View Full Version : Here's a question...
This is currently being hotly debated on another forum I frequent... interested as to what people's opinions on here are.
Question:
A plane is sat on a runway that moves - think of it like a conveyor belt. The plane moves in one direction, and the conveyor belt 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?
(its not a trick question btw as far as I'm aware lol)
Sod it, im going for NO :) Lol
General Baxter
02-04-06, 09:06 PM
Sod it, I'm going for NO :) Lol
I'm going for yes as i dislike you lol
I'm going for yes as i dislike you lol
lmao, i'm going to say NO.
I'm going for yes as i dislike you lol
We are even then ;) lol
Welsh Dan
02-04-06, 09:36 PM
Yes.
I'll go for no also. It would be the air that would create the uplift for the plane to leave the ground, and as the plane isn't moving through the air (as it's technically stationary)... No.
Edit: That explanation was bull**** and I'm bored so here's a diagram
http://www.ueet.nasa.gov/StudentSite/images/engines/wingairflow.gif
That was my thinking/\
If the planes not moving, theres no air flow to lift it.
Welsh Dan
02-04-06, 10:19 PM
That's where you're wrong though, its not stationary. It just has double the drag on the wheels.
You didnt say how fast the plane is actually moving forwards. As long as the plane is moving fast enough for it to take of, it will, regardless of wether the floor is moving in the opposite direction or not.
It is aint it ??
Lol
as road moves > way at 100mph
plane moves < way as same speed
Its like trying to walk backwards on one of those moving floor things at the airport lol
i would say no it can't. we run on treadmills near enough same speed that the roller is moving underneath you. stay averagely same and you run going nowhere. we speed up and you go too far forward and hit the computer bit. so if the plane was going at same speed as thing underneath, i would say no it couldn't take off? but then i did fail science :P lol
Welsh Dan
02-04-06, 10:51 PM
A plane doesn't use its wheels for propulsion.....
it just rolls on the conveyor...
If the plane is stationary, the conveyor isnt moving.
It doesn't matter how fast the wheels are turning, you need a high flow of air under the wings to create uplift. And using Sh0rty's treadmill example, If you run really fast you don't feel any wind blowing in your face, so why would a plane on a conveyor experience enough airflow to create uplift.
A similar but maybe more confusing conundrum, what happens if an unstoppable car hits an immovable wall?
It,s got to be no or else it would have been used by now, imagine the land it would save without those huge runways. Be a good pilot though who could land back on it lollol
Welsh Dan
02-04-06, 11:03 PM
ok.
Lets assume the planes axles provide negligable friction, so we can ignore that. The plane applies thrust with its engines, and moves forwards, lets say it reaches 30mph, the conveyor speeds up to 30mph in the other direction. The speed at the wheels of the plane is 60mph, but the speed of the plane is 30mph. It matters not one bit what speed the conveyor moves at to the plane, unless the wheelbrakes are on, or its moving so fast that the axles/landing gear/tyres break.
Re-read the question, it says nowhere that when the plane tries to move, its stationary.
Ah, I see now, Xen0phobiak is spot on. The the conveyor belt could be moving 2000mph and it doesn't matter because if the the plane is moving at forward at 30mph it is still moving forward at 30mph. The power aint coming from the wheels.
That's thinking outside the box mate, nice one :thumb:
Ahh i get it.
The conveyor is moving that way>, which in turn moves the plane the opposite way <
So it speeds it up.
So once the plane has enough speed, Yes it will take off.
Either that or im mega confused lol
Welsh Dan
02-04-06, 11:13 PM
The speed of the conveyor doesnt affect the plane, in a perfect world. In the real world the friction will slow it down a bit, but planes are made with excess thrust available anyway.
The answer is yes the plane will still take off but the wheels will be going twice as fast because the plane will be moving at take off speed one way the the conveyor belt at takeoff speed the other way.
The thing to remember is that the plane does not get its drive from the wheels but its jet engines that work on thrust. So it really does not matter what the ground is doing because the plane only uses that to support its weight until take off :D
But it still comes back to problem of airflow over the wing, if the plane isn,t moving, which it would,nt be, there won,t be any.
Nope the wheels have nothing to do with its speed. So a belt going to opposite way will make no difference what so ever. A plane gets dragged through the air by its engines hence it will move and take off as normal.
Stanley
03-04-06, 12:13 AM
if the plane were to shut its engines off, it would stay on the conveyor belt and move along with it.
so by having the engine on, it would stay stationtary. regardless of what the belt is doing (i.e. - the wheels just roll. they have no power to them. its all done by the engine)
therefore, the engine would have to do twice as much work to move the plane in the opposite direction of the belt and take off.
air speed and land speed are different
the plane must have sufficient air speed to take off (air running over and under the wings producing lift)
Welsh Dan
03-04-06, 12:17 AM
:tard:
ok - let me try again. The planes drive comes from the engines that drag it through the air. This is how a plane can fly without being attached to the ground. The planes wheels are free wheeling, So if the plane moves forward at 10mph the conveyor belt will go in the opposite direction at 10mph. This means that the wheels will be going at 20mph. Not that the plane will then slow down by 10mph because the forward power is given by thrust which has nothing to do with what the ground is doing. The only thing that willo happen is the drag created by the wheels will be a 'little' more.
Or another way to think of this is if you put on some skates and get on the same conveyor belt but get a mate to push you along at 5mph (who is not on the conveyor belt) you will be going 5mph like your mate but the skate wheels will be doing 10mph.
Another way for you to get your head around this is to think about it a little more and work out how a plane is going to stay in the same spot on full thrust with the conveyor belt not moving. IT CAN'T. Ready - If you think that the plane will not move from its spot because of the alternate action of the conveyor belt then the as soon as the plane starts to move the conveyor belt will move and bring it to rest, at which point the conveyor belt will slow down again. So put the plane on full thrust and for the plane not to take off it will have to be stationary with the conveyor belt stationary as well IMPOSSIBLE unless the plane is teathered to something solid.
^ Well it's late and that confused the hell out of me.
But I get the logic, nice one Xen0phobiak you clever cookie. I feel quite the fool lol
Crazy Ry Ry
03-04-06, 07:51 AM
Nope the plane wont take off !!! regardless of speed at wheels the plane will remain in the same position as a fixed object next to it ie a dead bird , it's the movment through the air that causes the pressure beneath and above the wings to be different which is what causes lift .
OK - I give up. If you think the plane won't take off I would urge you to think about the problem some more.
Crazy Ry Ry
03-04-06, 10:55 AM
if it could be done dont you think aircraft carriers would have them ? instead of a long flat section and a ramp on the end ???????
Crazy Ry Ry
03-04-06, 11:00 AM
regardless of thrust and all that the plane isnt actually doing any speed !!!
it aint going to bunny hop in the air is it !!!!!!
Crazy Ry Ry
03-04-06, 11:10 AM
your nova is on a convayor ... doing 100mph the convayor is moving the opposite way at 100mph ... there is a speed camera next to you ... would it flash . NO because your not actually doing any relative speed !!! same principal ! its the forcing of air up under the wings that causes take off not an actuall mph speed so as the plane is stationry so to speak it does not create any upwards thrust !! tired now zzzzzz lol
Thats because a Nova drives through its wheels a jet does not!
You seem to think that im guessing here. I actually 'know' the answer. lol.
If you still don't believe me go here - http://www.avweb.com/news/columns/191034-1.html and have a little read of the section marked Coveyer-belt runway.
But if you can't be bothered to go to the link here is the last paragraph for you.
It was an interesting argument, but as things progressed, more rational heads prevailed, pointing out that the airplanes do not apply their thrust via their wheels, so the conveyor belt is irrelevant to whether the airplane will takeoff. One guy even got one of those rubber band powered wood and plastic airplane that sell for about a buck, put it on the treadmill someone foolishly donated to the Lounge years ago, thinking that pilots might actually exercise. He wound up the rubber band, set the treadmill to be level, and at its highest speed. Then he simultaneously set the airplane on the treadmill and let the prop start to turn. It took off without moving the slightest bit backwards.
Anyway im off to llandow for a test session.
initially i thought "hmm no it wont" but then the jet bit reminded me that it would..
the best explaination was dars one of the bloke on roller skates and his mate pushing him. thats the easiest way to get your head round it
Crazy Ry Ry
03-04-06, 12:49 PM
but for a wing to work it has to be moving through a mass wether it a liquid or a gas . if its on a conveyor then its not moving through anything ?
craig green
03-04-06, 12:50 PM
I was gonna say before I saw the diagram. You need air speed/lift over the wings.
Not sure a passing conveyor belt is gonna do that.
Crazy Ry Ry
03-04-06, 12:56 PM
the plane in that story had a prop which will pull through the air but that a different thing to a jet engine isn't it ?
^^^ No the jet is a glorified prop at the end fo the day, they both work with air/liquid (air is a liquid from a dynamics point of view)
if the wheels arent driven (which they arent on a plane) then the jet will move forwards at what ever rate/speed it wants (unless the brakes are on)
Crazy Ry Ry
03-04-06, 01:20 PM
but the prop will actuall pull on air which passes it below the wings where a jet actually pushes the wings past the air ? which wouldnt work on a conveyor as the plane isn't moving through anything ?
Not trying to fall out with anyone honest !:cry:
Welsh Dan
03-04-06, 01:22 PM
jets and props have the same effect.
Crazy Ry Ry
03-04-06, 01:27 PM
How can a jet and a prop have the same effect when one pulls on a gas and the other pushes on an actual object ?:confused:
Welsh Dan
03-04-06, 01:29 PM
fuel+air in, thrust out.
How can a jet and a prop have the same effect when one pulls on a gas and the other pushes on an actual object ?:confused: Jet thrusts air that way >, so it pushes the object forward <
Prop pulls air in from the front, so then pushes the air back >, which also pushes the object forward <
Actually, no. lol
Ahhh, wheres me coat.
Crazy Ry Ry
03-04-06, 01:39 PM
Guess ill admit defeat !lol
Good idea lol
This thread rules!!
Welsh Dan
03-04-06, 03:43 PM
This thread rules!!
http://www.xen0phobiak.f2s.com/novaload/rocks.jpg
:D
F**kin ell Jack, what have you done? I still say it won,t take off if it,s not moving, which it isn,t, no matter what it,s powered by,rubber bands or chicken sh*tlol
The plane will always be stationary and so the flow of air under and above the wings (creating upthrust) will only be as strong as the breeze is blowing that day. Assuming its blowing in the right direction....
Anyone own a model r/c aeroplane and a supermarket checkout??
Welsh Dan
04-04-06, 01:27 PM
The plane will only be stationary when the pilot decides that that's what he wants.
The only effect the conveyor has is to make the wheels spin faster.
But if the conveyor belt matches the speed of the wheels they would never be able to gain any forward motion... its a paradox :D
Heres an easy experiment which proves it.
Run on a treadmill. Your legs are providing the forward motion therefore you will remain stationary as you run against the moving belt.
Now try the same thing while holding a firemans hose pointing backwards. I guarantee you smash your knackers all over the little LCD measuring your 'burnt caliries'.
The forward motion provided from the hose is acting against the air pressure behind you NOT on the moving belt. Same principal applies with the plane, its not moving forwards from force from the wheels, its moving forwards from the air pressure behind the engines!
...but to move forward the wheels will have to move faster than the belt.
In the example of treadmill and hose, the force of the hose would push you forward, yes, but your legs would lose contact with the treadmill or skid over it. If you were on rollerskates you'd either fall forward or skid forwards. If the treadmill matched the rotation of your wheels on the skates you'd need to break contact to move forwards.
In the example of the plane on the runway it won't move unless friction causes the wheels to lose contact with the runway (so the aircraft skids or bounces forward) OR the wheels break away from the aircraft if there is another force keeping them in contact with the runway.
...IMO :p
Welsh Dan
04-04-06, 09:00 PM
Question: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).
Plane speed, not wheel speed.
...but to move forward the wheels will have to move faster than the belt.
In the example of treadmill and hose, the force of the hose would push you forward, yes, but your legs would lose contact with the treadmill or skid over it. If you were on rollerskates you'd either fall forward or skid forwards. If the treadmill matched the rotation of your wheels on the skates you'd need to break contact to move forwards.
In the example of the plane on the runway it won't move unless friction causes the wheels to lose contact with the runway (so the aircraft skids or bounces forward) OR the wheels break away from the aircraft if there is another force keeping them in contact with the runway.
...IMO :p
LMAO, your either convinced or a wind up merchant lol
The plane will open the throttles, the plane will move forwards. at 10mph, the belt will be moving at 10mph in the opposite direction = wheel speed 20mph.
Lets say take off speed is 130mph. Plane speed 130 mph. Belt speed 130mph in opposite direction = wheel speed 260mph. Provided the wheels are designed to cope with this sort of speed, the plane will take off.
Yes, the plane will probably need a bit more thrust to cope with the added friction of the wheels spinning, but take off it will!
How does a jet propelled car work? it doesnt have drive to the wheels for a start! It uses thrust out the back of the jet engine to move forwards! So basically it would quite happily move forwards even if it doesnt have any wheels, and just scraped along on its belly!
Plane speed, not wheel speed.
If it tracks the aircraft speed then yeah it can take off, as you say the wheels will rotate at twice the speed. But I was referring to the conveyor matching the wheel speed above:
But if the conveyor belt matches the speed of the wheels they would never be able to gain any forward motion... its a paradox :D
;)
Welsh Dan
04-04-06, 10:07 PM
ah ok
The only aircraft to take off from a stationary position are choppers and jump jets,erm,are hot air balloons aircraft:confused: :roll:
Razorjack - wheel speed should mean the forward motion of the wheels which would be the same as the aircraft in question. So it would take off.
If you think of wheel speed as how fast the wheels are rotating. Then the thing will just continue to accelerate and the wheel bearings will probably overheat and seize but will the plane have enough time to take off before this happens?lol
http://www.ctgilles.net/images/pictars/goyou.jpg
boredbloke
04-04-06, 11:44 PM
...It wouldn't take off......
the only way the plane could take off is if the front wheels were to leave the belt, and to do that it'd need air pressure to tilt the aircraft, once it tilted up slightly the trust would puh the plane into the sky, all the while all the wheels touch the conveyor belt it would match the speed.
meaning the plane on the conveyor belt is exactly like the tread mill for us. We don't feel a breeze when running so the plane wont get the air pressure needed.
I like the question though Jack does make ya think abit.
the plane would hvae to move though the air to fly. alos the rollers undernneither could not keep up with the thrust from the jets so it would "run off the front of the tred mill" and then fly as it is passing though air
boredbloke
05-04-06, 12:06 AM
^^^ the question say it will MATCH the plane speed, so your theory goes completely out of the window, it doesn't say theres any kind of limit to how fast the conveyor belt could go.
but the force of the jet would be greater than the grip on the wheels on the roller bnecause its displace air which it "still and the wheels are free
boredbloke
05-04-06, 12:17 AM
no the engines push the plane forwards only, the up and down are controlled by the wings which is why a plane uses a runway it gains speed forwards then tilts it wings so the front lifts and again pushes forwards only.
Due to the angle of the plane (i.e 45 degrees up wards) it lifts off, if the plane can't get the air pressure to lean back and to get away from being horizontal it can only push forwards, meaning no matter how fast it goes on the belt the belt moves with it and the plane stays still
boredbloke
05-04-06, 12:49 AM
bollox to the above...had me some ice cream and it made me think straight... the plane takes off only if the following assumptions are made...
the wheel bearings can take the extreme speeds it would needs
the plane is capable of twice the speed it needs to get off the ground
the rollerskates and rope thing swayed it for me,
The only aircraft to take off from a stationary position are choppers and jump jets,erm,are hot air balloons aircraft:confused: :roll:
Harriers very rarely use VT as it wastes a LOT of fuel. They tend to do a short run up, angle the thrust vents, and either use a ramp to "jump" into the air, as you see on carriers (hence the name), or use a short runway.
Razorjack - wheel speed should mean the forward motion of the wheels which would be the same as the aircraft in question. So it would take off.
But as soon as the wheels start to turn the runway/conveyor belt would match their speed (assuming the runway matches the wheel speed, not the aircraft airspeed), negating any forward motion.
When the aircraft is in the air, the wings effectively take the place of the wheels - as a medium for allowing the engines to move it through the air. If the wind speed matches the wing speed it won't fly (in this case it, wing and wind would need to be going in the same direction, but its the same theory). Same goes for the wheels, if the wheels move at 5mph forwards and the belt at 5mph backwards the plane goes nowhere, it can't move as its ability for moving is cancelled out by the runway/belt.
If the runway/belt matches the wheel speed then W+R=0 where W = wheel speed (positive, forwards) and R = runway speed (negative, backwards).
Crazy Ry Ry
05-04-06, 11:29 AM
Are we saying it wont take off now ? im with you razor i tried saying all this before !
Razorjack im sure your taking the piss now :D
If not remember that the wheels are FREE wheeling. This means that they have very little effect on the planes motion. The only effect they have is the rolling friction they generate which is minimal.
What the people in the it won't take off camp don't seem to be able to grasp is that planes don't drive through the wheels. Unlike cars. Get a car on the conveyor belt and do then same thing and it will stay stationary i.e. 5mph at the wheels and -5mph on the belt. This however does not apply to a jet engine because it uses 'thrust' which pulls it through the air, so what the ground is doing is irrelevant because it has no impact on the planes forward motion.
EDIT: Just been speeking to my mate who is an aircraft engineer and we came to the conclusion that people are thinking that the plane will stay stationary so therefore cannot takeoff. However the plane WILL be going at the speed it needs to take off. The conveyor belt will be going the same speed in the other direction and the wheels will be going twice that speed.
EDIT: Just been speeking to my mate who is an aircraft engineer and we came to the conclusion that people are thinking that the plane will stay stationary so therefore cannot takeoff. However the plane WILL be going at the speed it needs to take off. The conveyor belt will be going the same speed in the other direction and the wheels will be going twice that speed.
Dar, you're thinking of the runway/belt moving at the speed of the aircraft, which is not the point I'm debating - if the runway/belt moves at the speed of the aircraft then yes it can take off as you say. If it matches the wheel speed then the wheels can't do twice the speed of the runway/belt.
For the plane to take off it needs lift.
To create lift, it needs air to move over the wings.
To create an airflow over the wings the aircraft must move forward.
To move forward the wheels must rotate - even unpowered and just freewheeling the wheels must rotate (else whats the point of them being there?!).
As soon as the wheels start to rotate, the belt/runway moves in the opposite direction at the same speed of wheel rotation.
This creates a paradox.
IF the belt/runway matched the aircraft speed, then yeah the wheels would rotate twice as fast as normal. But if it matches the wheel speed then theoretically the aircraft cannot move and thus not take off.
Where going over old ground here and I swear your just stringing it out. The plane WOULD move forward. It really does not matter what the ground is doing. I see exactly where your coming from hence my post about the wheel bearings overheating, if you think about wheel rotational speed, because the wheel speed would increase exponentially, however I also don't think that is what the question was all about.
Did you read the info in the link I posted about the person who actually tryed this with a model plane?
boredbloke
05-04-06, 11:04 PM
Razor mate the question says the conveyor matches the plane speed...
beavy69
05-04-06, 11:06 PM
I managed to read up to page four and gave up. Its really quite simple. Like Dar said yes it will take off. All it is, is a plane taking off as normal with a moving floor undernieth.
As it is the floor that is moving and not the air around the plane (which is the thing that the plane "pulls" on to move along) the floor will only have the affect of moving the wheels quicker. The frictional force from that is not enough to stop a plane from taking off. However, as the plane increases speed if the floor has to match this, the wheels will be moving at twice the speed they are designed to and the bearings may seize. Even then, the plane would simply drag them across the floor by this point and take off anyway!
If the belt matches the plane speed the plane won,t move, therefore no take off, simple:roll:
-tucny-
06-04-06, 11:34 AM
im saying theres some funny theorys going on here. (and no, i couldnt be bothered reading all the pages to this thread before i posted this!)
i see this as:- the conveyor will only move if the plane does. so if the plane does 10mph the conveyor does the same. 10> - 10< = 0, 100> - 100< = 0 (> = direction. as said with the treadmill explanation.
the engine works by pulling air in at the front at speed and shooting it out the back. therefore this propels the plane, the speed of the plane is also matched by the conveyor so the speed is still 0mph.
planes take off because of the speed air travels over the wings creating lift (if the flaps are in the position to lift)
so mph = 0
air speed over wings = 0
air speed through turbine = irrelivent as there is no airflow over the wings.
wheel speed = irrelivent as there is no connection between this and airflow over the wings.
NO it will not take off, dnt be silly!
still not convinced?
a formula 1 car is fitted with a rear spoiler to create downforce to the rear of the car. the front spoiler is also fitted to create down force to the car at the front. so lets say that the front spoiler is removed to get the car on a rolling road, the cars started and shoots up to 200mph. the rollers are moving the same speed as the cars wheels just on the opposite direction will the front of the car flip up? Dont be daft, its stationary so theres no down force created by the rear spoiler.
Doh!! Stop comparing Jet engines with cars. Cars drive through their wheels. So can remain stationary on a rolling road. Now put a jet on a rolling road and run it up. Make sure its strapped down - You don't want it shooting through the back of the workshop. Run up the jet - what the rolling road isn't going??? humm - Thats because jets don't drive through their wheels, so cannot in any way shape or form be compared to a car on a rolling road or a ruddy conveyor belt lol
Please go and do some reading on the net, this subject has been covered to death.
beavy69
06-04-06, 12:00 PM
LOOK ITS SIMPLE: A PLANE EFFECTIVLY GRABS ON THE AIR IN FRONT OF IT TO MOVE (NOT THE MOVING FLOOR) SO TAKE OFF IS UNAFFECTED.
STILL DON'T GET IT READ ON:
FOR THOSE OF YOU WITH A VISUAL MIND LIKE ME: IF YOU (THE PLANES ENGINES SUCKING AIR IN) ARE MOVING A MODEL PLANE FORWARD ON A SUPERMARKET CONVEYOR BELT (WHICH IS MOVING IN THE OPPOSITE DIRECTION) YOU CAN STILL MOVE THE PLANE FORWARD AND LIFT IT UP AS YOU ARE THE ENGINE AND ALL THE BELT SERVES TO DO IS SPIN THE WHEELS FASTER.
STILL DON'T GET IT READ ON:
IF A MOVING FLOOR STOPPED A PLANE MOVING FORWARD RELATIVE TO THE AIR IT NEEDS TO TAKE OFF, THOSE PILOTS AT AIR DISPLAYS WHO DO THE RUNWAY TOUCH DOWN AT SPEED AND THEN LIFT UP TO CARRY ON FLYING WOULD STOP DEAD AND CRASH.
ALSO:
IF IT WERE THE RUNWAY ANNNDD AIR MOVING IN THE OPPOSITE DIRECTION AT THE SAME SPEED THE PLANE WOULD APPEAR TO BE STATIONARY BUT WOULD STILL TAKE OFF AS AIR IS MOVING OVER THE WINGS AS NORMAL.
i.e. the whole riddle is bullshish just to confuse you!
Crazy Ry Ry
06-04-06, 12:29 PM
No one has said a jet drives through its bloody wheels !
what there saying is the plane needs to move through the air to get lift !
if it aint moving forward then there is no lift no air movement and no joining the mile high club !lol
hendrix
06-04-06, 01:27 PM
No it wont take off.
The jet engine produces thrust that in turn propells the plane through the air. The wheels have no drive whatsoever, however as the plane starts to move the conveyor counters this so the net speed is 0. The speed plane with respect to the observor is 0 as is the air speed however the wheels are at the speed equivalent to what the speed would be if the runway was conventional. The plane hence is not moving at all through the air and since a plane relies on air moving over the wings to create lift and this isnt happenning due to the land speed of the plane being zero there is no air flowing on the wings and thus no lift
Dar im sorry but i have to disagree with you, yes jets dont drive throught their wheels but how on earth do they move?? think of a person on rollerskates on a treadmill, as the treadmill increases speed the wheels on the roleskate increase at an equivalent rate so that net movement is zero, even if you add some sort of propulsion to this it merely increases the amount of force for forward motion, which would, if the treadmill remained at a constant speed, then send the person forward, but if you counteract this by increasing the treadmill speed then your foward motion will be nullified and thus not forward motion, barely an equilibrium is reached and then again no motion.
For every action there is an equal and opposite reaction..
think of the plane again. on a conventional runway the planes speed with respect to the ground increases as there is more thrust from the engine. this is +ve speed and once it reaches a great enough ground speed the force of the air traveling over the wings creates enough lift to take it into the air. the wheels then stop turning but the plane caries on up up and away. Now if the plane is trundling along the runway at +ve speed 100 but the runway then starts to counter this by moving in a -ve speed (that is running in the opposite way the plane is traveling ) of 50 then the net speed overall with respect to some one standing next to the runway is now only going to be +50, and so if the negative speed on the runway is increased to -ve 100 then the net overall is going to be 0 (+100 + -100 = 0).
You can also thing of a person on an infinate length treadmill. the treadmill is running at 10km/h and you are only running at 9km/h, you will move backwards at 1km/h even though you are going at 9km/h
so in conclusion
NO IT WONT TAKE OFF!!!
think about the roller skate exmaple again people.. its the same principle.
it will take off....
http://www.avweb.com/news/columns/191034-1.html
Crazy Ry Ry
06-04-06, 03:13 PM
If it is possible why aint there any around ?
If a jumbo jet can take off in the space of its own length why is there runways all over the place when only a couple would be needed for landing ?
the plane will still move forward.....
just because the convoyer belt is moving the same speed as the plane, doesn't mean the plane wont more forward, all that will happen is the wheels will turn faster, that wont affect the place forward motion
Crazy Ry Ry
06-04-06, 03:26 PM
the plane cant move forward as any thrust is lost by the wheels freewheeling on the coveyor
Crazy Ry Ry
06-04-06, 03:27 PM
and if it is possible why aint there one at every airport in the country ?
I give in. But I offer one last link for the doubters. If you read this and still don't get it then im never ever going to explain it well enough.
http://www.kottke.org/06/02/planes-conveyor-belt-2
the plane will take off. Its wheels will ahve effectively covered double the distance they would have on a fixed runway, and they will be rotating at double the speed they should do.....
im going to look at making a mock up model to try and fix this......
the plane cant move forward as any thrust is lost by the wheels freewheeling on the coveyor
But the thrust acts on the air, not the wheels.
Test it! Go get some rollerskates, a treadmill and some rope.
Tie the rope to the wall in front of you. Stand on the treadmill with the rollerskates on, set the treadmill to 1mph. Pull yourself along the rope at a rate of 1mph. You will move forwards at 1mph, and your wheels on the skates will rotate at 2mph.
beavy69
06-04-06, 09:30 PM
the plane cant move forward as any thrust is lost by the wheels freewheeling on the coveyor lol lol lol lol lol
OK so thrust of the engine is lost by the wheels spining at twice the speed! lol
and if it is possible why aint there one at every airport in the country ?
because it costs quite a bit to build one hundred giant conveyor belts that run at twice the speed of a plane taking off 24hrs a day.:cry:
No it wont take off.
The jet engine produces thrust that in turn propells the plane through the air. The wheels have no drive whatsoever, however as the plane starts to move the conveyor counters this so the net speed is 0.
So what you are saying is that a moving platform moving in the opposite direction will counteract the propulsion produced from two rolls royce jet engines producing silly amounts of thrust, acting only on a set of wheels which are free wheeling? THINK ABOUT IT!
The speed plane with respect to the observor is 0 as is the air speed however the wheels are at the speed equivalent to what the speed would be if the runway was conventional. The plane hence is not moving at all through the air and since a plane relies on air moving over the wings to create lift and this isnt happenning due to the land speed of the plane being zero there is no air flowing on the wings and thus no lift
only if the plane was getting its forward propulsion from its wheels! THINK ABOUT IT
Dar im sorry but i have to disagree with you, yes jets dont drive throught their wheels but how on earth do they move??
They move by sucking in air, compressing it, adding fuel and then blasting it out the back, thus producing forward motion, thus not actually mattering one bit what its rolling on! THINK ABOUT IT
think of a person on rollerskates on a treadmill, as the treadmill increases speed the wheels on the roleskate increase at an equivalent rate so that net movement is zero, even if you add some sort of propulsion to this it merely increases the amount of force for forward motion, which would, if the treadmill remained at a constant speed, then send the person forward, but if you counteract this by increasing the treadmill speed then your foward motion will be nullified and thus not forward motion, barely an equilibrium is reached and then again no motion.
Your theory only works if the opposite force is equal to the forwards force. In the case of the plane, your effectively saying that the forward force the engines are creating are being equaled by a moving floor acting on a set of free wheeling wheels NO NO NO NO NO
For every action there is an equal and opposite reaction..
think of the plane again. on a conventional runway the planes speed with respect to the ground increases as there is more thrust from the engine. this is +ve speed and once it reaches a great enough ground speed the force of the air traveling over the wings creates enough lift to take it into the air. the wheels then stop turning but the plane caries on up up and away. Now if the plane is trundling along the runway at +ve speed 100 but the runway then starts to counter this by moving in a -ve speed (that is running in the opposite way the plane is traveling ) of 50 then the net speed overall with respect to some one standing next to the runway is now only going to be +50, and so if the negative speed on the runway is increased to -ve 100 then the net overall is going to be 0 (+100 + -100 = 0).
You can also thing of a person on an infinate length treadmill. the treadmill is running at 10km/h and you are only running at 9km/h, you will move backwards at 1km/h even though you are going at 9km/h
so in conclusion
NO IT WONT TAKE OFF!!!
YES IT WILL
One final attempt from me also, and seeing as people need to use cars to try to understand... Here goes.
A normal car is sat on a treadmill. As it begins to drive along the treadmill (via its rear wheels, placed on the treadmill). the treadmill counteracts the drive from the wheels by effectuively passing the floor under the car, so no matter how much the car tries to move forwards, the floor moves under the car instead = No forward motion. im sure everyone gets me up to this point.
Now try to imagine the same car, but the rear wheels have been removed, and replaced with extra long driveshafts so the driving wheels straddle the treadmill (so they are sat on terra firma each side of the treadmill.) The front wheels are still sat on the treadmill. Are you still following me??
The car starts to move forwards again. The treadmill begins to move in the opposite direction, but the car will move forwards as the driving wheels are not on the treadmill right? The front wheels will be spinning twice as fast as normal as they are still on the treadmill.
Now try to imagine these rear wheels which are driving the vehicle forwards, (which are not in contact with the treadmill) are the jet engines of the aircraft, (which are also not connected to the treadmill.) The front wheels of the car will be like the landing gear of the aircraft, spinning twice as fast as normal.
If you dont get that example, then there really is no point in carrying on this thread lol
and add to the fact people REALLY NEED to disconnect from the thought of driven wheels and cars for this one!!!
good description lee.
wanna setup something like Jack described?? and film it. Would make comedy viewing
wanna setup something like Jack described?? and film it. Would make comedy viewing
LMFAO there's an idea lol
How about we get one of the people who don't think the plane will take off, strap them to a treadmill on rollerskates.... :D
sickrabbit
06-04-06, 10:48 PM
Take off what - its under crackers ??
ok, so the plane moves forward OFF the conveyer and takes off as normal but not ON the conveyer:cry:
Yes I give in,it will take off, I was thinking of a conveyer the size of the plane not the whole runway
hendrix
09-04-06, 04:57 PM
it wont take off!!
if the conveyor belt can spin at a speed = to c (speed of light)
result lol
hendrix
09-04-06, 05:05 PM
No it wont take off.
The jet engine produces thrust that in turn propells the plane through the air. The wheels have no drive whatsoever, however as the plane starts to move the conveyor counters this so the net speed is 0.
So what you are saying is that a moving platform moving in the opposite direction will counteract the propulsion produced from two rolls royce jet engines producing silly amounts of thrust, acting only on a set of wheels which are free wheeling? THINK ABOUT IT!
depends on how fast the conveyor will spin (see above)
The speed plane with respect to the observor is 0 as is the air speed however the wheels are at the speed equivalent to what the speed would be if the runway was conventional. The plane hence is not moving at all through the air and since a plane relies on air moving over the wings to create lift and this isnt happenning due to the land speed of the plane being zero there is no air flowing on the wings and thus no lift
only if the plane was getting its forward propulsion from its wheels! THINK ABOUT IT
again if this problem becomes relativistic it wont take off
Dar im sorry but i have to disagree with you, yes jets dont drive throught their wheels but how on earth do they move??
They move by sucking in air, compressing it, adding fuel and then blasting it out the back, thus producing forward motion, thus not actually mattering one bit what its rolling on! THINK ABOUT IT
i know how a jet works, what i was saying was that the plane moves on its wheels, it will require some thrust just to keep it stationary as the plane is not anchored to anything
think of a person on rollerskates on a treadmill, as the treadmill increases speed the wheels on the roleskate increase at an equivalent rate so that net movement is zero, even if you add some sort of propulsion to this it merely increases the amount of force for forward motion, which would, if the treadmill remained at a constant speed, then send the person forward, but if you counteract this by increasing the treadmill speed then your foward motion will be nullified and thus not forward motion, barely an equilibrium is reached and then again no motion.
Your theory only works if the opposite force is equal to the forwards force. In the case of the plane, your effectively saying that the forward force the engines are creating are being equaled by a moving floor acting on a set of free wheeling wheels NO NO NO NO NO
yes it will if the speed of the treadmill is proportional to the speed the plane would be travelling at from the amount of thrust from the engines, i wasnt saying it was equal, the conveyor would have to be travelling much faster
For every action there is an equal and opposite reaction..
think of the plane again. on a conventional runway the planes speed with respect to the ground increases as there is more thrust from the engine. this is +ve speed and once it reaches a great enough ground speed the force of the air traveling over the wings creates enough lift to take it into the air. the wheels then stop turning but the plane caries on up up and away. Now if the plane is trundling along the runway at +ve speed 100 but the runway then starts to counter this by moving in a -ve speed (that is running in the opposite way the plane is traveling ) of 50 then the net speed overall with respect to some one standing next to the runway is now only going to be +50, and so if the negative speed on the runway is increased to -ve 100 then the net overall is going to be 0 (+100 + -100 = 0).
You can also thing of a person on an infinate length treadmill. the treadmill is running at 10km/h and you are only running at 9km/h, you will move backwards at 1km/h even though you are going at 9km/h
so in conclusion
NO IT WONT TAKE OFF!!!
YES IT WILL
depending on what case you consider
theoretically if the conveyor increases to an infinite speed the plane wont take off.
however...it may take off in normal conditions
hendrix
11-04-06, 01:33 PM
me too lol
boredbloke
12-04-06, 12:18 AM
ai think of this,
you have in your hand a toy car, you place it on the conveyor belt at the fastest possible speed the belt goes, now the toy has quality wheels that can't possibly fall off or break
you place the toy car on the belt which is going the opposite way, are you saying that if you moved the car forwards with your hand that it couldn't possibly move forwards?
the toy car has no power in it's wheels, it's your hand that pushes it forwards
same with jet the engines push through the air and the wheels just spin like fook carrying it.
hendrix
12-04-06, 03:02 PM
ai think of this,
you have in your hand a toy car, you place it on the conveyor belt at the fastest possible speed the belt goes, now the toy has quality wheels that can't possibly fall off or break
you place the toy car on the belt which is going the opposite way, are you saying that if you moved the car forwards with your hand that it couldn't possibly move forwards?
the toy car has no power in it's wheels, it's your hand that pushes it forwards
same with jet the engines push through the air and the wheels just spin like fook carrying it.
the thing is you are correct, however the toy car requires some force just to keep it stationary otherwise it would move in the direction of the conveyor belt, now if the belt could spin at EXACTLY the maximum speed that the jet engine could push the plane forward (normally) then it wouldnt take off as some forward force is required just to keep the plane stationary
yay or nay??
andy
the thing is you are correct, however the toy car requires some force just to keep it stationary otherwise it would move in the direction of the conveyor belt, now if the belt could spin at EXACTLY the maximum speed that the jet engine could push the plane forward (normally) then it wouldnt take off as some forward force is required just to keep the plane stationary
yay or nay??
andy
Yes, but thats not the original question is it! lol.
And its not speed thats the issue, it force. if the belt could spin backwards fast enough to create the same backwards force on the plane that the engines create forwards force then theoretically the plane would stay stationary, but the speed the belt would have to be spinning backwards would be hurrendous and the bearings in the wheels would never be able to cope with it anyway ;)
also the belt is CONTROLLED so its not jsut gonna spin up at max speed immediately.... its going to ramp its speed up.
beavy69
12-04-06, 09:48 PM
Even if the belt could got fast enough (which would need to be at least five times the speed of the plane) all it could serve to do is heat up the bearings in the wheels to the point where they lock up. However, the power of the jet engines would simply drag the plane along anyway and rip the tyres apart if neccessary.
novadicko
13-04-06, 12:27 PM
think of this if the plane needs moving air to take off but belt going 100mph and plane 100mph it would not move so if it was possible iff u sat on the wing it would not b windy at all but if it was doin 100mph normaly u would probly b blown off. that make sense to eny 1?:(
novadicko
13-04-06, 12:33 PM
i just asked sum 1 that worked in the raf fixin planes and he recons no. said every force has an oposite or equal 1 and it will not take off aparently?
http://i13.photobucket.com/albums/a266/razorjack/Misc/zzzz.jpg
hendrix
13-04-06, 02:39 PM
lol @ razorjack
All the limiting factors mentioned above would result in whether it would take off or not but what I wrote would be if everything was perfect and didn't break i.e. nothing was flawed or had a limit as to how fast/how much force it could go/take
Elthrin
13-04-06, 05:01 PM
This is such a stupid question. You are not given enough details to answer it.
I can only guess that they are being misled by the poor wording of the question.
It just proves that if you ask an ambiguous question you are not going to get a accurate answer.
The original question:
Question:
A plane is sat on a runway that moves - think of it like a conveyor belt. The plane moves in one direction, and the conveyor belt 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?
This could be taken to mean at least two different things.
A:
A plane is sat on a runway that moves like a conveyor belt.
The plane is pointed in one direction, and the conveyor belt moves in the opposite direction.
This conveyer has a control system that tracks speed of the plane through the air and tunes the speed of the conveyer to be exactly the same (but in the opposite direction). Can the plane take off?
Or
B:
A plane is sat on a runway that moves like a conveyor belt.
The plane is pointed in one direction, and the conveyor belt moves in the opposite direction.
This conveyer has a control system that tunes the speed of the belt so that the plane does not move forward. Can the plane take off?
Answers:
A:
Yes the plain would take off because it is wind speed that contributes to lift. It would in fact take slightly more power too get of the ground as you would have to overcome the slightly increased drag due to the wheel bearing friction.
B:
The whole idea that you need to get if this is the question is. The force off the jet engines has to be exactly counteracted by the force created by the friction in the tyres and wheel bearings as the belt moves in the opposite direction.
This is a harder question to answer as the real question is:
If you had a conveyor belt the size of a runway how fast would it have to move to make to air 20 foot above the surface move at over 180 MPH (reasonable take of speed for a big airplane). Again it is about air speed and not wheel speed, however I guarantee the tyres would blow ages before the time you got your conveyor belt up to the sufficient speed for the air about it to be moving at 180mph.
If however you were going to pretend that nothing was going to break and you could move something the size of a football pitch at the sufficient speed, the airplane could take off. However once you got near to the end of the runway the air would not be travelling as quickly and the airplane would sink back down. So the answer to this question could be either yes or no.
Anyway it’s a silly question that can not be answered without making assumptions
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A runway size conveyor belt wouldn't get any snow lying on itlol
Somebody needs to put an end to this madness. Admin, PLEASE stop this thread before Nova driver's brains all over britain similtaniously explode!
they already have exploded lol
beavy69
15-04-06, 03:37 PM
Part of the plane took off but the wheels will remain spinning on the conveyor belt until this thread is forgotten.
The pilot meanwhile has crashed the half of the plane he managed to get off the ground and is now enjoying his new job as part of the cast of LOST.
THE END
********* CLOSED *********
ps, admin close post lol
The pilot meanwhile has crashed the half of the plane he managed to get off the ground and is now enjoying his new job as part of the cast of LOST.
Apparently the end of Lost S2 is going to go into more detail as to why the plane crashed. Cue pilot:
"Well what happened was, there was this biiiiiig conveyor belt..." lol
They could make a film with the usual planeload of misfits trying to take off for a couple of hours.
if it was Bryanair, it would be on the wrong conveyor anyway
beavy69
16-04-06, 01:53 PM
Ok so they were on the wrong conveyor [that was travelling at 4815162342mph ;) so the wheels came off and remain there....] and this is why the plane was lost.
(Beavis, 2006 - "The Lost Conspiracy" - ?9.99 @ any good book store)
treeted
22-04-06, 09:06 AM
Could always use a harrier jump jet vertical take off its the way ahead!
beavy69
22-04-06, 10:35 PM
Isn't it the way up? lol
I don't think there's any more to say about planes, what about a ocean going liner being launched down a huge conveyer belt slipway, would it ever get in the waterlol
it could depends on the dirtshion or the belt :P
someone kill this post Plex for all out sake
big up Razor for the post !!!
Philsutton
23-04-06, 12:34 PM
please let this post die
http://www.itsnamita.com/wallcategory/web/funny_pics/bike_crash.jpg
If I start at point A at 12:00, walk 4km south at 4kph, turn west and walk 2km at 3kph, then wait for 30mins and run 5km north-west at 10kph, catch a bus east at 50kph for 10 mins, get off and walk 6km north at 5kph; whats my mother's maiden name?
Philsutton
23-04-06, 01:01 PM
derk
mad-driver
23-04-06, 11:13 PM
guess its like a rolling road isnt it? which means it probably wouldnt take off, because evn if you think its not stationary, how can it actually be moving if something is counteracting its movements?:confused:
i confused myself now lol
guess its like a rolling road isnt it? which means it probably wouldnt take off, because evn if you think its not stationary, how can it actually be moving if something is counteracting its movements?:confused:
i confused myself now lol
STOP NOW PLEASE
http://www.picpop.com/gallery/albums/userpics/10059/jeez.jpg
hendrix
25-04-06, 01:35 PM
the conveyor would be pointless as it would need to be longer than a conventional runway! lol
unless the plane and coveyor were both going in the same direction!
now
STOP THIS THREAD
http://paulmccain.worldmagblog.com/paulmccain/make-it-stop.jpg
hendrix
25-04-06, 01:35 PM
the conveyor would be pointless as it would need to be longer than a conventional runway! lol
unless the plane and coveyor were both going in the same direction!
now
STOP THIS THREAD
http://paulmccain.worldmagblog.com/paulmccain/make-it-stop.jpg
beavy69
25-04-06, 03:09 PM
1 the plane would drive off a rolling road.
2 two, will anyone thinking of trying to answer the question actually read the rest of the tread before writing somthing stupid.
3 IT WILL TAKE OFF!!!
4 Is there a world record for the longest thread about the most pointless and obvious question?
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