Re: CyBookie - Plane on a Treadmill
Yes, but those forces are negligible compared to the force of this:
Yes, but those forces are negligible compared to the force of this:
Plane on a Treadmill
- Thread starter Warder60
- Start date
- Status
Re: CyBookie - Plane on a Treadmill
This is an interesting problem. Someone ask Dr. Haan next time you see him.
I can see why both are a possibility. If we're talking a perfect treadmill and perfect wheels, the thrust could be exactly cancelled by the forces of the wheels. In the ideal system, the velocities cancel, meaning the plane stays in the exact same place. No movement means no airflow, no airflow means no lift. Think of it another way. Get rid of the treadmill and put infinitely strong chalks under the wheels, so that the plane can't move. Throttle up all the way and rip off the wheels. Does the plane take off? Depends on whether the thrust being generated by the engines is large enough to give the aircraft enough forward velocity (ergo lift) before it hits the ground.
The thing that makes me think that it would take off is the real effects. I'm beginning to wonder if the treadmill itself wouldn't generate the airflow. I mean, if it's infinitely long, how thick is the boundary layer going to be? Like it or not, there is air moving close to the treadmill to satisfy continuity. If the boundary layer is thicker than the height of the wings, we're going to get takeoff.
Garbage like this is why I do Orbital Mechanics. You people can take your small mean free path and stick it where the sun don't shine.
This is an interesting problem. Someone ask Dr. Haan next time you see him.
I can see why both are a possibility. If we're talking a perfect treadmill and perfect wheels, the thrust could be exactly cancelled by the forces of the wheels. In the ideal system, the velocities cancel, meaning the plane stays in the exact same place. No movement means no airflow, no airflow means no lift. Think of it another way. Get rid of the treadmill and put infinitely strong chalks under the wheels, so that the plane can't move. Throttle up all the way and rip off the wheels. Does the plane take off? Depends on whether the thrust being generated by the engines is large enough to give the aircraft enough forward velocity (ergo lift) before it hits the ground.
The thing that makes me think that it would take off is the real effects. I'm beginning to wonder if the treadmill itself wouldn't generate the airflow. I mean, if it's infinitely long, how thick is the boundary layer going to be? Like it or not, there is air moving close to the treadmill to satisfy continuity. If the boundary layer is thicker than the height of the wings, we're going to get takeoff.
Garbage like this is why I do Orbital Mechanics. You people can take your small mean free path and stick it where the sun don't shine.
Re: CyBookie - Plane on a Treadmill
To me tis is a completely different problem. Here you're actually preventing the wheels from moving, where in the treadmill exercise you're only requiring them to spin twice as fast.
To me tis is a completely different problem. Here you're actually preventing the wheels from moving, where in the treadmill exercise you're only requiring them to spin twice as fast.
Re: CyBookie - Plane on a Treadmill
I mean, there obviously is a point at which you can develop a wheel system that has enough friction to overcome the forward thrust of the engines, in theory.
OK, what if the aircraft's brakes are applied to increase the coefficient of friction?
I mean, there obviously is a point at which you can develop a wheel system that has enough friction to overcome the forward thrust of the engines, in theory.
Re: CyBookie - Plane on a Treadmill
Is it, though? The original problem stated the treadmill can match the speed of the airplane. You're just putting the forces on the wheels on steroids.
Is it, though? The original problem stated the treadmill can match the speed of the airplane. You're just putting the forces on the wheels on steroids.
Re: CyBookie - Plane on a Treadmill
It would be interesting to see what kind of response you'd get if you told a bunch of seasoned aircraft engineers that rolling resistance is negligible...
It would be interesting to see what kind of response you'd get if you told a bunch of seasoned aircraft engineers that rolling resistance is negligible...
Re: CyBookie - Plane on a Treadmill
Somebody go to the gym. Start running real fast on a treadmill and then extend you arms out and report back to us "what you feel".
I don't see how lift is generated - but I also don't know how you'd get any sort of device to act as a treadmill at such speeds.
FWIW - I think in many planes you can push the engines to near take off speed while the landing gear is locked (see aircraft carrier jets). yet nothing happens and the plane remains stationary.
Somebody go to the gym. Start running real fast on a treadmill and then extend you arms out and report back to us "what you feel".
I don't see how lift is generated - but I also don't know how you'd get any sort of device to act as a treadmill at such speeds.
FWIW - I think in many planes you can push the engines to near take off speed while the landing gear is locked (see aircraft carrier jets). yet nothing happens and the plane remains stationary.
Re: CyBookie - Plane on a Treadmill
If you're running on a treadmill and someone pushes you in the back, do you fall forward?
If you're running on a treadmill and someone pushes you in the back, do you fall forward?
Re: CyBookie - Plane on a Treadmill
Edit: disregard...... I changed my mind in a later post.
Some of you are making this way too hard. Bottom line is if the plane has no forward motion, it can never take off. No matter what is providing the motion.... wheels, prop, turbine, etc..... if it sits still relative to the air around it, it will not develop lift. The lift is provided by the differential air flow over the top vs. bottom fo the wings. End of story.
It's a very simple problem, but you have to define the assumptions first. No forward motion equals no lift off.
Edit: disregard...... I changed my mind in a later post.
Some of you are making this way too hard. Bottom line is if the plane has no forward motion, it can never take off. No matter what is providing the motion.... wheels, prop, turbine, etc..... if it sits still relative to the air around it, it will not develop lift. The lift is provided by the differential air flow over the top vs. bottom fo the wings. End of story.
It's a very simple problem, but you have to define the assumptions first. No forward motion equals no lift off.
Last edited:
Re: CyBookie - Plane on a Treadmill
Exactly...it's not a difficult question. The plane will not fly. Quite simple infact.
People just like the debate, but it is really a fundamental answer and the answer is no take off.
Exactly...it's not a difficult question. The plane will not fly. Quite simple infact.
People just like the debate, but it is really a fundamental answer and the answer is no take off.
Re: CyBookie - Plane on a Treadmill
You're oversimplifying the problem. If the airplane were driven from the wheels, the treadmill would move when the wheels pushed against it, providing no forward movement.
It's pulled (or pushed) by a propeller or pushed by a jet engine, so it doesn't need the traction between the wheels and the ground to move forward. The question then is, what effect does the moving treadmill have on the plane? Is the effect enough to keep the plane stationary. If not, is the plane capable of taking off (at which point the treadmill would presumably have no effect on the aircraft)?
You're oversimplifying the problem. If the airplane were driven from the wheels, the treadmill would move when the wheels pushed against it, providing no forward movement.
It's pulled (or pushed) by a propeller or pushed by a jet engine, so it doesn't need the traction between the wheels and the ground to move forward. The question then is, what effect does the moving treadmill have on the plane? Is the effect enough to keep the plane stationary. If not, is the plane capable of taking off (at which point the treadmill would presumably have no effect on the aircraft)?
Re: CyBookie - Plane on a Treadmill
Please explain how a treadmill is going to overcome thousands of pounds of thrust from jet engines.
Your answer would be correct if a plane were driven by its wheels, but it is not.
Please explain how a treadmill is going to overcome thousands of pounds of thrust from jet engines.
Your answer would be correct if a plane were driven by its wheels, but it is not.
Re: CyBookie - Plane on a Treadmill
[edit] I am very curious as to how they are going to create a treadmill that large. In reality they could just have a similar effect by just blocking the wheels.
I concur with this for the record. Planes require lift from the wings to generate lift. No movement relative to the air means no lift, unless you direct the engine thrust down rather than backwards like in a Harrier.
[edit] I am very curious as to how they are going to create a treadmill that large. In reality they could just have a similar effect by just blocking the wheels.
Last edited:
Re: CyBookie - Plane on a Treadmill
Edit: disregard...... I changed my mind in a later post.
Edit: disregard...... I changed my mind in a later post.
Last edited:
Re: CyBookie - Plane on a Treadmill
Edit: disregard...... I changed my mind in a later post.
.
Edit: disregard...... I changed my mind in a later post.
.
Last edited:
Re: CyBookie - Plane on a Treadmill
I agree, this experiment may be impossible......
But, if it were possible to have a plane on a treadmill that kept the plane perfectly stationary relative to the air and the ground around it, there is no way it would take off. This is really a simple question that has been answered several times in this thread.
The only way you could get a stationary (relative to the ground) airplane to take off is by generating very high winds blowing directly into the nose of the plane. This would simulate the aircraft going fast down the runway (I don't know how fast they need to be going) and would allow take off. As soon as the plane left the artificial airflow it would come down. In the fake wind it would be like a glider.
I agree, this experiment may be impossible......
But, if it were possible to have a plane on a treadmill that kept the plane perfectly stationary relative to the air and the ground around it, there is no way it would take off. This is really a simple question that has been answered several times in this thread.
The only way you could get a stationary (relative to the ground) airplane to take off is by generating very high winds blowing directly into the nose of the plane. This would simulate the aircraft going fast down the runway (I don't know how fast they need to be going) and would allow take off. As soon as the plane left the artificial airflow it would come down. In the fake wind it would be like a glider.
Re: CyBookie - Plane on a Treadmill
Please look at what you are posting and then think a little harder about it.
If the plane moves at 10 mph ground speed (independent of the treadmill) and the treadmill is moving at 10 mph going the opposite direction, the wheels are rotating at 20 mph, but the planes thrust is still much more than able to overcome the very slight friction that exists in the wheel bearings.
If the plane's takeoff speed is 80 mph, then the plane reaches 80 mph and takes off, while the wheels are rotating at 160 mph.
The treadmill is not going to be able to push the plane backwards, no matter how much some of you think it would be able to.
Please look at what you are posting and then think a little harder about it.
If the plane moves at 10 mph ground speed (independent of the treadmill) and the treadmill is moving at 10 mph going the opposite direction, the wheels are rotating at 20 mph, but the planes thrust is still much more than able to overcome the very slight friction that exists in the wheel bearings.
If the plane's takeoff speed is 80 mph, then the plane reaches 80 mph and takes off, while the wheels are rotating at 160 mph.
The treadmill is not going to be able to push the plane backwards, no matter how much some of you think it would be able to.
Re: CyBookie - Plane on a Treadmill
But again.....how are you going to keep the plane stationary when the wheels are freewheeling aside from very slight friction and thousands of pounds of air thrust that is independent from the treadmill?
LS2 Forums - *** THE OFFICIAL *** "Plane On a Treadmill" BETTING THREAD! Place your bets now!!
Not sure if you have to log in to that board to see our discussion or not.
But again.....how are you going to keep the plane stationary when the wheels are freewheeling aside from very slight friction and thousands of pounds of air thrust that is independent from the treadmill?
LS2 Forums - *** THE OFFICIAL *** "Plane On a Treadmill" BETTING THREAD! Place your bets now!!
Not sure if you have to log in to that board to see our discussion or not.
Re: CyBookie - Plane on a Treadmill
Again....think about this. The treadmill is not moving unless the plane is moving, correct? If the plane moves forward at 1 mph, the treadmill is moving backward at 1 mph. 80 mph and 80 mph and so on. Do you not believe that the friction in the wheel bearings cannot be overcome by jet propulsion or propellers?
No magic fairy dust needed......the plane would easily take off.
Again....think about this. The treadmill is not moving unless the plane is moving, correct? If the plane moves forward at 1 mph, the treadmill is moving backward at 1 mph. 80 mph and 80 mph and so on. Do you not believe that the friction in the wheel bearings cannot be overcome by jet propulsion or propellers?
No magic fairy dust needed......the plane would easily take off.
Re: CyBookie - Plane on a Treadmill
So your saying that if a plane is moving at 10mph (with the thrust of the engines) and the treadmill is running at 10mph in the opposite direction (ie. no air movement over wings) that the thrust of the engines (that is moving the plane at 10mph) is enough to lift the plane?
If that is what your saying your wrong on many levels.
So your saying that if a plane is moving at 10mph (with the thrust of the engines) and the treadmill is running at 10mph in the opposite direction (ie. no air movement over wings) that the thrust of the engines (that is moving the plane at 10mph) is enough to lift the plane?
If that is what your saying your wrong on many levels.
- Status
