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Why don't they just pull the motor from it and call it a glider?
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iirc, i believe the original plane on a conveyor belt was a trick question. it was a jet and all the conveyor belt had to do was go backwards as fast as the *wheels* were rolling forward.
in that scenario, the wheels on the backwards moving conveyor belt are a red herring. on a jet (and on a prop plane) the wheels simply remove friction from the forward motion provided by the jet engine (or the prop). the conveyor belt would *only* prevent flight if it were the wheels themselves (connected to some engine) that were providing the acceleration.
it's the same thing as asking the question: could a jet on sleds (instead of wheels) take off on ice?
the heart of the matter is that the conveyor belt is doing nothing to prevent forward motion of the plane since the plane's thrust is generated by an equal and opposite reaction to the action of ejecting air backwards....and *not* the opposite reaction to the wheels pushing against the ground.
the plane flies because the conveyor belt has *no ability* to prevent the forward motion of the plane.Comment
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Oh god I cant argue this anymore... Im still tired from the LAST time!
Ill just wait for this episode to prove you all wrong.Imagine, being able to be magically whisked away to... Delaware. Hi... Im in... Delaware...
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OK, if I'm wrong, and I may be, why are there not belts like this on an aircraft carrier where space for excelleration is an issue? I'm just wondering...Originally posted by RobRR View PostOh god I cant argue this anymore... Im still tired from the LAST time!
Ill just wait for this episode to prove you all wrong.
Seventhson,
So if I'm reading your post right, they can't move the conveyor belt fast enough to negate the thrust of the plane, right? Physics will negate this, correct? The belt and the wheels are moving in the same direction, in the video at least. So I'm a bit confused about this...
Not being a smart ass at all. I don't know ALL the answers. Just trying to understand the concept that those on the other side have...I'm angry because you're stupidComment
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because a conveyor belt on a carrier does is NOT preventing the plane from moving forward.Originally posted by Bengal View Post
correct, the conveyor belt is a red herring wrt to the plane moving forward. the disconnect is that everyone believes that the conveyor belt can keep the plane stationary, but it can't.Seventhson,
So if I'm reading your post right, they can't move the conveyor belt fast enough to negate the thrust of the plane, right? Physics will negate this, correct? The belt and the wheels are moving in the same direction, in the video at least. So I'm a bit confused about this...
Not being a smart ass at all. I don't know ALL the answers. Just trying to understand the concept that those on the other side have...Comment
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Someone better post this episode on youtube!
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SS,
So in the original video, if the match the speed of the tarp with the speed of the thrusting airplane, the airplane wins? Right? How does the plane trump the moving tarp underneath?
EDIT: I think I get the theory. The plane isn't moving because of the tires moving, it's moving do to the thrust of the air behind the prop, right? So the tires do nothing but cause less friction as the plane moves forward. We could have blocks of wood instead of tires and the plane would still "roll" down the runway because of the air thrust...
OK, I understand the other side now. Man, this is interesting. I've never watched an episiode of Mythbusters before but I'm all over this one...Last edited by Bengal; 01-29-2008, 05:59 PM.I'm angry because you're stupidComment
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I don't believe that at all.Originally posted by SeventhSon View Post
I believe the experiment is that the conveyor belt and the plane are going the same speed but in opposite directions.
<- Conveyor @ n speed vs Aircraft @ n speed ->
Net speed 0.Comment
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+1Originally posted by SeventhSon View Post
I was typing as George was posting, and I think we're coming from the same angle...
The last time we had a thread on this, I did a fair bit of reading on this one. The quick answer most people come to is that the plane will get no lift if the conveyor belt can keep it from moving forward. I completely agree with this, but the whole game hinges on whether you can make a real-world conveyor belt that can meet the criteria. It's not as easy as it sounds, because the wheels are free-spinning, and the only force the conveyor can exert against the plane is the friction of the wheel bearings. My gut feeling is that they aren't going to be able to build a conveyor belt that can go fast enough to create enough frictional force to hold the plane in place.
Basically, I think the whole plane-on-a-conveyor question is flawed from the get-go because it makes a huge assumption that you can counteract the plane's acceleration with the conveyor. They either didn't take that into account when they made up the problem, or they were just being really clever and made it a trick question.
So, that's my long-winded way of saying that I think the planes will probably take off on the Mythbusters show, but I think it will be because the criteria for the question (as it is usually worded) won't be met.
Here is a Straight Dope column that kind of says something similar:
Last edited by dg; 01-29-2008, 06:06 PM.Comment
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So who wants to put money on this?Comment
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In a perfect world with no friction, you could spin the conveyor very fast, but it would only spin the wheels of the plane but would not apply a backwards force to the plane itself. In reality, there is a small amount of friction that occurs from spinning the plane's wheels. As a thought experiment, think about applying the brakes on the plane a bit. The more you apply the brakes, the harder it is to take off of the conveyor. But the brakes are just increased the friction that is always there anyway. So answer #1 is: if you had a conveyor belt that had no limit to how fast it would turn, you could in fact stop a plane from taking off because of friction. But, it would have to turn ridiculously fast. So answer #2 is a real-world conveyor cannot stop a real-world plane. Both answers #1 and #2 are correct I would say._________________________________________________
"Artists should be free to spend their days mastering their craft so that working people can toil away in a more beautiful world."
- Ken MComment
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In the same vein, to reduce a planes speed on the runway, or increase it, you throttle back on the prop/engine. The engine doesn't turn the wheels, like in a car, the thrust turns the wheels but only as a by product of the thrust from the prop...
Do planes have brakes on the tires like a car? I'm sure they do. But I would guess that it's the loss of inerta (sp) from the throttled down engines that stop the plane. The brakes just bring it to a complete stop...
Call me John Kerry cuz I'm a flip floppin'...I'm angry because you're stupidComment
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A plane pulls/pushes itself through the air with a propeller, just like how you'd swim through water. Don't need wings here.
However, a plane just happens to have wings, and when they move through this air at a certain speed, generate lift.
Plane 5mph forward + belt 5mph backward, wheels see 10mph
plane 50mph forward + belt 50mph backward, wheels measure 100mph
plane never sits still.
Or think of this. Strongman contest, guy can pull plane down runway.
So put a conveyor underneath the plane and set it to go.
He can just stand there and hold it still? No matter how fast the belt is running. (to an extent)
Last I checked, a propeller or jet engine surely puts out more force that it takes to keep it in place. The thrust necessary to keep a plane motionless on a belt moving at any speed, is just enough to overcome any friction in the wheels.
My engineer father believes it wont take off, so I can only hope this experiment accurately works or notComment
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What happens if it lands in water; will it float? :ROTF:I feel my soul go cold... only the dead are smiling.Comment
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You fail to see that the conveyor backwards speed only very minimally affects the forward aircraft speed.Originally posted by JacksonDean View PostComment
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