Will it take off?

[Dave M]

I'll make my final comments too.

The only way to keep the plane from flying in the system described would violate the original statement. That is why it is illogical.

The only way to keep the plane grounded against the thrust of the engines is with zero wheel speed. Any tire rotation at all means that the air speed and conveyor speed are not the same (violation).

There is some amount of force (very small compared to the engines capability) required to start a still plane moving. Once the wheels move, "free-wheeling begins" and any acceleration by the conveyor only spins the wheels faster and has virtually zero effect on the forward momentum fo the plane. Unfortunately, zero wheel speed from the observer means the plane is traveling backwards on the conveyor and therefore has a negative airspeed. Meaning the conveyor speed (or wheel speed) is not equal to plane speed. This violates the question parameters.

Here is another real problem I see. Think about the table cloth magic trick. Slow-pieces don't move, fast-everything stays in place. Airplane engines generate so much forward thrust, that a conveyor accelerating that quickly (even with a motionless plane) would start the wheels turning. There is an acceleration limit where the wheels will start to spin, instead of the plane moving.

The parameters of the question can never logically be met and any attempt to do so (ie. Mythbusters) will definately result in a flying plane. I am 100% sure of this. No conveyor system could ever stop the wheels from turning against the planes opposing thrust. If you could ever build such a theoretical system, the planes speed would not be equal to the conveyor speed.

I just brought the horse back to life, didn't I. hehehe

What I don't think you're grasping is even if you did replicate it accurately, it would fly. The conveyor would not keep the plane staionary!! The plane does not drive with it's wheels!! It is pulled or pushed through the air by the thrust of the engines only. It's the air speed that matters and not any speed in relation to any thing on the ground. If a 50 mph head wind came along the plane would get lift even if the engine wasn't running and the plane was going nowhere. The wheels and any movement of the ground has absolutely no effect on what the plane's movement does.

[thomas]

I guess Im just dumb, but wouldnt it be like running on a treadmill or a dyno? Yes the engines are trying to push the plane but if the brakes are off then its trying to move but the belt is moving in the opposite dirrection so the plane hasnt really moved so theeres no lift under the wings?

Ahhh, the horse is dead!!!!

[Joe K. 99 Zeee!!]

One more beating....

What kind of plane is it? A 757? That'd need to go about 160mph to become airborne. That means the tires would be turning at 320mph. Are they rated for that speed? If the tires fail you're not going anywhere!!

Check it out!
http://www.aerospaceweb.org/question...ce/q0088.shtml

[Sean 94z28]

What I don't think you're grasping is even if you did replicate it accurately, it would fly. The conveyor would not keep the plane staionary!! The plane does not drive with it's wheels!! It is pulled or pushed through the air by the thrust of the engines only. It's the air speed that matters and not any speed in relation to any thing on the ground. If a 50 mph head wind came along the plane would get lift even if the engine wasn't running and the plane was going nowhere. The wheels and any movement of the ground has absolutely no effect on what the plane's movement does.

If you look at my reply on the first page, that was the very first thing that I understood. I still agree with everything you said.

So if the plane that we both agree will fly is accelerating (which it has to do), at what point in time is the belt ever going the same speed as the plane? The answer is never (which voids the questions assumptions) and it doesn't matter anyway. Once the wheels start turning the plane will fly.

I understand what you are saying, but of the scenarios described meet the conditions of the question. Kevin tried to describe a scenario where the plane won't fly, I tried to point out that those condtions can't be met within the parameters (if a belt is keeping a plane from flying, it certainly isn't going the same airspeed as the plane). Trace made the point of why the plane will fly, but that scenario also could never meet the condtions described (a belt that "tracks" the planes speed will always lag the accelerating plane). Therefore there speed is not "exactly" the same and the wheels turn.

The question is illogical and unacheivable.

[Roger in Kensington]

Can I play?

Let me pose the following situation:

Superman wants to get some exercise. He attaches the plane to his head. Same plane, but plane has no engines.

Superman stands on the treadmill (i.e., the conveyor belt). Conveyor belt starts. Superman starts running (same as you would on a treadmill). Conveyor belt perfectly matches Superman's speed; the faster he goes, the faster the conveyor belt goes so he gets lots of exercise, but he stays in one spot.

Will the plane develop sufficient lift to fly?

If so, then how are the wings developing lift?

If not, then how is this any different from the original question?

Just curious.

[Jeff_in_Atl]

Let me pose the following situation:

Superman wants to get some exercise. He attaches the plane to his head. Same plane, but plane has no engines.

Superman stands on the treadmill (i.e., the conveyor belt). Conveyor belt starts. Superman starts running (same as you would on a treadmill). Conveyor belt perfectly matches Superman's speed; the faster he goes, the faster the conveyor belt goes so he gets lots of exercise, but he stays in one spot.

Will the plane develop sufficient lift to fly?

If so, then how are the wings developing lift?

If not, then how is this any different from the original question?

Just curious.

No. Because you are measuring superman's speed from the treadmill not from a fixed point. That is not the same situation.

[Jay 02 TA ws6]

Let me pose the following situation:

Superman wants to get some exercise. He attaches the plane to his head. Same plane, but plane has no engines.

Superman stands on the treadmill (i.e., the conveyor belt). Conveyor belt starts. Superman starts running (same as you would on a treadmill). Conveyor belt perfectly matches Superman's speed; the faster he goes, the faster the conveyor belt goes so he gets lots of exercise, but he stays in one spot.

Will the plane develop sufficient lift to fly?

If so, then how are the wings developing lift?

If not, then how is this any different from the original question?

Just curious.

It would fly. Because its Superman.

[Jay 02 TA ws6]

I guess Im just dumb, but wouldnt it be like running on a treadmill or a dyno? Yes the engines are trying to push the plane but if the brakes are off then its trying to move but the belt is moving in the opposite dirrection so the plane hasnt really moved so theeres no lift under the wings?

Ahhh, the horse is dead!!!!

The plane cannot be stationary. The only force acting on the plane is the thrust of the engines.

The treadmill does not exert a force on the plane, and thus, cannot counteract its speed. The treadmill only effects the speed of the wheels, and the wheels spin freely - they do not exert a force on the plane and thus cannot slow it down. You are picturing a stationary plane, but in fact, that is not possible.

Running on a treadmill is not the same thing... because in those situations, the treadmill is acting on your leg which is acting on your body. Again, the treadmill does not effect the plane at all (except for the friction in the bearings of the wheels - which is a very small amount compared to the thrust of the motor).

[blackthunder50]

The plane cannot be stationary. The only force acting on the plane is the thrust of the engines.

When the plane is either sitting still or moving there is a normal force acting upward, a gravitational force downward, and a force forward and backwards from thrust and drag. When the plane moves on a solid non-moving ground (no conveyer belt) It receives a velocity great enough for the wings to add the "magical force to the force diagram which is lift"!!

However if the plane does not receive velocity forward, keep in mind it will have a speed of, lets say 200 mph while the conveyor counteracts at 200 mph the palne will have no velocity and no lift.

The plane has zero velocity in the positive direction and with no velocity there will be no lift to get it off the ground.

Just my thought after mechanical physics last year

[Trash man]

trace best explained it, the engines or props, pull the plane thru the Air to gain speed. the wheels are just rollers, like on a shoping cart.

[Jay 02 TA ws6]

However if the plane does not receive velocity forward, keep in mind it will have a speed of, lets say 200 mph while the conveyor counteracts at 200 mph the palne will have no velocity and no lift.

The plane has zero velocity in the positive direction and with no velocity there will be no lift to get it off the ground.

Your last statement is correct, it's your first statement that erroneous. The conveyor cannot counteract the motion of the plane. It exerts no force on the plane at all. Why? Because the only things that the conveyor belt exerts force on are the wheels of the plane - which are free-spinning, and (aside from friction in their bearings) exert zero force affecting the motion on the plane. Therefore, the conveyor's motion is immaterial to the motion of the plane.

[TraceZ]

I just got home from the Dave Mathews Band concert. It was a great time!!!

If somebody were to replace the entire stage with a giant treadmill, and the band members all had motion sensors on their ankles, what would happen if Dave Mathews farted?

[Dave M]

Someone mentioned a shopping cart, which is a good way to look at this problem. If you placed a grocery cart on a treadmill and started the treadmill, the cart would remain stationary because the wheels would simply freewheel underneath it (In reality there would be a slight bacward motion because of the friction in the wheel bearings, but if we can have a treadmill the size of a runway we can have no friction in our bearings too). Now, keep in mind we have a grocery cart on a treadmill with the treadmill moving underneath it. The cart is staionary to the objects around it, but the wheels are moving because they're in contact with the treadmill. You come up behind the cart and give it a push with your hand. Is it going to go anywhere or is it simply going to stay staionary on the treadmill? It will move forward, even if the treadmill speeds up, because your hand is an outside force acting on this system. The treadmill does not affect the force your hand puts on the cart at all. Your hand, in this case, is the engine. If the engine has enough thrust to overcome the friction within the wheels, it will accelerate down the treadmill, no matter how fast the treadmill is moving in the opposite direction. It is not at all like a runner or car on a treadmill, because the "engines" that power runners or cars are in direct connection to the treamill and their power will be cancelled out exactly by the reverse motion of the treadmill. In these cases the engines need the treadmill, or contact with the ground, in order to move forward. They are based on ground speed. An airplane does not need this. It only needs contact with the air to move forward. Anything the ground is doing is irrelevent.

In order for the analogy to extend to airplanes, the AIR would need to be moving in the direction the airplane wants to go. If the air sped up as the plane sped up, then there would be no net airflow over the wings and you'd get no lift, no matter how fast the plane was travelling on the ground. For instance, if you need a 100 mph airspeed to lift off, and you've got a 100 mph tailwind, then you need the airplane to go 200 mph to takeoff. If you've got a 50 mph headwind then the plane only needs to go 50 mph to get a net 100 mph windspeed over it's wings (this is why airplane always take off and land into the wind). Note that in the instances it doesn't matter if the ground is going forward, backward, or doing nothing, the engine's contact with the air is all that matters and is all that is needed to propel the plane forward.

After all, how does a plane move forward when there's no ground underneath it at all? It's the engines and the air, nothing more.

[Jeff_in_Atl]

I just got home from the Dave Mathews Band concert. It was a great time!!!

If somebody were to replace the entire stage with a giant treadmill, and the band members all had motion sensors on their ankles, what would happen if Dave Mathews farted?

The crowd would move in the opposite direction with an equal speed of the gas coming out his butt. But that depends on where the speed sensor is located at. If it is on the tread mill the speed of the gas would be either less than or greater than the speed of the treadmill depending on whether you are standing in the direction the tread mill is moving or not. Of coarse if you are standing to the side it does not effect the speed of the gas. Bla bla bla….

Dave Mathews Band - What Would You Say

[Jeff_in_Atl]

In order for the analogy to extend to airplanes, the AIR would need to be moving in the direction the airplane wants to go. If the air sped up as the plane sped up, then there would be no net airflow over the wings and you'd get no lift, no matter how fast the plane was travelling on the ground. For instance, if you need a 100 mph airspeed to lift off, and you've got a 100 mph tailwind, then you need the airplane to go 200 mph to takeoff. If you've got a 50 mph headwind then the plane only needs to go 50 mph to get a net 100 mph windspeed over it's wings (this is why airplane always take off and land into the wind). Note that in the instances it doesn't matter if the ground is going forward, backward, or doing nothing, the engine's contact with the air is all that matters and is all that is needed to propel the plane forward.

Boy that clears things up. NOT! LOL You are correct though.