162 replies to this topic

[The Boss.]

It won't take off with no lift.

[AA752]

Raise your hand if you have taken high school Physics *raises hand* If your hand is down please don't answer this yet. If your hand is up and you don't think it can take off then you must not have been paying attention.

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.

[Penguin.]

If you don't think it'll fly, go back to ###### elementary school physics.

And for gods sake, don't go near an airplane.

[wyoairbus]

dolbinau, on Jan 1 2007, 12:00 AM, said:

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i didn't say tire speed
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.

[dolbinau]

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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.

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.

[wyoairbus]

dolbinau, on Jan 1 2007, 01:31 AM, said:

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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.

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.

True, there is lots of thrust coming from the engines, but i don't think you understand. The conveyor belt is moving the same speed of the aircraft, right?



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.

[Penguin.]

You rest your case on the fact that you don't understand how aircraft propel themselves.

Laughable at best.

[wyoairbus]

Penguin., on Jan 1 2007, 01:56 AM, said:

You rest your case on the fact that you don't understand how aircraft propel themselves.

Laughable at best.

That isnt even what we are discussing. I know how aircraft propel themselves, but did you even read my post or are you just trying to pull away from the subject of the matter of fact that you are wrong?


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.

[Penguin.]

Because you're too dense to read.

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?

[wyoairbus]

Penguin., on Jan 1 2007, 02:10 AM, said:

rolling at exactly TWO TIMES their normal speed on takeoff.

So you are saying the aircraft IS moving on the conveyor belt? I believe we are taking about a conveyorbelt Large enough to fit an aircraft and the rest being like a treadmill, but the way you are explaining it makes me think more of walking on a moving sidewalk.

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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?

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.

[Penguin.]

You don't get it.

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.

[HighFlyin]

I actully see how this has any relevents to avation what so ever. And no it would not take-off. speed in one direction VS. the same speed in opposite direction cancels out. Its just like walking the wrong way on an escalator. If you walk the wrong way at the speed the escaltor is going but oppoiste you will find you actully do not move! Amazing!!

150knots--> VS. <--150Knots =0Knots and no one cares.

Edited by Westjet737, 01 January 2007 - 02:48 AM.

[wyoairbus]

Yes, the engines use the air to power the aircraft forward, no?

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.

[wyoairbus]

Westjet737, on Jan 1 2007, 02:47 AM, said:

I actully see how this has any relevents to avation what so ever. And no it would not take-off. speed in one direction VS. the same speed in opposite direction cancels out. Its just like walking the wrong way on an escalator. If you walk the wrong way at the speed the escaltor is going but oppoiste you will find you actully do not move! Amazing!!

150knots--> VS. <--150Knots =0Knots and no one cares.

exactly what I have been trying to explain to Peguin.  

[Penguin.]

It's not the same. People propel themselves by acting against the conveyor belt. Cars propel themselves through their wheels.

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.

[dolbinau]

The conveyor belt is the same length as the runway. It has already been mentioned. There is a huge difference between walking up an escalator and flying an aircraft. We walk relative to the ground. Aircraft fly relative to the air.

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.

Quote

This is like saying that a seaplane wouldn't take off in a current against it.

Great example.

Edited by dolbinau, 01 January 2007 - 03:00 AM.

[HighFlyin]

Yes but if the converyor belt is moving the same speed the plane is but in the opposite direction then the plane is not moving right. Its like running on a treadmill. Well if thr plane is not moving the it is not cutting the air so it cannot fly.

[Penguin.]

######!

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!

[wyoairbus]

Penguin., on Jan 1 2007, 02:57 AM, said:

Unless the parking brakes are on, it's going to move.

No, if the parking brakes were on the plane would fly off the other end of the belt, same as putting a stationary object on a treadmill and turning it up all the way. Then the plane would move, but in the oppsoite direction and off the belt, it would not be going 0 mph but as fast as the belt but in the opposite direction.



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

[Penguin.]

Yeah smartass, I have a treadmill, and I've launched planes off of it. That's how it know it's true.