You have a plane and a conveyor belt.

[cKGunslinger]

Originally posted by: themorningbells
Is the question essentially: if a plane was able to remain stationary, yet spin up its engines to a speed/thrust output sufficient for ordinary take off, could it then achieve flight?

Gods no! The whole point is that the plane *doesn't* remain stationary, it moves across the surface of the treadmill just as it would the ground, as the force created by its jets doesn't not care how fast the wheels on the bottom of the plane are spinning - it's pushing the plane forward.

Like has been said before. Turn on your treadmill at home. Get a toy car. Push it along the treadmill. Was it impossible? Even if the treadmill was going "really" fast? No, your hand it not affected by the treadmill, only the wheels of the car are, but they are not providing the mechanism for movement.

 

[Schfifty Five]

Originally posted by: cKGunslinger

Originally posted by: HeroOfPellinor

The wheels aren't. The conveyer belt is. The air passing over the wing is creating upward thrust, but to actually get the plane off the ground so it can begin using air as friction rather than the landing strip it needs to grip something to pull itself along.

Heh, I see those 3 college Logic classes you bandy about have failed you yet again. :laugh:

Perhaps if you had ditched one and went and played a game of billiards at the pool hall, you would have learned a bit more, like the concept of putting "draw" on the cue - hitting the ball such that it spins backwards, yet travels forward.

But how can that be! According to you, in order for an object to move forward it must have enough grip to pull itself along! Zounds!

Originally posted by: PurdueRy
before believe so strongly in this....draw the FBD

Quick Purdue, ask him how many Physics classes he took in college! That's how he believes all arguments can be resolved. :laugh:

haha nice

 

[PurdueRy]

Originally posted by: HeroOfPellinor

Originally posted by: PurdueRy

before believe so strongly in this....draw the FBD

I don't believe so strongly in this. I might be wrong. But I think the analogy of the rollerblader on the treadmill, on which you're all basing your arguments is wrong.

Take a guy standing on a treadmill wearing street shoes. Now there's a guy standing on the ground infront of him and he pulls the guy on the treadmill using a rope. The guy on the treadmill moves the conveyer belt forward as he's pulled forward. That's the "extra" affect induced on the rollerblader on the treadmill. The wheels aren't being turned any faster than the treadmill, but the treadmill itself is being turned.

Why do we care about a guy wearing street shoes? The plane has wheels! In basic mechanics you learn that when you draw the FBD for rollers...all there is is a normal force...no x component whatsoever

 

[Squisher]

Originally posted by: jagec
This thread (a)delivers, and (b)destroys my faith in humanity.

I thought more of ATOT, woe is me.

 

[themorningbells]

Originally posted by: cKGunslinger

Originally posted by: themorningbells
Is the question essentially: if a plane was able to remain stationary, yet spin up its engines to a speed/thrust output sufficient for ordinary take off, could it then achieve flight?

Gods no! The whole point is that the plane *doesn't* remain stationary, it moves across the surface of the treadmill just as it would the ground, as the force created by its jets doesn't not care how fast the wheels on the bottom of the plane are spinning - it's pushing the plane forward.

Like has been said before. Turn on your treadmill at home. Get a toy car. Push it along the treadmill. Was it impossible? Even if the treadmill was going "really" fast? No, your hand it not affected by the treadmill, only the wheels of the car are, but they are not providing the mechanism for movement.

So you're saying the plane is not remaining stationary in space? I thought that was the whole stipulation to the setup of this question (i.e. the conveyor belt accounts for any forward movement of the plane, and holds it stationary in space). If the plane can gain ground on the conveyor belts backward movement, this whole question is null.

 

[kevinthenerd]

Originally posted by: cKGunslinger

Originally posted by: HeroOfPellinor

The wheels aren't. The conveyer belt is. The air passing over the wing is creating upward thrust, but to actually get the plane off the ground so it can begin using air as friction rather than the landing strip it needs to grip something to pull itself along.

Heh, I see those 3 college Logic classes you bandy about have failed you yet again. :laugh:

Perhaps if you had ditched one and went and played a game of billiards at the pool hall, you would have learned a bit more, like the concept of putting "draw" on the cue - hitting the ball such that it spins backwards, yet travels forward.

But how can that be! According to you, in order for an object to move forward it must have enough grip to pull itself along! Zounds!

Originally posted by: PurdueRy
before believe so strongly in this....draw the FBD

Quick Purdue, ask him how many Physics classes he took in college! That's how he believes all arguments can be resolved. :laugh:

I'm not defending anybody's position, but never make fun of classes in the subject of physics. Physics is the core of engineering, and without engineering, you're never going to have airplanes and treadmills in the first place.

 

[PurdueRy]

Originally posted by: themorningbells

Originally posted by: cKGunslinger

Originally posted by: themorningbells
Is the question essentially: if a plane was able to remain stationary, yet spin up its engines to a speed/thrust output sufficient for ordinary take off, could it then achieve flight?

Gods no! The whole point is that the plane *doesn't* remain stationary, it moves across the surface of the treadmill just as it would the ground, as the force created by its jets doesn't not care how fast the wheels on the bottom of the plane are spinning - it's pushing the plane forward.

Like has been said before. Turn on your treadmill at home. Get a toy car. Push it along the treadmill. Was it impossible? Even if the treadmill was going "really" fast? No, your hand it not affected by the treadmill, only the wheels of the car are, but they are not providing the mechanism for movement.

So you're saying the plane is not remaining stationary in space? I thought that was the whole stipulation to the setup of this question (i.e. the conveyor belt accounts for any forward movement of the plane, and holds it stationary in space). If the plane can gain ground on the conveyor belts backward movement, this whole question is null.

not quite Your having the same problem right now. Draw the FBD...it will help you

 

[GuitarDaddy]

The conveyor belt has about as much chance preventing the plane from taking off as I do of stoping this thread

 

[Rogodin2]

If that is the question as I understand it, I think that it could get of the ground, but its nose would immediately go slamming back down into the ground because of the huge force being exerted upon it all at once. I think that it having no momentum before building up to such a violent thrust would have a serious impact. I believe it's similar to having your head out a window in a car, and the car accelerating from 0-80 in a span of 30 seconds vs. accelerating from 0-80 instantly.

The plane will stay in flight, there is no huge force all at once. The plane would take off as normal.

Rogo

 

[kevinthenerd]

Problem 1, as stated all over the Internet: The belt compensates for the linear movement of the airplane. The plane takes off, no problem.
Problem 2, as stated by the OP: The belt compensates for the rotation of the wheels. The belt accelerates rapidly to fight the rotational inertia. The plane stays put.

/thread

 

[Armitage]

Originally posted by: NanoStuff
If it's true that a jet engine can defy the laws of physics like some here believe to be the case, maybe the space shuttle SHOULD have it.

Please explain? What has been said about jet engines that violates the laws of physics?

 

[jagec]

Originally posted by: themorningbells
So you're saying the plane is not remaining stationary in space? I thought that was the whole stipulation to the setup of this question (i.e. the conveyor belt accounts for any forward movement of the plane, and holds it stationary in space). If the plane can gain ground on the conveyor belts backward movement, this whole question is null.

The OP subtly suggests that the plane remains stationary, but it's a trap. Part of the "test" is determining whether physics allows a plane to roll forward on a backwards-moving treadmill, and it does.

 

[jagec]

Originally posted by: kevinthenerd
Problem 1, as stated all over the Internet: The belt compensates for the linear movement of the airplane. The plane takes off, no problem.
Problem 2, as stated by the OP: The belt compensates for the rotation of the wheels. The belt accelerates rapidly to fight the rotational inertia. The plane stays put.

/thread

This is the only part I disagree with. The rest is true.

 

[Armitage]

Originally posted by: HeroOfPellinor

Originally posted by: PurdueRy

Originally posted by: HeroOfPellinor

Originally posted by: PurdueRy

Originally posted by: HeroOfPellinor

Originally posted by: Rogodin2
I think the main problem is that people aren't able to picture the plane moving forward on a treadmill that is moving in the opposite direction.

So, let's make is a little easier and visualize a person (on rollerblades) on a 6' long foot tread mill (treadmill moving in reverse) holding a rope tied to a 1/4 scale RC airplane. Once the RC Plane is started and the engine at wto and the person holding the rope attached to the plane they will be moved forward regardless of how fast the tread mill is moving in reverse. This is because the RC Plane is providing the forward momentum.

Don't know if this helps.

Rogo

Possibly. But I'm not sure that's a valid analogy. If you replace the RC plane with somebody standing on a treadmill, that might be more accurate. The purson on the treadmill couldn't pull the rollerblader forward without some friction.

Does a model rocket need friction to take off?

That's a different form of propulsion. Take a helicopter. It does need friction. Air creates friction...just ask the feather.

Can you run hovering in zero gravity?

I am picturing a jet aircraft. However, I am interested how the wheels provide a force to the ground that equals the forward force the engines generate...Can you explain that? Because that is what you are implying

The wheels aren't. The conveyer belt is

Here's the thing about wheels - they roll. They conveyor belt can only exert a vertical force on the wheel equal to the planes weight (if everything is at rest).

The air passing over the wing is creating upward thrust, but to actually get the plane off the ground so it can begin using air as friction rather than the landing strip it needs to grip something to pull itself along.

I don't even know where to begin with this. It's like somebody claiming that ... hell I can't even come up with a sufficiently bizarra analogy.

Ok, step by step...
The air passing over the wing is creating upward thrust

Ok, the only thing I can't argue with. Air flowing over a wing creates a force - commonly referred to as lift.

but to actually get the plane off the ground so it can begin using air as friction rather than the landing strip

What is all this friction about? A wing doesn't generate lift via friction. A plane doesn't move forward via friction. A propellor is just a wing, but its lift is oriented forward. A just pushes air out the back - momentum is conserved so the plane moves forward. Nowhere does friction come into play. It doesn't pull itself through the air by friction, it doesn't pull itself along the runway by friction.

The wing behind the turbine would create lift, but not acceleration.

The wing would create lift, but it has absolutely nothing to do with its position relative to the engines.

In the rollerblader analogy. How does the rollerblader get pulled off the treadmill by the RC plane if the wheels never exceed the speed of the treadmill. Imagine instead of slippery wheels, you've got interlocking tractor treads.

I'm also still waiting for the relavence of the space shuttle engine comment.

Either your a troll, or you don't have even the most rudimentary grasp of physics. It must be strange to live in your world and see everything happen as if by magic.

 

[cKGunslinger]

Originally posted by: kevinthenerd
I'm not defending anybody's position, but never make fun of classes in the subject of physics. Physics is the core of engineering, and without engineering, you're never going to have airplanes and treadmills in the first place.

I believe my joke went straight over your head there, "kevin."

 

[mugs]

Originally posted by: kevinthenerd
Problem 1, as stated all over the Internet: The belt compensates for the linear movement of the airplane. The plane takes off, no problem.
Problem 2, as stated by the OP: The belt compensates for the rotation of the wheels. The belt accelerates rapidly to fight the rotational inertia. The plane stays put.

/thread

"Problem 2" describes an impossible situation, because the conveyor belt is not capable of holding the plane in space no matter how fast it moves, and that is the ONLY way the speed of the belt can be the same as the rotational speed of the wheels.

 

[jagec]

Originally posted by: mugs

Originally posted by: kevinthenerd
Problem 1, as stated all over the Internet: The belt compensates for the linear movement of the airplane. The plane takes off, no problem.
Problem 2, as stated by the OP: The belt compensates for the rotation of the wheels. The belt accelerates rapidly to fight the rotational inertia. The plane stays put.

/thread

"Problem 2" describes an impossible situation, because the conveyor belt is not capable of holding the plane in space no matter how fast it moves, and that is the ONLY way the speed of the belt can be the same as the rotational speed of the wheels.

Actually, that's not true. A conveyor IS capable of holding a plane steady with respect to the ground, but that's not the control system described in the OP.

 

[mugs]

Originally posted by: jagec

Originally posted by: mugs

Originally posted by: kevinthenerd
Problem 1, as stated all over the Internet: The belt compensates for the linear movement of the airplane. The plane takes off, no problem.
Problem 2, as stated by the OP: The belt compensates for the rotation of the wheels. The belt accelerates rapidly to fight the rotational inertia. The plane stays put.

/thread

"Problem 2" describes an impossible situation, because the conveyor belt is not capable of holding the plane in space no matter how fast it moves, and that is the ONLY way the speed of the belt can be the same as the rotational speed of the wheels.

Actually, that's not true. A conveyor IS capable of holding a plane steady with respect to the ground, but that's not the control system described in the OP.

Only if the plane's engines are so weak that it can't move on solid ground.

Again, the friction in the wheels is not dependent on the speed at which they are rotating, so the treadmill can rotate as fast as it wants and it won't overcome the thrust of the engines.

 

[jagec]

Originally posted by: mugs
Only if the plane's engines are so weak that it can't move on solid ground.

Again, the friction in the wheels is not dependent on the speed at which they are rotating, so the treadmill can rotate as fast as it wants and it won't overcome the thrust of the engines.

You can't overcome the rotational inertia of the wheels. That inertia provides a counter-torque to the force of the plane, and that torque depends on acceleration. In other words, you can keep the plane stationary as long as the conveyor can keep accelerating, but eventually the plane will run out of fuel and the system stabilize. I calculated it for a Cessna WAAAAY back in this thread; it's roughly 2000 kph IIRC.

Why do you think this thread has gone on for so long? It's not as cut-and-dried and it seems. Though I think most of the "will take off" people have a better grasp of WHY they're right, the "won't take off" people are right as well, in a way.

 

[PurdueRy]

Originally posted by: jagec

Originally posted by: mugs
Only if the plane's engines are so weak that it can't move on solid ground.

Again, the friction in the wheels is not dependent on the speed at which they are rotating, so the treadmill can rotate as fast as it wants and it won't overcome the thrust of the engines.

You can't overcome the rotational inertia of the wheels. That inertia provides a counter-torque to the force of the plane, and that torque depends on acceleration. In other words, you can keep the plane stationary as long as the conveyor can keep accelerating, but eventually the plane will run out of fuel and the system stabilize. I calculated it for a Cessna WAAAAY back in this thread; it's roughly 2000 kph IIRC.

Why do you think this thread has gone on for so long? It's not as cut-and-dried and it seems. Though I think most of the "will take off" people have a better grasp of WHY they're right, the "won't take off" people are right as well, in a way.

except they don't offer the rotational inertia explanation....

 

[jagec]

Originally posted by: PurdueRy

Originally posted by: jagec

Originally posted by: mugs
Only if the plane's engines are so weak that it can't move on solid ground.

Again, the friction in the wheels is not dependent on the speed at which they are rotating, so the treadmill can rotate as fast as it wants and it won't overcome the thrust of the engines.

You can't overcome the rotational inertia of the wheels. That inertia provides a counter-torque to the force of the plane, and that torque depends on acceleration. In other words, you can keep the plane stationary as long as the conveyor can keep accelerating, but eventually the plane will run out of fuel and the system stabilize. I calculated it for a Cessna WAAAAY back in this thread; it's roughly 2000 kph IIRC.

Why do you think this thread has gone on for so long? It's not as cut-and-dried and it seems. Though I think most of the "will take off" people have a better grasp of WHY they're right, the "won't take off" people are right as well, in a way.

except they don't offer the rotational inertia explanation....

yes, I doubt any of them (except for kevinthenerd) realize WHY they're right. In fact, they're right in a way that makes them wrong.

 

[mugs]

Originally posted by: jagec

Originally posted by: mugs
Only if the plane's engines are so weak that it can't move on solid ground.

Again, the friction in the wheels is not dependent on the speed at which they are rotating, so the treadmill can rotate as fast as it wants and it won't overcome the thrust of the engines.

You can't overcome the rotational inertia of the wheels. That inertia provides a counter-torque to the force of the plane, and that torque depends on acceleration. In other words, you can keep the plane stationary as long as the conveyor can keep accelerating, but eventually the plane will run out of fuel and the system stabilize. I calculated it for a Cessna WAAAAY back in this thread; it's roughly 2000 kph IIRC.

Why do you think this thread has gone on for so long? It's not as cut-and-dried and it seems. Though I think most of the "will take off" people have a better grasp of WHY they're right, the "won't take off" people are right as well, in a way.

Ah, good point.

 

[spidey07]

Originally posted by: PurdueRy
post #1000!

People need to stop thinking the conveyor imparts a large force on the body of the aircraft...but I have a feeling that would solve nothing

I could easily build a conveyor that would hold your plane back.

You're not thinking big picture here man.

The best analogy so far is pushing against a toy car on a treadmill with your finger and feel the force of gravity/friction.

It all comes down to the force of the treadmill vs. the motor.

 

[jagec]

Originally posted by: spidey07

Originally posted by: PurdueRy
post #1000!

People need to stop thinking the conveyor imparts a large force on the body of the aircraft...but I have a feeling that would solve nothing

I could easily build a conveyor that would hold your plane back.

You're not thinking big picture here man.

The best analogy so far is pushing against a toy car on a treadmill with your finger and feel the force of gravity/friction.

It all comes down to the force of the treadmill vs. the motor.

The question isn't "CAN you make a treadmill keep a plane from taking off" The answer to that is indeed "yes". The conveyor, as described in the OP, doesn't impart enough force to the aircraft to keep it from taking off. A simple reworking of the control system could change that.

 

[MrPickins]

Originally posted by: jagec

Originally posted by: mugs
Only if the plane's engines are so weak that it can't move on solid ground.

Again, the friction in the wheels is not dependent on the speed at which they are rotating, so the treadmill can rotate as fast as it wants and it won't overcome the thrust of the engines.

You can't overcome the rotational inertia of the wheels. That inertia provides a counter-torque to the force of the plane, and that torque depends on acceleration. In other words, you can keep the plane stationary as long as the conveyor can keep accelerating, but eventually the plane will run out of fuel and the system stabilize. I calculated it for a Cessna WAAAAY back in this thread; it's roughly 2000 kph IIRC.

Why do you think this thread has gone on for so long? It's not as cut-and-dried and it seems. Though I think most of the "will take off" people have a better grasp of WHY they're right, the "won't take off" people are right as well, in a way.

Wouldn't overcoming the rotational inertia equate to the tires breaking traction with the conveyor belt and, if there is enough thurst from the engines, skidding forward relative to the belt?

I'm still trying to visualize what factoring rotational inertia throws into the mix.