I don't think this has been posted yet......... Mythbusters will run an episode on this in December.[/quote] THE PLANE WILL NOT LIFT Lift . .unless I am mistake is created by the rush of the air moving around the wing. The air is moving because the plane is moving forward The original question is a bit flawed. . . The bolded portion is the problem I think what was meant was . . as the WHEELS OF THE PLANE ACCELERATE the Conveyor belt matches its speed in the opposite direction So 100 MPH ---> vs <--- 100 MPH means the sum velocity of the plane is 0 MPH While the conveyor and the wheels are moving overall the plane is not. Unless the d*mn thing is a Harrier it will not be able to have the wind rush over the wing enough to cause lift [Unless it is in a hurricane] Rocket River the answer is NO!
That was why I brought the "ice slick" idea. If you have a vehicle whose total thrust depends upon the wheels spinning, you will not move. Anyone who has lived up north knows this. (or it may veer and spin rapidly, but that is another topic.) A jet plane on an ice slick will move forward, just like sea planes do on skids. Their forward motion has nothing to do with what is underneath them. As I stated earlier, I figured it out. Regardless of a conveyor, the plane will move forward. But the tires will have more wear on them with the reverse conveyor idea. BOTTOM LINE: The conveyor idea is a stupid idea. Unless you like the idea of planes being able to lift while in standing motion on an ice lake.
I was originally of the camp that said it won't lift. Then I was convinced that the plane would lift because the wheels are not spinning to push the plane... they just happen to be turning because the plan is already moving. However, I had another thought. If the plane was on the conveyor belt and the engine was turned off, and the conveyor started to move backwards... what would happen? The plane would start moving backwards. The wheels wouldn't just spin while the plan stayed in place. So if that were the case, the engines would have to overcome certain forces for it to go forward. They are not completely separate. Or am I confusing matters?
A hair. If the plane was moving backwards, and chose to start its engines and propel itself, it would stop the back ward wind, and the backward progress. But it would also have to overcome the negative wind with more power to speed up and lift off. Or it could be a super magical plane that was able to use the backwards wind and transform itself invertedly to use it to its advantage. Bottom line: A conveyor belt should be treated like a frozen lake. Planes can move on it. Cars cannot. Reason? Difference in propulsion. Y'all let me know when you have a plane that can keep flying on ground being the propelant. I've got a 100 Indy car racers that will prove they can fly. They just cant sustain it because there is no longer any forward thrust. The conveyor system simply is impossible. However, a U-shaped wind-tunnel may be feasible for shorter runway ideas.
So when does this episode air, do you know? I can't wait to see it on youtube. The suspense is killing me!!!
Earlier in the thread, they said December. I'm willing to take wagers on my theory. Seriously. I'll even give 2-1 odds. Or sig bets, or drinks. I know I'm right. I'm willing to bet the house on it.
I thought my Hulk example would solve this. But now it seems I need to use a Superman example. Lets say the plane is on the conveyor belt, indeed "spinning in place", with engines at full throttle. Now Superman is flying nearby to save a cat in a tree, but has to fly low and doesn't see the plane spinning in place...and unfortunately, he hits the plane in the back at high speed. Would the collision move the plane forward? Or would Superman just stop when he hit the plane simply because the plane is on a conveyor belt? What about if I said it was Earl Campbell and Vince Young who swooped in and hit that plane from behind? Would Earl and Vince just bounce off?
It would definitely fly with a jet engine because it sucks in air. I think the question would depend on whether the engines are strong enough to lift without needing a high ground speed.
It won't take off unless there is a seriously b****in' headwind. Otherwise you have thrust with no lift being generated because of lack of air movement. Put an airplane on a conveyor belt inside a wind tunnel and it'll work.
Guys, the plane WILL take off, for one simple reason: The whole problem stems from the lack of clarity in the stated purpose of the 'experiment' - ie are they trying to *impede* the plane's forward motion, or are they trying to *negate* it? If all you are trying to do, or, for that matter, all you MANAGE to do, is *impede* the plane's progress, then all it will need is a sufficiently strong engine to overcome the impedance, which is what it already does anyway when it moves the very heavy mass of the plane in the first place; this whole experiment does nothing except make the plane's job harder to some degree. Since the whole point of an 'experiment' is to gain knowledge, that whole exercise would seem to be rather pointless, since we already KNOW that knowledge: a strong force can overcome a weaker obstacle. What knowledge would anyone gain from such an experiment? It was never an experiment in the first place then, it was merely a 'stunt'. If, on the other hand, they are actually trying to do, and somehow actually MANAGE (which they never will, with this conveyor-belt idea), is to NEGATE the forward motion of the plane, then that is a different animal altogether. Now you have an actual experiment from which something might be learned. The question then becomes: could the wind-motion caused by the engine(s) of a plane generate enough quantity and even-ness of airflow over the whole area of the wings in order to actually lift the mass of the plane into the air? Whether it works or not, you have at least learned something from the result. However, it's a moot point, as long as it's tied to this 'conveyor-belt' idea, as that will never work anyway. The only way to actually negate the plane's forward motion would be to chain it to some point behind it, to give it free range of motion in every direction except forward. If they don't do something liek THAT, then the whole thing is meaningless. So, if anyone is wanting to make a wager, put your money on the 'it WILL take off' side.. anything else is a sucker's bet.
Well, the problem says that the belt matches the speed of the plane so it does not turn on until the plane has escaped inertia and established some momentum moving forward. But if this was the case, it would still take off as the jet engines would still overcome moving backwards. No matter how fast the plane was moving backwards, at some point the plane would slow down and stop and then start moving forward.
Ok, first off...this is Mythbusters here...and as the name of the show implies, they are simply testing myths, which is what this is. Second of all, I think within the realm of all experiments, something always can be learned, whether its something new or simply reaffirming what you already know. And third, if they were trying discover what would happen if you negated the forward motion of the plane, then you don't even need to run an expirement because the answer is obvoius (and already proven)...if a plane has no forward motion then it can't generate any lift to take off....take for instance a fighter jet on a carrier....it's essentially chained down (or rather the front wheel is blocked by a kind of dolly) until the engine power reaches a certain level, after which the dolly is released and the jet rockets forward at a high enough speed to take off from the shortened runway. But it doesn't take off when it's held back because it's not generating any lift. ...... I think a lot of ya'll are still thinkin that the forward motion is caused by the wheels turning. I like the sea plane scenario, but then let's go a step further and put the sea plane on ice, which is the closest to a frictionless surface you are gonna get on earth. Now let's imagine that the plane, moving at speed, hits a patch of ice that is moving in the opposite direction at equal speed. Considering that the ice is nearly frictionless, it will pass underneath the skids of a plane without much resistance...so the plane might be slowed down a little, but it will keep moving forward and therefore will still be able to fly. Now let's go back to the plane on a conveyor. It's at speed then hits a conveyor that is moving at equal speed but in the opposite direction. If those wheels are rotating perfectly, as in the bearings are completely frictionless, then the plane will pass over the conveyor just like it was the ice moving underneath the skids...because the wheels having nothing to do w/ a plane's forward motion. Now, as I've said, will the Mythbusters find such a plane where the wheels are free of fiction...well obviously no, because that will defy the laws of physics. Will they be able to find a plane w/ wheels that are nearly frictionless...i dunno. So basically, theoretically I think it's possible...but realistically it probably won't happen.
This isn't exactly true. The belt would exert a frictional force between the conveyor and wheels and also the ball bearings. However, that frictional force is almost negligible compared to the force generated by the prop/turbine moving in the opposite direction. I like the roller skate example, though. I think some people are getting force and velocity mixed up. True, they are related - force is needed on a mass to create acceleration and velocity and all that. But, they are almost totally exclusive of one another in this case. If we're talking force exerted on the airplane: (and I'm making these numbers up, but I think they're close) Force from engine thrust moving in +x direction (100 kN) vs. Force generated by the conveyors frictional force in the -x direction (10 N) = 99.99 kN in the +x direction The engines force wins and will create acceleration of the plane with respect to the earth (not the conveyor), and the plane takes off.
THE PLANE WILL NOT LIFT Lift . .unless I am mistake is created by the rush of the air moving around the wing. The air is moving because the plane is moving forward The original question is a bit flawed. . . The bolded portion is the problem I think what was meant was . . as the WHEELS OF THE PLANE ACCELERATE the Conveyor belt matches its speed in the opposite direction So 100 MPH ---> vs <--- 100 MPH means the sum velocity of the plane is 0 MPH While the conveyor and the wheels are moving overall the plane is not. Unless the d*mn thing is a Harrier it will not be able to have the wind rush over the wing enough to cause lift [Unless it is in a hurricane] Rocket River the answer is NO![/QUOTE] Actually its the plane moves 100MPH---->, the conveyor moves 100MPH <-----, but the wheels, because they are in contact with the conveyor and the plane, would move 200MPH ------>. So, the resultant velocity of the wheels would be 200MPH. However, this velocity is only applicable to the force generated on the ball bearings of the wheels. Basic physics tells us that Force = mass x acceleration, but in real world engineering applications it's not this simple. There is a proportionality constant k that needs to be applied. This is the key. Now, here are the forces will be acting on the plane: Engine thrust Frictional force from wheels/conveyor/ball bearings, etc. normal force due to mass of plane air resistance For the engine thrust, the proportionality constant is close to 1 because the engines are physically attached to the plane. The design of the engines are so that the plane accelerates using as much of the engine force as possible. Now, contrast that with the design of the ball bearings which has the opposite intent - to dissipate as much of the force as possible. Hence, the proportionality constant is significantly lower at around 0.05. This is why the force generated by the thrust of the engines is overwhelmingly more than that of the frictional force. For the air resistance, the k is even lower, making this force negligible. The normal force is the same with or without a conveyor, so it doesn't apply to the argument.
Yeah, if the engine is strong enough, it would be like tethering glider wings in a wind tunnel. The tether in this case is the treadmill.
But if Ditka was flying the plane, it would take off even it had no wheels, had no wings, and had no engines.
You could think of it this way and take the treadmill out of the equation. 1- If there is no wind and the the plane is chained to the ground, Can the plane get off the ground w/ just the forward engine thrust. 2- Once the plane gets off the ground, and the chain is released, will the plane take off.
