Going to settle the plane on a treadmill once and for all. - Page 3

ballz2wallz · 01-22-2007, 11:35 PM

Originally Posted by 7960

no

if there was no friction in the wheels/bearings then the plane would accelerate and take off EXACTLY like a plane on a regular runway. The pilot wouldn't notice a thing unless he looked directly down at the runway, the passengers would see the trees go by EXACTLY like any other "normal" flight.......... the plane would behave EXACTLY like any other plane.

Not if the treadmill was already moving.

ballz2wallz · 01-22-2007, 11:36 PM

Originally Posted by Ardentfrost

Wait, why would the treadmill move at all? I mean, isn't the thrust of the jets propelling the plane, therefore the treadmill would have no effect whatsoever? A treadmill affecting the movement of the plane would mean that the motile function of the plane generated from its wheels, but it actually generates from it's wings, right?

I'm not an aerospace engineer, that's just how it seems to me.

That's what I said...if it wasn't moving, then yes, the plane would take off. But if it was motorized like the ones at the gym, then we have a different story.

ballz2wallz · 01-22-2007, 11:37 PM

Originally Posted by Kytro

Seaplanes have no wheels and they take off fine.

But if the water was moving so fast it pushed the plane back it woldn't take off fine

7960 · 01-23-2007, 12:20 AM

Originally Posted by ballz2wallz

Not if the treadmill was already moving.

starting with the plane at a stop and the treadmill at a stop (like the scenario says), if there is no friction in the bearings/wheels then the plane will take off exactly like a plane on a normal runway.

do you agree with that?

nbiggershaft · 01-23-2007, 12:44 AM

Originally Posted by nbiggershaft

Here Ballz, Does the little man in this picture pull himself forward, despite the treadmill moving very fast in the other direction?

Dumpy Dooby · 01-23-2007, 01:39 AM

omg! The plane/treadmill thing made it to LL.

Dumpy Dooby · 01-23-2007, 01:47 AM

Oh, and yes the plane takes off.

On a side note: I actually used to enjoy going into forums and starting these threads, and then trolling the people that knew what they were talking about. I would make up all sorts of funny shit like "the tires would get really hot and become sticky, causing the plane to stick to the ground and not take off." It was so funny. I won't do that here, though.

It's difficult to explain to people that just don't "get it." But yes, the plane takes off because the wheels freespin. They are only there to keep the plane from hurting its belly. Imagine one of those planes that can take off from the water. Stick some ice on the bottom of those little skis and stick it on a treadmill. Will the treadmill stop it? Probably not. What about the current when the plane is in the water? Does that prevent it from taking off? Not really.

The treadmill would have an impact, but not much because it's pushing/pulling (depending if it's a plane or a jet) against the wind, rather than using the wheels to make it go forward. Take all of the wheels off of a car, and try to go somewhere, will it move? No. Take the wheels off of a plane, and try to go somewhere, will it move? Yes.

nbiggershaft · 01-23-2007, 01:53 AM

Originally Posted by Dumpy Dooby

Oh, and yes the plane takes off.

On a side note: I actually used to enjoy going into forums and starting these threads, and then trolling the people that knew what they were talking about. I would make up all sorts of funny shit like "the tires would get really hot and become sticky, causing the plane to stick to the ground and not take off." It was so funny. I won't do that here, though.

It's difficult to explain to people that just don't "get it." But yes, the plane takes off because the wheels freespin. They are only there to keep the plane from hurting its belly. Imagine one of those planes that can take off from the water. Stick some ice on the bottom of those little skis and stick it on a treadmill. Will the treadmill stop it? Probably not. What about the current when the plane is in the water? Does that prevent it from taking off? Not really.

The treadmill would have an impact, but not much because it's pushing/pulling (depending if it's a plane or a jet) against the wind, rather than using the wheels to make it go forward. Take all of the wheels off of a car, and try to go somewhere, will it move? No. Take the wheels off of a plane, and try to go somewhere, will it move? Yes.

Yeah to be honest, I figured everyone had already heard the whole plane on a treadmill thing, I was just going to address a couple more interesting aspects of it through my prof. Namely that friction in bearings is directly related to the angular velocity of the wheels and is not constant.

Kytro · 01-23-2007, 02:20 AM

Originally Posted by ballz2wallz

But if the water was moving so fast it pushed the plane back it woldn't take off fine

Who said the the treadmill pushes the plane back? Unless the treadmill matches wheel speed and not the speed of the aircraft, it will take off.

ballz2wallz · 01-23-2007, 08:57 AM

Originally Posted by Kytro

Who said the the treadmill pushes the plane back? Unless the treadmill matches wheel speed and not the speed of the aircraft, it will take off.

I think it will, because there is friction.

But I'm beginning to see what you guys are saying. I've always hated physics.

7960 · 01-23-2007, 09:48 AM

Originally Posted by Dumpy Dooby

What about the current when the plane is in the water? Does that prevent it from taking off? Not really.

It would if the plane was heading up-river and current was fast enough

ballz2wallz · 01-23-2007, 09:49 AM

Originally Posted by 7960

It would if the plane was heading up-river and current was fast enough

Yeah!

DosEquis · 01-23-2007, 01:18 PM

The only way this airplane is to take off is if the acceleration of the plane is greater than the treadmill. End of story.

The plane falls off the back when you turn it on unless you match acceleration. It is not frictionless. Assuming it was frictionless and take off speed for the airplane is 200 mph. Your treadmill was moving at a constant 50mph, wheels spinning, yet the plane is stationary. Your airplane will still accelerate to 200mph before takeoff, though the wheels will be spinning at the equivilant to 250mph.

You need wind to take off...there is no way around it.

AVengeance · 01-23-2007, 02:58 PM

Originally Posted by ballz2wallz

Look, when the jets propel the plane, how does it move? The wheels...if the plane begins to push forward, but the friction of the tires moves the treadmill under the plane instead of the plane through the air, then it will not create lift. You're thinking of this in the wrong way; yes, you're right, the tires create no friction themselves as there is no engine, but the jet propels the plane across the ground via THE TIRES, friction from the tires on the ground, which gives it enough lift. If the ground moves intead of the plane, there is no lift created!

OMFG, I can't read anymore, or my coworkers are going to wonder WTF is making me laugh so hard.

The wheels have no effect except for friction generated from the fixed-to-rotating parts (bearings) and rotating-to-moving parts (tire to contact patch). For the sake of argument, we'll say that the bearings will generate no friction, and the treadmill and tires have no max speed. Now, tires exploding and bearings seizing aside, the jet will take off just like you would see it take off from a runway. The tires are just there for the weight of the jet to sit on. The jet could just as easily be sitting on a magnetic field, or a cushion of air, and it would still take off the same way.

This is because the propulsion mechanism is in the body of the craft, and not through the wheels.

Dumpy Dooby · 01-23-2007, 05:07 PM

Originally Posted by DosEquis

The only way this airplane is to take off is if the acceleration of the plane is greater than the treadmill. End of story.

That story had a boring ending. 2/10

Dumpy Dooby · 01-23-2007, 05:13 PM

Originally Posted by 7960

It would if the plane was heading up-river and current was fast enough

The current would have to be pretty fucking fast. Even sail boats can go against the current just fine with a fast enough wind, and they have a significantly greater percentage of the craft submerged in the water. Seaplanes only have a couple of skis. Moreover, seaplanes have a propeller.

7960 · 01-23-2007, 05:28 PM

Originally Posted by Dumpy Dooby

The current would have to be pretty fucking fast. Even sail boats can go against the current just fine with a fast enough wind, and they have a significantly greater percentage of the craft submerged in the water. Seaplanes only have a couple of skis. Moreover, seaplanes have a propeller.

Whoa there big guy, I wasn't arguing from a real-life standpoint. I was talking about it in an hypothetical sense. Perhaps "if" wasn't indicative enough for you, but when people say "if [so and so]..." it's generally understood, by us normal English-speaking people, that the person is extending constraints on the situation.

Dumpy Dooby · 01-23-2007, 06:06 PM

Originally Posted by 7960

Whoa there big guy, I wasn't arguing from a real-life standpoint. I was talking about it in an hypothetical sense. Perhaps "if" wasn't indicative enough for you, but when people say "if [so and so]..." it's generally understood, by us normal English-speaking people, that the person is extending constraints on the situation.

(I still love you, bud

)

In any event, "the current would have to be pretty fucking fast."

WickedLou9 · 01-23-2007, 07:26 PM

I saved this from when the issue was on OT.

Yes I wrote this myself.

First off, as for the two variations on this issue. The way I see it, the first one is the only one worth talking about.
The second one presupposes the answer. In the second variation, the question tells you that the treadmill prevents forward motion
by spinning at any speed necessary. As any elementary school student will tell you, unless a plane moves it can't fly.
That is aside from the obvious problem of the wheels exceding thier maximum rated speed and turning into burning heaps of metal and
rubber leading to the ultimate destruction of the plane itself as it falls onto the runway, which itself, is moving at speeds well above
anything I would consider rational. So with that aside, I will address question #1

This is a fairly simple physics problem if you know what the important factors are...

For one, you need to understand what a force vector is. A force vector is a force that has both a maganitude and a direction.
When you have 2 seperate forces you add them together and come up with a resultant force vector.. like the following:

http://users.iafrica.com/m/ms/mshenker/assets/images/Vector_402.jpg

Fv is the force pulling upwards. Fh is the force pulling forward and Fr is the resultant force vector. Fr indicates the direction
that an object , if forces v and h were both acting on it, would be accelerated towards.

It might be obvious but please notice that we are not adding speeds here. We are simply looking at two distinct forces acting on the
object and coming up with thier net result. Once you have that net result you can determine the rate of acceleration and thus the speed
of the object at any point in time.

Ok, so in the problem of the plane on a treadmill we have an object. The object happens to be a jet plane but that's not really all that
important. The essential question is, given two forces acting on the object, can the object move and if so, which direction?

To understand the forces acting on the plane we need to know a couple of things about it. One is the jet engine.
The jet engine works by accelerating air in one direction and thus pushing the plane in the other direction. Newton 's law. Every action
has an equal and opposite reaction. Jet engine blows air out in one direction, the engine pushes the plane in the other. Simple enough.

The force from the Jet engine is considerable. Just for the sake of specifics lets use an F-16.
The engine in an F-16 can provide 27,000 pounds of thrust.
So lets call the force from the engine 'F1'.
F1 = 27,000 lbs

What other forces are acting on the plane?

Well there are probably a few such as gravity, but the only one we are concerned with is the force being applied by the treadmill.

Since the wheels on the plane are "free rolling" the only force that the treadmill can apply is through friction in the bearings themselves
and through the 'moment of intertia' in the wheels. The 'moment of intertia' refers to the force it takes to spin the wheels faster and
faster. If you have ever put a bicycle upside-down and tried to pedal it as fast as you could you know what this force is.
Once you get the wheel spinning really fast it gets harder and harder to make the wheel spin any faster, even though there is nothing