Plane on a Treadmill

[htownclone]

if a plane is on an infinitely long treadmill that is capable of accelerating to match the speed of the plane, will the plane take off?

this is saying the treadmill is going as fast as the plane. so using this myth we are talking about, the plane should never be able to go faster than the treadmill because its constantly matching the speed.

 

[CyPlainsDrifter]

So numerous people have stated that the treadmill and plane are moving at the same speed, and the wheels are moving faster....sooooooo....the plane is not moving down the treadmill it is essentially staying in place. Am I right?

No, no you're not....... not even close.

Try to picture the treadmill as the normal runway, but with a huge belt like a treadmill. The plane would progress down the runway as normal, using the thrust from the engines. (Pick any speed you want)

The treadmill belt (or runway surface, would be moving opposite the plane at the same speed as you pick above. This would not measureably affect the speed of the plane.

The wheels would be rotating in the normal direction, but at the speed of the plane + the speed of the runway surface. This "speed of the wheels" is the only thing the treadmill belt is changing from a normal takeoff.

 

[cmoneyr]

So numerous people have stated that the treadmill and plane are moving at the same speed, and the wheels are moving faster....sooooooo....the plane is not moving down the treadmill it is essentially staying in place. Am I right?

Wrong, the plane is moving at whatever speed it is moving at, and the wheels move twice as fast to compensate for the treadmill.

but the whole myth is that the plane, not the wheels is moving as fast as the treadmill.

Correct, but again I say, just because the treadmill and the plane are moving at the same speed doesn't mean the plane isn't moving. Read my shopping cart example as I think that really illustrates the point well.

Let's try the rollerblade example again. If you're on a treadmill, you're wearing roller blades and the treadmill is moving at 5mph. You would be stationary on the treadmill, but your wheels would be moving at 5mph. Now, have someone push you with enough force so that if you were on the solid, flat ground you would move at 5mph. If they attempt to push you on the treadmill are they stopped in there tracks? No matter how hard they push you remain stationary on the treadmill? Think about that for a second, it makes no sense.

 

[jdoggivjc]

No, no you're not....... not even close.

Try to picture the treadmill as the normal runway, but with a huge belt like a treadmill. The plane would progress down the runway as normal, using the thrust from the engines. (Pick any speed you want)

The treadmill belt (or runway surface, would be moving opposite the plane at the same speed as you pick above. This would not measureably affect the speed of the plane.

The wheels would be rotating in the normal direction, but at the speed of the plane + the speed of the runway surface. This "speed of the wheels" is the only thing the treadmill belt is changing from a normal takeoff.

In a sense Adam and Jamie already proved that the plane will take off when they did that Knight Rider myth about whether you could actually park a car into a moving truck without losing control of the vehicle. In theory, as soon as the vehicle's wheels touch the ramp the vehicle should lose all control and go careening through the wall on the opposite side of the trailer. In fact, as soon as the tires hit the ramp the rotation of the tires slowed down and the vehicle eased its way into the moving truck trailer, much like they did in Knight Rider.

 

[cmoneyr]

this is saying the treadmill is going as fast as the plane. so using this myth we are talking about, the plane should never be able to go faster than the treadmill because its constantly matching the speed.

The plane can't move faster than the treadmill for purposes of this myth, and it doesn't have to. The plane will eventually get up to the speed it needs to take off, and the treadmill will follow suit, but since the plane is going its required speed it will take off.

 

[htownclone]

Wrong, the plane is moving at whatever speed it is moving at, and the wheels move twice as fast to compensate for the treadmill.


Correct, but again I say, just because the treadmill and the plane are moving at the same speed doesn't mean the plane isn't moving. Read my shopping cart example as I think that really illustrates the point well.

Let's try the rollerblade example again. If you're on a treadmill, you're wearing roller blades and the treadmill is moving at 5mph. You would be stationary on the treadmill, but your wheels would be moving at 5mph. Now, have someone push you with enough force so that if you were on the solid, flat ground you would move at 5mph. If they attempt to push you on the treadmill are they stopped in there tracks? No matter how hard they push you remain stationary on the treadmill? Think about that for a second, it makes no sense.

It doesn't make sense, and it's not what I said, if someone pushed you, your speed WOULD increase but the treadmill's speed would also increase(which is what the myth says). Therefore you wouldn't be moving forward on it.

 

[balken]

I must point out a third possibility that many are neglecting to consider. The plane may look to its side to check out a hot chick on the adjacent treadmill, stumble, fall on its nosecone and experience complete humiliation.

How often do we overlook the obvious?

 

[DaddyMac]

In a sense Adam and Jamie already proved that the plane will take off when they did that Knight Rider myth about whether you could actually park a car into a moving truck without losing control of the vehicle. In theory, as soon as the vehicle's wheels touch the ramp the vehicle should lose all control and go careening through the wall on the opposite side of the trailer. In fact, as soon as the tires hit the ramp the rotation of the tires slowed down and the vehicle eased its way into the moving truck trailer, much like they did in Knight Rider.

No, no, no, no, NO!

It's totally different because Knight Rider is a car and it's propulsion comes from the wheels themselves. We're talking about the propulsion not coming from the wheels, but rather the jets or prop.



Ok - I have no idea if that's true or not, just seemed appropriate and I got it throw in my face about a dozen times.... :wink:

(ps - nor do I care, so save the correction responses)

 

[cmoneyr]

It doesn't make sense, and it's not what I said, if someone pushed you, your speed WOULD increase but the treadmill's speed would also increase(which is what the myth says). Therefore you wouldn't be moving forward on it.

You're not reading right. I said the treadmill is going 5mph and you are going 0mph. So, that doesn't match with the myth, but it makes it easier to understand the next step which does match the myth. So you're going 0mph, no thrust, and the treadmill is going 5mph. Now, add in 5mph of thrust, you are now going 5mph forward, and the treadmill is still going the same 5mph backwards, matching your speed. The wheels however are rotating at 10mph.

 

[htownclone]

You're not reading right. I said the treadmill is going 5mph and you are going 0mph. So, that doesn't match with the myth, but it makes it easier to understand the next step which does match the myth. So you're going 0mph, no thrust, and the treadmill is going 5mph. Now, add in 5mph of thrust, you are now going 5mph forward, and the treadmill is still going the same 5mph backwards, matching your speed. The wheels however are rotating at 10mph.

Again with the wheels, the wheels have absolutely nothing to do with it. If you are going 5mph and the treadmill is going 5mph in the opposite direction, so you are not moving forward.

 

[aeroclone08]

Re: CyBookie - Plane on a Treadmill

Here's what I posted on page 2:

Forget about the wheels for a moment since they're only there to prevent the underbelly of the plane from being destroyed on takeoff/landing. Imagine the plane hovering stationary a few feet above the treadmill (like someone just photoshopped the wheels out). Now increase the thrust of the engines and start the treadmill as well. What is there to keep the aircraft from moving forward (and creating a pressure differential on the wings)? Nothing, the aircraft will move forward and eventually lift off.

Now if we put the wheels back in the picture they act the same way- they only keep the body of the aircraft off the ground. The will spin freely (up to infinity velocity if you want), but there is no force there to counter the forward thrust of the engines (whose thrust is NOT transferred through the wheels.)

Also I'll bust out the free-body diagram again.

Show where the force to overcome the engine thrust will come from.

 

[ISUCyclones]

htownclone, you must be the one on the right of your display photo.)

 

[DaddyMac]

I'm (sadistically) enjoying this thread. However, anyone else got a splitting headache from it?

Tomorrow's quandry to ponder for everyone - what do women want/think? (ladies present, feel free to substitute, "what the hell was he thinking" - my wife seems to say that alot)

A man walking along a California beach was deep in prayer. All of a sudden he said out loud, "Lord grant me one wish."

At once the sky clouded above his head and in a booming voice the Lord said, "Because you have TRIED to be faithful to me in all ways, I will grant you one wish"

The man said, "Build a bridge to Hawaii, so I can drive over anytime I want to."

The Lord said, "Your request is very materialistic. Think of the logistics of that kind of undertaking. The supports required to reach the bottom of the Pacific! The concrete and steel it would take! I can do it, but it is hard for me to justify your desire for worldly things. Take a little more time and think of another wish, a wish you think would honor and glorify me."

The man thought about it for a long time. Finally he said, "Lord, my wife says that I am uncaring and insensitive. I wish that I could understand women. I want to know how they feel inside, what they are thinking when they give me the silent treatment, why they cry, what they mean when they say "nothing", and how I can make a woman truly happy."

After a few minutes God said, "You want two lanes or four on that bridge?"

 

[jdoggivjc]

Again with the wheels, the wheels have absolutely nothing to do with it. If you are going 5mph and the treadmill is going 5mph in the opposite direction, so you are not moving forward.

This is where you're not understanding - FREE-ROTATING WHEELS have EVERYTHING to do with this. The fact that the wheels are free to rotate on the plane is the reason why the plane will take off whether the treadmill is moving at 100 mph or not moving at all.

 

[Clonefan94]

Well, if the whole treadmill thing is screwing people up, can we look at it like a water plane in a river, traveling downstream? The ground (or water or treadmill) in this case, has nothing at all to do with the propulsion of the aircraft. (hence the word aircraft) For air travel we use air pressure to push planes along. It really doesn't matter what the ground is doing It doesn't affect the airplanes thrust at all. Once you apply thrust, it's propelled forward. Now, if you could control a tailwind to blow as fast as the plane could accelerate, if probably wouldn't take off.

 

[htownclone]

This is where you're not understanding - FREE-ROTATING WHEELS have EVERYTHING to do with this. The fact that the wheels are free to rotate on the plane is the reason why the plane will take off whether the treadmill is moving at 100 mph or not moving at all.

So the plane can take off now if it is not moving at all simply because it has free rotating wheels? What you all are not understanding is that THE PLANE CANNOT MOVE FASTER THAN THE TREADMILL! Talk about pushing it all you want, etc etc, but if you push the plane/thrust/whatever, the treadmill MUST also increase in speed, the plane is NOT moving, there is no wind whatsoever to create lift. I really don't know how I can be any more clear.

 

[twittkop]

Again with the wheels, the wheels have absolutely nothing to do with it. If you are going 5mph and the treadmill is going 5mph in the opposite direction, so you are not moving forward.

So you're saying if a car (yes I know this is dangerous to bring back into the argument) were driving 10 mph on an infinitely long treadmill while the treadmill was going 5mph in the reverse direction that the car would not be going anywhere with respect to the stationary ground below the treadmill?

 

[wolverine68]

Forgive me my ignorance, but wouldn't it be true to say that the force of gravity will be acting on the plane regardless of thrust. I know that those who believe that the thrust of the plane would overcome the speed of the treadmill, allowing the plane to gain lift and therefore take off. But if gravity continues to act on the plane, and the treadmill can match the speed of the wheels, then there is no lift. Maybe I am misunderstanding the arguments for lift off, but I think that they are forgetting about the force of gravity that keeps the wheels on the ground (thrust is trying to move the plane forward, not up, the movement of the air over the wings provides lift).

Oh, Well.

 

[htownclone]

So you're saying if a car (yes I know this is dangerous to bring back into the argument) were driving 10 mph on an infinitely long treadmill while the treadmill was going 5mph in the reverse direction that the car would not be going anywhere with respect to the stationary ground below the treadmill?

It WOULD be moving if the car was going 10mph and the treadmill was going 5mph. but the myth is about these 2 moving the SAME SPEED.

 

[jdoggivjc]

So the plane can take off now if it is not moving at all simply because it has free rotating wheels? What you all are not understanding is that THE PLANE CANNOT MOVE FASTER THAN THE TREADMILL! Talk about pushing it all you want, etc etc, but if you push the plane/thrust/whatever, the treadmill MUST also increase in speed, the plane is NOT moving, there is no wind whatsoever to create lift. I really don't know how I can be any more clear.

Tell me something - how does a plane take off when on a runway? The free-rotating wheels move exactly as fast as as the plane is moving, until the plane lifts off, when the wheels stop rotating completely. The exact same thing will happen if the plane is on the treadmill, except the wheels will rotate at twice the speed to compensate for the treadmill. The only way the wheels will rotate at the same speed as the treadmill is if you apply absolutely no thrust to to the plane. Why is it so hard for you to understand this concept, and why is it you can come up with no principles of your own to support your position?