Plane on a conveyor belt?

Craig

Craig

Unofficial Member (Gold)
Club Member
Right, seen this before on a couple of other forums, apparaently Mythbusters have just done this myth, so thought I'd see what members on here think.

Basically there is a plane that is placed upon a conveyor belt which will always match it's speed - can the plane ever take off?


I say no, the plane is not moving forward so the wings cannot generate any lift to counter the weight of the plane.
The plane is not moving forwards because now matter how much thrust the plane generates with it's engines to increase it's groundspeed, the belt will just match that speed - if the plane goes twice as fast, so does the belt.

What do others think?

Craig
 
repost

oh and btw it would take off, because there is nothing stopping the plane from moving forward. its momentum is generated by jet engines that push from the air, unlike a car that goes via the wheels.
 
depends how long the conveyor belt is cause at some point its bound to run out :p lol!! (sorry)

humm.......what it sounds like is all the kinetic energy of the plane is transfered into the conveyor belt?? nearly same principles as a treadmil / running machine except the plane is powering the converyor belt...matching its speed so therefore never going to take of cause infact stationary, with no forward thrust that a plane requires???
 
Interesting. Initially, the plane would remain on the conveyor belt. The confusion arises where the plane would normally take off...

Because on a runway the plane is moving forward through the air, there is air passing under and over the wings which creates lift.

Where the plane is actually stationary (i.e., no actual forward movement) there will not be any lift. The plane should just get faster and faster on the conveyor belt until the undercarriage sheer off from the forces at work. If sufficient air were to be passed over the wings however (using some really big fans!!) then it is possible that it would take off.

That's my reasoning anyway!
 
so you think that a rocket placed on a conveyor would stay stationary if it was on a roller skate?

please...

the jet is not affected by the coveyor. a plane say a jumbo jet takes off at about 185mph "air speed" this has nothing to do with ground speed. if there was a trailing wind the ground speed would be around 240mph but the air speed would still be 185mph. and again if there was a nose wind you could do 140mph ground speed and still take off with the wind doing 185mph against the wings.

remember the wheels arent being driven. so you could spin the wheels around at a million miles per hour, makes no difference as the thrust is moving the craft forward through air not across the ground.

lets put it another way (god i said all this the first time) if you changed to size of the wheels of a plane for bigger ones, would this change the speed a plane takes off at? would it change the acceleration? no, not even slightly as all they are there to do is allow the craft to roll across the ground at whatever speed is needed to take off.

does this make sence now?

how about this...... get a tea tray or a flat piece of wood.

get a small corgi or simalar toy car one that free wheels smoothely.

place the car on the tray and rapidly pull the tray from under the car back and forth.... notice the car stays still and the tray rolls under it?

now imagine the car has a huge jet engine strapped to it..........would it realy make any difference what speed the tray was pulled from under it?

no as there is another force now acting on the car, a forward thrust, but there is still no backwords thrust or braking effort.

thus i have just proven that the whole myth is a farse and a waste of 5 minutes of my time.!
 
Antony...Go have a cup of tea, or a beer and relax now. I will take over from here to explain that it will still take off.



Antony is right it will take off as he explained just now:laugh:
 
as anthony said.. it will of course take of... UNLESS!!!! the bearings in the wheels are really bad and cause a lot of friction then lock up with the heat and act as brakes. lol
 
there are some really interesting answers on that link for both sides of the coin!!!

my first answer was based on Craigs brief (sorry) question! plus without knowing more facts etc its guess work.......but that link says the conveyor is moving in the opposite direction.....

at the gym.....on a running machine....on say speed 15.......i can stay still on the belt, move up the belt or move towards the edge.....depending on my speed!!!!

the conveyor belt moves the same as the planes speed....so if i wher to speed up my pace...it would to.........which i think would allow me to still move up the treadmill....as there is not another force acting on me or object (wall) stopping me!!!!??

a hamster in a wheel....yes it cant progress as its confined to moving a wheel rather than a staight line....the force of the object moving up a circle causes the wheel to rotate?? not really the same lol!!!! but the hamster still doesnt stay stationary it moves first before being forced back......

i need more facts me thinks!!!
 
try it with the plane on casters, or ski's, or on a flowing river,....

or anything else for that matter, cos even if it was on a real runway the ground does move backwrods at the same speed as the plane moving forward, or else the tarmac would follow the plane...

hows that for baking your noodle?
 
The conveyor belt has nothing to do with it, it would only turn the wheels. A plane can take off on water because it moves air with its prop not land with its wheels otherwise the moment it takes off it'd lose speed and land again.

Take your mind off cars and think like a pilot.
 
sorry but taking off on water.......umm no.......sorry, call me stupid if you want i dont mind, as im actually clever so it doesnt bother me :p

the "wheels provide the momentum to actually get off the ground"......unless it could slide on its undercarriage to speeds of 150mph and then have leverage to tilt the flaps/aileron ...with enough air underneath and over top.......

so if they are submerged in water.....ok a puddle yes it would take off bu.....thast why you have water boats???? they dont have wheels???

im not arguing.....mearly expressing an opinion to gather greater knowledge!!!

thanks
 
Napster said:
sorry but taking off on water.......umm no.......sorry, call me stupid if you want i dont mind, as im actually clever so it doesnt bother me :p

the "wheels provide the momentum to actually get off the ground"......unless it could slide on its undercarriage to speeds of 150mph and then have leverage to tilt the flaps/aileron ...with enough air underneath and over top.......

so if they are submerged in water.....ok a puddle yes it would take off bu.....thast why you have water boats???? they dont have wheels???

im not arguing.....mearly expressing an opinion to gather greater knowledge!!!

thanks
Click to expand...

this is totaly innacurate and untrue. heres how it works.
the "momentum provider" as you put it is the engines thrust, the wheels do nothing at all other than hold the plane off the floor.

again, a sea plane on a moving river can take off up river if it wanted to as the water passing under the ski's (or sponsons) have nothing to do with the speed of the air passing through the engine nor the thrust passing out of the back.

i dont know how else to explain this.

a roller skate and a baloon, enough thrust from the baloon to force the skate forwards.

its the same as a boat with a jet engine...

or a plate taking off on the back of a moving train or any other way of doing the same thing...
 
ollyc98 said:
The conveyor belt has nothing to do with it, it would only turn the wheels. A plane can take off on water because it moves air with its prop not land with its wheels otherwise the moment it takes off it'd lose speed and land again.

Take your mind off cars and think like a pilot.
Click to expand...


Yes, but the big thing about this is that the conveyor is moving backwards at the same speed that tht thrst of the plane's engines are pushing it forward, so if there is enought thrust to propel the plane forward 10m/s-1 and the conveyor was moving in the other direction at the same speed, then - in one second - the plane would move forward along the conveyor belt 10m BUT the conveyor belt would move 10m in the opposite direction (relevant to a fixed stationary point) so, although the plane has a velocity of 10m/s-1, the ground also has a velocity of 10m/s-1 but in the opposite direction so - relative to the fixed stationary point - the plane has moved nowhere.

This is all based upon my assumption tht as the plane increases in velocity, someone cranks the speed of the conveyor belt up a bit.


P.S. didn't see the orig. thread (searching is for geeks :D )

Also, all the conveyor belt does is counter out the forward thrust provided by the engines - imagine if the plane were bolted to the belt, if the belt were turned on then the plane would move backwards, no? However, if the engines were turned on to provide enough thrust to move the plane forward at the same speed as the belt is moving it the other way, the plane would become stationary as both forces would cancel each other out.
 
Antony said:
the "momentum provider" as you put it is the engines thrust, the wheels do nothing at all other than hold the plane off the floor
Click to expand...

i agree its not wheels making the movement as they are not driven, but they provide the fundamental reason as to why it can takes off...as they allow the airplane to reach the required speed......easily and effectivly.........yes they are there for landing mainly but allow the "free flowing momentum" required!!! dont they?? which is why its tricky answering a question without all the facts!! and even then im sure someone would disagree with facts!!!!

i should stop why im not ahead it seems but this is interesting stuff!!

what happens if you just focusing on the wheels and the conveyor belt? rather than a bigger picture and work back / forwards eliminating ideas
 
yes but the plane isnt stationary if the engines are on, as they would be acting on the stationary air not the moving belt thus pulling or pushing the plane forward.

lets do some easy physics

for an object to stay stationary all forces must be EQUAL.

what equal force is there to the thrust of a plane at take off?

do you honestly think that a little bit of extra rotational friction on the wheels is enough to stop the plane moving forward?

so what would happen, in technical terms,

a jet engine is an air pump, pushing and pulling on the air arround it..... so lets substitute the jet engine on the plane for a winch and some string, the same principles exist, forward "thrust" is now being generated in the same way as before but in an easier way to grasp. the wheels i shall change to casters with ball bearings on the end... as they have no need to be a single axis rotating wheel, or even have rubber on them as there is no need for traction or the aplication of a rotational force. so i shall actulay grease the conveyor too.
connect the winch to the conveyor via a gearbox in order for the to opperate together and at the same velocity..... one forwards and one backwords....

the winch would pull the plane forwards across the moving conveyor as the castors would spin twice this speed as the conveyor is now travveling twice the nominal speed of the plane and its surrounding environment, including the surrounding air. thus at a high enough speed, with a big enough runway and winch cable (thrust) the plane will generate lift and take off......

again, the wheels are irrelavent as is the conveyor as they have no bearing on the one force that is unequal to the rest of the equation. THRUST.

if you dont understand that one have a look in the salters horners guide to A level physics.

sorry that sounded rude.
 
Yes, the forces are unequal BUT the ground on which the plane is upon is moving backwards as fast as teh plane can move forwards - consider my example where the plane is bolted to the belt, all the wheels allow is both objects to move freely.

People talking about extra wheel friction are, IMO, missing the nub of this problem.
 
Craig said:
Yes, but the big thing about this is that the conveyor is moving backwards at the same speed that tht thrst of the plane's engines are pushing it forward, so if there is enought thrust to propel the plane forward 10m/s-1 and the conveyor was moving in the other direction at the same speed, then - in one second - the plane would move forward along the conveyor belt 10m BUT the conveyor belt would move 10m in the opposite direction (relevant to a fixed stationary point) so, although the plane has a velocity of 10m/s-1, the ground also has a velocity of 10m/s-1 but in the opposite direction so - relative to the fixed stationary point - the plane has moved nowhere.

This is all based upon my assumption tht as the plane increases in velocity, someone cranks the speed of the conveyor belt up a bit.


P.S. didn't see the orig. thread (searching is for geeks :D )

Also, all the conveyor belt does is counter out the forward thrust provided by the engines - imagine if the plane were bolted to the belt, if the belt were turned on then the plane would move backwards, no? However, if the engines were turned on to provide enough thrust to move the plane forward at the same speed as the belt is moving it the other way, the plane would become stationary as both forces would cancel each other out.
Click to expand...

ah, this is the mistake people make..
the ground isnt moving backwords at 10m/s-1, its stationary and only the surface the plane is sat on is moving backwords.... so in relation to the earth the plane would still be moving forwards at 10m/s-1 and so would take off...

again if the plane was bolted to the conveyor, yes it would move backwords with the conveyor untill the thrust was applied and then the backwords force of the conveyor and the forwards thrust of the engine would be equal and the plane would stay still...... but it isnt bolted down its free to move as it likes and will do as the force of the belt is negated by the wheels its sitting on....
 
Ant i agree with that! friction was not apart of what i was getting at!!!

the plane will take off.........


quote:
"See, that makes this a riddle about how the wheels on a plane work, not about physics."

The brilliance of the riddle is that it combines the two. If you tried the same experiment on a car, there is no way that the car could move forward because a car relies on the contact of the wheels with the ground in order to gain its propulsion. A plane, on the other hand, can move forward without its wheels touching the ground. Therefore, if we assume that the wheels on the axle have minimum friction, they don't effect how the plane moves forward.

end of!!!

thanks!!!
i have another riddle for you lol!!
 
thats it, if the wheels have no friction they would act in the same way as if they werent there at all.... hmmm.... like a plane flying for instance...

it WILL take off. period. ha.


best bit is, i just know ollie and alan are gonna join in and add a whole different head ache to deal with...lol
 
hold on...you have the movement forward and the movement backwards on the wheel at the same speed(from thrust & belt).......which direction would the wheels on the plane turn!!!! as the plane would have to increase speed to counter act the reverse direction of the belt, but the belt would then match the wheel speed?? which is what the questions asks???

a wheel cant go in two directions at the same time? but may just flow over the top?
 
It wouldnt take off, it's air moving over the wings that creates lift which makes the plane take off, as the plane is actually stationary in the true sense of the word (as its forward momentum is counteracted by the conveyor belt) as there's no forward movement, there is no air movement over the wings, therefore no lift.
 
do the wheels on the plane just roll over the belt, regardless???

or

finds the belt a force and wouldnt know which way to turn??
 
Have you all eaten a bowl of stupid for breakfast?

It wouldnt take off. It needs air to be flowing over the wings for it to take off. It doesnt use wheel propulsion for forward movement because it FLIES. There is no ground upon which to get traction when you are airborne.

For the purposes of this experiment, lets say that there is no wind at all, the plane is normal sized, the conveyor is huge and can match the speed of the plane wheel rotation exactly.

Without any thrust and with the conveyor moving, the plane would move with the belt and eventually fall off the end. This is because a plane weighs a lot, for the same reason that smooth metal train wheels can grip smooth metal track. Plus, no-one said the conveyor would suddenly start moving at a thousand miles an hour.
With the conveyor still and with thrust applied, the plane would fly off the other end of the conveyor.
With both moving at EXACTLY the same speed, their directions are equal. Air is not flowing over the wings so the plane stays in the same position. The wheels just spin.

With a rocket on a roller skate, if the conveyor belt could match the skate's acceleration EXACTLY then the skate would stay still but again the wheels would spin.
 
the conveyor would need to be powered to move, the wheels have no drive on an aircraft, therefore they wouldn't put any reactive force on the belt, if it weren't powered the plane would simply roll off the end of the belt provided it wasnt long enough to let the plane reach take off speed.
 
sonic said:
It wouldnt take off, it's air moving over the wings that creates lift which makes the plane take off, as the plane is actually stationary in the true sense of the word (as its forward momentum is counteracted by the conveyor belt) as there's no forward movement, there is no air movement over the wings, therefore no lift.
Click to expand...

But the wheels don't affect the air moved by the engine so it would
 
Corbs said:
Have you all eaten a bowl of stupid for breakfast?

It wouldnt take off. It needs air to be flowing over the wings for it to take off. It doesnt use wheel propulsion for forward movement because it FLIES. There is no ground upon which to get traction when you are airborne.

For the purposes of this experiment, lets say that there is no wind at all, the plane is normal sized, the conveyor is huge and can match the speed of the plane wheel rotation exactly.

Without any thrust and with the conveyor moving, the plane would move with the belt and eventually fall off the end. This is because a plane weighs a lot, for the same reason that smooth metal train wheels can grip smooth metal track. Plus, no-one said the conveyor would suddenly start moving at a thousand miles an hour.
With the conveyor still and with thrust applied, the plane would fly off the other end of the conveyor.
With both moving at EXACTLY the same speed, their directions are equal. Air is not flowing over the wings so the plane stays in the same position. The wheels just spin.

With a rocket on a roller skate, if the conveyor belt could match the skate's acceleration EXACTLY then the skate would stay still but again the wheels would spin.
Click to expand...

But the conveyor belt doesn't move the air which the engines push against.
 
lol I love these questions. For something to stay stationary all FORCES must be equal. The wheels on a plane free-spin, so there is relatively little friction. Speed of anything is irrelevant. Its forces/friction. The only way you would stop the plain moving forward would be to have the belt moving so fast that the friction in the wheel bearings equalled that of the engines trying to push the plane, or the brakes were on. If all forces equal nothing will move, but the force of the engines is far greater than that of the wheels/bearings so it will move and take off as normal.
 
When a plane is in the air it moves across land right? So are you saying everytime a plane flies over a supermarket with a conveyor belt it STOPS MOVING?
 
ollyc98 said:
But the wheels don't affect the air moved by the engine so it would
Click to expand...

The air moved by the engine pushes the plane forwards. This allows more air to flow over the wings to create lift. If the engines are pushing the plane forwards merely to keep it stationary e.g. on a conveyor belt, then no more air than usual is going over the wings so no lift is generated.
 
Ed said:
lol I love these questions. For something to stay stationary all FORCES must be equal. The wheels on a plane free-spin, so there is relatively little friction. Speed of anything is irrelevant. Its forces/friction. The only way you would stop the plain moving forward would be to have the belt moving so fast that the friction in the wheel bearings equalled that of the engines trying to push the plane, or the brakes were on. If all forces equal nothing will move, but the force of the engines is far greater than that of the wheels/bearings so it will move and take off as normal.
Click to expand...

See you get it!!!
 
Corbs said:
For the purposes of this experiment, lets say that there is no wind at all.
Click to expand...

and....what if there is wind......as the question doesnt actually explain that part?

the air to create lift is generated from the movement of moving forward is it not! the quicker and quicker it gets etc.......equals more wind presure for lift??
 
ollyc98 said:
But the conveyor belt doesn't move the air which the engines push against.
Click to expand...

but the engines push against the air behind the plane, pushing it forward, creating lift, more thrust from the engines = more speed = more lift, if the thrust from the engines is counteracted by the conveyor then there can't possibly be any lift.
 
Ed said:
If all forces equal nothing will move, but the force of the engines is far greater than that of the wheels/bearings so it will move and take off as normal.
Click to expand...

The question clearly states that the conveyor can match the aircraft's speed exactly. Its a super dooper conveyor.
 
But thrust from something like a jet engine can't be affected by a conveyor belt. Blow on a conveyor belt and the air still moves.
 
ollyc98 said:
But thrust from something like a jet engine can't be affected by a conveyor belt. Blow on a conveyor belt and the air still moves.
Click to expand...

The thrust from the engines is merely there to push the plane forwards. it doesn't make it lift off on its own. Thats why they have wings.


If the wheels have no effect, lets say the plane gets up to desired 'speed' and then retracts the undercarriage.
CRUNCH!
 
But the thrust from the engines would propel the plane forward with or without wheels, it moves air outside the field of the conveyor belt as the belt is flat and the air is up as well as across.

I'm gunna get a model plane and a belt and prove it will take off.
 
ollyc98 said:
If it was a mahoosive fan instead of a conveyor belt it'd work but with the belt it's just stupid.
Click to expand...

like a wind tunnel, a plane will fly in a wind tunnel given that the fan can provide enough wind speed to allow the neccesary lift, but the plane would stay geostationary if the windspeed and engine thrust were equalised.
 
Actually I have just realised I may be wrong, damn.... oh wait no I'm not, if the wheels were free spinning it'd be like a skateboard on a treadmill, unaffected by the belt. Ha lol that's a good example actually, if I stand on a treadmill on a skateboard and you put it up to maximum speed the wheels will spin, then if I grab the rail and pull myself along I will move regardless of treadmill direction.
 
Corbs said:
The air moved by the engine pushes the plane forwards. This allows more air to flow over the wings to create lift. If the engines are pushing the plane forwards merely to keep it stationary e.g. on a conveyor belt, then no more air than usual is going over the wings so no lift is generated.
Click to expand...

The belt would hardly cause any ground air effects or interference. So can pretty much be ignored, none of the belts energy (or force) would be transferred to the plain as the wheel bearings are very low friction.

Speed has nothing to do with it.

Forces have EVERYTHING to do with it.

You cannot apply a force to something if its essentially disconnected by wheel bearings, which in this case it is.

The plane would move as normal.
 
sonic said:
like a wind tunnel, a plane will fly in a wind tunnel given that the fan can provide enough wind speed to allow the neccesary lift, but the plane would stay geostationary if the windspeed and engine thrust were equalised.
Click to expand...

i was agreeing Sonic up till you said "windspeed and engine thrust were equalised"............regarding "geostationary".............cause if a plane is going down the runway and it reaches 8omph......and on coming windspeed is 80mph......your saying the plane will stay still??
 

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