conveyor belt is causing. If this keeps up until the plane is at full thrust, it won't take off. It would be a very fine balancing act, and the conveyor would probably have to move faster than it would to just move the plane at that speed. I would imagine the landing gear would also give out resulting in a huge mess
That's my thought. Am I right? I haven't a clue. What is the right answer? Until it can be done in real life, who knows.

Shives

[Lohman446]

The only 2 facts everyone seems to agree on are...

1) Air needs to move across the wings to provide lift.
2) The jet engines don't provide lift or air flow over the wings.

People are pointing out that the tires and conveyor belt act like a frictionless surface. So, the engines should "slide" he plane along despite what the wheels are doing. Other people think the conveyor belt will hold the plane back.
The big problem I see in the discussion is that people want to leave some parts "real world" while other parts "ideal".
I looked at it sort of upside down. The treadmill starts moving. If the planes wheels were frictionless, they would start turning, and the plane thanks to inertia, would stay still. The wheels aren't frictionless, so the plane would start to move, in this case backwards. Now, say the pilot starts to feel this backwards movement and powers up the engines giving it a little forward thrust. The plane is not moving anywhere in relation to the air around the wings. If the conveyor belt speeds up, the pilot will also have to increase thrust to stay stationary. However, he will still be just keeping up w/ the backwards movement the conveyor belt is causing. If this keeps up until the plane is at full thrust, it won't take off. It would be a very fine balancing act, and the conveyor would probably have to move faster than it would to just move the plane at that speed. I would imagine the landing gear would also give out resulting in a huge mess
That's my thought. Am I right? I haven't a clue. What is the right answer? Until it can be done in real life, who knows.

Shives

While realistically the plane has some friction in the bearings the thrust will overcome that bit of friction and create movement when forward power is applied by the engined.

[nippinout]

The only 2 facts everyone seems to agree on are...

1) Air needs to move across the wings to provide lift.
2) The jet engines don't provide lift or air flow over the wings.

People are pointing out that the tires and conveyor belt act like a frictionless surface. So, the engines should "slide" he plane along despite what the wheels are doing. Other people think the conveyor belt will hold the plane back.
The big problem I see in the discussion is that people want to leave some parts "real world" while other parts "ideal".
I looked at it sort of upside down. The treadmill starts moving. If the planes wheels were frictionless, they would start turning, and the plane thanks to inertia, would stay still. The wheels aren't frictionless, so the plane would start to move, in this case backwards. Now, say the pilot starts to feel this backwards movement and powers up the engines giving it a little forward thrust. The plane is not moving anywhere in relation to the air around the wings. If the conveyor belt speeds up, the pilot will also have to increase thrust to stay stationary. However, he will still be just keeping up w/ the backwards movement the conveyor belt is causing. If this keeps up until the plane is at full thrust, it won't take off. It would be a very fine balancing act, and the conveyor would probably have to move faster than it would to just move the plane at that speed. I would imagine the landing gear would also give out resulting in a huge mess
That's my thought. Am I right? I haven't a clue. What is the right answer? Until it can be done in real life, who knows.

Shives

The pilot doesn't get a license in matching thrust to forces acting against forward motion. When you have 200,000 pounds of thrust available, you don't need to worry about a dumb conveyor belt, river, wind, or Mr. T holding the plane back.

[bleachit]

When you have 200,000 pounds of thrust available, you don't need to worry about a dumb conveyor belt, river, wind, or Mr. T holding the plane back.

sig worthy, if only sigs were around..


cant believe people are still arguing it.. click on the link in the second page.. I think it was the second page.

[MantisMag]

opening this thread has made me dumber.

[silentdeath55]

If I understand this corectly, the plane wont move at all, just as a person running on a tredmill wont move at all no matter how fast they run (if they keep increasing the speed of the belt). Furthermore, aircraft need lift as was mentioned before. If you look up Bernulies (sp?) Principle you will find that fast air creates low pressure, therefore the shape of the wing coupled with the movement of air around it creates low pressure allowing the aircraft to take off.

[nippinout]

If I understand this corectly, the plane wont move at all, just as a person running on a tredmill wont move at all no matter how fast they run (if they keep increasing the speed of the belt). Furthermore, aircraft need lift as was mentioned before. If you look up Bernulies (sp?) Principle you will find that fast air creates low pressure, therefore the shape of the wing coupled with the movement of air around it creates low pressure allowing the aircraft to take off.

If you run on a treadmill, and a friend shoved your forward, do you stay in place? No, you move forward.

[MantisMag]

no it would be more like if you were the coyote and you strapped on roller skates and a rocket pack. no matter how fast that treadmill goes do you really think it can stop you with your wheels and rocket pack?

[Army]

THE PLANE WILL FLY! THE PLANE WILL FLY!! THE PLANE WILL FLY!!!

Anybody not get that yet? Do I need to repeat it? You, in the back? No?


THE PLANE WILL FLY! THE PLANE WILL FLY!! THE PLANE WILL FLY!!!

Any more questions? Anyone? Buehler? Buehler? Buehler?

[anomoly40]

To the guy who says the earth isn't moving as fast as the plane isn't realizing the earth rotates 360* in 24 hours. Now the earths circumference is approx 25,000 miles. Divide that by 24 and you get about 1040 miles an hour. Now I've seen jets take off just as good east as they can west with the same wind.

[nippinout]

What if I was on a treadmill, facing backwards, blindfolded, in a vacuum, and holding a baby wildebeast?

[nippinout]

To the guy who says the earth isn't moving as fast as the plane isn't realizing the earth rotates 360* in 24 hours. Now the earths circumference is approx 25,000 miles. Divide that by 24 and you get about 1040 miles an hour. Now I've seen jets take off just as good east as they can west with the same wind.

Don't forget the Earth's orbit speed around the sun. Might as well factor in Einstein's frame-dragging while you're at it.