Found this on Nasioc and in one single day it generated 25 pages so far worth of debate, so I am bringing it here to see what everybodies thoughts are on the subject. Imagine a plane is set on the beginning of a massive conveyor belt/travelator type arrangement, as wide and as long as a runway, and intends to take off. The conveyer belt is designed to exactly match the speed of the wheels at any given time, moving in the opposite direction of rotation. There is no wind. Can the plane take off?
No, I believe that the assumption was that it was a typical airplane. Lets just say for our purposes its a 747.
Then... no. The wheels spinning on a moving surface has the same net effect on the actual plane as it would sitting still. And this generated 25 pages?
i'll leave this to the smart GT peeps and various other brainiacs on this site...i vote for no if i had to though, unless there's no gravity :ugh:
No it cant take off. In order to take off you need actual air flowing over the wing. Get a big fan on one end of the conveyor that pumps air at the same speed and volume that the plane's wheels are moving and the plane would lift straight up. How did this take 25 pages?
http://forums.nasioc.com/forums/showthread.php?t=891480 There is a lot of debate about the conveyer/treadmill and the wheels which made absolutely no sense.
A plane with veritcal takeoff could (ie. harrier). The wheels are not moving and therefore neither is the belt. A lot of assumptions could be made. What if the plane was a toy and made of balsa wood? Does the conveyor produce wind which could produce enough of a pressure delta to create lift? And on and on...
Actually, re-reading the question it doesn't say that the plane remains stationary. Since the engines are moving the plane through the air and the wheels are merely supporting it, you'd think that the plane could still move through the air regardless of what the wheels are up to... but if the belt matches wheel speed... Crap, wouldn't that mean the wheels have to spin infinitely fast for the plane to move forward? What'd probably happen is the wheels would slip along the surface and it'd actually take off... now that I see it's more than 'will a stationary plane take off?' it's actually interesting.
here's my take at it the plane will move forward and it will take off... this is because the plane moves forward due to thrust generated by the engine, not by applying any force to the ground... therefore the relative motion of the ground should not matter (except for small frictional forces) im curious whether it is theoretically possible to design a conveyor belt that can match the speed of the wheels... i guess it depends on how u define 'the speed of the wheel'... 1) if u define it as translational velocity at the center of the wheel relative to the earth, then it will work... the velocity of that point is the same as the velocity of the plane regardless of the speed of rotation... the conveyor simply has to move in the opposite direction and match the speed of the plane 2) for other definitions of speed, it might not be possible to design the required conveyor any comments?
I believe the plane would take off. When it takes off, the wheels will not be spinning and the conveyor will be moving forward at the speed required for enough lift to be generated to get off the gound. The wheels don't propel the plane, so there will not be movement by the conveyor in the opposite direction that would cause the plane to remain stationary.
I'm going to say no way... you could spin the engines/wheels a million miles an hour, you need wind hitting the flaps to generate lift.... unless I'm reading the question wrong...I'm to sleepy to put too much thought into it though...
I am going to say yes. My take would be to say that the plane only needs to build enough thrust to overcome the kinectic (and rotational) friction that the surface of the conveyor is applying to its wheels and vice versa. We cannot forget of course the direction force against the desired forward motion of the plane. Once the plain overcomes this, the thrust of the engines should allow the plain to move forward such at a speed that it is POSSIBLE to overcome the force due to gravity. At this point it should be able to obtain just enough lift to allow for take off. Once there is absolute 0 contact, the thrust will allow the plain to accelerate at a rate which will propel it onward. So recapping my brief thoughts. Overcome the force which is pulling on the plane in the reverse direction (static friction). Overcome the kinetic friction of the plane versus the belt and then the rotatonal friction between the surfance of the belt and the surface of the wheels. Once this is accomplished, the thrust provided by the jets will push the plain the forward direction allowing it to build a value of speed that generates enough lift to overocme the force due to gravity. With this, the plain can have absolute 0 contact to the ground and continue to take off. The existence of wind is neglible in the fact that it only makes take off more difficult (head wind) or easier (tail wind). However, this, like all "classical physics" requires a few assumptions. As well as leaves out a good bit of variables (drag, etc).
wow 25 pages thats a whole lot of discusion for this question, and yes it can take off since forward motion is not caused by the wheels.
I still dont buy it unless the air is moving over the wing. The plane can sit there with its turbines pumping to high heaven but if the conveyor belt matches the speed the plane sits stationary. A stationary plane that takes off with lift over its wings will not take off sitting stationary. The airfoils need air flowing over them to create lift. The lifting force needs to overcome the weight of the plane, in order to get that force you need a certain volume of air moving rapidly over the wing.
right but the turbines create thrust which will cause the plane to move forward causing there to be air flowing over the wings.
I say it won't take off because it won't move. Forget the thrust for a second; If the belt is moving the same speed as the wheels in the opposite direction the plane can not move forward(that's impossible). Think if you where to hold a model plane on a treadmill; If you moved the plane forward on the treadmill the wheels would be going faster than the belt. The fact that they have to go the same speed would cause the belt/wheels to rise to incomprehensible speeds(infinite) very quickly, but the plane won't move.
bump to Bobby... no wind / no worky... I worked on F-16's for 4 years and have a little knowledge on the subject. First, there are too many holes in this scenario to make anything more than an educated guess... Second, When diagnosing engine problems on F-16's, we ran jets in full burner on the ground(with the tailhook chained to the ground, of course), and the jet had no desire to lift due to thrust(24,000lbs of it). To me, this scenario has the jet on a huge dyno... It would be a good way to find out peak horsepower/torque, but there would be no takeoff... my .02
Ha! More like 40+ pages. Still going stong past the thousand post mark last time I checked. Anyway, I said that you can think of it as the plane "sliding". Imagine if there was no friction. The wheels would not spin. Doesn't matter though, as there is still thrust. Basically, wheel spin doesn't matter. The force is not projected from the engines to the wheels which move the plane. There is thrust, and no counteractive forces (well, there is friction). Net imbalance of force = acceleration, movement, and lift.
I think what people are missing is that the plane would be moving forward thus creating lift(wind). It would accelerate just like normal, and just before liftoff be moving at 150-170 mph depending on load. The only difference is instead of the wheels rolling as the plane moves forward, the conveyor belt would be moving forward at 150-170mph as the wheels stood still (actually the wheels would be moving forward at 150-170mph with the rest of the plane, but would not be rotating).
I say no. The question plainly states that the plane only intends to take off, but says nothing about actually turning the engines (turbines, props, whichever) on and moving forward. In fact, the question implies that the plane will remain still while the wheels roll. the wheels only support the plane anyway, they dont propel it, so the wheels shouldn't even matter in this case. I intend to move objects with the force all the time... but it never happens because I dont have a high concentration of midichlorians... duh!! Same principle... :rofl:
The main thing to think about here is that airplane wheels are not like car wheels, they are more like front bicycle wheels and can freely spin on their axles. to setup: ok you have five forces at start, the static friction of the wheels against the supports(rubber on steel) at coefficent of about .7., the thrust of the plane which is 52000 pounds force or 280000 N for a 747, force of gravity and normal force at of 373500 kg * 9.8 or around 3,500,000 Newtons. This makes the force of friction on the ground to wheel rubber around 2,450,000 Newtons. However the last force, the ball bearings of the wheel axles have a significantly less coefficient of kinetic friction, like .1, which the plane thrust-ground conveyor system is very capable of attaining at the instant the plane gains velocity off the start. So here's what happens As the plane is stationary to start, the conveyor belt is not moving. The wheels are firmly planted on the ground and the plane starts to thrust,the axle to wheel friction at this point is higher than the planes thrust, so the plane is directly connected to the ground and will move forward for an instant. The ground will move backward with the speed and immediately creates KINETIC friction at the axle to wheel connection, because the axle-wheel friction is less than the wheel-ground friction. This breaks static friction's hold on the plane and allows the wheels to freely turn like a burnout. Think of the bicycle analogy again, except that your bicycle has a rocket engine strapped to it and that you have two rotary drills connected to your wheels spinning the wheels forward, it's the same effect. You're gonna move forward, your wheels are moving actually in a forward direction quicker than normal as the regular spin coincides with the conveyor's motion, so even if the axles to wheel connection "caught" it would move the airplane forward quicker. Bottom line, plane takes off eventually because of axle to wheel slippage.
i wonder what E-Mol is doing.. Weapon : Hey E-Mol...what are you doing? E-Mol : Im taking a shit whitey, you wanna come watch? Weapon : Nah..I think I'll pass..Good luck with that though!
Haven't posted my answer for this here so here goes. In order for a plane to take off, it needs to reach a set takeoff speed. For example a 737 needs to reach 150 mph. Since the plane is on a conveyor, the wheels may be spinning at 150 mph, but the plane itself is moving at 0 mph. Since the plane is not moving, just the wheels. No lift is being created. Along with the takeoff speed, lift has to be created on the main wing. Since the plane is not moving, no lift is being created to allow the plane to takeoff. Now the engines are creating thrust, and that thrust is being directed over the rear wing where the elevators are located. Using the elevators and thrust, I think it may be possible to get the front landing gear off the ground, but that is it. Now if we are talking about something more along the lines of a rocket engine straped to the plane, then once the pitch of the plane reaches a certain angle, and the thrust from the engine is being directed at the ground, it may be possible for the plane to lift off, but again this is only with a rocket engine. In order for a plane to remain airborne, it needs to maintain a speed above the specifies stall speed. If the plane were to somehow take off on the conveyor, which is not possible, the second it got into the air, it would be well below stall speed and would come right back down. So, my answer is plain and simply no, the plane can not take off.
This is making my head hurt know the answer.... do you.. A plane is standing on a runway that can move (like a giant conveyor belt). This conveyor has a control system that tracks the plane's speed and tunes the speed of the conveyor to be exactly the same (but in the opposite direction) instantly. Will the plane be able to take off? and Why... Discuss........... This was posted on another board and me and one guy have been going back anforth for about 45 mins now and i dont think it will take off. What do you think?
wow i saw this on ia months ago and it turned into a 45 page debate. their end result was yes it could but i think it was only cause the other side decided to not argue any more. now onto my answer. i would have to say no. the reason i say no is because for the plane to take off it has to generate lift. if the plane is standing still there is no wind flow over the wing to generate the lift.
NO, first the thrust from the engine alone is NOT enough to make the jet take off...Wind creates lift. Which is why atleast here at lockheed jets take off and land into the wind to help lift. Unless you are a harrier as the engine can force thrust downward to allow a short takeoff.
The conveyor cannot not track the speed like that. It would have to track the thrust of the aircraft and calculate how fast the plane would be going. Its poorly worded and thus causes the long debates. Anyway...as long as the conveyor is keeping the aircraft from moving forward it isn't going to take off.
I've heard some variants on this making it a lot harder to discuss since people interpret the thing differently. If the conveyor moves in the opposite direction (IE plane goes north, conveyor moves south) it'll just double the speed of the wheels. So if the plane's moving at 200mph forward the wheels will move at 400mph relative to the conveyor. The issue that comes into place is friction/rolling resistance, but I can't see how the plane could not overcome that... If the conveyor is moving in the same direction as the plane it'll take off just fine. In either case the plane builds speed relative to its environment (wind) by way of thrust (the wheels don't generate any acceleration) and it'll take off.
it states that it has a treadmill effect...if you're running on a treadmill you feel like you are running but at the same time you're not going to feel air going by you. you stay in place. therefore how can you take off. the idea of a plane taking off without air going over the wings is impossible. thrust merely pushes the plane through the aair in order for the air to go over the wings. whether it has props, jet engines, or rockets, if you can't get the plane to move b/c the conveyor belt moving in the opposite direction won't let the plane go anywhere, how can the plane take off?
No, it can't. In my interpretation the plane will remain stationary on the treadmill. I think it was poorly worded with wheelspin (since so many are arguing they would slip). I'm interpretting it as the treadmill matches the speed of the plane. Thus the plane will never gain any ground. Thus there will be no lift. I mean think about it; relative to the earth the the plane has a velocity of zero no matter how fast it goes on the treadmill. So even if it was to somehow take off, it would have to accelerate from 0-whatever speed it takes to keep the plane up, instantly. Not gonna happen. But yeah it is a poorly worded question so I guess it's open to interpretation...but I'm right Sorry for helping to rekindle an extremely old thread.
I doubt it would, ask a bunch of people about this. If it was to lift off, it would need a lot of air to be pushed around the wings. I don't see a plane from literal stand-still and just suddenly starts to fly.
A conveyor moving in the opposite direction of the wheels will only match the speed of the wheels if the plane is stationary. The thrust will make the plane move forward. Hence the conveyor will never match the speed of the wheels. The plane will take off.
The only way the plane will move forward is if the plane wheels are spinning faster than the conveyor belt. And that's impossible because the conveyor belt matches the speed.