Fun little physics question..

[OwnageMobile]

I see where we are butting heads now.

So I take that as it's matching the forces-- in the way that if the plane starts to move, the belt moves fast enough to stop the plane's movement.
If we say that the belt only matches the speed of the plane, then it is a different problem. The plane would be able to take off if in this case. It is poorly worded...

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[DrBowtie]

I see where we are butting heads now.

So I take that as it's matching the forces-- in the way that if the plane starts to move, the belt moves fast enough to stop the plane's movement.
If we say that the belt only matches the speed of the plane, then it is a different problem. The plane would be able to take off if in this case. It is poorly worded...

I took it to mean that the belt ******s the planes movement to stop it as well.

 

[bruinfan32]

Aircraft flight is depended on an achieved speed of the "realitive wind", the term used to describe the velocity of the fluid moving over the wing...if the wing isn't moving through that fluid (ie foward in that fluid, or having the fluid move over it), than lift caused by a pressure differential will not be achieved and the plane will sit there. The thrust applied is being cancelled by an artifical drag vector, so unless the thrust is antiparallel from the ground and is generating a thrust so great as to simply lift the plane off the ground (like a rocket), it won't budge.

 

[liverotcod]

If God had intended jet aircraft to fly, He would not have put them on treadmills.

But I am perplexed by the problem. At time zero, the thrust is, say, 10,000 lbs, and the frictional response (assuming realistic friction, as noted if no friction then the thrust is the only input) is very small. So the plane must accelerate, no? Then as it accelerates, the frictional response increases. But the plane is still accelerating in the frame of reference important for lift (the airmass), since for quite some time its thrust will be much more than the friction.

There's another gem pilots argue about all the time about reversing course in a headwind.

Edit: OK, I see you guys have already thought that through. A problem of definitions.

 

[OwnageMobile]

Case closed? I'm gonna go work out-- please don't let this thread pass the 4 page mark guys.

 

[cfdavid]

So if the plane is stationary relative to the conveyor belt, it is stationary relative to the air. No "wind", no take-off.

yes. i agree. but, medicalbound (a pilot) made an interesting point.
he seemed to suggest that because the "movement" was caused by jet engines (pushing existing air), versus torque at the wheels, that the plane would/could lift.

my response was that there must be something to the design of the exact location of the jet engine relative to the plane/wings.

it's easier to picture a jet engine in the back of the plane, behind the wings. so, it's very unlikely that enough air flow would be created (by the intake and thrust of the jet-in the back) would create enough of a pressure differential over/under the wings to allow for buoyancy, since there would not be (due to the opposing motion of the conveyor) the typical relative air motion over the wings as would be created if the plane was thrusting forward and making relative motion to the ground, thereby creating significant relative motion to the air also (disregarding any wind).

 

[mercaptovizadeh]

You guys are making this problem WAY too complicated.

It's a regular plane with normal wheels with friction.

The speed of the plane is perfectly counteracted by the speed of the moving belt.

The speed of the plane relative to air is thus zero.

As the speed relative to the air is zero, the lift, too, is zero.

No lift, no takeoff.

Simple as that.

 

[SeventhSon]

if there is no slip between the wheels and the conveyor belt then there can be no displacement.

 

[cfdavid]

You guys are making this problem WAY too complicated.

It's a regular plane with normal wheels with friction.

The speed of the plane is perfectly counteracted by the speed of the moving belt.

The speed of the plane relative to air is thus zero.

As the speed relative to the air is zero, the lift, too, is zero.

No lift, no takeoff.

Simple as that.

agreed. but, again, there could be some tendancy to lift. this would depend on the thrust capacity of the jet (and assuming the conveyor could go fast enough to offset such thrust).

because, it's possible that enough air flow could be created by the jet displacing enough air (i.e. causing enough air to flow from in front of the plane towards its rear), it could cause enough flow over/under the wing to create the necessary pressure differential.

like a fan, the jet would take air from one spot (in front of it), and push it back (behind it, if you will). thus creating air flow.

would this flow differential over/under the wing be sufficient to cause buoyancy??? that depends on the air flow, and thereby the pressure differential created. if the differential was great enough, the plane COULD lift.

but, i guess that would have to be one mammoth jet engine!

 

[C.P. Jones]

I've been a pilot since 1998, it is airspeed that is the deciding factor for flight not groundspeed. Here is an example: the rollout speed for a Cessna is about 65 knots (airspeed). If you theoretically have a 60 knot direct headwind, you would have to be going only 5 knots relative to the ground to start flying. That is also why a plane can fly 200 knots (ground speed) with only enough thrust to fly at 100 knots in the air (100 knot tailwind).

The outcome of the problem would be different if the power were applied to the wheels, but it is not.

TIME OUT!

i stopped reading at this post, so sorry if it was discussed further....

so if there is a 737 next to a box of the same weight, and same general height/width/length......could a strong enough wind lift the plane, and not budge the box? i am not saying this in doubt to you saying the air speed stuff, i just didn't know this......are there planes small enough that a wind that wouldn't blow much around picks a plane up?

 

[rockitman]

Yes, if there was a 200mph wind coming at you straight on you would be able to take a 747 off without moving an inch. You could also fly the 747 forward, but you would actually be travelling backwards relative to the ground.

 

[dajimmers]

are there planes small enough that a wind that wouldn't blow much around picks a plane up?

Not really, though ultralights are close. But, what you are describing is basically a kite, and yes, kites fly w/ very little wind.

 

[spaceman_spiff]

Yes, if there was a 200mph wind coming at you straight on you would be able to take a 747 off without moving an inch. You could also fly the 747 forward, but you would actually be travelling backwards relative to the ground.

so what you're saying is, the answer to the question is YES! the plane could take off, but only in a hurricane.

 

[rockitman]

^

that was the answer to the question asked in post #60

 

[OwnageMobile]

Ok, look-

If the plane's jet force is matched by the belt's force on the wheels:

Case #1: Wheels are frictionless (belt can do no work) Answer = yes, the plane can take off.
Case #2: Wheels are not frictionless Answer = no, the plane doesn't move.

If the plane's speed is matched by the belt, but in the opposite direction:

Case #3: The plane can move, and thus it can fly.

It would make more sense to have the question set to where the speed of the plane is matched in an opposite fasion. It would be like having a tailwind constant at half your ground speed.

This question is hard due to its ambiguity, not its physics setup.

 

[lattimer13]

You lost me when you used "fun" and "physics" in the same heading...

 

[JustBreathe]

I agree with medicalbound. I think some people are missing the difference in the way an airplane is accelerated to take-off speed vs. the way a car is powered. The runway is pretty much irrelevant here since the airplane's "traction" comes from the air not the runway. A car on this runway would have its wheels spinning but not be going anywhere. But an airplane would have its wheels spinning twice as fast as usual but still be accelerating at the normal rate in the normal direction. A moving runway is not capable of counteracting the acceleration of the airplane.

Think of it this way: Imagine you have a remote control car on the checkout belt of a supermarket. You have it going forward, but the belt is going backward. So standing in line and observing this, you see the car standing still in space. But if you just turned the motor on the car off and used your hand to push it along while standing on the ground, it wouldn't matter how fast the belt was going. You would be able to push it forward at the same speed whether the belt was on or off. The airplane is like you pushing the car. It's using a force that isn't relative to the ground it's sitting on, so it isn't a problem if that ground is moving.

It is correct that airplanes have to be moving relative to the air in order to have lift and fly, but I think everyone is jumping to the conclusion that the runway could prevent the airplane from moving relative to the air, which I don't think is right. Airplanes are propelled by taking air from in front of the plane, accelerating it, and then shooting it out behind the plane. And since every force has an equal and opposite reaction, this produces thrust propelling the airplane forward. The air is not affected by the runway’s motion.

Sorry, that was really long... I'll stop it there

 

[Nikki2002]

Worst Thread Evvvvveeeerrrrrr!! Boo Hiss!!

 

[liverotcod]

I think some people are missing the difference in the way an airplane is accelerated to take-off speed vs. the way a car is powered.

Some are, but not all.

A moving runway is not capable of counteracting the acceleration of the airplane.

But please read back through the thread. A valid point was made that the treadmill runway could impart enough drag on the plane via friction to counteract the thrust.

 

[JustBreathe]

But please read back through the thread. A valid point was made that the treadmill runway could impart enough drag on the plane via friction to counteract the thrust.

It takes some small amount of force to overcome the friction in the wheels and bearings. So I guess that if the runway was moving at some astronomical speed, the engines would be using all their thrust just doing that. But that's really a reach, in my opinion.

 

[MoosePilot]

My thought is that the thrust is imparted against the air. So the plane's movement is relative to the air mass around it, not the runway belt. The runway will roll backwards, attempting to counter the movement of the plane, but because the wheels are free spinning, that will just cause the wheels to spin faster, which will cause the belt to spin faster, which will cause the wheels to spin faster. In reality, the wheels would probably disintegrate, but the plane should take off with no problem, because the thrust is moving it in relation to the air mass.

That's my thought, but I'm having trouble really envisioning all the results.

 

[liverotcod]

It takes some small amount of force to overcome the friction in the wheels and bearings. So I guess that if the runway was moving at some astronomical speed, the engines would be using all their thrust just doing that. But that's really a reach, in my opinion.

Well, this is a physics puzzle, after all. Reality need not impinge
But that's exactly what's being argued, correctly in my opinion. My point above was that from time zero at every moment up until the drag from the wheels equalled the thrust, there should be acceleration.

 

[JustBreathe]

Well, this is a physics puzzle, after all. Reality need not impinge
But that's exactly what's being argued, correctly in my opinion. My point above was that from time zero at every moment up until the drag from the wheels equalled the thrust, there should be acceleration.

Okay, I agree.

 

[medicalbound]

Let’s take a look at the limits of the example. Expand the conveyor belt to be huge. Let’s say it has a circumference of ca. 25,000 mi and is rotating at ca. 1,000 mph (roughly the circumference and surface rotational speed of the Earth). You are sitting in the plane and are going to attempt to take off going in the opposite direction to the direction of rotation. Assume that max thrust only allows you to get up to 200 mph. All other factors being equal, would you be able to take off?

Of course. Anyone who has taken off from a west facing runway can vouch for that. This example is no different.

 

[MoosePilot]

Well, this is a physics puzzle, after all. Reality need not impinge
But that's exactly what's being argued, correctly in my opinion. My point above was that from time zero at every moment up until the drag from the wheels equalled the thrust, there should be acceleration.

Ok, now I get it. Basically, the result would be as if the plane was locked into an engine run stand while the wheels spun insanely fast and the runway-belt spun insanely fast to hold the plane in one place relative to the air. Because that's the definition of how fast the runway-belt runs, just fast enough to hold the plane in one place relative to the air.

 

[JustBreathe]

Of course. Anyone who has taken off from a west facing runway can vouch for that. This example is no different.

Unfortunately, I'm no pilot. Though that would be fun!

 

[MoosePilot]

Let’s take a look at the limits of the example. Expand the conveyor belt to be huge. Let’s say it has a circumference of ca. 25,000 mi and is rotating at ca. 1,000 mph (roughly the circumference and surface rotational speed of the Earth). You are sitting in the plane and are going to attempt to take off going in the opposite direction to the direction of rotation. Assume that max thrust only allows you to get up to 200 mph. All other factors being equal, would you be able to take off?

Of course. Anyone who has taken off from a west facing runway can vouch for that. This example is no different.

The world doesn't spin faster. Imagine the runway was controlled by sensors which detected movement of the plane relative to a fixed point that wasn't on the track. The track went however fast it took to keep the plane stationary in relation to that fixed point.

It helped me to imagine a case where the runway moved faster than a slowly accelerating plane. The plane would move backwards in relation to the air mass around it. If you slowed the runway down to where there was no airflow over the wing, that's the imagined scenario.

 

[medicalbound]

The world doesn't spin faster. Imagine the runway was controlled by sensors which detected movement of the plane relative to a fixed point that wasn't on the track. The track went however fast it took to keep the plane stationary in relation to that fixed point.

It helped me to imagine a case where the runway moved faster than a slowly accelerating plane. The plane would move backwards in relation to the air mass around it. If you slowed the runway down to where there was no airflow over the wing, that's the imagined scenario.

The "fixed point" idea is not part of the original assumptions. Only that the speed of the "runway" is variable and opposite to the speed of the plane. Why should we assume that there is a [significant] force opposing the thrust? In my world analogy, the runway is not only going equal and opposite to the speed of the plane, it is pushing it 800mph backwards from the perspective of a stationary point not on the "track". This does not affect the thrust on the air which causes the plane to accelerate. As the plane accelerates (moves through the air), the runway will move faster and faster in the opposite direction (e.g. ground speed will increase), but so what? The airspeed will also increase effecting lift and flight.

 

[MoosePilot]

The "fixed point" idea is not part of the original assumptions. Only that the speed of the "runway" is variable and opposite to the speed of the plane. Why should we assume that there is a [significant] force opposing the thrust? In my world analogy, the runway is not only going equal and opposite to the speed of the plane, it is pushing it 800mph backwards from the perspective of a stationary point not on the "track". This does not affect the thrust on the air which causes the plane to accelerate. As the plane accelerates (moves through the air), the runway will move faster and faster in the opposite direction (e.g. ground speed will increase), but so what? The airspeed will also increase effecting lift and flight.

It's how I understood the initial set-up. If you want it to be your way, that's fine. I know you like your earth example, but the earth example is really pointless, because the plane is at rest in relation to the earth and the air mass to begin with, then begins to move in relation to the earth and the air mass due to thrust. In other words, it's the most boring, everyday, average setup possible and doesn't really merit inclusion in an fun physics question thread.

 

[QuikClot]

It will not take off.

I really don't think I understand your question, because it looks way too easy. As I read it, the plane is not moving relative to the surrounding air, therefore there would be no pressure gradient on the wings whatsoever.

Seconded. The relative motion of the air to the wings creates the pressure gradient, which creates the lift. A stationary plane can't take off.

 

[JustBreathe]

Seconded. The relative motion of the air to the wings creates the pressure gradient, which creates the lift. A stationary plane can't take off.

The plane would still be moving relative to the air. See my long post for the full explanation.

 

[rockitman]

Take a bike and put it upside down. Imagine you have an electric paintroller that spins on its own(these probably dont exist) and you turn it on and press it against the back tire. Will it move forward? No. The tire will always spin at the same speed as the paint roller, and no matter what speed, it wont go anywhere. That would be the equvalent of a car trying to drive on our fantasy conveyor belt.

Now, you take a non-electric, regular paintroller and you spin the pedal to make the back wheel turn at 10 mph. While maintaining the 10 mph pedaling, you press the paintroller against the back pedal and you push it forward at 1 mph. Will it move forward? Yes. You can make the bike tire spin as fast as you want to, and you will still be able to move the paintroller forward. This is the equivalent of the plane example. Your arm is providing the thrust just as the jet is providing thrust with air. In the plane example, the conveyor belt could be moving at any speed, and the plane would still be able to take off.

I think its easier to think about this situation in reverse to help visualize it. A plane that is in flight is coming in for a touch and go at 150 mph. The conveyer belt runway is also moving at 150mph. As soon as the plane's wheels make contact with the runway, does the plane instantly stop. No, the plane will still move forward at 150 mph, the belt will move backwards at 150mph, and the wheels will spin at 300mph. If I dangled you from a helicopter just above the moving runway 500 feet from where the plane touched down, you would get hit by the plane.

 

[QuikClot]

The plane would still be moving relative to the air. See my long post for the full explanation.

Depends how you read the question. I get the sense that the countermovement is limited -- the poster stressed that the wheels were free-rolling and asked "can it even move?" -- which implies that the force on the plane from the wheels is not necessarily equal and opposite. If it were an MCAT question, I would take that as a hint the plane can move -- and hence can take off.

 

[JustBreathe]

Take a bike and put it upside down. Imagine you have an electric paintroller that spins on its own(these probably dont exist) and you turn it on and press it against the back tire. Will it move forward? No. The tire will always spin at the same speed as the paint roller, and no matter what speed, it wont go anywhere. That would be the equvalent of a car trying to drive on our fantasy conveyor belt.

Now, you take a non-electric, regular paintroller and you spin the pedal to make the back wheel turn at 10 mph. While maintaining the 10 mph pedaling, you press the paintroller against the back pedal and you push it forward at 1 mph. Will it move forward? Yes. You can make the bike tire spin as fast as you want to, and you will still be able to move the paintroller forward. This is the equivalent of the plane example. Your arm is providing the thrust just as the jet is providing thrust with air. In the plane example, the conveyor belt could be moving at any speed, and the plane would still be able to take off.

I think its easier to think about this situation in reverse to help visualize it. A plane that is in flight is coming in for a touch and go at 150 mph. The conveyer belt runway is also moving at 150mph. As soon as the plane's wheels make contact with the runway, does the plane instantly stop. No, the plane will still move forward at 150 mph, the belt will move backwards at 150mph, and the wheels will spin at 300mph. If I dangled you from a helicopter just above the moving runway 500 feet from where the plane touched down, you would get hit by the plane.

Nice example.

 

[dajimmers]

Nice example.

Except I was confused as to what a "paintroller" was. Trolling for pain? Oh well, I got it now. Or perhaps someone who hunts trolls is a paintroller?

Anyways, I think we've covered about all we can. If you still don't get it, try replacing the wheels with skis, and the conveyer surface with ice or snow or something. Now, the skis can slide on the conveyer just fine (free rolling wheels). If the engines provide thrust, the plane will move forward, sliding along the conveyer that is moving ever faster trying to prevent the forward thrust. Now, as snow/ice have some friction, if the conveyer were to move fast enough instantaneously to produce the same frictional force as the engine thrust force, the plane would indeed be held "still" be this tremendous frictional force. It would then burn up and explode too, as that would be a lot of friction for some poor skis to endure.

I reiterate, call Mythbusters.

 

[bruinfan32]

Moose I've always wondered what kinda planes you fly

 

[isobel]

wow. this did not require 4 pages of discussion. you don't even need the 3 points at the end of the question b/c is it sooooo obvious the plane isn't going to take off.

 

[OwnageMobile]

Ok, look-

If the plane's jet force is matched by the belt's force on the wheels:

Case #1: Wheels are frictionless (belt can do no work) Answer = yes, the plane can take off.
Case #2: Wheels are not frictionless Answer = no, the plane doesn't move.

If the plane's speed is matched by the belt, but in the opposite direction:

Case #3: The plane can move, and thus it can fly.

It would make more sense to have the question set to where the speed of the plane is matched in an opposite fasion. It would be like having a tailwind constant at half your ground speed.

This question is hard due to its ambiguity, not its physics setup.

I too am dissapointed that this has passed the 4 page limit. I am quite confident that what I posted ^^^ is correct. The difficulty is agreeing on how the problem is set up.

I guess it's probably people who don't bother reading our trial and tribulations and just post their theories on whether the plane flies or not. READ THE PRIOR POSTS PEEPS. Unfortunately those who skip the reading probably aren't reading this... and those who do read it, read the whole thread.

 

[spaceman_spiff]

(sorry to beat a dead horse, but if you're still interested read on)

how can the plane move (with respect to the ground) if the belt is continously variable with the speed of the plane? the speed vectors cancel. the accel vectors cancel. NO movement.

think of a hamster wheel - the faster the hamster runs, the faster the wheel moves but he's still not going anywhere.

can we agree that the plane is not moving with respect to the ground?

if so then am i correct in this conclusion: once the plane reaches 160-180 mph (wrt the conveyor belt of course) (and assuming it's like a 737) it will be pulling the same amt of air as it would if it were moving on a stationary runway just before takeoff, and would then actually lift off - then it would accelerate (in the air) from an airspeed of 160mph and a groundspeed of zero. is this possible?

 

[Telemachus]

(sorry to beat a dead horse, but if you're still interested read on)

how can the plane move (with respect to the ground) if the belt is continously variable with the speed of the plane? the speed vectors cancel. the accel vectors cancel. NO movement.

think of a hamster wheel - the faster the hamster runs, the faster the wheel moves but he's still not going anywhere.

can we agree that the plane is not moving with respect to the ground?

if so then am i correct in this conclusion: once the plane reaches 160-180 mph (wrt the conveyor belt of course) (and assuming it's like a 737) it will be pulling the same amt of air as it would if it were moving on a stationary runway just before takeoff, and would then actually lift off - then it would accelerate (in the air) from an airspeed of 160mph and a groundspeed of zero. is this possible?

Are you correct? NO.

You are confusing the movement relative to the surface of the runway with movement relative to a distant observer not on the moving runway. The fact that the runway is moving does not mean the air is moving.

The whole premise of the question is what seems to be confusing most people. The idea of matching the speed of the plane in reverse with a moving runway is nonsensical because it matters not what the body of the plan is doing relative to the ground, only relative to the air (and, by the way, the ground that isn't part of this magical nonsensical runway).

Imagine if you will a person wearing rollerskates on a very long treadmill who is pulling themselves hand-over-hand forward with a rope connected to an object off the front of the treadmill. You can do anything with the speed of the treadmill belt -- the negative of the hand-over-hand speed is one value, but eleventy billion is another possible value -- and the person's forward speed relative to a fixed observer not on the treadmill surface is still only determined by their hand-over-hand speed.

 

[MrDreamWeaver]

There has to be static friction for the plane's wheels to move the conveyor belt (wheels have static friction). The plane does not have kinetic friction because it isn't sliding.

Thus, I think it's safe to assume that the conveyor will move exactly the same speed as the wheels of the plane (as originally proposed, so this IS CORRECT). The conveyor and wheels accelerate; however, the plane stays at constant velocity: 0. Thus, the plane never accelerates which ultimately means it won't lift off.

Why? Because the static frictional force exerts a backward force on the plane that is equal in magnitude but opposite in direction of the thruster force. We all now that if there is no net force on an object, it isn't going to acclerate. Further, without the plane actually accelerating from 0 velocity, the plane will stay at rest. Without a moving plane for wind leverage, how in the world is it going to take off? There is no net force in the Y direction!

Of course every answer is right if you TWIST the variables. Let's work with the original question.

 

[liverotcod]

I too am dissapointed that this has passed the 4 page limit. I am quite confident that what I posted ^^^ is correct. The difficulty is agreeing on how the problem is set up.

I guess it's probably people who don't bother reading our trial and tribulations and just post their theories on whether the plane flies or not. READ THE PRIOR POSTS PEEPS. Unfortunately those who skip the reading probably aren't reading this... and those who do read it, read the whole thread.

I am also amused by people who imply that the rest of us are stupid because we don't agree with their half-thought-through answers. Your summary is the most correct.

Do you have any thoughts about my question re: acceleration due to inequality of forces at any given time until the maximum thrust of the engines is met? I'm having trouble wrapping my anatomy-addled brain around that.

 

[spaceman_spiff]

er... never mind

 

[Telemachus]

telemachus: but aren't you assuming that the plane will move forward because of the engines' hand-over-hand 'grip' on the air? i thought it was from pushing against the ground (not the air) that allows planes to move fast enough and get enough air over the wings to create lift?

It's all about the air.

 

[medicalbound]

It's all about the air.

Perhaps the difficulty is that we forgot to account for the average airspeed velocity of an unladen swallow...

 

[BasesofHumanity]

It's going to take a long time to read all the replies, so, at the risk of someone else having already said this, I'll attempt to answer.

Given all the criteria on this problem, the plane will not fly (in my opinion). I think that, in addition to creating a negative and positive pressure difference on opposite sides of the wings, the plane needs momentum as well for take off (momentum is the product of mass by velocity p=mv). We cannot deny that the plane is massless, but because it is moving forward on a runway that is ultimately moving backward with the same speed (thanks to the gliding wheels), based on the "frame of reference" of someone inside the plane or even outside the plane and away from the runway, the plane is not moving at all. It's just burning fuel! So, no velocity means no momentum which means that the plane will not be able to lift off.

Second of all, the forward movement of the plane (which I just tried to prove does not occur) is what creates the positive and negative pressures on opposite sides of the wing; therefore, in this problem, the pressures are equal because the air molecules that surround the wings of the plane do not see a moving plane, but a stationary one.

The plane stays put and only burns fuel and I paid $3.30 a gallon for gas a few months back and I was not happy with that at all.

I could be completely wrong. Let me know how I did.

 

[JustBreathe]

It's going to take a long time to read all the replies, so, at the risk of someone else having already said this, I'll attempt to answer.

Given all the criteria on this problem, the plane will not fly (in my opinion). I think that, in addition to creating a negative and positive pressure difference on opposite sides of the wings, the plane needs momentum as well for take off (momentum is the product of mass by velocity p=mv). We cannot deny that the plane is massless, but because it is moving forward on a runway that is ultimately moving backward with the same speed (thanks to the gliding wheels), based on the "frame of reference" of someone inside the plane or even outside the plane and away from the runway, the plane is not moving at all. It's just burning fuel! So, no velocity means no momentum which means that the plane will not be able to lift off.

Second of all, the forward movement of the plane (which I just tried to prove does not occur) is what creates the positive and negative pressures on opposite sides of the wing; therefore, in this problem, the pressures are equal because the air molecules that surround the wings of the plane do not see a moving plane, but a stationary one.

The plane stays put and only burns fuel and I paid $3.30 a gallon for gas a few months back and I was not happy with that at all.

I could be completely wrong. Let me know how I did.

You should read the rest of the posts. There's much more to it.

 

[liverotcod]

Perhaps the difficulty is that we forgot to account for the average airspeed velocity of an unladen swallow...

What, African or European?

 

[MoosePilot]

(sorry to beat a dead horse, but if you're still interested read on)

how can the plane move (with respect to the ground) if the belt is continously variable with the speed of the plane? the speed vectors cancel. the accel vectors cancel. NO movement.

think of a hamster wheel - the faster the hamster runs, the faster the wheel moves but he's still not going anywhere.

can we agree that the plane is not moving with respect to the ground?

if so then am i correct in this conclusion: once the plane reaches 160-180 mph (wrt the conveyor belt of course) (and assuming it's like a 737) it will be pulling the same amt of air as it would if it were moving on a stationary runway just before takeoff, and would then actually lift off - then it would accelerate (in the air) from an airspeed of 160mph and a groundspeed of zero. is this possible?

The air mass and the speed of the stationary ground (the non-runway belt ground) are the same as far as reference points, as long as there is no wind. So if the airplane is not moving relative to the ground, it's not moving relative to the air mass and will not take off.

The question is whether the plane *will* move relative to the ground. I think you could experiment by going to a treadmill, taking a roller skate or toy car, turning the treadmill on, and pushing on the model. You could see that if the thrust is high enough, then the model definitely could move relative to a stationary object not on the treadmill. I thought the set up assumed a runway belt that could move at whatever speed required to nullify the movement of the airplane, but I'm not sure. It all depends on the set up. I do know that likely the wheels would disintegrate in real life, because they generally have a tire limiting speed. For instance, one plane I flew had a tire limiting speed of 182 Knots. So if the plane was moving that fast *relative to the runway belt*, the tires might disintegrate (of course the speed they tell me isn't the speed at which they'll actually blow, due to engineering tolerances).