A jet plane on a large treadmill

[flyandski365]

Wrong question. What if it was circumcised?

More friction?

[Ted Striker]

Ha, ha, here come ten more pages.

The OP makes no mention of a treadmill. It talks about a conveyor belt which, in theory, could be two miles long.

Except in the thread title

Yup, it would be the same answer. I was responding to this, per my interpretation of "the treadmill question isn't attainable," a rather clumsy phrase, which I interpreted to mean that thrust of the jets would move the jet forward, off the treadmill, onto the runway. I can't figure out what else he could have meant by the phrase "the treadmill question isn't attainable."

That's why I'm not a law talking guy.

I'm not talking about the airplane moving off the conveyor belt. I'm talking about the premise of the original logic riddle, which states the conveyor belt matches the wheel speed of the airplane, not the actual speed. That's the part that can't be achieved by experiment because the wheel speed goes to infinity. Now that I've reread the OP's post, I see that he says the airplane's speed (which is what they did on mythbusters too), so strike that "not attainable" part altogether.

It could be restated that the force of the river is equal to the force of the propeller.

No. No it couldn't. That's not what it is.

Actually, yes, in my example (not the original premise) that's exactly what it is. Thrust is equal to drag.

It was never posited in the premise that the treadmill would act in such a way that it would restrict the forward speed of the airplane to zero.

Quite the opposite. The treadmill only moves backwards if the plane moves forwards. That's the fucking premise. Go read it again. Think about it for like five seconds. If the plane doesn't move forwards, the treadmill doesn't move backwards. If the plane moves forwards, how can it be standing fucking still?

The plane takes off. The wheels spin twice as fast. It isn't a physics riddle, it's a logic riddle.

Yeah, I know the plane takes off. I even said it in my post.

when you put the airplane on wheels, there isn't enough friction (or connection) between the airframe and the treadmill to prevent the airplane from moving. The wheel bearings are meant to roll. Spinning wheels apply so little force that the airplane can easily overcome that force, and will move forward. The plane takes off because the premise of the treadmill question isn't attainable.

You missed my point. You are right about me needing to go back and reread the OP though, because going from memory I was thinking of how this problem worded the first time I heard it, not the way the OP stated it, which is what I was getting at with "attainable" i.e. the belt can't accelerate to infinity).

My point with the float plane scenario was to illustrate what the 'no fly' people are thinking about (because there were so many of them in this thread). That when when there is a force applied to the airframe that is equal to, and in the opposite direction of, the force of the engine(s), the airplane doesn't move. But the conveyor belt doesn't apply such a force because the wheels are free spinning. That's why I said "the question is wrong". Put another way, the people who said the airplane doesn't take off are correctly answering the wrong question.

The fact that you thought that I'm in the 'no take off' camp means that I must not have made my point very well.

[Ted Striker]

No. There is no airflow over the lifting surface.
0 Knots True Airspeed.
It's Ground Speed could be 400KTA relative to the tread mill, but as long as there is 0KTA over the airfoil, it can't take off.
That's why planes take-off and land into the wind. While the plane may be fighting a head wind and have a lower ground speed, its airspeed is higher by however many knots the headwind is.
for example: at 200kts ground speed in a 10kt headwind, the kta is 210kts. and off into the wild blue yonder you go.


Morans.
http://en.wikipedia.org/wiki/Airfoil

This is exactly what I was talking about. Correct answer to a different question; wrong answer to this one.

It would depend on the size of the treadmill. If it was miles long and wide enough, then it would affect the air above it and result in a big headwind. The jet might lift off without moving forward but only for a second before encountering normal air and falling. At which point it would fly up as it encounters the fast airstream ... and then fall again.

No.

What force moves the airplane forward? What force holds it back?

[stuckathuntermtn]

I can't fucking believe some of you. This isn't magic. It doesn't matter what propels it. It matter how fast air is moving over the airfoil

Sent from my DROID2

[Tippster]

[Mustonen]

That last part sounds pretty wrong to me. If the treadmill matches the speed of the rotating wheel in the opposite direction, how does it move forward? I, mean that's how a treadmill works right?

The treadmill doesn't match the speed of the rotating wheels. The treadmill matches the speed of the airplane. I, mean that's how the question is stated right? (Sic)

I'm not talking about the airplane moving off the conveyor belt. I'm talking about the premise of the original logic riddle, which states the conveyor belt matches the wheel speed of the airplane, not the actual speed. That's the part that can't be achieved by experiment because the wheel speed goes to infinity. Now that I've reread the OP's post, I see that he says the airplane's speed (which is what they did on mythbusters too), so strike that "not attainable" part altogether.

!!

Actually, yes, in my example (not the original premise) that's exactly what it is. Thrust is equal to drag.

Water is obviously not frictionless - but if water speed is equal to the max speed of the airplane (and not the airplane's actual speed), the force of the river (even just that force being applied to the airplane) is far greater than that of the props. I'm guessing that a combination of plane+lift from the wings are necessary for a plane to actually get out of the water - though I suppose I don't know that for a certainty. Either way, bad analogy, and even if it wasn't bad it bears little relation to either the OP scenario OR this stupid frictionless interface overcoming forward motion scenario that so many are stuck on.

You missed my point. You are right about me needing to go back and reread the OP though, because going from memory I was thinking of how this problem worded the first time I heard it, not the way the OP stated it, which is what I was getting at with "attainable" i.e. the belt can't accelerate to infinity).

You missed mine. The premise you stated was ridiculous - as you pointed out. That's great, except it's not the premise stated in the OP. That was my point.

[flyandski365]

I can't fucking believe some of you. This isn't magic. It doesn't matter what propels it. It matter how fast air is moving over the airfoil

Sent from my DROID2

Obviously, but to generate airspeed the aircraft has to move forward. That is assuming the treadmill isn't in a wind tunnel...

[Art Shirk]

It doesn't matter what propels it. It matter how fast air is moving over the airfoil

Sent from my DROID2

Am I understanding correctly that you are stating that this thing wont take off (I could be way off on this, seriously just not following you)? And you think it is because air isn't moving over the wing fast enough? But you also believe thrust doesn't matter?

What makes air flow over and under the wing when a plane is airborne?

[toast2266]

What makes air flow over and under the wing when a plane is airborne?

unicorn farts (duh.)

[Captain Anal]

I can't fucking believe some of you. This isn't magic. It doesn't matter what propels it. It matter how fast air is moving over the airfoil

Sent from my DROID2

Obviously it's all about how fast air is moving over the airfoil. I don't think anybody is disputing that. But it DOES matter what propels it. If it's just the wheels propelling it, no air will move over the airfoil. If there is A FUCKING JET ENGINE propelling the plane, the jets will ignore the treadmill and cause the plane to move forward in space, thus moving air over the god damn airfoil for christ's sake.

[ak_powder_monkey]

I liked the Mythbusters with the retard pilot who thought the plane wouldn't take off... Of course it did, like it was nothing

[Mustonen]

If it's just the wheels propelling it, no air will move over the airfoil.

Ah. See. You're wrong there. Go read the OP again. Treadmill moves when the plane moves. If the plane doesn't move the treadmill doesn't move. For the treadmill to move, the plane must also be moving. If the plane is moving, air will move over the airfoil. It doesn't matter what's propelling it. For goddamn christ's sake.

[philth]

This is retarded...cant believe I just stumbled upon this thread....

I can't fucking believe some of you. This isn't magic. It doesn't matter what propels it. It matter how fast air is moving over the airfoil

Hard for some of these folks to comprehend

[Captain Anal]

Go read the OP again.

Okay okay. So the OP is stupid/poorly worded/not enough information or something. What is the plane moving in relation to? The air? The treadmill? GSA?

[Brock Landers]

After much careful analysis, the airplane will not go anywhere

[Mustonen]

Okay okay. So the OP is stupid/poorly worded/not enough information or something. What is the plane moving in relation to? The air? The treadmill? GSA?

Really? I didn't think so. I mean, you can turn it into some metaphysical discussion about reality ("We're all MOVING, maaannnn") but the OP is pretty clear. What I think is remarkable is how people add their own crap to it and try to defend it to the death.

[Captain Anal]

Really? I didn't think so. I mean, you can turn it into some metaphysical discussion about reality ("We're all MOVING, maaannnn") but the OP is pretty clear. What I think is remarkable is how people add their own crap to it and try to defend it to the death.

I'm not adding anything to it. If the plane is only being propelled by the wheels how can the fucking thing MOVE if the conveyor is moving in the opposite direction? It would sit still with only the wheels spinning beneath it. Since there is really no movement in relation to the air, then there is no air moving over the airfoil and so there is no lift. But if you turn on the jets, then the plane will actually 'move' and air will flow over the airfoil creating lift and allowing the plane to take off.

[Dantheman]

[flyandski365]

Ah. See. You're wrong there. Go read the OP again. Treadmill moves when the plane moves. If the plane doesn't move the treadmill doesn't move. For the treadmill to move, the plane must also be moving. If the plane is moving, air will move over the airfoil. It doesn't matter what's propelling it. For goddamn christ's sake.

I'm pretty sure you're wrong here man. How does the plane move forward if it is being propelled by the wheels and the treadmill is matching speed in the other direction? It doesn't. As far as I understand it, the treadmill is basically being used to mimic a frictionless surface. Something driven by wheels uses torque and friction to propel the object forward. No friction = no forward motion.

All of that really doesn't matter though does it? Planes don't use wheels for propulsion.

[Captain Anal]

I've got to be at the office for 2.5 more hours, I've got no work left to do, this day was going slow as shit already, checking the spare at 5:30.

[Mustonen]

I'm not adding anything to it.

Bullshit. OP says the plane moves in a direction. You started talking about friggin wheelspin. Who brought up wheelspin? You did. The treadmill doesn't give a shit about wheelspin, it cares about the plane moving in a direction. It doesn't counter it, it just moves at the same speed in the opposite direction.

[Dantheman]

If the plane is only being propelled by the wheels how can the fucking thing MOVE if the conveyor is moving in the opposite direction? It would sit still with only the wheels spinning beneath it.

Incorrect. Plane moves forward at X, conveyor moves backward at -X, wheels spin at 2X.

[Mustonen]

How does the plane move forward if it is being propelled by the wheels and the treadmill is matching speed in the other direction?

Because the treadmill is matching airplane speed, not wheel speed. The two are not inseperable.

All of that really doesn't matter though does it? Planes don't use wheels for propulsion.

None of this actually matters. Shit dood, it's Friday afternoon over here. It is sort of fundamental, though, to understanding the scenario as presented.

[beaterdit]

Heh, always amusing to see this pop up. This was the thread that brought me to TGR way back in '05 from a link on [cough]tele-tips[cough]. After reading that drivel for a couple years I thought the innernets were dead until I found this place. I remember LOLing constantly at some of the stuff here. What ever happened to that? Did I kill teh TGRs?

No. There is no airflow over the lifting surface.
0 Knots True Airspeed.
It's Ground Speed could be 400KTA relative to the tread mill, but as long as there is 0KTA over the airfoil, it can't take off.
That's why planes take-off and land into the wind. While the plane may be fighting a head wind and have a lower ground speed, its airspeed is higher by however many knots the headwind is.
for example: at 200kts ground speed in a 10kt headwind, the kta is 210kts. and off into the wild blue yonder you go.


Morans.
http://en.wikipedia.org/wiki/Airfoil

It would depend on the size of the treadmill. If it was miles long and wide enough, then it would affect the air above it and result in a big headwind. The jet might lift off without moving forward but only for a second before encountering normal air and falling. At which point it would fly up as it encounters the fast airstream ... and then fall again.

Quality trolling here guys. Bravo!

This is exactly what I was talking about. Correct answer to a different question; wrong answer to this one.



No.

What force moves the airplane forward? What force holds it back?

Hook, line, and sinker!

[Captain Anal]

Bullshit. OP says the plane moves in a direction. You started talking about friggin wheelspin. Who brought up wheelspin? You did. The treadmill doesn't give a shit about wheelspin, it cares about the plane moving in a direction. It doesn't counter it, it just moves at the same speed in the opposite direction.

Okay, so what I am gathering from your argument is that in your interpretation of the question, the treadmill actually does not even play a factor in this whatsoever. So if we go with your interpretation, the plane might as well be sitting on pavement, a herd of cattle, or boiled hot dogs and it wouldn't make any difference.