Will the plane takeoff?

[H2 rocks me]

A plane is standing on a runway that can move (like a giant conveyor
belt). This conveyor has a control system that tracks the plane's
speed and tunes the speed of the conveyor to be exactly the same (but
in the opposite direction) instantly.

Will the plane be able to take off?

[dеiтайожни]

Yes.

[KenP]

No. The plane is "standing".

Or:

No. The plane isn't moving.

[PARAGON]

Depends on the plane.

The tires might blow due to the speed.:giggling: ;)

[PARAGON]

No. The plane is "standing".

Or:

No. The plane isn't moving.be able to

[BlueTJCO]

it would take off. just think physics, F=m*a. The forward force (from the thrust) in both case is always bigger than the backward force (due to the friction of the wheel and ground, and it's very small compare to the thrust force), therefore the net force is always forward. So the plane will accelerate forward in both cases and take off.

:yawn:
Next Please

[BlueTJCO]

Depends on the plane.

The tires might blow due to the speed.:giggling: ;)

Thats the correct answer. At 500mph the tires would blow for sure... Aircrafts average take off speed is 120 MPH I think.......

[Mrs.ssippi]

Blue? No, no the answer is yellow. Yes, yellow and that is my final answer. Wait, can I use my phone a friend?

[CO Hummer]

How do you figure the plane can take off when there is no wind moving over the wings to create lift? Can't happen.

[BlueTJCO]

How do you figure the plane can take off when there is no wind moving over the wings to create lift? Can't happen.

what do you want to bet?:popcorn:

J/K..........Damn, this question gave me a headache like 3 years ago when it originally popped up on the internet........;)

[DennisAJC]

How do you figure the plane can take off when there is no wind moving over the wings to create lift? Can't happen.

X2 Unless it's a Harrier.

[Adam in CO]

Atlanta, Georgia.

[Wisha Haddan H3]

Yes for self-propelled airplanes but No for gliders towed behind ground vehicles.

In self-propelled airplanes thrust is delivered from the props or jets directly to the air, not to the ground. Since no forward thrust is delivered through the wheels, the conveyor will remain stationary. In fact, the conveyor may even move forward slightly with the plane depending on the amount of friction from the axles and the tire's contact patch. As the plane moves forward through the air, relative airspeed increases, lift is generated on the wings and the plane takes off.

With gliders, thrust is provided by a tow vehicle. If the tow vehicle is a truck on the conveyor, it would deliver its thrust through the wheels to the conveyor. Forward movement would be negated by the conveyor's movement, resulting in zero forward motion. The truck could be going 100 mph (relative to the conveyor) but its airspeed and groundspeed (next to the conveyor) would still be 0. No air would pass over the glider's wings and no lift would be generated for takeoff.

[Mrs.ssippi]

Atlanta, Georgia.That is not the answer it is yellow!!!!!!!!!!!!!!!:D

[PARAGON]

Yes for self-propelled airplanes but No for gliders towed behind ground vehicles.

In self-propelled airplanes thrust is delivered from the props or jets directly to the air, not to the ground. Since no forward thrust is delivered through the wheels, the conveyor will remain stationary. In fact, the conveyor may even move forward slightly with the plane depending on the amount of friction from the axles and the tire's contact patch. As the plane moves forward through the air, relative airspeed increases, lift is generated on the wings and the plane takes off.

With gliders, thrust is provided by a tow vehicle. If the tow vehicle is a truck on the conveyor, it would deliver its thrust through the wheels to the conveyor. Forward movement would be negated by the conveyor's movement, resulting in zero forward motion. The truck could be going 100 mph (relative to the conveyor) but its airspeed and groundspeed (next to the conveyor) would still be 0. No air would pass over the glider's wings and no lift would be generated for takeoff.

Nope

keep trying

[CO Hummer]

That is not the answer it is yellow!!!!!!!!!!!!!!!:D


Yellow is always a good answer. :cool:

[Adam in CO]

Four?

[h2co-pilot]

How do you figure the plane can take off when there is no wind moving over the wings to create lift? Can't happen.

X2

[Wisha Haddan H3]

How do you figure the plane can take off when there is no wind moving over the wings to create lift? Can't happen.
True that a plane can't take off w/o airflow over the wings to generate lift.

So the underlying question is ... "can a plane generate forward motion (into the wind) on a runway that moves in the opposite direction?"

A car could not, because it generates forward motion by transferring energy to the ground, which would be negated by the conveyor's opposite motion. But a self-propelled plane could still move forward, because it accelerates by pushing the air, irrespective of ground speed or conveyor direction.

[CO Hummer]

But a self-propelled plane could still move forward, because it moves forward by pushing the air, irrespective of ground speed or conveyor direction.

Doesn't the conveyor prevent the plane from moving at all? If so, no movement of air over the wings, no lift.

[h2co-pilot]

You don't get any extra wind flow while on the treadmill.

[CO Hummer]

You don't get any extra wind flow while on the treadmill.

Except if Ken is in the vicinity.

[Wisha Haddan H3]

Doesn't the conveyor prevent the plane from moving at all? If so, no movement of air over the wings, no lift. Unless the plane is physically attached to the conveyor, the conveyor has nothing to do with the plane's speed. The props push the air and the plane moves forward through the air, rolling right over the conveyor. Forward motion -> relative air motion over wings -> lift

[PARAGON]

True that a plane can't take off w/o airflow over the wings to generate lift.

So the underlying question is ... "can a plane generate forward motion (into the wind) on a runway that moves in the opposite direction?"

A car could not, because it generates forward motion by transferring energy to the ground, which would be negated by the conveyor's opposite motion. But a self-propelled plane could still move forward, because it accelerates by pushing the air, irrespective of ground speed or conveyor direction.That really has nothing to do with it.

Wheels have to turn in either situation. In the case of the plane, it has to move relative to air to lift off, a car doesn't. That is the only difference. How they apply their power has no bearing on this riddle.

Even if a plane is "pushing the air" it has to push against that air (thrust) to make the plane move, gaining speed. As it gains that speed the conveyor is matching the speed in the opposite direction, same as a car would.

[PARAGON]

Unless the plane is physically attached to the conveyor, the conveyor has nothing to do with the plane's speed. The props push the air and the plane moves forward through the air, rolling right over the conveyor. Forward motion -> relative air motion over wings -> lift

Can't move forward relative to the air around it if the wheels turn at a speed that nets zero relative to that air due to the conveyor.

[Mrs.ssippi]

Okay I want to change my answer from yellow to 2:30 am.:giggling:

[h2co-pilot]

It says that the conveyor will change speed according to the plane's. So it will not move via air or land.

[PARAGON]

There are 2 answers to this question.

[BlueHUMMERH2]

http://www.straightdope.com/columns/060203.html

[PARAGON]

http://www.straightdope.com/columns/060203.htmlHey thongboy, got something better than a link to some ignorant liberal columnist?

[BlueHUMMERH2]

Ok, fine, here's a link to another site.

http://www.newton.dep.anl.gov/askasci/phy05/phy05023.htm

[BlueHUMMERH2]

And another:

http://www.airliners.net/discussions/tech_ops/read.main/136068/

[h2co-pilot]

WhoTF is Fransico?:D:D

[PARAGON]

Ok, fine, here's a link to another site.

http://www.newton.dep.anl.gov/askasci/phy05/phy05023.htm Have you used a brain before? Tried comprehension before?

That's not the same question as the one asked here.

[BlueHUMMERH2]

Have you used a brain before? Tried comprehension before?

That's not the same question as the one asked here.

Doesn't matter. It's not really about the mass of the aircraft that's important.

[PARAGON]

Doesn't matter. It's not really about the mass of the aircraft that's important.WTF are you talking about. Who said anything about Mass.

You really don't get it. You are not comparing apples and apples.

Two completely different questions.

[PARAGON]

WhoTF is Fransico?:D:DSan?

[BlueHUMMERH2]

WTF are you talking about. Who said anything about Mass.

You really don't get it. You are not comparing apples and apples.

Two completely different questions.

This

Hi there is a question going around on a remote control plane forum that goes like this:
"Imagine a plane is sat on the beginning of a massive conveyor
belt/travelator type arrangement, as wide and as long as a runway,
and intends to take off. The conveyer belt is designed to exactly
match the speed of the wheels at any given time, moving in the
opposite direction of rotation.
There is no wind.
Can the plane take off?"

is only different from this

A plane is standing on a runway that can move (like a giant conveyor belt). This conveyor has a control system that tracks the plane's speed and tunes the speed of the conveyor to be exactly the same (but in the opposite direction) instantly.

in the fact that it's about a model aircraft. The wheels have nothing to do with this problem.

It's about physics of thrust, mass, and lift and how they pertain to the aircraft.

[PARAGON]

This

Hi there is a question going around on a remote control plane forum that goes like this:
"Imagine a plane is sat on the beginning of a massive conveyor
belt/travelator type arrangement, as wide and as long as a runway,
and intends to take off. The conveyer belt is designed to exactly
match the speed of the wheels at any given time, moving in the
opposite direction of rotation.
There is no wind.
Can the plane take off?"

is only different from this

A plane is standing on a runway that can move (like a giant conveyor belt). This conveyor has a control system that tracks the plane's speed and tunes the speed of the conveyor to be exactly the same (but in the opposite direction) instantly.

in the fact that it's about a model aircraft. The wheels have nothing to do with this problem.

It's about physics of thrust, mass, and lift and how they pertain to the aircraft.

I am beginning to think you really ARE this fvcking stupid and it's not all an act. Geezus...... QUESTIONS goofnuts QUESTIONS The question asked here is not the same question asked in the links you provided. Then you spew out this Mass crap like it has anything to do with the discussion here.

QUESTIONS

I stated "That's not the same question as the one asked here." To which you reply "Doesn't matter. It's not really about the mass of the aircraft that's important."

THE QUESTIONS ARE FVCKING DIFFERENT

[Wisha Haddan H3]

I am beginning to think you really ARE this fvcking stupid and it's not all an act. Geezus...... QUESTIONS goofnuts QUESTIONS The question asked here is not the same question asked in the links you provided. Then you spew out this Mass crap like it has anything to do with the discussion here.

QUESTIONS

I stated "That's not the same question as the one asked here." To which you reply "Doesn't matter. It's not really about the mass of the aircraft that's important."

THE QUESTIONS ARE FVCKING DIFFERENT
Don't have a heart attack, paragon. The questions are worded slightly differently, but the scenarios are exactly the same. Only the scale is different, which isn't relevant as long as we're talking about models that can actually fly. The physics of flight are the same regardless of size/scale/mass.

Go eat some dinner. I think maybe your blood sugar is off.

[PARAGON]

Don't have a heart attack, paragon. The questions are worded slightly differently, but the scenarios are exactly the same. Only the scale is different, which isn't relevant as long as we're talking about models that can actually fly. The physics of flight are the same regardless of size/scale/mass.

Go eat some dinner. I think maybe your blood sugar is off.:lame:

No, not stupid for you too.

Speed is relative. Figure that the fvck out and you will see why the questions are totally different.

[Wisha Haddan H3]

There are 2 answers to this question.

Let's hear it :)

[PARAGON]

Let's hear it :)

Simple

Yes

and

No

[PARAGON]

Don't have a heart attack, paragon. The questions are worded slightly differently, but the scenarios are exactly the same. Only the scale is different, which isn't relevant as long as we're talking about models that can actually fly. The physics of flight are the same regardless of size/scale/mass.

Go eat some dinner. I think maybe your blood sugar is off.

So our two resident lieberal einsteins don't quite understand comprehension. I'll 'splain it.

The questions posed in the links provided by the pretzel pusher say "the speed of the wheels"

The question posed here says "the plane's speed" Now, I might only have an IQ of 180+ but those are not the same.

[H2Finally]

Is this similar to tying the tail off a (model) airplane and gunning the engine and see if the plane will lift vertically off without any forward horizontal movement?

If under normal conditions a plane's engine must work with or against prevailing wind to create enough trust for lift, then presumably you can get one with big enough jets or propellers that will be able to create enough backwash of airstream to lift the plane without the plane actually moving forward.

So if the engine is big enough and/or in the right place relative to creating the airstream against the wings, maybe?

Now, wheather or not the plane can control yaw and pitch the moment it's airborne, without "normal" airstream, I'm not certain..

[Wisha Haddan H3]

That really has nothing to do with it.

Wheels have to turn in either situation. In the case of the plane, it has to move relative to air to lift off, a car doesn't. That is the only difference. How they apply their power has no bearing on this riddle.

Even if a plane is "pushing the air" it has to push against that air (thrust) to make the plane move, gaining speed. As it gains that speed the conveyor is matching the speed in the opposite direction, same as a car would.
Somehow missed this post. On the contrary, how airplanes apply their power is central to this riddle.

For example, when we walk or run, our propulsion is based on applying force to the ground. We push backwards and resistance sends us forward relative to the ground and air. On a treadmill, our feet push the conveyor belt and all our walking force is spent keeping up with it. We feel no wind in our face because our speed (relative to the ground and air) is zero. A car, bicycle or any vehicle that uses ground propulsion would experience the same effects on a conveyor belt.

However, an airplane's engines don't push the ground. They apply force directly to the air. When the air pushes back, the plane is thrust forward through the atmosphere at ground level. The wing's movement through the surrounding static air creates lift and the plane takes off.

On a conveyor belt runway, the exact same process occurs ... the engines push air backwards and the plane is thrust forward through the atmosphere. The conveyor belt can spin all it wants to, but it will only make the wheels spin faster. It can't hold the plane back because it isn't attached to the plane. Since the plane thrusts directly on the air, it doesn't rely on the conveyor belt for propulsion the way a person or car would. Instead, it slices through the air and takes off when enough lift is achieved.

[SnakeH2]

A plane is standing on a runway that can move (like a giant conveyor
belt). This conveyor has a control system that tracks the plane's
speed and tunes the speed of the conveyor to be exactly the same (but
in the opposite direction) instantly.

Will the plane be able to take off?

Yes

[Wisha Haddan H3]

Simple

Yes

and

No

Thanks for clearing that up :p

[h2co-pilot]

Okay, just stop.

EVERYONE JUST STOP!:crying:

[PARAGON]

Somehow missed this post. On the contrary, how airplanes apply their power is central to this riddle.

For example, when we walk or run, our propulsion is based on applying force to the ground. We push backwards and resistance sends us forward relative to the ground and air. On a treadmill, our feet push the conveyor belt and all our walking force is spent keeping up with it. We feel no wind in our face because our speed (relative to the ground and air) is zero. A car, bicycle or any vehicle that uses ground propulsion would experience the same effects on a conveyor belt.

However, an airplane's engines don't push the ground. They apply force directly to the air. When the air pushes back, the plane is thrust forward through the atmosphere at ground level. The wing's movement through the surrounding static air creates lift and the plane takes off.

On a conveyor belt runway, the exact same process occurs ... the engines push air backwards and the plane is thrust forward through the atmosphere. The conveyor belt can spin all it wants to, but it will only make the wheels spin faster. It can't hold the plane back because it isn't attached to the plane. Since the plane thrusts directly on the air, it doesn't rely on the conveyor belt for propulsion the way a person or car would. Instead, it slices through the air and takes off when enough lift is achieved.

Not entirely true.

The plane has to gain distance over time. If the conveyor moves the plane rearward for every instance in time the plane's thrust attempts to move it forward, the net movement relative to the air would amount to zero.:D

[PARAGON]

Thanks for clearing that up :pI can argue this either way due to the manner in which the question was asked. Hence the reason for the yes, no answers.

The question actually needs more clarification or one has to make some assumptions to answer it without saying a definitive yes due to VTOL aircraft.

With that, I will be going and reading the big book of questions with my daughter.

[H2Finally]

A simple yes is wrong. Otherwise, airports will do away with long runways, and helicopters will be obsolete.

We need H2 GTS to chime in here...

[deserth3]

Speed of a planes wheels during take off is irelevent (other than the tire will blow if it rotates too fast) to the plane.
Relative wind speed across the wing is what's important for the wing to provide lift.
Thus a plane with a take off speed of 60 knots is capable of taking off in a 60 knot headwind and not move with relation to the earth. This is why small planes are tied down when parked.

[PARAGON]

I predict Ken will ask something about a fly

[Wisha Haddan H3]

That's not true. Newton's law of motion states that the rocket or plane wants to stay still. As power is applied, as soon as it wants to start to roll, the conveyor moves, sending the motion back to a zero point.

That's where the conundrum lies with this version of the question. The plane can really never get up to any speed because it can't get past zero simply due to the limitations of the question IF you make certain assumptions OR it will take off IF you make other assumptions.

If the speed of the plane will always be instantaneously matched, the forward movement of the plane will never increase relative to it's surroundings.

If the plane starts to move at x MPH and instaneously the belt moves it -X MPH, the body of the plane remains still and actually does not move from a math standpoint.

But, assuming it's not a fictional question and the plane can move past this fictional "barrier of movement" then, as the plane increases it's speed, the plane is moving through the air and the belt is moving beneath and theoretically moving the wheels twice as fast.

That's why there were apparently different versions of the question. The one here was too vague and allowed for the No answer to be argued. The ones Bluehummer posted, that said speed relative to the wheels, changes the whole argument and allows the "body" of the plane to move without respect to the wheels.

Thank you for the coherent explanation. The only flaw in your evaluation lies in your application of the 3rd law of motion. "For every action there is an equal and opposite reaction".

A car on the conveyor would behave exactly as you describe, since its forward motion is dependent on the force its wheels apply to the conveyor surface. The wheels turn, exerting rearward force on the conveyor belt. The conveyor rolls, absorbing the force and negating forward motion relative to the ground next to the conveyor and the air around it. In other words, although the car moves forward relative to the conveyor, it remains stationary relative to the ground and air.

However, an airplane doesn't have drive wheels. Its forward motion depends the force of the props applied directly to the air. The props turn, exerting force on the air. As air is pushed rearward, the props are pushed in the opposite direction and the plane moves forward through the air, rolling over the conveyor's surface. Meanwhile the conveyor tries to spin, as if to counteract the forward motion of the plane, but the plane's wheels roll freely over it at higher and higher speeds. As the props push air rearward, the wings slice through the static air around the plane until the airflow over the wings produces enough lift for takeoff.

Nothing can stop the plane from taking off unless the tires blow out. Then, the extra friction between the landing gear and the conveyor could crash the plane or slow it down enough to prevent takeoff velocity.

[PARAGON]

Thank you for the coherent explanation. The only flaw in your evaluation lies in your application of the 3rd law of motion. "For every action there is an equal and opposite reaction".

A car on the conveyor would behave exactly as you describe, since its forward motion is dependent on the force its wheels apply to the conveyor surface. The wheels turn, exerting rearward force on the conveyor belt. The conveyor rolls, absorbing the force and negating forward motion relative to the ground next to the conveyor and the air around it. In other words, although the car moves forward relative to the conveyor, it remains stationary relative to the ground and air.

However, an airplane doesn't have drive wheels. Its forward motion depends the force of the props applied directly to the air. The props turn, exerting force on the air. As air is pushed rearward, the props are pushed in the opposite direction and the plane moves forward through the air, rolling over the conveyor's surface. Meanwhile the conveyor tries to spin, as if to counteract the forward motion of the plane, but the plane's wheels roll freely over it at higher and higher speeds. As the props push air rearward, the wings slice through the static air around the plane until the airflow over the wings produces enough lift for takeoff.

Nothing can stop the plane from taking off unless the tires blow out. Then, the extra friction between the landing gear and the conveyor could crash the plane or slow it down enough to prevent takeoff velocity.

You simply don't get it. It has nothing to do with it.

The question itself is self-limiting. Regardless of tires, planes, trains or automobiles. The moment it states that the conveyor will match speed with the airplane, period, it is stating that the plane will never move relative to the air. It will never gain speed.

Has nothing to do with physics. It's logic being applied to the question. THAT'S THE REASON FOR THE YES/NO ANSWER.

The question is in itself flawed.

The crap you are reading on some physics site is accurate if you pose the question where the speed is relative to the planes wheels or relative to anything. But since it is left wide open, an assumption would have to be made to suggest that the plane ever moves.

The reason is because due to the limits of the question, it's suggesting that the plane never breaks from zero speed.

It doesn't matter what type of propulsion is used. Whether its magnetic, some big hand, jet, prop, plasmic or whatever. The plane can never move simply because the equation offered by the question says it can't.

[KenP]

This is from a pilot relative in his early 50's that has been flying since he was 15. He's flown and had license to fly pretty much every type of aircraft. He was even a 'copter pilot in one of the Rambo movies. He currently flies for Southwest.Ahhh, the old moving conveyor belt trick!!! The airplane will NOT takeoff. It has no airspeed with which to generate lift. Look at it this way. If the thrust of the engines were to generate 100 mph of forward movement but the conveyor belt cancelled the movement by moving the same speed in the opposite direction, you could stand to the side of the belt and hold onto the wing of the airplane cause it isn't moving relative to the ground. Now, since it isn't moving relative to the ground, and no mention was made of a wind blowing, the airspeed would be zero. No airspeed, no lift, no fly!. On the other hand, you could attach a cable to the nosegear so the airplane can't move across the ground and then blow a 100 mph wind over the wing from a giant fan, and the airplane would sense an airspeed of 100 mph and it would indeed fly, just like the Wright brothers did in the strong winds at Kitty Hawk with their tethered airplanes.

[Wisha Haddan H3]

You simply don't get it. It has nothing to do with it.

The question itself is self-limiting. Regardless of tires, planes, trains or automobiles. The moment it states that the conveyor will match speed with the airplane, period, it is stating that the plane will never move relative to the air. It will never gain speed.

Has nothing to do with physics. It's logic being applied to the question. THAT'S THE REASON FOR THE YES/NO ANSWER.

The question is in itself flawed.

The crap you are reading on some physics site is accurate if you pose the question where the speed is relative to the planes wheels or relative to anything. But since it is left wide open, an assumption would have to be made to suggest that the plane ever moves.

The reason is because due to the limits of the question, it's suggesting that the plane never breaks from zero speed.

It doesn't matter what type of propulsion is used. Whether its magnetic, some big hand, jet, prop, plasmic or whatever. The plane can never move simply because the equation offered by the question says it can't.
A plane is standing on a runway that can move (like a giant conveyor
belt). This conveyor has a control system that tracks the plane's
speed and tunes the speed of the conveyor to be exactly the same (but in the opposite direction) instantly.

Will the plane be able to take off?

The question is not flawed. It also never states the plane never breaks from zero speed. It is clear, direct and perfectly logical. Here's why. The conveyor can match the plane's forward velocity in the opposite direction because it is not connected to the airplane in any way, neither by physical attachments nor by forces. Since the airplane rolls on wheels, it can move forward at 100 knots while the conveyor moves backward at 100 knots. The relative speed between the two is 200 knots, and there is no contradiction in either logic or physics. Or the conveyor can move forward with the plane so the relative speed between them is 0 knots. Either way, the plane is moving at 100 knots relative to the air it is pushing through.

There is a logical flaw but it lies in your assumption that the relative speed between the plane and the conveyor determines the relative speed between the plane and the static air around it.

A ground-based conveyor cannot hold back a freewheeling vehicle that uses air for its locomotion. If the scenario involved an airplane in a wind tunnel, a submarine in a water current, a car on a conveyor or any vehicle where the medium of propulsion could be reversed, you would be absolutely correct. But that's not the case here.

The conveyor is a ground-based reversal, but the air around the airplane hasn't been touched. It remains static and the props can pull the airplane through it, causing airflow, lift and takeoff. This is the correct solution to the riddle.
______________

To me what makes this question interesting isn't just the physics. It's our human approach to the problem. Human experience is ground-based. We see birds and airplanes fly, but we cannot. Whether we walk, drive, skate or bicycle, we depend on forces pushing against the ground for locomotion. So our instinctive approach to this problem is also ground-based.

When we imagine ourselves on a conveyor, we realize that unless we walk on it, it will carry us along. We also realize that if the conveyor matches our walking speed, our position relative to the ground and air next to us will remain the same.

Our experience tells us that if we put an airplane on the conveyor, it will also be carried along, and if it tries to move forward it will also remain in the same place relative to the ground and air next to it. We also know that lift requires airflow, and if the plane's position is stationary relative to the air, there can be no lift and it cannot take off.

We assume all this from our ground-based experience ... but the reality is counter-intuitive.

First, there's the question of friction on the conveyor. When we stand on a treadmill, our feet stick to it through friction and we are pulled along unless we walk. However, the airplane is mounted on wheels that roll freely on it. It does not stick to the conveyor and is not pulled backwards as we would be. Thus, the conveyor cannot hold the airplane back.

Second, there's the question of propulsion. When we walk on a conveyor, our movement results from pushing against the moving conveyor with our feet. However, an airplane doesn't drive on the conveyor using its wheels ... the wheels roll freely over the conveyor, as the props push against the static air above it. Newton's 3rd law allows the plane to move forward, independently of the ground-based conveyor. The wing is drawn through the static air around it and the resulting airflow creates lift, allowing the plane to take off.

Thus, the speed and direction of the conveyor below the plane is irrelevant unless the tires blow.

[PARAGON]

A plane is standing on a runway that can move (like a giant conveyor
belt). This conveyor has a control system that tracks the plane's
speed and tunes the speed of the conveyor to be exactly the same (but in the opposite direction) instantly.

Will the plane be able to take off?

The question is not flawed. It also never states the plane never breaks from zero speed. It is clear, direct and perfectly logical. Here's why. The conveyor can match the plane's forward velocity in the opposite direction because it is not connected to the airplane in any way, neither by physical attachments nor by forces. Since the airplane rolls on wheels, it can move forward at 100 knots while the conveyor moves backward at 100 knots. The relative speed between the two is 200 knots, and there is no contradiction in either logic or physics. Or the conveyor can move forward with the plane so the relative speed between them is 0 knots. Either way, the plane is moving at 100 knots relative to the air it is pushing through.

There is a logical flaw but it lies in your assumption that the relative speed between the plane and the conveyor determines the relative speed between the plane and the static air around it.

A ground-based conveyor cannot hold back a freewheeling vehicle that uses air for its locomotion. If the scenario involved an airplane in a wind tunnel, a submarine in a water current, a car on a conveyor or any vehicle where the medium of propulsion could be reversed, you would be absolutely correct. But that's not the case here.

The conveyor is a ground-based reversal, but the air around the airplane hasn't been touched. It remains static and the props can pull the airplane through it, causing airflow, lift and takeoff. This is the correct solution to the riddle.
______________

To me what makes this question interesting isn't just the physics. It's our human approach to the problem. Human experience is ground-based. We see birds and airplanes fly, but we cannot. Whether we walk, drive, skate or bicycle, we depend on forces pushing against the ground for locomotion. So our instinctive approach to this problem is also ground-based.

When we imagine ourselves on a conveyor, we realize that unless we walk on it, it will carry us along. We also realize that if the conveyor matches our walking speed, our position relative to the ground and air next to us will remain the same.

Our experience tells us that if we put an airplane on the conveyor, it will also be carried along, and if it tries to move forward it will also remain in the same place relative to the ground and air next to it. We also know that lift requires airflow, and if the plane's position is stationary relative to the air, there can be no lift and it cannot take off.

We assume all this from our ground-based experience ... but the reality is counter-intuitive.

First, there's the question of friction on the conveyor. When we stand on a treadmill, our feet stick to it through friction and we are pulled along unless we walk. However, the airplane is mounted on wheels that roll freely on it. It does not stick to the conveyor and is not pulled backwards as we would be. Thus, the conveyor cannot hold the airplane back.

Second, there's the question of propulsion. When we walk on a conveyor, our movement results from pushing against the moving conveyor with our feet. However, an airplane doesn't drive on the conveyor using its wheels ... the wheels roll freely over the conveyor, as the props push against the static air above it. Newton's 3rd law allows the plane to move forward, independently of the ground-based conveyor. The wing is drawn through the static air around it and the resulting airflow creates lift, allowing the plane to take off.

Thus, the speed and direction of the conveyor below the plane is irrelevant unless the tires blow.The logic simply eludes you.

You are making an assumption to come to your conclusion. An assumption that is not offered by the question.

tracks the plane's speed

plane's speed relative to what? Relative to the conveyor? Airspeed, relative to the surrounding air?

If it's airspeed, the very point at which the plane breaks the hold and theoretically begins to move, the conveyor would be moving it backwards and the wheels would never rotate and the plane would remain stationary. The plane is not being held stationary by any physical force, it's being held by the question. You have to assume that the plane starts to move and rotate the tires for the plane to gain airspeed. Well the question limits this assumption because one can make an assumption that allows for a different answer, therefore the question is flawed in that it allows for a yes and an no answer.

If you can't see the simplicity of logic. I can't help further.

You have to go and make it "fit" into

[NEOCON1]

i want to see paragon hit the dash :jump:

[PARAGON]

i want to see paragon hit the dash :jump:I can accomodate very easily. It would be nothing to do it since you have all that hair to grab and smash your head into it with.

[paragoon]

It certainly won?t take off if I am driving it :giggling:

[Wisha Haddan H3]

i want to see paragon hit the dash :jump:
I think he just hit my windshield and the wipers are smearing him around

:jump: :jump: :jump:

[Wisha Haddan H3]

The logic simply eludes you.

You are making an assumption to come to your conclusion. An assumption that is not offered by the question.

tracks the plane's speed

plane's speed relative to what? Relative to the conveyor? Airspeed, relative to the surrounding air?

The plane's speed relative to anything but the air is irrelevant to lift. The conveyor system can track whatever it wants and move the conveyor at any speed forward or backward. It wouldn't matter because the plane freewheels over its surface and propels itself by pushing static air.

If it's airspeed, the very point at which the plane breaks the hold (There is no hold - nothing attaches the plane to the conveyor) and theoretically begins to move, the conveyor would be moving it backwards (How? nothing attaches the plane to the conveyor) and the wheels would never rotate and the plane would remain stationary. (The wheels would roll but their rotation is irrelevant - they don't move or drive the plane) The plane is not being held stationary by any physical force, it's being held by the question. (False, the question does not create a scenario of zero velocity.) You have to assume that the plane starts to move and rotate the tires for the plane to gain airspeed. (Not so. the wheels are irrelevant except as a friction reducer between the plane and runway ... the same outcome would hold if it were a seaplane on pontoons over an ocean current, or on skis over a moving ice floe. Besides, if the conveyor followed the plane, the wheels wouldn't move either, but the plane would nonetheless move forward through the air, creating lift.) Well the question limits this assumption because one can make an assumption that allows for a different answer, therefore the question is flawed in that it allows for a yes and an no answer. (The assumption you say I "have to assume" is based on a false premise - the premise that the motion of a conveyor belt under a freewheeling air-powered vehicle can affect its linear motion)

If you can't see the simplicity of logic. I can't help further. (Right back at you, brother :))

You have to go and make it "fit" into
One more analogy and I'm done ...

Imagine a moving sidewalk like those at the airport. If you walk in the direction of the movement, you travel at double your walking speed relative to the windows next to you. If you walk in the opposite direction, you remain stationary relative to the windows.

Why? Because the source of your motion is your feet pushing on the on the walkway thanks to friction.

Now, put on a pair of roller skates. I'll walk next to the moving sidewalk and pull you onto it with a rope. No matter what direction we take on the sidewalk, you will travel at the speed I'm walking. If we travel with the sidewalk, your wheels won't roll, because I'm walking as fast as the sidewalk. If we travel against it, the wheels will roll twice as fast as if I was pulling you over the carpet.

Why? Because the source of your motion is no longer your own feet "attached" to the conveyor through friction ... it comes from my feet exerting force on the stationary floor next to you while you freewheel on your skates.

Or if you like, I'll tie the rope to the wall and you can haul yourself up the rope towards me. The source of your motion is no longer me, it's you ... exerting force on the rope connected to the stationary wall. The moving sidewalk can speed up, slow down or stop, but it doesn't matter. Your motion relative to the windows next to you depends on your arms pulling the static medium of the rope tied to the wall while your skates freewheel below you.

Likewise, an airplane exerts its force directly on the static air around it ... not on the ground. The conveyor under the wheels can do what it wants (regardless of the sensors or relative speed) because the plane's engines are acting on the air while the tires freewheel below it. The plane's motion relative to the air around it depends on its engines pushing the wing through the static air, thus creating airflow and lift.

Consequently, the plane absolutely can take off within the parameters of this question as stated.

Have a nice day and thanks for the brainteaser. This was great!
:perfect10s:

[SnakeH2]

A simple yes is wrong. Otherwise, airports will do away with long runways, and helicopters will be obsolete.

We need H2 GTS to chime in here...

Wrong. You're basing you assumption on the plane NOT moving.

[SnakeH2]

A simple yes is wrong. Otherwise, airports will do away with long runways, and helicopters will be obsolete.

We need H2 GTS to chime in here...

:giggling: :giggling: Ahh yeah...that makes sense.:giggling:

[GLBLWARMR]

The answer all depends on whether or not I am on the plane. Because I will be pissed if I do not make my connecting flight.

[KenP]

No. The plane is "standing".

Or:

No. The plane isn't moving.You're stupid. It will take off.

All the conveyor will do is cause the wheels to spin wildly. Imagine a rocket on wheels on the same conveyor. That rocket is going to take off...with the wheels spinning off.

What the wheels and conveyor do is irrelavent as none of that provides any propulsion. The wheels lower friction and provide for braking.

Theoretically, the conveyor could be moving backwards at double the speed of the plane and it still wouldn't matter. That would only cause the wheels to spin even faster, but the plane will still be getting thrust, moving forward and generating lift.

[SnakeH2]

You're stupid. It will take off.

:clapping: :clapping:

Best arguement yet!!!

[PARAGON]

You're stupid. It will take off.

All the conveyor will do is cause the wheels to spin wildly. Imagine a rocket on wheels on the same conveyor. That rocket is going to take off...with the wheels spinning off.

What the wheels and conveyor do is irrelavent as none of that provides any propulsion. The wheels lower friction and provide for braking.

Theoretically, the conveyor could be moving backwards at double the speed of the plane and it still wouldn't matter. That would only cause the wheels to spin even faster, but the plane will still be getting thrust, moving forward and generating lift.

That's not true. Newton's law of motion states that the rocket or plane wants to stay still. As power is applied, as soon as it wants to start to roll, the conveyor moves, sending the motion back to a zero point.

That's where the conundrum lies with this version of the question. The plane can really never get up to any speed because it can't get past zero simply due to the limitations of the question IF you make certain assumptions OR it will take off IF you make other assumptions.

If the speed of the plane will always be instantaneously matched, the forward movement of the plane will never increase relative to it's surroundings.

If the plane starts to move at x MPH and instaneously the belt moves it -X MPH, the body of the plane remains still and actually does not move from a math standpoint.

But, assuming it's not a fictional question and the plane can move past this fictional "barrier of movement" then, as the plane increases it's speed, the plane is moving through the air and the belt is moving beneath and theoretically moving the wheels twice as fast.


That's why there were apparently different versions of the question. The one here was too vague and allowed for the No answer to be argued. The ones Bluehummer posted, that said speed relative to the wheels, changes the whole argument and allows the "body" of the plane to move without respect to the wheels.

[KenP]

I didn't look at his links (:shhh:) so I can't speak for that.

I do know that if I take a bottle rocket and attach it to a Matchbox on a beltsander spinning at full speed, light the rocket, it's going to go. Unless I accidentally sand my fingertips off.:o

I got my answer by cheating and reading a physics site. No, I didn't read all 15 pages!!!! Just the first and last few.:D

BTW, when I'm driving down the road and a fly is in the car, why doesn't the fly it the dash when I hit the brakes. And if the fly is flying around from front to back while I'm driving 55, what's the fly's speed in each direction?:giggling: :popcorn:

[shakazulu12]

Ok I'm getting dizzy reading all these posts, but for those that say it won't take off, you are right.

Planes need forward movement through the air in order to generate negative pressure above the wing surface, thus creating lift. If the wing isn't moving through the air, then it doesn't matter what you do, it won't take off.

I think someone else already explained this, but this is the dumbed down version.

[PARAGON]

I didn't look at his links (:shhh:) so I can't speak for that.

I do know that if I take a bottle rocket and attach it to a Matchbox on a beltsander spinning at full speed, light the rocket, it's going to go. Unless I accidentally sand my fingertips off.:o

I got my answer by cheating and reading a physics site. No, I didn't read all 15 pages!!!! Just the first and last few.:D

BTW, when I'm driving down the road and a fly is in the car, why doesn't the fly it the dash when I hit the brakes. And if the fly is flying around from front to back while I'm driving 55, what's the fly's speed in each direction?:giggling: :popcorn:

speed relative to what?:giggling:

he's basically hovering in the car since the air in the car is "not moving"

the mass of the air and his mass is so small that he can accomodate the change in speed of the car because the "air" he's hovering in doesn't all go rushing to front.

Say, like if the car's interior was 1/4 full of water. All the water would rush to the front and a fish that was hovering in the water would go with it.

[KenP]

Would he smack the dash? I want to see something hit the dash.:jump:

[Dug]

I never opened this thread till today. Nice arguement by the way. I read 3/4 of the post and got tired. I really want to know the answer . My redneck guess would be No Fvcking Way! How the hell does a normal airplane take of with no wind for lift. If anyone can prove otherwise lets see it. Doug:popcorn:

[Wisha Haddan H3]

I never opened this thread till today. Nice arguement by the way. I read 3/4 of the post and got tired. I really want to know the answer . My redneck guess would be No Fvcking Way! How the hell does a normal airplane take of with no wind for lift. If anyone can prove otherwise lets see it. Doug:popcorn:
Answer 2 questions and you'll have the answer to this riddle ...

1. How does an airplane take off on a normal runway?

An airplane uses jets or props to push against the air with enough force to accelerate. As the wings slice through the still air, relative airflow creates lift and the plane takes off.

2. Could a conveyor turning backwards under the wheels hold it back?

No ... since the airplane's landing gear rolls freely, the conveyor has nothing to push against and cannot cancel out the plane's forward motion. It would spin the wheels faster than usual but the plane would take off normally.

[Agriv8r]

WHO GIVES A SH!T:D

BUT THE ANSWWER IS NO, WHEELS ARE FOR LANDING, THRUST IS FOR MOVEMENT TO FORCE AIR OVER THE WINGS FOR LIFT. A BETTER WAY TO PICTURE IT IS TO HAVE THE SAME AIRPLANE ON AN AIRCRAFT CARRIER DOING 60KNOTS INTO A 60 KNOT HEADWIND.

SO NOW THE REAL QUESTION IS, WHO GIVES A SH!T:D

[DURAMAX TIM]

You're stupid. It will take off.

All the conveyor will do is cause the wheels to spin wildly. Imagine a rocket on wheels on the same conveyor. That rocket is going to take off...with the wheels spinning off.

What the wheels and conveyor do is irrelavent as none of that provides any propulsion. The wheels lower friction and provide for braking.

Theoretically, the conveyor could be moving backwards at double the speed of the plane and it still wouldn't matter. That would only cause the wheels to spin even faster, but the plane will still be getting thrust, moving forward and generating lift.

same as a float plane or plane w/ skis, wheels don't have to roll to take off.

[ROX]

A plane is standing on a runway that can move (like a giant conveyor
belt). This conveyor has a control system that tracks the plane's
speed and tunes the speed of the conveyor to be exactly the same (but
in the opposite direction) instantly.

Will the plane be able to take off?Yes, but only if you add enough Tequilla.:beerchug:

[CO Hummer]

Answer 2 questions and you'll have the answer to this riddle ...

1. How does an airplane take off on a normal runway?

An airplane uses jets or props to push against the air with enough force to accelerate. As the wings slice through the still air, relative airflow creates lift and the plane takes off.

2. Could a conveyor turning backwards under the wheels hold it back?

No ... since the airplane's landing gear rolls freely, the conveyor has nothing to push against and cannot cancel out the plane's forward motion. It would spin the wheels faster than usual but the plane would take off normally.

I see your point now. I agree!

[usetosellhummer]

so where did the plane go, and what was served for dinner?

[KenP]

so where did the plane go, and what was served for dinner?After not going anywhere, the passengers and crew walked to McDonalds.

[ROX]

After not going anywhere, .They did too! They flew off to Las Vegas, where they landed safely on another converyor belt, and walked into the Bellagio.

The landing conveyor belt is tilted at a 15degree angle and is spinning at the same speed as the earth at the equator.

[usetosellhummer]

I like your answer, did they go to the Garden and check out the fall colors or throw bones at the table? the view from the suite we stayed in, wow
wish I had money to go every year!

[Mr. I - Man]

yes it will take off. At some point

Planes take off from near frictionless sources all the time ie. snow, ice and water. The wheels are not producing thrust or power applied to ground.

To test this let us put your hummer on a 4 wheel dyno peg the needle right nothing happens because energy from the wheels is transfered to the rollers (conveyor belt). Now lets strap some JADO bottles to the back of your hummer. Its going go through the wall. Thrust is only relevant to which it is applied to ie. if you strapped the JADO bottle to your wheels they would spin very fast however the thrust energy would transfer to the rollers and your truck would go nowhere.

[DRTYFN]

yes it will take off. At some point

Planes take off from near frictionless sources all the time ie. snow, ice and water. The wheels are not producing thrust or power applied to ground.



And the plane is going to acquire lift from where? Wheel speed doesn't produce lift for wings.

[Mr. I - Man]

Oh yeah I almost for got. You can test this is the air. I was flying a cessna 152 practicing stalls, slow flight and spin recoveries. And found when in slow flight if the winds aloft are faster than your V-speed and you face into them you can look at your ground track and you are actually flying backwards and at the same speed as the winds aloft your plane stays stationary, BUT YOU ARE STILL FLYING!!!!