A plane on a runway, how smart is r3vlimited?

[benDASHDASH]

what if you take a sailboat, then put a huge fan on the boat and aim it at the sail... then turn it on.... will it move the boat?

i think even the "smarties" can agree with me on this one. no.

[benDASHDASH]

Ben, it will not.

ya huh!

[dirty30]

now take that same fan and mount it on a dock and aim it at the sail.....

[benDASHDASH]

Justin, would a car move forward?

[Justin B]

<Merlin> Do you remenber the pic of the kid with down syndrom running that people were using in there arguments
<kfunk> some people get locked into a dumb answer, and refuse to change their mind, or else theyd be admitting they're a fool
<Justin> yeah I do sam
<Merlin> Kfunk you hit it on the head
<Merlin> thats what your fighting J
<Justin> rofl
<Justin> i am going to post that in the thread
<Justin> thank you

[benDASHDASH]

im still waiting for you to prove me wrong :)

[Justin B]

Oh Ben, lol :)

First of all the plane is not powered like a car, it does not get the drive from its wheels, it gets it from a jet engine creating force through the air not through contact with the ground. The jets will push it through the air.

Here's how it will work really easy like, we'll assume there is no resistance at all on the wheels, even though there is, it is negligible and will not cause the plane to stay stationary.

We'll separate the accelerations of the plane and the roller underneath to make it really simple.

1) Conveyor belt starts turning backwards at 100mph, since the plane has no drag on the wheels it stays stationary. The planes wheels however, are spinning at 100mph to keep the plane stationary. As far as they are concerned, the plane is traveling at 100mph.

2) Plane accelerates to 100mph instantly (for sake of the example), now, the plane is going fast enough to lift off, and the wheels are now going at 200mph to keep up with the plane, and the belt spinning backwards. Really though as far as airflow over the wings though is concerned, and in reality, the plane is only traveling 100mph.

Now, the questions requirements are satisfied, the conveyor belt is going as fast as the plane is, and the plane may lift off.

If you want to get technical and throw in wheel drag in there, take two examples-

1) The plane on a normal runway will have a certain amount of drag from its wheel to reach and maintain 100mph. Great.

2) The plane on the conveyor belt will need to use a little bit more thrust, andwill need to accelerate for a slightly longer period of time to reach 100mph ground speed. Ground speed, meaning speed of things to the side of the belt, the rest of the world. The wheels are spinning at 200mph, its a miniscule amount of extra drag, but its there, but possible to overcome.



I'm going to dinner. I'll be right back :) At least I am getting in a lot of typing.

[benDASHDASH]

see, you're missing one important detail: gravity. the plane will be glued to the ground. if the plane is going 100 mph forwards, the belt will be spinning 100 mph backwards. because they will always go the same pace, they will be canceled out, thus creating a net movement of 0. i dont know where you got yout 200 mph number from. sure, the plane's wheels can roll at 200 mph, but the belt will be going just as fast. doesnt matter what kind of vehicle it is for that matter. the "plane" part is a distraction. its still being held to the belt by gravity, no jet is going to change that.

[benDASHDASH]

im winning votes, better come up with better propaganda :-p

[DarkWing6]

I agree with Ben. It's not that the plane is driven by the wheels, it could be Jordan's car driven by a jet engine for all I care. The plane needs to move along the ground to create this force under the wings. If the belt is moving the opposite direction the same speed as the wheels (or the plane, same thing) it will not create this force. The jet engines propel the plane across the ground just like our cars are moved by our engines, drive line, etc. The wheels are relevant unless the plane takes off early and flys really low before actual "take off", which is not what this thread is even about.



Think about it this way. Put wings on your car and drive it really fast. It will take off if you were able to go fast enough. Once off the ground you would be screwed, but for the actual take off it would work. The jet engines or whatever is making the plane go are irrelevant. It is the force created under the wings.

[RobertK]

That GIF is wrong. The conveyer doesn't apply any force on the plane directly, just through the wheels, which can be assumed as frictionless.

WTF.. There is no such thing as frictionless wheels. Is this question based on reality or science fiction?

[benDASHDASH]

WTF.. There is no such thing as frictionless wheels. Is this question based on reality or science fiction?

science fiction. last i checked, theres no such thing as conveyor belts for airplanes that detect and instantly mirror wheel the wheel speed

[chucko]

The plane will NOT take off if it is facing opposite the direction the conveyor belt is moving. The plane WILL take off if it is facing the direction the conveyor belt is moving.

Assuming the plane is facing opposite the direction of the conveyor belt, and assuming the conveyor belt is capable of moving at an infinite speed, the wheels of the plane will NEVER move the plane forward relative to some initial position (inertial frame). The only way a plane can take off is with forward momentum relative to a fixed position and atmosphere (air). Remember, a plane needs no jets to take off, just needs to be moving faster than the air around it. Conveyor belt moves at an infinite speed to the left, the wheels of the plane move at an infinite speed to the right. The air around the plane does not move so the plane does not take off (jets have no impact on this problem).

That is the answer to your question folks!

[benDASHDASH]

The plane will NOT take off if it is facing opposite the direction the conveyor belt is moving. The plane WILL take off if it is facing the direction the conveyor belt is moving.

Assuming the plane is facing opposite the direction of the conveyor belt, and assuming the conveyor belt is capable of moving at an infinite speed, the wheels of the plane will NEVER move the plane forward relative to some initial position (inertial frame). The only way a plane can take off is with forward momentum relative to a fixed position and atmosphere (air). Remember, a plane needs no jets to take off, just needs to be moving faster than the air around it. Conveyor belt moves at an infinite speed to the left, the wheels of the plane move at an infinite speed to the right. The air around the plane does not move so the plane does not take off (jets have no impact on this problem).

That is the answer to your question folks!

be sure to vote :pimp:

[RobertK]

Ritalinkid -

Your diagrams show the conveyor belt cancelling out all of the thrust of the airplane by matching the resistance of the wheels at a certain speed.

Yes but I think you missed my point. What I'm trying to say is that in order to solve this problem the amount of thrust required to increase the speed of the plane on the conveyer must first be determined by the amount of power needed to overcome friction & drag created by the wheels.

The question clearly states that the conveyor belt is matching the speed of the plane. If the plane is stopped relative to the surrounding ground, the conveyor belt should not be moving either. I see where you're coming from but its wrong. The conveyor belt in your diagram should be moving at half its speed so that the forward motion and the belt are both moving at the same rate, and the same rate of acceleration etc.

Again.. not the point I'm trying to make to begin with.

The point is that on a normal runway, lets say for the plane to fly it needs to get up to a certian speed we'll call S, and to do that, it will need the thrust T to over come not only the rolling resistance of the wheels, but the airflow and drag over the whole plane. Now, move it onto our special runway with a moving track, all it needs is a radar gun on one side attatched to a speed control for the track to roll only at the speed the plane is actually moving forward. That is the question. Will it fly? Yes, of course, to get up to S, it will need a little more than T, but less than 2T as it wont be pushing twice the air, just overcoming the slight bit of more rolling resistance from the runway at twice the speed the plane is actually traveling through the air/ surrounding ground.

That's what I've been thinking but I cannot prove it without the correct coefficients needed to calculate the thrust needed to overcome the friction at the wheels.

The plane will take flight, but using your model of the rolling resistance, which really isnt included in the question, all it needs is a little more thrust to overcome the wheels spinning underneath, which should be entirely doable. The worst that could happen would be that the runway would have to be a little bit longer for the plane to get up to speed.

Ok.. now everyone listen the fuck up.. are we arguing theory or real world probability?

Because in theory it's easy you find the amount of thrust needed to obtain take off speed and overcome the drag created by the wheels and the fucker still flys.

In reality there is a high probability that the plane's wheels will malfunction before take off but I cannot prove it without calculating the proper coefficients into the equation.

If Mythbusters were to take this on my money would be that the plane's tires either blow out or the wheel bearing fry before thrust overtakes wheels friction for take off.