Mythbusters to take on - PLANE ON A TREADMILL!!!

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Chris_Ford said:
Okay, get a toy airplane out, one with wheels.

Push it forward at the tail, on the ground.

Notice how when you do that, the wheels spin? The wheels aren't creating the acceleration, but they're certainly responding to it.

Now let's think of that toy plane on a treadmill. Let's assume the treadmill is already moving. There's a required force by your finger to keep the airplane stationary. Now, as you roll it forward on the treadmill, the wheels spin faster...

If the speed of the wheels were met by the treadmill, the whole system would speed up to infinity at the rate of acceleration, the tires would explode long before that, but either way the airplane wouldn't be able to overcome the treadmill with the engine thrust (as it is when the aircraft speed is being matched)
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I think I see where you're going with this. Are you saying that the very small but definitely existent friction of the wheels, when they start spinning at that insanely high speeds will overcome any force the engine can produce? I don't think the wheel's speed has anything to do with rolling friction in theoretical physics, but it may certainly affect it in reality.
 
ok ok.. i thought of an equivalent system tha tmight help seeing this..

imagine you hav eyour plane on the treadmill and when the threadmill starts moving, the plane (with no thrust or anything yet) will obviously start to move along with the treadmill..

now, instead of the engines on the airplane pushing it, imagine a big fat string (IMAGINE!) attached to a stationary object on the ground, on Earth! lol... OK, so if the treadmill starts going and there is no power, as in the string is let to unroll or something.. again teh plane goes along with the treadmill.. BUT! imagine now the strings starts to wind up.. this is as if the thrust is now being produced, the treadmill can speed up to 1000knots, but if the string is winding up, it WILL pull the plane along the treadmill towards the stationary object that the string is attached too.. THIS is what happens when the thrust is applied..

also, if, while you are pulling the plane with the string and the treadmill is accellerating to insanity trying to keep the plane back, and you start to apply thrust via the engines, and ifyou match this force with the force with which you are pulling with.. you will have only the force of the treadmill onto the airplane via the mechanical linkages of the tires remaining in the string.... and the only damage this can do is physically reaching the yield points of the linkages involved...

anyone understand my analogy? lol.. sometimes things are clearer in my head than out my mouth.;)
 
gevo said:
ok ok.. i thought of an equivalent system tha tmight help seeing this..

imagine you hav eyour plane on the treadmill and when the threadmill starts moving, the plane (with no thrust or anything yet) will obviously start to move along with the treadmill..
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Incorrect, the plane will fall off the end of the treadmill. This demonstrates that perhaps you are unfamiliar with how a treadmill works.

now, instead of the engines on the airplane pushing it, imagine a big fat string (IMAGINE!) attached to a stationary object on the ground, on Earth! lol... OK, so if the treadmill starts going and there is no power, as in the string is let to unroll or something.. again teh plane goes along with the treadmill.. BUT! imagine now the strings starts to wind up.. this is as if the thrust is now being produced, the treadmill can speed up to 1000knots, but if the string is winding up, it WILL pull the plane along the treadmill towards the stationary object that the string is attached too.. THIS is what happens when the thrust is applied..
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Everyone gives this example or similar and it's inherently faulty. If the treadmill were at a constant speed, it would be valid, but as soon as the string brought the wheels forward, the hypothetical treadmill would speed up to match the speed of the wheels. In your example, there's a clear excess of Force that is not matched by the treadmill.
 
Chris_Ford said:
Incorrect, the plane will fall off the end of the treadmill. This demonstrates that perhaps you are unfamiliar with how a treadmill works.



Everyone gives this example or similar and it's inherently faulty. If the treadmill were at a constant speed, it would be valid, but as soon as the string brought the wheels forward, the hypothetical treadmill would speed up to match the speed of the wheels. In your example, there's a clear excess of Force that is not matched by the treadmill.
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:banghead::banghead:... you're pulling our legs huh?

Chris, I once saw a treadmill.. in the window of a gym.. that count??? :rolleyes:

ok.. I don't know how else to say it really.. the reason the airplane goes forward is NOT the wheels.. that is perhaps the most obvious statement in the world. so.. what is the difference if something is accellerating the wheels or not???? man.. maybe mythbusters really should do this experiment. no matter what, unless you restrain the airplane it will go forward once thrust is applied.. UNLESS!!! you bend space-time and feed the turbine the air in a circular motion... or something.. haha.
 
Chris_Ford said:
In your example, there's a clear excess of Force that is not matched by the treadmill.
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In your example, what force is the hypothetical treadmill creating when it matches the speed of the wheels?

This should really be a pretty simple question, which you are avoiding at all cost.

Another thing to think about is what is the MAXIMUM force the treadmill could ever impart on the wheels/airplane? That would have to be a wheels-locked condition, since a free spinning wheel, regardless of direction or speed (even just shy of infinity velocity), will never produce as much friction as a locked wheel. Yet we know airplanes will roll forward with the wheels locked.
 
Clocks said:
In your example, what force is the hypothetical treadmill creating when it matches the speed of the wheels?

This should really be a pretty simple question, which you are avoiding at all cost.
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I've said it numerous times, it's the same force that keeps a human leg in check. This hypothetical treadmill accelerates at the same time and at the same rate as whatever is on it, so if I'm running on it and I speed up, so does the treadmill. I don't go running off the front end of the treadmill, and neither would an airplane. My foot does not "create" the force as you have suggested before, that force is actually created by my leg, and carried out by my foot, much like the wheels carry out the thrust input for the engine.

The problem is that you keep thinking of a conventional treadmill and use examples that are not relevant to our hypothetical super treadmill.

Let's try the building block philosophy, ok?

On a normal runway, when you add thrust, do the wheels spin faster? Yes. They do. The wheels aren't CREATING any sort of force or anything, but they certainly do spin faster, right?
 
Chris_Ford said:
I've said it numerous times, it's the same force that keeps a human leg in check.
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And again, you're completely ignoring the difference between the way an aircraft propels itself and the way a human (or car) propels itself. One pushes off the ground, the other pushes off the air (the ground could be moving forward, backwards, sideways, be stationary, or not exist at all, and the aircraft is still only pushing off the air).

The only way an airplane (which is pushing against the air) could be held stationary is if an equal and opposite force was holding it back. And a treadmill under free-spinning wheels cannot produce that much force.

Chris_Ford said:
much like the wheels carry out the thrust input for the engine.
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I'm not trying to sound sarcastic here, but are you a pilot?
 
Chris_Ford said:
... much like the wheels carry out the thrust input for the engine.
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So, on the planet you live on, there is a drive connection between the engine and wheels of an airplane?

:laff::laff::laff::laff::laff::laff::laff::laff::laff::laff::laff:
 
SteveC said:
Don't sweat it. In my opinion CF doesn't believe the crap he's posting here any more than you or I do.
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It would be sad if he's really spending his time arguing a position he doesn't believe. Although the more he repeats the exact same thing and ignores very simple questions, the more I believe this is just a lame joke on his part.

Although it's worth coming back to this thread just to see his avatar :)
 
MDPilot said:
So, on the planet you live on, there is a drive connection between the engine and wheels of an airplane?

:laff::laff::laff::laff::laff::laff::laff::laff::laff::laff::laff:
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Did I say that?

On a dry runway, when you advance the thrust, do the wheels spin?

Yes.

The airplane's movement causes the wheels to spin, not the engine inputs, but the wheels do spin.
 
SteveC said:
Don't sweat it. In my opinion CF doesn't believe the crap he's posting here any more than you or I do.
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In every single one of your examples (plural you, not you in particular, Steve), it's dependent upon the wheels speeding up to a speed faster than the treadmill is going. In my hypothetical situation, this is impossible.
 
Chris_Ford said:
In every single one of your examples (plural you, not you in particular, Steve), it's dependent upon the wheels speeding up to a speed faster than the treadmill is going. In my hypothetical situation, this is impossible.
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In a vehicle that doesn't rely on the ground for propulsion, why does the speed (or direction) the wheels are spinning have any effect on its acceleration?
 
Clocks said:
In a vehicle that doesn't rely on the ground for propulsion, why does the speed (or direction) the wheels are spinning have any effect on its acceleration?
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The vehicle needs a surface to gain its speed on. So it is reliant upon the ground for propulsion until it acquires enough airspeed to fly on its own.

Now, that being said, I see both sides of this argument and I think my primary point is that this isn't as "open/shut" as some of you seem to think it is.
 
Chris_Ford said:
The vehicle needs a surface to gain its speed on. So it is reliant upon the ground for propulsion until it acquires enough airspeed to fly on its own.
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That is ridiculous and shows a fundamental lack of knowledge.

I am now convinced you either don't believe what you are saying and are trying to be amusing, or you have such a huge gap in your knowledge of basic physics that this conversation is meaningless. I am finished either way.
 
Plane on skis . . .

Treadmill = ground, ice, snow; no movement, nothing, zilch, nada

Wheels = stationary, fixed skis; no movement, nothing, zilch, nada

Treadmill speed = wheel speed = 0 = nothing, zilch, nada

Power application, aircraft sliding across ground, acceleration, and takeoff


It works! Yay!
 
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