A plane on a treadmill - physics question

[Andy D]

What would happen is the plane would pitch forward and probably would flip over to it's back.

 

[ScottM]

LOL, funny thread. Amazing how you can take a physics problem, apply only 'a' perspective of those laws and get it completely wrong, but think you are right, or at least there is a conundrum created. (Any problem really, welcome to the echo chambers)

Airplanes 'fly' based on relative air movement past the aircraft surfaces, not how fast the wheels are spinning. I don't think there are any 'standard aircraft' where the wheels actually have drive mechanisms to move the aircraft. They always use the method of propulsion to move on the ground the same as they would use in the air when moving themselves. That would be expanding air from a jet, or physically moving the air like a fan does.
Pilots know that it doesn't matter what the ground speed is, or even what the true airspeed is, Indicated Airspeed is the master, that tells you the amount of air moving across the wing and if you are flying or falling. You always fly IAS (straight and level flight) to determine that.

I think in the case of the original premise, the result would be a lot more tire and bearing wear, but the aircraft would accelerate and fly as normal because its still moving the air, as planes don't move the ground

 

[bob]

Of course it will take off. It doesn't matter how fast or in what direction the wheels are turning. it's the plane's engines that drive it forward, not the wheels.

 

[Andy D]

Airplanes 'fly' based on relative air movement past the aircraft surfaces, not how fast the wheels are spinning. I don't think there are any 'standard aircraft' where the wheels actually have drive mechanisms to move the aircraft. They always use the method of propulsion to move on the ground the same as they would use in the air when moving themselves.

There is no confusion about what propels the plane; it's the thrust of the engines, not the wheels, the engine's thrust is independent from the ground & the wheels are free moving, not motorized...That is understood, Okay?
But the wheels are just as critical to flight as the wings and engines... answer this one question:
A plane must be moving forward at around 180mph to take off, how will a plane move forward if it's wheels cannot go faster than the ground?

 

[ScottM]

There is no confusion about what propels the plane; it's the thrust of the engines, not the wheels, the engine's thrust is independent from the ground & the wheels are free moving, not motorized...That is understood, Okay?
But the wheels are just as critical to flight as the wings and engines... answer this one question: how will a plane move forward if its wheels cannot go faster than the ground?

The only scenario where that would actually apply is if the tires or bearings fail due to over speeding creating brakes. The wheels could be spinning at 500 mph, and while there would be the obvious gyroscope effect, if the aircraft's thrust was able to accelerate it in relation to the relative wind, not the ground plane or wheel speed, it would still takeoff.

For example, an aircraft could, and has, taken off without any ground roll at all in high winds or micro-bursts, the wheels never turned at all. Its the movement of air that is important, not how fast the wheels are, or are not spinning.

 

[Andy D]

when the wheels are traveling at 500mph, the treadmill is also traveling at 500mph
when the wheels are traveling at 10,000mph, the treadmill is also traveling at 10,000mph
when the wheels are traveling at the speed of light, the treadmill is also traveling at speed of light.....
That plane ain't going anywhere...

 

[Andy D]

For example, an aircraft could, and has, taken off without any ground roll at all in high winds or micro-bursts, the wheels never turned at all. Its the movement of air that is important, not how fast the wheels are, or are not spinning.

That would be an example if the treadmill was propelling the plane forward, into high winds.

 

[Gino]

But if you had a helicopter or whirlybird, you don't even need a tread mill. You can use a milkbox.

 

[ScottM]

That would be an example if the treadmill was propelling the plane forward, into high winds.

And don't forget, when a airplane is flying and makes a turn downwind it has to speed up to keep from falling out of the air as well...

 

[Andy D]

But if you had a helicopter or whirlybird, you don't even need a tread mill. You can use a milkbox.

Gino, please try and stay inside the lines of the premise.

 

[Andy D]

I think your tying the speed of the wheels to the speed of the plane too much. Think of the wheel as a frictionless plane. Much like two sheets of 3m backing, setting face to face (ie; the slickest surface known to man). Sure, the treadmill is going to explode trying to go backwards faster than the plane, but since there is no friction, it has no way to enact force on the plane.

I'm actually saying that the plane won't move more than a few inches.
When the plane 1st nudges forward the treadmill would speed up to match the wheel speed & because of the downward force of gravity, nudge it back, regardless of the free moving wheels.
The force the engines thrust and the treadmill matching speed would cause a chain reaction, & the wheels would be moving incredibly fast within a millisecond... The only thing that would be flying would be the wheels, when they flew off the plane..

 

[Gino]

I think this whole thing is for naught. I've never seen a treadmill big enough to hold a frickin' plane, .let alone go much over 15mph. Who in the heck is gonna make this humongous treadmill for Andy ??

 

[MikePatterson]

To answer your question. Who cares!!! But yes the plain will take off.

If a plain is flying 400 and there is a fly inside the cabin flying from tail to nose at 2 mph? Is the fly flying at 402 or just 2?

 

[Andy D]

I think this whole thing is for naught. I've never seen a treadmill big enough to hold a frickin' plane, .let alone go much over 15mph. Who in the heck is gonna make this humongous treadmill for Andy ??

LOL, Gino mind exercises keep your mind sharp... plus I'm enthralled with physics and other sciences, I listen to is those types of podcasts when I can.

If a plain is flying 400 and there is a fly inside the cabin flying from tail to nose at 2 mph? Is the fly flying at 402 or just 2?

The air inside the plane has been propelled to 400mphs, so the fly is moving 2mps in relation to the plane and its microenvironment, but over or under than 402 mph ,
depending which way the plane is traveling, in relation to rotation of the earth.

 

[Andy D]

One more time :
If the treadmill is going 10,000 mph the plane's wheels must be going 10,001 mph to move the plane forward at 1mph...
but it can't even do that when the treadmill matches its speed instantly.

 

[Taryn]

Oh, oh, I think I know!
Taking the original question into mind (ie, ignoring frictionless wheels, ignoring the fact that wheels "have nothing to do with taking off", not calculating for an as of yet unmentioned wind speed, etc., etc.), then the answer is: plane's not going to move. Using Newton's third law of motion, the jets on the plane wings are acting as the initial point of force, so it would move. On the other hand, an EQUAL FORCE is being exerted on the plane in the opposite direction via treadmill. The total net force is now 0, like two incoming equal-sized and equal-weighted cars hitting each other head on. No movement. To add, the plane uses forward movement via jets and wheels to create that air draft needed to even begin to lift off, so removing the wheels from the equation is like saying you don't need side "b^2" to prove "a^2+b^2=c^2".

Now on the FRICTIONLESS wheels, that bugger will be GONE SO FAST. Friction is the opposite force required for motion to function as we see it every day. Friction is such an integral part of things moving that it may as well be Newton's first law. The plane wasn't moving to begin with, there's no friction to stop it. The jets kick on, there's no friction to slow it, the treadmill is pointless power consumption! Bye plane.

The wheels generate the friction required for the plane to slow down. The same with cars. Friction is used in the brakes of a car. The jets and wheels of a jet can be (somewhat inaccurately) be compared to the wheels and brakes of a car.

 

[Notarealsignguy]

There is no force being put on the plane. The wheels are an idler and don't have any opposite force on the plane besides minimal friction loss from the bearings. It is essentially acting like a hovercraft, nothing ties it down to the surface so there is no irregular force to overcome.
If you tied a rope to the front of the place, it would not take anything real substantial to hold it in place. That same rope could not hold the plane in place against its own thrust.

 

[Taryn]

...then if there's no force being put on the plane, how's it gonna move in the first place?

 

[Notarealsignguy]

...then if there's no force being put on the plane, how's it gonna move in the first place?

I mean force from the treadmill. With zero friction, which would not be physically possible, the plane would just sit there with the treadmill running. The only thing holding it on the belt is the friction of the wheels so the plane would probably not even move as fast in reverse as the treadmill is going because it is not physically locked to it.
You ever go on a people mover in the airport? Are you able to push your suitcase or a stroller on it or do you have to pick it up because it will only go backwards while you walk forwards?

 

[Taryn]

Oh, gotcha! I included the lack of friction because I thought it was funny that it was brought up earlier.

Also....what's a people mover? I haven't left my island in two years so I'm technically still in 2018.