Will the plane take off?

[Jaffa]

Right, some fuckwit posted this up on Midshiteracing and considering all those inbreds shit IQ points every time they go to the toilet, I thought I would present it to the elite to see what you all think:

A plane is standing on a runway that can move (some sort of conveyer belt). The plane moves in one direction, while the conveyer moves in the opposite direction. This conveyer has a control system that tracks the plane speed and tunes the speed of the conveyer to be exactly the same (but in the opposite direction).

Can the plane take off?

Discuss.......

[Big G]

It depends if the plane has VSTOL capabilities (Vertical/Short Take Off and Landing)

But other than that no

[Grant]

no, as whilst the planes wheels will move the plane will not be moving from the original spot, therefore not able to generate any lift.

[Mike H]

Motion of the plane creates the downforce needed....and as in effect it would be stationary....it wouldn't take off.

It wouldn't actually be moving through the air.

[Jaffa]

Exactly as I initially thought.

But then, think of how the plane is driven. It isn't through the wheels, so the conveyor will spin the opposite way and theres no friction in the wheels to slow the plane down?

Would it still move?

Its really a head scratcher.

[TRAVIS]

Wheres the plane going? How much does it weigh? And how much fuel is it carrying.

[Tony]

Exactly as I initially thought.

But then, think of how the plane is driven. It isn't through the wheels, so the conveyor will spin the opposite way and theres no friction in the wheels to slow the plane down?

Would it still move?

Its really a head scratcher.

The plane would need the same forward thrust as if it was on a standard runway. As you say, it has nothing to do with the ground and wheels it is to do with the airflow over and under the wings.

[Teknobry]

The plane is moving.

Think of a roller skate on a treadmill, if you push the rollerskate forward with your hand, it doesn't matter if the conveybelt is moving in the opposite direction and turning the wheels, the rollerskate is still being pushed forward.

Drive DOESN'T come from the wheels, thrust is generated by the force of the engines on the plane.

If the plane was FWD, it would be a different story :lol:

[Big G]

It depends if the plane has VSTOL capabilities (Vertical/Short Take Off and Landing)

But other than that no

The reason no is the physics of air over and under the wings, but as the plane is still stationary apart from the wheels moving due to a Bex size treadmill thus there is no sufficient air to get under the wings and create the lift needed.

[Mad-Dan]

It's a no brainer, it just wouldnt happen, as said, the belt/wheels have nothing to do with the plane flying.

Pointless question, someone Ban jaffa for wasteing bandwidth

[Beaver]

There will be equal force on both sides so the plane would not be going far.

[Teknobry]

Forward thrust isn't being transfered to the wheels, its pushing the plane by way of the thrust of the jet engines, the wheels are just to keep it off the floor, not to provide forward momentum.

[Big G]

Forward thrust isn't being transfered to the wheels, its pushing the plane by way of the thrust of the jet engines, the wheels are just to keep it off the floor, not to provide forward momentum.

But the momemtun is being thwarted by the Bex treadmill, so the plane is sat there like a Corsa in Maccies revving its tits off for no reason

[Teknobry]

Ahhhh, the power of google:




The unwary tend to reason by analogy to a car on a conveyor belt--if the conveyor moves backward at the same rate that the car's wheels rotate forward, the net result is that the car remains stationary. An aircraft in the same situation, they figure, would stay planted on the ground, since there'd be no air rushing over the wings to give it lift. But of course cars and planes don't work the same way. A car's wheels are its means of propulsion--they push the road backwards (relatively speaking), and the car moves forward. In contrast, a plane's wheels aren't motorized; their purpose is to reduce friction during takeoff (and add it, by braking, when landing). What gets a plane moving are its propellers or jet turbines, which shove the air backward and thereby impel the plane forward. What the wheels, conveyor belt, etc, are up to is largely irrelevant. Let me repeat: Once the pilot fires up the engines, the plane moves forward at pretty much the usual speed relative to the ground--and more importantly the air--regardless of how fast the conveyor belt is moving backward. This generates lift on the wings, and the plane takes off. All the conveyor belt does is, as you correctly conclude, make the plane's wheels spin madly.
A thought experiment commonly cited in discussions of this question is to imagine you're standing on a health-club treadmill in rollerblades while holding a rope attached to the wall in front of you. The treadmill starts; simultaneously you begin to haul in the rope. Although you'll have to overcome some initial friction tugging you backward, in short order you'll be able to pull yourself forward easily.

As you point out, one problem here is the wording of the question. Your version straightforwardly states that the conveyor moves backward at the same rate that the plane moves forward. If the plane's forward speed is 100 miles per hour, the conveyor rolls 100 MPH backward, and the wheels rotate at 200 MPH. Assuming you've got Indy-car-quality tires and wheel bearings, no problem. However, some versions put matters this way: "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

:D


<edit source for the quote:
http://www.straightdope.com/columns/060203.html >

[Natty]

Forget all the bollox with treadmills and wheels.

Hard to Explain on a forum but :

If the belt is matching the planes speed, then even with jets on full, the plane is still actually residing in the same section of air, and therefore the airs not disrupted enough to cause lift or drag.

Plane will just stay grounded.

[Teknobry]

Sorry Natty, you're wrong.




You can test this with a piece of paper and a matchbox car (which has free rolling wheels like an airplane… or like a car in neutral.) Place the paper on a table, and place the matchbox car on the paper. Take your hand, and hold the car still with a lightly placed finger on top of the car. At this point you are providing no forward thrust, and the “conveyor belt” is not moving. The car remains stationary. Now, continuing to hold the airplane with a lightly placed finger, and start to pull the paper out from under the car, in the backwards direction. According to Neal’s logic, the car should push back on your finger with the same force that you are exerting on the paper… but this is not what will happen. You will find that your lightly placed finger is not stressed to any noticeable extent. The paper will slide out, and the wheels will spin, but the car will not be propelled backwards. The reason for this is is that the rotation of the wheels is not related to the movement of the matchbox car except by the very small friction component of the axle, which your lightly placed finger can easily control.

So now we have established that movement of the surface beneath a free wheeling object does not exert a noticeable force on the object. Next, we’ll see what happens when the object is trying to move forward. Attach a string to the matchbox car. Place the car at one end of the paper, and use the string to start pulling the car forward with a steady force. As the car moves forward, start pulling the paper out from under the car, backwards. Do you feel increased resistance as you pull the string? Of course not. The wheels are free rolling! Spinning the wheels does not make the object move!

When an airplane takes off, there is one major forward force… the forward thrust. The main rearward force is air resistance. The turning of the wheels provides a small frictional force, but because the wheels are free-rolling, this friction is very small. Unless the wheels are locked, the friction is always going to be less than the thrust, which means that the overall force is still forward, and the plane will still move.

Gah… people are freakin’ stupid.

Update: There is a variation on this riddle that says that the conveyor belt matches the speed of the plane. It doesn’t matter… the plane still takes off. The conveyor belt could be going 5 times as fast as the plane, and the plane would still take off. You’d get into issues about tires blowing out, but assuming that the wheels can take the strain, the airplane would still take off.


http://txfx.net/2005/12/08/airplane-on-a-conveyor-belt/

[Mad-Dan]

ok ok, look at it this way....

if you park the plane in liverpool and some fucker nicks the wheels and leaves it on bricks.

would the plane fly?

[Teknobry]

To put it another way:




Picture this - you're standing on a skateboard that is riding on a treadmill. One person is standing in front of the skateboard on firm ground, and the two of you are holding a rope. This person pulls on the rope that you're holding so that the rope moves exactly an inch per second, advancing you forward. No matter what speed the treadmill is going, as long as that person maintains the same rate of pull, you'll advance forward an inch per second. Your skateboard wheels might go faster or slower in relation to the speed of the belt, but you'll pretty easily advance forward. Change the rope to a stick, and the conveyor belt can travel in either direction at either speed and be just as irrelevant.

The airplane's engines provide the forward force, pushing against the air behind their outputs. The air is like the person standing firm (as firm as air can be) and the engines pushing against that air provide the same kind of force that someone pulling on the rope provides. In both cases, the speed of the conveyor belt has no correlation with the force that the rope or engines produce against the air or the person standing firm.

Granted, in both cases, wheel friction will come into play. With a skateboard and treadmill, friction might be noticeable. With the kind of forces a jet turbine can produce the wheels would probably melt off before the engines noticed anything.



Do I need to keep finding more examples or have people seen the light yet? :lol:

[Tony]

ok ok, look at it this way....

if you park the plane in liverpool and some fucker nicks the wheels and leaves it on bricks.

would the plane fly?

simple, no it wouldn't.






The fuckers over in Liverpool wouldn't just take the wheels, they would strip it bare. Therefore no engine = no thrust = no flight

[Big G]

Bry, that is a load of Testicles.
The planes relies on Air going under the wings to gain lift, the engines do not give it that lift, they merely provide enough power to acheive a speed where take off can be accomplished by airflow.

If what your saying about the engine is correct Bry, then why are flaps used on the wings to create a greater upforce on take off.

[Big G]

What your saying Bry is that the engine creates the air force thingymebob to make shit happen,

Please quote and answer here -

So, what about a glider then, they have no engine to create this big amount of air pressure to lift it, but if you tow 1 to a determind speed then it will lift off ENGINELESS

[hooligan]

it wouldnt fly
it need air presure to lift
u could stick a huge fan in front of it and get to levitate
how cool would that be
now thats magic :lol:

[Beaver]

no cause they wouldnt just steal the wheels would they?

[Mad-Dan]

look, we all know how planes work. we all know if a plane can not gain forward motion it will not fly.

what i have fuck all idea about is, how would a jogging machine stop the plane gaining forward motion?

all the belt would do is make the plane's wheels spin at a speed not relevent to the speed the plane was traveling at.

not all planes have wheels anyway.

the question is not relevent, putting the plane on a belt that can match the speed of the planes wheels would not stop it from moveing

[Teknobry]

<bangs head on desk>

G, the glider example is EXACTLY the same point about the skateboard on a rollerskate being pulled along. It ISN'T pulled/pushed by the wheels, but by another plane/car etc.

Think of it this way..

You've got your glider on the conveyor belt. Parellel to the conveyor belt is a normal road. A car has a tow rope from the back of the car to the plane. The car drives along the normal road, whilst pulling the glider which is on the conveyor belt.
Now, are you saying that the car which is doing 60mph going to be stationary?! No, it'll be towing the glider at 60mph, doesn't matter that the gliders wheels are doing 120mph in reverse, they are freewheeling and have no effect on the glider, which is moving forward at 60mph and will happily take off.

[Jaffa]

I'm with you on this Bry.

I completely agree.

We know that no wind under the wings means no lift.

But the plane IS moving. The engines are still pushing the plane forward. All the conveyor does it spins the wheels, doesn't have much of an effect on the planes speed whatsoever.

[Big G]

Nope.
Think we should go the pub and sort it out with fag packets, matchboxes and straws for objects to use in description.

Because i am right :wink:

[Teknobry]

Nope.
Think we should go the pub and sort it out with fag packets, matchboxes and straws for objects to use in description.

Because i am right :wink:

:lol: :lol:

G You're being purposely awkward now, you know full well that the plane has taken off with a full compliment of p1ssed up scousers going to magaluf.

[Teknobry]

Does sound like a good excuse to go the pub and make a mess with paper, toy cars and matchboxes :lol:

[Big G]

Nope.
Think we should go the pub and sort it out with fag packets, matchboxes and straws for objects to use in description.

Because i am right :wink:

:lol: :lol:

G You're being purposely awkward now, you know full well that the plane has taken off with a full compliment of p1ssed up scousers going to magaluf.

Nah, its EasyJet, another 3 hour delay