Physics Question

[letdown427]

Originally posted by: g8wayrebel
I read all the posts.
You are still wrong.
The plane would never have forward motion. If you are on a treadmill running 11 m/s (just under the world record) does the wind blow your hair back and your hat off? NO , it does not. There is no wind.
A plane , no matter the propulsion system, would not have any either.
It would initially move slightly forward to cause the conveyor to start according to the OP who says the conveyor "matches the speed " of the plane. From that point forward , the forward motion of the plane would be negated by the rearward motion of the conveyor.
The fact that the plane has wheels merely allows it to roll and accelerate on the conveyor faster.. Even if it were on it's belly , if it had enough thrust , it would begin to move and start the conveyor.
From that point forward , the result would be the same.It would be sationary relevent to the atmosphere and never develop lift.
THIS BIRD WON"T FLY!

This has been an extremely interesting question.. I am going to take this to another forum and see if I get any answers worth repeating.
BTW , I have a treadmill and am trying to convince a friend of mine to bring an RC plane over to prove the point. I will not stand in front of it , but don't expect any damage to plane or basement in the process. On second thought , guess I'll move the treadmill outside. There is more air out there. Yeah that's it , there's more air outside. LOL
If this takes place (doubtful) I will put it on video for all.

Nope. lol.

Can you do me a favour? Instead of risking that model aircraft, tie a firework onto a rollerskate/skateboard. Set your treadmill to whatever speed you want. Light the firework.

Then continue your argument.

Surely you can think about this with your brain and miss out the experiment entirely? You are honestly telling me that a rocket tied to a skateboard could be held in place by a suitably fast treadmill? No, surely you aren't. Are you?


Thank you for reading all of the posts though, welcome to the discussion!

 

[Confused]

A person running on a treadmill is transferring their power to move through their feet(wheels).

An RC plane on a treadmill is transferring it's power to move through the air.

Therefore the RC plane will move forwards, and will take off (given that the treadmill is long enough)

 

[g8wayrebel]

The power to move the air, from the plane, is equalled by the motion of the conveyor.The energy is expelled behind it just as a fan would do. Since the air is being moved through the engines/props , not over the wing , their is no energy applied to the plane itself , just the area behind the setup. In essence , you have a giant fan.
It is ,in theory ,possible to tether a prop plane and have it move enough air to lift and "fly" at the end of the tether without forward motion , but that isn't the question.
I am unaware of a plane that has the ability to develop that much energy from a propeller if it started out taught on the tether in the first palce, just so no one says I said there was one.
In any case, I believe the aerodynamic of the wing would have to be for this specific purpose rather than for conventional travelling flight.

Confused,
There is no difference where or how the energy is transferred , they are still defeating friction.
You can do the exact same thing in the water that a plane does in the air.
No matter , you are still defeating gravity exerted on the mass in order to create motion whether you do it with (or in) air , water , or on the ground.
Each has it's own dynamic and human limitations to contend with , but they are all defeating the same gravitational forces.

 

[giantpinkbunnyhead]

Originally posted by: g8wayrebel
The power to move the air, from the plane, is equalled by the motion of the conveyor.The energy is expelled behind it just as a fan would do. Since the air is being moved through the engines/props , not over the wing , their is no energy applied to the plane itself , just the area behind the setup. In essence , you have a giant fan.
It is ,in theory ,possible to tether a prop plane and have it move enough air to lift and "fly" at the end of the tether without forward motion , but that isn't the question.
I am unaware of a plane that has the ability to develop that much energy from a propeller if it started out taught on the tether in the first palce, just so no one says I said there was one.
In any case, I believe the aerodynamic of the wing would have to be for this specific purpose rather than for conventional travelling flight.

Confused,
There is no difference where or how the energy is transferred , they are still defeating friction.
You can do the exact same thing in the water that a plane does in the air.
No matter , you are still defeating gravity exerted on the mass in order to create motion whether you do it with (or in) air , water , or on the ground.
Each has it's own dynamic and human limitations to contend with , but they are all defeating the same gravitational forces.

Nope, still wrong! the conveyor cannot counteract the thrust from jet engines. As an example, our Boeing 727's at work generate 42,000 lb of forward thrust at max power. Exactly how is the conveyor belt going to channel the opposing force? All the conveyor belt can do is spin the wheels on the jet. It has EVERYTHING to do with how the energy is transferred. Consider this: Put a 727 and a truck on a dry runway and both can accelerate at their normal rates. Put them both at an icy runway and the truck is essentially stuck while the 727 will still take off at its normal rate. (I know this; it's winter up here and I do this for a living). An airplane does not care what the surface is like underneath it (unless it impedes the forward motion physically, such as deep snow or grass). The fact that there is a conveyor belt underneath will only spin the wheels faster, nothing else. The plane's force does NOT apply against the conveyor belt. It only applies against the air.

Try this out: Take a skateboard, and put a hollow metal tube across the top of it sideways. Now, give the skateboard a kick forward. What happens to the bar? I'll bet it didn't go forward with the skateboard. By this same logic, moving a conveyor belt under an airplane is like kicking that skateboard with the bar on it. All that happen is the bar (or wheels) will simply spin more rapidly.

 

[Armitage]

Originally posted by: g8wayrebel
I read all the posts.
You are still wrong.
The plane would never have forward motion. If you are on a treadmill running 11 m/s (just under the world record) does the wind blow your hair back and your hat off? NO , it does not. There is no wind.

Your legs are pushing against the treadmill, which is moving backwards. So you don't move.
Try this - tie a rope to the wall in front of your treadmill, then get on it with rollerskates holding onto the rope. Can you pull yourself forward on the treadmill? That's exactly what the plane is doing.

A plane , no matter the propulsion system, would not have any either.

An airplane is not pushing against the treadmill. That's the bottom line.

It would initially move slightly forward to cause the conveyor to start according to the OP who says the conveyor "matches the speed " of the plane. From that point forward , the forward motion of the plane would be negated by the rearward motion of the conveyor.

I've asked this a dozen times in this thread with answer from the "won't fly" crowd.. What force is counteracting the thrust of the aircraft? What is the mechanism by which it is applied.

If you have unbalanced forces, it will move.

The fact that the plane has wheels merely allows it to roll and accelerate on the conveyor faster.. Even if it were on it's belly , if it had enough thrust , it would begin to move and start the conveyor.
From that point forward , the result would be the same.It would be sationary relevent to the atmosphere and never develop lift.
THIS BIRD WON"T FLY!

This has been an extremely interesting question.. I am going to take this to another forum and see if I get any answers worth repeating.
BTW , I have a treadmill and am trying to convince a friend of mine to bring an RC plane over to prove the point. I will not stand in front of it , but don't expect any damage to plane or basement in the process. On second thought , guess I'll move the treadmill outside. There is more air out there. Yeah that's it , there's more air outside. LOL
If this takes place (doubtful) I will put it on video for all.

Please videotape this experiment. But do yourself a favor and don't stand in front of the treadmill!

 

[JujuFish]

Wow... I can't believe this thread is still going. :Q

The OP should be editted with the real answer so people stop arguing. The plane will take off, as has been reiterated time and time again on this thread. Planes do not move by pushing off of the ground. If this were so, they'd never be able to fly, as their speed would immediately decrease once the wheels left the ground, thus bringing them back down. It would be impossible for them to maintain speed required for flight. Now, because they are not required to push off the ground to get forward motion, the motion of the ground will not be great enouh, assuming it only moves as fast as the plane, not faster, to prevent the plane from moving. The plane WILL move, and therefore WILL be able to get enough wind over the wings and WILL take off.

 

[kitkat22]

This is rediculous, no the plane cannot take off. Here's an another analogy. Let's assume you are swimming upriver in a river that flows at 3m/s if you swim at 3m/s you do not move relative to the ground, you perform no work. (Work = Force x Change in Distance) Let's then assume you have a propellor attached to your back and you no longer need to swim because the propellor is providing forward thrust at 3m/s. You still do not move. No work is performed.

A plane can take off on ice because the ice is not moving in the opposite direction and the thrust comes from the engines not the wheels on the ground. Pushing against a desk on a wheeled chair on a conveyor belt will not move you anywhere and no that will not work. There is no lift generated because the plane is technically not moving there is no work generated by the plane. Remember it's not F=ma it's the sum of forces. Work is not W=Fx it's the Force times distance.

End thread/

 

[JujuFish]

Originally posted by: cscpianoman
This is rediculous, no the plane cannot take off. Here's an another analogy. Let's assume you are swimming upriver in a river that flows at 3m/s if you swim at 3m/s you do not move relative to the ground, you perform no work. (Work = Force x Change in Distance) Let's then assume you have a propellor attached to your back and you no longer need to swim because the propellor is providing forward thrust at 3m/s. You still do not move. No work is performed.

A plane can take off on ice because the ice is not moving in the opposite direction and the thrust comes from the engines not the wheels on the ground. Pushing against a desk on a wheeled chair on a conveyor belt will not move you anywhere and no that will not work. There is no lift generated because the plane is technically not moving there is no work generated by the plane. Remember it's not F=ma it's the sum of forces. Work is not W=Fx it's the Force times distance.

End thread/

You are wrong. See my post. A more proper analogy would be you swimming in a, for the most part, still river, and the ground beneath the river is moving.

 

[Chryso]

No takeoff.

 

[kitkat22]

I got it. It has to do with the wheels. However, you will need plenty of thrust to get the plane physically moving.

Edit: I was wrong. Under the conditions of thrust working through the wheels then, yes, I would have been correct.

 

[Rayden]

THE PLANE MOVES! The conveyor belt does note exert any force on the plane! All it does is spin the wheels. NOWHERE does it say that the conveyor belt exerts any force on the plane SUFFICIENT to keep it from moving. How are you guys inferring that?

If you wish to argue that the plane does not move, please use some physics and prove that the force of the plane's engine equals the force from the conveyor belt.

 

[So]

Originally posted by: cscpianoman
I got it. It has to do with the wheels. However, you will need plenty of thrust to get the plane physically moving.

Edit: I was wrong. Under the conditions of thrust working through the wheels then, yes, I would have been correct.

You are wrong. If the wheels are non ideal (edge case scenario) or if there is a car it'd not move, but the treadmill will have NO EFFECT on a plane.

 

[Chryso]

Originally posted by: Rayden
THE PLANE MOVES! The conveyor belt does note exert any force on the plane! All it does is spin the wheels. NOWHERE does it say that the conveyor belt exerts any force on the plane SUFFICIENT to keep it from moving. How are you guys inferring that?

If you wish to argue that the plane does not move, please use some physics and prove that the force of the plane's engine equals the force from the conveyor belt.

Why do you think the plane moves? This is from the original post:
"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 the opposite direction)"

 

[Vegitto]

The kitty doesn't like your question...

 

[Coldfusion]

Depends on the "plane".

If it's a jet, it can't take off. In order for a jet to take off, the jet propels the plane forward and the motion of the plane generates the air over the wings.

If it's a propeller plane, then it can. The propeller moves the air over the wings, which creates the lift, regardless of whether the plane is moving relative to the ground.

 

[jagec]

Originally posted by: flashbacck
OP should put whether or not we're in physics-magic-land where the conveyor belt and airplane wheel barings are frictionless and industructible. If we are, then I'm gonna say no, the plane cannot take off.

Yeah, in that land the plane can't take off, because basically all the force the engines are exerting is being converted (via the conveyor belt) into angular momentum in the wheels. Worse, that angular momentum has no place to go, so it just keeps building...and building...and building until our fuel runs out.:Q

Originally posted by: letdown427
even if they were indestructible (physics thought experiments are often in physics magic land, as it makes things easier/more complicated) the conveyers speed is governed by the planes movement, as defined in the original question.

there is no way that the friction the conveyor can provide at any speed below 200mph could compete with the thrust of the plane. you must be able to see that? and since at that 200mph the plane would be gone anyway, it can take off, off into the physics magic land sky, immune from viscous drag.

No, he's right. Friction isn't the only way energy is taken up in this problem. A bit of the energy of the system becomes angular momentum in the wheels. No? Imagine that each wheel weighed 4 tons. Now imagine the treadmill slowly starts moving backwards. You'd have to give it a surprising amount of thrust to keep the plane from also moving backwards. Then (this being magical physics land) you can shut off the engines, and the plane will merrily sit at one place, with the wheels slowly turning on the treadmill.

Now imagine this is a continuously accelerating system. You'd have to keep the engines turned on to make sure the plane stayed put. Now up the acceleration a bit...full thrust!

...of course, the lighter the wheels, the more acceleration you have to throw on the conveyor belt to keep the plane from moving. It's a good thing we're in magical physics land where there is no material failure.

 

[Confused]

I'm surprised the last few posters have got it so wrong.

Go back, re-read my own or letdown427's posts, and try again.

 

[Chryso]

I don't think so. The plane has zero airspeed. The treadmill is meaningless. Is the plane a Harrier? I don't know of any other planes that can take off with zero airspeed.

 

[dawks]

Originally posted by: Coldfusion
If it's a propeller plane, then it can. The propeller moves the air over the wings, which creates the lift, regardless of whether the plane is moving relative to the ground.

Thats Partly wrong.. While its true the propeller moves air over the wings, the main idea is the propeller pulls the plane through the air, and that provides the lift for the wings. It works much like a turbo-fan or jet plane. Just imagine if you put a propeller plane to full throttle with the breaks on.. its not gonna lift off.. you have to be moving forward.

 

[elkinm]

Wow this is a long thread about almost nothing.

Anyway, if the conveyor matches the speed of the plane and the speed is directly proportional to the speed of the wheels and it had infinite friction between the wheels and the conveyor it cannot take of as from the point of view of an observer standing of the conveyor the plane is not moving.

But realistically, a plane is not a car and does not rely on the wheels for propulsion. The engines will still move it forward and if the wheels are free to rotate like they should be the plane WILL take off at whatever speed it needs and the conveyor will move in the opposite direction at the same speed and the wheels will spin backwards at double the speed. Somehting that was already said before.
And if the brakes are engaged then at some point the thrust will break the force of friction and simply slide on the conveyor until take off.

Have you ever tried a non powered treadmill. As you push to walk forward you push the tread back, or if you try to jump off a boat, what happens. The boat goes backwards and you land in the water (unless you jump really far.) But no imagine if you move not by pushing against the surface under you but from the air then you will move forward.

So a real plane in this scenario will take off.

 

[Chryso]

Originally posted by: elkinm
Wow this is a long thread about almost nothing.

Anyway, if the conveyor matches the speed of the plane and the speed is directly proportional to the speed of the wheels and it had infinite friction between the wheels and the conveyor it cannot take of as from the point of view of an observer standing of the conveyor the plane is not moving.

But realistically, a plane is not a car and does not rely on the wheels for propulsion. The engines will still move it forward and if the wheels are free to rotate like they should be the plane WILL take off at whatever speed it needs and the conveyor will move in the opposite direction at the same speed and the wheels will spin backwards at double the speed. Somehting that was already said before.
And if the brakes are engaged then at some point the thrust will break the force of friction and simply slide on the conveyor until take off.

Have you ever tried a non powered treadmill. As you push to walk forward you push the tread back, or if you try to jump off a boat, what happens. The boat goes backwards and you land in the water (unless you jump really far.) But no imagine if you move not by pushing against the surface under you but from the air then you will move forward.

So a real plane in this scenario will take off.

How are the wings getting any lift if the plane is not moving?

 

[Rayden]

Originally posted by: Chryso

Originally posted by: Rayden
THE PLANE MOVES! The conveyor belt does note exert any force on the plane! All it does is spin the wheels. NOWHERE does it say that the conveyor belt exerts any force on the plane SUFFICIENT to keep it from moving. How are you guys inferring that?

If you wish to argue that the plane does not move, please use some physics and prove that the force of the plane's engine equals the force from the conveyor belt.

Why do you think the plane moves? This is from the original post:
"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 the opposite direction)"

Where does it say that the plane doesn't move? It says the conveyor moves backwards with the same speed that the plane moves forward. How does the conveyor moving affect the plane?

 

[Chryso]

Originally posted by: Rayden

Originally posted by: Chryso

Originally posted by: Rayden
THE PLANE MOVES! The conveyor belt does note exert any force on the plane! All it does is spin the wheels. NOWHERE does it say that the conveyor belt exerts any force on the plane SUFFICIENT to keep it from moving. How are you guys inferring that?

If you wish to argue that the plane does not move, please use some physics and prove that the force of the plane's engine equals the force from the conveyor belt.

Why do you think the plane moves? This is from the original post:
"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 the opposite direction)"

Where does it say that the plane doesn't move? It says the conveyor moves backwards with the same speed that the plane moves forward. How does the conveyor moving affect the plane?

That is pretty much the definition of not moving.
Let's say that the plane is going 100mph and the conveyor is going 100mph in the other direction. 100 - 100 = 0.

 

[Armitage]

One more time ...

All the naysayers - please tell me what force opposes the thrust of the engines to keep the plane stationary?

 

[juiio]

Originally posted by: Chryso

How are the wings getting any lift if the plane is not moving?

The plane is moving. The plane's velocity is not the same as the angular velocity of the wheels.