A plane on a runway, how smart is r3vlimited?

[RobertK]

Yes, they just match the speed of the plane, and unless the plane can move, the treadmill won't move. So, if you have forward thrust provided by the engines, the plane will be travelling 200 mph (lets say to lift off), while the treadmill will be spinning 200 mph in the opposite direction, which means that the wheels are spinning at 400 mph. It's quite simple really.

No.. the wheels are like gears plus since nothing is 100% efficient at converting energy drag would be created in the xfer of energy from the forward force of the plane and the backward force of the treadmill. In reality the bearing would eventually burn up or the tires would blow out.

[Axxe]

Hahaha, it momentarily dropped while the ball was in the air, and then it returned to the previous level :)

[Erick]

What if the engines were not on....and the belt was turned on. DOes tha plane go backward...yes it has to. The wheels wont just spin unless they get some power. The power comes from the engines whether they are directly powering the wheels or not.
The effect of takeoff goes directly into the wheels because the plane is trying to prepel itself forward.

Read Axxe's confirmation ^^^

If the engines are off, then the plane is stopped and the belt wont spin.... the belt works against any foward motion that the plane is producing... if the plane isnt producing (engines off) then the belt also wont be moving.

[george graves]

good but easy...

Ok here is a better one: A guy is sitting in a row boat, that is floating in a pool full of water. He is holding a bowling ball. He throws the bowling ball overboard and it(the bowling ball) sinks to the bottem. Now, what had happened to the level of the water in the pool?

[Axxe]

I dont think a lot of you understand the quesiton..... the belt will match the speed that the airplane can create... no matter how much the plane accelerates.

Yes, they just match the speed of the plane, and unless the plane can move, the treadmill won't move. So, if you have forward thrust provided by the engines, the plane will be travelling 200 mph (lets say to lift off), while the treadmill will be spinning 200 mph in the opposite direction, which means that the wheels are spinning at 400 mph. It's quite simple really.

[joshh]

No, no, no. The wheels are completely independent of what makes the plane fly. It doesnt matter if the wheels are spinning or not.

The plane could be parked, completely turned off with no one in it. If the weather goes crazy and suddenly there is a wind gust hitting the plane head on, matching the amount necessary for a plane to take off (example: 100knot headwind for a plane that requires 100knots to take off)... then the plane will take off... even with NO one in it.

The problem is that since we are assuming no headwind, and the belt doesnt allow the plane to move foward to generate this lift, then the plane cannot take off.

That's how I see it. I dare MythBusters to prove me wrong.

- Erick

What if the engines were not on....and the belt was turned on. DOes tha plane go backward...yes it has to. The wheels wont just spin unless they get some power. The power comes from the engines whether they are directly powering the wheels or not.
The effect of takeoff goes directly into the wheels because the plane is trying to prepel itself forward.

[erik325i]

As long as the plane were light enough. Most large (if not all) planes these days need both power and lift.

haha, the weight of the plane has nothing to do with it.

It would take the exact same amount of time for the plane to take off. The plane would propell forward the exact same distance before lift-off. The only thing different about having the plane of the conveyor belt is that the wheels are going to spin twice as fast as the plane is moving.

This is my last post in this thread. Either you got it, or you don't.

-Erik

[Erick]

I dont think a lot of you understand the quesiton..... the belt will match the speed that the airplane can create... no matter how much the plane accelerates.

[Axxe]

After having thought about this some more I am changing my initial answer from No Fly to definite FLY .

The conveyer belt will have to be as long as it takes the plane to take off from the runway in a normal situation .
But YEs the plane will eventually take off in its usual manner and lenght .

Yes, we have a convert. Atta boy :)

[Teaguer]

After having thought about this some more I am changing my initial answer from No Fly to definite FLY .

The conveyer belt will have to be as long as it takes the plane to take off from the runway in a normal situation .
But YEs the plane will eventually take off in its usual manner and lenght .

[joshh]

Maybe my interpetation of the setup is distorted but the core basic theory I base my "No fly" answer on is this:

The two forces at work here are the conveyer belt in one direction, and the jets in exactly the opposite direction to match speed.

You can fire those jets as fast as you want, but there is no air movement around the wings. No air movement = no lift.

Conversely, if you put the same plane in a wind tunnel and generated wind in sufficient volume and directly at the plane, you could generate lift without even firing the jet engine. You could tether the plane to limit movement from the stationary point to keep the plane in the wind current, and it would hover in that spot as lift was being generated - and you wouldn't need the turbine.

As long as the plane were light enough. Most large (if not all) planes these days need both power and lift.

[RobertK]

I think what is more relevant here is the exact speed of the treadmill, the total force the plane's engines are capable of doing and the amount of power needed to move the plane fast enough to create lift. The wheels (and wheel size) will only lower the amount of power needed to overcome the conveyer but not completely.

If the plane requires that it travel 80mph to sustain lift then it's engines would only have to be capable of achieving enough HP push equivlent to make the plane travel 160mph. (80mph to match the speed of conveyer and 80mph to achieve lift.)

To those of you who argue the since the engines are pulling the plane it doesn't matter then consider this. Attach a small basket scale to a string and attach that to the front of a toy car. First drag it across a treadmill without turn it on and note the measurment on the scale. Next turn the treadmill on 2mph and pull the car across the treadmill and note the measurement. It will require more pulling force in lbs to pull the car across the 2nd time.

Every action needs a equal and opposite reaction.

[Erick]

The thrust of the engines have to make the wheels go forward don't they. The weight of the plane sits on the wheels correct? ......so if the wheels are already spinning as fast as the engines can propel the aircraft forward, the plane will not take off.
The treadmill simulates the power of the engines forcing the plane mass forward.

No, no, no. The wheels are completely independent of what makes the plane fly. It doesnt matter if the wheels are spinning or not.

The plane could be parked, completely turned off with no one in it. If the weather goes crazy and suddenly there is a wind gust hitting the plane head on, matching the amount necessary for a plane to take off (example: 100knot headwind for a plane that requires 100knots to take off)... then the plane will take off... even with NO one in it.

The problem is that since we are assuming no headwind, and the belt doesnt allow the plane to move foward to generate this lift, then the plane cannot take off.

That's how I see it. I dare MythBusters to prove me wrong.

- Erick

[LINUS]

Well, of course it may not be obvious to everyone, but that is the point of the thread. The question is not mis-stated. You just need to think about it...

If it were a car on the conveyor belt, it would stay stationary because it uses it's wheels to drive forward. With the conveyor belt moving backward, it can't move.

In the case of the airplane, the plane uses jet engines to propell itself, so the speed of the conveyor belt is irrelevant. The example Borat stated with the toy car attached to a string on a treadmill is perfect. Even if the treadmill goes the same speed as you are pulling the string, the car will still move forward.

-Erik

Maybe my interpetation of the setup is distorted but the core basic theory I base my "No fly" answer on is this:

The two forces at work here are the conveyer belt in one direction, and the jets in exactly the opposite direction to match speed.

You can fire those jets as fast as you want, but there is no air movement around the wings. No air movement = no lift.

Conversely, if you put the same plane in a wind tunnel and generated wind in sufficient volume and directly at the plane, you could generate lift without even firing the jet engine. You could tether the plane to limit movement from the stationary point to keep the plane in the wind current, and it would hover in that spot as lift was being generated - and you wouldn't need the turbine.

[erik325i]

How in the hell? The question says the belt works backwards with the airplane meaning the airplane remains stationary. The wheels spin, but the plane itself.... stays stationary to anyone watching from the outside.

Erick, you are thinking about it like it were a car.
Just because the belt is spinning backward does not mean the plane is staying stationary. The thrust from the jet engines has nothing to do with the ground.

PS: If it really WOULD take off... why dont compact planes use these "rollers"? Somehow aircraft carriers still rather bet on the flat grounds.

Putting a plane on a huge conveyor belt would not be of any benefit. The plane would still need the exact same amount of runway to take off, whether or not the ground is moving...

-Erik