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Message
re: Can this 747 take off?
Posted on 4/11/24 at 12:03 pm to LNCHBOX
Posted on 4/11/24 at 12:03 pm to LNCHBOX
I don’t think this argument, which requires you to disregard friction, the impracticality of a 747 treadmill, or any other number of real world conditions, was designed to get people thinking about lift, negative feedback loops, or the speed of the conveyor.
It was designed to think about how the plane will move forward because it doesn’t act against the treadmill.
I think people are afraid to admit their first guess of the plane not taking off was wrong, so they’re bogging the issue down with semantics.
It was designed to think about how the plane will move forward because it doesn’t act against the treadmill.
I think people are afraid to admit their first guess of the plane not taking off was wrong, so they’re bogging the issue down with semantics.
2
Posted on 4/11/24 at 12:03 pm to tigerfoot
quote:
Have you ever seen a conveyor belt?
Sure have, ifthe wheels aren't being driven, what force is making the belt spin?
quote:
If the plane was attached to the conveyor belt and the belt was going fast enough for the wings to create lift, would the plane lift? Yes.
Nothing to do with the question.
quote:
The movement of the plane is essential, if the scenario described below and the energy created from the engines is not pushing the plane forward, but being used by the wheels to match the conveyor. For the energy to be applied to forward momentum of the plane it would have to exceed the energy of the treadmill, which in this absurd scenario will not happen.
There would be no energy from the treadmill, as the plane is not driven by its wheels. Y'all would have an argument if this was a car.
Posted on 4/11/24 at 12:04 pm to G2160
quote:
I think people are afraid to admit their first guess of the plane not taking off was wrong, so they’re bogging the issue down with semantics.
This.
Posted on 4/11/24 at 12:18 pm to tigerfoot
quote:
For the energy to be applied to forward momentum of the plane it would have to exceed the energy of the treadmill, which in this absurd scenario will not happen.
No.
Just stop.
The wheels on the plane "free wheel". Just like a hot wheel car.
The treadmill exerts zero force on the plane (only the wheels).
Thus... the jet engines' thrust the plane forward (because the wheels are freewheeling... and the speed of the treadmill has no bearing on the engine's thrust).
When the plane thrusts forward, the wheels are moving faster than the treadmill. And the question is broken. Because the force of the treadmill is absorbed by the freewheels of the plane, the plane will always thrust forward. And the wheels will always move at a faster rate than the treadmill.
This post was edited on 4/11/24 at 12:24 pm
Posted on 4/11/24 at 12:21 pm to meansonny
Nothing moves besides the treadmill, wheels and time marches on.
Posted on 4/11/24 at 12:23 pm to cubsfan5150
quote:The only reason the plane is keeping up with the treadmill is because it's pulling air through its engines and over and under its wings.
If the wheels are irrelevant, how do you get air flow under the wings? If the aircraft stays stationary, there’s no air flow.
Maybe I’m missing something
Posted on 4/11/24 at 12:23 pm to baldona
quote:
FWIW, the argument that it would take off with wheels locked up seems even more absurd.
You may not be aware of plane designs which do not have wheels.
It is not uncommon.
And if a 747 can fly 800 miles per hour, I would imagine it has enough thrust to move forward on small points of contact with no wheels.
Posted on 4/11/24 at 12:26 pm to LNCHBOX
quote:The force generated by the engines that are turning the wheels, and given that there is no force multiplier and the wheels match EXACTLY there is no additional force to move the plane.
what force is making the belt spin?
Posted on 4/11/24 at 12:27 pm to meansonny
quote:Why do they turn? Put your hot wheel car on a treadmill then apply force pushing the car, You would have to apply force to keep the plane from going backwards, correct? The faster the treadmill moved the more you would have to apply.
The wheels on the plane "free wheel". Just like a hot wheel car.
This post was edited on 4/11/24 at 12:29 pm
Posted on 4/11/24 at 12:28 pm to tigerfoot
quote:
The force generated by the engines that are turning the wheels
Oh boy
quote:
and given that there is no force multiplier and the wheels match EXACTLY there is no additional force to move the plane
When trying to sound smart goes wrong.
Posted on 4/11/24 at 12:29 pm to LNCHBOX
quote:So you suggest the wheels turn from a energy source that is not the engines? What force is that?
Oh boy
Posted on 4/11/24 at 12:30 pm to tigerfoot
quote:
So you suggest the wheels turn from a energy source that is not the engines? What force is that?
You have taken the lead for biggest dumbdumb in this thread, and that's quite the achievement,.
Posted on 4/11/24 at 12:33 pm to CocomoLSU
quote:
The way it’s written, if the conveyor truly does “match the speed of the wheels” then it can’t take off.
That is incorrect. And a huge problem apparently with a lot of people with the problem.
The speed of the wheels says nothing, absolutely nothing, about the speed of the aircraft.
It is free spinning with zero connection to propulsion.
Forget matching the speed of the plane. The conveyor can be going at Mach 2, and as long as the wheels don’t fly apart, not only will the plane take off, it will do so almost as well as a stationary runway.
The only loss is not from the linear motion of the platform, but from friction in the bearings of the wheel spinning so fast.
Posted on 4/11/24 at 12:34 pm to LNCHBOX
quote:
You have taken the lead for biggest dumbdumb in this thread, and that's quite the achievement,.
There is always the fourth answer to this old question that I haven't seen yet. May have been joked about earlier in the thread.
The plane is sitting on the runway. All speeds are 0, engines off, treadmill isn't moving, no thrust. You satisfy all conditions of the question exactly. It does not take off.
This post was edited on 4/11/24 at 12:35 pm
Posted on 4/11/24 at 12:35 pm to meansonny
quote:
The wheels on the plane "free wheel". Just like a hot wheel car.
The treadmill exerts zero force on the plane (only the wheels).
Thus... the jet engines' thrust the plane forward (because the wheels are freewheeling... and the speed of the treadmill has no bearing on the engine's thrust).
Again, this is a dumb hypothetical. But to your point, its simply wrong.
The wheels do not nor have they ever simply "free wheeled". There is a ton of friction from the load of the plane on them.
If you put a stroller on a conveyor in an airport it doesn't just sit there in place. It will move down the conveyor.
In regards to the 747 taking off without wheels rolling, lol. Okay
Posted on 4/11/24 at 12:36 pm to Dam Guide
quote:
There is always the fourth answer to this old question that I haven't seen yet. May have been joked about earlier in the thread.
The plane is sitting on the runway. All speeds are 0, engines off, treadmill isn't moving, no thrust. You satisfy all conditions of the question exactly. It does not take off.
But the question is "can it take off?" Your answer doesn't answer that in any meaningful way.
Posted on 4/11/24 at 12:37 pm to LNCHBOX
quote:
But the question is "can it take off?" Your answer doesn't answer that in any meaningful way.
That's why the question is designed to cause interaction and argument. You answered the question, people aren't going to be happy with the answer.
This post was edited on 4/11/24 at 12:38 pm
Posted on 4/11/24 at 12:38 pm to baldona
quote:
The wheels do not nor have they ever simply "free wheeled". There is a ton of friction from the load of the plane on them.
You really want to argue that there is more friction than thrust? quote:
In regards to the 747 taking off without wheels rolling, lol. Okay
You're just mad because it's true. Assuming nothing breaks, which is just as reasonable assumption as a magic conveyor belt, what would stop it?
Posted on 4/11/24 at 12:39 pm to G2160
quote:Well, this is wrong. The plane is supported by the wheels which are in contact with the treadmill. There's no way for the plane to move forward under the hypo.
It was designed to think about how the plane will move forward because it doesn’t act against the treadmill.
Posted on 4/11/24 at 12:39 pm to Dam Guide
quote:
That's why the question is designed to cause interaction and argument. You answered the question, people aren't going to be happy with the answer.
But your answer doesn't answer the question. A better question for your answer would be "will the plane take off"
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