permalink for this thread : http://search.catflaporama.com/post/browse/1811054
Johnny_Thunder Posted on 02/04/2010 21:21
Will the plane take off?

OK boys and girls...........
This has just ben done to death on another forum I frequent, but some people are just so stubborn they refuse to accept the truth.

There are some right stubborn tw@ts on here, so it should be interesting.

It is an old one, but it is still a good one..!!!

The question:

A jet plane tries to take off on a conveyor belt which is programmed to match the wheel speed of the plane.

Can it take off?



Please feel free to discuss, or more likely, have a typical abusive argument.[^]

fylde_coast_pies Posted on 02/04/2010 21:23
Will the plane take off?

Effectivly static, No airspeed...No.

YOUDOYLE Posted on 02/04/2010 21:24
Will the plane take off?

dont know about a jet plane
but mythbusters did one with a normal plane
and it wouldnt take off(i think)
they managed to do it with a model though

subbuteo_171 Posted on 02/04/2010 21:24
Will the plane take off?

Yep.

If it's a Harrier.

Johnny_Thunder Posted on 02/04/2010 21:25
Will the plane take off?

[smi]

Jonny_Ingbar Posted on 02/04/2010 21:25
Will the plane take off?

No, the airflow over the wings is nil, therefore there is no uplift and no flight.

QED [^]

Johnny_Thunder Posted on 02/04/2010 21:26
Will the plane take off?

How long before someone calls someone else a mong?

[smi]

subbuteo_171 Posted on 02/04/2010 21:26
Will the plane take off?

Unless it's a Harrier.

[^]

comejoiners Posted on 02/04/2010 21:26
Will the plane take off?

in my opinion
no
i would think it would have to be travelling to get some wind under the wings
on a conveyerbelt it is not moving
it is only turning the wheels round

Johnny_Thunder Posted on 02/04/2010 21:26
Will the plane take off?

BTW, the plane will take off.[^]

subbuteo_171 Posted on 02/04/2010 21:27
Will the plane take off?

Unless it's a Harrier.

[^]

shackman99 Posted on 02/04/2010 21:27
Will the plane take off?

Shurrup ya doyle [:D]

Johnny_Thunder Posted on 02/04/2010 21:27
Will the plane take off?

Lift is created by differential airflow over/under the wing.


[;)]

subbuteo_171 Posted on 02/04/2010 21:29
Will the plane take off?

Unless it's a Harrier.

[^]

Wheater_Walks_On_Water Posted on 02/04/2010 21:30
Will the plane take off?

No thrust from the engines (I am assuming that they are not running) so it is effectively a glider.

So no

Unless it IS a glider, in which case it may travel for a short distance, like throwing a paper aeroplane.

Johnny_Thunder Posted on 02/04/2010 21:31
Will the plane take off?

Nothing to do with a Harrier.

I am talking about a normal jet ie. a 747.

[^]

subbuteo_171 Posted on 02/04/2010 21:31
Will the plane take off?

Why didn't you say so in the first place, you XXXXXXing dipstick. [;)]

Johnny_Thunder Posted on 02/04/2010 21:32
Will the plane take off?

You are all mongs.

It will take off.


[;)][smi]

Johnny_Thunder Posted on 02/04/2010 21:32
Will the plane take off?

subbuteo.[smi]

Jonny_Ingbar Posted on 02/04/2010 21:33
Will the plane take off?

If there is no airflow over the wing then it cant take off, surely?

JT you have me second guessing myself now [:(!]

comejoiners Posted on 02/04/2010 21:34
Will the plane take off?

how long is the conveyerbelt and is it travelling with the wheels or against the wheels
if it is as long as a runway and the belt is travelling with the wheels then yes

Johnny_Thunder Posted on 02/04/2010 21:35
Will the plane take off?

It is a good one Jonny.

Even when the penny drops, you will still find it really difficult to explain to everyone.


I am correct though, it will take off.[;)]

Jonny_Ingbar Posted on 02/04/2010 21:35
Will the plane take off?

If the conveyor belt is travelling with the wheels, rather than against, then this is a very annoying trick question [sad]

Johnny_Thunder Posted on 02/04/2010 21:36
Will the plane take off?

The conveyor belt is travelling in the opposite direction to the plane.[^]

Jonny_Rondos_Disco_pants Posted on 02/04/2010 21:36
Will the plane take off?

As stated the airflow over the wings create a differential pressure over the wings which provides lift. The plane cannot take off.

Jonny_Ingbar Posted on 02/04/2010 21:37
Will the plane take off?

Go on then, out us out of our misery [rle][:D]

Edit: spoke too soon.

Johnny_Thunder Posted on 02/04/2010 21:37
Will the plane take off?

Jonny, absolutely 100%


















































wrong.[;)]

Wheater_Walks_On_Water Posted on 02/04/2010 21:39
Will the plane take off?

I suppose if the convayer belt was quick enough for it to reach it's take off speed then it would leave the ground (take off) but it would immediately drop below it's take off speed (because there is no thrust from the engines) so it will land straight away.

So I suppose it will take off for a few seconds

Jonny_Ingbar Posted on 02/04/2010 21:41
Will the plane take off?

Is it to do with the engines rather than the wings?

Johnny_Thunder Posted on 02/04/2010 21:44
Will the plane take off?

WWOW, it will take off as normal.


Jonny, miles away, but starting to think in the right direction.[;)]

subbuteo_171 Posted on 02/04/2010 21:46
Will the plane take off?

I've worked it out.

Using the formula:

((a X b squared) X (b squared)/c)/d X e / a) / (c-a)

where:
a= conveyor belt speed
b= thrust
c= air speed
d = ground speed
e = weight

Then the plane can take off when relative air speed is 15,628.983 miles per hour.

[;)]

Jonny_Rondos_Disco_pants Posted on 02/04/2010 21:49
Will the plane take off?

Engines only provide forward thrust on take off. They do not provide upthrust.

flaps Posted on 02/04/2010 21:50
Will the plane take off?

Yes it will.

Johnny_Thunder Posted on 02/04/2010 21:50
Will the plane take off?

You are correct there Jonny.[^]

Johnny_Thunder Posted on 02/04/2010 21:50
Will the plane take off?

Please explain flaps.[;)]

flaps Posted on 02/04/2010 21:53
Will the plane take off?

They're making the mistake of thinking a plane is a car with wings.

A car with wings can never take off because the power source creates rotary power that moves the car forward, allowing the wings to provide lift. The treadmill will cancel out the rotary movement of the wings, and render the powersource useless.

A plane has engines that provide thrust,not powered wheels. It doesn't matter what the treadmill does, it can't keep the plane still. The plane will move forward and then take off.

Consider this: if you had a shopping trolley on the same treadmill, and you were stood next to it and not on the treadmill, do you the treadmill moving in the opposite direction could prevent you from moving it forward?

Jonny_Rondos_Disco_pants Posted on 02/04/2010 21:54
Will the plane take off?

Oh and the other thing is the plane would fall off the back of the giant treadmill without any engine forward thrust.

borolad259 Posted on 02/04/2010 21:58
Will the plane take off?

In short, the plane takes off, but the wheels and the conveyor rotate more and more quickly without affecting the forward motion of the plane in relation to the air.

Edit, I thinkalso that the plane ill be airborne more quickly than usual because of reduced friction/resistance.

Jonny_Rondos_Disco_pants Posted on 02/04/2010 21:59
Will the plane take off?

Think I was reading the conveyor going from nose to tail and not tail to nose.

Wheater_Walks_On_Water Posted on 02/04/2010 22:00
Will the plane take off?

The speed of the air passing over (and under) the wings provides the upward thrust.

As I said, if the only thing that is causing the plane to move forward is the conveyor belt, then as soon as it leaves the belt it will start to slow down.

Unless of course the conveyor belt is on the side of a hill/mountain and the plane can maintain (or increase) air speed by travelling downwards then it will probably continue to fly. Until it hits the ground of course.

armchair_supporter Posted on 02/04/2010 22:01
Will the plane take off?

What if the conveyer belt was on Mars?!

borolad259 Posted on 02/04/2010 22:02
Will the plane take off?

It would be like a plane taking off on ice.

Johnny_Thunder Posted on 02/04/2010 22:02
Will the plane take off?

So, the engines thrusts, and the plane starts to move forward, but the belt counteracts the forward movement by turning at the same speed as the wheels.[^]

Johnny_Thunder Posted on 02/04/2010 22:04
Will the plane take off?

No tricks here.

The plane is on earth, taking off from left to right, and the conveyor belt is turning from right to left.

flaps Posted on 02/04/2010 22:04
Will the plane take off?

The point is the conveyor belt cannot counteract the movement of the plane.

The plane will move forward and take off, whether its on a treadmill or ice.

The wheels do not provide power.

Johnny_Thunder Posted on 02/04/2010 22:09
Will the plane take off?

The wheels are what allows it to move though flaps.

When a force is applied in a forward direction, the outcome is the turning of the wheels, and the movement in a forward direction.
The belt counteracts this though. It turns in the opposite direction.

Jonny_Ingbar Posted on 02/04/2010 22:10
Will the plane take off?

The treadmill wont counteract the effect of the planes engines because the engines dont drive the wheels, therefore theoretically the plane would still take off.

flaps Posted on 02/04/2010 22:14
Will the plane take off?

Yes Johnny_thunder, the wheels of a plane allow it to move forward by reducing the friction between the plane and the ground.

But the wheels arent *why* the plane moves, the thrust provided by its engines is. Thats why the plane will still move, regardless of what the treadmill is doing.


Johnny_Thunder Posted on 02/04/2010 22:16
Will the plane take off?

But, as fast as the wheels turn, so does the conveyor belt.

flaps Posted on 02/04/2010 22:18
Will the plane take off?

It doesn't matter. The plane will still move forward because the wheels are not what is providing movement.

The thrust of the engines will still move the plane forwards.

Jonny_Ingbar Posted on 02/04/2010 22:19
Will the plane take off?

But since the wheels dont provide power to the plane it will remain stationary if the engines weren't providing thrust - once the engines are providing thrust there will be forward motion, as they aren't effected by the treadmill

Therefore the plane would take off [^]

borolad259 Posted on 02/04/2010 22:21
Will the plane take off?

As flaps says, it's quite simple, the wheels reduce friction with the ground. If the ground is moving effectively WITH the wheels, the the friction will be reduced further. The plane takes off more quickly.

borolad259 Posted on 02/04/2010 22:23
Will the plane take off?

To put it another way, rather than the plane exerting energy to no effect, as you might imagine, the motor on the conveyor is obliged expend a lot of energy just to keep up with the wheels, but to no effect upon the forward motion of the plane.

oooooo Posted on 02/04/2010 22:24
Will the plane take off?

Flaps, the thrust is why it moves forward when it is on wheels. If thrust alone was enough to launch it into the air, why would it need wheels?

It flies because the rushing air creates lower pressure areas that cause it to be pushed up - lift FFS!

If you are on a treadmill, there's no on-rushing air, you need lots rushing under to get enough lift to lift that heavy object.

borolad259 Posted on 02/04/2010 22:27
Will the plane take off?

OOO that is because it is the friction of the feet on a treadmill causing propulsion.

The plane creates forward motion because the engines act upon the air, not the treadmill.

Johnny_Thunder Posted on 02/04/2010 22:27
Will the plane take off?

borolad, wtf does this mean:

"To put it another way, rather than the plane exerting energy to no effect, as you might imagine, the motor on the conveyor is obliged expend a lot of energy just to keep up with the wheels, but to no effect upon the forward motion of the plane."


[smi]

flaps Posted on 02/04/2010 22:28
Will the plane take off?

"If thrust alone was enough to launch it into the air, why would it need wheels?"

Because a plane on its belly on the ground would have too much friction.

Planes don't specifically need wheels to take off, thats why sea planes work. A plane on ice with skis would also work. Or indeed a plane with fast moving mechanical legs.

There is 'rushing air' that generates lift because, as ive said several times, the treadmill wont stop the plane moving because the plane is moved by the thrust generated by its engines, not by having powered wheels.

Jonny_Ingbar Posted on 02/04/2010 22:30
Will the plane take off?

"If you are on a treadmill, there's no on-rushing air, you need lots rushing under to get enough lift to lift that heavy object"

But on a treadmill your legs are providing forward motion by interacting with the runner, a planes wheels dont provide any forward motion, the engines do by interacting with the air.

Probably [:D]

borolad259 Posted on 02/04/2010 22:30
Will the plane take off?

Johnny, it means that the forward motion in relation to the air, that creates lift, is achieved by sucking air in and propelling it out more quickly.

How does a hovercraft move forwards Johnny?

flaps Posted on 02/04/2010 22:32
Will the plane take off?

Johnny Thunder already knows the plane will take off, he's just being a cheeky chappy.

oooooo Posted on 02/04/2010 22:33
Will the plane take off?

You need to consider what allows flight. Moving forward into air is the usual way a bird and a plane flies. The conveyor belt holds it in the same place relative to the air it needs to pass through. It needs to move into it pretty quickly to gain lift.

"OOO that is because it is thr friction of the feet on a treadmill causing propulsion."

Friction? Friction is allowing the plane to grip the belt so it can roll forward and keep up with it. Without it, the belt would seem smooth and the plane would accelerate forwards as if it was on ice.

"The plane creates forward motion because the engines act upon the air, not the treadmill."

The engines suck air in to breath, not to push it out the back to propel it. They don't work like oars. The air rushing in allows them to burn the fuel and that provides the thrust. That chemical reaction stops the plane getting slung off the treadmill.

borolad259 Posted on 02/04/2010 22:33
Will the plane take off?

I know he knows, I;m just trying to explain it in simpler terms. I'm probably not doing very well at that.

flaps Posted on 02/04/2010 22:34
Will the plane take off?

"The conveyor belt holds it in the same place relative to the air it needs to pass through"

It doesn't hold it in place. It cannot hold it.

You need to consider that it is the thrust of the plane that moves it forward, not the movement of the wheels.

If you think logically about this, and especially consider my shopping trolley example from earlier, you'll eventually get it.

swindonred Posted on 02/04/2010 22:34
Will the plane take off?

I wish i'd never read this thread.

My head hurts [cr]

borolad259 Posted on 02/04/2010 22:35
Will the plane take off?

OOOO, oh dear, propellers work exactly like oars.

Jonny_Ingbar Posted on 02/04/2010 22:37
Will the plane take off?

"The engines suck air in to breath, not to push it out the back to propel it"

Aircraft engines, whether jet or prop shaft, do exactly that - use the air for propulsion.

oooooo Posted on 02/04/2010 22:37
Will the plane take off?

A plane needs to be moving forward into air to get lift and it needs to be doing it quickly, hence why we have runways.

The jet is no different, it just uses the forces of thrust from its burning engines rather than propellers.

****** It sounds like a ludicrous experiment so imagine if they made the conveyor belt vanish, what would happen? ******

Johnny_Thunder Posted on 02/04/2010 22:38
Will the plane take off?

Referring to ice is a really poor analogy.
Ice is not a conveyor belt.
Ice is static, while a conveyor belt is moving and counteracting the turn of the wheels.

oooooo Posted on 02/04/2010 22:39
Will the plane take off?

"use the air for propulsion"

Yes, but not to gain lift. They use the propulsion to move themselves forward but require high speeds to get pass through enough 'air' molecules to gain take-off.

Even aircraft on carriers from full thrust need a runway.

flaps Posted on 02/04/2010 22:40
Will the plane take off?

"A plane needs to be moving forward into air to get lift and it needs to be doing it quickly"

Yes it does. And, despite the treadmill moving counter to the rotation of the wheels, the plane will still take off because it will still be moving forward. Because it is powered by engines that provide thrust, not powered wheels like a car.

You see?

oooooo Posted on 02/04/2010 22:40
Will the plane take off?

Ah, I'm being trolled. [:D]

Enjoyed the exercise though.

flaps Posted on 02/04/2010 22:41
Will the plane take off?

"****** It sounds like a ludicrous experiment so imagine if they made the conveyor belt vanish, what would happen? ******"

The plane would drop a few feet then, forgetting damage, it would continue moving forwards at the same speed it was when the treadmill was there.

borolad259 Posted on 02/04/2010 22:41
Will the plane take off?

OK, here's th easiest way to understand it.

The jet plane flies through the air when off the ground by thrusting air/energy backwards.
It is not dependent in any way upon contact with the ground.

In the example cited here, imagine that the plane is already in the air.
The motion of the conveyor and the motion of the whells are just cancelling each other out, If you apply the conveyor to the wheels, the plane's forward motion is not affected at all.

flaps Posted on 02/04/2010 22:42
Will the plane take off?

"Ah, I'm being trolled."

I'm not trolling you. I'm explaining why a treadmill cannot stop a plane from taking off.

Jonny_Ingbar Posted on 02/04/2010 22:42
Will the plane take off?

Simplest explanation;

Conveyor belt is turned on, plane does not move (the wheels counteract the CB movement)

The plane turns on its engines and forward momentum is achieved, the plane takes off.

The impact of any friction at work will be more or less negligable.

red_shamrock Posted on 02/04/2010 22:44
Will the plane take off?

Theres quite a lot of debate on it.

Heres a bit of cut and paste

This is somewhat of a "trick" question. Not because it is phrased in a
deliberately tricky way, but because people tend to have trouble
thinking about the operation of other vehicles apart from cars which
they know so well.

The heart of the confusion is simply these two important facts:
* cars propel themselves by pushing against the ground via friction
* airplanes propel themselves by pushing against the air
If you can let go of how cars operate and think about what an airplane
does, you'll be able to see the problem clearly.

One good way of tackling this problem is to find a good analogy. But
the analogy must be a valid one else you'll just get more confused.
For example, someone posted the analogy of running on a treadmill. Why
is that a bad analogy? Because one runs by pushing against the ground
via friction between their shoe and the ground. This is how a car
propels itself! It is not how an airplane propels itself, by pushing
against the air. Bad analogy.

Let's use this analogy. Instead of looking at the airplane, let's back
up and go into the airport. Suppose you're walking down to your gate
and pulling your carry-on bag behind you. It's a nice new bag with low
friction wheels. No problem! Up ahead you see one of those moving
walkways. You don't see anyone coming, so you decide to do a little
experiment. You go over to the walkway that is moving TOWARDS you and
place your bag on it. Meanwhile, you step off to the side of the
walkway, and still holding on to the handle of your bag, you continue
to walk along. In fact, you intentionally walk along at the same speed
that the moving walkway is going, just in the opposite direction.
Question: does the bag move or does it remain stationary as you keep
walking? Obviously it moves with you. So why does your bag move
forward when you are walking at the same speed of the conveyor going
in the opposite direction?

The answer to that question is also the answer to the
airplane-conveyor question. To complete the analogy, the pull of your
arm is analogous to the force of the airplane engines. The bag's
wheels are analogous to the airplane tires. Do the nice low-friction
wheels on your bag on the conveyor pull against you anymore than they
do when you're just pulling your bag along normally? No, they don't.
They are free-wheeling, after all. Meanwhile, you're pulling the bag
with the same force in both cases. So in both cases, the bag keeps
moving forward. Likewise with the airplane, the pull of the engines
doesn't change nor does the force on the airplane imparted by the
tires change no matter what the ground is doing underneath the tires.
You have the same force imbalance in either case, and since Force =
mass x accceleration, you have the same acceleration. Remember, we are
talking airplane engines which push against the AIR, not the ground.
The acceleration is with respect to the AIR, thus the airplane
develops a speed relative to the air and can eventually take off.

That's a long winded analogy. Here's a quicker solution. Engineers
learn to draw Free Body Diagrams to understand such problems. A FBD is
just a block diagram which illustrates the forces acting upon an
object. The net force can be calculated from all the contributing
forces. If that net force is not zero, the object accelerates in the
direction of that force. Let's draw a FBD now. Represent the airplane
by a simple rectangle (the shape doesn't matter). Indicate the force
of the engines pulling on the plane with a large arrow, labeled "F_e"
with e for engines. What force are the tires imparting to the plane?
Remember, they spin freely except for bearing friction and rolling
friction, which produces forces that are quite tiny compared to the
engines. Represent those forces with a small arrow, labeled F_t where
t means tire. What other forces are operating? There is a drag force
too. But remember this drag force is also small compared to the
propulsion of the engines at least at takeoff speeds. Label that F_d.

FREE BODY DIAGRAM

F_d |----------| F_e

|----------|

Johnny_Thunder Posted on 02/04/2010 22:44
Will the plane take off?

You cannot assume the plane is already in flight.

It has to get off the ground first.

Johnny_Thunder Posted on 02/04/2010 22:46
Will the plane take off?

Red, I don't think that has helped.[;)]

Julios_Hairband Posted on 02/04/2010 22:46
Will the plane take off?

I think the question is flawed. I don't think you could get a conveyer belt to match the wheel speed - increasing the conveyer belt speed will increase the wheel speed.

The plane is pushing agaist something that is static with respect to the conveyer belt (the air), so once it reaches a certain level of thrust (far lower than it is capable of) the friction between it and the ground is going to make little difference to the plane's airspeed, and so having it on a conveyer belt will similarly not reduce its airspeed, which is the important thing with regards take off.

red_shamrock Posted on 02/04/2010 22:48
Will the plane take off?

[:D] I know ....shot down before it took off

borolad259 Posted on 02/04/2010 22:48
Will the plane take off?

Sheesh, it doesn't matter Jonny, as well you know.
The important thing to know is that the conveyor belt is only acting upon the rubber of the wheels, not the plane itself.

Johnny_Thunder Posted on 02/04/2010 22:50
Will the plane take off?

Julios, why can you nor get a conveyor to match the wheel speed?

Planes are not that fast when they take off.
Maybe a couple of hundred mph at most.

Assume for this argument that the conveyor is capable of massive speeds.

flaps Posted on 02/04/2010 22:50
Will the plane take off?

johnny's nearly got his ton

Wheater_Walks_On_Water Posted on 02/04/2010 22:51
Will the plane take off?

As I've already said, the speed of the air passing over and under wings (caused by forward motion) gives the plane lift.

This is done by the upper surface of the wing being curved (which gives it a larger surface area than the under surface of the wing) which means that the air passing over the wing has to move faster than the air passing under the wing. The faster movement of the air passing over the wing creates a reduction in air pressure (compared to the air passing under the wing). The higher air pressure under the wing creates lift which lets the plane fly.

The plane must have forward movement to create air flow over and under the wings. It has nothing to do with the speed of the wheels. However if the breaks were left on the plane wouldn't go anywhere.

Julios_Hairband Posted on 02/04/2010 22:51
Will the plane take off?

By anology, suppose I'm walking on a path alongside a conveyer belt, and I pull a trolley that's on the conveyer belt. If the conveyer belt is static, the wheels are doing a certain number of revolutions. Turn the conveyer belt on, the wheel speed will increase, and the trolley will still move at the same speed as me with respect to a fixed point.

borolad259 Posted on 02/04/2010 22:54
Will the plane take off?

The problem in reverse is:
same plane on the conveyor with engines off. Turn the conveyor belt up to run at 200 miles an hour. Will the plane take off? Will it shoot backwards at 200 miles an hour?

Johnny_Thunder Posted on 02/04/2010 22:56
Will the plane take off?

Walking alongside the conveyor is not applying a force that is appropriate to this equation.

We have a plane and a conveyor belt.

Wheater_Walks_On_Water Posted on 02/04/2010 22:56
Will the plane take off?

We are talking about planes not trolleys

The speed of the wheels has nothing to do with it, it is all to do with the forward movement of the plane.

borolad259 Posted on 02/04/2010 22:57
Will the plane take off?

Nearly there Jonny.

flaps Posted on 02/04/2010 22:57
Will the plane take off?

How is it different?

Johnny_Thunder Posted on 02/04/2010 22:58
Will the plane take off?

But how can the plane get forward movement?

The conveyor moves at the exact speed the wheels do.

borolad259 Posted on 02/04/2010 22:58
Will the plane take off?

Right, the plane feckin takes off.
And I'm taking off to bed.

flaps Posted on 02/04/2010 22:58
Will the plane take off?

jesus

flaps Posted on 02/04/2010 22:58
Will the plane take off?

i mean jesus moves the plane

red_shamrock Posted on 02/04/2010 23:01
Will the plane take off?

Still no further forward, its all up in the air still.

br14 Posted on 02/04/2010 23:01
Will the plane take off?

Can't be bothered to read all the above.

But I assume by now everyone realises it will take off always assuming the belt is long enough of course.

The engine thrust is against the atmosphere, not against the conveyor belt. The wheels will simply turn faster.

Doesn't matter what the conveyor belt does.

Johnny_Thunder Posted on 02/04/2010 23:02
Will the plane take off?

It would be up in the air if it could get off the conveyor belt.

flaps Posted on 02/04/2010 23:03
Will the plane take off?

props to johnny for a scintillating debate

flaps Posted on 02/04/2010 23:03
Will the plane take off?

i like the cut and thrust of physics debate

Johnny_Thunder Posted on 02/04/2010 23:04
Will the plane take off?

flaps, would props be a different debate though, or is it the same as a jet?

[;)]

br14 Posted on 02/04/2010 23:05
Will the plane take off?

Seems to have been an uplifting discussion.

Johnny_Thunder Posted on 02/04/2010 23:07
Will the plane take off?

flaps, you had me rumbled didn't you.[smi][^]



oooooo Posted on 02/04/2010 23:08
Will the plane take off?

I must admit, sometimes these things come along that challenge your beliefs. Reading back, I'm starting to have doubts on my position.

A few months back, they proved that it *was* actually possible to jump as an elevator hit the ground and preserve the robot that did it. Where they'd previously failed was that they could not time the jump properly so it always got smashed. Which just goes to show how intuition can be wrong sometimes.

Julios_Hairband Posted on 02/04/2010 23:09
Will the plane take off?

Congrats Johnny.

I'm right though [ref][;)]



I think [:(]

red_shamrock Posted on 02/04/2010 23:09
Will the plane take off?

What about one of them Waterboats

Johnny_Thunder Posted on 02/04/2010 23:14
Will the plane take off?

The wheels are the important part in this one.[;)]

You have to realise that they are not wheels as in a car though.

They are purely separation between plane and conveyor.

For the sake of this experiment the wheels will be turning much faster than on a runway, but the plane would just hit it's usual take off speed and take off.

The wheels are not driving the plane forward.
They are isolating the plane from the conveyor.

Julios_Hairband Posted on 02/04/2010 23:18
Will the plane take off?

That was pretty much my point - increasing the conveyer belt speed will therefore increase the wheel speed (no. of revolutions of the wheels, per sec.). Therefore the question is a trick.

Towell Posted on 02/04/2010 23:36
Will the plane take off?

I reckon the wheel bearings would fail through working at roughly twice the revolutions they're used to.

The wheels would seize, the tyres would burst and the plane would career off the runway/treadmill.

borospark Posted on 02/04/2010 23:51
Will the plane take off?

Is that a record for the fastest ton ever???

Johnny_Thunder Posted on 03/04/2010 07:27
Will the plane take off?

Here you go boys:


Link: Mythbusters.

Sea_Harrier Posted on 03/04/2010 08:09
Will the plane take off?

"Yep.

If it's a Harrier."
[^][^][^][^][:D]




The_263 Posted on 03/04/2010 08:34
Will the plane take off?

The weight of the plane (weight = mass x gravity) in relation to the thrust must be a massive factor. To acheive uplift you need air movement and on a 747 that is achieved by the pressure drop across the wings (Bernouli theorem) and in the question I cannot see how air movement is created. If there is an equivalent amount of air being blasted at the nose of the plane when on a conveyor belt then I would be confident that this would enable uplift and provided there is sufficient thrust the plane will take off. If there is no air movement but lots of thrust then yes it will take off just like a Harrier.

degsyspesh Posted on 03/04/2010 08:46
Will the plane take off?

Think about it as horizontal forces acting on the plane.

The thrust from the engines acts against the air and provides a horizontal force trying to push the aircraft forwards.

The conveyor belt may be travelling in the opposite direction to this force, but it can't actually impart any force onto the aircraft as it's wheels are effectively just casters.

Therefore you have an imbalance of forces on the aircraft and so it moves forward causing a differential air pressure over the wings and hence takes off. piece of p1ss


The_263 Posted on 03/04/2010 08:50
Will the plane take off?

If it was true then airports would have a much smaller footprint as we'd have conveyor belts enabling a 747 to take off. Utter bollox.

The_263 Posted on 03/04/2010 08:54
Will the plane take off?

C&P

The case of the plane on a conveyor belt has been extensively discussed in the online world, and still doesn't have a definite conclusion. Or rather, there are two opposing sides which believe wholeheartedly in their explanation, and these sides will never agree. The question is this:

A plane is standing on a runway that can move (some sort of band conveyer). 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?

I've read a thousand people's opinions about this and heard every comparison ranging from a skateboard on a treadmill to a weightless car on a sheet of paper. Taking into account some major assumptions (a plane on a conveyor belt is actually plausible; frictionless wheels, bearings, conveyor belt; no wind; ideal/instantaneous control system), my take on it is this: The plane won't take off [Edit: I changed my mind]. Here's my reasoning:

1. In order for a plane to take off, it needs to have air passing over its wings at a certain speed. This air can come from the plane moving down the runway, or it can come from wind. Theoretically, a plane can take off while sitting completely still, as long as there is a significant amount of headwind. However, since there's no wind in this example, the plane must be moving forward at a considerable velocity.

2. A plane's wheels are "dumb". In other words, they're only there to reduce friction. A plane could just as easily have no wheels and just rest on its belly on the runway. It could still take off because its motion is produced by thrust from its engines or the movement of air from its propellers. The wheels will spin when the plane is in motion and in contact with a surface.

3. As many people have pointed out, the question's wording can be confusing.

a. If "plane speed" means "angular velocity of the wheels with respect to a stationary/ground observer", the conveyor belt would spin at an infinitely increasing rate, which is logically impossible. For example, if the wheels started to spin at 100 rpm, the conveyor would ramp up and spin at 100 rpm. But this would cause the wheels to actually be spinning at 200 rpm from the point of view of a stationary observer because the ground is no longer stationary but is moving at 100 rpm in the opposite direction. This would force the conveyor belt to spin at 200 rpm, 400 rpm, 800 rpm, etc., ad infinitum.

b. If "plane speed" means "angular velocity of the wheels with respect to the conveyor belt", the velocity of the conveyor belt would always equal the velocity of the wheels, no matter what. This means that the plane wouldn't move, no matter what. If the wheels started to spin at 100 rpm, the conveyor would ramp up and spin at 100 rpm. From the point of view of the conveyor belt, the wheels would still be spinning at 100 rpm even though they're actually spinning at 200 rpm from the point of view of a stationary observer. No matter what speed the wheels spun, the conveyor would always be spinning at the same speed as the wheels. This would prevent any forward motion of the plane.

c. If "plane speed" means "linear/horizontal velocity of the plane with respect to a stationary/ground observer", the plane speed would always be zero because the conveyor belt would always cancel out any forward motion of the plane. For example, if the plane started moving at 100 mph to the right (with motion derived from thrust), the conveyor belt would immediately begin moving at 100 mph to the left. Although the wheels would be spinning at an incredibly high rate (the wheel diameter doesn't equal the conveyor belt diameter, so the conveyor belt speed of 100 mph would translate to a wheel speed of something like 100,000 rpm [total guess, but the concept is there]), the plane would not change position from the point of view of a stationary observer. If it started at point A, it would stay at point A. This is the same result as part b.

d. If "plane speed" means "linear/horizontal velocity of the plane with respect to the conveyor belt", it's the same as part a. The conveyor belt would spin at an infinitely increasing rate.

So in conclusion, the plane wouldn't take off because it wouldn't move from its original location.


Not_Smog Posted on 03/04/2010 10:04
Will the plane take off?

I'm with The_263 on this one.

Where does the lift come from it the plane is stationary?



flaps Posted on 03/04/2010 10:29
Will the plane take off?

263's copy and paste is incorrect. The plane isn't stationary.

Read the thread.

borolad259 Posted on 03/04/2010 10:30
Will the plane take off?

The plane isn't stationary, as has been explained ad infinitum.

The_263 Posted on 03/04/2010 10:43
Will the plane take off?

So it's all to do with thrust and nothing to do with Bernouli theroem?

Why do you need wings if you can take off without them?

flaps Posted on 03/04/2010 10:46
Will the plane take off?

The plane needs wings to take off.

It needs to be moving forwards to take off.

The plane will still move forwards, even on the treadmill.

Please read this again: the plane will still move forwards, even on the treadmill.


The_263 Posted on 03/04/2010 10:53
Will the plane take off?

So I'll repeat, is air flow over the wings not a factor on this conveyor belt?

flaps Posted on 03/04/2010 10:56
Will the plane take off?

Air will flow over the wings because the plane will move forwards, like how any other plane takes off.


The_263 Posted on 03/04/2010 11:01
Will the plane take off?

Your failing to recongnise the balance between thrust and drag combined with lift and gravity.

Unlike good sex, it's not just thrust that's important.

NeddySeagoon Posted on 03/04/2010 11:08
Will the plane take off?

"A jet plane tries to take off on a conveyor belt which is programmed to match the wheel speed of the plane"

Therefore when the plane starts moving, the conveyor belt will move to stop the wheels rotating. That means that the belt will move in the same direction as the plane, actually increasing it's speed and shortening take off time as someone said WAY UP THERE^^^^^^^

The belt cannot match the wheel speed by moving in the opposite direction.


flaps Posted on 03/04/2010 11:09
Will the plane take off?

"it's not just thrust that's important."

That's all that is important. Because thrust is what drives the plane forwards allowing it to take off. The plane isn't moved forward by the rotation of the wheels.

You're overcomplicating the effect of the treadmill on the movement of the plane, hence your failure to understand the problem.

Please read the thread.

NeddySeagoon Posted on 03/04/2010 11:14
Will the plane take off?

"So I'll repeat, is air flow over the wings not a factor on this conveyor belt?"

The plane moves relative to the ground, not relative to the conveyor belt, so it still developes ground speed and lift.

Towell Posted on 03/04/2010 11:22
Will the plane take off?

People are used to seeing cars and bicycles on rolling roads, where the motive force is provided by driving the wheels.

Aeroplanes obviously don't work in this fashion the propeller or jet engine provides thrust which provides the acceleration by acting against the air and not friction with the ground.


The_263 Posted on 03/04/2010 11:23
Will the plane take off?

"Because thrust is what drives the plane forwards allowing it to take off. The plane isn't moved forward by the rotation of the wheels."

For a Harrier true, that is light and has thrust capacity. Thrust is one of 4 acting forces on a 747. Continue to ignore drag, gravity and lift.

Towell Posted on 03/04/2010 11:28
Will the plane take off?

The thrust force is still greater than the drag forces and the frictional forces due to the wheels contact with the ground and through the bearings.

Why would the drag force be any greater for a plane on a conveyor than for a plane on a runway? Assuming that the bearings are reasonably free.

Therefore if thrust is greater than drag then the plane accelerates relative to the air, this creates airspeed over the wing, this creates lift, when the lift is greater than acceleration due to gravity then the plane accelerates in the upwards direction and take off?

flaps Posted on 03/04/2010 11:28
Will the plane take off?

A 747 is not a car with wings. It uses jet engines to generate thrust which propel it forwards down a runway, allowing it to gain lift and take off.

A runway that is a treadmill will not prevent the plane from moving forwards, hence the plane will still take off.

Please read the thread.

borolad259 Posted on 03/04/2010 11:30
Will the plane take off?

Flaps, the penny will drop for most, but clearly not everyone. I would have lost patience by now. [:D]

The_263 Posted on 03/04/2010 11:36
Will the plane take off?

If a 747 had the thrust capacity to overcome the forces of drag, gravity and much reduced friction via the wheels it wouldn't be a 747.

Towell Posted on 03/04/2010 11:38
Will the plane take off?

Sorry?

flaps Posted on 03/04/2010 11:40
Will the plane take off?

The_263: what do you think the difference is between a 747 trying to take off from a runway and the same plane trying to take off from a runway-length treadmill rotating counter to the movement of the plane's wheels?

degsyspesh Posted on 03/04/2010 11:44
Will the plane take off?

To anyone who did GCSE Physics this should be straight forward. All movement is caused by a force. You have the planes engines creating a force in one direction but the conveyor can't create a force in the other as the planes wheels are just castors.

Even without the planes engines running, if you assumed that the bearings on the planes wheels were frictionless then you could run the conveyor as fast as you liked and the plane would just sit there with it's wheels spinning due to inertia.

In reality the planes wheels won't be frictionless but this is negligble compared to the thrust of the engine.

Julios_Hairband Posted on 03/04/2010 12:01
Will the plane take off?

Degsys- [^]

The_263 Posted on 03/04/2010 12:08
Will the plane take off?

"The_263: what do you think the difference is between a 747 trying to take off from a runway and the same plane trying to take off from a runway-length treadmill rotating counter to the movement of the plane's wheels?"

Answer: a hypothetical question.

Is thrust alone sufficient to create flight: answer yes.

Is the level of thrust available on a fully laden conventional 747 with standard tyres sufficient to cause it to fly off a perfectly designed conveyor belt that can run at any rpm? My opinion = No.

flaps Posted on 03/04/2010 12:18
Will the plane take off?

Yes it is a hypothetical question. This whole discussion is about a hypothetical question.

Can you explain why a plane on this treadmill will not move forwards as it would on a normal runway?

flaps Posted on 03/04/2010 12:25
Will the plane take off?

Here's a link for you:


It's also on youtube.


Link: Mythbusters

morning_roary Posted on 03/04/2010 12:30
Will the plane take off?

depends how bloody windy it is [^]

The_263 Posted on 03/04/2010 12:48
Will the plane take off?

Using an ideal and perfectly designed conveyor belt, it will not move forward until the force of the thrust exceed the forces of drag, mass, gravity exerted on the belt. Whether a 747 has sufficient thrust to acheive this point on a perfect belt is bordering on unimaginable. What is completely inconceivable is whether thrust alone can create any uplift on a fully laden 747 that has its own ground speed limitations anyway.

flaps Posted on 03/04/2010 13:58
Will the plane take off?

Nobody has suggested that thrust alone can create uplift for a normal plane. The thrust is what provides forwards movement, which is what a plane needs to take off.

The point of this question is whether the conveyor belt will make any difference to the forward movement of the plane as it takes off. People often mistakenly think it will, as they imagine the conveyor belt forcing the plane to stay in place - which is not what would happen as the wheels are free-wheeling.

I'm repeating what has been said numerous times in this thread, which you could have read for yourself had you: read the thread.

br14 Posted on 03/04/2010 14:59
Will the plane take off?

Bloody hell, is this still going on. It's basic basic physics.

Lift is developed by the planes wings moving through air.

Thrust is basic Newtons Laws. Action and reaction are equal and opposite.

Thrust against the air pushes the plane forward - not it's bloody wheels. It's not a car. If it was driven by it's wheels the minute it got in the air it would crash to the earth because there'd be no traction.

Of course it takes off.

The conveyor belt would need chains tied to the planes wheels to prevent it happening!