Will it take off?

[Christopherrr]

...I think about it more and more and I come to this conclusion.

if there isn't flowing air rushing by the wings there isn't any lift generated. If there isn't lift...the plane isn't going anywhere.

no wind = no lift
no lift = you ain't going anywhere

I really like to see this in real life.

[DierDesire824]

This thread has 2 opinions in it

the people reading the thread as if a plane is sitting on a belt and the belt goes backwards the plane will go backwards to

and the people that see it like this the treadmill doesnt matter because the wheels arent pushing the plane the jet engines are so does the treadmill matter no the jet could easily take off but the tires would be moving faster that doesnt really matter though

bottom line if the plane is full throttle the belt can go backwards as fast as possible it wont matter the plane will still go forward as normal

[Sean 94z28]

"This conveyer has a control system that tracks the plane speed and tunes the speed of the conveyer to be exactly the same (but in opposite direction)."

Plane speed = the speed of the plane relative to the surrounding environment.
Plane speed = conveyor speed (quote above)
Wheel speed (until the plane takes off) = Plane speed + conveyer speed

Saying that the plane is moving 100mph AND the conveyor is moving 100mph does not mean the plane is standing still. It only means the wheels are going 200 and the plane IS going to take off.

Now if the question said that the conveyor constantly adjusted to try to match the speed of the planes wheels, then take-off would not occur as long as the conveyor could keep speeding up indefinately. Once the conveyor reached its max speed, the plane would accelerate away at a normal rate.

Trace had it exactly right in his first post. Change it to a plane with skids on an ice conveyor and the answer is obvious because there are only 2 speeds. The plane speed and the conveyor speed.

Or think of it this way. If a plane is stationary with its wheels moving on a 100MPH conveyor. Then there are not moving the same speed!

If the plane is moving 100MPH on a 100MPH conveyor, it is still moving 100MPH and WILL fly.

[fastTa]

Uhhh, I don't know where you got that idea but the question is whether the plane can take off or not. It does not ask whther it "could provide an aircraft the capacity to fly. "

Jeff...Jeff...Jeff. In order for a plane to fly it must "take off". Equally but inversely consequently, it must "take off" to fly. Semantics my brother.

[fastTa]

Trace had it exactly right in his first post. Change it to a plane with skids on an ice conveyor and the answer is obvious because there are only 2 speeds. The plane speed and the conveyor speed.

Sorry, but even ice has a much larger surface coefficient of friction than you likely suspect, especially as the opposingly relative velocity and vector parallel variances amongst the tires of the aircraft and the surface of the ice. It is an irrelevant argument to replace the converyor belt surface with the theoretical ice. Let's be thorough and accurate here.

[Jeff_in_Atl]

Jeff...Jeff...Jeff. In order for a plane to fly it must "take off". Equally but inversely consequently, it must "take off" to fly. Semantics my brother.

What???
You said...

...It merely questioned whether or not a moving runway (as opposed to a stationary runway) could provide an aircraft the capacity to fly. The answer is....IT CANNOT.

You said "provide". That is not the question. Of coarse it wouldn't provide the capacity to fly. Even if it were moving in the same direction it wouldn't provide the capacity to fly unless the brakes were on.

I believe the addition of the moving treadmill is just put to confuse the issue when it has no bearing on the issue.

[fastTa]

What???
You said...

You said "provide". That is not the question.

Yes, it is. There is no other way to interpret it Jeff. It is a cause and effect proposed theory. Some thing has to cause an effect on something else. That is identical to saying "giving something the capacity". Energy is never wasted, only trasformed. Given that, there are two parent types of energy....Potential and kinetic. That makes the question exactly what I said it was....a question of potential capacity. Think about it.

I agree that the runway thrown into the lackingly self-suppostive equation is essentially worthless.

[Jeff_in_Atl]

Yes, it is. There is no other way to interpret it Jeff. It is a cause and effect proposed theory. Some thing has to cause an effect on something else. That is identical to saying "giving something the capacity". Energy is never wasted, only trasformed. Given that, there are two parent types of energy....Potential and kinetic. That makes the question exactly what I said it was....a question of potential capacity. Think about it.

I agree that the runway thrown into the lackingly self-suppostive equation is essentially worthless.

My daughter who is taking geometry now has math question in school that throw in more information than what is required for an equation. I see this the same way. The moving runway has no bearing on this equation because the thrust is gained from friction to the air not the runway. Now if this were a vehicle that achieved it's propulsion from the turning of the wheels it would have a large bearing on the equation. I think you are reading too much into the question and making assumptions not in evidence by what is written in the question.

When it comes down too it, the plane has to move forward in order for the tread mill to turn. But what does it matter that the tread mill is turning, the plane is still moving forward. The tread mill is not going to stop the plane from moving because the wheels free spin. Yes there will be some drag but that is very minimal. So the question is can the plane achieve enough forward speed to fly. Well we just established that the tread mill is not going to stop it from going forward so why wouldn't it achieve enough forward speed to fly. I can't see a reason.

[fastTa]

My daughter who is taking geometry now has math question in school that throw in more information than what is required for an equation. I see this the same way. The moving runway has no bearing on this equation because the thrust is gained from friction to the air not the runway. Now if this were a vehicle that achieved it's propulsion from the turning of the wheels it would have a large bearing on the equation.

Funny and agreed.

I think you are reading too much into the question and making assumptions not in evidence by what is written in the question.

Merely, trying to be thorough and conclusive based upon specific perspectives.

When it comes down too it, the plane has to move forward in order for the tread mill to turn. But what does it matter that the tread mill is turning, the plane is still moving forward. The tread mill is not going to stop the plane from moving because the wheels free spin. Yes there will be some drag but that is very minimal. So the question is can the plane achieve enough forward speed to fly. Well we just established that the tread mill is not going to stop it from going forward so why wouldn't it achieve enough forward speed to fly. I can't see a reason.

I always agreed that the plane would eventually fly if it were moving forward relative to the ground, BUT the original question, I feel, strongly incinuated that the plane would be sitting still relative to the ground with the conveyor runway moving backwards beneath it's wheels. That's where I found fault.

[Jeff_in_Atl]

I think the problem is coming down to how is the speed of the plane being measured. From the stationary ground or the moving tread mill.

[Jay 02 TA ws6]

Ok, so this is going around the 'net. HUGE threads of people arguing back and forth...

A plane is standing on a runway that can move (some sort of band conveyer). The plane moves in one direction, while the conveyer moves in the opposite direction. This conveyer has a control system that tracks the plane speed and tunes the speed of the conveyer to be exactly the same (but in opposite direction).


The question is:

Will the plane take off or not? Will it be able to run up and take off?


The plane WILL take off. The wheels do not affect the thrust of the airplane, they just support it. People cant seem to grasp the concept that they are free rotating wheels and this is not a wind tunnel we are talking about.

The plane will not take off.

Freebody diagrams, relative motion, ... what am I... back in college?

This is a relative motion problem, what you have to decide is what is the planes motion observed by?

If the plane's motion is observed by a stationary bystander (someone sitting in the control tower), then yes, it can take off - of course assuming it generates the necessary thrust and lift to do so.

If the plane's motion has no motion observed by that same bystander, then no, it will not take off.

If you are standing in the control tower, and you are watching this... and you see a plane standing still, you assume it is not moving, correct? If you get closer and realize the plane's wheels are actually moving forward at 100 mph, then that must mean the conveyor belt is also moving at 100 mph in the opposite direction, agree? It doesn't matter if the wheels accelerate to 200 mph, if the conveyor belt matches its speed and is moving 200 mph, the plane is - in effect - stationary to the air meaning zero lift is generated as no air is moving under and over the wings. (no more than a plane that is stationary)

Now... if you are standing in the control tower and you see a plane accelerating across a runway, you assume the ground is stationary, correct? But what if it wasn't? ... What if the ground was moving in reverse at the exact same speed you are observing the plane moving in? (Remember, you are a stationary bystander) If you see a plane traveling at 10 mph across a runway... there could be a conveyor belt under it moving 10 mph... but that would mean the plane's wheels are spinning at 20 mph. The plane could accelerate to 100 mph (relative to the stationary observer), and the conveyor belt could accelerate to 100 mph to match that, but that would mean the plane's wheels were spinning at 200 mph.

So... can the plane take off? Yes and no. It depends on what the frame of reference was and who is observing this "motion".

If the question is asking what I think it was intending to - then no, it cannot take off.

Picture yourself running on a treadmill. You are running at 5 mph, the treadmill is in reverse at 5 mph. What is your effect velocity relative to the ground? It's 0. To the ground, and to the air, you are not moving. In this situation, you are generating no more lift or air resistance than you would be standing still.

When you are driving down the freeway at 70mph and a car going the other way crosses your path at 70mph - the car looks to you as if it were traveling 140 mph (assuming a zero degree angle of observance ... GET OUT OF THE WAY!!!! ... hehehe... just kidding) To the bystander, both cars appear to be moving 70 mph.

Want to really bake your noodle? Stand still on a windy day. Don't move. While your velocity relative to the ground is 0, you possess a true airspeed that is exact opposite of the speed of the wind. If the wind is moving 25 mph, to the air, you are moving 25 mph.

[Jeff_in_Atl]

OK so the problem is confusion about measuring the plane speed. Do you measure it from a stationary position or based on the moving ground speed. The question says "The plane moves in one direction, while the conveyer moves in the opposite direction." means they both are moving based on a stationary position.

If the plane speed is based on the speed of the moving ground then what is the speed of the moving ground based on? You can't say the speed of the plane of from the moving ground and then say the speed of the ground is from a non moving item. You also can't say the plane speed is based on the moving ground and the moving ground speed is based on the plane because that would always be zero. So I don't see how the speed of both can be based from anything but a stationary object.

[Sean 94z28]

Sorry, but even ice has a much larger surface coefficient of friction than you likely suspect, especially as the opposingly relative velocity and vector parallel variances amongst the tires of the aircraft and the surface of the ice. It is an irrelevant argument to replace the converyor belt surface with the theoretical ice. Let's be thorough and accurate here.

Far from irrelevent. A stationary airplane (regardless if it has wheels or skids) on a 100 MPH treadmill is going zero MPH. A 100 MPH airplane (also regardless of its landing configuration) on a 100 MPH treadmill, is still going 100MPH and will fly.

It might take more thrust to overcome the additonal friction you refer to. It doesn't change the circumstances of the question at all. Unless of course, you assume wheel speed = airplane speed. I don't.

[Jay 02 TA ws6]

OK so the problem is confusion about measuring the plane speed. Do you measure it from a stationary position or based on the moving ground speed. The question says "The plane moves in one direction, while the conveyer moves in the opposite direction." means they both are moving based on a stationary position.

Exactly... I think some people are just interpreting different things from the question - but in reality there are multiple scenarios.

If the plane speed is based on the speed of the moving ground then what is the speed of the moving ground based on? You can't say the speed of the plane of from the moving ground and then say the speed of the ground is from a non moving item. You also can't say the plane speed is based on the moving ground and the moving ground speed is based on the plane because that would always be zero. So I don't see how the speed of both can be based from anything but a stationary object.

hahaha... what is this? Chicken or the egg?

Hold up a toy car. Spin its wheel relative to your stationary position at 10 mph. Put it in on a treadmill that is spinning at 10 mph. To your stationary position, the car will not move forward or backwards on the treadmill. This is how I interpret the question, and in this scenario, the plane will not take off.

[Jay 02 TA ws6]

Far from irrelevent. A stationary airplane (regardless if it has wheels or skids) on a 100 MPH treadmill is going zero MPH. A 100 MPH airplane (also regardless of its landing configuration) on a 100 MPH treadmill, is still going 100MPH and will fly.

It might take more thrust to overcome the additonal friction you refer to. It doesn't change the circumstances of the question at all. Unless of course, you assume wheel speed = airplane speed. I don't.

You're half right... the plane's wheels don't dictate the plane's speed. But the only velocity that matters to the plane is airspeed. If it took 150 mph true airspeed to take off, the plane could be sitting still and would take off if it was hit with a 150 mph gust of wind. Think of things flying around in a hurricane. It's all about lift and you can't generate that without airspeed. There are a lot of variables at work...