Imagine a plane is sitting on a treadmill, Mythbusters test it!

[TurdFergeson]

Not if it's tied down.

An airfoil only works when air is moving over it at a sufficient speed to generate a pressure differential and thus create lift. A propeller doesn't provide lift by driving air over the wings. It just generates thrust so that the entire aircraft moves through the air. You can see this with push props (where the propeller is actually at the rear of the aircraft).

I never thought of that. You're right. I was thinking more of a jet plane with the engines on the wings themselves. But even they do not actually produce lift on the wings themselves.

However, the planes are not tied down according to the information given, so they would still take off on the treadmill.

If they were tied down, they would not.

 

[John Doe]

I never thought of that. You're right. I was thinking more of a jet plane with the engines on the wings themselves. But even they do not actually produce lift on the wings themselves.

However, the planes are not tied down according to the information given, so they would still take off on the treadmill.

If they were tied down, they would not.

In the riddle the aircraft is stationary relative to the air around its wings, isn't it? In that case it won't take off.

 

[Sean]

In the riddle the aircraft is stationary relative to the air around its wings, isn't it? In that case it won't take off.

Wrong. The ground moving has bugger all to do with it. As long as the wheels are freee to turn, the engines will drive the plane through the air. The wheels will just be turning twice as fast as the plane is moving.

 

[Brains_N_Boobs]

......

 

[CTYankee]

Not if it's tied down.

In the riddle the aircraft is stationary relative to the air around its wings, isn't it?

That isn't -- and never was -- the premise of the myth.

A *tied down* aircraft can't move through the surrounding air, can't generate lift and can't fly REGARDLESS of any conveyor belt or treadmill.

The premise/question of the myth was: Will a moving conveyor BENEATH an aircraft prevent it from taking off?

The answer is no -- because almost any aircraft (conventional prop, pusher, jet turbine) will move the airframe through the surrounding air regardless of what the ground is or isn't doing beneath it.

Being "tied down" was never part of the equation.

I think I'm done with this.

 

[John Doe]

Wrong. The ground moving has bugger all to do with it. As long as the wheels are freee to turn, the engines will drive the plane through the air. The wheels will just be turning twice as fast as the plane is moving.

I'm not talking about the ground. I don't care about the ground. Fuck the ground with a big rubber dick.

If the air speed over the wings is not sufficient to generate lift the aircraft will not take flight, period.

 

[TurdFergeson]

......

lol

Actually, they never said which way the treadmill will go, just that it can go backwards.

It might actually move forwards due to the resistance of the wheels turning.

You are supposed to assume the treadmill will automatically move backwards, negating the forward motion of the plane. Not so.

 

[Sean]

I'm not talking about the ground. I don't care about the ground. Fuck the ground with a big rubber dick.

If the air speed over the wings is not sufficient to generate lift the aircraft will not take flight, period.

Right. So what's your problem? The engines drive the plane forward until there is sufficient lift for it to take off.

 

[MechaBlade]

But that's the whole point . . .

The propeller WILL "move the aircraft through the surrounding air" (thus generating lift) -- REGARDLESS of what the ground beneath the aircraft is doing.

Movement of the ground (i.e., the treadmill) would only matter if the aircraft were being driven BY ITS WHEELS -- which it is clearly not.

No it wouldn't. The aircraft isn't suspended in air. It's being held to the ground by gravity and held there by friction.

What they should have used is a plane with bricks for wheels. If the propeller was strong enough to pull the plane forward when it's traveling on a conveyor belt (which it could never be, by definition of the problem) then it should at least be able to pull a plane on bricks forward and make it fly. I'm betting that it couldn't.

As long as it's touching the ground (with even part of its weight pulling it down), the plane is held motionless by its wheels.

 

[MechaBlade]

You are supposed to assume the treadmill will automatically move backwards, negating the forward motion of the plane. Not so.

That is the entire premise of the riddle. The treadmill isn't moving at a set speed. It's moving as fast as the wheels turn. In effect, the plane is tied to the ground.

 

[The Heretic]

It depends on the airplane - very few could take off given that situation. The speed that is important is the speed of the air across the wings, no the speed of the airplane relative to the ground.

 

[firespin]

It's far better than that, you also get to work with Kari Byron!

http://www.tvsquad.com/media/2006/05/mythbuster-kari.jpg

Woof!

Wow! Too bad Jamie and Adam are gay.

 

[Sean]

No it wouldn't. The aircraft isn't suspended in air. It's being held to the ground by gravity and held there by friction.

What they should have used is a plane with bricks for wheels. If the propeller was strong enough to pull the plane forward when it's traveling on a conveyor belt (which it could never be, by definition of the problem) then it should at least be able to pull a plane on bricks forward and make it fly. I'm betting that it couldn't.

As long as it's touching the ground (with even part of its weight pulling it down), the plane is held motionless by its wheels.

Wrong.

 

[TurdFergeson]

That is the entire premise of the riddle. The treadmill isn't moving at a set speed. It's moving as fast as the wheels turn. In effect, the plane is tied to the ground.

I think the riddle was said incorrectly.

It's supposed to be a plane on a free moving treadmill.

Most people would assume that the wheels spinning wouldn't be able to move the plane forward, since the treadmill would provide zero resistance unlike steady ground.

Now, if the treadmill is purposely going backwards, it still woundn't matter, the plane could easily overcome the small resistance caused by the wheel bearings and move forward regardless of how fast it's wheels and the treadmill were spinning.

 

[The Heretic]

But that's the whole point . . .

The propeller WILL "move the aircraft through the surrounding air" (thus generating lift) -- REGARDLESS of what the ground beneath the aircraft is doing.

Only if the airplane is allowed to move. If the aircraft is tied down or otherwise not allowed to move then the prop won't help - not enough air goes past the wings with enough speed to provide the lift. It will just sit there tugging on its tethers.

 

[MechaBlade]

I think the riddle was said incorrectly.

It's supposed to be a plane on a free moving treadmill.

Every time I've seen this riddle it says "The conveyer belt is designed to exactly match the speed of the wheels, moving in the opposite direction."

Google it.

 

[Sean]

Every time I've seen this riddle it says "The conveyer belt is designed to exactly match the speed of the wheels, moving in the opposite direction."

Google it.

The speed of the wheels is not relevant. It has no bearing on the speed of the plane through the air.

 

[CTYankee]

No it wouldn't. The aircraft isn't suspended in air. It's being held to the ground by gravity and held there by friction.

What they should have used is a plane with bricks for wheels. If the propeller was strong enough to pull the plane forward when it's traveling on a conveyor belt (which it could never be, by definition of the problem) then it should at least be able to pull a plane on bricks forward and make it fly. I'm betting that it couldn't.

As long as it's touching the ground (with even part of its weight pulling it down), the plane is held motionless by its wheels.

Why do you insist on changing the premise(s) of the original myth?

Wheels are friction reducers. That's what they're there for.

The riddle ISN'T:

"If a wheel-less plane were placed on a conveyor . . ."

or

"If a plane with bricks in place of wheels were placed on a conveyor . . ."

or (as others have tried)

"If a plane is TIED DOWN atop a moving conveyor . . ."

 

[Wok]

Thrust, gravity, drag and lift. No big mystery to it.

 

[CTYankee]

Whaddya say, SeanH?

Let's go get us a beer & be done with this?

 

[Sean]

Whaddya say, SeanH?

Let's go get us a beer & be done with this?

LOL, the pedagogue in me won't quit sometimes.

 

[meat_robot]

No it wouldn't. The aircraft isn't suspended in air. It's being held to the ground by gravity and held there by friction.

What they should have used is a plane with bricks for wheels. If the propeller was strong enough to pull the plane forward when it's traveling on a conveyor belt (which it could never be, by definition of the problem) then it should at least be able to pull a plane on bricks forward and make it fly. I'm betting that it couldn't.

As long as it's touching the ground (with even part of its weight pulling it down), the plane is held motionless by its wheels.

I feel I'm missing something glaringly obvious when I can't understand the above post.

Yes gravity is exerting force holding the plane on the tarmac. Yes friction keeps the plane motionless. However what makes any plane start to move initially? The propeller or the thrust produced by the jet engine no?! Which are independent of what the wheels are doing. The propulsion system pulls/pushes the plane through the air. I fail to see what the ground has to do with anything.

The idea that the coefficient of friction between the steel on steel of the wheel bearings is equal to brick on concrete/asphalt is preposterous. Overcoming the initial friction of brick on concrete is way more than steel on steel.

I still feel I'm totally missing something obvious

 

[Paendragon]

Found the video

http://www.youtube.com/watch?v=IbRcg3ji_Pc

Woof!

That's completely not what I understood the myth to be.

 

[TurdFergeson]

Every time I've seen this riddle it says "The conveyer belt is designed to exactly match the speed of the wheels, moving in the opposite direction."

Google it.

Oh well that's why I added the 2nd part:

"Now, if the treadmill is purposely going backwards, it still woundn't matter, the plane could easily overcome the small resistance caused by the wheel bearings and move forward regardless of how fast it's wheels and the treadmill were spinning."

 

[CTYankee]

LOL, the pedagogue in me won't quit sometimes.

Ditto.

I feel like I should be able to make it crystal clear to anyone. If not, it's *my* failure, not theirs. *shrug*