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re: Myth Busters/Can a plane take off on a conveyor belt
Posted on 12/4/07 at 11:28 am to SG_Geaux
Posted on 12/4/07 at 11:28 am to SG_Geaux
quote:
I am assuming that they plane to have the plane on a giant treadmill basically. It comes down to airflow. If there is no air flowing across the wings, the plane can not take off.
In theory, the plane will take off. Although I'm with the Colonel... I doubt they'll be able to prove it either way because it would essentially take a runway-length treadmill to do so.
Posted on 12/4/07 at 11:30 am to LSUBoo
quote:
In theory, the plane will take off.
It is impossible for the plane to take off if there is no air flowing across the wings.
If the plane is on a treadmill and technically not moving forward against the air.... explain to me how air will flow across the wings.
This post was edited on 12/4/07 at 11:32 am
Posted on 12/4/07 at 11:32 am to LSUBoo
even if they get a runway length treadmill, it won't cancel out the rotational velocity of the wheels unless the plane is stationary. If the conveyor belt speeds up to try to match it when the plane starts moving, the rotational velocity of the wheels and the conveyor belt immediately both go to infinity. It's an interesting physics question under ideal conditions, but it's moronic to actually try to do it. It won't work.
Posted on 12/4/07 at 11:34 am to SG_Geaux
quote:
It is impossible for the plane to take off if there is no air flowing across the wings.
True, but the treadmill has NOTHING to do with air flow across the wings. All the treadmill will do will affect WHEEL-speed, which is irrelevant. The tread-mill is just a red-herring (and you fell for it).
Posted on 12/4/07 at 11:34 am to SG_Geaux
quote:
It is impossible for the plane to take off if there is no air flowing across the wings.
If the plane is on a treadmill and technically not moving forward against the air.... explain to me how air will flow across the wings.
read the thread
Posted on 12/4/07 at 11:34 am to Colonel Hapablap
quote:
Everybody is getting caught up in the linkage and friction of the wheels and that's not the issue. If the plane isn't moving at all. The treadmill is moving 100kts, the planes wheels are spinning at what would be 100kts. The plane is resting motionless in space but the wheels and tread mill are running full blast. This is the spirit of the myth. If this is the case. The plane is going nowhere, regardless of how high you jack up the speeds. Even if it is a theoretical 10000mph. There is still no air going over the fricking wings and the plane is spinning its wheels really fricking fast on the ground.
This is the correct answer
Posted on 12/4/07 at 11:36 am to LSUBoo
quote:
read the thread
This is all I needed to read.
quote:
If a plane is traveling at takeoff speed on a conveyor belt, and the belt is matching that speed in the opposite direction, can the plane take off?
The answer to this question is no.
Posted on 12/4/07 at 11:39 am to SG_Geaux
quote:
The answer to this question is no.
You're missing the trick. The conveyor belt cancels out the plane's airspeed. So... if the plane is flying 100 MPH to the left, and the conveyor is moving 100 MPH to the right, the wheels are moving at 200 MPH to the left. The plane still moves, the conveyor belt can't prevent the plane from moving, it just causes the wheels to work double-time. So, the plane still moves, the plane still takes off.
Posted on 12/4/07 at 11:39 am to SG_Geaux
quote:
quote:
If a plane is traveling at takeoff speed on a conveyor belt, and the belt is matching that speed in the opposite direction, can the plane take off?
The answer to this question is no.
No, the answer is that it is a physically impossible system.
UNDER NO CIRCUMSTANCES CAN THE PLANE BE TRAVELING AT TAKEOFF VELOCITY AND THE CONVEYOR BELT BE MATCHING THE WHEEL SPEED IN THE OPPOSITE DIRECTION.
This post was edited on 12/4/07 at 11:44 am
Posted on 12/4/07 at 11:42 am to Colonel Hapablap
quote:
THE CONVEYOR BELT BE MATCHING THE WHEEL SPEED IN THE OPPOSITE DIRECTION.
The problem states that the conveyor matches the plane's takeoff speed in the opposite direction... not wheel speed. This is why it will in theory work with a long enough treadmill for the plane to reach takeoff airspeed.
Posted on 12/4/07 at 11:44 am to LSUBoo
that's stupid on it's face. One is a rotational velocity and the other is linear.
Posted on 12/4/07 at 11:46 am to LSUBoo
quote:
The problem states that the conveyor matches the plane's takeoff speed in the opposite direction... not wheel speed.
The plane will never reach takeoff speed on a treadmill. Wheel speed will increase, but the physical mass of the plane itself will not move forward.
If you run on a treadmill as fast as you can, you still never move forward.
This post was edited on 12/4/07 at 11:49 am
Posted on 12/4/07 at 11:49 am to SG_Geaux
quote:
The plane will never reach takeoff speed on a treadmill. Wheel speed will increase, but the plane will not move forward.
If you run on a treadmill as fast as you can you still never move forward.
You just don't get it, do you?
I'm done trying to explain it for the hundredth time... read through the thread if you really want to know why the plane will, in theory, take off.
Posted on 12/4/07 at 11:51 am to LSUBoo
I read the thread.
Posted on 12/4/07 at 11:53 am to LSUBoo
Boo don't sweat it. You are right. Some minds just have a hard time grasping things such as these.
Posted on 12/4/07 at 11:54 am to Colonel Hapablap
quote:
that's stupid on it's face. One is a rotational velocity and the other is linear.
Come on Colonel, it should be "that's stupid on its face" for starters!
quote:
One is a rotational velocity and the other is linear.
The point of the problem is that the wheels negate the force of the treadmill, allowing the plane to still move forward in relation to the air. The jet engines propel the plane forward, not the wheels. The wheels just keep it folling against a stationary runway. If the runway is a treadmill, and thus not stationary, the wheels will react accordingly as the plane still moves forward in relation to the air around it.
You are right though, it's going to be damn near impossible to prove this... at least at full scale. It might be able to be computer modeled accurately?
Posted on 12/4/07 at 11:55 am to ags01
quote:
Boo don't sweat it. You are right. Some minds just have a hard time grasping things such as these.
Just another reason I could never be a good teacher... not enough patience with people.
Posted on 12/4/07 at 11:55 am to SG_Geaux
Air-speed is what makes a plane take off and fly, not wheel-speed. When a plane is cruising, how fast are its wheels going? ZERO.
The conveyor belt is a red herring, don't fall for it.
The conveyor belt is a red herring, don't fall for it.
Posted on 12/4/07 at 11:58 am to SG_Geaux
quote:
Wheel speed will increase, but the physical mass of the plane itself will not move forward.
Yes it will b/c the engines of the plane will push it forward. Wheel speed is irrelevant.
Posted on 12/4/07 at 12:00 pm to LSUBoo
yeah, I have a problem with its and it's 
I understand the point of the problem, but IMO the spirit of the issue has to have the conveyor belt negating the wheels and not the body of the plane. The question seems to simple if the conveyor only negates the speed of the fuselage. Either way the plane takes off, it's just a question of whether the wheels are rotating at infinity or not.
Also, the frictionless nature of the wheels in the original question is completely blasted when you try to do the experiment.
I understand the point of the problem, but IMO the spirit of the issue has to have the conveyor belt negating the wheels and not the body of the plane. The question seems to simple if the conveyor only negates the speed of the fuselage. Either way the plane takes off, it's just a question of whether the wheels are rotating at infinity or not.
Also, the frictionless nature of the wheels in the original question is completely blasted when you try to do the experiment.
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