Will it fly?

I have no idea, but I'm curious for the hive to explain it. I've read some very interesting debates already, that made sense for both sides, but I don't know who to believe.

The plane will take off after reaching the correct air speed. They even did this on smaller scale on myth busters. 
 

If it was a car, it wouldn't move because the propulsion comes from the wheels, which are on the belt moving backwards as they rotate forwards. 

Lift and flight are not dependent on ground speed. A plane uses propulsion from the air. The jet engines do not push from the ground. They push against the air behind them. Same with a propeller. The conveyor belt is irrelevant since it has nothing to do with air speed, which is what causes lift and flight. 
 

Planes use air speed, and a conveyor belt is ground speed. Unrelated. 
Im not sure how to explain it better. 
 

^ what he said.

An airplane's wheels don't have drive to make them roll, it's the jet pushing the whole craft. Take the wheels off and put skis on it and it will still move.

Imagine pushing a toy car on a treadmill with your hand.

Well yes that part makes sense, engines are on the wings after all.

But would the rolling ground mess with the air pressure?

In reply to RevRico :

If the belt was rolling from front to back on the plane fast enough, it might generate enough lift to get the plane to leave the ground without using it's engines.
If the belt was rolling from back to front, it would create a tail wind, letting the engines generate more thrust.

The KEY factor in this that a lot of people don't take into account is how any RPMs the wheels can take before they fly to pieces. The plane will never lift if the wheels come apart, the landing gear sticks into the treadmill and it gets punted off of the back and breaks. 

Imagine a sea plane. They work on rivers. Same thing here. If you have Hulu I think that episode of mythbusters is available. The guy who owned the plane and tested it for them was wrong. He didn't think it would work. 
 

Now you could have a big fan pointed at the nose of the plane to counteract the effects of the jet engines thrust, and the plane wouldn't move forward, but it would have sufficient lift to leave the ground. It'd be neat to see that done on large scale. 

Brett_Murphy (Ex-Patrón) said:

In reply to RevRico :

If the belt was rolling from front to back on the plane fast enough, it might generate enough lift to get the plane to leave the ground without using it's engines.
If the belt was rolling from back to front, it would create a tail wind, letting the engines generate more thrust.

The KEY factor in this that a lot of people don't take into account is how any RPMs the wheels can take before they fly to pieces. The plane will never lift if the wheels come apart, the landing gear sticks into the treadmill and it gets punted off of the back and breaks. 

Brett,

The word you are looking for with regard to the extra airspeed caused by the treadmill belt is "Entrainment". It is a thing, but very small. For an example, if we run the wind tunnel belt at 175mph (with no wind) the airspeed generated at the nose of the car is ~3mph. That would not be anywhere near enough to induce enough lift on an airplane to get off the ground.

Rev, Without the engines powered your imagined airplane on a treadmill will never take off. With the engines powered up, it would take off almost as if the treadmill were not running, ASSUMING the wheel assemblies don't grenade first from over speeding.

And thus ends today's lesson in imaginary aerodynamics.

I can't believe people this is really a question. Wings work due to air speed. That's all you really need to know.

RevRico said:

Well yes that part makes sense, engines are on the wings after all.

But would the rolling ground mess with the air pressure?

No.  The plane takes off no matter what because the engines are pushing on the ambient air, not on the ground.

The worst case scenario is that the landing gear / treadmill thing goes into an infinite feedback loop and flies apart trying to stop the wheels from rolling forward.  But the airplane takes off regardless.

[edit] ...unless, as noted by Brett above, the wheels fly apart before the airplane makes liftoff speed.  But that has nothing to do with the treadmill preventing the airplane from taking off.

Mythbusters did an episode on this - you can find the video on YouTube, search for 'mythbusters airplane conveyor' or 'mythbusters airplane treadmill'.

barefootskater (Shaun) said:

Now you could have a big fan pointed at the nose of the plane to counteract the effects of the jet engines thrust, and the plane wouldn't move forward, but it would have sufficient lift to leave the ground. It'd be neat to see that done on large scale. 

No, you'd need the fan pointed at the tail of the airplane, not the nose.  Airplanes take off into the wind all the time - it's the preferred direction unless there is absolutely no other choice.  Even with a full tail wind aircraft can still land and take off; it just takes more space and ground velocity.

Everything about an airplane begins and ends with the speed of air moving over the airfoil.

Provided the tires don't fly apart, it will still take off.

And, provided the resulting friction of the tires against the treadmill doesn't offer enough resistance to prevent achieving enough airspeed to provide lift.

So my answer is, if you take those factors out of the equation (friction and tires exploding), then yes, it will take off just the same.  In reality, the question is mathematically impossible to answer.  It's like asking "how big is infinity."

The problem is, as the plane moves forward and the tires roll, the treadmill moves back.  Then as the tires move faster, the treadmill moves faster.  In order for the airplane to move forward (which it will IRL) the treadmill's speed would be squared relative to the actual speed of the plane.  The plane's tire speed will have to increase exponentially higher as the plane accelerates relative to "real" ground speed (not treadmill ground speed).

If the plane is moving forward at 5 mph, the treadmill will be moving 25mph in reverse and accelerating to attempt to stop the plane.  The way the question is worded, it's an exponential impossibility.  If the plane moves forward relative to real ground/air, then the phrase "exactly match the speed of the wheels in the opposite direction" is an impossibility.  The very fact that the plane moved violates the text of the question because the conveyor belt failed to exactly match the speed of the wheels.  In order for the plane to take off, the speed of the wheels must exceed the speed of the treadmill.  If the phrase "exactly match the speed of the wheels" is true, then forward motion cannot happen and the plane can't take off.

The question and its premise is inherently flawed, and it's my guess that it was designed to not be answered in any one way.  It's Schroedinger's Plane.

barefootskater (Shaun) said:

Lift and flight are not dependent on ground speed. A plane uses propulsion from the air. The jet engines do not push from the ground. They push against the air behind them. Same with a propeller.

Minor correction, but jet engines are actually pushing against the exhaust gasses, not against the air around them.  This is why rockets work in a vacuum -- Newton's first law.

And yes, wheel speed is irrelevant to airspeed:

Also think about the planes that are tied down in a severe windstorm.  There are a few videos of planes “trying” to fly, and they have zero ground speed, but a lot of “airspeed” caused by the wind.

The wheels and conveyor would create a feedback loop. It would be a sort of paradox, because wheel speed is not related to airplane momentum.

As pointed out, the jet is propelled by the thrust of engines, not from the wheels rolling.

As soon as the jets reach enough thrust, the plane moves forward. The wheels roll, and the conveyor would roll. But the conveyor would NOT push the plane backwards. The conveyor would cause the wheels to spin faster. Which would cause the conveyor to move faster. Which would cause the wheels to spin faster...

The airplane would accelerate at essentially its normal rate, but the wheels and conveyor would rapidly approach infinity or self destruction.

Put on the brakes.  The tires are locked to a position on the conveyor. Add thrust and the plane accelerates the tread  mill and the plane.  It takes off.

But this violates the tires/conveyor belt in equal and opposite velocities.

So let the tires be rolled forward by engine thrust and some motive power moves the conveyor belt the opposite direction.     

Plane still takes off, not caring that the  tires are being spun really fast by the conveyor belt in order to keep up. 

Probably twice as fast as they would on a normal take off.  And the matching speeds rule is not violated.  Though the tires probably were not designed for a 300mph takeoff.

The best explanation I've read.  Also, it's XKCD, so you know its good

Basically you can have three interpretations of the problem.  Whether it takes off depends on the interpretation and how far you're willing to compromise physics and mechanical limitations

https://blog.xkcd.com/2008/09/09/the-goddamn-airplane-on-the-goddamn-treadmill/

In reply to Keith Tanner :

Exactly.  Wings lift , wheels do not

Based on the question of the original post, it's possible, but since the tires will be spinning twice the normal speed, the will almost certainly disintegrate before take off speed.  Once the tires disintegrate it's likely the gear would collapse under the forces involved.

The takeoff speed of a 757 for example, is 160 mph.  Doubling that would mean the tires would need to stay together up to 320mph!  That is HIGHLY unlikely.

Airliners generally have a LOT of excess power.  E.g. a twin engined one needs to be able to safely climb, at full load, with an engine out.  So drag from dragging rims may not be an issue, that is why I suspect the gear would collapse first.  So.... it might make it into the air, but landing again will be a HUGE issue.

Obviously this question is meant to confuse airspeed with wheel speed.  As noted, flight is ONLY concerned with airspeed. The question, as stated, is only about the ability of the landing gear to take twice normal speed (which is a pretty silly question when you think about it that way).

Ya' know, the original question said nothing about using the engines hence the wheels aren't turning, the conveyer (matching the wheel speed) doesn't move AND the airplane sits there.

Disclaimer, I am a smartass and always look for the loophole.

I think we're disregarding the "air speed" of this discusion, lol.

aircooled said:

 

The takeoff speed of a 757 for example, is 160 mph.  Doubling that would mean the tires would need to stay together up to 320mph!  That is HIGHLY unlikely.

Since it is not just speed involved, but acceleration, the speed of the treadmill would have to attempt to square the speed of the tires.... 25,600 mph.

But it's a moot point.  It says the treadmill DOES exactly match, not attempts to.  Therefore the question is impossible to answer as it is based on a physical and hypothetical impossibilities.  If the treadmill exactly matches the wheel speed, it is impossible for forward motion to occur.  Since we're all smart and we know that planse have enough force to overcome a treadmill, it sets up a paradox in our brains and we try to reason through it.  If such a treadmill were to exist, AND if it were able to overcome forward motion, here is how it would happen.  Add thrust to the engines.  As the tires begin to roll, the treadmill would have to move at a speed that generates enough friction in the tires/bearings to overcome the force of the thrust.

This question is internet trolling 101. It's like asking "If your car's engine generates 154hp at peak, what's the price of spinach in Honduras?"  They are completely independent of each other and the internet goes wild trying to explain it.

This is a classic Schroedinger Paradox test.  There is no answer.  The process of critically thinking is the reason for asking.  The problem is, people start to fill in the gaps with additional data to try and solve for X, or they apply real-world hypotheticals to resolve the paradox in their own way.

If you're not intimately familiar with Schroedingers Cat paradox, look it up.  It involves cats dying.... or does it?  There is no answer, and the philosophical process is the intended result, not an answer.

Curtis73 (Forum Supporter) said:

 

But it's a moot point.  It says the treadmill DOES exactly match, not attempts to.  Therefore the question is impossible to answer as it is based on a physical and hypothetical impossibilities.  If the treadmill exactly matches the wheel speed, it is impossible for forward motion to occur.

You have to define wheel speed.  Is wheel speed the speed that the axle travels at?  Is it the speed that the outer diameter of the tire is seeing?  Is it something else?

Respectfully sir, I am pretty certain you are incorrect. The OP says "matches the speed of the wheels... in the opposite direction".   I am not sure how the treadmill will sense this speed, since there are no acceleration forces on the wheels.  I would have to assume it somehow knows the airspeed.

When the plane accelerates to 10 mph, the belt would turn at 10 mph, in the opposite direction (making the wheel speed 20 mph, 10 mph airspeed + 10 mph reverse treadmill movement).  The drag of the wheels turning twice the speed will be very minor (other then the whole eventual exploding thing).   I am sure there is some drag (bearings, tire deflection etc.), but it cannot be that large.  I am sure the wheel drag on a land speed car is very small compared to the air drag.

It is obviously pretty nonsensical question in general. The confusion (it's meant to create) is that if you put a typical car on the treadmill, which is powered through it's wheels, matching the speed will make the car not move.  Move the power of the car from the wheels to a rocket in the trunk, and there are no acceleration forces on the wheels.  If the treadmill was setup to sense the acceleration forces (which makes the most sense), with the rocket car, the car would accelerate as normal, and the treadmill would not move.  If the treadmill was setup to match the airspeed of the car (probably the most reasonable way to interpret "matches wheel speed in the opposite direction") then it would simply double the wheels speed.

To be clear, I think your interpretation of "matching speed" seems to imply that the treadmill will attempt to stop the forward motion of the plane with opposite movement of the treadmill.  In that case, yes, the treadmill would have to accelerate to some insane speed rather quickly since there is very little drag from the wheels (even at high speed), and a LOT of power from the plane.  In that case, by definition, the plane could never take off (it would never generate any air speed) and I suspect, the tires would disintegrate within seconds.

Anyway, interesting, if not slightly silly, thought experiment. 

Mr_Asa said:

Curtis73 (Forum Supporter) said:

 

But it's a moot point.  It says the treadmill DOES exactly match, not attempts to.  Therefore the question is impossible to answer as it is based on a physical and hypothetical impossibilities.  If the treadmill exactly matches the wheel speed, it is impossible for forward motion to occur.

You have to define wheel speed.  Is wheel speed the speed that the axle travels at?  Is it the speed that the outer diameter of the tire is seeing?  Is it something else?

This is my point and you're brilliant for bringing this up.... It's not the answer, it's how you reason with the question.  It's a hypothetical question with no answer.  The point of Quantum Superposition and Copenhagen Interpretation is that there cannot be an answer.  Just like with Schroedinger's Cat... the cat is both alive and dead.  In this question, the plane both flies and doesn't.

One of the originators of the Copenhagen Interpretation was Werner Heisenberg who believed that the observation of quantum phenomena was discongruent with the actual phenomena and therefore can't be intrinsically observed at all, thereby implying there was a sharp cut between the phenomenon and the observer or instrument.  Much like the conundrum of contemplating if the color red looks the same through your eyes as it does mine.  (Also, hence why Walter White chose the pseudonym "Heisenberg" as his drug name... symbolically separating his criminal life from being observable by law enforcement)

In this way, several thought experiments (like Schrodinger's Cat) were designed as ways of quantifiably and mathematically attempting to theoretically define that which can't be defined - quantum mechanics.

These types of questions are theoretical and DO NOT HAVE AN ANSWER.  They have a process

Edit to continue because I hit the wrong button:  Take for instance the age old question... if a tree falls in the woods and no one is there to hear it, does it make a sound?  Classic philosophy.  People try to answer it in one of two ways:  A) sound is the generation of pressure waves in the medium around it, so yes, it makes a sound, or B) sound isn't really sound unless it crosses that medium and is observable by an ear or recording device, so it isn't sound unless it's heard.  (basically, since no one heard it, it wasn't sound)

In both of those conclusions, we added variables to the argument.  We applied further data to reach a conclusion.  The answer is not the reason for the question.  The thought process is the reason.  Just like this Airplane/Treadmill question.  The point is the process, not a yes or no answer.