Will the plane fly?

[ViperArry]

A plane is standing on runway that can move (some sort of band conveyer). The plane moves in one direction, while the conveyer moves in the opposite direction. 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 opposite direction).

This riddle sais that the conveyor belt is moving in the same speed as the wheels of our object......


This is too simple......

You just don´t seem to get it......

The thrust of the object makes the object move.
Wheter it moves on wheels or with skates or watsoever isn´t important.

The movement of the object is equal to 0. But, with the thruster on.... the wheels will start spinning revs and revs.

You seem to forget that an airplane has to gain LIFT in order to takeoff.
Without a forward motion..... wich is now described at least 5 times by me... there won´t be an airflow.
Without the airflow no lift.... thus no takeoff.

Only thing that can move this object is a towing force wich isn´t connected to the conveyor belt...... (All things in the object are linked to the conveyor).
The external force has to achieve a little motion wich will move the object.....

[Mosca]

Originally posted by ViperArry
This riddle sais that the conveyor belt is moving in the same speed as the wheels of our object......

No, it doesn't. The word "wheels" is never in there. It says the speed of the conveyor will be the same as the speed of the plane. But the wheels act as bearings, spinning at twice the speed of either the plane or the conveyor.

Do an experiment. Get a windup plane and put it on a treadmill. Set the treadmill to whatever speed you want; set it to 10 mph. The plane will take off. It won't sit in one place and raise straight up; it will move opposite the movement of the treadmill, with the wheel speed being (treadmill speed + plane speed).

[Aurora40]

Originally posted by ViperArry
I tried to explain it with the world for example... but I couldn't

This thing keeps up in my mind all the time......

I thougt about it this morning driving to work.

If not convinced, then what do you feel would happen? Say the car had no engine and no tranny, but the wheels were there basically in neutral. When you fire the rocket up, what do you think would happen? Would the wheels just spin in the dyno drums faster and faster as the rocket burns, but the car goes nowhere? How would the rocket cause the wheels to spin? They dyno drums are free-rolling. That doesn't really make sense when you lay it out like that.

This is exactly what I thought.....
The rocket will burn..... creating a forward moving force.
But, the conveyor belt will move exactly the other way... with the same force......

Ok, forget all about the plane and conveyor belt, and think about this example again. The car's wheels have absolutely nothing connected to them. There is no motor and no tranny. The rocket is just attached to the car.

They dyno wheels have no motors. They can't spin on their own. They just sit there and free wheel. All they really are is calibratedly heavy. But they just spin. You can spin one with your hand.

So, the rocket fires up, and you contend the dyno wheels and car wheels will somehow start spinning? How do you explain that happening? How is the thrust of the rocket somehow translated into spinning wheels on a stationary car?

Again with the Hot Wheels, imagine you are holding a Hot Wheels car, and you drive it around on the ground with your hand. If you put the hot wheels car on a set of rollers, can you still drive the car off of them? Or would you push the car harder and harder along the ground while the rollers and Hot Wheels wheels just spin faster and faster? Your hand exerting a pushing force on a Hot Wheels is exactly like a rocket exerting a pushing force on car.

[rusty bumper]

Originally posted by Mosca
Ah, but it is not, and that is the catch. It is matching the plane's airspeed, not its thrust. The plane moves forward at 20 miles an hour, the conveyor moves backwards at 20 miles an hour, and the wheels move at 40 miles an hour to offset the conveyor. The plane moves at 20 miles an hour relative to the earth, and at 40 miles an hour relative to the conveyor. It's not as if the conveyor is holding the plane anchored to the ground via its retrograde motion.


Tom

Ok, I see where you are coming from. I'm still not fully convinced that the plane will fly, but we're starting to get into an area of physical science that is a little beyond my comprehension.

I still don't think you can discount the effects of gravity, mass and the movement of the conveyor belt. The plane's thrust is going to have to counteract that motion, and it would seem to me that the effort required to do that would be enough to keep the plane grounded....Even if the plane did manage to make a little air speed.

But this is all common sense theory on my part too. The law of physics might say otherwise.

I know that it takes a lot of effort to launch jet aircraft off of a carrier. The ship has to be traveling in the direction of the wind, the plane is held in place until the throttle is at full thrust (plus there is a thrust barrier behind the plane).

And finally the plane needs a catapult to help get it airborne. That's a lot of effort needed for mass to break away from gravity!

If a plane can fly off of a conveyor belt as some of you say, then it might take a mighty long runway.

I think I've said enough too.

[Mosca]

"IT'S ALL ABOUT AIRSPEED"

"While the speed of the conveyor belt in the opposite direction is superficially attractive in saying the airplane cannot accelerate, it truly is irrelevant to what is happening with the airplane, because the medium on which it is acting is the air. The only time it could be a problem is if the wheel speed got so high that the tires blew out."

From http://www.avweb.com/news/columns/191034-1.html, an excellent page outlining the conundrum, explaining why it is so persuasive to think that the airplane won't fly (I did at first), and relating it to other fallacies such as downwind turns and rockets in space.

Tom

[Bence]

Originally posted by Rusty Bumper


If a plane can fly off of a conveyor belt as some of you say, then it might take a mighty long runway.

I think I've said enough too.

OH MY! IT IS SOOOOOOOOOOOOOOO SIMPLE!

Everybody please! Is it a Jim Carrey film (D&D) or what?

Rusty, no, the runway necessary for liftoff would be absolutely the same.

[Mosca]

"Put another way, consider the problem with the [airplane] mounted on a hovercraft body (yes, similar things were tried about 30 years ago). The hovercraft lifts the airplane a fraction of an inch above the conveyor belt, and so no matter how fast the conveyor spins, it cannot prevent the propeller -- acting on the air -- from accelerating the airplane to takeoff speed. It's the same with wheels rolling on the conveyor belt. Those wheels are not powered and thus do not push against the belt to accelerate the airplane. Were that the case, the vehicle could not reach an airspeed needed to fly, because then the conveyor, the medium acted upon by the propulsive force, would be able to negate the acceleration relative to the air and ground."

[cydewaze]

Originally posted by ViperArry
(All things in the object are linked to the conveyor).
The external force has to achieve a little motion wich will move the object.....

All things aren't linked to the conveyor. The engines **** air in and spit it out back in the form of thrust, and that air is not connected to the conveyer.

As the plane moves forward, the conveyor turns and the wheels spin, but that won't stop the plane. As it moves along the wheels will simply spin 2x as fast as normal, because the conveyor is matching the plane speed.

It's just like a sailboat moving against a current. If it was a motorboat, it gets forward motion by pushing against the water, so if the current is flowing against the direction of the boat and matching the prop speed, the boat stays still. But on a sailboat, the wind will push the boat along no matter how fast the current is going.

The engines move the plane relative to the air around it, regardless of what the wheels are doing. The wheels just spin faster than normal if there's a conveyer.

[rusty bumper]

Originally posted by Mosca
"IT'S ALL ABOUT AIRSPEED"

"While the speed of the conveyor belt in the opposite direction is superficially attractive in saying the airplane cannot accelerate, it truly is irrelevant to what is happening with the airplane, because the medium on which it is acting is the air. The only time it could be a problem is if the wheel speed got so high that the tires blew out."

From http://www.avweb.com/news/columns/191034-1.html, an excellent page outlining the conundrum, explaining why it is so persuasive to think that the airplane won't fly (I did at first), and relating it to other fallacies such as downwind turns and rockets in space.

Tom

Ok, I must have skimmed too fast the first time and missed the link.

Still, I wonder if some of these heavy aircraft in use today would be able to take off like that small plane did.

I bet it would take a longer runway, just because of the shear weight of a large jet.

Just speculation on my part though.

[Desertdawg]

Originally posted by Rusty Bumper I still don't think you can discount the effects of gravity, mass and the movement of the conveyor belt. The plane's thrust is going to have to counteract that motion, [/B]

Wrong, the conveyor is counteracting the wheel speed. NOT the thrust of the power plant.

We have given about 25,384 different ways to say it will fly, the naysayers give us one reason why it won't, I officially give up trying to explain how the plane will fly..

[rusty bumper]

Originally posted by Desertdawg
Wrong, the conveyor is counteracting the wheel speed. NOT the thrust of the power plant.

We have given about 25,384 different ways to say it will fly, the naysayers give us one reason why it won't, I officially give up trying to explain how the plane will fly..

I don't agree.

There is a certain amount of mass that has to be overcome. I'm not saying the plane can't fly though.

[Desertdawg]

Where did it say that the plane had to move the conveyor (mass)??

I thought is was a given that the conveyor is self powered.

[rusty bumper]

Originally posted by Desertdawg
Where did it say that the plane had to move the conveyor (mass)??

I thought is was a given that the conveyor is self powered.

I was talking about the mass of the plane. If the engines were off then the plane would move backward with the conveyor. So in order for the plane to fly, the plane's engines have to overcome the backward motion of the conveyor....be it little or be it much.

Anyway, I have run my course with this thread. It was intersting, to say the least, but I am going to unsubscribe from it for now since all I have to offer is speculation.

NEXT!

[ViperArry]

After having read the link in one of the reactions above...

I have to believe the plane will fly....

But I don´t understand a bit of it.....

Why is the plane capable of moving on the conveyor?
Because it only weighs 40 pounds?
This could be overcome by the thrust.... so it will actually roll on the conveyor... the conveyor not being able to hold it down?

Can someone explain this?

Because.....
The wind was calm... so the airspeed can only be created with a motion of the plane.

The plane has to get moving to 45 mph (with the wheels spinning at 90) in order to achieve enough airspeed.

When doing this..... the plane should be moving from a to b.

When someone explains this you have me.... then I fully understand that the plane will fly.......

[the other pc]

Man, this is like a bag of potato chips. I'd sworn I wouldn't stick my fingers in it again! But I can't help myself.

So, just one more chip....

Originally posted by ViperArry
...I have to believe the plane will fly....

Well done sir. You are correct.

Originally posted by ViperArry
...But I don´t understand a bit of it.....

Actually, It sounds like you're very close, you've got all the pieces.

Originally posted by ViperArry
...Why is the plane capable of moving on the conveyor?...

The same reason it can move on a normal runway, its engine pushes it with thrust and its landing gear wheels just roll freely along.

Originally posted by ViperArry
...Because it only weighs 40 pounds?......

As long as the wheels roll freely the weight is irrelevant. If the engine can push it enough to lift off of a normal runway it will also lift off of the conveyor.

Originally posted by ViperArry
...This could be overcome by the thrust....

Absolutely! The force from the conveyor is ZERO, zip, nil, nada, nothing.

Originally posted by ViperArry
.... so it will actually roll on the conveyor.....

Absolutely!

Originally posted by ViperArry
.... the conveyor not being able to hold it down?.....

There is nothing to hold it back and the wheels will roll freely.

Originally posted by ViperArry
...Can someone explain this?.....

The conveyor moves but doesn't "hold" the aircraft at all. It merely spins the wheels.

Originally posted by ViperArry
... the airspeed can only be created with a motion of the plane....

Absolutely! And since the conveyor doesn't hold the aircraft the aircraft will roll along the conveyor and pick up speed with respect to the air and earth. It will gain airspeed and then lift off, exactly the same as it would on a normal runway.

Originally posted by ViperArry
...The plane has to get moving to 45 mph (with the wheels spinning at 90) in order to achieve enough airspeed......

Yes.

Originally posted by ViperArry
...When doing this..... the plane should be moving from a to b....

It will be.


PC.