You have a plane and a conveyor belt.

[sunase]

Originally posted by: Vinfinite
Seriously those of you that says NO are total fvcken dumbasses, I can't believe it took 32+ pages just to discuss this

THE FVCKEN PLANE TAKES OFF

if you read the damn link and still don't understand, god you're freakin retarded

Text

READING COMPREHENSION FTW.

Okay so a plane is moving forward on a treadmill going backwards at the same rate as the wheels moving forward, a plane uses its JET ENGINES for propulsion, so WHO GIVES A SH@T about the wheels moving backwards? The plane pushes itself with its engines, the wheels are just there so the fvcken plane doesnt explode due to friction.

Read the damn article!

I'm just looking in, but I find it amusing that this poster didn't understand the article he cites. The article says the plane takes off when the belt speed matches the plane speed. It refuses to give an answer when the belt speed matches the wheel speed (as is stated in the first post of this thread), which it claims is impossible.

 

[Thegonagle]

Still going...

The wheels of a plane just freewheel while the engine(s) react with the AIR, not the ground (or conveyor belt). So the plane takes off. Seems simple to me. Do people not understand how a plane actually leaves the ground?

But things that seem simple to me have been known to baffle others many times in my life. This is an example of that.

 

[SophalotJack]

To this thread and OP and company:

STFUSTFUSTFUSTFUSTFUSTFU!!!!!!!!!!!!!!

 

[DivideBYZero]

1 = 0.999999999999

 

[Suspicious-Teach8788]

I think everyone fails to realize that in this discussion, we assume:

1) 100% static friction between wheels and conveyor belt
2) 0 friction in the axle so the wheels rotate freely (with 0 resistance)

According to those assumptions, if you placed a plane on the conveyor belt with its engines off, and turned the conveyor belt on.......

The planes wheels would turn at the same speed the conveyor belt moves at and the plane does not move.

Once you flip the engines on, it will push the entire plane forward.

Remember a plane is not a car. They function completely differently in terms of wheels. Cars use wheels engines which turn the wheel. Planes use engines which push the entire aircraft and wheels are only there to spin FREELY.

Plane takes off.

 

[skace]

Lol, there are still people saying it won't take off?

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

http://www.avweb.com/news/columns/191034-1.html

Read the second link all the way from the small toy plane on a treadmill to a real life plane on a giant treadmill to the theoretical plane on a hovercraft.

I'll quote this tidbit:

"I'm reminded of the New York Times editorial when Robert Goddard's rocket experiments were first being publicized. The author of the editorial said that rockets can't work in space because they have nothing to push against. It was laughably wrong, ignoring one of Sir Isaac's laws of physics that for every action there is an equal and opposite reaction. Here the propeller is pushing against the air, as it does every time an airplane takes off. How fast the airplane is moving over the surface on which its wheels rest is irrelevant; the medium is the magic. On a normal takeoff -- no conveyor involved -- if there is a 20 mph headwind, Manfred and the J-3 will lift off at 45 mph indicated airspeed; but relative to the ground, it is only 25 mph"

Now, can we all be in agreement the friggen thing would take off?

 

[Ramma2]

Originally posted by: skace
Lol, there are still people saying it won't take off?


Now, can we all be in agreement the friggen thing would take off?

No, it all depends on what the plane has for cargo. What if it was carrying some very dense materials and gravity was figured differently?

 

[Kelemvor]

Originally posted by: Throwmeabone

Originally posted by: FrankyJunior
OK. Some people obviously aren't grasping the concept so I'll try to make it real simple.

Most physics problems assume that there is no friction between moving parts so let's assume that there is no friction between the airplane's wheel and the axle/hub that it spins on. THe ball bearings or whatever are perfectly designed and all friction is gone.

Bassed on this fact, the spinning of the wheels has nothing to do with causing the airplane to move or not. Let's say the airplane has it's engines turned off. The treadmill can run as fast as it wants and this will cause the wheels to spin at the same rate, but the airplane will not move.

Now let's say the treadmill is off. If the plane turns its engines on, the thrust pushing the air through the engines and out the back will cause the plane to move. THe only reason the wheels move is because they are touching the ground. THey have nothing to do with actually propelling the airplane.

SO now if we combine those two, when the plane moves forward and the treadmill spins the opposite direction, the wheels will spin very fast, but they put forth no force on the airplane because of the frictionless hubs the wheels spin on. The airplane will move forward because it uses the AIR to move and not the ground.

Now if this question were worded that a carr with wings was on the same treadmill, then it would not take off because the car gets its movement by pushing itself along on the ground. SO if the treadmill spins the other way, it is jsut like riding a bike on a treadmill, you don't actually move.

But since a plane doesn't get it's pwoer from wheels pushing it, the treadmill can spin at 10,000 mph and the wheels will spin at the same rate, but that has no affect on the plane.

Does that sum it up well enough? Is anyone still confused about this?

bravo that is the best explanation so far

Thanks. I tried to make it simple enough even for the average ATOTer. But since there's another 100 posts after that one, apaprently I overestimated the intelligence of some people here.

Oh well. At least we know the truth. They can be delusional all they want.

THe fact that the OP said somethign about no airflow over the wings is stupid. Once the plane turns on it's engines, it will move, and there will be airflow. the treadmill is dumb.

I do like the post about the treadmill being attached to the plane already in flight and will it fall from the sky. That was a good one.

 

[Kev]

If a plane moving at 1 km/sec is on a conveyor belt moving at .99999999 km/sec does the universe explode?

 

[Cheetah8799]

after debating this with my coworkers, and going over the solution on the web site I'm linking we have all changed our minds and now understand that the plane WILL take off.

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

 

[hellokeith]

Did the original poster later specify that article is his reference? Because what is stated in the original post is not the same as what is in that article.

If we take only the OP's statement, then there is not enough information to determine the outcome.

For those saying it will definitely always take off, you do not have a full understanding of the pre-lift situation. Jets are catapulted off aircraft cariers because jets are too heavy to reach a high enough speed, even at full throttle, with the limited runway length, to achieve lift.

For those saying it will definitely never take off, you are assuming the conveyor belt is instantaneously providing equal force in the opposite direction.

With only the information given by the OP, most likely the plane will nosedive or turn sideways due to vibrations. But again, not enough information is given in the OP to know for sure.

 

[JujuFish]

Originally posted by: LukeMan
Please do not extend this thread past 1000

That may already be to late if you consider the fact that the first thread was over 400 and this is over 600.

 

[PurdueRy]

Originally posted by: hellokeith

Originally posted by: Penththe wheels really have nothing to do with the propulsion or velocity of an airplane.

Incorrect.

The problem is in the language of the hypothetical situation:

The belt compensates for the rotation of the wheels in reverse, as in the belt moves in reverse exactly as fast as the wheels move forward.

If we interpret that the plane wheels' velocity is matched by the conveyor belt counter-velocity, with the wheels having 100% static friction (and 0% inertial friction) on the treadmill surface, then we conclude the plane will never move. We may derive this from the fact that most conveyor belts have their own power source, and that the conveyor belt acceleration is a perfect curve (not delayed) to the plane wheels' acceleration curve. Any backwards force the plane wheels are applying to the belt is equaled by a forward force the belt is applying to the wheels.

If we interpret that the forward force of the plane engine causes the plane wheels to move, and the force of the plane wheels is what is causing the conveyor belt to move in the opposite direction, then we conclude the plane will move ever so slightly (in agreement with action force <--> equal opposite reaction force), and with enough conveyor belt runway length, the plane will eventually reach a ground speed fast enough to achieve enough airflow to provide lift.

The wheels cannot apply a force to the treadmill...this is the whole concept of the problem.

 

[newParadigm]

Originally posted by: CadetLee

Originally posted by: Evadman

Originally posted by: deathkoba
You people are retarded. It will not take off as the sole lift mechanism (the wings) will not be getting any airflow. The engines only push the aircraft so that enough air can flow over the wings. Only then will the aircraft achieve any level of lift. I'm a private pilot with instrument license.

Now if there is enough headwind, even when the plane is visually stationary, it's possible that the headwind itself can push the plane up a bit but it would be very uncontrolled and will simply flip the plane over.

Quoted for posterity so we can all laugh later.

I think many of us (myself included) are misunderstanding the situation -- as a former student pilot (powered & glider) myself, I have an idea how these things fly..if you take this from the OP:

belt moves in reverse exactly as fast as the wheels move forward.

The wheels would necessarily rotate in direct proportion to the speed of the aircraft, which would leave me assuming that the aircraft is remaining in one position on the ground. Without a headwind, it couldn't take off.

What am I missing?

Edit: Which direction is reverse?

The q is worded rong it should say that the conveyor moves backward at exactly twice the forward speed of the AIRCRAFT.

"The conveyer belt is designed to exactly match the speed of the wheels at any given time, moving in the opposite direction of rotation." This language leads to a paradox: If the plane moves forward at 5 MPH, then its wheels will do likewise, and the treadmill will go 5 MPH backward. But if the treadmill is going 5 MPH backward, then the wheels are really turning 10 MPH forward. But if the wheels are going 10 MPH forward . . . Soon the foolish have persuaded themselves that the treadmill must operate at infinite speed. Nonsense. The question thus stated asks the impossible -- simply put, that A = A + 5 -- and so cannot be framed in this way. Everything clear now? Maybe not. But believe this: The plane takes off.

 

[PurdueRy]

Originally posted by: newParadigm

Originally posted by: CadetLee

Originally posted by: Evadman

Originally posted by: deathkoba
You people are retarded. It will not take off as the sole lift mechanism (the wings) will not be getting any airflow. The engines only push the aircraft so that enough air can flow over the wings. Only then will the aircraft achieve any level of lift. I'm a private pilot with instrument license.

Now if there is enough headwind, even when the plane is visually stationary, it's possible that the headwind itself can push the plane up a bit but it would be very uncontrolled and will simply flip the plane over.

Quoted for posterity so we can all laugh later.

I think many of us (myself included) are misunderstanding the situation -- as a former student pilot (powered & glider) myself, I have an idea how these things fly..if you take this from the OP:

belt moves in reverse exactly as fast as the wheels move forward.

The wheels would necessarily rotate in direct proportion to the speed of the aircraft, which would leave me assuming that the aircraft is remaining in one position on the ground. Without a headwind, it couldn't take off.

What am I missing?

Edit: Which direction is reverse?

The q is worded rong it should say that the conveyor moves backward at exactly twice the forward speed of the AIRCRAFT.

"The conveyer belt is designed to exactly match the speed of the wheels at any given time, moving in the opposite direction of rotation." This language leads to a paradox: If the plane moves forward at 5 MPH, then its wheels will do likewise, and the treadmill will go 5 MPH backward. But if the treadmill is going 5 MPH backward, then the wheels are really turning 10 MPH forward. But if the wheels are going 10 MPH forward . . . Soon the foolish have persuaded themselves that the treadmill must operate at infinite speed. Nonsense. The question thus stated asks the impossible -- simply put, that A = A + 5 -- and so cannot be framed in this way. Everything clear now? Maybe not. But believe this: The plane takes off.

I don't think the question is worded wrong. In that quote they say the wheels are going 10 MPH forward. However, they are spinning at that speed but they are still only moving 5 MPH forward. This leads to 5 MPH treadmill speed and all is fine. It does depend on how you interpret the problem however.

 

[JRich]

Flight 1024 to Physics, USA will be taking off as scheduled!

 

[hellokeith]

Originally posted by: PurdueRy
The wheels cannot apply a force to the treadmill...this is the whole concept of the problem.

Only if you are discounting gravity, which would be a fairly large assumption to make. The whole situation, whether we're using the OP's statement only or using the external article, henges on gravity being normal.

 

[FoBoT]

do the wheels provide lift? or the wings?

 

[JujuFish]

Originally posted by: hellokeith

Originally posted by: PurdueRy
The wheels cannot apply a force to the treadmill...this is the whole concept of the problem.

Only if you are discounting gravity, which would be a fairly large assumption to make. The whole situation, whether we're using the OP's statement only or using the external article, henges on gravity being normal.

The very minor frictional force would hardly do anything to stop the plane, so for our discussion, it can be essentially neglected. It's not discounting gravity at all.

 

[exdeath]

The plane is provided forward motion only due to direct air stream thrust from the engines (i.e.: the wheels are not powered at all).

But if the belt was moving backward as the plane attempted to move forward (causing the wheels to rotate as if going forward) the plane would not lift off.

The wings only attain lift when they have a relative velocity to the air (ie: airspeed). The engines themselves only provide the forward thrust necessary to push the entire plane forward and allow the wings to do their job; they would not pull or push enough air in any configuration to provide enough air flow over the wing volume. The only exception would be a military fighter with exceptional thrust to weight ratio like the F-15 which can accelerate the aircraft against gravity under engine power alone, but this is merely the high thrust engines acting as a rocket without wings. Thus an F-15 could not take off in this manner either, unless perhaps 90 degrees and launching straight up.

So the end effect is that you have the conveyer negating the forward thrust of the engines and all you would have is a plane running full throttle and making a lot of noise and not going anywhere. If you were to weigh the plane its weight would be its normal parked curb weight.

FYI you can experiment with this on the runway by holding the gear brakes and pushing up the throttle, the same thing happens: you go nowhere.

Now if you suddenly stopped the conveyer in this condition, youd feel a kick in the pants, the plane will take off, and you will probably stress the sh1t out of the airframe and have problems landing after you blow your wheels to shreds.

 

[hellokeith]

Originally posted by: FoBoT
do the wheels provide lift? or the wings?

Originally posted by: JujuFish
very minor frictional force

Airflow provides lift. Put wings on an Indy car.. it will not fly at 20mph, but it will take off at a high speed. It will however not stay in the air for long, because it no longer has the force applied through friction on the road.

The plane's undercarriage attachments to the wheels are dependent on friction. Otherwise the plane on a normal runway would never be able to take off, or for that matter, brake effectively when landing.

Friction is necessary all throughout the system of a plane reaching a high enough speed to achieve enough airflow across the wings to provide lift. Those who are saying the plane wheel is freely spinning with no friction are not understanding that friction is required for the wheel to stay connected to the undercarriage.

 

[JujuFish]

Originally posted by: exdeath
The plane is provided forward motion only due to direct air stream thrust from the engines (i.e.: the wheels are not powered at all).

But if the belt was moving backward as the plane attempted to move forward (causing the wheels to rotate as if going forward) the plane would not lift off.

The wings only attain lift when they have a relative velocity to the air (ie: airspeed). The engines themselves only provide the forward thrust necessary to push the entire plane forward and allow the wings to do their job; they would not pull or push enough air in any configuration to provide enough air flow over the wing volume. The only exception would be a military fighter with exceptional thrust to weight ratio like the F-15 which can accelerate the aircraft against gravity under engine power alone, but this is merely the high thrust engines acting as a rocket without wings. Thus an F-15 could not take off in this manner either, unless perhaps 90 degrees and launching straight up.

So the end effect is that you have the conveyer negating the forward thrust of the engines and all you would have is a plane running full throttle and making a lot of noise and not going anywhere. If you were to weigh the plane its weight would be its normal parked curb weight.

FYI you can experiment with this on the runway by holding the gear brakes and pushing up the throttle, the same thing happens: you go nowhere.

Now if you suddenly stopped the conveyer in this condition, youd feel a kick in the pants, the plane will take off, and you will probably stress the sh1t out of the airframe and have problems landing after you blow your wheels to shreds.

Have you read any of the thread?

 

[spidey07]

Originally posted by: exdeath
The plane is provided forward motion only due to direct air stream thrust from the engines (i.e.: the wheels are not powered at all).

But if the belt was moving backward as the plane attempted to move forward (causing the wheels to rotate as if going forward) the plane would not lift off.

The wings only attain lift when they have a relative velocity to the air (ie: airspeed). The engines themselves only provide the forward thrust necessary to push the entire plane forward and allow the wings to do their job; they would not pull or push enough air in any configuration to provide enough air flow over the wing volume. The only exception would be a military fighter with exceptional thrust to weight ratio like the F-15 which can accelerate the aircraft against gravity under engine power alone, but this is merely the high thrust engines acting as a rocket without wings. Thus an F-15 could not take off in this manner either, unless perhaps 90 degrees and launching straight up.

So the end effect is that you have the conveyer negating the forward thrust of the engines and all you would have is a plane running full throttle and making a lot of noise and not going anywhere. If you were to weigh the plane its weight would be its normal parked curb weight.

FYI you can experiment with this on the runway by holding the gear brakes and pushing up the throttle, the same thing happens: you go nowhere.

Now if you suddenly stopped the conveyer in this condition, youd feel a kick in the pants, the plane will take off, and you will probably stress the sh1t out of the airframe and have problems landing after you blow your wheels to shreds.

Exactly. You can't take off if you can't move.

From the OP the plane is forbidden to move.

If it does move forward then the rules of the OP are broken.

 

[JujuFish]

Originally posted by: spidey07
Exactly. You can't take off if you can't move.

From the OP, the plane moves.

Fixed.

 

[exdeath]

Originally posted by: hellokeith

Originally posted by: FoBoT
do the wheels provide lift? or the wings?

Originally posted by: JujuFish
very minor frictional force

Airflow provides lift. Put wings on an Indy car.. it will not fly at 20mph, but it will take off at a high speed. It will however not stay in the air for long, because it no longer has the force applied through friction on the road.

The plane's undercarriage attachments to the wheels are dependent on friction. Otherwise the plane on a normal runway would never be able to take off, or for that matter, brake effectively when landing.

Friction is necessary all throughout the system of a plane reaching a high enough speed to achieve enough airflow across the wings to provide lift. Those who are saying the plane wheel is freely spinning with no friction are not understanding that friction is required for the wheel to stay connected to the undercarriage.

Uhm no, engine thrust alone accelerates a plane on the ground or in the air. Wheels are just a convienient way for the plane to sit on the ground and be able to move while in contact with the ground. Friction has nothing to do with this problem and the wheels have absolutely no bearing on the ability of a plane to take off.

It's all about air speed relative to the wings of the aircraft and angle of attack. Nothing more.