A plane on a runway, how smart is r3vlimited?

[tonytony]

HOLY shit this page has jumped 4 pages in 20minutes~~!!!!

[sticksdaman]

name calling isnt necessary

first off this is a theoretical problem theres no point in trying to relate it to real world conditions seeing how there is no possible means for us to instantly match the speed of the conveyor to the object ontop of it ... that being said if what your saying is true then the conveyor belt would have to be the length of a runway or longer in order for the plane to build enough speed relative to the ground below it to create lift

[e304me]

hahahaha this thread is funny. the plane will take off end of story. pretend the propeller thrust is a rope towing it through the air. no matter how fast the ground underneath it is moving the plane will always be going as fast as the rope is towing it

[erik325i]

Ok, a couple of things here.
2) I've said before that this is a fictional scenario and optimal conditions are assumed. Meaning max belt speed is infinity and max wheel speed is infinity. Wheel bearing friction is neglected.

I agree 100% with you here. Obviously this is a hypothetical situation, because there no real conveyor belt runway. Therefore I completely agree with you that max wheel speed is infinite, max belt speed is infinite, and most importantly, wheel bearing friction is neglected. I'm glad we both agree with that.

In your scenario the wheels on the missile have to be moving faster than the conveyor belt, and I'm saying you cant go faster than my conveyor belt. So if that's the case the wheels really have to be off of the belt for the thing to move.

Of course the wheels on the missile are moving faster than the conveyor belt. That is how you prove that the missile is accually moving forward (relative to the air).
According to the original question, the wheels NO NOT have to go the same speed as the conveyor belt. The plane has to go the same speed as the conveyor belt. If someone were to stand next to the conveyor belt, with a radar gun measuring the speed of the plane, that is how the speed is measured. Not by the wheel speed. The wheels are just free spinning and can do whatever they want. They are not a correct form of measurement of the accuall plane speed.

Two things are necessary for flight, sufficient thrust and lift. Your example is neglecting the lift portion, which is why I said the missile won't fly through the air. Obviously the jet engine will push an object through the air, just like my feet will push my body through the air, doesn't mean I'm flying.

The reason my example didn't involve lift is because the first thing I established in my example is that we can all agree that if the plane moves fast enough through the air, it will create enough lift to take off.
This is the one fact that nobody is arguing with.
My point then was to prove that the plane will be able to provide the thrust needed to take off.

Obviously the jet engine will push an object through the air.

So, now you are agreeing with the basis of my argument. Simply put, a jet engine will push an object though the air. I'm glad that you see the light. The engines will continue to push the plane though the air until it has enough lift to take off.


So, now I think you should get it now. I explained everything I could as clearly as possible. I answered all of your doubts.
If still don't think the plane will take off, please re-read everything that I just posted in this post.

-Erik

i just read EVERYTHING... and i still think it wont fly ...if the machine matches the plane speed instantaneously and the wheels are connected to the plane then no matter how much the plane thrusts the conveyor cancels it out so there is no forward motion and no lift and no lift equals no flight

Did you not read anything that I posted?!

[ptownTSI]

you are fucking stupid.

put a skateboard on a treadmill, put the speed to 2 mph, can you hold the skateboard in a stationary position with the wheels rolling backward?

yes.

put the speed to 5mph

can you still hold it?

yes

What I have just demonstrated is equivalent to the jet engine overcoming the friction of the wheels, you hand is acting like the jet engine.

Now push the skateboard forward, does the skateboard not move forward even with the wheels spinning backwards?

yes it does.

your hand is no different than a jet engine.

you could put the treadmill to 1000mph and your hand would still be able to push it forward, just like the jet engine. It could still easily get up to speed and take off.

Actually, what I said in my post that you're quoting is 100% factual. I specifically said FLYING, and an airplane can't fly until it is moving much faster than the air around it. Lift is created when moving air is pushing against the underside of the wing.


Read my post again, I said that a jet will not push a plane through the air (MEANING FLYING), in other words, a jet will not cause a plane to fly through the air unless the plane has reached a sufficient speed relative to the air around it. I must be speaking greek or something.


If you think my posts are stupid then you certainly don't need to respond to them. You're taking this thing way too personally. Honestly I could just as easily argue that the plane would take off. There is no right answer to this problem because the problem is too ambiguous. I still think your logic is flawed though.

Lift is created by the pressure of the air above the wing being less than the air pressure under a wing. This is why the shape of a wing has a flat bottom and a curved top. The air moving over the top of wing must move faster than the air under it it. I know it seems to defy common sense, but because the air is moving faster, this relieves the pressure above the wing allowing it to rise. Our whole argument is that it's plainly obvious that the jet engines can and will get the plane up to take off speed despite the fact that there is a belt trying to fight against it.

Your argument that it's possible for the plane to not take off is terribly weak and that's what you simply refuse to understand.

[sticksdaman]

i just read EVERYTHING... and i still think it wont fly ...if the machine matches the plane speed instantaneously and the wheels are connected to the plane then no matter how much the plane thrusts the conveyor cancels it out so there is no forward motion and no lift and no lift equals no flight

[chucko]

HOly fucking shit batman. I was coming back to edit the post to say I'm going to bed but you're way off your rocker. Get back on your meds, or maybe you need to come off them because they're effecting your thought process. Planes MOVE BY PUSHING AIR through their jet engines, pr pulling it through their propellers (same thing really as the jet turbines)! They're not going to get ANY speed relative to the air around them if the jets aren't doing the work!

Actually, what I said in my post that you're quoting is 100% factual. I specifically said FLYING, and an airplane can't fly until it is moving much faster than the air around it. Lift is created when moving air is pushing against the underside of the wing.

You're way too stuck in a rut, in fact I think while trying to get out you caved it in on top of yourself, you cant even see the light out and I feel sorry for you. A jet pushing the plane through the air does not necessarily mean its flying, its the jets job to suck in and push air past the plane to propel it forward.

Read my post again, I said that a jet will not push a plane through the air (MEANING FLYING), in other words, a jet will not cause a plane to fly through the air unless the plane has reached a sufficient speed relative to the air around it. I must be speaking greek or something.

I'm going to bed. Think about how stupid that post was, see if a full day of thought will allow it to register are you sure you're a real engineer? Ive heard of building engineers but thats just a fancy name for janitors. Ill check this after work tomorrow but may just entirely slip your posts.

If you think my posts are stupid then you certainly don't need to respond to them. You're taking this thing way too personally. Honestly I could just as easily argue that the plane would take off. There is no right answer to this problem because the problem is too ambiguous (the problem doesn't even mention a jet). I still think your logic is flawed though.

I feel the need to clarify my above explanation a little further

So, I said the plane has travelled .99" in one second. This means that .99"/second is the new velocity of the plane. If we were to leave the engine and the belt running, the belt counters this by slowing down to that velocity.

Now, the important addition to my clarification is that we can say the plane's JET ENGINES are set to propel the plane at a rate of 1"/second (I know, unrealistic numbers, but please play along because it's important in understanding that the only source of movement a plane has is through those engines which suck in air).

So obviously what happens is that the jet engines are trying to maintain a velocity of 1"/second, but friction is only allowing a velocity of .99"/second. Remember the wheels will simply spin. If we stand at our starting point, we can watch the plane moving moving foward at a rate of .99"/second. The requirements of the problem have all been satisfied because the speed of the plane and the speed of the belt are equal. So, if we throttle the engines up to a much higher constant velocity, lets say 300mph, the plane may still be able to move forward at a constant velocity but the drag of friction may only allow it to reach 299mph. This is why that one physics professor that somebody asked on here said we could not answer the question without information regarding the maximum thrust of the engine and the coefficient of friction. However, I'm confident that with today's technology there are engines with more than enough thrust to overcome such added friction.

This makes this even easier to explain without friction. If there's no friction, then it doesn't even matter if the belt exists. The wheels can spin as fast as they want and they won't create any drag and the plane will take off without any effort.

[erik325i]

Ok, I still didn't get it right...

Is the plane discussed on this topic moving trough the air mass or not?

Everyone talking cross with each other, and question is stated the that I can't realy tell.

Roughly, if the plane is not moving to landscape, it is not moving trought the air mass and lift is not generated.

So tell, if that kind of setup was made, would the plane move compared to landscape.

I'm still thinkin that runner on the stepper, he's not moving forward on landscape, the belt is moving on certain speed, he's running(quite) the same speed and stays stationary to landscape, I can't see why would the example jet be different. I know, I might be totaly wrong, but please tell me the way I can understand it.

Yes, the plane is moving relative to the landscape.

The reason it is different than a runner on a treamdill is because the wheels on the plane are free-spinning. The plane plane is being pushed though the air by the jet engines. The conveyor belt has no effect on the airplane besides making the wheels spin faster than the plane is moving.

-Erik

[Rocla]

And MY O.T. B.S.

Two cars(make them identical) race on the race track.

#1 starts 5 seconds before #2.

Both cars drive identical lap times, on every lap, lets even make that both cars run completely identical way.

On every corner the car #2 catches up a little the car #1, on the begining of each straight car #1 makes a bigger gap to car #2.

That can't be true, can it?

And the reason is not that "car #1 has more power, but #2 has a better driver", as many people tend to say on _ANY_ track event :)

[Rocla]

Ok, I still didn't get it right...

Is the plane discussed on this topic moving trough the air mass or not?

Everyone talking cross with each other, and question is stated the that I can't realy tell.

Roughly, if the plane is not moving to landscape, it is not moving trought the air mass and lift is not generated.

So tell, if that kind of setup was made, would the plane move compared to landscape.

I'm still thinkin that runner on the stepper, he's not moving forward on landscape, the belt is moving on certain speed, he's running(quite) the same speed and stays stationary to landscape, I can't see why would the example jet be different. I know, I might be totaly wrong, but please tell me the way I can understand it.

[chucko]

OK everyone, let's take this one step at a time. Try to stay with me here.

We all know that the plane will fly if it is able to reach a great enough air speed. Nobody is arguing with that.
The part in question is, is the plane able to travel forward though space fast enough to fly, or will it sit stationary on the conveyor belt?

Yes this is where the difference of opinion lies.

1. First of all, you must realize that in this situation, a missile acts the same as an airplane. It is thrust forward though the air just like a jet engine. I am going to be using a missile in the rest of my argument because it is very simple to see how it works...
2. Take a missile and attach a set of wheels on the bottom, so it can roll freely, just like the airplane.
3. Set the missile onto the conveyor belt.
4. Launch the missile in a horizontal direction.
5. Now the conveyor belt is to instantaneously match the speed of the missile (backward of course)
6. Does the missile stay stationary on the conveyor belt, or does it pick up speed and launch out of sight (rolling on the wheels of course)?

If you are saying that the airplane sits stationary on the conveyor belt and does not take off, then you are also saying that the missile will stay stationary on the conveyor belt, because we already decided that the missile and plane are the same in this situation.


I know chucko already told me that the missile will not go anywhere. Here's a picture to demonstrate what chucko believes will happen:


Look at that picture and tell me if you really think that it is possible for a missile/airplane to stay stationary on a conveyor belt if it is being powered by jet engines which push it though the air. The speed of the conveyor belt is not going to keep a missile/airplane from moving forward.

Ok, a couple of things here. 1) Is the guy in that picture supposed to be me? cause I'm not that skinny ;-). 2) I've said before that this is a fictional scenario and optimal conditions are assumed. Meaning max belt speed is infinity and max wheel speed is infinity. Wheel bearing friction is neglected. In your scenario the wheels on the missile have to be moving faster than the conveyor belt, and I'm saying you cant go faster than my conveyor belt. So if that's the case the wheels really have to be off of the belt for the thing to move. Yes this can happen if the frictional forces holding the object onto the belt are overcome by the thrust of the engine (if the missile is massive enough relative to the engine size, the thrust may not be enough to overcome the frictional forces keeping the wheels planted on the belt). I've already said that in earlier posts. Two things are necessary for flight, sufficient thrust and lift. Your example is neglecting the lift portion, which is why I said the missile won't fly through the air. Obviously the jet engine will push an object through the air, just like my feet will push my body through the air, doesn't mean I'm flying.

[chucko]

Quote 3 -
You really dont pay attention to any of my posts now do you.

This is true! Actually I do pay attention to your posts, but we are disagreeing on how this system is operating. That's perfectly ok, because the problem is posed ambiguously enough to require some imagination and does not rely on pure physics.

you already asked me that before. I said, as far as the question is concerned its fucking magical, who gives a shit. If you want a solution, put a radar gun at one end of the runway belt, with magical electronics and all that jazz to make an instantaneous change in speed on the belt. You could even make it so magic that the belt would predict the planes acceleration before the speed of light gets to the radar gun! Can you tell I'm being a little sarcastic? Come on, you say you read my posts, but I call bullshit. I write too much for you to care about.

No you're not understanding what I'm asking you. I'm not asking you to describe in detail how the control system works, I'm asking you to tell me how you are referencing speed. Understand that there are two ways you can reference speed in this problem. Within the system and outside of the system. Speed is used by the control system to determine how fast in needs to activate the belt. If you only reference speed from outside of the system (basically the air speed of the plane) and those are the numbers that get fed into the control system, how in the world could you ever have the belt moving at any mph while the plane is sitting still at 0mph? These two things have to be equal based on what the problem states. Please just think about that before you move on to something else.

If you want the belt to sense the plane from within, you could do that too, just like you have suggestd, just that the belt would only be required to go half the speed of the wheels traveling on it. Airspeed airspeed airspeed, thats what its all about bud. You could say the plane is "going nowhere fast" just like on a treadmill, its going nowhere. I've said it a few times now, the overall net speed of the plane, is 0. Argue that, it wont work.

Justin, I don't know where you keep getting this 1/2 number from, there's no reason at all the belt should be moving 1/2 the wheel speed unless you have very specific knowledge of wheel diameter, thrust and a host of other factors.

If you want to be right, the only way you are is that we both are. I'll let you feel that way, just like youth sports now, because they don't keep score.

I have to laugh man because you are really sure that you have the right answer to this problem aren't you? Let me say this, you have a possible right answer (only two possibilities), but I'm not agreeing with your logic. I do appreciate that you have thought this through and have made this topic fun.