A jet plane on a large treadmill

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Originally Posted by AaronWright

Even if the conveyor matches the wheel speed, I'm sure that the wheel bearings could tolerate the 350 kts(twice a 747s takeoff speed) and still take off. Like I said, we're doomed.

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If the conveyor matches the wheel speed, then the plane never generates any speed relative to the ground, and therefore does not generate lift, and does not take off.

It's really not difficult at all to understand. The plane must generate about 200mph of ground speed to take off, so the wheels must spin at 200mph faster than the conveyor. If the conveyor is matching the wheel speed this never happens. If the conveyor is matching the ground speed of the airplane, then the wheels are spinning faster than the conveyor. Once the plane is traveling at 200mph the conveyor will be moving at 200mph and the wheels will be spinning at 400mph. Voile, the plane takes off.

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Originally Posted by Jethro

Here is another question, from high school physics 25 years ago. Two identical cars, each traveling 50mph crash into one another in a perfect, straight on head on crash. they come together at a speed of 100 mph. Do the occupants experience a wreck equal to 100mph into a solid concrete wall, or 50 mph into a wall?

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Because the cars are identical then the force experienced by the occupants of the cars is the same as hitting the concrete wall.

If one car is heavier than the other then the occupants of the smaller car experience more force while the occupants of the bigger car experience less. Not being a physics geek I don't know if the difference in forces is proportional to the difference in weights, but I suspect it is.


Flyoverland Captive - I'm with you because that's the practical answer to this question. What DJsapp and Doughboy are talking about is a different take on the question that focuses on the wheel speed vs. conveyer speed, and they are right as long as we are talking about the rotational speed of the wheel. The only way that the wheel speed can be the same as the conveyer is if the plane is not moving, and in the real world the only way that would happen is if the plane was anchored to a stationary point off the conveyer and it's engines didn't come into play OR the engines are tuned to provide just the perfect amount of thrust to perfectly counteract the rolling resistance and bearing friction in the wheels and thus hold the plane in place.

I have only ever seen this question asked the way it was asked in the OP of this thread - that the conveyer matches the plane's speed. In that scenario the wheels are pretty much irrelevant.

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Originally Posted by doughboyshredder

If the conveyor matches the wheel speed, then the plane never generates any speed relative to the ground, and therefore does not generate lift, and does not take off.

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How can the conveyor prevent the wheels from going faster then it goes? I do not see how the conveyor can determine the speed of the jet through the wheels thus preventing it from taking off. The jet's engines force is on the air surrounding the plane. It pushes/pulls against the air to move the jet forward. For the force of the jet's engines pushing against the air to be negated(keeping the jet stationary) the treadmill would need to apply an equal or greater force in the opposite direction to the plane through the free spinning wheels to the landing gear. Simply matching the speed of the plane would not apply a force great enough to hold the jet in a stationary position.

That's why the wheel speed = conveyer speed idea is not a very realistic idea and is tougher to wrap your head around than the conveyer = plane speed idea.

Let's look at this in the real world and pretend that someone did indeed build a giant conveyer belt upon which rests a conventional airplane. When the conveyer is turned on, the airplane will move backwards at the same speed as the conveyer belt. This is because the rotation of the wheels isn't frictionless in the real world. There is rolling resistance of the tire and friction in the wheel bearings. In order to make the wheels turn at the same speed as the conveyer, something needs to keep the plane motionless in relation to the ground. As I mentioned above, this could be accomplished by tying the plane to anchors off the conveyer, or by using the plane's engines to provide just the right amount of thrust to overcome the rolling resistance of the wheels & bearing friction. This satisfies the requirement that the conveyer speed always matches the wheel speed and in order for this to be true the plane cannot be moving with relation to the ground. The only way the plane can take off in this scenario is if it's somehow provided with a head-wind strong enough to generate the required lift. So, put a fan in front of the conveyer that can generate a 200mph wind and the answer becomes yes, the plane will take off. Otherwise in this scenario it can't because it's constrained by the artificial requirement that the conveyer speed matches wheel speed.

I don't know if someone already explained this to you retards or not but I can't leave this untouched.

The plane would never take off. What causes a plane to fly is not thrust directly. Thrust is a means of producing the movement necessarily to achieve lift. Lift is a change in air pressure between the air below and above the wing. That's why wings are flat on the bottom android d on top. The round tops create a larger surface area leading to air passing over more slowly than the air passing under. The delta in that air speed creates lift.

So if the plane is motionless the. There is no air passing over the wings thus no lift and no takeoff. No matter how high the thrust of he engines.

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Originally Posted by Skirotica

So if the plane is motionless the. There is no air passing over the wings thus no lift and no takeoff. No matter how high the thrust of he engines.

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What is holding the plane motionless? Can the conveyor/treadmill apply enough force through the wheels to the axle and landing gear to negate the force of the jet/prop pushing the plane forward?

I am not that smart and I get this... WHY IS THIS SO HARD???????

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Originally Posted by Chainsaw_Willie

That's why the wheel speed = conveyer speed idea is not a very realistic idea and is tougher to wrap your head around than the conveyer = plane speed idea.

Let's look at this in the real world and pretend that someone did indeed build a giant conveyer belt upon which rests a conventional airplane. When the conveyer is turned on, the airplane will move backwards at the same speed as the conveyer belt. This is because the rotation of the wheels isn't frictionless in the real world. There is rolling resistance of the tire and friction in the wheel bearings. In order to make the wheels turn at the same speed as the conveyer, something needs to keep the plane motionless in relation to the ground. As I mentioned above, this could be accomplished by tying the plane to anchors off the conveyer, or by using the plane's engines to provide just the right amount of thrust to overcome the rolling resistance of the wheels & bearing friction. This satisfies the requirement that the conveyer speed always matches the wheel speed and in order for this to be true the plane cannot be moving with relation to the ground. The only way the plane can take off in this scenario is if it's somehow provided with a head-wind strong enough to generate the required lift. So, put a fan in front of the conveyer that can generate a 200mph wind and the answer becomes yes, the plane will take off. Otherwise in this scenario it can't because it's constrained by the artificial requirement that the conveyer speed matches wheel speed.

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Yes, if you restrict the power of the plane it cannot takeoff from a treadmill/conveyor.

There is nothing saying the jet is restricted to only use enough thrust to match the conveyors speed. In this situation the conveyor has to overcome the thrust of the jet to prevent it from taking off. How can a conveyor do this?

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Originally Posted by Skirotica

I don't know if someone already explained this to you retards or not but I can't leave this untouched.

The plane would never take off. What causes a plane to fly is not thrust directly. Thrust is a means of producing the movement necessarily to achieve lift. Lift is a change in air pressure between the air below and above the wing. That's why wings are flat on the bottom android d on top. The round tops create a larger surface area leading to air passing over more slowly than the air passing under. The delta in that air speed creates lift.

So if the plane is motionless the. There is no air passing over the wings thus no lift and no takeoff. No matter how high the thrust of he engines.

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Quoting for future hilarity.

Too many posts to see if this was covered but this a question for Myth Busters !

I'm with the lift issue otherwise the US Navy would have put this into use with seriously lighter aircraft !

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Originally Posted by Big Snowballs

Too many posts to see if this was covered but this a question for Myth Busters !

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http://www.youtube.com/watch?v=0KsdMuhYJPw

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Originally Posted by Big Snowballs

I'm with the lift issue otherwise the US Navy would have put this into use with seriously lighter aircraft !

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and again, NASA did put this into use with the Quiet Short-Haul Research Aircraft, which puts the jets above the wing causing the generation of much more lift and the ability to takeoff almost on a dime:

http://www.youtube.com/watch?v=_4QiW-ROJtg#t=1m10s

more modern investigative designs could allow a commercial jet to take off in as little as 2000ft:

http://www.youtube.com/watch?v=Sa-w6M5UR5U

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Originally Posted by Cross

Yes, if you restrict the power of the plane it cannot takeoff from a treadmill/conveyor.

There is nothing saying the jet is restricted to only use enough thrust to match the conveyors speed. In this situation the conveyor has to overcome the thrust of the jet to prevent it from taking off. How can a conveyor do this?

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Realistically it can't. That's the problem with the conveyer speed = wheel speed argument, or the beauty of it depending on your point of view.

There are two different problems that have gotten tangled up in this thread.

The original question, way back when, involved conveyer speed = plane speed. In that case the plane clearly takes off and the wheels will be spinning at twice the plane's and conveyer's speed when it does.

The second question is more problematic because a condition was stated in it that can only come true if the plane doesn't move relative to the ground. That condition is that conveyer speed = wheel speed. As long as that MUST be true, the plane cannot take off because it won't move.

It's not that it's not physically able to move, it's not that you couldn't crank up the engines and make it move, it's not that the conveyer is somehow preventing it from moving, it's that you are working within the constraints posed by the question, that the wheel speed MUST match the conveyer speed. The only way that can happen is if the plane doesn't move, and if the plane is not moving it can't take off unless you find another way to create enough airflow over the wings to provide lift (the fan).

I've already answered how preventing the plane from moving can be accomplished, either by anchoring the plane to the ground somehow, or using the plane's engines to perfectly match the rolling resistance of the wheels.

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Originally Posted by f2f

http://www.youtube.com/watch?v=0KsdMuhYJPw

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Thanks for that and I need to ask... is this a case of the propeller generating enough wind power over the wings to create the lift needed ?

I figured that the question is about a jet engine and its ability to act like a rocket to create instant lift !

Seven fucking years. It's like a whole new generation of retards has been born.

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Originally Posted by iceman

Seven fucking years. It's like a whole new generation of retards has been born.

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Alrighty then... enlighten all the retards and explain it Albert http://jonathanturley.files.wordpres...ein_tongue.jpg

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Originally Posted by Big Snowballs

Thanks for that and I need to ask... is this a case of the propeller generating enough wind power over the wings to create the lift needed ?

I figured that the question is about a jet engine and its ability to act like a rocket to create instant lift !

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No, it has to do with the propeller of the plane using the air to push/pull against, to move the plane forward. Much like the prop on a boat motor uses the water to move the boat, in the case of a plane the water is air. The wheels are just something to reduce the friction of the place across the ground until the plane gets into the air. The treadmill has no effect on how much thrust the propeller can create since they have no interaction. The only thing the treadmill effects is the speed of the wheels in relation to the planes air speed. If you were to stand on a treadmill wearing roller skates and there is a rope anchored to a tree in front of you, you would be able to pull yourself forward moving against the movement of the treadmill with out much effort. This is what a planes does the rope is the air and the propeller is your hands pulling the plane forward. The air moving around you is the same air that would move around the plane allowing it to take off if speeds generate enough lift. The tread mill cannot create enough force against the plane to slow it down enough to not allow it to take off. The speed of the wheels or the treadmill have very little to do with whether or not the plane can take off. It is all about forces. The propeller pushes the plane one direction faster and faster until the speed of the air over the wings is enough for it to generate lift. To prevent this from happening the ground would have to exert a equal or greater force against the plane in the opposite direction. Just the ground moving in the opposite direction will not create a force against the plane since the wheel in between the two is designed to keep that force at a minimum.

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Originally Posted by Chainsaw_Willie

If one car is heavier than the other then the occupants of the smaller car experience more force while the occupants of the bigger car experience less. Not being a physics geek I don't know if the difference in forces is proportional to the difference in weights, but I suspect it is.

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You are correct. F=M*A
In this instance A is constant so the increase in force is linear.
example: 1000kg * 20m/s^2 = 20000 newtons
and for every 1000kg mass you add you get 20000 newtons more force.

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Originally Posted by Skirotica

I don't know if someone already explained this to you retards or not but I can't leave this untouched.

The plane would never take off. What causes a plane to fly is not thrust directly. Thrust is a means of producing the movement necessarily to achieve lift. Lift is a change in air pressure between the air below and above the wing. That's why wings are flat on the bottom android d on top. The round tops create a larger surface area leading to air passing over more slowly than the air passing under. The delta in that air speed creates lift.

So if the plane is motionless the. There is no air passing over the wings thus no lift and no takeoff. No matter how high the thrust of he engines.

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I'll let the poor explanation of Bernoulli's principle slide (except to say that the air is faster over the top of the wing), and just ask you this: what force attempts to push the aircraft forward, and what force is holding it back?

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Originally Posted by Chainsaw_Willie

The second question is more problematic because a condition was stated in it that can only come true if the plane doesn't move relative to the ground. That condition is that conveyer speed = wheel speed. As long as that MUST be true, the plane cannot take off because it won't move.

It's not that it's not physically able to move, it's not that you couldn't crank up the engines and make it move, it's not that the conveyer is somehow preventing it from moving, it's that you are working within the constraints posed by the question, that the wheel speed MUST match the conveyer speed. The only way that can happen is if the plane doesn't move, and if the plane is not moving it can't take off unless you find another way to create enough airflow over the wings to provide lift (the fan).

I've already answered how preventing the plane from moving can be accomplished, either by anchoring the plane to the ground somehow, or using the plane's engines to perfectly match the rolling resistance of the wheels.

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Where is the second question stating the speeds have to be equal?

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Originally Posted by Cross

Where is the second question stating the speeds have to be equal?

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As DBS pointed out, that was the original question floating around the 'net circa 2005.

The OP of this thread posed the watered down version that doesn't reference wheel speed.

This thread make me give up on the world

Quick! Someone call Boeing and tell them they have it all wrong!

It appears this

http://youtu.be/nFs80rf9D4Q

is inevitable.

Remember the words of the OP

"this conveyor has a control system that tracks the planes speed and tunes the speed of the conveyor to be exactly the same (but in the opposite direction)."

We are talking hypotheticals here. We aren't applying forces up the landing gear and all that. We simply turn a belt in the opposite direction at exactly the right speed needed to negate what would be the acceleration of the aircraft.

You take friction coefficients and belt transmissions out of the equation because it's all hypothetical. The plane starts to move forward. It's first couple of feet are positive then the belt kicks in and suddenly the wheels are spinning in place covering ever more belt but the belt keeps coming because it is somehow moving super fast.
There are unpowered treadmills that will do this to a limited extent. Eventually though you can overpower the free spin capability of the unpowered treadmill. This hypothetical assumes you can never overpower the treadmill. That's the rule set by the OP. play in his world or create your own.

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Originally Posted by Chainsaw_Willie

Realistically it can't. That's the problem with the conveyer speed = wheel speed argument, or the beauty of it depending on your point of view.

There are two different problems that have gotten tangled up in this thread.

The original question, way back when, involved conveyer speed = plane speed. In that case the plane clearly takes off and the wheels will be spinning at twice the plane's and conveyer's speed when it does.

The second question is more problematic because a condition was stated in it that can only come true if the plane doesn't move relative to the ground. That condition is that conveyer speed = wheel speed. As long as that MUST be true, the plane cannot take off because it won't move.

It's not that it's not physically able to move, it's not that you couldn't crank up the engines and make it move, it's not that the conveyer is somehow preventing it from moving, it's that you are working within the constraints posed by the question, that the wheel speed MUST match the conveyer speed. The only way that can happen is if the plane doesn't move, and if the plane is not moving it can't take off unless you find another way to create enough airflow over the wings to provide lift (the fan).

I've already answered how preventing the plane from moving can be accomplished, either by anchoring the plane to the ground somehow, or using the plane's engines to perfectly match the rolling resistance of the wheels.

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And, that is the answer my friends.

What is most amazing is that there have been literally thousands of pages of arguments about these questions.

If you don't use the plane's engines to match the rolling resistance of the wheels, the spin up of the wheels to infinite speed will happen almost immediately, the bearings will seize, and then we come to the crux. Will the plane drage the melted tires across the treadmill and take off, or will it fall over?

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Originally Posted by Skirotica

Remember the words of the OP

"this conveyor has a control system that tracks the planes speed and tunes the speed of the conveyor to be exactly the same (but in the opposite direction)."

We are talking hypotheticals here. We aren't applying forces up the landing gear and all that. We simply turn a belt in the opposite direction at exactly the right speed needed to negate what would be the acceleration of the aircraft.

You take friction coefficients and belt transmissions out of the equation because it's all hypothetical. The plane starts to move forward. It's first couple of feet are positive then the belt kicks in and suddenly the wheels are spinning in place covering ever more belt but the belt keeps coming because it is somehow moving super fast.
There are unpowered treadmills that will do this to a limited extent. Eventually though you can overpower the free spin capability of the unpowered treadmill. This hypothetical assumes you can never overpower the treadmill. That's the rule set by the OP. play in his world or create your own.

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You are interpreting the question incorrectly. Which, btw, is the biggest problem in this entire thread. You are thinking that the treadmill is matching the wheel speed. It is not in the OP's question. It is matching the planes speed. So, when the plane is doing 10mph, the treadmill is doing 10mph, and the wheels are spinning at 20mph. As the plane accelerates, the treadmill matches that acceleration, and the wheels double that acceleration. The plane takes off.

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Originally Posted by Skirotica

Remember the words of the OP

"this conveyor has a control system that tracks the planes speed and tunes the speed of the conveyor to be exactly the same (but in the opposite direction)."

We are talking hypotheticals here. We aren't applying forces up the landing gear and all that. We simply turn a belt in the opposite direction at exactly the right speed needed to negate what would be the acceleration of the aircraft.

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No, we're not. Like DTM posted multiple times, and others have in different ways, the OP states that if X= velocity forward, then Conveyor belt goes -X. All the wheels have to do is spin at 2X. Thus the plane accelerates forward, the belt accelerates backward, and the wheels rotate 2x as fast.

For the last fucking time: The plane still moves forward, thus causing air to go over the wings, thus causing lift, thus taking off. A normal car would stay stationary. A car with a fucking JET ENGINE on it would move forward, since the wheels aren't the motive force.

I can't believe we added 50% to a thread that was a settled issue.

doughboy and Tippster are correct. The conveyor is doing nothing but reacting to what the plane does. It can do nothing to prevent the plane from inevitably taking off.

This thread always reminds me why I am paid so much as an engineer. Jesus christ.

For the last fucking time !
There is no last fucking time !

Don't like whats been repeated, stated, explained then don't look, don't post.

How fuck'n arrogant can you get or is it that you ragers need Midol or some other femine hygiene products.

So what .. it flies it doesn't !!!
This is interesting Thread and that's matters !!

Chile Super-Start-Guys Chile or go take a Midol !! :nonono2::nonono2::nonono2::nonono2:

^^^ I don't even know what you just said, but I agree that this is entertaining in a perverse sort of way.

Big Snowballs, pack me a bowl dood

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Originally Posted by f2f

http://www.youtube.com/watch?v=0KsdMuhYJPw

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That pilot thought he wouldn't take off? Wtf???

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Originally Posted by Big Snowballs

Don't like whats been repeated, stated, explained then don't look, don't post.

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I just did what I was arguing against and barked orders.... my bad !!!

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Originally Posted by Skirotica

Remember the words of the OP

"this conveyor has a control system that tracks the planes speed and tunes the speed of the conveyor to be exactly the same (but in the opposite direction)."

We are talking hypotheticals here. We aren't applying forces up the landing gear and all that. We simply turn a belt in the opposite direction at exactly the right speed needed to negate what would be the acceleration of the aircraft.

You take friction coefficients and belt transmissions out of the equation because it's all hypothetical. The plane starts to move forward. It's first couple of feet are positive then the belt kicks in and suddenly the wheels are spinning in place covering ever more belt but the belt keeps coming because it is somehow moving super fast.
There are unpowered treadmills that will do this to a limited extent. Eventually though you can overpower the free spin capability of the unpowered treadmill. This hypothetical assumes you can never overpower the treadmill. That's the rule set by the OP. play in his world or create your own.

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DBS has the correct answer.

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Originally Posted by doughboyshredder

You are interpreting the question incorrectly. Which, btw, is the biggest problem in this entire thread. You are thinking that the treadmill is matching the wheel speed. It is not in the OP's question. It is matching the planes speed. So, when the plane is doing 10mph, the treadmill is doing 10mph, and the wheels are spinning at 20mph. As the plane accelerates, the treadmill matches that acceleration, and the wheels double that acceleration. The plane takes off.

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Originally Posted by Arno

That pilot thought he wouldn't take off? Wtf???

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Well, he is flying an ultralight... how smart can he be?

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Originally Posted by Big Steve

Big Snowballs, pack me a bowl dood

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Forsure !
Great idea... time to get airborne !

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Originally Posted by Arno

That pilot thought he wouldn't take off? Wtf???

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most likely scripted, in my opinion. they needed at least one less-than-perspicacious opinion.

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Originally Posted by f2f

http://www.youtube.com/watch?v=0KsdMuhYJPw

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All that's doing is over powering the conveyor belt.

Stuck, the wheels are a low friction interface between the plane and the conveyor. The plane will go forward regardless of the conveyor speed. You know the trick where a waiter yanks the table cloth out from under the dishes? think of the conveyor as the sheet. It does not affect the plane.