Airplane and conveyor belt thread...
Discussion
hugoagogo said:
This results in NO forward motion
it's like galileo innit
"Eppur si muove" "and yet it moves" we've had all this many times over, wheels make no difference to a plane, they jsut spin freely, if it was on skids on ice it would still take off. we'll suffice to say you are wrong, and move on
It really, really bugs me when people insist that their junk science is correct. And you managed to drag Galileo into it. Poor fellow must be turning over (in place) in his grave!!!!
Hugobubbo, you are right about the skids/skis. You are dead wrong about the wheels. Powering up a plane results in a "push forward" on the plane by the air (Newton, remember) BUT that results in the wheels being pushed an rotating, causing the plane attached to them to move forward.
Now put it on a conveyor belt that matches the wheels' speed at all times. The wheels rotate, but the plane does not move forward. No movement, no airflow over wings, no lift, and therefore, no takeoff. Simple. Jet engines push really hard. So the wheels will end up spinning very quickly. That's all. Since it is a given that the conveyor belt that the plane is sitting on is always exactly matching the wheel speeds at all times, the plane will never get to move forward, ie. it will not accelerate from its initial speed of zero. No change from speed = zero means zero speed relative to the air at all times.
Would you agree that the following experiment is a valid illustration of the principles involved?
You put a fan on a skateboard and put it on a treadmill. Fan is on setting 1. Treadmill can be set to a speed that causes skateboard to sit in place, wheels rotating freely.
Now you switch fan to setting 2 (higher speed). And you switch treadmill to a higher speed. Again, if you can get the skateboard to sit still, wheels rotating, then it proves that if wheel speed is matched by conveyor belt speed, the skateboard does not move.
The only thing left is to think about the change in speed from setting one to two. You can deduce logically that if beginning and ending speeds are matched, with no forward motion, then if acceleration is matched at all times, that would also result in no forward motion.
If you do not agree with the logical deduction, then you will need a bicycle with computer to figure out the treadmill's acceleration rate from one speed to another, and set up the skateboard to match it. To slow the skateboard's acceleration, you can add ballast (eg, pounds of flour), to speed it up you can set the fan to setting 3 or higher.
Would you agree that this experiment is valid? If so, I can try to reproduce it and post a video here.
If you don't agree with the experiment, then pray tell what you think is a proper experiment.
>> Edited by orgasmicliving!! on Tuesday 23 May 17:12
Mods... LOCK IT.... LOCK IT NOW!
mechsympathy said:
Have I missed a handbag session??
orgasmicliving said:
It really, really bugs me when people insist that their junk science is correct.
Do you annoy yourself often??
The subject came up in a different thread, and I didn't want to derail that one. Apparently this has been discussed here before?
Bliarout, instead of just insisting on your (incorrect) viewpoint, why don't you back it up with science/evidence/experimentation?
orgasmicliving!! said:
Hugobubbo, you are right about the skids/skis. You are dead wrong about the wheels. Powering up a plane results in a "push forward" on the plane by the air (Newton, remember) BUT that results in the wheels being pushed an rotating, causing the plane attached to them to move forward.
and in the skis example, I presume that the '"push forward" on the plane by the air' results in the little ski faries popping into existence and pushing the skis along, causing the plane attached to them to move forward?
Look, when 1,000,000,000 better qualified people explain why your warped view of physics is totally wrong, its usually time to give up!
motco said:
like this? 
That's exactly it. They just need to match two parameters--the skateboard wheel speed and the "belt" or paper speed. The moment they do, I bet you the skateboard would appear to be sitting in place, wheels rotating merrily.
pdV6 said:Last I heard, skis did not rotate? So, you push on them, it results in translational motion.
Look, when 1,000,000,000 better qualified people explain why your warped view of physics is totally wrong, its usually time to give up!
Wheels do rotate. When you push on them about their pivot point, it resuts in rotational motion. Objects attached to the axle experience translational motion. Except when the wheels rotate in place. If you have an airplane hanging by cables in the air, and rotate the wheels, does it move forward? Of course not.
If the plane is resting on the ground, and the wheels rotate on top of a belt rotating in the other direction, again, there is no forward motion of the axle. And the plane attached to the axles also does not move forward.
>> Edited by orgasmicliving!! on Tuesday 23 May 17:21
orgasmicliving said:
Apparently this has been discussed here before?
I have no idea, but I don't imagine we have. It just amused me that you slagged off "junk science" while talking such utter bollox.
As far as I understand your POV, you think that planes have driven wheels and therefore placing one on a conveyor belt would mean that it wouldn't move. In which case what happens when the wheels leave the ground? Why doesn't the plane slow down again?
orgasmicliving!! said:
Wheels do rotate. When you push on them about their pivot point, it resuts in rotational motion. Objects attached to the axle experience translational motion. Except when the wheels rotate in place. If you have an airplane hanging by cables in the air, and rotate the wheels, does it move forward? Of course not.
If the plane is resting on the ground, and the wheels rotate on top of a belt rotating in the other direction, again, there is no forward motion of the axle. And the plane attached to the axles also does not move forward.
Surely the plane would take off regardless, it's wheels merely moving in reverse very quickly prior to liftoff.
The wheels turn due to friction between the tyre and ground and the fact the plane is being pushed forward by thrust from it's engine(s), not the other way round. Ofcourse if the wheels were driven directly then it'd a different story.
The wheels turn due to friction between the tyre and ground and the fact the plane is being pushed forward by thrust from it's engine(s), not the other way round. Ofcourse if the wheels were driven directly then it'd a different story.
orgasmicliving!! said:I'll bite.
Must say I don't really understand the calls for censorship/pleas to lock it down. You don't want to talk about it, don't talk about it. You don't want to read it, don't read it. Why censor others who do?
The original thread's original question suggested to me that you were supposed to assume that there was no airspeed over the wings. Therefore there is no lift, therefore it doesn't take off.
Now in reality that is a slightly silly thought experiment because however fast the conveyor belt ran backwards, it wouldn't stop the plane from moving forwards and gaining some airspeed. This is because in the thought experiment the only thing opposing the thrust of the engines are the frictional losses in the wheels (a combination of the rolling resistance of the tyre and the friction in the bearings). In order to stop the plane pushing itself off the conveyor belt, the conveyor belt would have to be running backwards at an enormous speed and the heat generated in the tyres and the bearings would be equivalent to the heat generated by the engines ... they wouldn't last very long. In any case, I doubt the tyres are capable of generating enough grip to overcome the engine thrust, i.e. if you put the plane on a runway and locked the wheels the aircraft would probably skid forward under full thrust. But all of this is "in reality", and is not what the original question was considering.
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