Plane on a conveyor belt
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well I thought about this one through and through debated it with my roommate and I descovered the crux of the issue, there are two schools of thought that will clash on this. the free thinkers and those who are bound to constraints. if you don't think outside the box, the plane will never take off. but since I don't think like that I came to the solution rather quickly. negating the obvious errors in the queston and assuming that by saying plane they ment airplane not aircarft and most certianly not just a "plane".
the solution I arived at is that since the question did not set any limitations on the craft, at a certian point the airplane would achieve an amount of pounds thrust that is greater then the mass of the aircraft. in essense turning the craft into a rocket and negating the need for wings at all. it will move simply by newtons laws of motion. and at such a point the only way to stop it from moving is to increase it's mass to something greater then what the engine is capable of producing thrust to compensate for. but no matter what with the right amount of thrust the craft will move no matter what. even if you tie it to the earth. with a amount of thrust that is totally unrealistic of achieving it would move the earth as well and become yet another spacial object.
but this is only taking into account that you do not limit the solution to restraints that the question never stated. this is how advances are made in science by forgetting about past flaws, if people didn't think like this, the earth would still be flat, the sun would revolve around us and apples wouldn't fall.
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ok. here is my line of thought..
let plane speed = A
let conveyor speed = -A (since theyre exact opposites of each other)A + -A = 0 meaning no forward movement.
no forward movement = no flow over/under the wings = no lift
i understand your thoughts about how the plane's wheels will just keep spinning.. but arent the wheels attached to the plane? if so, if all the wheels are doing is spinning, how is the plane moving forward? to me it would be like trying to run on a treadmill. if its moving the same speed as youre running, your head wont go anywhere even though your legs are trying to move you forward.
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That is because your legs are your source of propulsion on the treadmill, for the airplane, it is the engines pushing air and the wheels have nothing to do with it. How do Ski/float planes take off without wheels, because they aren't necessary so it doesn't matter how the wheels are moving, the plane is pushing forward with air.
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It's a little different than that, in my opinion I guess. What you are assuming is that the planes ability to move forward is directly tied to the wheels (it is not I'm assuming in this situation). Let's use the treadmill analogy. You put a skateboard on a moving treadmill. If the wheel bearings of the skateboard are perfectly frictionless (like what I'm assuming with the plane's wheels here), the skateboard itself will not move. The wheels will spin with the treadmill, but the skateboard itself will not move. Now we have the wheels vs conveyor thing illustrated. They negate each other. The only force left acting on the plane is the thrust of the engines. This is the only force left (magically of course). Since it is the only force left, the plane moves forward and takes off.
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yeah the plane's jets are pushing it forward.. but gravity is holding the plane down onto the belt. since the wheels are actually what are touching the belt.. theyre just going to spin. ski/float planes dont take off of something moving the same speed in the opposite direction.
im trying to understand.. but my common sense (at 3 in the morning) says it cant happen.
edit: written before the above post. i think i got it.
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That's a big 10-4 on the 3 in the morning biz. If I hadn't slept all day cuz I was working all night last night I'd be in bed so long ago. The gravity holding the plane down on the belt as a way of holding it from moving horizontally is negated by the magic of the ever popular assumed frictionless bearings. Lots of assumptions and whatever in all this bizness, interesting question Chuck
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ok, heres my take....you need the airflow above and below the wings to make the plane leave the ground. If you've ever run on a treadmill, you'll know that you get hot because no matter how fast you run, there is no airflow going over your body. If you run around a track or outside or something, the airflow will cool your body.
With no airflow, the plane stays on the ground.
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So, Dubbsy
Explain too me why the foreword thrust wouldn't move the tires more.Plane has thrust on it's body, pushing the plane a 50mph, the wheels, attached to the plane, spin at 50. The "Treadmill" spins at 50.
The plane has thrust pusing it's body too 100mph, that means the plane needs too acelerate, forewords, because we need too go forwords to generate lift, we all know that.
so, if the plane goes forword, the wheels turn forword, the Treadmill matches the wheels.Which means it matches the plane.
Which means that it doesn't matter what speed the Jets are pushing the plane, the wheels are going that fast too, and as long as they are, the treadmill is matching.
I understand what u are saying, but, it's not possible too me.
If u can explain it, please do.
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Sweet-WRX-Lovin wrote:
They negate each other. The only force left acting on the plane is the thrust of the engines. This is the only force left (magically of course). Since it is the only force left, the plane moves forward and takes off.
For the plane to move forword, the wheels must move forword, which means the tradmill moves the other way.Unless u can kill my theory.
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Phats wrote:
So, Dubbsy
Explain too me why the foreword thrust wouldn't move the tires more.Plane has thrust on it's body, pushing the plane a 50mph, the wheels, attached to the plane, spin at 50. The "Treadmill" spins at 50.
The plane has thrust pusing it's body too 100mph, that means the plane needs too acelerate, forewords, because we need too go forwords to generate lift, we all know that.
so, if the plane goes forword, the wheels turn forword, the Treadmill matches the wheels.Which means it matches the plane.
Which means that it doesn't matter what speed the Jets are pushing the plane, the wheels are going that fast too, and as long as they are, the treadmill is matching.
I understand what u are saying, but, it's not possible too me.
If u can explain it, please do.
that is what i was thinking, but that is in a perfect world.
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I just thought of an explanation/analogy, let me know what you guys think of it.
Reading a couple of the posts here, people like to try to think of this in terms of a treadmill, so we will use that.
Imagine standing on a treadmill wearing a pair of rollerblades. Now, someone is standing behind you (off of the treadmill). Turn the treadmill on, and have the person behind you push you forward. Do you start moving forward in relation to the ground? Hopefully, the answer is yes.
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Phats wrote:
For the plane to move forword, the wheels must move forword, which means the tradmill moves the other way.Unless u can kill my theory.
With the assumptions I am making about the wheels of the plane and everything else the conveyor could be actually moving in the direction the plane wants to go or the opposite as in this case at ludicrous speed (or infinite velocity) and the plane would still not move. A body at rest will stay at rest, unless it is acted upon by a force. In my magic frictionless scenario the only force on the plane is its own thrust and I guess of course aerodynamic resistance as it accelerates which is needed to fly.
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Ok, time to put this to rest
Think about it this way if you are driving a motorcycle with a side car on it at 50MPH and the conveyor is ONLY on the side car you can still drive the motorcycle at 50MPH, however the sidecars wheel(s) will be traveling 100MPH. Same principal applies here. The planes motors providing thrust would be the motorcycle in above analogy and the planes wheels would be the side car. It is very possible for the plane to take off.
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I think I know why Kirkeide quit.
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Phats wrote:
So, Dubbsy
Explain too me why the foreword thrust wouldn't move the tires more.Plane has thrust on it's body, pushing the plane a 50mph, the wheels, attached to the plane, spin at 50. The "Treadmill" spins at 50.
The plane has thrust pusing it's body too 100mph, that means the plane needs too acelerate, forewords, because we need too go forwords to generate lift, we all know that.
so, if the plane goes forword, the wheels turn forword, the Treadmill matches the wheels.Which means it matches the plane.
Which means that it doesn't matter what speed the Jets are pushing the plane, the wheels are going that fast too, and as long as they are, the treadmill is matching.
I understand what u are saying, but, it's not possible too me.
If u can explain it, please do.
You're looking at it wrong...
I think there's a very big thing here that everyone is totally looking past, but I can't figure out how to explain it so people will understand it...Imagine that the wheel bearings are 100% efficient and produce no friction. The plane would stay in the very same spot no matter what direction the conveyor moved...forward or back. Now the actual efficiency of the bearing isn't that bad so they are free to roll as they wish, however they will drag the plan with them a bit... BUT, it's not enough to keep the plane in one spot.
look at chucks analogy because it just about perfectly describes this..
if the motorcycle has a speed of 50mph, the conveyor is spinning 50mph the opposite direction. The wheel on the side car however is spinning at the combined speeds of the conveyor and the motorcycle...
Now to bring friction into this.. the motorcycle will have to work a bit harder to reach 50mph than if they were on a static surface because they have to fight the little bit of friction in the side-car wheel (although, I did read that the friction in the wheel bearing doesn't change from 50 to 100mph (or any other speed), so this may not be applicable).now throw that over to the plane. The Jet engines are the motorcycle.. The motorcycle pushes the side-car, the jets push the plane. The motorcycle force is acting on static ground while the jets are acting on the static air above the conveyor.
The only time that thrust is applied AND the speed of the plane is zero is when the brakes are applied. **It defies the limits of the question **to say that the conveyor is moving and the plane is staying in one spot, because if the plane is sitting in one spot then it's speed is zero. The question says the conveyor matches the plane's speed, so therefore the conveyor would not move. If neither are moving, then what's holding the plane in one spot with thrust applied? brakes?
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I win.
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Sweet-WRX-Lovin wrote:
I think I know why Kirkeide quit.No, I think she actually liked me Schulzy. The school board on the other hand.......:rolleyes:
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I in no way meant you. Too bad they couldn't work something out, she was the best.
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