Will it take off?

[Ray Garrison]

You are so *COMPLETELY* missing the point. The car generates forward velocity by *PUSHING AGAINST THE GROUND* with its *WHEELS*. The plane generates forward velocity by *PUSHING AGAINST THE AIR* with its *ENGINES*. There is *NO DRIVING FORCE* associated with a planes *WHEELS*. All they do is rotate freely in response to the relative motion between the plane and the ground. Whether the plane is moving forward, or the ground is moving backward, or both are moving, it doesn't matter.

[sputnik]

Sputnik wrote:

Can anyone from the "will not fly" brain trust explain how any horizontal force from the conveyor is transferred to the structure of the aircraft?

If you can't answer that, you can't support your conclusion.

Here is why the above proposition is wrong. The conveyor is in contact with the plane, and thus, PART of the plane. So, the force countering the jet engine IS IN FACT the conveyor.

Maybe planes are too intriguing. Try a car. What if the car is on a treadmill, and however much the driver speeds up, the treadmill speeds up in the opposite direction. Will the car fly? Hell no. It will stay in one place - AND THERE WILL BE NO WIND - ABSOLUTELY, POSITIVELY NO WIND. So, feel free to use a convertible for this experiment (your hair won't be windblown).

Now, put some wings on the car. Will it all the sudden fly in the absence of this wind? I win!

You're wrong again. This was covered in previous posts.

[Jeff Matthews]

I'd look for another law partner. Ok, you're wearing roller skates on a flat treadmill. Instead of someone pushing you, suppose you are pulling (hand over hand) on a rope attached to the wall in front you. The pulling force is similar to the aircraft thrust. With each pull on the rope you're moving toward the wall regardless of the treadmill speed.

No, Sput. We already addressed this and realized it was an apples and oranges comparison. You are pulling on a rope. The cause of your movement forward is because you have shortened the rope. When you effectiely shorten the rope, you are ACCELERATING and surpassing the speed of the treadmill. Surpassing the speed of the treadmill is NOT ALLOWED. Remember the treadmill must move as fast as the object on it.

[jacksonbart]

You can get a good look at a bull by sticking your head up a butcher's @ss,but...wait...no it has to be your bull.

[Jeff Matthews]

I can't believe this woke up again. This is such a simple question and it gets over-analyzed to death here. Here is the simplest analogy I can come up with.

The plane's engines exert a force on the plane. They push it forward. Let's replace the engines force with another force. Say, uh, how about the force of gravity. Instead of igniting jet fuel and oxygen to generate a "longitudinal force vector" (aka "push"), tilt the ground so the plane is rolling downhill. If we tilt the ground steep enough, and the plane gains enough speed, it will generate lift and begin to fly. Of course, eventually we come to the bottom of the hill and smash into the ground, but let's leave that aside for the moment.

Now, while we're rolling merrily down the hill, before our wheels leave the ground, start up our conveyor belt, moving in the opposite (uphill) direction. Will the plane stop rolling downhill and come to a stop (relative to the ground under the conveyor belt)? Will it begin rolling backwards, up the hill? No, unless our wheel bearings cease up or something. No matter how fast the conveyor belt moves under our plane, we're going to continue rolling downhill faster and faster. Eventually we'll lift off. The belt could be moving at any arbitrary speed under us, it's not gonna matter. All it does is make the wheels spin faster. That is, if our downhill velocity is 50 mph and the belt is going uphill at 50 mhp, our wheels are turning at the equivalent of a 100 mph taxi. Likewise, if we're going downhill at 50 mph and the belt is moving uphill at 1,000 mph, our wheels are revolving at the equivalent of a 1,050 mph speed. Doesn't matter, we still roll downhill.

Now, put our plane on a level surface and replace the force of gravity with the force of the engines. Same exact thing.

Duh.

Ray, double DUH back at you! Gravity = 9.8 meters/second squared. It is a force of ACCELERATION. Now, let's match your force of ACCELERATIONa with another force of acceleration. For example, all masses generate a certain degree of gravitational force. That's why the Sun keeps the earth in orbit.

Now, if you took a mass that generated a gravitation force in equal magnitude as that of the earth BUT IN THE OPPOSITE DIRECTION, you would in fact stop falling down that hill. Remeber, the forces are completely offsetting. In your example, Ray, you are countering a non-accelerating force with an accelerating force. It will not work.

[sputnik]

Jeff,

You and your partner have fallen into the common trap of thinking that the conveyor imparts a horizontal force on the plane that opposes forward acceleration. My challenge to you is to prove that the conveyor, at any speed, influences the forward motion of the plane (or lawyer on roller skates).

[Champagne taste beer budget]

You are on a treadmill with roller skates - the same example many of you have used. Also, to keep you from going backwards (i.e. to get past the initial friction), somebody puts a little force behind your back - just enough to get the wheels spinning.

Now, you're in a state of equilibrium - going as fast on the skates as the treadmill spins. Then, somebody comes up from behind you and pushes you real hard in the back to speed you up. Instantaneously, the treadmill speeds up to compensate. Are you going to move forward and gain any ground? NOT!

Using your example, tell me what happens when:

1) The person pushing the skater is standing on the ground.

2) The "pusher" is right up against the "pushee", arms folded against his chest.

You're saying that as the "pusher" extends his arms forward and pushes on the person on the skates, that the person on the skates will not be forced forward and away from the "pusher" because his conveyor speeds up? Huh? [:^)]

[Jeff Matthews]

You are on a treadmill with roller skates - the same example many of you have used. Also, to keep you from going backwards (i.e. to get past the initial friction), somebody puts a little force behind your back - just enough to get the wheels spinning.

Now, you're in a state of equilibrium - going as fast on the skates as the treadmill spins. Then, somebody comes up from behind you and pushes you real hard in the back to speed you up. Instantaneously, the treadmill speeds up to compensate. Are you going to move forward and gain any ground? NOT!

Using your example, tell me what happens when:

1) The person pushing the skater is standing on the ground.

2) The "pusher" is right up against the "pushee", arms folded against his chest.

You're saying that as the "pusher" extends his arms forward and pushes on the person on the skates, that the person on the skates will not be forced forward and away from the "pusher" because his conveyor speeds up? Huh? [:^)]

That is EXACTLY the case because the treadmill speeds up. If the treadmill was going a constant speed, the result you want would be achieved.

[oldtimer]

You were onto something about wheel speed versus plane speed. Now you are going backwards. Could it be that you are confusing an accelerating force (plane's engine acting against air) with a non-accelerating force (spinning conveyor belt)? What part of freely spinning wheels don't you get? Dr.Who had it on the very first page by saying that the wheels would simply spin twice as fast.

[Jeff Matthews]

Maybe planes are too intriguing. Try a car. What if the car is on a treadmill, and however much the driver speeds up, the treadmill speeds up in the opposite direction. Will the car fly? Hell no. It will stay in one place - AND THERE WILL BE NO WIND - ABSOLUTELY, POSITIVELY NO WIND. So, feel free to use a convertible for this experiment (your hair won't be windblown).

Now, put some wings on the car. Will it all the sudden fly in the absence of this wind? I win!

Somebody prove this statement wrong. It is complete absurdity to think all you have to do is add wings to a car in a windless environment and it will fly.

[Ray Garrison]

"Now, if you took a mass that generated a gravitation force in equal magnitude as that of the earth BUT IN THE OPPOSITE DIRECTION, you would in fact stop falling down that hill. Remeber, the forces are completely offsetting. In your example, Ray, you are countering a non-accelerating force with an accelerating force. It will not work."

That is *EXACTLY* the point. Using your terms, the conveyor belt is a "non-accelerating force". It exerts *NO* force on the plance, other than the minute amount of force due to the rolling resistance of the wheels / bearings. Your example of putting another gravitational force in the opposite direction would be the equivalent of mounting another pair of engines on the plane, pointing in the other direction, *NOT* moving the ground under plane.

Take another example. A sea plane trying to take off going upstream against a current. Can it? Depends on how fast the current is flowing. The plane must generate enough force to move its pontoons through the water at whatever velocity is required to take off - around 65 mph in a Cessna 152, for example. Let's say the engines can exert enough force to move the plane through the water at, uh, 80 mph. If the river is flowing at less than 15 mhp against us, we can take off. If the river is flowing at faster than 15 mph against us, we can't take off. The pontoons exert too much drag and we can't reach the required 65 mph airspeed. Wheels on a conveyor belt have, for all practicle purposes, no drag. The belt can move beneath us as fast as it wants, we'll still take off.

[oldtimer]

I still think that there is an amount of force necessary to move the mass of the plane forward. Once this is achieved, the wheels and the belt can spin as fast as they want but the plane will move with the force propelling it. I think the question is posed to make one think. Obviously not enough propulsion results in no flight, but enough is enough.

[oldtimer]

Maybe planes are too intriguing. Try a car. What if the car is on a treadmill, and however much the driver speeds up, the treadmill speeds up in the opposite direction. Will the car fly? Hell no. It will stay in one place - AND THERE WILL BE NO WIND - ABSOLUTELY, POSITIVELY NO WIND. So, feel free to use a convertible for this experiment (your hair won't be windblown).

Now, put some wings on the car. Will it all the sudden fly in the absence of this wind? I win!

Somebody prove this statement wrong. It is complete absurdity to think all you have to do is add wings to a car in a windless environment and it will fly.

The car question is irrelevant to the plane question because of how it is propelled. Add a jet to the car, add some wings, then it might take off. See "Fireball 500" for the sixties example of Chryslers experimental jet car, starring Frankie Avalon.

[sputnik]

Maybe planes are too intriguing. Try a car. What if the car is on a treadmill, and however much the driver speeds up, the treadmill speeds up in the opposite direction. Will the car fly? Hell no. It will stay in one place - AND THERE WILL BE NO WIND - ABSOLUTELY, POSITIVELY NO WIND. So, feel free to use a convertible for this experiment (your hair won't be windblown).

Now, put some wings on the car. Will it all the sudden fly in the absence of this wind? I win!

Somebody prove this statement wrong. It is complete absurdity to think all you have to do is add wings to a car in a windless environment and it will fly.

I think that you missed Ray's earlier post.

You are so *COMPLETELY* missing the point. The car generates forward velocity by *PUSHING AGAINST THE GROUND* with its *WHEELS*. The plane generates forward velocity by *PUSHING AGAINST THE AIR* with its *ENGINES*. There is *NO DRIVING FORCE* associated with a planes *WHEELS*. All they do is rotate freely in response to the relative motion between the plane and the ground. Whether the plane is moving forward, or the ground is moving backward, or both are moving, it doesn't matter.

[Jeff Matthews]

You were onto something about wheel speed versus plane speed. Now you are going backwards. Could it be that you are confusing an accelerating force (plane's engine acting against air) with a non-accelerating force (spinning conveyor belt)? What part of freely spinning wheels don't you get? Dr.Who had it on the very first page by saying that the wheels would simply spin twice as fast.

Dr. Who did not get it right. If you run on the normal ground at 15 miles an hour, you move forward at 15 miles an hour. If you suddenly jump onto the treadmill (which is going 15 miles an hour contraflow) and you keep running at 15 miles an hour, you go nowhere. That does not mean your feet are now moving 30 mph.

Ah! But you'll say wheels are different than feet. Not at all. Here's why. Put the wheel on the conveyor and run it at 100 mph. The wheel spins at 100 mph. But does it? No, it will not - not unless you apply some force to the axle to keep the wheel stationary. So, let's say you run the conveyor belt with the plane on it. The plane WILL go backwards with the belt UNLESS there is a counter-force. This counter-force can be a rope attached to an imaginary ceiling. In this case, this new force will allow the wheel to spin and have no movement of the plane - forward or backward - IF AND ONLY IF the force equals the opposing force. So, when the rope tied to the ceiling stops the plane from going backward at 100 mph, it is actually pulling the plane forward at 100 mph. Thus, the wheel spins and the plane does not move. Substitute the rope for an equal force of jet propulsion, and you get THE EXACT SAME RESULT.

[customsteve01]

Jeff,

Please go back to practicing law and stay off of any aeronautice cases. If this was a case you were defending you would loose your a$$. Sorry but you are all wrong on your ideas.

It doesn't matter what is going on under the wheels of the airplane. Yes it might take a little longer to get airborne due to drag from the wheels having to spin alittle more but it would not keep it on the ground.

Steve

[oldtimer]

Except you reach the point of thrust overcoming the weight and therefore drag of the plane, then it moves forward no matter how fast things spin. The measurement of a wheels "speed" is the hangup here. Try thinking more in terms of rpm's.

[Jeff Matthews]

Maybe planes are too intriguing. Try a car. What if the car is on a treadmill, and however much the driver speeds up, the treadmill speeds up in the opposite direction. Will the car fly? Hell no. It will stay in one place - AND THERE WILL BE NO WIND - ABSOLUTELY, POSITIVELY NO WIND. So, feel free to use a convertible for this experiment (your hair won't be windblown).

Now, put some wings on the car. Will it all the sudden fly in the absence of this wind? I win!

Somebody prove this statement wrong. It is complete absurdity to think all you have to do is add wings to a car in a windless environment and it will fly.

The car question is irrelevant to the plane question because of how it is propelled. Add a jet to the car, add some wings, then it might take off. See "Fireball 500" for the sixties example of Chryslers experimental jet car, starring Frankie Avalon.

No, you are missing the point. Force is force is force. There are different causes of force, but it all works together in the same way. Equal opposing forces cancel each other out. It does not matter that you pit a jet engine against a treadmill vs. a car against a treadmill. In both cases, there is a force required to move the thing forward.

Where everyone is getting it wrong is they forget about this little thing called gravity. They assume that if you put a plane on a treadmill and the engines are TURNED OFF, the plane wheels will just sin and spin, and the plane will go nowhere. That is NOT the case. Then, they add little examples about how, with the wheels in place, all it takes is a nominal force to keep the plane stationary on the treadmill. Again, this is wrong. If that plane is on the treadmill - wheel and all - it will move 100 mph backwards if the engine is off. Period. We should ALL agree with that, and if you don't, well....... (it really is that basic).

Now, you say, "Oh, but it only takes a little bitty force to start the wheel spinning and that little, tiny force will allow the plane to sit motionless while the wheel spins and spins. Not true. It takes whatever force is necessary to offset the force of the treadmill. Anybody heard of Newton's law? (I forget which one it is; he had a few).

[Champagne taste beer budget]

I think we need to get a Navy Admiral involved in this. []

First off, I want to know what happened when my pusher pushed the pushee. If the pushers arms truley extended out in from of him, then the distance between the two people increased. That should be basic. If we are standing front to back, and I press against you, extending my arms fully, there has been a change in the amount of distance between us. Someone moved. If the pushee did not move, then obviously the pusher must have moved backwards on firm ground by the force of the conveyor belt? Or was the pushee so locked into place by his magic wheels that the pusher pushed himself backwards with his arm strength?

Without rereading the whole thread, which I still don't think you've done, I forget all the great points brought up by both sides. Even so, I'll make you a deal.

Lets get you on a treadmill, on roller skates, set up with a acceleromotor like in a subwoofer, the faster you skate, the faster the treadmill spins. Now, you're saying that if I strapped a small jet pack to your back and fired it off, you would remain on the treadmill? I think not.

Still hung up on the wheel thing, I know. Seems that's where most people see the light, is realizing that the wheels on the treadmill are just a ruse to take your mind away from the fact that you have a 12,000 HP jet engine pushing said plane forward by apply thrust against the air.

[Ray Garrison]

How many examples do we need to come up with before this sinks in? Sigh...

Here's another. Take a rocket engine. No wheels, no body, just a rocket engine. Lay it on the ground. Light it. Assume it doesn't fly up, but just shoots off along the ground. Will it move? Yep. How fast? Real damn fast. Now, lay it down on a conveyor belt. Light it. Start the belt. Will the rocket move? Yep. How fast? Not quite as fast, because there's some drag, but I be it'll go a lot faster than the conveyor belt would. Okay, so speed the conveyor belt up until it's moving as fast as the rocket, in the opposit direction. That is, if the rocket is moving at 1,000 mhp north, the conveyor belt is moving at 1,000 mph south. (This means that the relative speed of the rocket to the conveyor belt is 2,000 mph.) Now, attach some wheels to our rocket and repeat the test. The *ONLY* difference is the additional mass of the wheels (slows acceleration a bit), and the reduction of drag on the surface by replacing the rocket body sliding along the ground with the wheels rolling on the ground (goes a lot faster.)

The only difference between the rocket engine and a jet engine, of course, the the jet doesn't carry it's oxidizer with it, but otherwise exactly the same. Attach some wings to our rocket engine. Will it take off? Off course it will.

I think I've finally come to understand the problem. There is a finite amount of intelligence in the world, and the population keeps increasing.