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re: Myth Busters/Can a plane take off on a conveyor belt
Posted on 12/6/07 at 10:41 am to Colonel Hapablap
Posted on 12/6/07 at 10:41 am to Colonel Hapablap
Also consider that friction is defined as something that opposes movement
In the case of the conveyor belt, the belt at the point of contact with the wheels is actually encouraging the wheels to move in the direction they're in. So you might have losses in kinetic friction as well.
For example, consider the following figure:
If you're looking at a 2D picture of a plane going left to right, the rotational motion of the wheels will be clockwise as it is in the picture. If the belt is moving left (opposite linear direction of the plane as described in the problem) then at the tangential point on the wheel it's actually going the same direction, so it could essentially be reducing the friction compared to what you would expect with a regular run way.
Of course this would have to assume that the belt was made of a material with the same physical properties of the concrete.
In the case of the conveyor belt, the belt at the point of contact with the wheels is actually encouraging the wheels to move in the direction they're in. So you might have losses in kinetic friction as well.
For example, consider the following figure:
If you're looking at a 2D picture of a plane going left to right, the rotational motion of the wheels will be clockwise as it is in the picture. If the belt is moving left (opposite linear direction of the plane as described in the problem) then at the tangential point on the wheel it's actually going the same direction, so it could essentially be reducing the friction compared to what you would expect with a regular run way.
Of course this would have to assume that the belt was made of a material with the same physical properties of the concrete.
Posted on 12/6/07 at 10:46 am to Powerman
quote:
Of course this would have to assume that the belt was made of a material with the same physical properties of the concrete.
I think it's safe to say that won't be the case. Either way it'll be largely inconsequential to the problem, I think.
Posted on 12/6/07 at 10:47 am to Powerman
Not sure I buy that. Friction between the wheel and the surface is static. Internal friction in the wheel will oppose the rotation of the wheel. Maybe I'm misunderstanding you.
Posted on 12/6/07 at 10:48 am to LSUBoo
No air going across the wings means no lift which means no take off.
Duh
Duh
Posted on 12/6/07 at 10:49 am to Colonel Hapablap
quote:
Can we get a tally of all the people who don't think it'll fly? On page 12:
VanRich
Coco
diat150
MulesAFPilot (he gets extra points since he's a pilot)
SCTiger
SG_Geaux
Dale Murphy
Who else? We intend to make fun of you when the plane takes off...
penthouse (more bonus points, assuming he's not lying in his profile...)
ETA: oh, and faxis apparently.
This post was edited on 12/6/07 at 10:50 am
Posted on 12/6/07 at 10:49 am to Powerman
quote:
Also consider that friction is defined as something that opposes movement
In the case of the conveyor belt, the belt at the point of contact with the wheels is actually encouraging the wheels to move in the direction they're in. So you might have losses in kinetic friction as well.
For example, consider the following figure:
If you're looking at a 2D picture of a plane going left to right, the rotational motion of the wheels will be clockwise as it is in the picture. If the belt is moving left (opposite linear direction of the plane as described in the problem) then at the tangential point on the wheel it's actually going the same direction, so it could essentially be reducing the friction compared to what you would expect with a regular run way.
Of course this would have to assume that the belt was made of a material with the same physical properties of the concrete.
I think you may be over thinking it. Notwithstanding any differences in material make-up of the surfaces, the wheels moving over tarmac won't be any different than the wheels moving over the conveyor belt, except for speed.
Regarding the start-up (static versus kinetic friction) it depends on when you start the experiment - at the point the conveyor is turned on, or after it is already turning.
Posted on 12/6/07 at 10:50 am to Colonel Hapablap
quote:
Friction between the wheel and the surface is static. Internal friction in the wheel will oppose the rotation of the wheel.
That's what I was thinking, as well.
Posted on 12/6/07 at 10:51 am to LSUBoo
updatedAs of page 15:
Colonel Hapablap
just me
Powerman
LSUBoo
aggie dude who started the thread
Putty
Jimbeaux
---karma line---
VanRich
Coco
diat150
MulesAFPilot (he gets extra points since he's a pilot)
SCTiger
SG_Geaux
Dale Murphy
faxis
penthouse (extra points here as well)
there was another pilot in the list too.
Colonel Hapablap
just me
Powerman
LSUBoo
aggie dude who started the thread
Putty
Jimbeaux
---karma line---
VanRich
Coco
diat150
MulesAFPilot (he gets extra points since he's a pilot)
SCTiger
SG_Geaux
Dale Murphy
faxis
penthouse (extra points here as well)
there was another pilot in the list too.
This post was edited on 12/6/07 at 10:53 am
Posted on 12/6/07 at 10:53 am to Colonel Hapablap
quote:
Friction between the wheel and the surface is static
Sure, while it's not moving
As soon as it's moving, it's kinetic
quote:
Internal friction in the wheel will oppose the rotation of the wheel. Maybe I'm misunderstanding you.
Sure the internal friction will oppose it, just like it would without the belt. But if you apply external force, there is no reason why the wheels wouldn't move faster.
Think of it as putting your ceiling fan on low and then hitting it really hard to try to make it go faster. Except in this case the force is continuous.
Say you're testing bearings on a car(or tires or whatever...what you're testing doesn't matter). Maybe you'd have some device that would lift the car up and keep it in place but with the wheels at the contact of a conveyor belt with the car in neutral and turned off. Obviously there is friction but with enough force(in this case from a conveyor belt of sorts), the wheels will turn right?
Posted on 12/6/07 at 10:53 am to LSUBoo
I'm starting to get nervous about flying. I think that the only pilot who understands this so far is Az, and he's too old to drive, much less fly.
Posted on 12/6/07 at 10:54 am to Jimbeaux
It's SITTING STILL.
There is no lift being generated by the wings.
It could be an F15 in full burn and as long as the treadmill matches the thrust in the opposite direction, IT'S SITTING STILL.
That's all that matters.
Now if you put a fan in front of it while it's doing all this and you crank that fan up to an airspeed where the plane is capable of lift, it will take off. But with no air going over the wings, it's not going anywhere.
There is no lift being generated by the wings.
It could be an F15 in full burn and as long as the treadmill matches the thrust in the opposite direction, IT'S SITTING STILL.
That's all that matters.
Now if you put a fan in front of it while it's doing all this and you crank that fan up to an airspeed where the plane is capable of lift, it will take off. But with no air going over the wings, it's not going anywhere.
Posted on 12/6/07 at 10:54 am to Putty
quote:
very, very good analogy . . . can a sea plane take off upriver
agreed, that's a great analogy... not exactly the same, but the same premise.
Posted on 12/6/07 at 10:56 am to Powerman
quote:
Sure, while it's not moving
As soon as it's moving, it's kinetic
negative, the contact between the wheels and the surface is static unless the plane starts to slide. That's the whole beauty of a wheel.
quote:
Sure the internal friction will oppose it, just like it would without the belt. But if you apply external force, there is no reason why the wheels wouldn't move faster.
Agreed, but I think that the faster rotation just increases the internal frictional force, right?
Posted on 12/6/07 at 10:56 am to Powerman
By the way Powerman, I don't think you're an a-hole and certainly not a complete a-hole.
Posted on 12/6/07 at 10:58 am to Colonel Hapablap
quote:
---karma line---
I'm famous!
Posted on 12/6/07 at 11:01 am to Putty
quote:
very, very good analogy . . . can a sea plane take off upriver
I would think it can, as long as it is able to produce enough power to overcome the river current and generate the needed takeoff speed.
I give up trying to make heads or tails of the arguement. My gut reaction is that an airplane cannot take off from a treadmill/conveyer that is able to match the forward speed of the aircraft. However, knowing Mythbusters they will do it.
Posted on 12/6/07 at 11:01 am to Colonel Hapablap
quote:
negative, the contact between the wheels and the surface is static unless the plane starts to slide. That's the whole beauty of a wheel.
I'll take your word for it but I'm a bit skeptical
quote:
Agreed, but I think that the faster rotation just increases the internal frictional force, right?
It will increase the heat, but I'm not sure if it will increase the frictional force.
shite you might be right. I think kinetic friction can be a function of speed. But we're talking about a jet engine so it would be enough to overcome that friction.
Where you might run into a problem is that the bearings on the wheels would be moving much faster than they're designed and couldn't withstand the heat and you could damage the bearings. But assuming they could withstand the extra heat at high speeds, I think everything would work out
Posted on 12/6/07 at 11:04 am to ags01
quote:
If a plane is traveling at takeoff speed
There's the whole key that I think was not placed in the wording when this problem was put on the O-T a long time ago. We didn't know if the conveyor belt was matching the wheel spin.
If the conveyor belt matches the wheel spin, the plane is stationary and doesn't take off because there is no lift created over the wings.
But in this case, the plane is traveling at takeoff speed, so it doesn't matter what the wheels and conveyor belt is doing. Wind over the wings causes lift, and the plane takes off.
Posted on 12/6/07 at 11:07 am to PJinAtl
quote:
as long as it is able to produce enough power to overcome the river current
that is one factor ... to be a "true" analogy, the river would be moving at a rate of flow equal to takeoff speed ... but, in theory, that is irrelevant
as soon as the plane is able to counteract the opposite force, whatever that may be, forward motion, postitive ground speed, and lift is achieved...after that, it's all just a matter of degree
the obvious flaw with the seaplane example is the much much greater friction of the water and the question as to whether the thrust of the plane would be sufficient to overcome this and move forward
Posted on 12/6/07 at 11:11 am to faxis
quote:
It's SITTING STILL.
There is no lift being generated by the wings.
It could be an F15 in full burn and as long as the treadmill matches the thrust in the opposite direction, IT'S SITTING STILL.
That's all that matters.
Now if you put a fan in front of it while it's doing all this and you crank that fan up to an airspeed where the plane is capable of lift, it will take off. But with no air going over the wings, it's not going anywhere.
Why do you think the plane will be sitting still?
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