Plane on a conveyor belt
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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. 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.
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)
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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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http://www.avweb.com/news/columns/191034-1.html
This guy knows what he is talking about.
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chiming in late here but i think people are looking to deep into it, air speed and ground speed are 2 different things, the landing gear wheels should be thrown out, because they are nuetral doing what ever forces acting apon them want them to causing no affect on the speed of the plane or the conveyor
say the plane needs 50mph of air flying by it to create lift, being the wheels are nuetral why would 50 mph of payment moving under it in the other direction causing the plane to act any differently
think of it this way remembering that air speed and land speed are totaly seperate things
super man is flying along at 50mph of AIR SPEED with a ball bearing pizza cuter in his hand, now flying at this speed he finds a 50 foot long tread mill moving at 50mph LAND SPEED in the other direction
as he fly's by this this tread mill he reaches out and touches the pizza cuter to the moving belt, now does he just stop in mid air?
NO, other than the friction of the pizza cuter his air speed will stay un-affected
but the real question here is how long does it take super man to flay by this 50 miles long tread mill??
makes sense to me but having a simple mind some thing just come more simple to me
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I feel sorry for you guys that don't get this when Schell does.....j/k bud, good analogy
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Damn, I missed out on this argument. Thanks to all of my advanced mechanical engineering classes...Wait, I don't need any of them. It flys. It would be the same as with a runway that is stationary. The only small difference is the greater rotational friction force from the wheels spinning faster, which is going to be relatively small. Planes move from thrust not like a car...
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tjamz wrote:
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 equationFuck. You got me there. I was imagining a scenario where static friction is strong enough to hold the plane in place. I reread the first post and saw that the belt moving at the same speed as the plane, in which case it wouldn't. Bastard..
2005 Mercedes-Benz C240 4Matic
1993 Mazda Rx-7 Twin Turbo (sold) -
YAY, I WIN HERE TOO!!!
I think I just ended a 130+ page long argument on phys.org with my analogies as well. I rule!
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well, Mythbusters is going to take on this one on January 30th....just thought I'd bring this thread back from the dead for some good arguments til then.
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