Airplane on a conveyor belt?
#21
Posted 01 January 2007 - 12:02 AM
#22
Posted 01 January 2007 - 12:20 AM
When I first learned this in Physics it confused me too. In order for an object to move there must be a net force. Well, when a hammer drives a nail into wood, the nail moves, but the net force between the hammer and the nail-head is zero. How does the nail move? The hammer is not acting on the wood, the nail is acting on the wood; therefore, the net force of the nail and hammer have nothing to do with whether or not the nail moves. The important component is the forces between the nail and wood. If there was a net force acting between the hammer and nail then the hammer and nail would be smashing through each other!
The wheels spin independently from the aircraft, so if the treadmill matches the speed of the aircraft it only means the wheels will be spinning twice as fast. The two components are treadmill/wheels and thrust/aircraft, i.e., the treadmill is coming in contact with and acting directly upon the wheels, and the center of thrust from the aircraft engines is acting directly upon the body of the aircraft. Just like the hammer and nail example, you cannot compare the two components.
I'm no teacher of Physics, I'm only a student of it who understands this principle, so if my explanation has failed to convey my understanding I apologise.
Edit: I forgot to add that I cannot believe we are having this argument again. Someone needs to rehost that video because the old link to the video (found in another topic about this) doesn't work anymore.
Edited by AA752, 01 January 2007 - 12:24 AM.
#23
Posted 01 January 2007 - 12:44 AM
And for gods sake, don't go near an airplane.
#24
Posted 01 January 2007 - 01:21 AM
dolbinau, on Jan 1 2007, 12:00 AM, said:
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the conveyor matches the speed at which the plane would go, or wants to go
It is meant to be tire speed.
Yes, it will takeoff.
No, it will not take off. The reason planes can even take-off is because of the lift created by the air flowing over the wing.
You take away the lift gained by the airflow (in short: if you take away the airflow) your plane will not get off the ground. Period.
Tire speed has Nothing at all to do with the plane getting lift.
#25
Posted 01 January 2007 - 01:31 AM
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You take away the lift gained by the airflow (in short: if you take away the airflow) your plane will not get off the ground. Period.
The airflow is not being taken away. What is happening is a conveyer belt the size of a runway is trying to match the speed of the wheels. So be it. All the wheels do is cancel (or reduce dramatically) the friction between the ground and the aircraft. The aircraft will still move forward by thrust from the engines. It doesn't matter how fast the wheels are spinning or in what direction. Thousands of pounds of thrust from the engines will push the aircraft forward and eventually to takeoff.
#26
Posted 01 January 2007 - 01:49 AM
dolbinau, on Jan 1 2007, 01:31 AM, said:
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You take away the lift gained by the airflow (in short: if you take away the airflow) your plane will not get off the ground. Period.
The airflow is not being taken away. What is happening is a conveyer belt the size of a runway is trying to match the speed of the wheels. So be it. All the wheels do is cancel (or reduce dramatically) the friction between the ground and the aircraft. The aircraft will still move forward by thrust from the engines. It doesn't matter how fast the wheels are spinning or in what direction. Thousands of pounds of thrust from the engines will push the aircraft forward and eventually to takeoff.
Say they were to test this theory in real life and you were to whitness it. It would be just like watching a person run on a treadmill. They would be powering themselves forward but they wouldnt acually go anywhere
You are saying that an aircraft essentually going nowhere (by this I mean it is going very fast on the belt itself but you could stand a ways away and watch it go no further from the spot and objects around it was earlier) is going to lift off.
Imagine this, an aircraft staying in the same spot would lift off the belt, and then what? would it still just hover in the same spot above the treadmill or would it be like a star wars space ship and all of a sudden gain speed out of no where and fly off?
I rest my case, it would be impossible for the plane to takeoff
Edited by wyoairbus, 01 January 2007 - 01:55 AM.
#27
Posted 01 January 2007 - 01:56 AM
Laughable at best.
#28
Posted 01 January 2007 - 02:05 AM
Penguin., on Jan 1 2007, 01:56 AM, said:
Laughable at best.
If I am wrong, would you mind to explain what would happen to the aircraft after it would takeoff from the conveyorbelt? AS I said earlier, would it hover in the same spot above the belt or would it magically get power out of no where and jet off?
The aircraft would not takeoff. It is essentually standing still in one spot, the wheels and the belt below are moving but not the aircraft. In a takeoff, the plane would move and the ground would not.
If it would takeoff, I'm sure many airports would be built with this "space saving" conveyorbelt, seeing as aircraft could stand in one spot and takeoff without a problem.
Why build large 2-mile long runways when you could have planes takeoff in one spot? Because its not possible.
Edited by wyoairbus, 01 January 2007 - 02:08 AM.
#29
Posted 01 January 2007 - 02:10 AM
They won't take off in one spot, conveyor belts don't move air, so the takeoff roll will remain exactly the same. The WHEELS, which are the only part of the aircraft that can respond to the force of a conveyor belt, will be rolling at exactly TWO TIMES their normal speed on takeoff.
How can the conveyor belt create a force that would react against the thrust of the engines. Remember, airplanes could care less about what the wheels are doing, unlike a car.
Ask yourself that, HOW is the conveyor going to act against the thrust of the engines. It can't move air, so how WILL IT COUNTER THE AIR MOVING FROM THE ENGINES?
#30
Posted 01 January 2007 - 02:20 AM
Penguin., on Jan 1 2007, 02:10 AM, said:
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Exactly. The belt will not move air, the engines are moving the aircraft forward on the belt, and at the same speed but in the opposite direction the belt is moving so the plane is not moving, it is relative to all the objects around it .
The air moving from the engines will power the plane forward but if the plane cannot gain any acual speed it is not going to go anywhere, it will stay in the same spot still relative to all the objects around it, unless it acually gains more speed than that of the belt.
#31
Posted 01 January 2007 - 02:34 AM
The motion of the conveyor belt CANNOT cancel the thrust of the engines. The belt acts upon the wheels. The engines act upon the air. It will move, it will fly, the wheels will be spinning to holy ###### and back, but the ###### airplane will fly.
It's been done in models, it's been done in simulations. It's been proven backwards and forwards, and makes people think outside the box.
You have to think like you understand how aircraft work, and stop relating it to cars, people, rabbits, or yettis.
#32
Posted 01 January 2007 - 02:47 AM
150knots--> VS. <--150Knots =0Knots and no one cares.
Edited by Westjet737, 01 January 2007 - 02:48 AM.
#33
Posted 01 January 2007 - 02:50 AM
I think I see what you are getting at, but I don't see how it could be done.
I don't know how many times i must say this but if the aircraft is going 0 mph (compared to the objects around it) because the engines are indeed propeling the aircraft forward but it is not going anywhere seeing as the "ground" below it is canceling out any movement forward, will the aircraft not continue to go 0 mph or instead will it just rotate up and fly off of some magical power?
I think what you are saying is you think the aircraft will start to move and not just stay in one spot and then lift off. The enignes use air to move the plane I know, but the whole idea of this topic (or so i believe) is that the plane is not moving from one spot but is on a giant treadmill.
If the treadmill wouldn't counter out speed gained by the aircraft then yes it would eventually takeoff but only because it was allowed to gain speed.
In short, what I am saying is that if the aircraft isnt moving from its one spot, it will not takeoff
As for these "tests" you say and that it has been "proved", I would like some proof of these "tests" otherwise it is just your word.
#34
Posted 01 January 2007 - 02:52 AM
Westjet737, on Jan 1 2007, 02:47 AM, said:
150knots--> VS. <--150Knots =0Knots and no one cares.
#35
Posted 01 January 2007 - 02:57 AM
Aircraft MOVE AIR! THEY DON'T CARE ABOUT THE BELT! THE WHEELS ARE FREE! THEY GO WHICHEVER WAY THE AIRCRAFTS ENGINES PROPEL THEM!
Unless the parking brakes are on, it's going to move.
Please people, go reread Newton's Laws of Motion.
This is like saying that a seaplane wouldn't take off in a current against it.
#36
Posted 01 January 2007 - 03:00 AM
Let's use your example of a person on a treadmill.
Say there was a person on a treadmill riding a skateboard, the treadmill is moving very fast however the person is going no where, the wheels are just spinning. Now someone gets a rope and pulls them along, it doesn't matter how fast the conveyor is going the person can still pull them forward, the wheels just move faster. Same situation with the aircraft.
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Great example.
Edited by dolbinau, 01 January 2007 - 03:00 AM.
#37
Posted 01 January 2007 - 03:06 AM
#38
Posted 01 January 2007 - 03:08 AM
Airplanes aren't like people. I don't have an engine on my back moving air. I act against the belt. The airplane's force is from acting on the air.
READ NEWTON'S LAWS OF MOTION!
#39
Posted 01 January 2007 - 03:10 AM
Penguin., on Jan 1 2007, 02:57 AM, said:
I don't think you at all get it. Do you have a treadmill? If not go to a healthclub and use one there.
Try this: Place a stationary object with no wheels or anyway of moving on a treadmill, i.e. a water bottle or a key chain. Next turn the treadmill up to full power.
What happens? The object flies off the treadmill, as oppsed to what you said where a stationary object on a treadmill turned up full would stay in the same place.
It doesnt work that way, the treadmill is moving very fast and if you have a stationary object on it like a key chain it WILL NOT stay stationary and will fly off the treadmill
An airplane at Full throttle on a treadmill going the exact same speed WILL NOT MOVE
Aircraft do not move air in the way you seem to think. They don't move all the air around them, just the air that goes through their engines. They still need air to pass over their wings which engines do not provide. Engines will provide thrust, much the same as a car, to propel the plane forward. they do not move all the air around the entire airplane as you seem to think
#40
Posted 01 January 2007 - 03:14 AM