neorichieb1971 wrote:Well I disagree the plane will take off. Its the wings which make the plane take off and there is no wind going under them. The more likely scenario is that the jet engines would burn out.
The only case where the plane will take off in such a scenario is if the jets were quicker than the escalator and the plane went forward anyway.
In reverse, I agree that if a 250mph wind was hitting the plane head on, the plane would take off with no thrust at all.
Considering this was already shown to work, I'll humor you with an explanation anyway:
The wheels on a plane are free-rolling for the most part. The propeller/engines are what accelerate it. The fact that there is something underneath the plane making the wheels roll backward is irrelevant.
Ed Oscuro wrote:Also, if that were a valid method for determining the perimeter of a circle, then the hypotenuse of a 45-45-90 right triangle would just be adding together the two shorter sides!
i like this analogy. just like austere's "set of points" clarification.
neorichieb1971 wrote:Well I disagree the plane will take off. Its the wings which make the plane take off and there is no wind going under them. The more likely scenario is that the jet engines would burn out.
The only case where the plane will take off in such a scenario is if the jets were quicker than the escalator and the plane went forward anyway.
In reverse, I agree that if a 250mph wind was hitting the plane head on, the plane would take off with no thrust at all.
Considering this was already shown to work, I'll humor you with an explanation anyway:
The wheels on a plane are free-rolling for the most part. The propeller/engines are what accelerate it. The fact that there is something underneath the plane making the wheels roll backward is irrelevant.
If the wheels held up I suppose its possible. I would bet $10k on mechanical failure before the plane left the ground. But since we are talking theory I suppose the way you explain it could work.
So did someone put a plane on a treadmill to test this then?
This industry has become 2 dimensional as it transcended into a 3D world.
I like this one. In fact, if you replaced the edges with a sinusoid, you will have a curve that is both differentiable and continuous, which converged onto the circle. The length of the shape will still be pi after an infinite number of iterations, as per my proof.
<RegalSin> It does not matter, which programming language you use, you will be up your neck in math.
neorichieb1971 wrote:Well I disagree the plane will take off. Its the wings which make the plane take off and there is no wind going under them. The more likely scenario is that the jet engines would burn out.
The only case where the plane will take off in such a scenario is if the jets were quicker than the escalator and the plane went forward anyway.
In reverse, I agree that if a 250mph wind was hitting the plane head on, the plane would take off with no thrust at all.
Considering this was already shown to work, I'll humor you with an explanation anyway:
The wheels on a plane are free-rolling for the most part. The propeller/engines are what accelerate it. The fact that there is something underneath the plane making the wheels roll backward is irrelevant.
If the wheels held up I suppose its possible. I would bet $10k on mechanical failure before the plane left the ground. But since we are talking theory I suppose the way you explain it could work.
So did someone put a plane on a treadmill to test this then?
neorichieb1971 wrote:Well I disagree the plane will take off. Its the wings which make the plane take off and there is no wind going under them.
Pretty much everyone agrees that a plane with no air moving over the wings doesn't take off. If you assume that the conveyor belt somehow stops the plane from accelerating, then of course it doesn't take off. The real disagreement is over whether it's sensible to say that a conveyor belt prevents the plane from accelerating. People often argue past each other because they don't realize that they disagree on this point. Another reason that this debate tends to zombify is that the problem is often presented in a physically nonsensical way, e.g. conflating force with speed.
neorichieb1971 wrote:If the wheels held up I suppose its possible. I would bet $10k on mechanical failure before the plane left the ground. But since we are talking theory I suppose the way you explain it could work.
So did someone put a plane on a treadmill to test this then?
I will admit I was wrong then. It seems that the trick works even at rather slow speeds. The wheels have to spin twice as fast as the momentum of the plane but really in that video its quite slow. Much slower than I thought was required.
This industry has become 2 dimensional as it transcended into a 3D world.
Where did you get that "twice as fast" figure from?
It doesn't matter how fast the wheels are spinning, because if they are spinning that means the whole body is free to be lifted by the blades. Even if you assume the wheels can rotate infinitely fast they will still not be doing anything to the body. What needs to happen to restrict the plane's forward movement is to stop the wheels dead, like locking them in place, or making them really tough to turn so they are exerting at least a large frictional resistance to the plane's forward movement. I assume that if you get preposterously big enough wheels and a small enough engine, you could make just the weight of the wheels stop it from flying at all! But that's not what the wheels are for, they're intended to simply let it roll into flight and roll to a stop.
The thing you haven't thought about is that it's air passing through the engine, and ultimately over and under the wings, that ultimately causes lift. The engine pulls air on through, so even if the body is not moving at all at least some engines (probably most if not all aviation engines) should be able to pull their airframes up even when tethered (how did you think helicopters work?)
I don't have any way currently of modeling a wing for lift of reverse air pressure, so I can't tell you if blowing air or otherwise moving the plane backwards against air moving as quickly as the air would be pulled through the engine will ultimately stop it from taking off (idea being that the air coming from behind will negate air being pulled from the engine, and hopefully air coming from behind will not cause the airframe to lift up by the wings...though you would need a LOT of air moving very fast to oppose the force of the engine, like you'd find in a very powerful wind tunnel maybe).
But the wheels normally shouldn't even be considered in. To even get different behavior would really require the conveyor be moving so fast that the plane is moving backwards so fast that it's being buffeted from behind by air so that the propeller can't turn. That much air might do something unexpected like flip the plane or even break it apart.
Ed Oscuro wrote:Where did you get that "twice as fast" figure from?
neorichie's posting goes:
escalator counters the thrust with the exact speed in the opposite direction
if that mean "moves with the exact speed in the opposite direction", then the wheels are moving between the plane and the belt at twice the takeoff velocity of the plane.
but the way it's worded: "counters the thrust", means that the net force is zero. meaning the wheels are very poor and really hold the plane in place.
Oh rite! In the Mythbusters attempt it appears that they had the wheelz moving at more than double the takeoff speed in a last ditch effort to arrest the launch it but that still wasn't enough to stop the plane from moving. There ought to have been a part of the video where the plane is moving back relative to its starting point on the ground, but I remember thinking it was hard to tell because the plane takes off pretty quickly, so the point where it's moving back comes and goes pretty quick.
Ed Oscuro wrote: There ought to have been a part of the video where the plane is moving back relative to its starting point on the ground, but I remember thinking it was hard to tell because the plane takes off pretty quickly, so the point where it's moving back comes and goes pretty quick.
moving back? not unless the belt is dragging the wind.
Ed Oscuro wrote: There ought to have been a part of the video where the plane is moving back relative to its starting point on the ground, but I remember thinking it was hard to tell because the plane takes off pretty quickly, so the point where it's moving back comes and goes pretty quick.
moving back? not unless the belt is dragging the wind.
I agree with your point but you don't understand me. When they started the full-size experiment on Mythbusters, with the plane on a tarp being dragged by a pickup, I thought they tried to give the plane some backwards motion by gunning the truck engine. As the plane is sitting on a tarp, it moves backwards relative to its starting position on the ground (i.e. the wheels don't just spin completely freely under the plane and it stays stationary due to inertia; the whole plane should actually move back a bit).
They aren't doing anything to the air other than moving the plane through it, though the idea is that if the plane is moving backwards against air that will make it harder to lift off. Obviously the plane needs to be moving backwards VERY fast for movement into surrounding air to have any effect - which is why I made the wind tunnel comment.
neorichieb1971 wrote:to be honest that video makes it look too easy. As if the treadmill had zero effect at all lol.
We haz winner! It's not zero but it's so close that it's not funny.
