Plane on a conveyor belt
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TsiTom wrote:
Planes dont take off based on how fast the wheels are spinning...how is it going to move at all with a conveyor matching its speed? It will just sit in one spot with the wheels spinning out of control....psst...
if the plane is sitting in one spot, the conveyor wont' be moving either..
this is something you need to think about.
Car speed is refering to wheel speed. If a car was on the same conveyor then yes, it would sit in the same place as the car's wheels would be moving 50mph in one direction and the conveyor 50mph in the other.however plane speed is measured as airspeed - speed relative to the air (or static spot on the ground). So for a plane to be moving 50mph it HAS TO BE MOVING in relative space. The plane's wheels could be moving 100mph, but if the plane has no air speed, the plane's speed is flat out ZERO (and it's sitting in one spot).
However, like people have said.. thrust acts on the air around the plane which is not moving...therefore the thrust will act just as it would if the plane was not on a conveyor...
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T ! N wrote:
NO, the plane will not take off. Like Nick said, in order for an airplane to lift off, air is required under the wings. The wheels are spinning, but the plane isn't moving=no air under the wings.but it will move! hands down, no doubt about it, it will move..
now yes there may be a very small range at low speed where the thrust of the engines is not enough to overcome the friction in the wheels.. HOWEVER, even so the airspeed of the plane would be zero, therefore the conveyor would not be moving either...
Essentially you're throwing out an impossible situation here... (short of holding the brakes).
People are say that even though there is thrust, the plane sits in the same spot because the conveyor is moving in the opposite direction. WRONG. if the plane is sitting in the same spot it's speed is ZERO. therefore the conveyor speed would be zero..
well if the conveyor speed is zero the plane is going to move.... -
The plane will take off. The conveyor will keep matching the wheels speed but the plane itself will continue to move forward in space due to it's propulsion being independent of the restrictions imposed by the conveyor.
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Dubbsy, you weren't supposed to post in this thread! Since people have begun linking to other threads already, I'll throw in my link (scotwithonet actually described the situation a lot better than people on other boards):
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Sweet-WRX-Lovin wrote:
The plane will take off. The conveyor will keep matching the wheels speed but the plane itself will continue to move forward in space due to it's propulsion being independent of the restrictions imposed by the conveyor.actuall that is partiall incorrect..
the conveyor will not match the wheel speed.. the wheel speed is the combined speed of the conveyor and the plane.
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Here is another interesting link:
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The plane will take off because the wheels are entirely independent from the plane's engines. The engines on the plane create thrust=displacement of air. The engines draw air under the wings more quickly then they pull air over the tops (der thats a given) so if the plane's engines can generate enough lift, even though the wheels are spinning a bajillion miles an hour, it will take off. The plane doesnt have to physcially move to take off, it just has to move enough air under its wings. Think about the reasons cars have diffusers under them. If the car is moving too fast (AIR IS MOVING TOO QUICKLY NOT THE ACTUAL CAR) it will generate lift and lose control.
-mitch
edit/ I just realized that is pretty much what sweetwrxlovin just said
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OK, so I went to the mythbusters site and was going to post this as an idea and come to find it's already on there in the discussion forum. It seems there is a video out there that proves that the plane WILL take off. So, if any of you are up to the task of finding it you're welcome to it, it's too late for me to search now but I might get a notion to tomorrow.
Sterling Archer: Oh my god! You killed a hooker!
Cyril Figgis: Call girl!
Sterling Archer: No Cyril! When they're dead they're just hookers!
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Ashli19 wrote:
The plane will take off because the wheels are entirely independent from the plane's engines. The engines on the plane create thrust=displacement of air. The engines draw air under the wings more quickly then they pull air over the tops (der thats a given) so if the plane's engines can generate enough lift, even though the wheels are spinning a bajillion miles an hour, it will take off. The plane doesnt have to physcially move to take off, it just has to move enough air under its wings. Think about the reasons cars have diffusers under them. If the car is moving too fast (AIR IS MOVING TOO QUICKLY NOT THE ACTUAL CAR) it will generate lift and lose control.-mitch
Mitch, if I"m reading this right...everything about it is wrong...
#1. Air travels faster over the tops of wings.. This creates a low pressure that in turns sucks the wing up (bring the plane up with it)
#2. The plane DOES have to physically move. The engines do not move enough air around the plane to create lift. ...but no matter what, when thrust is applied, the plane will move in relative space and the plane will take off just like there was no conveyor there in the first place.
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maybe im just physics retarded (never did take the class) but i still dont see how the plane can take off. since the plane needs air to flow over its wings to take off - and since the conveyor exactly matches the plane speed (to me, meaning the plane doesnt move forward at all) - it cant take off.
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dubbsy wrote:
actuall that is partiall incorrect..the conveyor will not match the wheel speed.. the wheel speed is the combined speed of the conveyor and the plane.
Right. It can't as the plane accelerates. Just tried the simple answer.
Amicheze, the planes way of moving forward, thrust from the engines, is totally independent and free from the coveyor moving and the wheels. The wheels end up acting like bearings (which they are I guess) and the more the conveyor trys to hold the plane in one place while it moves forward, the faster the wheels will spin and that's it. The plane itself will just continue to accelerate forward while the wheels and coveyor just keep spinning faster and faster.
In other words the conveyor and wheels don't exist and it's just the thrust of the engines moving the plane forward.
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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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