I would think some of you have seen this question before but there was a large discussion about it on another board, let's see what you guys think about 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 (http://forums.nasioc.com/forums/showthread.php?t=891480#) at any given time, moving in the opposite direction of rotation.
There is no wind.
Can the plane take off?

Nope

Not a chance

No

So essentially, the plane is standing still while the wheels are spinning? Why would the plane possibly take off??? I don't understand how a "big discussion" would generate from the scenario... Is the plane a Harrier? Then it could...

PLUS if the plane was sitting, the wheels aren't spinning, and the conveyor is supposed to match the speed of the wheels? Nothing's happening at all... LOL

The plane will take off just fine. The wheels will be traveling at twice their normal speed, but that would make very little difference.

The plane will take off just fine. The wheels will be traveling at twice their normal speed, but that would make very little difference.

Good point... if the plane is thrusting using it's engines... :o :D

If the props are generating enough airflow over the wings, sure, it'll take off. It works for kites all the time. :)

The plane will take off just fine. The wheels will be traveling at twice their normal speed, but that would make very little difference.

I agree, planes don't use their wheels for propulsion, they use the turbines, which by Newtons laws produce movement of the plane regardless of what the wheels were doing.

I CAN see why this would spark some discussion, but the fundemental mistake most people make is equating the acceleration of a car to that of an aircraft...

The conveyer belt is designed to exactly match the speed of the wheels (http://forums.nasioc.com/forums/showthread.php?t=891480#) at any given time, moving in the opposite direction of rotation.
There is no wind.
Can the plane take off?

Just like walking on a moving sidewalk (airport concourse).

Plane moves forward twice as fast reaching the proper airspeed sooner and lifts off just fine.

I would think some of you have seen this question before but there was a large discussion about it on another board, let's see what you guys think about 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 (http://forums.nasioc.com/forums/showthread.php?t=891480#) at any given time, moving in the opposite direction of rotation.
There is no wind.
Can the plane take off?
The question is "can the plane take off?". If you put a regular plane on the tarmac and removed the wings, you could taxi down the runway at the speed of sound, but, there would be NO lift and NO takeoff. Those wheels could spin as fast as possible but, unless there is airflow travelling beneath the wings there will be NO lift, hence, no take-off.

if your driving your car at the speed of light, (something i get accused of often) and you turn on the headlights, does anything happen?

Wings generate lift from AIRSPEED, not GROUNDSPEED.

If the conveyor belt were, through friction with the landing gear/wheels, pushing the plane forward with enough velocity, the plane would take off without any power at all from it's own engines. (Propulsion provided by the conveyor, instead of the turbines/props.) Kinda like a really big paper airplane.

If the conveyor were going the other direction, it would require twice as much power to take off, since it would have to first negate the speed at which it were traveling backwards, then it would have to generate the forward velocity (all relative to the air, not the ground) in order to generate lift. As someone else pointed out, the wheels would be spinning twice as fast as normal at the time of takeoff.

It would take off just fine, regardless of if the wheels are spinning twice as fast, or not at all.

The conveyor would not slow down or speed up the plane, and wind is irrelevant because the plane would still move fast enough to take off.

the only limiting factor here would be what speed the wheel bearings would overheat and actually cause enough friction to cause the plane to slow down or if they failed. otherwise it has no effect on the plane being that the engines act against the air not the ground. now if you change it to the wind (headwind) matching the thrust of the engines (forward AIR speed) then it gets interesting. would it take off stationary? most likely except that there would be severe turbulence caused by 150 mph winds over surface features surrounding the airfield.

hmmmmm

now on the headlights question... better ask albert einstein that one. better question is how much younger will i get by traveling the speed of light.

again hmmmmm

if your driving your car at the speed of light, (something i get accused of often) and you turn on the headlights, does anything happen?


The Second Postulate of the Special Theory of Relativity

The second postulate of the special theory of relativity is quite interesting and unexpected because of what it says about frames of reference. The postulate is: The speed of light is measured as constant in all frames of reference. This can really be described as the first postulate in different clothes. If the laws of physics apply equally to all frames of reference, then light (electromagnetic radiation) must travel at the same speed regardless of the frame. This is required for the laws of electrodynamics to apply equally for all frames.

This postulate is very odd if you think about it for a moment. Here is one fact you can derive from the postulate: Regardless of whether you are flying in an airplane or sitting on the couch, the speed of light would measure the same to you in both situations. The reason that is unexpected is because most physical objects that we deal with in the world add their speeds together. Consider a convertible approaching you at a speed of 50 miles/hour. The passenger pulls out a slingshot and shoots a rock 20 miles/hour at you. If you measured the speed of the rock, you would expect it to be traveling at 70 miles/hour (the speed of the car plus the speed of the rock from the slingshot). That is, in fact, what happens. If the driver measured the speed of the rock, he would only measure 20 miles/hour, since he is already moving at 50 miles/hour with the car. Now if that same car is approaching you at 50 miles/hour and the driver turns on the headlights, something different happens? Since the speed of light is known to be 669,600,000 miles/hour, common sense tells us that the car's speed plus the headlight beam speed gives a total of 669,600,050 miles/hour (50 miles/hour + 669,600,000 miles/hour). The actual speed would measure 669,600,000 miles/hour, exactly the speed of light. To understand why this happens, we must look at our notion of speed.

Speed is the distance traveled in a given amount of time. For example, if you travel 60 miles in one hour, your speed is 60 miles per hour. We can easily change our speed by accelerating and decelerating. In order for the speed of light to be constant, even if the light is "launched" from a moving object, only two things can be happening. Either something about our notion of distance and/or something about our notion of time must be skewed. As it turns out, both are skewed. Remember, speed is distance divided by time.

In the headlight example, the distance that you are using in your measurement is not the same as the distance that the light is using. This is a very difficult concept to grasp, but it is true. When an object (with mass) is in motion, its measured length shrinks in the direction of its motion. If the object reaches the speed of light, its measured length shrinks to nothing. Only a person that is in a different frame of reference from the object would be able to detect the shrinking - as far as the object is concerned, in its frame of reference, its size remains the same. This phenomenon is referred to as "length contraction". It means, for example, that as your car approaches the speed of light, the length of the car measured by a stationary observer would be smaller than if the car was measured as it stood still. Look at Fig 2 and Fig 3 below.


In Fig 2 the car is stopped at the stop sign. In Fig 3 the same car is moving past you. You will readily notice that the moving car in the figure is shorter than the stopped car. Note that the car would only be shorter in the direction it is traveling, its height and width are not affected - only its length. Length contraction only affects the length in the direction you are traveling. Imagine that you are running super fast toward an open door. From your perspective, the distance from the front of the door opening to the back of the door opening would decrease. From the doors perspective the width of your body - the distance from your chest to your back - would decrease.

Scientists feel that they have actually proved this notion of length contraction. Therefore, in reality, all objects are perceived to shorten in the direction they are traveling, if they are viewed by someone who is not in motion with them. If you are in a moving car and measure the length of the armrest, you will never notice the change regardless of how fast you are going, because your tape measure would also be shortened from the motion.

In our lives we do not ever perceive length contraction because we move at speeds that are very small with respect to the speed of light. The change is too small for us to notice. Remember the speed of light is 669,600,000 miles/hour or 186,400 miles/sec, so it is easy to see why our everyday speeds are negligible.

The Lorentz Transforms allow us to calculate the length contraction. How much contraction occurs is dependent on how fast an object is traveling with respect to the observer. Just to put some numbers to this, assume that a 12-inch football flies past you and it is moving at a rate of 60% the speed of light. You would measure the football to be 9.6 inches long. So at 60% the speed of light, you measure the football to be 80% of its original length (original 12 inch measurement was made at rest with respect to you). Keep in mind that all measurements are in the direction of the motion - The diameter of the ball is not changed by the ball's forward motion. Here are two points to keep in mind:

1. if you ran beside the football at the same speed, 60% the speed of light, you would always measure the length to be 12 inches. This is no different than you standing still and measuring the football while holding it.
2. if a lady running with the football measured a ruler that you are holding, she would measure you and your ruler to be length contracted as well. Remember, she has equal right to view you as being in motion with respect to her.

http://science.howstuffworks.com/relativity2.htm

The plane will take only when there is air flow suffient enough to result in the Bernoulli effect - the pressure under the wings is greater than the pressure above the wings which lifts the aircraft.

Just like walking on a moving sidewalk (airport concourse).

Plane moves forward twice as fast reaching the proper airspeed sooner and lifts off just fine.

The wheels have nothing to do with airspeed. The wheels are only there to provide for manuverability on the ground. Engine thrust is what makes a plane take off and fly. Same as a jet car, the wheels have nothing to do with it, its all thrust.

No matter what direction or how fast the wheels are spinning, the engines as long as they are turning will produce thrust, thus propelling the plane forward and generating the speed to take off.

Jeff

the only limiting factor here would be what speed the wheel bearings would overheat and actually cause enough friction to cause the plane to slow down or if they failed.

We'll use the same bearings in the plane wheels as we use in the conveyor.

If the conveyor were going the other direction, it would require twice as much power to take off, since it would have to first negate the speed at which it were traveling backwards, then it would have to generate the forward velocity (all relative to the air, not the ground) in order to generate lift.

Don't forget, since the conveyor always matches the speed of the wheels, there IS NO backward movement.

nice explanation oneofakind67, but will i get any younger?

If the planes not moving it can't take off, not a 747(or the like) anyway. If it could I would think this would be being done already (takeoff only of course).

... and wind is irrelevant ...

To the contrary, Derek.

Wind (or airspeed) is everything to an airplane.

With a 70 knot headwind, an airplane (i.e. Cessna) would appear to hover. It's airspeed would be 70 knots, but it's groundspeed would be 0. That's why aircraft carriers turn into the wind.

If the carrier is traveling into the wind at 20 knots, and you are facing into a 15 knot wind, then while standing still on the deck of the carrier, you already have an airspeed of 35 knots. If your airplane's stall speed (the threshhold speed at which the wings begin to generate/lose lift) is 60 knots, you only need to gain another 25 knots before you can take off.

Don't believe me? Stick your head out the window the next time you drive down the highway. Relative to the car, your not moving at all. Relative to the ground, it feels like a 65mph wind. If you have a 30mph headwind, it will feel like your facing into a 95mph wind.

There needs to be air movement over the wings to create lift. If the plane is not moving and there is nothing producing air movement over the wings, the plane will not lift.

If the conveyor belt were, through friction with the landing gear/wheels, pushing the plane forward with enough velocity, the plane would take off without any power at all from it's own engines. (Propulsion provided by the conveyor, instead of the turbines/props.) Kinda like a really big paper airplane.

If the conveyor were going the other direction, it would require twice as much power to take off, since it would have to first negate the speed at which it were traveling backwards, then it would have to generate the forward velocity (all relative to the air, not the ground) in order to generate lift. As someone else pointed out, the wheels would be spinning twice as fast as normal at the time of takeoff.The friction of the wheels would not be enough to have that much impact on the speed of the plane... it would only help it get to speed a little quicker, or a little slower. I doubt the wheels would have enough resistance to allow it to reach take-off speed without other means of propulsion, as wind resistance would slow the plane considerably.

There needs to be air movement over the wings to create lift. If the plane is not moving and there is nothing producing air movement over the wings, the plane will not lift.
why would the plane not be moving?

If the planes not moving it can't take off, not a 747(or the like) anyway. If it could I would think this would be being done already (takeoff only of course).
Yes, why have miles of runways when you could just land the plane on an oversized conveyor while the wheels are spinning at the speed of the conveyor. That way, we can build many more homes even closer to the airports, then have those stupid homeowners complain about the jet noise and petition to have the airport moved. Are you all ready to hijack this thread now, or have we already done that with the speed-of-light tangent?

If the plane isn't moving, you might as well drive...

Don't forget, since the conveyor always matches the speed of the wheels, there IS NO backward movement.

Good point.

The friction of the wheels would not be enough to have that much impact on the speed of the plane... it would only help it get to speed a little quicker, or a little slower. I doubt the wheels would have enough resistance to allow it to reach take-off speed without other means of propulsion, as wind resistance would slow the plane considerably.

True.

My remarks assumed that the conveyor was capable of moving the plane forwards/backwards at any particular speed. I didn't consider the dynamic nature of the belt, as Dan pointed out.

To the contrary, Derek.

Wind (or airspeed) is everything to an airplane.
Yes, I understand that, but the wind would be the same whether it's on a conveyor or on a normal runway... it's relevent to flight, but it is irrelevent to this equation... now if the wind matched the conveyor speed and direction, we'd have a whole new set of problems :D

Yes, why have miles of runways when you could just land the plane on an oversized conveyor while the wheels are spinning at the speed of the conveyor. That way, we can build many more homes even closer to the airports, then have those stupid homeowners complain about the jet noise and petition to have the airport moved. Are you all ready to hijack this thread now, or have we already done that with the speed-of-light tangent?
oops sorry about that.

Wait wait wait...


are those of you who think the plane CAN'T take off thinking there is no propellor, turbine, etc, that the motion relative to the conveyor is the only motion? ie, if you run a conveyor under the plane will the plane lift into the air?

Thats not how I took the question, but ok:


Without engines of any kind, lets substitute a glider, the motion of the conveyor won't generate lift, no, unless the conveyor acts like a fan and gets the air moving, which it won't in any real-world conveyor. So a glider on a conveyor won't lift off, no.

But a 747 on a conveyor has its own propulsion, conveyor is irrelevant other than friction, so it CAN take off.

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 (http://forums.nasioc.com/forums/showthread.php?t=891480#) at any given time, moving in the opposite direction of rotation.
There is no wind.
Can the plane take off?

"intends to take off" implies it's producing forward thrust from it's engines

Unless the plane is producing thrust from it's engines, the plane will stay in one place.

Once you get past the common mistake of the conveyors rotation negating the wheels rotation instead of adding to their forward rate of acceleration, it becomes clear that forward motion creating airflow over/under the wings creates lift and then flight.

I don't understand how a "big discussion" would generate from the scenario


What do you think now? :D

What do you think now? :D

ROTFLAMO

new problem... if the plane is moving from propulsion other than being driven by the wheels (which is true) it is physically impossible for the conveyor to match the speed of the wheels, except under one condition - the conveyor moves in the SAME direction as the plane, going exactly half the speed of the plane.

If the plane is going 100mph North, the conveyor would be going 50mph N and the wheels 50mph N. If the conveyor goes the opposite direction like it said in the problem (say 100mph S, the wheels would be going 200mph N)

So, in conclusion, the problem is flawed, and there is no answer ;)

We all seem to understand how lift will cause the plane to take off. The root of the problem is will the thrust of the engines cause the plane to move if it's on a treadmill that is designed to match the wheel speed of the plane? the question didn't use treadmill to discribe the device under the plane but that is exactly what it would be as described. On a standard runway the thrust will overcome the weight of the plane and cause the wheel to overcome friction and roll forward.

Lets look at how a treadmill works, you walk or run on it and are stationary. A bicycle rider uses a trainer called rollers. You ride the bike on the rollers and the bikes wheels spin on the rollers and you and the bike stay stationary. Going back to the plane, the runway size treadmill it's on should work the same as the other examples and as the planes engines are rev'd the speed of the treadmill will increase but the plane will remain stationary.

Assuming the wind isn't blowing at a speed that will generate lift for our example plane it is stationary and will not take off. Again this is based on the orig statement that the treadmill will match the wheel speed of the plane.

EXACTLY!!! Well said...

. . .and as the planes engines are rev'd the speed of the treadmill will increase but the plane will remain stationary.

Assuming the wind isn't blowing at a speed that will generate lift for our example plane it is stationary and will not take off. Again this is based on the orig statement that the treadmill will match the wheel speed of the plane.

The plane is stationary relative to the treadmill, not the air.

The plane's engines don't push against the wheels/treadmill like the bike trainer, they push against the air, hence forward motion/airspeed/lift.

The plane will fly, the tires will simply never wearout since the treadmill/ground is moving with them.

if your driving your car at the speed of light, (something i get accused of often) and you turn on the headlights, does anything happen?

OK,
in english......

This is sort of a trick question. If you understand, the ONLY way you can travel at the speed of light is if you are massless (light is made of photons, they are massless), the car could never travel at the speed of light. If it did, its mass would become infinite. Also, the distance that the car was traveling would become zero! This comes from the time dilation formulas and Einsteins special theory of relativity.

Lets say the car were traveling at 80% of the speed of light (c), and you turned the lights on. The light would still travel at 100% of c. So you could still see ahead of you.

The plane is stationary relative to the treadmill, not the air.

The plane's engines don't push against the wheels/treadmill like the bike trainer, they push against the air, hence forward motion/airspeed/lift.

The plane will fly, the tires will simply never wearout since the treadmill/ground is moving with them.
Then please explain how you get lLIFT from air passing over the wings if you have turbines BEHIND the wings. Now, if you have a propeller plane....

Derek is right about the wheels, the only way the conveyor can actually match is when v=0.


The plane is stationary relative to the treadmill, not the air.

The plane's engines don't push against the wheels/treadmill like the bike trainer, they push against the air, hence forward motion/airspeed/lift.



Exactly! Not the same thing... the wheels are stationary when their sucked up into the belly of the plane, the plane doesn't crash then!

Airspeed over wings is the only thing that matters here. Engines produce thrust, regardless of the wheels. Other than friction the wheels are irrelevent.

The only thing that matters is if we set the conveyor to be the same speed as the exhaust gasses coming out the turbine. Then it will negate the thrust. Or if you BLOCK the plane from moving, converting the thrust to compression of the block and the plane.

Neither of those is true, Derek points out the paradox in the wheel velocity, but in a PID loop for example the conveyor motor will approach zero by reducing the conveyor motor as the plane wheels speed up. Thus the conveyor will match ground speed after a few program cycles. Try it on a PID simulator or even a simple proportional loop, equation solution, etc.

REGARDLESS THE ENGINES WILL PRODUCE FORWARD THRUST PROPELLING THE PLANE FORWARD AND PRODUCING A DELTA BETWEEN THE AIR AND THE WING SPEEDS, GENERATING LIFT.

The plane is stationary relative to the treadmill, not the air.

So if that is the case the plane and the treadmill take off together...

Chris for the thrust to move the plane forward it has to over come the friction of the weight of the plane on the wheels on the treadmill. At that it becomes just like the person on a treadmill or bicycle on rollers. Think about it! On a runway the engines thrust overcomes friction and pushes the plane forward but only because the runway is fixed or stationary. Since the treadmill is the runway it moves under the plane and the plane stands still.

Alan, turbines don't move air over the wings, nor does a prop engine (or rather thats not how it generates lift). The turbines produce exhaust gasses which exit at high velocity. Every action has an equal and opposite reaction, so the inertia exerted by the turbines cause a reaction (we see it as forward motion of the craft) in the opposite direction, generating air movement, and lift.

Thrusters work in outer space (no air), although a combustion turbine won't burn, but the principle of Newton's laws apply.


If what you were saying was true, no rear-engined craft could take off, conveyor or not.

with no air passing over the wing to create lift it can not fly.

Derek is right about the wheels, the only way the conveyor can actually match is when v=0.






Exactly! Not the same thing... the wheels are stationary when their sucked up into the belly of the plane, the plane doesn't crash then!

Airspeed over wings is the only thing that matters here. Engines produce thrust, regardless of the wheels. Other than friction the wheels are irrelevent.

The only thing that matters is if we set the conveyor to be the same speed as the exhaust gasses coming out the turbine. Then it will negate the thrust. Or if you BLOCK the plane from moving, converting the thrust to compression of the block and the plane.

Neither of those is true, Derek points out the paradox in the wheel velocity, but in a PID loop for example the conveyor motor will approach zero by reducing the conveyor motor as the plane wheels speed up. Thus the conveyor will match ground speed after a few program cycles. Try it on a PID simulator or even a simple proportional loop, equation solution, etc.

REGARDLESS THE ENGINES WILL PRODUCE FORWARD THRUST PROPELLING THE PLANE FORWARD AND PRODUCING A DELTA BETWEEN THE AIR AND THE WING SPEEDS, GENERATING LIFT.

For the sake of the question you have to use the conditions set in the question. If it says the conveyor (treadmill) matchs the wheels speed then that is a given... It also says the conveyor travel is the opposite direction of the planes wheels negating any forward travel...

We all seem to understand how lift will cause the plane to take off. The root of the problem is will the thrust of the engines cause the plane to move if it's on a treadmill that is designed to match the wheel speed of the plane? the question didn't use treadmill to discribe the device under the plane but that is exactly what it would be as described. On a standard runway the thrust will overcome the weight of the plane and cause the wheel to overcome friction and roll forward.

Lets look at how a treadmill works, you walk or run on it and are stationary. A bicycle rider uses a trainer called rollers. You ride the bike on the rollers and the bikes wheels spin on the rollers and you and the bike stay stationary. Going back to the plane, the runway size treadmill it's on should work the same as the other examples and as the planes engines are rev'd the speed of the treadmill will increase but the plane will remain stationary.

Assuming the wind isn't blowing at a speed that will generate lift for our example plane it is stationary and will not take off. Again this is based on the orig statement that the treadmill will match the wheel speed of the plane.


If the bicyclist fired off a rocket strapped to his back, he would be propelled immediately off the rollers to an unpleasant landing.

I disagree,

The planes wheels at a given moment is 10mph.

The conveyor therefore turns 10mph, opposite direction. If the wheels were driven, (ex, jogger, bicycle on trainer, etc, as per your examples), no forward motion is produced.

If the conveyor is touching the wheels, there is a relative speed of the wheels of 20 mph. So we must ask which speed the conveyor is matching, the relative speed of wheel to conveyor or the angular velocity of the wheel, converted to linear velocity assuming a stationary surface.

If we assume the first, we had the wheel at 10, the conveyor responded with 10 in the opposite direction, the relative speed is now 20, paradox.

If what was meant was the conveyor is "meshed" to the wheels its a little different, I'm going by the wording which suggests to me a control loop.

Regardless the conveyor won't negate forward movement relative to the air.

If the bicyclist fired off a rocket strapped to his back, he would be propelled immediately off the rollers to an unpleasant landing.



LOL


Funny, but an excellant way to "make you say hmmmmmmm...."


and if he had wings on he WOULD generate lift.

So if that is the case the plane and the treadmill take off together...

Chris for the thrust to move the plane forward it has to over come the friction of the weight of the plane on the wheels on the treadmill. At that it becomes just like the person on a treadmill or bicycle on rollers. Think about it! On a runway the engines thrust overcomes friction and pushes the plane forward but only because the runway is fixed or stationary. Since the treadmill is the runway it moves under the plane and the plane stands still.

Think of it like a jet car, the wheels are only there to keep the underside shiney on take off. Thrust pushes on air, the wheels in contact with anything is not relative. The thrust would propel the plane forward by pushing off of the air, the wheels may be doing something completely diffrent, but the plane will still lift.

Take a herrier. It can lift off straight up, simply by rotating its thrust direction. In the case of a herrier the wheels could be spinning any direction they want, the thrust will still lift the plane. A standard jet works the same, the thrust will propel it forward no matter what the wheels are doing. Only diffrernce would be a standard jet has to go forward to gain the momentum.

Jeff

with no air passing over the wing to create lift it can not fly.But there's nothing in the equation that says there's no air moving over the wings. ;)

If a pig had wings, could he take off from a conveyor belt?

If a pig had wings, could he take off from a conveyor belt?

Not if he was running on the aforementioned negating conveyor :)

But if he had a rocket engine, (or propellor), we could finally confirm that pigs do fly! He can even have the headlights on.

I have read this post with great interest. DJD makes the only compelling argument I have read. With the treadmill matching the speed of the wheels the jet remains stationary relative to the ground and air. No Bernoulli effect, no take off.

If the bicyclist fired off a rocket strapped to his back, he would be propelled immediately off the rollers to an unpleasant landing.

Another example taking the question out of context. In the orig question it implies the roller will keep up with the wheels. On a real runway a jet doesn't drag the wheels down the runway until it reaches it's lift point, the wheels roll. Apply that to the question as stated where the treadmill keeps up with the wheels...

Another example taking the question out of context. In the orig question it implies the roller will keep up with the wheels. On a real runway a jet doesn't drag the wheels down the runway until it reaches it's lift point, the wheels roll. Apply that to the question as stated where the treadmill keeps up with the wheels...


Well, no, the treadmill is opposite, which means the wheels are rolling.

Even if the wheels are locked up, so long as the engines can overpower the wheels, the plane will move. Basic physics.

If you are suggesting the wheels can not separate form the conveyor, ever, because, after all, they are linked as per the description, then no, I supposed it can't take off without taking the whole conveyor with it. I was not thinking about all these little lawyer-loopholes, rather the spirit of the question.




Only one compelling arguement?!? :)


The wheels don't accelerate the plane, the engines do.

I have read this post with great interest. DJD makes the only compelling argument I have read. With the treadmill matching the speed of the wheels the jet remains stationary relative to the ground and air. No Bernoulli effect, no take off....but if he was right, we'd hear stories in the news daily about planes falling from the sky as they fly over conveyor belts.

The plane would take off, and here's why:

A) There is no wind, meaning the air is not moving, relative to ground-speed, not conveyor speed.

B) The plane is propelled by moving the air, like they always do.

C) The wheels roll freely - the only resistance the conveyor makes is the friction coefficient of the wheel-bearings, which jet engines easily overcome.

D) The plane moves the same relative to ground-speed as it would without the conveyor, with the exception of the minute ammount of friction at the wheels.

E) See A again

F) The plane is moving (D), the air is not (A) - Bernoulli effect of the air-pressures around the moving wings creates lift.

G) Plane flies, you get where you need to go.

But there's nothing in the equation that says there's no air moving over the wings. ;)

you are correct. I agree that the wheels have no bearing on this situation, other than to keep the bottom of the plane from getting scratched up. I agree the engines would generate forward thrust. If the belt was not designed in such a way as to generate reverse momentum to offset this forward thrust the plane would move forward regardless of the belt or its own wheels rotational speed. If the plane moves forward at a sufficient rate of speed to produce lift the plane will take off. I'd be more interested in figuring out how much power would be needed to move a belt large enough, fast enough to offset the forward thrust of a jet engine.

Interesting concept.... at first it seems simple, then after you think about it for a moment.....

Well, no, the treadmill is opposite, which means the wheels are rolling.

Even if the wheels are locked up, so long as the engines can overpower the wheels, the plane will move. Basic physics.

If you are suggesting the wheels can not separate form the conveyor, ever, because, after all, they are linked as per the description, then no, I supposed it can't take off without taking the whole conveyor with it. I was not thinking about all these little lawyer-loopholes, rather the spirit of the question.
Only one compelling arguement?!? :)


The wheels don't accelerate the plane, the engines do.

No not a lawyer loophole at all!! What makes the wheels roll? Thrust of the engine but not direct drive, right? If the wheel does roll it turns the conveyer in the opposite direction. The question states the conveyor exactly matches the speed of the wheels (that means keeps up). This is the spirit of the question as stated. What is stated doesn't allow for the thrust to over come the wheels and drag them down the conveyer.

Just because the situation may not be physically possible, the variables are set in the question and the answer has to be derived from the question and only from the question. In reality the thrust would as our kind nova friend points out over come the surface the plane sits on but the question provided conditions being met in such a way that the plane cannot over come the wheels and the conveyer it sits on...

.............................ARRIVALS............. .....DEPARTURES

Flight query............................................C ANCELLED

I think the plane takes off...
But just for argument's sake, what if the the plane's engines were off and the treadmill moved the plane backwards. As the treadmill accelerates, the engines are slowly brought up to speed. What happens?
Or, the treadmill moves the plane backwards at the negative of the liftoff speed. Then the plane fires up and the engines are brought to liftoff speed.
What happens.


And, not to sound like a nerd, but photons do have weight; think solar sails. One of the great paradoxes. Light acts like a wave and a particle, depending what experiment is being conducted.

I would think some of you have seen this question before but there was a large discussion about it on another board, let's see what you guys think about 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 (http://forums.nasioc.com/forums/showthread.php?t=891480#) at any given time, moving in the opposite direction of rotation.
There is no wind.
Can the plane take off?

How does the conveyor match the speed of the wheels? How does it know which motion of the wheel is caused by the plane and which is caused by the belt?

Since we have tossed out the plausible - that a treadmill the size of runway would have the instantaneous response to the acceleration of the wheels as the plane tried to taxi down the runway, why not use the point that DAN72 mentioned above about forward thrust overcoming locked up wheels.

Try this approach to the answer a plane will take off:

Given:

1) When the wheels are not rotating, the conveyor is also not rotating.
2) The plane will lift off only when the Bernoulli effect is great enough to lift the aircraft. - So air must be flowing over and under the wing which requires forward movement.


Solution: Lock the tires from rotating and use sufficient thrust to overcome the friction of locked tires and achieve a forward velocity great enough for the Bernoulli effect to lift the plane.

Ok, if we're going to get right down to it, define fly and/or take off. I'm assuming we're talking about conventional flight, which we all seem to agree would require the movement of air over the wing to create lift, but as has been pointed out VTOL planes can be punted into the sky with sufficient thrust to over come gravity, only after sufficient forward speed (air movement over the wings) is achieved do they actually "fly." I spent a few years working with helicopters, which achieve lift only in their blades, the rest of the deal is a cinder block drug along for the ride. The space shuttle achieves lift off and has the horses to over come the earth's gravity? It has wings that allow it to glide back to earth, but does it fly? Movement of the belt or the planes tires is of no importance, air movement across the wings surface is the issue. If the plane can be prevented from moving forward with sufficient speed to create the necessary movement of air, say on a belt that is moving it backward at the same rate that it is being propelled forward it will be static. No air will be moving over the wing and it will not fly. Of course the paradox is, can you cancel forward thrust against the air with the physical dragging of the plane back wards. One would think that given there would not be much friction between the axles, wheels and the belt that the belt could not maintain enough grip, for lack of a better word, on the plane to drag it back wards given a steady and/or increasing amount of forward thrust.

My, how matters can get complicated. The problem is simply stated, adding bearings and other issues is self defeating. As far as I understand the problem, a magic conveyor capable of compensating for the plane's moving wheels negates forward motion of the aircraft. No forward motion, no differential pressures acting on the wings, no lift, no fly. The aircraft isn't identified as a prop so no air movement can be associated with that.

The only obvious issue is the phrase "moving in the opposite direction of rotation." You have to make an assumption about what that means. For a plane attempting to take off left to right, the bottom portion of the wheel--the part in contact with the conveyor's surface--is traveling clockwise. That clockwise rotation is right to left movement of the wheel at contact point. If the conveyor is moving opposite, or left to right, it would actually push the aircraft down the runway and off it would go into the wild blue.

However, if you read that phrase the other way, that the conveyor belt is traveling in a direction opposite to the rotating wheel--going backward while the plane attempts to go forward--then it is effectively compensating for the aircrafts forward motion. No fly.

No airspeed,no airflow over the wings=no lift, plane sits there in the same spot.

I use to take my rc car and put it on the treadmill, set it for 5mph or so the accelerate the car till it just sat there,kinda fun to see it running wide open but making no forward/backward movement.

That would be cool to do a full size car like that.

As far as I understand the problem, a magic conveyor capable of compensating for the plane's moving wheels negates forward motion of the aircraft. No, it doesn't - that's the trick of the question. Wheels don't make planes move, propellers or turbines do. The wheels are irrelevent. There is no possible way the conveyor can have any effect on the thrust of the prop or turbines, only wind-speed can, which as stated in the problem, there is no wind, so it won't be effected.

Put a car on the conveyor, and it will stay still because it is driven by the wheels. Put a rocket on the car, and it will accellerate even if the car is in neutral, no matter what the ground below it does.

You guys are outsmarting yourselves by overanalyzing this thing!


If the plane has wings, and there is air(not in a vacuum), and the engines have appropriate thrust, it doesn't matter if the wheels turn twice as fast or even in the oposite direction, or the don't turn at all, the plane will take off at it's designed air speed!!!

The way I see it, no matter what type of thrust or propulsion you use the treadmill is going in the opposite direction the plane is trying to move, canceling the movement, making the plane stationary.

I'm glad you guys don't design planes, because the correct answer would then be "no plane has ever been capable of flight" because they would slow down and land every time the drive-wheels left the tarmack :D

Allright, somebody has got to put wings on their ride and go to the dyno to see if it will take off, at least up to the wall!

The way I see it, no matter what type of thrust or propulsion you use the treadmill is going in the opposite direction the plane is trying to move, canceling the movement, making the plane stationary.NO, the air does not move with the conveyor. The plane is propelled by air, not the ground SHEESH :clonk: :D

You know tho Derek, if you really simplify your thinking and take it right down to where logic doesn't come in to it, the plane wouldn't move.

Logically it would go, yes.

But if you take any logic out of it, and assume the wheels stay in contact with the conveyor belt and spin the entire time it wouldn't move. Obviously this wouldn't happen in any real world testing, as the thrust would over power the belt and we would be in the air. But if the wheels stayed in contact and you had some incredible conveyor system that could spin at the thrust speeds it wouldn't move.

The question just says the conveyor spins at the same speed as the wheels but in reverse. So as long as the wheels stay spinning and in contact the plane would not move forward and therefore would not generate any airspeed. As long as the plane is connected to the wheels and the wheels to the belt, it wouldn't move.

This can only happen if you remove every ounce of logic from the question and answer. Any real world test, would put the plane in the air.

Jeff

NO, the air does not move with the conveyor. The plane is propelled by air, not the ground SHEESH :clonk: :D


I dont get your complaint with my reply, im saying the plane will stay still, it will not take off.

You've got thrust coming from the engines pushing it foward, the conveyor is going in the opposite direction the engines is trying to push the plane, the foward movement of the plane is cancelled out by the rearward movement of the conveyor.

Relative to the conveyor belt the wheel is not moving, but relative to the outside environment the plane is moving forward at the speed of the belt. If it moves forward fast enough to generate enough lift to overcome the weight of the airplane, the wing will fly whether the engine is producing thrust or not. As soon as it is airborne, drag will overcome lift if there is no engine or prop thrust, and the wing will slow to stall speed, forcing the plane back to Earth.

Gentlemen,

A part of me can kind of see what they are saying, but as mentioned, alot of logic and real world REALITY :) must be removed to make the plane stick to the ground.

This has been my position:
The problem states the conveyor matches the speed of the wheels. That is not the same cancelling the thrust.

It says nothing about cancelling the forward motion of the craft. That is an assumption that is being made based on the fact that on the ground the wheel speed is the same as the forward motion of the aircraft.

It is possible to have the craft moving forward by thrust only, and the wheels turning at a rate related to the conveyor. Since they cancel each other out you can "strike them" from the equation.

Now, I will give you that if you consider the conveyor "meshed" with the wheels, by which I picture gear teeth or something similiar, the conveyor is firmly anchored to the ground, and there is no possibility of "skipping of teeth", etc, the wheels are therefore not allowed to progress down the length of the conveyor. Whenever the engines push the craft forwards the wheels try and turn, the conveyor reacts by turning in the other direction at the same speed. What all this means is that the only way for the plane to move is for the wheel to turn at a faster speed than the conveyor, which if we follow the exact letter of the problem (this is where the lawyer reference came from, btw :) )is not allowed.

BUT CONSIDER THIS!!!:

At this point, I can see two things. Wheel speed aside, on a real conveyor the wheel would be forced to make forward progress due to the tremendous thrust of the engines at the same time as not turning at a different rate than the conveyor. How? An analogy we can probably all picture is a 4wd truck, in 4wd, with smaller tires on the front than on the back. All four tires are linked together, and must travel at the same angular frequency. But since they are different diameters the actual angular velocity at the circumference of the tires is different front to rear, and yet they are still all coupled to the same road! What happens? The front tires turn at a different rate than the rears, either the front or the rears actually scrub or skip a little, and the truck moves forwards. Same thing here...the plane wheels may scrub since they are linked to the conveyor SPEED (not necessarily glued to it, mind you) but the thrust of the engines are much more powerful, the craft moves, and accelerates, lifts off, etc.

If we declare that skipping/scrubbing is not allowed EVEN IF THE ANGULAR VELOCITY IS THE SAME then yes, I suppose that means the plane is effectively anchored, and the thrust of the engines will not allow the plane to move, all of the energy will be expended as compression of the plane and heat. This is what I meant about the lawyer stuff (sorry if it comes across as insulting, btw), as I do NOT think saying that the wheels are turning the same speed as the conveyor means the wheels can't move along them while turning, albiet at a different rate than would normally occur.

Again I think the spirit of the conveyor is to trick people into thinking about the wheels of the aircraft as being the driving elements like on a car. I don't think it was intended to mean that the aircraft isn't allowed to lift away, or that if does, the wheels must spin the same speed up in the air, or anything like that.

You can prove it with an RC plane and a treadmill, if you wanted. You would need a control loop, which introduces delays, hence you should use PID or something similar, hence not quite the same as the problem outlined above. Maybe a crude simulation on a computer?

Yes, I assume a certain minimum thrust...that we are doing this on planet Earth, with air at some normal pressure, gravity, etc.

When the plane is at rest it sits on it's wheels. To reach the magic speed where lift takes effect it rolls on those wheels. It doesn't matter that the wheels are not driven by the jet or prop engine. The wheels help the plane over come the friction generated by the planes weight and gravity. Remove the wheels and set the plane on the ground on it's belly and fire the engines, it will move, might even reach a speed to allow it to take off but not like it does with wheels.

Planes just don't start flying because you rev the engine...

Remove the wheels and set the plane on the ground on it's belly and fire the engines, it will move, might even reach a speed to allow it to take off but not like it does with wheels.

If I didn't know better I'd say you were agreeing with me! :)

Ok, But we told ya'll it wouldn't move......

If i have to i'll build a damn model.

If I didn't know better I'd say you were agreeing with me! :)

I would bet against that!:)

What he is saying is the plane relys on the wheels to gain airspeed. With no wheels, the plane isn't rolling easily to get to the point where it lifts. If you keep the wheels in contact with the belt, the plane would act like a car on a dyno wheel. It would spin at all the speed you want, but never move forward.

Jeff

O.k., if you want to use the question word for word, the plane takes off. The original question states the conveyor turns in the opposite direction as the wheels, therefore moving it forward. The conveyor would have to spin in the same direction as the wheels to hold it in one place, like a dyno. If the belt turns in the opposite direction, it would move the plane down the runway without the plane even powering up.

Jeff

:)

I know it won't move forward as easily, but it kind of sums up everything I've been trying to say, and others too.

Wheels aside, you can still lift off.

Car on a dyno isn't quite the same, that is also my arguement. With a car forward thrust COMES FROM the wheels. Not so with aircraft. And hopefully I've given an example that we can live with of how things can be linked in angular velocity and still make forward progress.

You can spin the tires of your car on ice, going uphill, and the car still goes backwards, right (downhill). A guy can come out a push your car up the hill at the same time, right? Or sideways? All while spinning the tires?

Ok, not great examples, but I am trying help the picture that wheels can do one thing and the craft something else. Wheel speed and ground speed, while USUALLY related, do not have to be.

Jeff, now we must define direction as left to right vs clockwise to counterclockwise!!! Opposite effect. I think someone mentioned that earlier but my head hurts too much for me to look it up!


On a dyno, the car wheels go, for example, clockwise, the dyno wheel counter clockwise. The turn opposite directions by this definition. This is what I think the problem states.

However, on a dyno, the rubber contacting the roller moves, say, right to left, and the part of the dyno wheel touching the tire moves also right to left, NOT opposite, if thats how you define direction.

O.k., if you want to use the question word for word, the plane takes off. The original question states the conveyor turns in the opposite direction as the wheels, therefore moving it forward. The conveyor would have to spin in the same direction as the wheels to hold it in one place, like a dyno. If the belt turns in the opposite direction, it would move the plane down the runway without the plane even powering up.

Jeff

Not really, he stated that The conveyer belt is designed to exactly match the speed of the wheels at any given time, moving in the opposite direction of rotation.

The plane wheels are turning counter clockwise when viewed from the left side of the plane, so the conveyor is turning clockwise cancelling out the wheel turning (ground speed), therefore the wheel is stationary, including the plane, no matter what the thrust.

I think this post needs to be closed, or someone build a model or something.

The plane wheels are turning counter clockwise when viewed from the left side of the plane, so the conveyor is turning clockwise cancelling out the wheel turning (ground speed), therefore the wheel is stationary, including the plane, no matter what the thrust.

Wheel speed is not equal to ground speed, necessarily. This is the fundemental mistake. See tire scrubbing example, above.

:)

this is fun..... I say we pitch in and build said runway, rent a 747 and settle this best two our of three attempts. Loosers buy .....:beers:

I think opposite turning means like a car on a dyno. But not like a car on the dyno push comes from jet engine propulsion does this mean the plane can move itself but the wheel speed will be different? I'm stumped really, at first I thought no movement possible but now I'm not sure.

Could this be rocket science?:waving:

Ok,i got it , from another post on another board.

Think of it like this, ever seen a plane stand still in the air? most of the time its a model plane but anyway think of this.

A plane is flying through the air at 150mph and a gust of air hits it head on (opposite direction) at 150mph ,the plane will stop dead in the air and hangs there, 1 because the air speed of the plane was just matched by the oncoming air and 2 it will hang in the air because there is a 150mph air flow over the wings,creating lift,even though it is not physically moving through the air, key here is AIRFLOW, the treadmill does not have AIRFLOW.

I figured it out! You guys are all wrong on purpose to drive me insane!

I've got my tin-foil hat on, so I can now think clearly... and I'm still right ;) The plane takes off!!!

I can't believe the site I come to for technical info is filled with so many dummies :clonk: ...who's the real dummy? Me I guess, for listening to you knobs. :D

Think of it like this, ever seen a plane stand still in the air? most of the time its a model plane but anyway think of this.

A plane is flying through the air at 150mph and a gust of air hits it head on (opposite direction) at 150mph ,the plane will stop dead in the air and hang there, 1 because the air speed of the plane was just matched by the oncoming air and 2 it will hang in the air because the is a 150mph air flow over the wings.

Tranfer these ideas to the treadmill, other than the lift,because the plane IS stationary.

Not the same, my friend. In that case, the thrust of the engine is equal to the acceleration due to gravity.

The "treadmill" does not match the speed of the craft through the air, per se. The problem says it matches the wheel speed. You want to make those two things equal, under all conditions, which is a mistake. It is possible to have the wheel speed match the conveyor speed AND STILL MOVE THROUGH THE AIR by moving across the conveyor! Right?

See tire scrubbing example, above. :)

Forward motion does NOT presuppose airflow, although lift does. Forward motion comes about because of the thrust. Then and only then, is there airflow, and lift.

Not really, he stated that

The plane wheels are turning counter clockwise when viewed from the left side of the plane, so the conveyor is turning clockwise cancelling out the wheel turning (ground speed), therefore the wheel is stationary, including the plane, no matter what the thrust.

I think this post needs to be closed, or someone build a model or something.

Draw exactly what you said on a piece of paper and look what happens. If, viewing from the left side of the plane, the front wheel is turning counter clockwise and the belt is turning clockwise(opposite) the belt is actually speeding up the wheels in a forward direction.

The belt would need to go counter clockwise as well to stall the plane in its tracks.

So if you take the question as it is written, the plane takes off using less fuel than it normally would be the conveyor belt is helping the plane pick up speed.:D

Jeff

Jeff I disagree with what you said, slightly. The surface to surface speed is sped up, yes, because we are comparing the surface of one wheel to the conveyor as opposed to the wheel compared to the ground. The paradox Derek mentioned.

But the wheel frequency (period, actually), the time it takes for a wheel to go around, once, is unchanged.

Again, all in what our definition of velocity is!

On a dyno the wheel/roller turn opposite directions (clockwise, counterclockwise), and the surface-to-surface speed is 0. That is how I understand the problem.

O.k so it doesn't actually speed it up, but it wouldn't stop it in its tracks either. The belt would have to rotate in the same direction in order for it to stop the plane in its tracks. The belt going the opposite direction is not going to be any hinderance to the plane at all.

Jeff

A car on a chassis dyno, unless it is an AWD dyno doesn't go anywhere because of the chains, straps and blocks holding it in place. Unless the dyno is freewheeling with the brake fully released.

Something else to confuse:
I dont think that a conveyor could be built to do what is stated in the question because in order to determine that the wheels' RPM has increased, there needs to be some minute amount of time during which there is a speed differential. That way the conveyor can sense that it needs to accelerate. Which also takes some small amount of time. The conveyor will be always catching up. Especially as the rate of RPM increase increases.

Take a think on this: Take one instant at a time. The thrust of the aircraft is what causes the aircraft to move forward. This forward motion is what causes the wheels to roll. So, as the aircraft moves forward, the wheels to begin to rotate. The conveyor senses this, and compensates by rolling opposite. This, assuming instantaneous response by the conveyor, would negate any forward motion of the aircraft. So, if the aircraft moves forward one inch, the conveyor moves it backward one inch.

It isn't the aircraft's wheels that cause the conveyor to know how quickly to move, it is the motion of the aircraft that tells the wheels how quickly to roll, and the rotation of the wheels that tells the conveyor how quickly to roll.

My conclusion, after thinking about it a bit, is that I need a beer, and a machine shop with all you guys in it to make a model.

If there is someplace around here to do it, I'll donate the treadmill, some rotary encoders and a PLC controller if you guys have a PLC and an RC plane. :D

K

The thrust of the aircraft is what causes the aircraft to move forward. This forward motion is what causes the wheels to roll. So, as the aircraft moves forward, the wheels to begin to rotate. The conveyor senses this, and compensates by rolling opposite. This, assuming instantaneous response by the conveyor, would negate any forward motion of the aircraft. So, if the aircraft moves forward one inch, the conveyor moves it backward one inch.

It isn't the aircraft's wheels that cause the conveyor to know how quickly to move, it is the motion of the aircraft that tells the wheels how quickly to roll, and the rotation of the wheels that tells the conveyor how quickly to roll.




Well said, plane is stationary,correct.

Chevello, you and I see eye-to-eye on the real-world part. That's why I mentioned PID, etc.

I think we left reality some time ago, remember, this is a magic conveyor :)

You can still have a nice tight PID loop, and the angular velocities match perfectly, and still skid the rotory encoder across the conveyor!

Another example, a belt sander, spins at a certain rate. If you turn it on and set it down, it will try and drive away. Put a "magic" conveyor under it, and it will stay in place, but you can still grab it (thrust) and draw it across the conveyor, sanding it.

Jeff, I think if you look at a dyno, you will see the wheel and roller turn in opposite directions.

Micheal, you can't imagine the wheel skipping while still turning at the same rate as the conveyor?

Yes! :D

I have thought about this entirely to long. My head is now completely confused as to what is happening and I still say it takes off.:thumbsup:

If someone can come to a conclusive answer could you please post it in a diffrent color, so I can skip right to it and read it instead of further confusing myself:clonk:
Thank you:D

Jeff

So that means if this plane had 2000 lbs of birds on board and you kept half of them flying inside the gross weight of the plane would be 1000 lbs less?

Mark

So that means if this plane had 2000 lbs of birds on board and you kept half of them flying inside the gross weight of the plane would be 1000 lbs less?

Mark
NO!, NO!, not another science question...I just took my propeller cap off 'cuz it was smokin'...What kind of birds are these? Was the plane on a magic scale? Were any birds harmed in the production of this experiment? ooooooh!, my head is hurting...oooooooooooh!

A simple drawing to explane the wheel rotation and the conveyer rotation direction...

AC the 1st is a statement not a question> It's out of context do to the fact that the initial question says the conveyer is able to keep up with the wheel... Apply that to teh bike and rocket and the roller can keep up with teh bike...

I'd say yes, due to the opposite and equal reaction. The thrust is going to push the plane forward. The conveyor would only match the rotational speed of the wheels, but the plane would be moving. The plane cannot remain stationary, even if sitting on giant treadmill. It must, by Newton's Law of motion (don't recall which one), move forward. As the forward ground speed of the aircraft increases, the treadmill will simply speed up to match the rotational speed of the wheels as they continue to turn faster and faster, without impeding the forward progress of the aircraft.

Okay...some one call NASA or MIT already! :)

A car with wings is built.

It needs to go 120mph for the air, flowing over the wings, to generate enough lift for it to fly.

It's put on a dyno, and the dyno moves in the opposite direction of the wheels, matching their speed.

Will the car take off?

NO! (forgive me if this has been said before, I just couldn't read them all...)

Note: pressing MORE on the accelerator will not alter the speed of the car - regardless if it uses a jet thruster or regular engine for propulsion. The wheels have to move for the car to move, and since the dyno matches the wheels, the car NEVER moves - the car CAN'T go "twice as fast" as the wheels... The dyno IS the "equal and opposite reaction". Ever try to run off a treadmill that matches the speed of your feet?

Prop planes - interesting possibility, as they would generate airflow, but I don't think so. They generate airflow over too small a section of the wings.

A simple drawing to explane the wheel rotation and the conveyer rotation direction...http://www.chevelles.com/forums/attachment.php?attachmentid=1311&d=1133391717

This is all you need..

A car with wings is built.

It needs to go 120mph for the air, flowing over the wings, to generate enough lift for it to fly.

It's put on a dyno, and the dyno moves in the opposite direction of the wheels, matching their speed.

Will the car take off?

NO! (forgive me if this has been said before, I just couldn't read them all...)

Note: pressing MORE on the accelerator will not alter the speed of the car - regardless if it uses a jet thruster or regular engine for propulsion. The wheels have to move for the car to move, and since the dyno matches the wheels, the car NEVER moves - the car CAN'T go "twice as fast" as the wheels... The dyno IS the "equal and opposite reaction". Ever try to run off a treadmill that matches the speed of your feet?

Prop planes - interesting possibility, as they would generate airflow, but I don't think so. They generate airflow over too small a section of the wings.


Put a rocket or turbine engine on the car that creates rearward thrust which acts independently of the wheels, it will gain enough forward speed to create lift over the airfoil surfaces. The treadmill in this theoritical question is designed to match the rotational speed of the wheels. The airplane can accelerate forward AND the treadmill can match the rotational speed of the wheels so long as propulsion is provided by some means other than the wheels. Now, as was mentioned before, the wheels will really be churning and turning by the time the aircraft reaches takeoff speed, but theoretically, it is possible.

With thrust, the axles which goes through the wheels, will start moving forward regardless of what the wheels do. The wheels can be rotating clockwise, counterclockwise, or stay stationary, it doesn't matter; the axles are moving forward, along with the rest of the plane.

if your driving your car at the speed of light, (something i get accused of often) and you turn on the headlights, does anything happen?

Yes, you get smacked by your wife.

Yes. Since the conveyer has to match the speed of the rotation of the WHEELS and not the forward speed of the plane, the wheels and conveyer have zero effect on the airplane's speed.

Think of this: If the conveyer was moving 600 mph backwords, and, therefore, the wheels are rotating 600mph forwards, will the plane be able to stand still?

Of course, in the real world, you'd need something (but neat really that much) to hold the plane in place, but that is due to frictional forces. In reality, the wheels and conveyer don't want to rotate at the same speed.

With thrust, the axles which goes through the wheels, will start moving forward regardless of what the wheels do. The wheels can be rotating clockwise, counterclockwise, or stay stationary, it doesn't matter; the axles are moving forward, along with the rest of the plane.

No question as to which way the wheels are turned... As you say the axle moves the wheel spins on the axle and as the question states, the conveyer belt goes the opposite way the axle and wheel goes. (see drawing above) Refer back to the orig question for the part about the conveyors speed and direction. I like refering teh the conveyer as a treadmill because it visualizes better. I also know many feel the conveyer goes in the same direction as the plane would if it were moving forward but there was nothing to indicate that in the question...

Gotta go, have fun!!

Yes. Since the conveyer has to match the speed of the rotation of the WHEELS and not the forward speed of the plane, the wheels and conveyer have zero effect on the airplane's speed.

Think of this: If the conveyer was moving 600 mph backwords, and, therefore, the wheels are rotating 600mph forwards, will the plane be able to stand still?

Of course, in the real world, you'd need something (but neat really that much) to hold the plane in place, but that is due to frictional forces. In reality, the wheels and conveyer don't want to rotate at the same speed.

Last bit I promise...

The orig statement says the conveyer will match the wheel speed, read that as sync up it doesn't say go the same speed. Think of 2 gears one large and one small ring and pinion if you wish. When they are matched up one turns faster than the other they still match up though. If you wish read it no traction loss between the conveyer belt and the tire...

:beers:

I think of it like taking your car to the emmisions or dyno and put it on the conveyor wheel thingy. I think a plane has to be MOVING AT 85mph in order for it to take off. Air has to be flowing over and under the wing in order for it to takeoff. Like a Chevelle on a dyno: It may by cranking out 5,000 RPMs but it aint going anywhere.

Alright, I'll give it a try:

You have a toy car sitting on a treadmill. The treadmill is designed just like that conveyor, so it will always match the speed of the wheels on the toy car. Now, assuming that there's no friction in the system, the wheels and the conveyor can start instantaneously and accelerate to an infinite rpm: Can you push the toy car off the treadmill?

This is exactly the same problem at a smaller scale, and it will hopefully be obvious that you can push the car off the treadmill, but you will have to overcome the friction between the wheels and the treadmill as they are always moving at the same speed. As far as the plane goes, it won't move until it breaks the traction between the wheels and the conveyor.

It is also obvious that it's totally impossible for the conveyor to behave like you assume in the problem. Look at the toy car again, and you'll see that if the conveyor is always trying to overcome any movement of the car, it will instantly start spinning at an infinite speed when you try to push the car just a fraction of an inch, and come to a dead stop as soon as you quit pushing. Yes, you do assume that this is possible, but there's no point in discussing the problem if it's set up to make you assume that there's friction between the wheels and the conveyor, but nowhere else.

Great problem to discuss over a beer though.

Unbelievable!!!:clonk:


I'll board the said plane and soar with the Eagles!!!:D


You geniuses who think the plane won't take off and leave the treadmill trying to catch up, can stay here on the ground with the TURKEYS!!!!:rolleyes:


MERRY CHRISTMAS!!!

:beers:

Ok,i got the buster..

assuming that there is absolutly no friction in the wheel bearings and no friction between the tire to belt then it would fly, if there is any friction at all then no it would not fly.


Since so far there is NO frictionless bearing, and there has to be friction between the tire and belt the plane will not gain ground speed and will not fly.

The only thing draging the plane back as the belt goes back is the friction in the bearings and tire to belt friction, if not for that then it would go foward.

Ok, I think Olle has the best explanation in there somewhere. :)

The belt can't apply any force to the plane to negate the thrust, it is impossible for the belt to keep up with the acceleration of the wheels.


EDIT:


Since so far there is NO frictionless bearing, and there has to be friction between the tire and belt the plane will not gain ground speed and will not fly.


If the plane has no ground speed, why would the wheels be turning? If the plane has ground speed, the wheels are moving faster than the belt.

Ok, I think Olle has the best explanation in there somewhere. :)

The belt can't apply any force to the plane to negate the thrust, it is impossible for the belt to keep up with the acceleration of the wheels.

No one said that it couldnt keep up with the wheels...This is a theoretical belt and the question states that it matches the speed, it doesnt pose any limits as to belt speed.

Physics imposes the limit. It's impossible for the belt to keep up.

EDIT: Full explaination:

The belt cannot impart any force onto the plane except the force of friction in the plane's wheel bearings. The resistance of the wheels to spin on the axels.
A plane creates more than enough thrust to overcome this friction or else it wouldn't be able to take off on a normal runway.
The thrust will overcome the miniscule force of the belt (really the friction in the bearings) and therefore accelerate relative to the belt.
The belt CANNOT keep up, it will not create the force needed at a given velocity to overcome the acceleration of the thrust.

If the belt could spin fast enough to create enough friction in the wheel bearings to negate the thrust, then no, the plane will not move nor take off. But in that case, the wheels would be keeping up with the belt, not the belt keeping up with the wheels as stated in the problem.

The end.

Wow! 9 pages already, this post has taken off faster than a plane on a conveyor belt.

I gave up reading all the replies since the answer has been said over and over and people still want to argue with it. What have the wheels got to do with flight, absolutely nothing. Spin them forward, spin them backward, lock them up with the brakes, if strong enough the engines will still move the plane forward and when the correct speed is reached, airflow over wings, you're airborn. Seaplanes don't use wheels, how do they fly? Wheels are just a lot cheaper than replacing the belly of the plane after every take off. Also makes landing a bit smoother. Other than that they have absolutely nothing to do with flight. Replace them with teflon pads, no rotation what so ever, you'll still get airborn. Replace them with a mag lift, even less friction, still no wheels and you're airborn. Take them off and replace them with nothing, scrape the belly of the plane off during takeoff, you'll still get airborn. Seems everyone agrees you don't need wheels to fly a plane but having them can stop you from flying a plane?:clonk:

And, not to sound like a nerd, but photons do have weight; think solar sails. One of the great paradoxes. Light acts like a wave and a particle, depending what experiment is being conducted.

Nonetheless, the photons are massless, otherwise they can't move at the speed of light. I agree light acts like a wave and a particle, but it doesn't have mass when it moves like a particle and no mass when acts like a wave.......

I believe I will start another thread about this one, would love to see everyone argue about this. But I just don't it'll have the same pull...

if your driving your car at the speed of light, (something i get accused of often) and you turn on the headlights, does anything happen?

Yes, the car disassembles itself....

Fred.

Ignore the wheels and treadmill, think of it this way. If you put the plan on it's tail, would the engines have enough power to make it fly? In this case, it doesn't matter if the plane is vertical or horizontal. There is no airflow over the wings from movement, just the power of the engines. Any airflow is being generated from the props, if it has any. If it has the power, it can fly, if not, it can't, I see it that simple. Rockets can fly and have no wings, (vertically) basically the same as in this case.

Fred.

I think you "FLYboys" have made a fundamental mistake. Your mistake lies in the assumption that the wheels of the plane are driving the conveyor. The way I understand it, the conveyor is self-powered and will be driven on its own to match the wheel speed. The correct way to think about it would be to ignore friction and momentum in the bearings and belt, and assume that the belt can instantaneously match the wheel speed. Yes, the thrust is thrust, not drive, but as the thrust begins to move the aircraft forward, the conveyor IMMEDIATELY matches speeds, preventing the aircraft from moving forward. As the aircraft, via thrust, tries to accelerate the aircraft faster, the conveyor senses the wheel speed, and compensates, preventing the wheels from accelerating over the ground by ALWAYS moving at a speed that matches the speed of the wheels. If there is no differential in speed between the wheels and whatever they are rolling on there is no horizontal motion of the wheel's axle.

As an aside, airflow over the wings is not caused by thrust, look at any military aircraft (F-14, 15, 16, 18, 22, 111, A-10, B-52, B-1), or civilian jet aircraft. None have the engines blowing on the wings.

Go Groundhogs!

So the "Groundboys" could comtemplate this: How can you envision a plane at full military thrust, without any tiedowns, being held in place strickly by rotating it's wheels? How can tons of thrust be overcome by spinning an un-driven wheel?

Yes, the thrust is thrust, not drive, but as the thrust begins to move the aircraft forward, the conveyor IMMEDIATELY matches speeds, preventing the aircraft from moving forward.

BZZT!

The only way to prevent the aircraft from moving forward is to negate the THRUST. You can't negate the thrust by spinning the plane's wheels in the opposite direction.

Just because the wheels on the plane are rotating, and the conveyor is moving at the same speed of the wheels, doesn't mean that the plane is not moving forward !

The wheel speed and conveyor speed may become extreme, but the thrust from the engines will propel the plane forward. Thus, it will take off when it reaches the necessary air speed. The plane will take off using the same distance as it would without the conveyor. In other words, the takeoff would appear completely normal, with the exception of the higher than normal wheel speed.

My guess is that the wheel speed at liftoff would be twice it's normal speed at liftoff.

N~

What a bunch of tools :D The plane flies because I said so. ;)

I think you "FLYboys" have made a fundamental mistake. Your mistake lies in the assumption that the wheels of the plane are driving the conveyor. The way I understand it, the conveyor is self-powered and will be driven on its own to match the wheel speed. The correct way to think about it would be to ignore friction and momentum in the bearings and belt, and assume that the belt can instantaneously match the wheel speed. Yes, the thrust is thrust, not drive, but as the thrust begins to move the aircraft forward, the conveyor IMMEDIATELY matches speeds, preventing the aircraft from moving forward. As the aircraft, via thrust, tries to accelerate the aircraft faster, the conveyor senses the wheel speed, and compensates, preventing the wheels from accelerating over the ground by ALWAYS moving at a speed that matches the speed of the wheels. If there is no differential in speed between the wheels and whatever they are rolling on there is no horizontal motion of the wheel's axle.

As an aside, airflow over the wings is not caused by thrust, look at any military aircraft (F-14, 15, 16, 18, 22, 111, A-10, B-52, B-1), or civilian jet aircraft. None have the engines blowing on the wings.

Go Groundhogs!
Well if the conveyor instantly matches the wheel speed all that does is cause the wheel to spin faster, still doesn't prevent the plane from moving forward. Again when the conveyor speeds up it doesn't stop the wheel from moving forward relative to the ground it just makes it spin faster. The horizontal movement is relative to the ground not the conveyor.

Your right that an aircraft's thrust is not used to directly cause airflow over the wings. They cause airflow over the wings by moving the plane forward through the air, not by moving the air over the wings. I'll say it again. If you can push a plane forward, relative to the ground and air, using engine thrust and gain flight then what is the difference if a conveyor is spinning the wheels forward, backward or you don't even have wheels.

Every action has an equal and opposite reaction.
The thrust of the engines pushing on the air behind the engine is also pushing the plane in a forward direction. When the thrust of the engines exceeds the weight of the plane plus any friction, I assume it hasn't been chained to the ground, the plane moves forward. The wheels spin, if they happen to be on this magic conveyor then they spin very fast but in either case they still move forward relative to the ground. Spin the conveyor in the opposite direction and they don't spin at all but they still move forward. The rate they spin has nothing to do with how fast they move horizontally. You're trying to relate the rate of spin with rate of horizontal movement. If they were in contact with the ground that would be different. The plane takes the wheels with it, they're just along for the ride, spin or don't spin they're still going for a ride.
Remember:
Every action has an equal and opposite reaction.
Apply 100,001 pounds of thrust behind a plane that weighs 100,000 pounds, we'll ignore friction, and that plane is going forward. Ain't no if's, and's, or but's about it. Spinning wheels, no wheels at all, doesn't matter. Once the thrust of the engine exceeds the resistance of the plane, weight, friction, etc., the plane is moving. Somehow you think the rate of the spinning wheels is going to cancel out a basic law of physics.

Apply 100,001 pounds of thrust behind a plane that weighs 100,000 pounds, we'll ignore friction, and that plane is going forward. Ain't no if's, and's, or but's about it. Spinning wheels, no wheels at all, doesn't matter. Once the thrust of the engine exceeds the resistance of the plane, weight, friction, etc., the plane is moving. Somehow you think the rate of the spinning wheels is going to cancel out a basic law of physics.

I agree with everything else you said, but this part is simply not true.

100,000 lbs of thrust is not needed to propell an object weighing 100,000 lbs.In fact it is much much less. Given it is on wheels, as is the subject of the topic here.

If this was the case, you'd need to produce 4000 lbs of thrust from your body to move your 4000 lb car by pushing it. In my prime I might have leg pressed 500 lbs at the local gym. I know I'd never do anything with 4000 lbs !!

You're getting into a very complicated area here. You have to take in to acccount rolling resistance caused by many many variables. Obviously, you're going to push your car easier with skinny tires inflated to 50 lbs each on a smooth level surface VS uphill with flat tires !!!

N~

Thrust required to move a craft is determined by fully loaded craft weight. It requires 10,000 lbs of thrust to propell an object weighing 10,000 lbs straight up, at a horizontal level this is a totally differnt story. The average human man can a hold a jet in place against it's afterburner, at full throttle with one hand....until that plane moves forward any amount, then look-out!

Meaningless jet tech since the topic of thrust vs. weight came up.

I agree with everything else you said, but this part is simply not true.

100,000 lbs of thrust is not needed to propell an object weighing 100,000 lbs.In fact it is much much less. Given it is on wheels, as is the subject of the topic here.

If this was the case, you'd need to produce 4000 lbs of thrust from your body to move your 4000 lb car by pushing it. In my prime I might have leg pressed 500 lbs at the local gym. I know I'd never do anything with 4000 lbs !!

You're getting into a very complicated area here. You have to take in to acccount rolling resistance caused by many many variables. Obviously, you're going to push your car easier with skinny tires inflated to 50 lbs each on a smooth level surface VS uphill with flat tires !!!

N~

Yup, you're right. I should have said a plane that provides 100,000 pounds of resistance, not a plane that weighs 100,000 pounds. Me bad, sorry.

So anyway I think we should get back to the photons.

Not to sound like nerd but they don't have weight since they don't have mass. Weight is the affect of gravitational influence on an objects mass. The affect on solar sails is referred to a radiation pressure or relativistic mass. Not the same as conventional mass.

Wow! 9 pages already, this post has taken off faster than a plane on a conveyor belt.

I gave up reading all the replies since the answer has been said over and over and people still want to argue with it. What have the wheels got to do with flight, absolutely nothing. Spin them forward, spin them backward, lock them up with the brakes, if strong enough the engines will still move the plane forward and when the correct speed is reached, airflow over wings, you're airborn. Seaplanes don't use wheels, how do they fly? Wheels are just a lot cheaper than replacing the belly of the plane after every take off. Also makes landing a bit smoother. Other than that they have absolutely nothing to do with flight. Replace them with teflon pads, no rotation what so ever, you'll still get airborn. Replace them with a mag lift, even less friction, still no wheels and you're airborn. Take them off and replace them with nothing, scrape the belly of the plane off during takeoff, you'll still get airborn. Seems everyone agrees you don't need wheels to fly a plane but having them can stop you from flying a plane?:clonk: This is the best yet, thanks Hank, the airplanes' gonna fly, the thrust is not limited. Daren:thumbsup:

So we all agree the plane flies, right? ;)

So we all agree the plane flies, right? ;)

It certainly will take off and fly with no problems. The wheels will be spinning at twice the normal rate, but that shouldn't bother things too much.

Whoh, nice thread discussion.

You guys can kick the crap out of me now :p

I thought the plane would fly, the wheels don't have much to do with getting the plane up in the air they are just a support system.

With the conveyor belt in place though, the wheels will be spinning much faster than without it, hope they are Z rated ;)

The only thing that would stop this movement would be big brakes or a wall. The planes engines would overpower any friction created in the bearings and tires on the ground and it would lift off like normal.

Using the sea plane example (possibly a weak arguement), would the plane not take off if the water current all of the sudden opposed the indicated airspeed (like the conveyor) that the plane was creating or attempting to create? The plane would still move forward and take off I say.

For the sea plane: Depends if there is enough friction between the moving water and the pontoons to negate the thrust. Just a guess but I don't think 50mph water would produce enough friction on the plane to negate 50mph worth of thrust.

This is different from the wheels and conveyer because there is almost no friction between those.

Another point/view,

Let's say one has a dead car on a conveyor belt under the same conditions as the plane and cannot move with it's wheels theoretically. But let's tie a rope to the bumper and pull it forward, can this car create forward momentum this way? If the tow car in front can overcome the fricional forces applied from the dead car on the conveyor I say yes because it has an outside force being applied to it so it can get off the conveyor. Same thing applies to the jet, the thrust is the rope so to speak.

Don't know if this made sense.

OMG, this has made it here too. I've been on this debait over at the Myth Busters forum on this for weeks. I then took it to an Aircraft forum and asked them, that got them started on it. I said I wouldn't bring it here, but I see it's has a life of it's own. I say no way it won't fly. This will never end.

Newton's Law of motion (don't recall which one),


Newton's Third Law






This should have been a poll!!!


The plane WILL fly. It will fly and fly and fly, and it won't even fly off the edge of the world, because the Earth is round...or is that another thread? I even fullfilled the request for colour.



I've wasted far too much of yesterday's workday on this ;) A lot of funny concepts on here, when you picture them.

Funny that its on Mythbusters because a practical system can never be built...

No, it doesn't - that's the trick of the question. Wheels don't make planes move, propellers or turbines do. The wheels are irrelevent. There is no possible way the conveyor can have any effect on the thrust of the prop or turbines, only wind-speed can, which as stated in the problem, there is no wind, so it won't be effected.

Put a car on the conveyor, and it will stay still because it is driven by the wheels. Put a rocket on the car, and it will accellerate even if the car is in neutral, no matter what the ground below it does.

What you say is true, but that's not the issue here. They are not saying the wheels are turning the conveyor like in a car. They're saying the conveyor can compensate for the turning of the wheels, which is a function of the plane's propulsion system. As the plane's engines try to push it forward (and, in turn, cause the wheels to rotate) the conveyor compensates.

I've wasted far too much of yesterday's workday on this ;) A lot of funny concepts on here, when you picture them.

Funny that its on Mythbusters because a practical system can never be built...Ditto :D

A practical model would be a hot-wheels car on a treadmill with a bottle-rocket taped to the roof. All you need to do is prove motion, and the flight part takes care of itself after that.

What you say is true, but that's not the issue here. They are not saying the wheels are turning the conveyor like in a car. They're saying the conveyor can compensate for the turning of the wheels, which is a function of the plane's propulsion system. As the plane's engines try to push it forward (and, in turn, cause the wheels to rotate) the conveyor compensates.


Yes, we know, but wheel speed does not necessarily equal ground speed.


See tire scrubbing example, belt sander, etc way way above.

IT WILL FLY! The wheel motion is NOT a function of the planes propulsion system, directly. This is where you guys go wrong. Rather it is a function of forward movement, which is a function of the propulsion system. Wheel speed is a side effect of forward motion, not a prerequesite.

So all of those in the "Flat Earth Society" :) tell me where the energy of the thrusters is expended, if not in motion, since it is not expended into the conveyor which is turning?

This is getting a little silly, I'm sorry to say. I can only dream up so many examples of how motion is possible.

OK...Nevermind the wheel speed and the conveyor speed and the "no wind" and the color of the pilots eyes and if it is winter or not...Is the friggen plane moving relative to the AIR (not to be mistaken for wind)?

After 11 pages of reading I for one am glad that this didn't turn into a "big discussion"...

They're saying the conveyor can compensate for the turning of the wheels, which is a function of the plane's propulsion system. As the plane's engines try to push it forward (and, in turn, cause the wheels to rotate) the conveyor compensates.
All the conveyor would do then is make the wheels spin faster.

- The plane needs to move before the wheels will roll, correct?
- The conveyor spins the opposite direction, thus making the wheels spin faster but does NOT slow the planes movement.

Lets just say the conveyor can spin 1,000,000,000mph
The plane takes off at an airspeed (same as groundspeed if no wind) of 100mph.
All the plane needs to do is reach 100mph airspeednot conveyor-speed
As soon as the plane moves 1mph, the conveyor goes the opposite 1mph - this doesn't stop the plane, it just makes the wheel spin 2mph. The conveyor will try to compensate, but the wheel will always be 1mph faster than the conveyor if the plane is moving 1mph. The conveyor will quickly reach 1,000,000,000mph, but guess what - the wheel is going 1,000,000,001mph because there is NOTHING stopping the plane from moving.

The plane will still take off when it's moving 100mph, even if the wheels are spinning 1,000,000,100mph.

Now lets use this same problem with LANDING the plane at 100mph.
The only difference is it's propulsion is now momentum rather than thrust.

When the wheels touch the magic conveyor, would the plane stop dead from 100mph as soon as it touches? NO The wheels would roll at whatever speed the plane is going + the speed of the conveyor while the plane moves forward like it normally does.

...So what is the ground speed of the conveyor that the plane is sitting on?

...So what is the ground speed of the conveyor that the plane is sitting on?approx 1000mph (roughly the speed of the earth's rotation depending on your distance from the axis (N & S pole) :D :waving: J/K

It is 0mph... the belt can go as fast as it wants, but the conveyor system is not travelling anywhere.

The only way that plane wouldn't take off is if the entire world would spin the opposite direction of the wheels and match wheel speed. Otherwise the planes ground speed from the thrust will overcome the wheel/conveyor speed and take off.

I like the previous example with the car.

Lets assume you have a car on a conveyor belt and you put the car in neutral, no drive to the wheels. If some one ahead of the conveyor with a truck were to hook a rope to the car and pull, it would come off the conveyor. Why, because of a force acting independent of the wheels and conveyor. The conveyor can only react to wheel speed of something ON the conveyor, a force not connected to the conveyor will move it forward. The wheel speed of the car on the conveyor may be 100mph, but the speed of the truck would only need to be 1 mph to get it to move forward, because it is not connected to the conveyor. The only way this wouldn't work is if the entire world was the conveyor. But that is not the question, the question is a fixed size conveyor.

Same thing with the plane except in the case of the plane the outside thrust is connected to the plane in the form of jets. The thrust pushes on air, not the conveyor belt. The wheels and belt could spin at 1000mph and the plane could move forward with thrust pushing on air.

Jeff

if the entire world was the conveyor


Well, if the world is flat, maybe we can try this....

:D

The only way that plane wouldn't take off is if the entire world would spin the opposite direction of the wheels and match wheel speed. Otherwise the planes ground speed from the thrust will overcome the wheel/conveyor speed and take off.
Last I checked, the world does in-fact spin ;)

This goes back to relative motion. The air moves with the world, so the plane can fly as long as the air moves under it, even if it matches the speed and direction of the world's rotation.

The only way the plane wouldn't fly is if it were in a vacuum. No air = no thrust and no lift.

If a plane is only capable of 100mph and there was a 120mph headwind, the plane would still fly just fine, but it would go backwards 20mph. Turn the plane the other direction and it's capable of 220mph.

I believe the problem needs a further definition of the speed-of-the-wheel. From basic dynamics the linear velocity of the point of a spinning wheel that contacts the ground equals the ground’s speed, otherwise there would be slipping (skidding). If by the term speed-of-the-wheel you were referring to the ground intersection point then the conveyer would never move. If speed-of-the-wheel means the linear velocity of the center of the wheel then the plane never moves and the ground reacts all of the planes thrust. Or are talking about rotational velocity?

The only way that plane wouldn't take off is if the entire world would spin the opposite direction of the wheels and match wheel speed. Otherwise the planes ground speed from the thrust will overcome the wheel/conveyor speed and take off.

I like the previous example with the car.

Lets assume you have a car on a conveyor belt and you put the car in neutral, no drive to the wheels. If some one ahead of the conveyor with a truck were to hook a rope to the car and pull, it would come off the conveyor. Why, because of a force acting independent of the wheels and conveyor. The conveyor can only react to wheel speed of something ON the conveyor, a force not connected to the conveyor will move it forward. The wheel speed of the car on the conveyor may be 100mph, but the speed of the truck would only need to be 1 mph to get it to move forward, because it is not connected to the conveyor. The only way this wouldn't work is if the entire world was the conveyor. But that is not the question, the question is a fixed size conveyor.

Same thing with the plane except in the case of the plane the outside thrust is connected to the plane in the form of jets. The thrust pushes on air, not the conveyor belt. The wheels and belt could spin at 1000mph and the plane could move forward with thrust pushing on air.

Jeff
Yes, I think Jeff has explained this very well. At first i thought it would not fly because of the Car/Dyno analogy. I think the plane will move wheels might spin faster then normal but it's jet engines should be powerful enough to overcome this drag/spin simply because movement is generated from a source outside the wheels themselves.

:clonk: My heads spinnin'
:clonk: Sure could use you guys to help me balance my checkbook

I havent read any of the responses yet, I just came straight here to post
my ignorance..

Yes, it can take off.
Unless your twisting your definition of the conveyor MATCHING the wheels speed, or some other tricky twist of facts.

The reason it can take off, is, the engines are pushing the airframe, the wheels aren't pulling the airframe. The engines could care less how fast the wheels are turning. The airplane would accelerate to take off speed and take off.
The wheels on the other hand are really going to be spinning fast.
The engines still don't care.

Now I'll go back and read..


I read.....WOW. :eek:

Would it help to visualize the airplane with skis instead of wheels?
Think if the landing gear as a means of eliminating the friction between the airframe and the concrete/conveyor and thats all.
The wheels turn freely on the axel, they are not pulling the airplane.
The engine is pushing it.

Didn't read all of the responses but, the plane needs to move forward for the wheels to turn. If the converer belt moved to counteract the wheel turning, then the plane would take off and leave the conveyer with the wheels not turning. It would still fly however, as the wheels have nothing to do with the movement of the plane.

Yes, we know, but wheel speed does not necessarily equal ground speed.


See tire scrubbing example, belt sander, etc way way above.

IT WILL FLY! The wheel motion is NOT a function of the planes propulsion system, directly. This is where you guys go wrong. Rather it is a function of forward movement, which is a function of the propulsion system. Wheel speed is a side effect of forward motion, not a prerequesite.

So all of those in the "Flat Earth Society" :) tell me where the energy of the thrusters is expended, if not in motion, since it is not expended into the conveyor which is turning?

This is getting a little silly, I'm sorry to say. I can only dream up so many examples of how motion is possible.

But there is no forward motion at all, and that's the key to the problem. It's the same as saying "On a conventional airstrip, if I apply the brakes and power the engines, can I take off?" If it's stated that the brakes, tires, etc. are sufficient to prevent forward movement, the plane can't take off.
These kinds of problems are interesting and fun because they get your mind going and subject you to different opinions and perspectives.

But there is no forward motion at all, and that's the key to the problem. It's the same as saying "On a conventional airstrip, if I apply the brakes and power the engines, can I take off?" If it's stated that the brakes, tires, etc. are sufficient to prevent forward movement, the plane can't take off.
The key to the question is that the only physically possible way for the conveyor to match the wheel-speed, is if the plane is not moving (V=0).
But there's nothing a conveyor can do to a plane with free-rolling wheels to prevent movement of the plane, no matter what speed it can go.

It's a bogus question, because it doesn't say anything about the plane's power, just the conveyor's speed (which has very little effect on the plane's speed)

What I had in my very tired minds eye last night was an RC airplane on a treadmill, lots of beers involved, and two guys trying this at home. One believer, and one non believer. Just who is going to do the explaining to the one persons' wife about said plane stuck into the wall, car, fridge etc. This is what kept me going until page 10 last nite. Daren

Ok, when an airplane lands, the wheels aren't turning at all.
Why doesn't it stop immediatly?
Its because the wheels are matching the airframe speed, not the
airframe matching the wheel speed.
Same concept as a drive pulley and a driven pulley.
The driven pulley is at the mercy of the drive pulley.
Put a conveyor on the driven pulley and match the speed of the driven
pulley. So? The drive pulley is just laughing at you and is free to do
what ever it wants.

But there is no forward motion at all, and that's the key to the problem.

Part of the key to the problem is not being open to movement. Wheel/conveyor is not necessary the same as movement of the aircraft.

These kinds of problems are interesting and fun because they get your mind going and subject you to different opinions and perspectives

It was fun, but I'm getting tired.

.

You are putting a physical limit on the conveyor, no where in the question does it state that it can't keep up.No matter what speed the plane goes, the conveyor cannot keep up.

If the plane moves 1mph, the conveyor will go 1mph backwards. This will not stop the plane, it simply makes the wheel turn 2mph. The conveyor speeds up to 2mph (to match the wheel speed) and then the wheel goes 3mph while the plane continues to move 1mph relative to the earth, not the conveyor.

I would think some of you have seen this question before but there was a large discussion about it on another board, let's see what you guys think about 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 (http://forums.nasioc.com/forums/showthread.php?t=891480#) at any given time, moving in the opposite direction of rotation.
There is no wind.
Can the plane take off?

I found the fly in the ointment. By the conditions stated, the plane is not allowed to move. Any movement of the plane whatsoever violates the conditions of the problem.

As defined by the problem, and pointed out by DjD, the conveyer can only move at the same speed, but opposite direction of rotation as the wheels.
So, if the wheel spins at 1 rpm. The treadmill produces 1 rpm in the opposite direction, causing the wheel's rotation to return to 0 rpm. As soon as this happens, the treadmill must stop it's rotation (Remember? it has to match the speed of the wheel.) As soon as the treadmill stops, the wheel's speed returns to 1 rpm again and the process repeats itself in a loop. Since the airplane itself is unaffected by the games going on below, it continues to move forward, creating a paradox between the wheels and the treadmill that will simply violate the conditions of the problem as stated.

The only way to stay within the conditions of the stated problem, is if the airplane doesn't move at all. Only then are all conditions met.

A: Flight Canceled.

The only way to overcome this, as someone else pointed out, is to lock up the wheels and drag them.

So, if the wheel spins at 1 rpm. The treadmill produces 1 rpm in the opposite direction, causing the wheel's rotation to return to 0 rpm.

Two wheels, touching, turning in OPPOSITE directions do not lock up, they turn in unison. Ex, two gears of equal size, meshed together. They turn opposite DIRECTIONS, to each other, and always the same speed, but do indeed turn...

How the hell has this managed to go on for 12 pages? Its pretty simple, just pure logic is all it takes, the answer was given about 3-5 posts in. THe wheels/conveyor have nothing to do with whether a plane takes off, the thrust of the engines will propel the plane forward which in turn will create lift and allow takeoff, the wheels have no other purpose but to create as little friction with the ground upon takeoff.

178 posts!

see what happens when the cars are put away for winter.

david

If it wasn't intend to be able to take off, the conveyor woud not have to be as long and wise as the runway; it would only have to be as big as the plane's footprint. So there! ;)

After further consideration (I drive an hour to work and an hour home each day) I have come to the conclusion that I was incorrect. I am no longer a groundhog, I am a FLYboy.

Here is why:

In order for the aircraft to move, the engines thrust air rearward out of the turbines. This action causes the airframe to move forward. This, in turn causes the wheels to rotate. I think we all sort of agree on that part.

Now it gets tricky.

The wheels don't hold the airframe back. They just spin. The THRUST causes the aircraft to move over the ground. The conveyor makes the wheels go twice as fast as the aircraft is moving over the ground. Actually, the conveyor and the wheels will just continually accelerate as the airframe accelerates. As said before, there isn't enough friction in the bearings for the wheels to hold the airframe back.

K

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?I changed my mind too ;) Let's analyze.

"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."

OK, the plane intends to take off, that means the jet engines or props are creating thrust trying to move the plane forward from a dead-stop.

"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 only one possible way this can happen, and that is if the plane is not moving relative to ground speed. (see previously mentioned paradox) Wheel-speed and conveyor speed must be equal and opposite each other, that's what the conveyor is designed to do.

For this conveyor to be an EFFECTIVE design, it must have something in it's design to keep the plane from moving. Ropes, chains, whatever, as long as it can hold the plane which intends to take off from any movement.

Since no forward motion occurs, the wheels do not turn, and the conveyor doesn't either.... makes for a pretty simple design :)

THE PLANE DOES NOT FLY! (sorry for calling you guys knobs earlier :waving: )

I love being a Mechanical Designer... especially a design like this - very simple: NO MOVING PARTS :D

As soon as I can find my Guillow's balsa rubber powered plane, I will dig out the treadmill. If not sensing wheel speed, I can at least try it at different speeds to see if the plane will take off from it. :thumbsup:

K

What were the results of your above test????:DA funnel with a horrible odor ;)

For this conveyor to be an EFFECTIVE design, it must have something in it's design to keep the plane from moving. Ropes, chains, whatever, as long as it can hold the plane which intends to take off from any movement.

I like how you conveniently made this part up to support your thoery.

The fact that the conveyor speed matches the wheel speed does not have to have a logical explanation about how it works. It's part of the question. There is no mention of anything holding the plane or attached to the plane. (rope, chains, whatever....)
Don't try to figure out how the conveyor speed matches the wheel speed. Just assume that it does.

The plane will take off and fly.
I'm sticking by my original post on this question.

Nate

Don't try to figure out how the conveyor speed matches the wheel speed. Just assume that it does.The only way it is possible is if the plane isn't moving. If the plane goes 1mph, wheel-speed will be 1mph faster than conveyor-speed, regardless of how fast the conveyor goes.

My answer is the only way to meet ALL of the parameters of the question.

I'm with you that a conveyor belt cannot stop a plane from moving, but for the conveyor to match wheel-speed, the plane cannot be moving. period.

The only way it is possible is if the plane isn't moving. If the plane goes 1mph, wheel-speed will be 1mph faster than conveyor-speed, regardless of how fast the conveyor goes.

My answer is the only way to meet ALL of the parameters of the question.

I'm with you that a conveyor belt cannot stop a plane from moving, but for the conveyor to match wheel-speed, the plane cannot be moving. period.

You need to open up your mind.

Maybe I can help explain.
What if the wheel speed was 10 million miles per hour ???? Imagine that !!

Just imagine the wheels beginning to turn, the conveyor beginning to turn with them, and then consider the thrust created by the engines. The plane will move forward on the conveyor, just the same as it would if there was no conveyor. All the conveyor is doing is matching the speed of the wheels. The wheels speed will increase more rapidly with the conveyor, vs if the ground was under it, but the conveyor isn't holding the plane in any way !!!

Actually, when I think about this some more, it may be possible that because the conveyor moves in the opposite direction of the wheel travel, the conveyor may actually reduce the rolling resistance of the craft. I would assume that if the conveyor was driven by an outside source and produced no additional drag on the tires, then the plane may in fact move forward easier than if it was in contact with the ground. It may attain the necessary air speed sooner and lift off in a shorter distance, than if it was on the ground ???????

hmmmmmmm????????????

Or would more friction between the tires and the conveyor (because of the increased wheel speed), cause more rolling resistance and cause the plane to require more power/thrust, to attain the necessary air speed for lift off ??????

N~

If the plane is moving (ground-speed) 2mph N, and the conveyor is spinning 1,000,000,000,000 mph S, the wheel-speed would be 1,000,000,000,002. -not the same.

I never said the conveyor belt keeps the plane from moving (in fact, I wrote about 15 responses explaining why it doesn't) but, the conveyor speed and wheel speed cannot be the same if the plane is moving.

If the plane is moving (ground-speed) 2mph N, and the conveyor is spinning 1,000,000,000,000 mph S, the wheel-speed would be 1,000,000,000,002. -not the same.

I never said the conveyor belt keeps the plane from moving (in fact, I wrote about 15 responses explaining why it doesn't) but, the conveyor speed and wheel speed cannot be the same if the plane is moving.

Sure they can !

What relevance is the wheels speed or conveyor speed to the planes speed ???

Think about this scenario. If a plane was flying along in the air with it's landing gear down and there was a majic flying conveyor under the tires that was spinning at 1 mph. Then the planes tires would be spinning at 1 mph, right !
This wouldn't make the plane stall and fall to the ground, would it !

N~

Kinzli get in here ;)

The plane flies.

How about someone on a treadmill with roller skates on, holding on the side handles and start her up. Can you pull yourself forward while you are rolling? Yes, an outside force is influencing your forward movement (your arms), like the thrust of the engines on a plane.

The wheels just move faster.

the conveyor speed and wheel speed cannot be the same if the plane is moving.

While this may be true, this is not what the question states.

The question states that the conveyor speed MATCHES the wheel speed. Think about it.

It doesn't say anything about the conveyor speed and the wheel speed being the same. Hence, the wheel speed will probably be much faster than the conveyor speed because the plane is moving forward and the conveyor is mounted stationary.

N~

have you ever done dyno test,no matter how fast you go you stand still!!!!!!!!!!!!!!! there is no difference airplane or car,it,s like asking if one pound iron is heavier than one pound cotton?

I've not read EVERY response but of the ones I read none seems to have mentioned this......Bernoulli's Principle. With no forward airspeed, therefore no airflow through the venturi (the top of a wing acts as half of a venturi and creates lift through the drop in pressure) there will be no lift and NO flying. There is also the problem with no increase in the angle of attack to the relative wind (of which there is none) so it won't fly.

Here is a link to one persons explanation on beroulli's principle.... http://www.centennialofflight.gov/essay/Dictionary/bernoulli/DI9.htm

I've been a certified flight instructor and airline transport pilot for 20+ yrs and have over 11,000 hours of flight time so I kind of understand how an airplane flies.

After saying all that...I think the question is flawed and not worded in a way that can support any true right or wrong answer but with no airspeed there will be no lift and with no lift there will be NO flight!

...With no forward airspeed, therefore no airflow through the venturi (the top of a wing acts as half of a venturi and creates lift through the drop in pressure) there will be no lift and NO flying. ....with no airspeed there will be no lift and with no lift there will be NO flight!

Who said there was no airspeed? There;'s no wind, but nothing says that the jets or prop can't move the plane forward and build airspeed. Who cares what the wheels or conveyor are doing? Nothing says that the plane is fixed in position, and nothing says it can't build speed. Depending on how you read the conveyor part, maybe it travels in the same direction as the plane, and the wheels don't rotate (but the plane moves forward through the air and takes off) or the conveyor rotates against the planes direction of travel, in which case the wheels turn really fast, but the plane moves forward and takes off. Maybe the coveyor rotates much faster than the plane, in the planes direction of travel, in which case it takes off. (even though it's wheels are now rotating backwards....)

I say it flies. Who cares about the conveyor. The plane is on wheels that have nothing to do with wether it can push itself forward and take off. The jets or prop will move the plane regardless. (unless the parking brake is on... :) )

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?[/QUOTE]

Again, the only way the wheel can attempt to start to rotate is if the plane moves forward by prop or jet propulsion.

If the conveyer moves in the opposite direction of the tire rotation at the same rate, then the wheel does not rotate and the plane gathers air speed without the wheel rotating.

Once enough air speed is attained regardless of tire rotation the plane lifts and is air born. What am I missing here?

Guys, I will point out some things one more time.

The plane WILL fly.


Ok, 1st, 2 wheels in opposition turn opposite directions. If the speed is matched IT DOES NOT MEAN THE WHEEL DOES NOT TURN. It means they are "meshed" together similiar to two gears. If they are the same diam, the same "timing marks" will always line up.

So the wheels don't sit still. It doesn't mean the forward motion is cancelled.

I have heard some guys mention that it is impossible to move forward with the wheels and conveyor linked. Not so. Again, I refer you to the tire scrubbing examples I named way above. Maybe not great examples but examples of wheels linked in speeds and linked to a surface, yet still trying to turn at different speeds by virtue of their diameters and yet still making forward progress.

The engines don't drive the wheels. Wheel motion is a side effect of forward motion, not a prerequisite. The engines WILL produce thrust.

Bernouli's Principle was mentioned, we all understand why a plane lifts off. IMO if you are going to start throwing weight around why everyone is off base you should probably read everyones posts, first.

Thrusters will produce motion, and flight.

This is not fun anymore :)

The plane WILL fly.

but for the conveyor to match wheel-speed, the plane cannot be moving. period.

but, the conveyor speed and wheel speed cannot be the same if the plane is moving.

Sure it can. Don't forget about acceleration! The conveyor instantly matches any change in the planes wheel speed (rpm).

Think about it this way. You have a scale model airplane in your hand and, while continuing to hold it, you place it in contact with a conveyor rotating at 1 rpm. The plane's wheels are now rotating at the same 1 rpm as the conveyor. Now you push the plane forward. The plane's wheel speed increased to say 1.5 rpms and the conveyor instantly accelerates to 1.5 rpm to match the wheel speed of the plane. They MUST accelerate at the same rate because they are in contact with each other. Of course, the assumption is that there is no slippage. This would work the opposite way too. While you're holding the plane, the conveyor speeds up. The plane's wheels speed up the EXACT same rate to match the conveyor. Getting back to the part where you pushed the plane forward. Your arm produced thrust the same way the planes engines would produce thrust. Did the airplane move? YES! This movement produces airflow under the wings! THE PLANE WILL FLY! As the plane is moving forward (accelerating) the wheel speed (rpm) keeps accelerating. The conveyor speed (rpm) is instantly matching the plane's wheels. They are both accelerating and will continue to until the plane lifts off.

Now you push the plane forward. The plane's wheel speed increased to say 1.5 rpms and the conveyor instantly accelerates to 1.5 rpm to match the wheel speed of the plane. They MUST accelerate at the same rate because they are in contact with each other. Of course, the assumption is that there is no slippage. This is where I disagree, but lets change RPM to MPH (wheel is not same circumference as length of the belt.)

If the plane moves forward 1.5mph, and the belt moves backward 1.5mph, the wheels are going 3mph. The belt will instantly go to 3mph (to match wheel-speed), but now the wheels are now going 4.5mph. Wheel speed is always conveyor-speed + plane speed. The only way conveyor speed = wheel speed, is if the plane speed = 0.

Did the airplane move? YES! This movement produces airflow under the wings! THE PLANE WILL FLY!
The plane did move, but the conveyor speed wasn't the same as wheel-speed, which is one of the parameters of the original question. Which is why my answer is that the only way it is possible to meet ALL of the required items is if the plane is acted on by another force. There is no outside force mentioned, but the part about the what the conveyor is designed to achieve, leaves the "design" open to whatever it takes to achieve it, whether it is ropes, chains, or a giant robotic arm that holds the plane in place so that conveyor-speed can be equal to wheel-speed.

Now that this is in place, there is no movement of the plane, which will not create movement at the wheels, which means the conveyor doesn't need to move either. V=0 is the only way to meet all parameters of the original question. :)

The original question says "speed" which I take to mean rotational speed which is rpm. The conveyor is stationary. It's analogous to a runway. It doesn't move. It only rotates.

You're correct though, the rpm's can't be the same because of the difference in diameters of the plane's wheels and the conveyor. But there's some ratio there that remains constant as the rpm's increase or decrease and that's what I was trying to illustrate, albiet poorly.

Take a 10" diameter gear with 60 teeth and mesh that together with a 5" diameter gear with 30 teeth. Rotate the 10" gear at 10 rpms and the 5" gear will rotate at 20 rpms. A 2 to 1 ratio that remains constant no matter how fast you rotate the gears. Same ratio our Chevy V8 engines have between the crankshaft and camshaft no matter what rpm the crank spins at.

What I think the question intends us to assume is that the rotation of the plane's wheels is offset by the rotation of the conveyor. Just like a car strapped to a chassis dyno. The car's wheels rotate at a different rpm than the dyno's drum but they offset each other and the car doesn't move forward. So, looking at my example again, if you're holding the model plane stationary on a rotating conveyor, and the rotational speed of the conveyor increases while you're still holding the airplane stationary (static), the rotation of the plane's wheels will also speed up. If you push the plane forward (thrust), the wheel's rotational speed increases and the conveyor's rotational speed also increases maintaining the static ratio. But the plane is moving forward.

The bottom line is, no matter how fast the conveyor spins, engine thrust will push the plane forward and it will take off.

This is fun :D

A lot of this is open to interpretation of the question.

Keith, You're looking at it with your aviation background, seeing how a conveyor belt will not effect forward movement of an airplane.

I'm looking at it from the viewpoint of the guy who has to check the design of the conveyor to be sure it works as specified before the conveyor is even built. My interpretation is that if the conveyor doesn't spin equal and opposite the plane-wheels, the design is flawed.

oh my - look at what jeff did
I've seen it all now
time for another rum and coke

can't understand why they think it won't fly
1. a plane doesn't need wind to fly - it will get it's lift from it's own movement
2. the wheels will spin at twice the speed
3. what is on the ground is not going to affect the thrust of the engines that are above the ground
4. ------ bet you there is a bunch of wind behind those engines though ----

This is fun :D

A lot of this is open to interpretation of the question.

Keith, You're looking at it with your aviation background, seeing how a conveyor belt will not effect forward movement of an airplane.

I'm looking at it from the viewpoint of the guy who has to check the design of the conveyor to be sure it works as specified before the conveyor is even built. My interpretation is that if the conveyor doesn't spin equal and opposite the plane-wheels, the design is flawed.
Did GM build the conveyor?

Here's some more thoughts for you who think that the plane will fly:

Imagine that the plane is rolling on a normal runway. Instead of a conveyor moving at the same speed as the wheels, you have a strong wind coming in from behind the plane. The wind speed matches the speed of the plane at all times. This is exactly the same problem, but turned around a bit (the plane is actually moving, related to the world around it). It's pretty obvious that the plane won't fly, as the wind speed always matches the plane's speed.

The original problem has a serious flaw though. Having the conveyor move at the same speed as the wheels is the same thing as not allowing the plane to move at all. If you think about it: The only way to start the conveyor would be to move the plane, but one of the postulates in the problem prohibits this. This means that you can't initiate any movement in the system whatsoever.
Time to have a beer and quit thinking about that darn thing. :beers:.

Did GM build the conveyor?it was engineered by african associates and fabrication company incorporated

Here's some more thoughts for you who think that the plane will fly:

Time to have a beer and quit thinking about that darn thing. :beers:.OK - I like your thinking

PEOPLE! THE GOSHDARN@##$%^%$#@$%$#@% PLANE WILL FLY!!! 'NUFF SAID. Steve

PEOPLE! THE GOSHDARN@##$%^%$#@$%$#@% PLANE WILL FLY!!! 'NUFF SAID. Stevedude --- your head just popped
now who is gonna clean that up :D

ok so 67chevy2 was parked in his microwave garage
while he was hanging out on his computer at the workbench
his wife walked up to the dial that sets the time (thinking it was the thermostat to turn up the heat 'cause she was cold) - which is mounted just to the left
just about the time she was hearing beep beep beep - she also heard pop
was his head in flight at the time of the pop - or shortly after?

So is anyone gonna reveal the true answer to this mystery or is it one of those things that's gonna get debated forever?

forever

no it will

NO or IT WILL?????


Just my eyes popped, not my head. Steve

Just my eyes popped, not my head. SteveI saw your head in that microwave oven
eyes popped compared to what I saw (pile of ashes)
I sure ain't buying a car from you
it would be a 6 cyl car turned into an ss w/ documentation:D

oh and the plane is will aren't not gonna maybe fly

I saw your head in that microwave oven
eyes popped compared to what I saw (pile of ashes)
I sure ain't buying a car from you
it would be a 6 cyl car turned into an ss w/ documentation:D

oh and the plane is will aren't not gonna maybe fly


WTHDYJS??????

I'm telling ya - it is the honest to goodness answer to the question
which question I'm not sure but a question
question didn't make sense so the answer was eqaully confusing
YEAH RIGHT
the plane will fly - or the fly will crash with the plane it is on
:confused: :confused: :confused: :confused: :confused: - hey this is my brain

Well, the plane takes off then crashes after reaching 100ft.

What's the record of the most posts in BR?

[QUOTE=THORSS70]Well, the plane takes off then crashes after reaching 100ft.

Tank Q.

Well, the plane takes off then crashes after reaching 100ft.

What's the record of the most posts in BR?not sure if it was a record but there were two threads that reached 1000 posts in bench racing within the past year
but they crashed 100 feet after the 1000 mark
jeff angerstein locked them up and said they had run their courses

Conveyer-Belt Runway



http://www.avweb.com/newspics/cartoon_fight.jpg

What I learned from Old Hack was that an updated version of a question aimed at confusing folks over relative measurements of airplane motion and the medium in which it operates had shown up on the Internet, and it was causing the fracas in the Lounge.
The question that has been going around is not particularly artfully worded, and I think that has caused some of the disagreements, but I'll repeat it as it is shown: "On a day with absolutely calm wind, a plane is standing on a runway that can move (some sort of band conveyor). The plane moves in one direction, while the conveyor moves in the opposite direction. The conveyor has a control system that tracks the plane speed and tunes the speed of the conveyor to be exactly the same (but in the opposite direction). Can the airplane ever take off?"
My comment: Notice that the question does not state that the conveyor's movement keeps the airplane over the starting position relative to the ground, just that it moves in the direction opposite to any movement of the airplane.
Initially, about a third of the folks here said that the airplane could not ever takeoff, because the conveyor would overcome the speed of the airplane and it could never get any airspeed. The rest said the airplane would fly.
The "It won't fly, Rocky" group said that the conveyor would hold back the airplane. They asked us to imagine a person running on a treadmill. As he or she sped up, the treadmill would be programmed to speed up, just as the conveyor in the problem, and the person would remain over the same locus on the earth, while running as fast as possible.
The argument was that if the airplane started to move forward, the conveyor program was set up to move the conveyor at exactly that speed, in the opposite direction, thus, the airplane would never move relative to the ground, and, because the air was calm, it could never get any wind over its wings. One of the analogies presented was the person rowing at three mph upstream in a river on a calm day. However, the current was flowing downstream at three mph, so the resultant speed with reference to the stream bank and air was zero, and thus there was no wind on the rowboat.
I watched and listened to the disagreement for a while and was fascinated to see that the argument seemed to split between those who had some engineering or math background, all of whom said the airplane would takeoff and fly without any problem; and those with some other background, who visualized the airplane as having to push against the conveyor in order to gain speed. Because the conveyor equaled the airplane's push against the conveyor, the airplane stayed in one place over the ground and in the calm air could not get any airspeed and fly.
It was an interesting argument, but as things progressed, more rational heads prevailed, pointing out that the airplanes do not apply their thrust via their wheels, so the conveyor belt is irrelevant to whether the airplane will takeoff. One guy even got one of those rubber band powered wood and plastic airplane that sell for about a buck, put it on the treadmill someone foolishly donated to the Lounge years ago, thinking that pilots might actually exercise. He wound up the rubber band, set the treadmill to be level, and at its highest speed. Then he simultaneously set the airplane on the treadmill and let the prop start to turn. It took off without moving the slightest bit backwards.