No, the treadmill speed would not stop the plane from moving. Forget about airplanes (this is the way I finally got it):Say we have two treadmills and two people. The first person puts on a pair of sneakers and runs on the treadmill. They stay in one spot. We all understand how the treadmill works. Now the second person puts on a pair of rollerskates, with very well oiled wheels. Then they strap a rocket to their back. Say we know on normal surfaces, that this rocket will make the person on rollerskates go 30mph. So, lets put the person with the skates on the treadmill and get the track moving 30 mph the other way. Now we fire up the rocket...The person will move forward at 30 mph (actually probably a little bit less due to friction, etc, but not by a significant amount). The first person's shoe is working against the treadmill. The treadmill moves back as they move forward. The second person's rocket is not working against the treadmill. If that person on rollerskates with no rocket would hold on to the handle, they would roll in place there. Stop thinking about lift and the wing of the plane. Nobody is arguing that point (this is where you guys lost me earlier).

>> Forget about airplanes (this is the way I finally got it):You know what kerosene31, this whole debate is very frustrating to me. But when I see that at least one person understands, that almost makes it all worth while. So, good for you!

It would help if people tried to explain it helpfully, rather than making personal attacks against someone's intelligence. I said, "the plane needs air over the wings to fly" and I was told "you don't understand how an airplane flies!". It is a perfect example of how the mind makes assumptions, and in problem solving will sometimes not go back and question those assumptions. We assumed that the treadmill would keep the plane stationary, because in all practical experience, that's what a treadmill is used for. Of course, a jet engine or other thrust source would make all the difference. It makes perfect sense after you look at it, but you have to fight the underlying assumption.

>>> Forget about airplanes (this is the way I finally got>it):>>You know what kerosene31, this whole debate is very>frustrating to me. But when I see that at least one person>understands, that almost makes it all worth while. So, good>for you!It seems to me that the debaters fall into several categories. Those who consider the basic physiscs of the problem and gets the solution without getting lost in IAS, ground speed and reference frames.Then there are those that purport to understand physiscs and aircraft concepts, but over-complicates the simple problem and gets lost in the reasoning.Then there are others that treat it as a mere problem of reference frames. This is probably the worst approach, as you have to realize the dynamics of the system to get it, that there is a net force in the forward direction.And of course there are some who haven't even read the original problem and move forward with their own private version of the problem.-

Look at the sketch in one of my earlier posts. That shows the aircraft moving to the left at a speed V and the treadmill moving to the right at a speed V.How is that not in the spirit of with "..this treadmill could match the forward speed of your aircraft exactly, but running in the opposite direction"? Like Oyvind, I'm beginning to wonder why I bother.

>It would help if people tried to explain it helpfully, rather>than making personal attacks against someone's intelligence. >>>I said, "the plane needs air over the wings to fly" and I was>told "you don't understand how an airplane flies!". >Well sometimes having to make the same point for the nth time can lead to some frustration and annoyance. Most of the posters are very convinced and thus more concerned with driving through their own opinion than actually reading opinions of others. I have sometimes been guilty of that myself too. -

It is a visualization problem too (I'm sending this to lots of people I know, and most, like me, get it wrong). When I read the problem, I visualized a treadmill as being just a bit bigger than the airplane itself. I took a person running on a treadmill, made it bigger, and stuck an airplane on there. All I need to do is make the scale bigger, but everything else stays the same. That is the "block" that prevents people from getting it. Everything is not the same, the propulsion method is different. Jet/prop engine vs a human foot. A lot of responses I am getting say, "why didn't you tell me the treadmill was really, really long". Of course, the original poster said nothing about the treadmill size, other than it was really big.

"A lot of responses I am getting say, "why didn't you tell me the treadmill was really, really long". Of course, the original poster said nothing about the treadmill size, other than it was really big"Well, the original poster DID state how long the treadmill is. He said that "the runway is actually a very large treadmill". I don't know about anyone else, but that suggests to me that the treadmill is the length of the entire runway.It's a strange problem, because you can get so bogged down in thinking about "friction", "airflow", and "relative velocity" that you forget to apply known physical laws. When you apply Newton's 3rd law of motion, it becomes very clear that there is hardly any force holding the plane back (a tiny bit of friction between the wheels and the treadmill itself).When I first posted earlier today, I was adamant that the plane would go nowhere, resulting in ZERO airflow, and therefore no chance of take off. However, when I decided to THINK about the problem (as opposed to stubbornly refusing to admit that I was wrong), the truth was revealed.Mind you, I would STILL like to see a demonstration ;-)Chris Low.

>Mind you, I would STILL like to see a demonstration ;-)In the other thread, I posted a link to a video demostration.

>Look at the sketch in one of my earlier posts. That shows the>aircraft moving to the left at a speed V and the treadmill>moving to the right at a speed V.>>How is that not in the spirit of with "..this treadmill could>match the forward speed of your aircraft exactly, but running>in the opposite direction"? Because your sketch does not reflect reality.

I dont know why so many people, (most of them smarter than I) cant see this............Simply put the aircraft will initially keep station with the treadmill, but as the thrust continues to build the aircraft will move forward. The wheels will still spin freely against the treadmill, and will have a colossul rotation speed but the aircraft witll "skateboard" over the treadmill as the wheels and the treadmill counteract one another. The importnat thing to look at is the WHEELS. they'll spin up but the drive (thrust) is not input tothe ground/treadmill via the wheels. they will be a free agentThe AIRFRAME and hence the wings will still accelerate and eventually generate sufficient wing lift to take off.Ian HProud member of Knight Air.

"Then there are others that treat it as a mere problem of reference frames. This is probably the worst approach, as you have to realize the dynamics of the system to get it, that there is a net force in the forward direction."Talk about rubbish. The speed frame of reference in this exercise is THE most critical point. I

>The ambiguity in the original problem

>I dont know why so many people, (most of them smarter than I)>cant see this............I think that the reason people can't see it has to do with human psychology, which is a product of our evolution. Imagine an animal, like a primitive human, out in the wilderness somewhere having to make a decision to go east or go west in search of water. If he is very malleable and open-minded, he may go West for a while and then stop and rethink his situation, and decide to go East. This may actually reduce his chances of finding water as compared to the person who just picks a direction and doggedly sticks to it no matter what.So the answer to the question, "why can't people see when they've made a bad decision?" may be as simple as, "because their ancestors were like that."This theory goes a long way toward explaining certain world events that we aren't allowed to discuss here.

Everyone, on both sides, take a step back and look at it this way.It all depends on your definition of this treadmill. Everyone who thinks the plane won't take off is thinking of it as the powered type of treadmill that "makes the first move" and you have to move against it to keep stationary. This treadmill is capable of infinite speed.Everyone who thinks the plane will take off is thinking of the non-powered type of treadmill that acts against the force you initially place on it with your foot, effectively keeping you stationary.I'm not a physicist, just a lowly flight instructor, but I think this can be explained entirely on both sides using primarily Newton's 3rd law of motion.Let's look at plain old unmoving concrete first. Any aircraft on the ground is, in fact, exerting a force on the ground, as a reaction to the force that the ground is exerting on it. As power is applied and the thurst from the propellor (or compressors/turbines) begins to pull the aircraft forward through the air, the force exerted by the airplane on the ground becomes more diagonal instead of completely vertical, i.e. there is some horizontal component of force against the ground now. The tire does not slide along the ground of course; the mechanics of the wheel allow it to roll. Since the ground itself does not move horizontally, there is no force acting against this forward component, so the more thrust you apply, the less vertical the net force between the ground and the wheel is. As the net thrust becomes more and more of a horizontal vector, the plane is able to move forward. Eventually the movement through the relative wind generates lift and the remaining vertical component of the initial state of the aircraft sitting on the ground is netted out.Now, what if the plane couldn't roll? What if the parking brake was set, a chock left in front of the wheel, or the plane didn't have wheels at all, just stumps? You'd need a lot more thrust, wouldn't you? The plane needs some way or overcoming the force acted upon it by the ground in order to move forward, get its airspeed, and generate lift. Wheels work very well on stationary ground, as long as there is not something like a chock or mud or something to render them ineffective. How about something that could counter 100% the ability of our wheels to enable us to move horizontally? That's what this treadmill can supposedly do. Stationary, level concrete can only exert so much horizontal force for the wheels to overcome, and all aircraft in existence have enough force to overcome this. This treadmill can supposedly counter as much horizontal force as it needs to in order to keep us from moving forward.Imagine a powered treadmill that could move backwards *faster* than the airplane can go. For example, say it can go backwards at 200 knots. If you placed a Cessna 172 on this treadmill. Even at its Vne of 161, (if it could go that fast with just engine thrust on a normal runway on a calm day), it would never be going forward through the relative wind, and could not take off. If the treadmill were only going 50 knots, the Cessna would eventually probably go fast enough to go forward through the air and rotate. The person who tried this experiment at home did not have the ability to match the treadmill's speed *perfectly exactly* to his airplane, so one of those two scenarios probably occurred.Thinking of some kind of "non-powered frictionless" treadmill is a different situation. If you were in a car and trying to accelerate on it, you wouldn't be able to, because the force is applied directly to the wheels and nothing else, the wheels on your car actually need friction in order to allow you to accelerate. For an airplane however, friction merely gets in the way of acceleration, so it wouldn't be a problem.Oh, oh! I just thought of a much better, much less technical explanation. Look at it this way. Imagine tying a string to the front of your airplane and pulling it towards you. This is exactly what an airplane engine does for our purposes. What we want is forward motion, right? That's what we need to get our relative wind and eventually our lift. If we, *not* standing on the treadmill ourselves but in front of it (again, we all can agree the thrust produced by the engine is not *directly* affected by the treadmill, so this is a similar scenario), pull our airplane towards us, you can imagine it would come quite easily, wouldn't it? In fact, the treadmill would actually move in the *same* direction as the airplane, since it has no friction and the only force acting on it is forward.However, with the powered treadmill, it's actually using your wheels against you. It is pulling the plane away from you, and the harder you pull, the faster it goes. Even if you were to yank with all your might, it yanks back the exact instant you yank forward. In this case, all the pull you provide can never get the airplane to actually move forward through the air.So you see, everyone is right (though a few still got some facts wrong in trying to explain). It all depends on what type of hypothetical, nonexistant treadmill you are talking about. ;)