Will a plane take off from a backwards moving treadmill?

AV8R_87

AV8R_87

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Posting this classic here, since I still see people arguing about it:

 
Dana said:
The only people who argue about it are those who don't understand very basic aerodynamics or physics.
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The only thing that one needs to understand is that the airplane’s engine is not connected to its wheels.
 
Roger Wilco said:
The only thing that one needs to understand is that the airplane’s engine is not connected to its wheels.
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I've had an aerospace engineering student ask how is the engine driving the wheels of the jet that was taxiing past us.
The answer we gave him? "Through a crankshaft."

A glider student pilot was quite intrigued by the small heli that had landed at our airfield. As the turboshaft spooled up and the tail rotor started spinning, you could hear the gears squeaking inside his head.
His bulb finally flickered on and he blurted "Oh, the engine exhaust is blowing on the tail rotor, that's how it turns!"

Roger Wilco said:
And because there aren’t enough arguments on PoA.
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Breaks the monotony of "high vs low wing" or "Bonanza vs Mooney" threads.
 
Yabut, can a Mooney take off from an escalator? It would already be on the step...
 
Roger Wilco said:
The only thing that one needs to understand is that the airplane’s engine is not connected to its wheels.
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Da propeller bone connected to da…engine bone
Da engine bone connected to da…firewall bone
Da firewall bone connected to da…fuselage bone
Da fuselage bone connected to da…gear strut bone
Da gear strut bone connected to da…axle bone
Da axle bone connected to da…wheel bone
 
AV8R_87 said:
I've had an aerospace engineering student ask how is the engine driving the wheels of the jet that was taxiing past us.
The answer we gave him? "Through a crankshaft."

A glider student pilot was quite intrigued by the small heli that had landed at our airfield. As the turboshaft spooled up and the tail rotor started spinning, you could hear the gears squeaking inside his head.
His bulb finally flickered on and he blurted "Oh, the engine exhaust is blowing on the tail rotor, that's how it turns!"


Breaks the monotony of "high vs low wing" or "Bonanza vs Mooney" threads.
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Yet two more examples that support the old maxim, the best way to learn is to teach.

In defense of your aerospace engineer, there have been recent proposals to equip jetliners with electric motors in the the wheels for ground operations. Like, one wheel on each bogey would have a motor instead of a brake.

As for your glider student, clearly he/she was demonstrating next-level understanding of the magical power of moving air. Did you then explain that the tail rotor powers the main rotor by means of a shaft?
 
GeorgeC said:
Yabut, can a Mooney take off from an escalator? It would already be on the step...
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So, if I’m cruising at F190 in a Mooney, how far from my destination should I begin de-escalating?
 
I think nobody wants to argue about the conveyor, so they're arguing about not arguing.
 
Yep, it's been about the right amount of time for this stupidity to resurface again. :cool:
 
M20K said:
Yep, it's been about the right amount of time for this stupidity to resurface again. :cool:
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For here, possibly. On the other hand, for Facebook, there's no amount of time required for stupid ideas to resurface!
 
IT WILL NOT

The only time the wheel speed will match the speed of the treadmill is if the airspeed is exactly zero.
If a treadmill speed is set to 100 miles per hour, the wheels will only be spinning exactly 100 miles per hour if the airspeed is zero.

If the plane accelerates to airspeed which will allow it to take off, the wheel's speed will non longer match the treadmill speed.
This is an undeniable fact.


https://www.tiktok.com/video/7130234127986707758
 
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Dana said:
The only people who argue about it are those who don't understand very basic aerodynamics or physics. Any pilot in that group should be scheduled for a 709 ride.
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The pilot in the Myth Busters experiment didn't think the plane would take off, but I think that was an ultralight, in which case no pilot certificate would have been required. Would that eliminate the FAA's ability to require a 709 ride?
 
Dana said:
The only people who argue about it are those who don't understand very basic aerodynamics or physics. Any pilot in that group should be scheduled for a 709 ride.
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If you were going to 709 any pilot that doesn't understand aerodynamics and physics, there wouldn't be anybody certificated at the FAA.
 
I always hated the question cause how its usually asked means there is no forward movement and things get infinite or wheels explode.
 
falconkidding said:
I always hated the question cause how its usually asked means there is no forward movement and things get infinite or wheels explode.
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[emphasis added]
That's the crux of the problem, and also where it falls apart in the long term.
It's a thought problem, not an experiment design. As long as the initial assumptions are maintained the problem is relatively simple. *Every* simplifying assumption fails at some point in a process, the thought problem concerns the time when they do not fail.

Nauga,
who has never seen a spherical cow
 
flyingron said:
If you were going to 709 any pilot that doesn't understand aerodynamics and physics, there wouldn't be anybody certificated at the FAA.
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What do we do to pilots who don't understand counterfactual hypothetical questions?
 
I think what this question does is makes pilots who don't think deeply, feel super superior because they get to yell at other people claiming they think that planes power come from the wheels which we all know it doesn't.

So that's a group of people that think it will take off based on a very shallow understanding of physics but a marginal understanding of aerodynamics.

The truth is no one in the question ever says by matching the speed of the wheels to the treadmill do they mean the speed at which the treadmill is moving or the relative speed of the wheels to the treadmill.

If a treadmill is set to 5 mph and the wheels have to be going 5 mph, the plane is not moving forward through the air at all.


Now if we take away the speed at which the treadmill is set and think about the actual speed of the belt it will always be identical to the wheel speed.

If the belt is moving 100 miles an hour and the wheels are moving 100 miles an hour the plane sitting still air speedwise.

If the plane accelerates to 100 mph air speed now the planes Wheels are going twice the speed that the treadmill is set to run but they will always match exactly the relative opposite motion of the belt.

My interpretation of the question was we have a treadmill set to go 100 miles an hour and the wheel speed must match the treadmill speed that will always be an airspeed of exactly zero.

I think most pilots believe the airplane will take off using the argument that speed comes from the propeller not the wheels.
I think those are the Embry-Riddle pilots.
 
SixPapaCharlie said:
I think what this question does is makes pilots who don't think deeply, feel super superior because they get to yell at other people claiming they think that planes power come from the wheels which we all know it doesn't.
. . .
I think those are the Embry-Riddle pilots.
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For the first time ever, I was about to say that we need more ERAU pilots.

Then I realized that you were just being facetious.
 
Larry in TN said:
I'm still wondering how a poorly-worded prompt prevents the airplane from moving forward.
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The paradox in the viral example is that the treadmill can exactly match the speed of the wheels. If that's the case, how can the wheels move forward? It creates an infinite feedback loop since an airplane will move forward on a treadmill when thrust is applied.
 
Baked Potato said:
The paradox in the viral example is that the treadmill can exactly match the speed of the wheels. If that's the case, how can the wheels move forward? It creates an infinite feedback loop since an airplane will move forward on a treadmill when thrust is applied.
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A most ingenious paradox. But it serves only as a misdirection ploy that distracts us from the simple fact that the speeds of the treadmill/conveyor belt and wheels are totally irrelevant.
 
Baked Potato said:
The paradox in the viral example is that the treadmill can exactly match the speed of the wheels. If that's the case, how can the wheels move forward? It creates an infinite feedback loop since an airplane will move forward on a treadmill when thrust is applied.
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One point that consistently gets overlooked is that the term "speed of the wheels" is not defined. Does it mean speed of the center of the wheels, or speed of the surface of the tires? If it's the former, are we talking about speed relative to the ground, speed relative to the surrounding air, or speed relative to the treadmill? In physics, all speed is relative, and there is no preferred reference frame. The reference frame must be specified in order to get a result.

If we're talking about the speed of the center of the wheels relative to the ground, and if as stated the treadmill is exactly matching the speed of the wheels in the opposite direction, then if the plane does not move, the speed of the wheels will be zero, so the speed of the treadmill will be zero. So then we have the absurd proposition that a stationary treadmill can prevent a plane from moving!
 
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