Plane on a conveyor belt?
- Thread starter Craig
- Start date
Napster
And the Wide Green Bug
but u will need a greater force than the treadmill to move over the belt?? but yes it could be done as its exactly what i said right back at the start......but remember the conveyor belt is matching the same pace so a greater force is required is it not? which just keeps getting greater?
ollyc98
Ex. Club Member
The conveyor belt matches the force of the plane, I don't doubt that, however that force doesn't affect the plane as it's disconnected by the wheel bearings.
You can rev your car engine all you like but if the clutch isn't engaged the wheels won't turn.
Am I gettin through to you at all?
You can rev your car engine all you like but if the clutch isn't engaged the wheels won't turn.
Am I gettin through to you at all?
Again its NOT SPEED ITS FORCE.
Forward thrust provided by engines MINUS opposite FORCE provided by head wind. - If both equal the plane will not move, if the wind speed is enough it will create lift so yes the plane will 'fly' but go no where. Just like how birds can fly 'stationary' in strong headwinds.
that's a completely kettle of fish, in theory yes it would stay still, but who in their right mind would put it to the test ? have you seen those sky diving simulators ? the work using this principle, air is blown upwards at a speed thats fast enough to counteract the thrust of the skydiver being pulled downwards by gravity.
Ed, imagine both plane and conveyor are stationary to begin with.
The plane applies jet thrust as normal. In normal practice (With no such conveyor) this would cause the plane to move forwards, rolling on its wheels (Which enable the forward motion by rotating).
BUT
As soon as the slightest bit of rotation is detected in the wheel, the belt moves in the opposite direction at the EXACT same speed.
Has the plane even started moving? (Speaking from a geographical standpoint).
The plane increases thrust.
The wheels rotate faster.
The conveyor speeds up.
The plane remains stationary.
And then all of a sudden somehow it takes off?
Yes, which is why it is more costly in fuel to fly one way around the world than the other.
The plane applies jet thrust as normal. In normal practice (With no such conveyor) this would cause the plane to move forwards, rolling on its wheels (Which enable the forward motion by rotating).
BUT
As soon as the slightest bit of rotation is detected in the wheel, the belt moves in the opposite direction at the EXACT same speed.
Has the plane even started moving? (Speaking from a geographical standpoint).
The plane increases thrust.
The wheels rotate faster.
The conveyor speeds up.
The plane remains stationary.
And then all of a sudden somehow it takes off?
Yes, which is why it is more costly in fuel to fly one way around the world than the other.
Another point. Most planes take off at iirc 100mph ish. Assuming this the greatest speed a conveyor belt would reach would be 200mph say if it was doing the opposite speed of the plane. Forces applied to the plain would be relatively tiny. The plane would then take off at a ground speed of 100mph, and off it would go.
Napster
And the Wide Green Bug
as the wheels are disconnected doesnt that make "free" movement of them in what ever direction a force is moving random??????........as in a force moving forwards and backwards on a wheel with "freeplay" in any direction abit hard to tell which way the wheel will choise to go if BOTH forces are equel?
Haha you must be on a deliberate wind up, or you may genuienly not get this?
A plane needs X airspeed mph to take off. Its sitting on a belt, it applies power, the plane begins to move, at 50mph you take a snapshot of what is going on. This is what you would see:
Air speed of plane relative to ground 50mph
Speed of plane relative to conveyor 100mph
The conveyor would make no difference, (well very little) once enough air speed is made over the wings (thats the only thing that matters, wheel speed which is what your referring to is irrelevant. It would take off.
Think of it the other way around. If the conveyor moved first, then the plane would have to move forwards somehow to stay in the same geographical position. It would probably use its primary means of propulsion i.e its engines.
If the plane did nothing, it would move backwards.
If the plane did nothing, it would move backwards.
Thats exactly what I feel like saying to you, sir.
How is air speed being made over the wings at all?
The conveyor is not dragging the air around it towards the plane. Therefore, no air is flowing over the wings. Therefore, no lift is generated.
The plane is having to apply the same amount of thrust as it usually would to achieve 50mph, just to stay still.
Correct, also it would take very little force from the engines to keep it stationary. Only that required to counter act the frictional forces in the wheel bearings.
Napster
And the Wide Green Bug
as i said before.......it would be abit easier to answer if we new all the facts, although dont think it would help people as they actually know the answer already!!! i cant answer this question as im unsure what would happen due to not knowing weight of plane (although we could take a normal planes weight)........speed of the convetor belt, size, thickness of belt!! size of engines and bhp?? oncoming airspeed! air temp! are the tyres pumped up............... what!!! or maybe none of it!!!!!
imo...if the belt was moving slowly (i think) the plane would move back!!
If I put a stationary skateboard on a stationary treadmill, then steadily increased the speed from 0mph to 5mph, the skateboard would move backwards and the wheels would not rotate, due to friction and gravity. Obviously you can affect this by acceleration speeds, a violent jerk might have a different effect, as Anthony was referring to with the matchbox cars and the tray.
I think that you are right there Napster.
How so? the belt surface will be smooth, its resistance to the air would be very high, the mechancial connection (if you like) would be very poor. Its effect would I expect be inversly proportional to its distance away from it. It would cause no effect several meters above where the wings are. It may make some difference but nothing to stop the plane doing what it would anyway. Like I said the plane would take off at about 100 mph, and so the maximum speed the belt would be moving would be 200mph, which the plane would easily be able to exceed and take off, regardless.
Napster
And the Wide Green Bug
but the mass of the plane would cause the belt to move it...............the plane would have to lose weight and be lifted up (by a crane) just so part of the wheel was touching and no weight...then the plane would stay stationary, wheels would turn and the belt rotate!!!
a heavier mass, contributing to gravity no? making it move with the belt? sorry no realy relavent
a heavier mass, contributing to gravity no? making it move with the belt? sorry no realy relavent
You dont need any more facts.
weight of plane - Irrelevant.
speed of the conveyor belt - equal to but in the opposing direction of the planes movement.
size, thickness of belt!! - Irrelevant
size of engines and bhp?? - irrelevant
oncoming airspeed! - assumed to be zero since none has been mentioned, but other than a minor ground effect caused by a smooth belt, irrelevant.
air temp! - irrelevant
are the tyres pumped up, - assumed to be a normal plane with no defects, therefore irrelevant.
You have to simplify a force question into its basic components, the only thing really stopping this plane moving is its rolling resistance. The is no point trying to complicate anything more than it needs to be with all the above suggestions.
Provided that this resistance (friction) is smaller than that of the engines thrust (which it will obviously be) the plane will take off every time.
ollys skateboard on a treadmill is a good analogy, if it was a powered treadmill moving at 10mph, and you were pushing the board at enough force to make it move at a speed of 10mph in the opposite direction of travel, then the board would stay still on the treadmill wouldnt it, there would be no air movement past our olly would there, so if olly was a plane he would have no lift, so no take off regard less of the effort put in.
Napster
And the Wide Green Bug
im pretty sure at least 80% that you would or who ever was the "acting mass" on the board was either holding onto something to keep pressure on the board or extremely heavy.......but im still not sure heavy would keep it in place........its fixture.....or holding onto something, hands out either side to poles???
Where does it say that? I imagined it to be like sandpaper, and the plane to have great big grippy tyres.
Nor does it say that the wheel bearing resistance will be zero. It might be, but the question does not say that.
So it comes back to what Napster says about all the variables involved would produce different results.
Napster
And the Wide Green Bug
sounds fine to me?
When you say 'stay still', do you mean the wheels are rotating? Were you holding onto an anchor point?
Otherwise, why when I already have forward motion on a skateboard normally, do I slow down?
Thats not what he said. Also what you have written does not make sense.
No, the board would be moving at 10mph (relative to the ground) in the direction your pushing it, and 20mph relative to the treadmill. He would hit the controls on the treadmill very quickly hahaha.
If you HELD the board still then its effectively doing 10mph in the opposite direction to the treadmill already, depending on which one you want to use as the reference base.
Napster
And the Wide Green Bug
but i was having a jokea bout variables!!! sorry!!! just new problems / parts of equations where poping up so thought id add some more!!! sorry!!! but they could be considered i felt, but Ed said not.
regardless then of any other variable and question at start??
If someone places an analogy then you take normal day to day assumptions, or anything is just totally unrealistic.
I would take a day to day example lets say a Boeing 747, with a total engine power of 500,000 HP which equates to about 253200 lb of engine trust.
Do you honestly think regardless of surface that any treadmill with which the plane would be possible to pass over would provide enough opposing forces (via the friction in the wheels and ground effect) to stop the plane moving in the direction in which it wanted to?
You could now be quite daft and say yes. But in reality anyone capable of seeing the real problem here would know the right answer immediately.
Napster
And the Wide Green Bug
lol!!! weight! safety! control! manoverability! airport rules! saving fuel(think engines are on anyway)!!and im sure many others!!
very interesting debate
lol Is this a serious question?
Clearly it is. If rolling resistance is zero then why, if I was to lean on the plane, would it not move? They use tractors to overcome the rolling resistance (yes I am aware that people can pull planes but they need to overcome the rolling resistance which is definately not zero).
previous question:
Yes, obviously. The question clearly states that the conveyor can match the plane exactly.
Call me daft if you wish but I do not think that personal comments can settle an arguement.
previous question:
Yes, obviously. The question clearly states that the conveyor can match the plane exactly.
Call me daft if you wish but I do not think that personal comments can settle an arguement.
It scales perfectly. Use a model plane, it would work exactly the same. My own one will take off in about 30 meters from stationary (at a guess), I can tell you now what no amount of conveyor belt or anything like that would stop it doing this.
Napster
And the Wide Green Bug
yes it would require more forward thrust.......and conveyor would then match it?
that makes sense........and so does what Ed said bout his little plane! i can see that taking off regardless!!! why!!! crazy!!! but as your plane picked up speed..........so would the conveyor, so it would need to be a long belt
The earth is the base thats moving at 0mph (stationary)
You place a conveyor belt on it, and a plane on that. You add forward thrust to the plane, this acts against the earth, not the belt and begins to move. As it does so the belt begins to move in the opposite direction at the same speed (so negative to earth) net result is the belt moves at double the speed of the plane reference to the plane in the opposite direction.
Plane speed reference to the ground (your geograpical base) + X mph
Plane speed reference to belt 2*X mph
Belt speed reference to ground -X mph
Please don't take this personally but if you dont understand that, I really cannot make it any clearer.
Napster:-
Exactly. However it seems that this debate reaches one point... whether, if the conveyor alone were moving the plane would move with the conveyor or stay in the same place.
I say that it would not roll without being pushed. If the conveyor moved beneath the plane, the plane would move with the conveyor. Ed says the opposite. I haven't put a plane on a conveyor yet though.
Lets try.
Ground 'Speed' = 0
Plane 'Speed' = +10
Belt 'Speed' = -10
Actual Plane Speed = ground speed + plane speed - belt speed = 0
I do not understand why the belt would be moving at double speed. If it was, the plane would move backward.
Ground 'Speed' = 0
Plane 'Speed' = +10
Belt 'Speed' = -20
Actual Plane Speed = ground speed + plane speed - belt speed = -10
Exactly. However it seems that this debate reaches one point... whether, if the conveyor alone were moving the plane would move with the conveyor or stay in the same place.
I say that it would not roll without being pushed. If the conveyor moved beneath the plane, the plane would move with the conveyor. Ed says the opposite. I haven't put a plane on a conveyor yet though.
Lets try.
Ground 'Speed' = 0
Plane 'Speed' = +10
Belt 'Speed' = -10
Actual Plane Speed = ground speed + plane speed - belt speed = 0
I do not understand why the belt would be moving at double speed. If it was, the plane would move backward.
Ground 'Speed' = 0
Plane 'Speed' = +10
Belt 'Speed' = -20
Actual Plane Speed = ground speed + plane speed - belt speed = -10
You need to re-read what I have said.
To move any mass in a direction you need to apply a force, the force of which is limited in this case by the resistance of the wheels etc..
So if you have say X tonns of metal connected to a belt by wheels with Y friction its going to take Z time to accelrate the plane upto the same speed of the belt as limited by how long it takes to transfer this energy via the wheels/bearings.
If you had a belt that immediately went from 0 to 10 mph, the plane would initally sit still then slowly start to move in the direction of the belt, as the mass of the plane is high and the friction relatively low, this would take a noticeable amount of time. In fact exactly the same amount of time pretty much (ignoreing wind) as it would then take the plane to roll to a stop if you suddenly stopped the belt.
I see where your going wrong now. Your using different points of references for your speed measurements.
Imagine your standing on the ground next to the plane, and the belt. The plane is doing 10 mph, so is going away from you, if the belt is doing 10mph in the opposite direction towards you then the total difference between the plane and the belt is 20mph. And both the belt and the plane are moving away from you in different directions, and the plane is infact moving.
But to me that sounds exactly the same as what I have said i.e. the difference between +10mph and -10mph is indeed 20.
The forces either side are equal and opposite. And so the plane is mechanically moving at 10mph, but geographically at 0mph. So, lift is not generated.
If belt speed remained at -10 and the plane accelerated to +11, the forces would not be equal, resulting in geographical plane movement of +1mph.
Napster
And the Wide Green Bug
i was still thinking about this going off to bed lol :sleepy:
i do think that the plane would take off!
if the plane was moving at 20mph and the belt 10mph (i know thats not the question)........would the plane take more time / less time / same time to take off?? as you guys say that the plane will take off regardless of the rearward motion of the belt on the free flowing wheels (yet the wheels and belt shouldnt be taken into consideration you have said so..........)?
either: the plane takes off due to the belt having no effect on the wheels and therefore the plane moves across the moving belt untill desired speed then lifts off
weight of the plane causes the belt to move it backwards so the plane has to add more forward thrust / momentum but the belt matches this and stops the plane from prgressing up the belt?? then the plane cant take off as its simulating 100mph on a stationary posotion??
is the fundamental answer todo with forces and friction? and Nothingto do with the wheels? weight? engine power??
i do think that the plane would take off!
if the plane was moving at 20mph and the belt 10mph (i know thats not the question)........would the plane take more time / less time / same time to take off?? as you guys say that the plane will take off regardless of the rearward motion of the belt on the free flowing wheels (yet the wheels and belt shouldnt be taken into consideration you have said so..........)?
either: the plane takes off due to the belt having no effect on the wheels and therefore the plane moves across the moving belt untill desired speed then lifts off
weight of the plane causes the belt to move it backwards so the plane has to add more forward thrust / momentum but the belt matches this and stops the plane from prgressing up the belt?? then the plane cant take off as its simulating 100mph on a stationary posotion??
is the fundamental answer todo with forces and friction? and Nothingto do with the wheels? weight? engine power??
ollyc98
Ex. Club Member
I gave up long ago but just to add to what you said Ed, the wheels will be spinning at 2x the speed as the plane isgoing at say 10mph, and the belt going at -10mph makes the wheels go round at 20mph.
The only relation between the belt and plane is the wheels the rest of the plane is unaffected.
Open your mind! lol
The only relation between the belt and plane is the wheels the rest of the plane is unaffected.
Open your mind! lol
The wheels may be turning at 20mph, but all they are there to do is keep the plane off the ground. The plane will still have its full weight resting on its wheels until it generates enough lift to keep itself in the air.
They could be moving at 500mph but the plane still wouldnt go forwards. Therefore, no lift, therefore, plane still wholly reliant on wheels.
They could be moving at 500mph but the plane still wouldnt go forwards. Therefore, no lift, therefore, plane still wholly reliant on wheels.
OP
OP
Well, mythbusters have done it, so I guess we will have to wait until that show is on - one way I thought of it is that if the wheels can turn freely, then whichever way the belt moves, it will not move the plane.
Oh crap, that means it would take off....
Oh crap, that means it would take off....
