A plane on a runway, how smart is r3vlimited?

[erik325i]

A jet will NOT push a plane through the air (meaning flying) unless the plane has reached a sufficient speed relative to the air around it.

I don't think you understand how a jet engine works... A jet engine will push the airplane forward through the air (just like a missile). It has nothing to do with the ground. The wheels are only there to allow the plane to roll freely.

-Erik

[Justin B]

Dude, you're cracking me up here. Ok I'll read your posts before I post, but I must say now that you are not referencing belt or plane speed properly when your measuring it relative to the ground. I keep telling you guys the speed must be measured from within the system (belt and wheels). Ok let's say for the sake of argument that you reference speed from a fixed position outside of the moving system and that measured speed is the speed the belt has to move in the opposite direction. Here's what happens:
1) The plane is sitting still on the belt.
2) Pilot in plane turns on jets to position 1(assume he can incrament the force the engine provides)
3) Plane creeps forward to 1 mph (relative to fixed position off the belt)
4) Belt matches the 1mph speed measured from fixed position (because you all say the belt reacts only to the speed of the plane relative to fixed position)
5) Plane starts slowing down (relative to fixed position) because the belt is now moving in opposite direction, so plane is now moving at less than 1 mph (but probably still moving forward due to initial speed before belt kicks in)
6) Since the plane is now moving slower than 1mph, the belt (which is basing its speed on the plane speed from a fixed position) must slow down to say .5 mph (to match the planes percieved reduction in speed).
7) Now the plane begins moving forward faster (say 1mph) because the belt has slowed down (jets still in position 1)
8 ) Now the belt speeds up because the plane has sped up relative to some fixed position.
9 The plane slows down again.......and the process repeats itself
In this scenario the plane is always moving forward and never sits at 0mph relative to fixed position. The plane doesnt reach the speed necessary to lift off. Now what if you did the same thing but put the jet control to position max? Well, lets see:

1) The plane is sitting still on the belt.
2) Pilot in plane turns on jets quickly toward Max position
3) Plane jumps forward to 50mph (relative to fixed position off the belt, assume a time lag for the belt to start)
4) Belt matches the 50mph speed measured from fixed position (because you all say the belt reacts only to the speed of the plane relative to fixed position)
5) Plane continues to accelerate but much slower because as the plane accelerates, the belt accelerates(relative to fixed position)
6) The question here is how fast does the plane continue to accelerate before max thrust is reached? The belt is also accelerating in parallel with the plane. It's difficult to say how much the plane would continue accelerating, my guess is that it would not reach the speed necessary to take off before the runway ended (so it depends on how long the runway is)
Now this scenario assumes you're measuring all speed relative to some fixed point outside of the system. My scenario measures plane speed from within the system, so the plane never even accelerates forward relative to a fixed position because the belt is moving with respect to wheel speed.

Ok now I'll read your other posts. ;-)

You are thinking waaaay too much.

The the plane doesnt always speed up and slow down to match with the belt, the belt just matches with the plane. If we're going to add in wheel resistance, the plane will be trying to go 10mph but it will actually be creeping at 5mph while the belt is going backwards 5mph, dragging the wheels back. That was your whole idea from the beginning.

I'm glad I'm cracking you up but you're one of the last people who have no clue what the hell they are talking about. Seriously, what the hell man? I can agree with you to an extent, because the plane is moving, as compared to the belt, but it is not moving at all compared to anything else. Its the belt, its not real movement, its moving in place, just like you "run in place" on a treadmill. There's two different speeds for the plane, and the important one here, is the airspeed which will actually change because there really is no drag in the question so all of this arguing is for nothing. You're right about one thing, the plane is trying to move, and IS MOVING as far as the belt is concerned, but in reality the airspeed is 0. Why the hell are we even bothering with that anyway? Lets go back to 0 drag, The plane can be going 10mph without any problem, and the belt can go backwards at 10mph without any problem, smooth as butter. Problem solved, just up the speed, wheels do twice the work.

Get on a treadmill, and run, you're running at a certain speed, I'll give you that. You're not GOING anywhere relative to the ground, and neither is the plane when its just chilling on top of the belt quite literally spinning its wheels. There are two ways that can happen, there is 0 resistance and the belt is just spinning when the plane isn't even TRYING to move, which is outside the boundaries of the solution, or, it has incredible resistance and the belt moves fast enough to keep the wheels from moving forward at all from the thrust of the jet. That of course still is out of the scope of the solution. You know why? Because if that was the case, they could, just like you said before, run the conveyor belt up to infinity mph and the wheels will blow out, and the whole thing will vaporize on impact of the belt. Ok, it will hold it in place. Great. Thats not the whole idea though, thats what the queston wants you to believe. There are two ways to interpret the problem, and one you see, and the other is what they feel is the solution because they plan that most people will see it the way you are. However with little or no drag which wheels usually have, it will be easy for the plane to move forward on the belt. That is the most simple answer, and once again they did not mention drag, so your little idea about keeping the plane in place by spinning the belt so damn fast the plane will "think" its going that fast by its wheels and only partial thrust because any more would actually make it go forward. Wheels don't have THAT much resistance no matter what they are and it would have to work with all planes including model planes that have such little weight on the wheels to begin with they would just lose traction over the belt and move forward anyway. Unless the conveyor belt and wheels were mechanically attatched to each other, like somehow its all gear driven with chains and whatnot holding the wheels against the chain with 100% grip, there is no way that at full thrust an airplane will not skid or hop forward on a flat conveyor belt. Your anti solution that I suppose I can call it because you're claiming its wrong, entirely over complicates things, and is beyond the scope of the question. If there was drag, I'll reiterate what I just said, the wheels will skip over the belt unless its a mechanical attachment.

Can we pleease stop arguing over semantics? The belt is not a chain with gears and cams to hold the plane down against it, there will be some movement forward, then that should be the speed that the belt is moving. ooohhh waaaait. If you say its a perfect world, and that the wheels will stay attached to the belt no matter what sort of drag they're producing or how much grip they have or what thrust the airplane has, then you can throw that all out the window anyway because in a perfect world there isn't drag either.

You are over complicateing the problem,and thats the end of it man. The problem as stated, is exaxctly what I explained. The speed of the plane is not relative to the belt at all.

[chucko]

The belt moves, and by your logic, if the wheels spin under the plane, the plane is technically moving too. It is not. The plane is stationary in space. Debunked.

Wrong. If the plane is not moving (meaning 0mph) then the belt should also be at 0mph right? because the belt is matched to the plane speed. Obviously the belt is not at 0mph in this example. That's why I'm telling you you can't reference the belt speed to a fixed position outside of the system.

Now, it IS possible, and all of us have agreed on this at one point or another I believe, for the plane to use its thrust to overcome the resistance of the wheels and roll forward on the belt in relation to the ground beside it.

I would agree with you on this point.

Mine, and everybody else that knows whats going on :P
Conveyor belt 10mph
Wheels 20mph (plane's thrust thinks its going 20mph)
Plane as a whole in space is only 10mph.
The plane is going at the same speed as the belt. Problem solved.

No, you are totally neglecting the control system which has to be keyed to something right? What is it keyed to in your scenario? If the planes thrust thinks it's going 20mph, then shouldn't the belt's control system be telling it to also go 20mph? Or (as I've said before) if the wheels are moving at 20mph, then shouldn't the control system be telling the belt to go 20mph? Why not?

[Justin B]

First quote - no, thats not the point, the only speed that is important to a plane is the speed of it moving forward through the air. I already agreed with you that it is moving as compared to the belt, but it moves through the air to get airspeed and that is what moves the belt.


Second quote -
You agree with me that the plane can move forward on the belt, while the belt moves backwards too. A point under the jet on the belt, and the jet itself, moving away from the starting point?

Hey, we have a solution that can work, then of course if you want to use your solution about somehow the jet not moving at all THROUGH the air (which is impossible because any thrust will move it forward with such low resistance in the wheels) you can call it right too, but its not the answer the question is actually looking for.

Quote 3 -
WHAT THE FUCK MAN. STOP POSTING. (For your peace of mind, I'm not mad, im just incredibly annoyed that you fail to pay attention to detail, thats you biggest problem, obviously) You really dont pay attention to any of my posts now do you, 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(or whatever it sees...) 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.

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.

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 dont mind all these posts, I'll be to 1k real fast. Especially if I stop editing all my latest posts to add in useless drivle like this, and posting new ones instead, but thats a waste. So is this.

[joshh]

I'm annoyed this thread is still going. It wont change how I eat this Snickers bar.

[Justin B]

Thank you for your contribution joshh, it truly makes a difference in the outcome of this thread. At least it really is more interesting than what chucko is posting.

I'll give you a gold star :)

yay, round of applause. Seriously it made me lol.

This IS my 50th post here. Damn. What a waste, but its interesting.

[erik325i]

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?


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.

Yes, if the belt is exactly opposite to the speed of the wheels the rocket will go nowhere.

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.

[E30 Wagen]

1) The plane is sitting still on the belt.
2) Pilot in plane turns on jets to position 1(assume he can incrament the force the engine provides)
3) Plane creeps forward to 1 mph (relative to fixed position off the belt)
4) Belt matches the 1mph speed measured from fixed position (because you all say the belt reacts only to the speed of the plane relative to fixed position)
5) Plane starts slowing down (relative to fixed position) because the belt is now moving in opposite direction, so plane is now moving at less than 1 mph (but probably still moving forward due to initial speed before belt kicks in)
6) Since the plane is now moving slower than 1mph, the belt (which is basing its speed on the plane speed from a fixed position) must slow down to say .5 mph (to match the planes percieved reduction in speed).
7) Now the plane begins moving forward faster (say 1mph) because the belt has slowed down (jets still in position 1)
8 ) Now the belt speeds up because the plane has sped up relative to some fixed position.
9 The plane slows down again.......and the process repeats itself
In this scenario the plane is always moving forward and never sits at 0mph relative to fixed position. The plane doesnt reach the speed necessary to lift off. Now what if you did the same thing but put the jet control to position max? Well, lets see:

1) The plane is sitting still on the belt.
2) Pilot in plane turns on jets quickly toward Max position
3) Plane jumps forward to 50mph (relative to fixed position off the belt, assume a time lag for the belt to start)
4) Belt matches the 50mph speed measured from fixed position (because you all say the belt reacts only to the speed of the plane relative to fixed position)
5) Plane continues to accelerate but much slower because as the plane accelerates, the belt accelerates(relative to fixed position)
6) The question here is how fast does the plane continue to accelerate before max thrust is reached? The belt is also accelerating in parallel with the plane. It's difficult to say how much the plane would continue accelerating, my guess is that it would not reach the speed necessary to take off before the runway ended (so it depends on how long the runway is)
Now this scenario assumes you're measuring all speed relative to some fixed point outside of the system. My scenario measures plane speed from within the system, so the plane never even accelerates forward relative to a fixed position because the belt is moving with respect to wheel speed.

Ok now I'll read your other posts. ;-)

Now, I'm no physics major, so I don't know if the coefficient of friction is a constant or a variable here, but I think it's probably irrelevent. I don't understand why you are ignoring how it plays into the scenario. The plane will not slow down just because the belt is moving in the opposite direction.

To prove that the plane can and will move:
1)Plane and belt are stationary. Plane throttles up the engine.
2)The plane starts moving forward. At the first second that the plane begins to move even 1", the belt moves in the opposite direction 1" for that one second.
3)Despite the belt's exact counter movement of 1"/second, the plane's wheels will merely spin 2" on the belt as the plane's engine will gladly continue to propel it forward. Because of the friction of the wheel bearings being spun by the belt, let's say that the plan may be hindered .01" (much less i'm sure), but yet in that one second the plane has indeed advanced forward .99" and wheels actually spun a mere total of 1.99".
4)The plane immediately shuts off its engines to cancel acceleration. The plane is again stationary, and so is the belt. Relative to our beginning position, we know the plane has advanced .99" in one second and the wheels spun a total of 1.99".

For every continuous increment that the plane moves forward, the belt can only attempt to counter it when all it is doing is spinning the wheels. Using some new numbers: If the plane advances 5ft/second, the belt will at the exact same time match this velocity yet the plane will still move forward even though extra friction generated by the belt may only allow it to move 4.9"/second, not forgetting that the wheels will have only spun 9.99". As the engines continue to propel the plane forward at higher velocities, the belt can match those velocities but the plane will not slow down BECAUSE THE WHEELS WILL SPIN. All the belt serves to do is to spin the wheels faster than normal to increases the friction and drag of the wheels, which in turn forces the jet engines to work harder to overcome it. I am sure, though, that by today's aircraft construction standards, that the extra effort needed to overcome this increase in friction is next to nothing and the jet engines will readily pull the plane through the air and into the sky.

edit: I think maybe what's confusing people is that the plane and belt are continuously matching their speeds. However, this has no effect on the movement of the plane because the wheels will merely spin. It's that simple.

edit #2

My scenario measures plane speed from within the system, so the plane never even accelerates forward relative to a fixed position because the belt is moving with respect to wheel speed.

The belt is not moving in respect to wheel speed. THERE IS NO WHEEL SPEED, ONLY THE SPEED OF THE ACTUAL PLANE.

[joshh]

Thanks but I really just wanted a cookie....;)

I see both sides I just don't know what would happen either way.

One thing to keep in mind...the missile has WAY more thrust force per pound than the plane does. I can't fing believe I just added (seriously) to this thread.

[Justin B]

A jet will NOT push a plane through the air (meaning flying) unless the plane has reached a sufficient speed relative to the air around it.

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! 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.

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.

Edit - hahahha okay, I see there's posts above me, I'll just know that theres stuff to catch up on above this post when I get back, but awesome pic Erik, I'll actually read all that and pay attention (woah) tomorrow.

[erik325i]

One thing to keep in mind...the missile has WAY more thrust force per pound than the plane does.

That has absolutely nothing to do with the fact that the conveyor belt will not keep it from moving.

You can point out a lot of differences between the plane and missile such as size, weight, color, manufacture, material, sexual orientation...
None of which has anything to do with the fact that the conveyor belt is not going to stop the plane/missile from moving.

[ptownTSI]

The plane takes off, the only resistance it has to overcome is the bearings on the wheels which are going to be spinning against the planes wheel bearing mounts, but that is it. A plane is not propelled through the wheels, but by a jet engine.

[joshh]

Whether you believe it or not I believe it does make a difference in this example.

[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.

[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.