Plane on a conveyor belt
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I just want to make another quick comment here before I go..
We are not arguing if the the plane has a speed of zero because I already said that it did. Hopping inside a hollowed out train would still do the same thing as the hopping on top of the train.
Here is one last analogy to help everybody understand:
If you were on a train and running as fast you can the opposite way as the train, which is going as fast as you are. Provided you can run forever, you are running towards a overpass bridge which is 10 meters ahead of you. There are infinitely many train cars.
You are at a stationary 10 meters from the bridge. If you jump while running, you remain in the same place. Unless you increase your speed GREATER than the train, you will not move. Given the plane scenario that the belt is continuously variable, if we apply it to this scenario we find that if we run faster the train will go faster the opposite way and --- vector addition, zero displacement. You are still 10 meters away from the bridge no matter how much you run, jump, whatever.
Wheel speed does not matter, it is the overall plane speed that does. If the wheel speed is less than the conveyor belt speed (using vector addition one last time) we have a negative displacement which means the plane will move backwards infinitely many times.
Have a good night you guys.
2005 Mercedes-Benz C240 4Matic
1993 Mazda Rx-7 Twin Turbo (sold)
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Here's my theory...
Think of a Kite; a kite can lift off w/o moving forward; I think the thrust of the engine will pull the air over/under the wings, and therefore it would take off.. I could be wrong, just an analogy...Oh and if it was a propellered plaine, Propellers in front of the wing; wouldn't that create air flow over/under the wing as well?
depends on what type of plane we're talking about too I guess.. -
Aceshigh, you are incorrect that planes using gearing in the wheels for take off, they entirely use their jet engines for this, how else do you think they accelerate so damn fast down the runway? You keep looking at this from the point of view that the plane is not moving which is not true, it may not be moving as fast with x amount of thrust when y amount of conveyor movement is pushing the opposite direction, but it is moving at will once it generates enough forward thrust to start the wheels spinning.
Your last analogy again assumes that the airplane is using its wheels to generate enough speed (approx 150mph I am told is what it takes to get an airliner airborn) to take flight which is fundamentally what is flawing your analogies. The wheels on a jet are free rolling units (at least on take off and landing) whose only purpose is for minor steering correction and to allow the plane to easily roll when thrust is applied. As soon as you realize that fact you will realize that it is possible for the plane to move forward while on a conveyor belt.
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That is an interesting way of putting it, but I hope you can see the fallacy:
The earth is rotating at a speed of 1670km/sec. A Harrier air craft takes off straight up from the earth. Does it magically appear in Seattle as it lands?
2005 Mercedes-Benz C240 4Matic
1993 Mazda Rx-7 Twin Turbo (sold) -
THE PLANE/JET WILL NOT FLY!!!111!!!!!1!!!!
you guys are crazy that think it will fly. put a lil more thought into it.
the plane is standing still, if a plane could just lift off the ground standing still, they wouldnt need engines that creat thrust.
they need to have air movement under the wings. the only thing moving is the wheels, DUH. -
It figures that Chuck started this thread, it's worse than a political thread except people don't get bent out of shape and close it for no reason. LOL
Of course the plane will take off, what the wheels are doing doesn't really affect the plane as it accelerates. The pilot will hit the throttle, the thrust of the jet engine will push the plane forward, irreguardless of whether there is a conveyor under the wheels, or not. The plane will gain airspeed (again, it doesn't matter what the conveyor below the wheels is doing, the wheels would be spinning like a mofo because of the conveyor speed, but it really won't affect the acceleration of the plane relative to the ground). The plane will gain airspeed until the wings provide enough lift for the plane to take off.
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[/size]If it makes it easier to grasp, what would happen if the conveyor was moving in the same direction as the plane? Would the plane take off twice as quickly? No, it would accelerate like normal, but the wheels would be spinning in reverse until the speed of the plane matched the conveyor, once the plane matched and then exceeded the speed of the conveyor, the wheels would come to a stop, and then start moving in the forward direction (again, not affecting the acceleration of the plane).
A plane never moves via gear drive to the wheels. The plane moves forward by the thrust of the engines. The plane has brakes, apply the brake on one side and the plane turns, apply the brake to the other side and it turns the other direction.
Now that I've spoken, there is nothing else to say, you might as well lock the thread now.
DaveH
'94 Supra- 7.77 @ 176mph -
camzaro28 wrote:
THE PLANE/JET WILL NOT FLY!!!111!!!!!1!!!!you guys are crazy that think it will fly. put a lil more thought into it.
the plane is standing still, if a plane could just lift off the ground standing still, they wouldnt need engines that creat thrust.
they need to have air movement under the wings. the only thing moving is the wheels, DUH.You need to put more thought into it...all the wheels do is allow for easy rolling. Nowhere does it say the plane will stay in one spot (it won't) as the force pushing it forward is the thrust of the motors, <u>***NOT THE ROTATION OF THE WHEELS ***</u>if it were dependant on wheel rotation to move forward you would be correct, but since it doesn't (see side car analogy AGAIN) the plane will move forward via thrust from the motors which will cause airflow over the wings which will allow it to take off.
Everyone needs to quit thinking of the plane as a car and realize that forward motion is caused by the prop/jets, the wheels just make it slide along the ground easier.
One more attempt to make people see the light here:
Imagine the most slippery substance on earth was applied to the runway, so slippery that the wheels on a CAR would just sit and spin with the car going nowhere, just doing a burnout upon shifting into gear. Now think what would happen if you attached a jet engine to the roof of the car and turned it on producing thrust. What do you think would happen to the car. Do you think it would stand still? No, of course not, even if you shifted the car into reverse and floored it and somehow managed to match your wheel speed with that of the air speed produced by the jet engine pushing you you would still move forward due to the wheels not getting any traction on this surface and the jet engine being able to push the vehicle at will as it doesn't rely on traction to move it forward..... Same principles apply to the jet on the run way.
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haha, yeah once i read dave's post i understood. i was under the assumption that no matter what the plane was at a standstill and was gonna take off like that! i read over it a lil to quick. ah, oh well. i get it now.
YES the plane will take off. maybe i should have read the 9 or so pages b4 posting
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DaveH wrote:
It figures that Chuck started this thread, it's worse than a political thread except people don't get bent out of shape and close it for no reason. LOLOf course the plane will take off, what the wheels are doing doesn't really affect the plane as it accelerates. The pilot will hit the throttle, the thrust of the jet engine will push the plane forward, irreguardless of whether there is a conveyor under the wheels, or not. The plane will gain airspeed (again, it doesn't matter what the conveyor below the wheels is doing, the wheels would be spinning like a mofo because of the conveyor speed, but it really won't affect the acceleration of the plane relative to the ground). The plane will gain airspeed until the wings provide enough lift for the plane to take off.
If it makes it easier to grasp, what would happen if the conveyor was moving in the same direction as the plane? Would the plane take off twice as quickly? No, it would accelerate like normal, but the wheels would be spinning in reverse until the speed of the plane matched the conveyor, once the plane matched and then exceeded the speed of the conveyor, the wheels would come to a stop, and then start moving in the forward direction (again, not affecting the acceleration of the plane).
A plane never moves via gear drive to the wheels. The plane moves forward by the thrust of the engines. The plane has brakes, apply the brake on one side and the plane turns, apply the brake to the other side and it turns the other direction.
Now that I've spoken, there is nothing else to say, you might as well lock the thread now.
YAY!!! Dave and I agree on something again....maybe there is hope for him afterall.
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I think I finally see where we are butting heads, Tjamz; in your example you assume that the wheels are frictionless; if in fact the wheels were frictionless, then yes the plane would be able to move.
I interpreted the original scenario to be not an ideal world but one in which friction exists. The plane is set such that it's velocity relative to the belt surface is perfectly counteracted by the velocity of the surface. Thus, the plane is stationary with respect to the air, with its thrusters on (after all, isnt that what is moving the plane in the first place?). If this wasn't the case and the plane would be stationary WITH or WITHOUT its thrusters then this really isn't a Physics problem at all, but common sense. A guy on an ice rink holding a big fan would start sliding. It would make more sense to have the question set to where the speed of the plane is matched in an opposite fashion (that is, the belt is actually retarding the advance of the plane).
If the situation was how I interpreted earlier then you would have two outcomes:
Case #1: Wheels are not frictionless Answer = no, the plane doesn't move (as I have been trying to get at). There are static frictional forces that the plane must overcome, and if it is already giving 100% thrust and not going anywhere, it isn't taking off). The postulate here is that the treadmill is imparting enough drag on the plane via friction to counteract the thrust.
Case #2: Wheels are frictionless (belt can do no work) Answer = yes, the plane can take off. If world was frictionless then the surface would not matter. The thrusters might as well be off, for the belt moving wouldn't affect the plane at all.
This question is hard due to its ambiguity, not its physics setup.
2005 Mercedes-Benz C240 4Matic
1993 Mazda Rx-7 Twin Turbo (sold) -
I posted this on another forum; and it seems it's just a never-ending argument! Where is the "PROOF" that it'll FLY or NOT? so it can end the madness
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AcesHigh wrote:
I think I finally see where we are butting heads, Tjamz; in your example you assume that the wheels are frictionless; if in fact the wheels were frictionless, then yes the plane would be able to move.I interpreted the original scenario to be not an ideal world but one in which friction exists. The plane is set such that it's velocity relative to the belt surface is perfectly counteracted by the velocity of the surface. Thus, the plane is stationary with respect to the air, with its thrusters on (after all, isnt that what is moving the plane in the first place?). If this wasn't the case and the plane would be stationary WITH or WITHOUT its thrusters then this really isn't a Physics problem at all, but common sense. A guy on an ice rink holding a big fan would start sliding. It would make more sense to have the question set to where the speed of the plane is matched in an opposite fashion (that is, the belt is actually retarding the advance of the plane).
If the situation was how I interpreted earlier then you would have two outcomes:
Case #1: Wheels are not frictionless Answer = no, the plane doesn't move (as I have been trying to get at). There are static frictional forces that the plane must overcome, and if it is already giving 100% thrust and not going anywhere, it isn't taking off). The postulate here is that the treadmill is imparting enough drag on the plane via friction to counteract the thrust.
Case #2: Wheels are frictionless (belt can do no work) Answer = yes, the plane can take off. If world was frictionless then the surface would not matter. The thrusters might as well be off, for the belt moving wouldn't affect the plane at all.
This question is hard due to its ambiguity, not its physics setup.
You ALMOST got it. How about case #3 where the bearing in the wheel and the wheel itself do provide friction, but not so much friction that thrust from the engines cannot overcome it and achieve the forward momentum required for the air to flow over the wings and cause lift.
In your case #1 example, it is impossible for the plane to take off under any circumstances as you are assuming that any friction put on the wheels/bearings is enough to keep it from moving forward under thrust from the engines when in reality the most resistance you are encountering is just to get the plane moving, once it is moving the resistance becomes almost a complete non factor in the equation as there isn't a significant amount of increase in resistance to spin the wheels at 100 mph than there is to spin them 200mph (the conveyor belt is the only thing roll the wheels directly btw...in a normal situation the relationship of the engines (jets, props, whatever...when I say "engine" those are what I'm refering to) pushing the plane forward on the ground would be causing them to roll.
I'm still right.:D
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camzaro28 wrote:
haha, yeah once i read dave's post i understood. i was under the assumption that no matter what the plane was at a standstill and was gonna take off like that! i read over it a lil to quick. ah, oh well. i get it now.YES the plane will take off. maybe i should have read the 9 or so pages b4 posting
I'm really glad you changed your mind.. CMK decided to call me this afternoon to inform me that you believed the plane would not take off....and Brian, I lost a lot of respect for you for a while there.
I'm done replying phisics bullshit....
I'll lose my mind over it.. -
heh, I'm arguing this point on like 6 forums now....two for airliners, here, MNSC, MisterCMK, and a physics board....fun stuff.
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And what are the outputs from the airliner forums? j/w!!!
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people on both sides of the fence there as well, kinda sad to think that a lot of our pilots seem to think that if their wheels are being spun they can't generate any forward thrust. The key to remember here is that the wheels spin in the same direction whether they are being driven by the thrust of the jet/prop or the conveyor belt...or both. If both forces are acting upon the wheels they double in the amount of rotations they'll make in a given period of time.
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