Will it take off ?!

Post by **Alchemist** » 26 Feb 2006, 23:16

The Jezster wrote:Are you for real?? seriously? its EXACTLY what is says!!!

Read the first line, whats the phrase in brackets??? (conveyor belt), then they have simply shortened the word to conveyor because noone in their right mind would have trouble understanding that!! Sorry, i didnt mean to sound like i was having a pop at you, im not, just a little staggered thats your argument...

Jez

Let hom have this small victory, for it is just a small battle, we shall still win the war.

The plane will take of if the belt or the whole conveyour system was to move

Post by **ONMEHEADSON** » 26 Feb 2006, 23:21

Chaps, I'll repeat again for clarity:

the conveyor has a control system (it doesn't explain what this is) that tracks the aircrafts speed (the distance travelled) and tunes the conveyor to be exactly the same in the opposite direction.

Thus, the aircraft doesn't move forward.

Jez, does your conveyer in your experiment have a control system that tracks the aircraft "speed"?

Post by **Alchemist** » 26 Feb 2006, 23:27

OMHS

Have you seen the bit in the italian job where they push the cars out of the back of the bus.

Your arguement would make this impossible!

Make the bus a very very long bus.

Now put a plane inside it.

Can you push it out the back??? I assume so.

If the bus is going at 600 mph the plane is going at 600mph the other way.

Relative to the bus the plane is going at 1200, but relative to the air it is going 600.

It is not stationary.

Post by **ONMEHEADSON** » 26 Feb 2006, 23:29

The plane will take of if the belt or the whole conveyour system was to move

Not if the plane isn't moving forward it wont take off......

Post by **ONMEHEADSON** » 26 Feb 2006, 23:43

Jez / Alchemist.....

Read my posts again.

The question is posed that the aircraft doesn't move - the aircraft speed is counteracted by the "control system" of the conveyor - thats what it says.

If this is not the case, then please explain to me what is.

Post by **Karrde** » 26 Feb 2006, 23:43

I have been away for a couple of days... and you are all still saying the same things!

I admire the stamina you guys are clearly packing!

Post by **Billy Whiz** » 26 Feb 2006, 23:55

ONMEHEADSON wrote:Jez / Alchemist.....

Read my posts again.

The question is posed that the aircraft doesn't move - the aircraft speed is counteracted by the "control system" of the conveyor - thats what it says.

If this is not the case, then please explain to me what is.

So you think the aircraft doesn't move? As I said above, if the aircraft doesn't move then it has zero speed, in which case under the conditions of the experiment the belt will have to be set at zero speed too. If neither the aircraft not the belt are moving, the wheels can't move either. But the engines are on. How can everything be just standing there stationary, but with the engines on turbo charge? Why is the plane not moving even though massively powerful engines are on forward thrust? Please answer!

PS The person running at "8mph" on a running machine actually has zero speed, because he is not covering any distance (this is why he remains in the room). The dial on the machine is a false reading - it's telling him that due to the force he is exerting on the treadmill he would be running at 8mph if he was on a solid, non-moving surface. But this is a virtual speed. His speed is in fact 0mph. Try relating this idea to the plane on the conveyor belt and it may make things clearer.

Post by **Alchemist** » 26 Feb 2006, 23:59

ONMEHEADSON wrote:Jez / Alchemist.....

Read my posts again.

The question is posed that the aircraft doesn't move - the aircraft speed is counteracted by the "control system" of the conveyor - thats what it says.

If this is not the case, then please explain to me what is.

No it does not say the plane does not move.

It says the planes speed.

The plane must therefore have speed, or this would be a very silly argument!

If the plane has speed it must be moving.

The fact that the belt/conveyor is moving underneath it at the same speed but in the opposite direction, has no effect other than to make the wheels spin twice as fast (Ask JaseC, he cottoned on earlier today)

With the wheels have no effect, the planes thrust drives it forward and into the air.

Post by **MrSmedley** » 27 Feb 2006, 00:16

I am confused by this. What's a conveyor if it's not a conveyor belt?

Yes Karrde the stamina of these guys is amazing. OMHS you seem to be repeating the same thing over and over again while not understanding any of the tens of explanations saying why what you're saying is wrong.

Essentially this is what's going on:

OMHS: The plane doesn't move. The conveyor goes the same speed in the opposite direction
Someone else: Yes it does move, this is why
OMHS: Read the question, it doesn't move because of the conveyor
Someone else: It does, here's another explanation
OMHS: But the plane doesn't move, the conveyor has a control system that stops it moving

Post by **Alchemist** » 27 Feb 2006, 00:20

MrSmedley wrote:I am confused by this. What's a conveyor if it's not a conveyor belt?

Yes Karrde the stamina of these guys is amazing. OMHS you seem to be repeating the same thing over and over again while not understanding any of the tens of explanations saying why what you're saying is wrong.

Essentially this is what's going on:

OMHS: The plane doesn't move. The conveyor goes the same speed in the opposite direction
Someone else: Yes it does move, this is why
OMHS: Read the question, it doesn't move because of the conveyor
Someone else: It does, here's another explanation
OMHS: But the plane doesn't move, the conveyor has a control system that stops it moving

Mr Smedley

What Offhisheadson is trying to imply is that not only the belt, but the belts drive mechanism, pulleys wheels motors etc can all move.

Akin to the shopping Mall moving as well as the escalator.

Dosent matter though. he's still wrong

Post by **djwhew** » 27 Feb 2006, 00:24

what came first the chicken or the egg

sorry just had to throw that in

i just hope the bloody tyres dont burst

Post by **uncsimes** » 27 Feb 2006, 08:41

OMHS, I don't think you fully understand the interaction between the conveyor and the plane, specifically the wheels / axle.

Near us, there are some shopping centres that have inclined conveyors for pulling wheelchairs up to the shopping level (not 'stepped' escalators like in the Tube, but an inclined 'flat' conveyor).

If you put a wheelchair at the top of this conveyor (with the brakes off) do you think that the wheelchair will be held steady by the upwards motion of the conveyor, or do you think it will roll down, despite the conveyor moving upwards?

Post by **uncsimes** » 27 Feb 2006, 08:51

Alchemist wrote:Not true

Wheels move twice as fast, so bearings/grease will both get slightly hotter

This will result in

a/ Tighter bearings providing more friction

b/ Less viscous oil, producing less friction

If A>B then longer take off time/distance

if A<B then shorter take off time/distance

if A=B then same take of time/distance

OK, I agree with you

I think that the above is pretty much the definitive word on the 'distance to takeoff' argument. (I'd not considered reduced friction as the bearing lubricant heats up).

Too many unknowns, therefore can't definitively say whether it needs more or less runway, but we're only talking about a couple of metres in either direction - doesn't affect the plane taking off, so the whole argument isn't relevant to the actual question. Sorry for complicating matters!

Post by **murf** » 27 Feb 2006, 09:02

Most conveyor belts are quite short and many are in shopping centres / airport buildings etc. If we assume the plane is sat on one of these it will soon reach the end and run into a wall or will have lost its wings by then anyway so it won't take off.

Why are we assuming it is on an infinitely (or at least several hundred metres) long runway with space either side so it doesn't catch its wings on anything?

Not forgetting the possibility of a roof........

Post by **ONMEHEADSON** » 27 Feb 2006, 09:34

by Alchemist: Mr Smedley

What Offhisheadson is trying to imply is that not only the belt, but the belts drive mechanism, pulleys wheels motors etc can all move.

Akin to the shopping Mall moving as well as the escalator.

Dosent matter though. he's still wrong

Ha... I like that one Alchie....... "Offhisheadson"

Madchester, please post this "new" question to your pilot friends for a bit of fun, and see how they respond:

An aircraft is standing on a very long runway that can move (a conveyor belt). The aircraft moves in one direction, while the conveyor belt moves in the opposite direction. This conveyor belt has a control system that tracks the aircraft's wheels speed and tunes the speed of the conveyor belt to be exactly the same as the wheels, but in the opposite direction. There is no wind. The pilot begins to add thrust to the engines...

Post by **uncsimes** » 27 Feb 2006, 09:44

ONMEHEADSON wrote:
by Alchemist: Mr Smedley

What Offhisheadson is trying to imply is that not only the belt, but the belts drive mechanism, pulleys wheels motors etc can all move.

Akin to the shopping Mall moving as well as the escalator.

Dosent matter though. he's still wrong
Ha... I like that one Alchie....... "Offhisheadson"

Madchester, please post this "new" question to your pilot friends for a bit of fun, and see how they respond:

An aircraft is standing on a very long runway that can move (a conveyor belt). The aircraft moves in one direction, while the conveyor belt moves in the opposite direction. This conveyor belt has a control system that tracks the aircraft's wheels speed and tunes the speed of the conveyor belt to be exactly the same as the wheels, but in the opposite direction. There is no wind. The pilot begins to add thrust to the engines...

Does this mean that you now think that the plane will take off? Sounds like it.

(nb - the speed of the planes wheels is the same as the plane itself. As all are attached, they must all be moving at the same speed, assuming bits don't fall off or accelerate away ahead of the airframe)

Post by **murf** » 27 Feb 2006, 09:47

uncsimes wrote: (nb - the speed of the planes wheels is the same as the plane itself. As all are attached, they must all be moving at the same speed, assuming bits don't fall off or accelerate away ahead of the airframe)

No!!! Wheel speed can be taken to be the rotational speed of the wheels (not the 'horizontal' speed) and this must be the same as the conveyor belt if the plane stands still.

Under most people's logic: The conveyor body itself is fixed and if the plane is moving forward at 100mph, the top conveyor belt moves backwards at 100mph meaning the wheels have a rotational speed of 200mph.

All assuming no wheelspin etc.

Post by **ONMEHEADSON** » 27 Feb 2006, 10:19

(nb - the speed of the planes wheels is the same as the plane itself. As all are attached, they must all be moving at the same speed, assuming bits don't fall off or accelerate away ahead of the airframe)

You clearly have mis-understood unscimes!!!

This is not the case!

Post by **uncsimes** » 27 Feb 2006, 10:19

murf wrote:
uncsimes wrote: (nb - the speed of the planes wheels is the same as the plane itself. As all are attached, they must all be moving at the same speed, assuming bits don't fall off or accelerate away ahead of the airframe)
No!!! Wheel speed can be taken to be the rotational speed of the wheels (not the 'horizontal' speed) and this must be the same as the conveyor belt if the plane stands still.

Under most people's logic: The conveyor body itself is fixed and if the plane is moving forward at 100mph, the top conveyor belt moves backwards at 100mph meaning the wheels have a rotational speed of 200mph.

All assuming no wheelspin etc.

The 'wheels', as a whole, must move at the same speed as the plane, as they are attached. At 10m/s, after 10 seconds, the plane, its wheels and other components have all travelled 100metres. Unless something has fallen off. Everything will have a displacement of 100m (i.e. travelled 100m in a particular direction, down the runway)

What most people are implying is that the speed of a point on the circumference of the wheels is higher than the speed of the plane. A point on the circ. of the wheel will have travelled a distance of 200m, and will have been travelling at a 'speed' of 20m/s.

If OMHS had said the speed of the tyres, then this is a different problem, and causes the 'impossible solution', i.e. you cannot get a steady state - either the plane stays still and both the tyres and belt travel at , say, 10m/s (in which case there is no force opposing the engines thrust and the whole thing is in contravention of Newtons 1st Law), or the plane moves forward and the belt then has to keep accelerating to match the increasing speed of the tyres (relative to the belt) until both are rotating at an infinite speed (which is silly).

Anyway, the question clearly states that the conveyor matches the speed of the plane. Why bother inventing different questions when some people still aren't convinced by the answer to the original question set?

Anyway - I thought you were in the 'sperical earth, normal laws of physics' camp, not the 'flat earth' one. You now seem to be implying that it is possible for the plane to stand still (and hence not take off). Or have I missed something?? (or am I just being an arse mentioning things which are irrelevant to the fact that the plane takes off

)

Post by **ONMEHEADSON** » 27 Feb 2006, 10:20

The 'wheels', as a whole, must move at the same speed as the plane, as they are attached

No No No No No!!!!!

Unscimes, read the thread again!

Post by **uncsimes** » 27 Feb 2006, 10:21

ONMEHEADSON wrote:
(nb - the speed of the planes wheels is the same as the plane itself. As all are attached, they must all be moving at the same speed, assuming bits don't fall off or accelerate away ahead of the airframe)
You clearly have mis-understood unscimes!!!

This is not the case!

Just being picky really - depends whather youre talking about speed or velocity, distance or displacement, wheels or tyres etc etc... None of which is relevant to the original question so I apologise for being awkward.

What about the wheelchair on the conveyor - had a chance to think whether it stays up or rolls down yet?

Post by **uncsimes** » 27 Feb 2006, 10:25

ONMEHEADSON wrote:
The 'wheels', as a whole, must move at the same speed as the plane, as they are attached
No No No No No!!!!!

Unscimes, read the thread again!

OK - maybe we've moved away from Zeus's original question and made up a new one, in which case I'll shut up!

Still interested to see how the wheels, as a whole (as opposed to a point on the circumference) can travel at a different speed to the aircraft, whilst remaining attached.

Please explain.

Post by **ONMEHEADSON** » 27 Feb 2006, 10:28

The wheels are free wheeling, they are not mechanically attached to anything.

If a giant Shrek could pick up our plane off the runway and turn it upside down, and brush his fingers over the wheels they would spin (the Aircraft is in his hand and not moving). Depending on how hard he brushes his big fat green fingers over the wheels determines how long they spin for.

Clear now?

Post by **uncsimes** » 27 Feb 2006, 10:55

ONMEHEADSON wrote:The wheels are free wheeling, they are not mechanically attached to anything.

If a giant Shrek could pick up our plane off the runway and turn it upside down, and brush his fingers over the wheels they would spin (the Aircraft is in his hand and not moving). Depending on how hard he brushes his big fat green fingers over the wheels determines how long they spin for.

Clear now?

Of course, as I said, the tyres would have a speed. This will be based on how fast Shrek is rubbing his hands over them. Say the wheels have a diameter of 50cm, the tryes will travel a distance of approx. 1.57m for every revolution. If Shrek makes them spin at 2 revolutions per second, the tyres will have a speed of 3.14m/s.

The wheels as a whole however have a speed of zero m/s (assuming Shrek isn't walking along at the same time). They are staying in the same place, spinning. They don't go anywhere. Nil distance travelled = nil speed.

This is all very interesting, although irrelevant to the original question posed by Zeus.

Although as you have stated that the wheels are freewheeling, and are not mechanically attached to anything, I assume that under the original question, you now accept that the plane will take off.

Is this true - are you now a 'flier'?

And are you now working on a different problem?

Post by **The Jezster** » 27 Feb 2006, 10:56

Bloodyhell!! OMHS is arguing FOR take off now...

Incidentally, according the laws of motion etc it is the centre point of the wheel (axis) that will be travelling at the constant speed (ie: 10mph) The very bottom part of the wheel (the part immediately touching the belt) will actually be travelling at 0mph at the exact moment it touches the belt, while the point at the very top (directly opposite the part touching the belt) will be going at 20mph at that exact same moment.

Post by **uncsimes** » 27 Feb 2006, 11:05

The Jezster wrote:Bloodyhell!! OMHS is arguing FOR take off now...

Incidentally, according the laws of motion etc it is the centre point of the wheel (axis) that will be travelling at the constant speed (ie: 10mph) The very bottom part of the wheel (the part immediately touching the belt) will actually be travelling at 0mph at the exact moment it touches the belt, while the point at the very top (directly opposite the part touching the belt) will be going at 20mph at that exact same moment.

Yeah - don't think there are any 'no flyers' left now.

You are of course correct - The axis will be travelling at the same speed of the plane.

Quick question though - are the speeds that you quote above for top dead centre and bottom dead centre right when the belt is also moving? On a static runway, I can see that the bottom dead centre will be travelling at zero mph and TDC at 20mph. If the belt is moving at 10mph in the opposite direction, does this mean that bottom dead centre is moving at -10mph at the point of contact.

For the avoidance of doubt - none of this has any bearing on whether the plane flies - its just an argument about definitions really.
Of course, the plane still takes off and flies.

Post by **Zeus** » 27 Feb 2006, 11:06

Christ on a bike I have created a monster.

Lets face it, we seem to have moved away from the point where some people were starting to understand where the 'fly' guys were coming from, and even gained a defector !

The whole basis of the argument isnt about speed matching etc, its about force. The conveyor cannot exert enough force on the freewheeling wheels to counteract the force exerted on the airframe by the engines.

Post by **ONMEHEADSON** » 27 Feb 2006, 11:06

Bloodyhell!! OMHS is arguing FOR take off now...

Incidentally, according the laws of motion etc it is the centre point of the wheel (axis) that will be travelling at the constant speed (ie: 10mph) The very bottom part of the wheel (the part immediately touching the belt) will actually be travelling at 0mph at the exact moment it touches the belt, while the point at the very top (directly opposite the part touching the belt) will be going at 20mph at that exact same moment.

No his isn´t....... he still believes that the way the question is worded it wont take off.

I fully understand the problem with the question Jez, and why you and the "believers" say it takes off.

Do you know what did it for me?
This quote from you:
"You are piloting a plane on a mile long treadmill. "

Why would the treadmill need to be 1 mile long, if it has a control system that negates the aircrafts speed?

The question is ambigious in it´s wording, as you as saying the aircraft is allowed to move forward.

Post by **The Jezster** » 27 Feb 2006, 11:09

The distance is irrelevant, it could be half a mile or 20 miles, it was just as an example to give perspective.

Post by **uncsimes** » 27 Feb 2006, 11:16

ONMEHEADSON wrote:
Bloodyhell!! OMHS is arguing FOR take off now...

Incidentally, according the laws of motion etc it is the centre point of the wheel (axis) that will be travelling at the constant speed (ie: 10mph) The very bottom part of the wheel (the part immediately touching the belt) will actually be travelling at 0mph at the exact moment it touches the belt, while the point at the very top (directly opposite the part touching the belt) will be going at 20mph at that exact same moment.
No his isn´t....... he still believes that the way the question is worded it wont take off.

I fully understand the problem with the question Jez, and why you and the "believers" say it takes off.

Do you know what did it for me?
This quote from you:
"You are piloting a plane on a mile long treadmill. "

Why would the treadmill need to be 1 mile long, if it has a control system that negates the aircrafts speed?

The question is ambigious in it´s wording, as you as saying the aircraft is allowed to move forward.

I'm sorry but I just don't understand where you're coming from.

You say that you understand the mechanics of why the plane moves but still don't think it does?

In which case you can never be persuaded. As long as you keep reading things into the question that aren't there then you will never believe that the plane can move, and no amount of logic or science will change that.

I guess we'll just have to agree to disagree. I don't see where else this can go and don't want to keep arguing with a fellow forum member.

EDIT: I posed the question on about page 2 of this thread as to what FORCE is opposing the force of the engines. No one has been able to answer this, because there isn't one (other than negligible friction / air resistance).

For the aircraft to stand still, an equal force must oppose the engine thrust. You understand that force isn't transmitted from the wheels/conveyor, as you stated about 5 or 6 posts ago. So where is this force coming from in your world where the plane isn't allowed to move. The speed of the belt is irrelevant - where is the opposing force????

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Will it take off ?!

Will it take off ?!