A jet plane on a large treadmill

[Beaver]

I give up.

[EPSkis]

AIRCRAFT DO NOT USE THIER WHEELS TO ACCELERATE THERFORE THE TREADMILL SPEED IS IRRELEVANT TO THE AIRCRAFT'S MOTION.

Beaver - the problem doesn't state or suggest anything about wheelspeed. The problem states "speed", which is translated to "forward movement".

The treadmill speed is DIRECTLY relavent to the forward progress of the plane. Simple logic would tell you that if the treadmill were going *faster* than the forward movement of the plane, the plane would fall off the BACK of the conveyor.

Test your theory by going to any gym with a treadmill. Turn it all the way up. Now, step onto the treadmill & report back to us the following:

1.) Whether or not the conveyor speed is relevant.
2.) Your hospital room info.

[DJSapp]

When the treadmill notices that the plane is moving forward and it speeds up the jet will continue forward because all the treadmill does is spin the wheels of the craft faster. It does not stop the thrust of the enjine against the air which is not affected by the wheel speed.

AIRCRAFT DO NOT USE THIER WHEELS TO ACCELERATE THERFORE THE TREADMILL SPEED IS IRRELEVANT TO THE AIRCRAFT'S MOTION.

Beaver, you are missing something, the plane's wheels cannot move faster than the treadmill in the groundspeed frame of reference.

[Beaver]

Top of page 3 Oh yeah.

Ha.

45678

[Dirty Hoar]

Oh yeah.

lol...you was page 3. Somebody just saw the light and deleted their post.

[cj001f]

Ha.

45678

making that treadmill go backwards

[The Suit]

Many years ago, a friend of mine was on the road show for his company's IPO. Because they had meetings in three different cities on the same day, they chartered a Lear 35. In one of the cities, the humidity was very high when they landed, so the plane's windows fogged up and the pilots drove off the taxiway. The plane was stuck.

My friend, sitting in the back of the plane with a couple of highly paid investment bankers, heard one of them say to the other "I think the wheels are spinning."

So for those of you who disagree with Beaver, you'll be pleased to know that - despite your appalling ignorance of physics - you're not too dumb to land a lucrative job on Wall Street.

[Dirty Hoar]

Then they will rip off cause no treadmill will stop a jet engine.

Prediction - This post will eventually shrink to one page.

This is hilarious... but I feel your frustration Beaver. I'll admit I've been on the wrong side of logic before but was absolutely positive I was right only to later realize I wasn't. However, this will go on your permanent record.

[Cornholio]

So if you are running on a treadmill and I put a rope on you and pull really hard and you turn up the treadmil speed as I pull you will not come towards me? Think hard about this and remember I am not on the treadmill. Your feet will be going like mad but I WILL pull you off the front of the treadmill because I (like the Jet engine pushing air) have nothing to do with the treadmill. The jet engine will push air regardless of what the wheels/treadmill are doing. IT WILL PUSH AIR which is NOT affected by a treadmill. THINK HARD, I have confidence that you are not stupid.

Thanks for your confidence.

Let's put me in a wheelchair to eliminate the complications of biomechanics.

Now, I'm sitting in a wheelchair, with a rope, pulled by you.

The treadmill runs so that my wheelchair speed doesn't increase in the room.

You pull.

The treadmill pulls back.

I don't move.

The wheels spin.

[cj001f]

Thanks for your confidence.

Let's put me in a wheelchair to eliminate the complications of biomechanics.

Now, I'm sitting in a wheelchair, with a rope, pulled by you.

The treadmill runs so that my wheelchair speed doesn't increase in the room.

You pull.

The treadmill pulls back.

I don't move.

The wheels spin.

[Big Blue]

Holy shit!!! I can't even believe the fucking carnage I'm reading here. Beaver is correct. Those of you who disagree are mentally retarded. Seriously. This is not a difficult problem. If anyone really, really believes that Beaver is wrong then I'll bet you a large sum of money that he is in fact correct. Then I'll get the video camera, a model rocket engine, and a toy plane and go to the gym.

[bklyn]

Why do aircraft carriers have slingshots?
Does light speed exist in absolute darkness?
Compared to all knowledge and wisdom to be acquired in a lifetime, what's a few IQ points between friends?

[Dr. Send]

Everyone pay attention.

Imagine the treadmill is connected to the back of a plane, so that when the plane goes forward, the treadmill moves backward at the same speed, as in this technical diagram:

The fact that the treadmill is connected to the plane guarantees that the treadmill will be going in the opposite direction of the plane at the same grounspeed as the plane, whatever that is. Clearly, from this scenario, the plane moves forward from the thrust generated by the engines, even though the treadmill is moving backward at the same speed.
Now everyone shut up.

[Cornholio]

Think about what happens if I'm on the treadmill, you're pulling, and the thing is running.

Then you let go.

I go flying backwards.

That force that you exert on me with the rope is equal to the force exerted through the wheels by the treadmill.

[EPSkis]

To clarify my position:

The plane will FALL off the front of the conveyor - it will NOT "take off".

edit:
1.)assuming the conveyor actually ends.
2.)for the love of God and all that is right and good: It doesn't matter how fast the damn wheels are spinning.

[cj001f]

Clearly, from this scenario, the plane moves forward from the thrust generated by the engines, even though the treadmill is moving backward at the same speed.
Now everyone shut up.

it moves forward relative to it's original position on the treadmill belt, not the outside frame of reference called air It needs to be moving forward relative to the air to take off

[Big Blue]

The treadmill runs so that my wheelchair speed doesn't increase in the room.

Actually, that's not what's stated in the problem. The problem states that the treadmill will move at the same speed that you move. So if you're moving forward (with respect to the room) at 1mph, then the treadmill will be moving the other direction at 1mph, and you're wheels will be spinning at 2mph. This concept should not be hard to comprehend.

[Cornholio]

I'm done arguing about this, actually, because there's some drastic misunderstanding taking place somewhere.

In my mind, and using the free-body diagrams I've sketched, there is no way the plane ever moves forward.

This is largely because I believe that the problem states that the treadmill pushes the plane back to match the force generated by the engines, and therefore the sum of the forces on the plane is Zero.

F=MA

There is no F.

There is no A.

There is no A, there is no Delta-V, so there is no V, so there is no airflow.

No airflow, no lift.

[dubu]

I feel for you Beaver its like talking to a brick wall..

lets try this again..

say you are skiing switch, and have a big rocket pack.. then right under your skis a slab releases, you in turn ignite your rocket engine, tht has say 1000pounds of thrust.. what happens?

[EPSkis]

I'm done arguing about this, actually, because there's some drastic misunderstanding taking place somewhere.

In my mind, and using the free-body diagrams I've sketched, there is no way the plane ever moves forward.

This is largely because I believe that the problem states that the treadmill pushes the plane back to match the force generated by the engines, and therefore the sum of the forces on the plane is Zero.

F=MA

There is no F.

There is no A.

There is no A, there is no Delta-V, so there is no V, so there is no airflow.

No airflow, no lift.

It doesn't state that it pushes the plane BACK, merely that it senses any forward movement and matches it - imo, that would suggest that the plane does, in fact - make small advances before the conveyor matches the planes speed.

I do agree that without sufficient airflow, the plane will not lift off.

[Big Blue]

This is largely because I believe that the problem states that the treadmill pushes the plane back to match the force generated by the engines, and therefore the sum of the forces on the plane is Zero.

No, the original problem says nothing about force.

This conveyor has a control system that tracks the planes speed and tunes the speed of the conveyor to be exactly the same (but in the opposite direction).

As you can see, it only matches the speed, not the force.

[Cornholio]

I feel for you Beaver its like talking to a brick wall..

lets try this again..

say you are skiing switch, and have a big rocket pack.. then right under your skis a slab releases, you in turn ignite your rocket engine, tht has say 1000pounds of thrust.. what happens?

If the force produced by the jetpack pushes you up to match the force produced by the slab through friction on your skis, you don't move relative to the trees you should have been skiing in to begin with.

[dubu]

I'm done arguing about this, actually, because there's some drastic misunderstanding taking place somewhere.

In my mind, and using the free-body diagrams I've sketched, there is no way the plane ever moves forward.

This is largely because I believe that the problem states that the treadmill pushes the plane back to match the force generated by the engines, and therefore the sum of the forces on the plane is Zero.

F=MA

There is no F.

There is no A.

There is no A, there is no Delta-V, so there is no V, so there is no airflow.

No airflow, no lift.

yes but the plain is coupled to the treadmill through the wheel bearings.

so the force applied on the plane is not the force of the tread mill..
it is the force of the coefficient of friction in the bearings,

for example
what would happen if you had a car (no engine no tranny just wheels)with wheel bearings with a coefficient of friction of 0, ie no friction. and the treadmill started to move.. the car would not move..

[DJSapp]

Cornholio, what is your frame of reference? Where does the treadmill's speed come from? The speed of the wheel compared to the treadmill or the speed of the aircraft as a whole from a stationary point (say, the control tower).

[Cornholio]

It doesn't state that it pushes the plane BACK, merely that it senses any forward movement and matches it - imo, that would suggest that the plane does, in fact - make small advances before the conveyor matches the planes speed.

I do agree that without sufficient airflow, the plane will not lift off.

I think I'm also assuming the control system is perfect-- that is, there's no lag (or some great prediction) between the sensing of the speed and the treadmill movement. That's fair enough for this hypothetical.

The treadmill MUST push the plane back.'

Velocity is all about force. The problem specifies speeds/velocities, but if you think about them as the result of forces, it's easier to see.