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Message
re: Can this 747 take off?
Posted on 4/11/24 at 10:38 am to LNCHBOX
Posted on 4/11/24 at 10:38 am to LNCHBOX
quote:
Absent the forces of friction, there are no horizontal forces to counteract the thrust produced by the engines; therefore the plane will absolutely move, and take off given enough length of runway.
Agreed. And when the plane moves forward will the wheels be spinning faster than the treadmill?
1
Posted on 4/11/24 at 10:39 am to meansonny
quote:
And if the plane is being thrusted forward on the conveyer belt, then the conveyer belt is not matching the speed of the wheels
Thank you!!!
The original question: 'If a planes wheels are moving the same speed as a conveyor belt, can the plane takeoff?'
There's NO air flowing over the wings, producing ZERO lift...how can it takeoff? All you slapdicks introducing other variables are conflating the issue. If the plane can produce sufficient thrust to overcome the speed of the belt and get to rotation speed, yes, it will take off (but engine thrust isn't a variable posed in the original question, at least per the OP.)
Tell me where I'm wrong...and I'm humble enough to admit if I am. I just need a compelling counter argument.
Posted on 4/11/24 at 10:40 am to FutureCorridor49
The wheels on the landing gear are free-wheeling. Despite the conveyor, the aircraft will still gain the necessary airspeed to become airborne.
Posted on 4/11/24 at 10:40 am to UpToPar
quote:
To remain in the same spot you have to run exactly 5 mph. To move forward on the treadmill you have to run faster than 5 mph.
Because your movement is based off of you pushing off the ground. A plane pushes against air.
Posted on 4/11/24 at 10:40 am to UpToPar
quote:
The friction force would be negligible with respect to the force of the engines. But you're missing the point (at least the one I'm arguing). The hypothetical is impossible to test in the real world. Instantaneously, both the wheels and the treadmill would increase their speed exponentially to infinity.
You would think it fairly intuitive that GROUND speed doesn’t matter when it comes to FLYING, but this place is full of surprises
Posted on 4/11/24 at 10:41 am to UpToPar
quote:
And when the plane moves forward will the wheels be spinning faster than the treadmill?
Since we are ignoring friction, they will be spinning at the same speed as the belt but moving in the direction of the plane. The rotation of the wheels have no effect on the plane. Kind of like a freewheel crank on a bike.
Posted on 4/11/24 at 10:41 am to dazedconfused
quote:
The wheels on the landing gear are free-wheeling. Despite the conveyor, the aircraft will still gain the necessary airspeed to become airborne.
Posted on 4/11/24 at 10:42 am to TD422
quote:
All you slapdicks introducing other variables
The wheels wouldn't spin at all absent "outside variable"
Posted on 4/11/24 at 10:43 am to TD422
quote:
There's NO air flowing over the wings, producing ZERO lift...how can it takeoff? All you slapdicks introducing other variables are conflating the issue. If the plane can produce sufficient thrust to overcome the speed of the belt and get to rotation speed, yes, it will take off (but engine thrust isn't a variable posed in the original question, at least per the OP.)
But as soon as thrust is applied then the wheels will move faster than the treadmill. The plane will move forward regardless of what the speed of the wheels is…increase the treadmill speed, the wheels increase speed regardless of the thrust. The plane moves forward relative to the ground, not the treadmill.
Posted on 4/11/24 at 10:43 am to LNCHBOX
quote:
Since we are ignoring friction, they will be spinning at the same speed as the belt but moving in the direction of the plane.
Nope. If the plane is moving forward (which it would) the wheels would have to be spinning faster than the treadmill.
Posted on 4/11/24 at 10:44 am to UpToPar
quote:Not nope.
Nope
quote:Nope. There's no friction, remember?
If the plane is moving forward (which it would) the wheels would have to be spinning faster than the treadmill.
Look, you can pick and choose which physical properties you want to turn off to make the argument that the plane would not move. But if you are evaluating this scenario in reality, the plane is going to move because the plane is propelled by thrust, not the wheels.
This post was edited on 4/11/24 at 10:47 am
Posted on 4/11/24 at 10:45 am to LNCHBOX
quote:
The wheels wouldn't spin at all absent "outside variable"
Bruh...you need to lay down and let the drugs wear off. IF THE WHEELS MATCH THE SPEED OF THE TREADMILL....it means they're moving. And the treadmill isn't an outside variable, it's part of the original proposition.
Posted on 4/11/24 at 10:47 am to LNCHBOX
quote:
Nope. There no friction, remember?
If you completely ignore friction then the wheels don't spin at all. But the hypothetical does not say to ignore friction.
I don't know how else to explain it. If the plane moves forward then the hypothetical is broken. Clearly in the real world the plane would move forward and take off because we cannot build a conveyor belt to instantaneously match the speed of the wheels to infinity.
Posted on 4/11/24 at 10:48 am to TD422
quote:
Bruh...you need to lay down and let the drugs wear off. IF THE WHEELS MATCH THE SPEED OF THE TREADMILL....it means they're moving. And the treadmill isn't an outside variable, it's part of the original proposition.
Where is the initial velocity for the wheels coming from for the treadmill to match the speed of the wheels?
Posted on 4/11/24 at 10:49 am to UpToPar
quote:
e cannot build a conveyor belt to instantaneously match the speed of the wheels to infinity.
Even if we could, there are no horizontal forces exerted that would stop teh plane from moving. This really shouldn't be this hard.
Posted on 4/11/24 at 10:49 am to TD422
quote:
Thank you!!!
The original question: 'If a planes wheels are moving the same speed as a conveyor belt, can the plane takeoff?'
There's NO air flowing over the wings, producing ZERO lift...how can it takeoff? All you slapdicks introducing other variables are conflating the issue. If the plane can produce sufficient thrust to overcome the speed of the belt and get to rotation speed, yes, it will take off (but engine thrust isn't a variable posed in the original question, at least per the OP.)
Tell me where I'm wrong...and I'm humble enough to admit if I am. I just need a compelling counter argument.
You are 99% there.
The plane is "free wheeling".
There is no "overcoming the speed of the belt".
The plane will always move forward.
What they lack is a fundamental understanding of the question.
Once the plane moves forward (and it always will with engines engaged), the wheels are moving faster than the treadmill is moving. It is a literal impossibility for the treadmill to keep up because it is a literal impossibility for the plane to remain stagnant.
The question is broken.
Posted on 4/11/24 at 10:49 am to LNCHBOX
quote:
But if you are evaluating this scenario in reality, the plane is going to move because the plane is propelled by thrust, not the wheels.
I'm not arguing otherwise. But as soon as the plane moves forward the hypothetical is broken.
Posted on 4/11/24 at 10:50 am to UpToPar
quote:
But as soon as the plane moves forward the hypothetical is answered with "yes"
FIFY
Posted on 4/11/24 at 10:50 am to meansonny
quote:
You are 99% there.
The plane is "free wheeling".
There is no "overcoming the speed of the belt".
The plane will always move forward.
What they lack is a fundamental understanding of the question.
Once the plane moves forward (and it always will with engines engaged), the wheels are moving faster than the treadmill is moving. It is a literal impossibility for the treadmill to keep up because it is a literal impossibility for the plane to remain stagnant.
The question is broken.
Correct.
Posted on 4/11/24 at 10:50 am to LNCHBOX
quote:
Where is the initial velocity for the wheels coming from for the treadmill to match the speed of the wheels?
OK, let's go with this. The treadmill belt is moving the wheels. Got it. Where does the airflow over the wings come from if engine thrust is never introduced? The wheel speed just matches the treadmill speed. STILL no lift provided. How will it take off?
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