A plane on a runway, how smart is r3vlimited?

[Justin B]

There is nothing in the problem which states this is the case. You're suggesting the plane can move for a fraction of a second before the belt moves right? If you design some fictitious control system which reacts to the thing that's touching it (the wheels) and its reaction is intstantaneous, the wheels will NEVER spin faster than the belt, no matter how much thrust you apply. If the wheels never move faster than the belt, the plane does not take off. That's my angle.

I seriously beg to differ. and NO, there is no fraction of a second, its a magical belt control system thing that moves the belt at exactly the same time the plane moves in the fake little world of this question. You asked for a real world example of how this could even be pulled off remotely closely, and I gave you my idea, take it or leave it man its always going to have a millisecond delay if its real life. Read all of my posts before you make any more rediculous comments, so I dont have to repeat the same thing over and over again.

A plane is sitting on runway that can move (some sort of giant conveyer belt). The plane moves in one direction, while the conveyer moves in the opposite direction. This conveyer has a control system that tracks the plane speed and tunes the speed of the conveyer to be exactly the same (but in opposite direction).

The question is:

Will the plane take off or not? Will it be able to run up and take off?

So regardless of the speed of the plane, whether its 0mph at a stand still, 1mph just starting to move, or 100mph, the belt will always be at EXACTLY the same speed as the airplane is traveling forward.

You're the control engineer or something, this is a control system to keep the belt at EXACTLY the same speed. It does have that as a constant, it must be always at the same speed of the plane, no difference. Otherwise we could just speed the belt up to whatever we want and make sure the plane wont go anywhere, but thats obviously not the case. Look at the question again and read its yourself. You're wrong just right there.

[chucko]

The belt can only move when the plane moves,and at the same speed the plane moves.

There is nothing in the problem which states this is the case. You're suggesting the plane can move for a fraction of a second before the belt moves right? If you design some fictitious control system which reacts to the thing that's touching it (the wheels) and its reaction is intstantaneous, the wheels will NEVER spin faster than the belt, no matter how much thrust you apply. If the wheels never move faster than the belt, the plane does not take off. That's my angle.

[Justin B]

I understand this whole situation is fake. I understand everything you're talking about. I am chill, all I want to know is how your conveyor belt prevents my plane from creating thrust and moving forward. Let me know that and I'll stop posting. Of course that wont happen though :)

If you want it realistically, you can have a radar gun on one end of this longass conveyor belt and its guts hooked up to a speed control or some bizzare thing, so as soon as it sees speed, it ups the belt speed. The belt will just slide underneath the wheels with minimal resistance though, and the plane will continue to come forward.

Wheel bearing resistance has been neglected as much as possible, and yes I understand this is an optimal scenario. I just keep being told about different drags people want to bring into the equation.

The only way a belt can hold an airplane back anyway is if the wheels had really bad rolling resistance and the belt spun fast enough to cancel out any thrust from the engine. Simple as that, but that isnt happening, the plane moves, and is allowed to accelerate.

Regarding the wheel speed vs belt speed, you're failing to recognize something very important. The speed of the aircraft is A, okay? The speed of the belt is B (well thats handy huh), okay? Well, since the wheels are moving the aircraft forward (air speed of say 50mph) they're traveling 50mph already before anything else is factored in. Of course the belt is meeting the aircrafts 50mph but in reverse, so it is sliding another 50mph under the wheels backwards, so the aircraft or belt don't see 100mph, but the wheels do. The aircraft is traveling at 50mph in relation to the AIR, hence the air speed I just mentioned, the surrounding trees, the dirt on the side of the belt. Plane is going forward, belt backwards, as we all know, how could you not understand how you get twice the wheel speed as the conveyor belt speed? Thats LITERALLY 1+1=2.

You can agree to disagree, but I cant let false answers rule.

ooh oh, something I just thought about about the wheel speed. Easier numbers

Its because the plane is doing 50, the belt is doing -50, the wheels total speed (the difference) is 100

[chucko]

Chucko, please just tie a hotwheels to a string, put it on a treadmill and tug on it.

haha, I'm going to try that one now.

[chucko]

Actually I have said that the control system of the belt is exactly matching the acceleration of the plane. And I mean EXACTLY. Engineers don't always know wtf they're talking about. We're HUMAN. Don't be telling me where you went to school or what training you have had, its irrelevant here, its brain vs problem, and thats the whole point, its supposed to confuse people. I am trying to explain why it works. It is similar to the bowling ball and the boat one too, but that has a definite answer, but opposite of what people may think and hold onto what they believe in if they don't really look into it. I mean no offense to you, or anybody else that disagrees that it will fly that is an engineer. Good for you, I wanted to be a mechanical engineer too till I got caught up doing other things. I know what I'm talking about.

One more time really simply, lets just say magically, because even the fastest electronics arent time machines, but that the runway matches EXACTLY to the 0th of a second how the acceleration and exact speed of the plane as it tries to accelerate.

As far as the propeller/jet engine is concerned it is sitting on any standard tarmac, and WILL pull the plane forward as long as its enough to break free of the resistance the wheel bearings give. Come on, man. Please please think about it a little more in depth, as the plane goes forward, exactly at the same time the belt goes backwards, the only resistance the plane will be experiencing assuming there is no wind and we don't get all into calculating wind resistance (still overcome-able), are the wheels rolling at twice the speed they should for what the plane is actually traveling at. Nothing more, the belt is not traveling any faster than the plane has "air speed". That is nothing at all compared to the inertia of the plane sitting there and not wanting to move from a rest anyway.

Dude, chill, I wasn't saying I'm an engineer to express my supremacy (even though I am..j/k) I was emphasizing that in this fictitious scenario, a control system is being used to drive a fictitious conveyor belt which is fictitiously able to match the speed of a fictitious plane. If you really want to look at this realisticly, you have to ask yourself how is the conveyor belt linked to the aircraft speed? Is there a wireless transmitter that's sending information from the cockpit to the conveyor belt system? If so, then there's a time delay associated with that. That time delay would cause the belt to not react instantaneously to the speed of the plane and the plane would take off. This problem is meant to be an optimal system, you can neglect wheel bearing resistance.

Ok, obviously we are not going to agreee, but ask yourself this question, how can the wheels ever spin twice as fast as the belt if the belt is designed to move as fast (opposite) as the wheel speed? Does your plane ever take off if the wheels cant move faster than the belt?

[Justin B]

That's exactly it, the plane can't move because of the magical conveyor.


What if the conveyor belt also accelerates twice as fast each time the wheels accelerate twice as fast, that's what I'm suggesting. Eventually each time you apply thrust, the wheels and the belt increase speed (simultaneously) until the wheel mechanism collapses, or the conveyor belt mechanism collapses, or infinity is reached.....whichever comes first.

That is entirely wrong, at your first sentence. Read the post I wrote in just above your own there, it challenges you to tell me how a plane wont move forward. Good luck with that one besides telling me that the belt prevents it, because all that does is make the tires spin faster. It doesn't prevent the thrust from occurring from the propeller or jet and wind around the plane, which will pull the plane forward as a whole. There is more drag pulling a big ass plane from a dead stop on a regular runway, than that plus the difference in drag of a wheel bearing being required to speed up a little faster.

You're still imagining the whole problem as a car, the thrust is coming thru the wheels, and the prop and jet have nothing to do with it, when in fact its the exact opposite. The wheels are just along for the ride and they roll with whatever the ground (belt) throws at them.

If you must, do the hot wheels trick, but this is pretty much a killer for you. You wont be able to prove me wrong any more. How the hell is a belt going to prevent any thrust. It pulls the airplane, and again, the wheels are along for the ride.

[O 16581 72452 5]

Chucko, please just tie a hotwheels to a string, put it on a treadmill and tug on it.

[chucko]

I think we need to explain now how the plane begins to move at all when if it tries to move, the conveyor that magically moves as fast as the plane (seriously, in this problem) cancels it out (err buzzz wrong), then there would never have been any movement of the plane in the first place.

That's exactly it, the plane can't move because of the magical conveyor.

All that the wheel bearings have to do is accelerate twice as fast to keep the landing gear to keep from collapsing

What if the conveyor belt also accelerates twice as fast each time the wheels accelerate twice as fast, that's what I'm suggesting. Eventually each time you apply thrust, the wheels and the belt increase speed (simultaneously) until the wheel mechanism collapses, or the conveyor belt mechanism collapses, or infinity is reached.....whichever comes first.

[Justin B]

No man, you're wrong. My emphasis in engineering school was control systems (no lie). This problem also says that the conveyor belt has a control system which increases the speed of the belt to match the increasing speed of the plane, your explanation neglects the effect of the control system on this problem. You say the thrust from the planes engines will cause the plane to move forward on the conveyor belt because the belt is not increasing its speed to match the output of the thrust from the engine. The control system will cause the belt to increase its speed (equal and opposite) to couteract any motion the thrust would contribute.

Actually I have said that the control system of the belt is exactly matching the acceleration of the plane. And I mean EXACTLY. Engineers don't always know wtf they're talking about. We're HUMAN. Don't be telling me where you went to school or what training you have had, its irrelevant here, its brain vs problem, and thats the whole point, its supposed to confuse people. I am trying to explain why it works. It is similar to the bowling ball and the boat one too, but that has a definite answer, but opposite of what people may think and hold onto what they believe in if they don't really look into it. I mean no offense to you, or anybody else that disagrees that it will fly that is an engineer. Good for you, I wanted to be a mechanical engineer too till I got caught up doing other things. I know what I'm talking about.

One more time really simply, lets just say magically, because even the fastest electronics arent time machines, but that the runway matches EXACTLY to the 0th of a second how the acceleration and exact speed of the plane as it tries to accelerate.

As far as the propeller/jet engine is concerned it is sitting on any standard tarmac, and WILL pull the plane forward as long as its enough to break free of the resistance the wheel bearings give. Come on, man. Please please think about it a little more in depth, as the plane goes forward, exactly at the same time the belt goes backwards, the only resistance the plane will be experiencing assuming there is no wind and we don't get all into calculating wind resistance (still overcome-able), are the wheels rolling at twice the speed they should for what the plane is actually traveling at. Nothing more, the belt is not traveling any faster than the plane has "air speed". That is nothing at all compared to the inertia of the plane sitting there and not wanting to move from a rest anyway.

Edit - Tell me why the plane will not move forward if the only thrust it creates is from a propeller or jet which obviously pushes air to move the whole contraption forward, no thrust or force intended to drive the wheels is exerted on the wheels in either direction besides mechanically being forced to follow the plane. The belt can only move when the plane moves,and at the same speed the plane moves, the planes engine will create enough thrust with the surrounding air, as any airplane does, to move. It will have a little bit more drag from the wheels spinning more once the plane lurches forward and the belt backwards, but thats about where your logic runs out of "road" ha ha get it? funny huh. sorry.

I'm tired, about to go to bed, if I don't respond again Ill catch up again later, but think about it a little more, you'll see it. The speed of the belt has no effect on it, thats why the original question before it was modified to have the plane and the belt at the same speed didn't specify that.

[Justin B]

I think we need to explain now how the plane begins to move at all when if it tries to move, the conveyor that magically moves as fast as the plane (seriously, in this problem) cancels it out (err buzzz wrong), then there would never have been any movement of the plane in the first place.

Want to know yet again why the plane moves? Its usually some sort of engine, and it spins this whatchajigg fast enough it pushes air behind it, and since this whatchajigg is mechanically attatched to this flying machine, it lurches forward, and makes the wheels turn on their bearings. Imagine that! All that the wheel bearings have to do is accelerate twice as fast to keep the landing gear to keep from collapsing, which they will gladly do as it is their mechanical job and the'yre stupid. The bearings that is, not you, in case for some reason you lost track of what I was talking about, again. In that case, start at the beginning of this post again. Kthx.

[chucko]

Ok. Maybe you're not smoking anything. Your brain has just been permafried from doing it so much before. Im kidding....Unless its true, in that case im sorry :P

Anyway, go back to the original problem, and notice that the plane is on the belt. Stopped. The plane begins to move, but as it tries to move, the belt starts cruising backwards. By your logic, this holds the plane in place, while in fact it doesn't, because once the plane begins making any sort of thrust at all it will start moving forward, at the same exact time that the belt starts moving back like I already said, but at the same time, all thats happening is the wheels accelerate twice as fast as they ordinarily would if on solid ground, Plane goes forward by pushing air past the fuselage, it never has any grip aside from a slight bit of drag on the belt. Once again, the belt doesn't move unless the plane moves forward, what comes first, fire or smoke? Same concept I guess, but either way, the plane is going to have to move for anything to turn, so you're flawed from the very beginning when you say the plane wont move to begin with!

Please just for both of our sakes, stop posting for at least a couple minutes and think really hard and just try to visualize the perspective I give you, google it, etc. I dont care, I've just about ran out of ideas to

No man, you're wrong. My emphasis in engineering school was control systems (no lie). This problem also says that the conveyor belt has a control system which increases the speed of the belt to match the increasing speed of the plane, your explanation neglects the effect of the control system on this problem. You say the thrust from the planes engines will cause the plane to move forward on the conveyor belt because the belt is not increasing its speed to match the output of the thrust from the engine. The control system will cause the belt to increase its speed (equal and opposite) to couteract any motion the thrust would contribute.

[O 16581 72452 5]

None of your business what crack I'm smoking, just admit that your logic is flawed. In order for the plane to move forward from a dead stop, the wheels will have to be moving faster than the conveyor belt, this problem states that the belt speed is equal and oppisite to the plane speed. In this case the wheel speed = the plane speed, you can not separate the two unless you apply an initial force to the plane before the belt starts moving. You can't do that in this problem.

How is wheel speed the plane speed? The wheels will be spinning as if the plane is moving say 400mph while in the real world, the plane is moving 200 miles per hour, emphasis on miles per hour because that's what the plane would be traveling if you shot a radar at it while the conveyor was doing 200mph in the opposite way.

Let me explain it like i made someone else understand it, say a plane has a speedometer like a car, driven by the wheels, the speedometer will say it's traveling 400mph, point a radar at it and it'll say the plane is moving 200mph, point a radar at the belt, it'll say it's moving 200mph. The conveyer means nothing, all the wheels do is hold the plane up before it takes off, it's free wheeling while there is thrust moving the plane forward.

It's basically like the plane is in air.

[Justin B]

None of your business what crack I'm smoking, just admit that your logic is flawed. In order for the plane to move forward from a dead stop, the wheels will have to be moving faster than the conveyor belt, this problem states that the belt speed is equal and oppisite to the plane speed. In this case the wheel speed = the plane speed, you can not separate the two unless you apply an initial force to the plane before the belt starts moving. You can't do that in this problem.

Ok. Maybe you're not smoking anything. Your brain has just been permafried from doing it so much before. Im kidding....Unless its true, in that case im sorry :P

Anyway, go back to the original problem, and notice that the plane is on the belt. Stopped. The plane begins to move, but as it tries to move, the belt starts cruising backwards. By your logic, this holds the plane in place, while in fact it doesn't, because once the plane begins making any sort of thrust at all it will start moving forward, at the same exact time that the belt starts moving back like I already said, but at the same time, all thats happening is the wheels accelerate twice as fast as they ordinarily would if on solid ground, Plane goes forward by pushing air past the fuselage, it never has any grip aside from a slight bit of drag on the belt. Once again, the belt doesn't move unless the plane moves forward, what comes first, fire or smoke? Same concept I guess, but either way, the plane is going to have to move for anything to turn, so you're flawed from the very beginning when you say the plane wont move to begin with!

Please just for both of our sakes, stop posting for at least a couple minutes and think really hard and just try to visualize the perspective I give you, google it, etc. I dont care, I've just about ran out of ideas to explain.

It doesn't matter if the plane starts moving and then hits the belt, both at speed, or if it starts moving on the belt both at rest, the same situation will still come about. Either the plane will be at a stop in mid air at 50mph wheelspeed stationary on the belt eventually, or it will continue on its way. My picture was the easiest way to draw an example without an animation.

[chucko]

Justin, read the problem again. It says that the plane is SITTING on a conveyor belt, that means it has no initial momentum, which means your scenario can't happen.

[Justin B]

Uh, r3v didnt even hit the surface.

Go here, its a phyiscs forum.

http://forum.physorg.com/index.php?showtopic=2417

Try 6695 (NOT A TYPO) replies, over 447 PAGES.

That beats our measly 100+ posts.

Well, its growing pretty quick. LOL

And so this problem makes it to r3vlimited...

Some people really need to think this through before posting.

mmm. yeah.

Justin, all that matters is that we know we are fighting the good fight

Yarr! lol