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

[Paendragon]

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.

Exactly. To me, I always thought that meant that if the engines were putting forth enough thrust, let's say, pushing the plane forward at 100 miles per hour, then the treadmill would be moving backward at 100 miles per hour, so the plane, would in essence, be stationary.

Boy did I misunderstand that one.

ETA: Please read my next post before commenting, m'kay?

 

[Sean]

Exactly. To me, I always thought that meant that if the engines were putting forth enough thrust, let's say, pushing the plane forward at 100 miles per hour, then the treadmill would be moving backward at 100 miles per hour, so the plane, would in essence, be stationary.

Boy did I misunderstand that one.

The treadmill could be going backwards at a million miles an hour, it still wouldn't matter.

 

[Paendragon]

Exactly. To me, I always thought that meant that if the engines were putting forth enough thrust, let's say, pushing the plane forward at 100 miles per hour, then the treadmill would be moving backward at 100 miles per hour, so the plane, would in essence, be stationary.

Boy did I misunderstand that one.

I should clarify, that I do understand that the wheels don't actually drive the plane, and it should still be able to take off.

I just had the format of the experiment wrong.

 

[Paendragon]

The treadmill could be going backwards at a million miles an hour, it still wouldn't matter.

See my next post.

 

[CTYankee]

Exactly. To me, I always thought that meant that if the engines were putting forth enough thrust, let's say, pushing the plane forward at 100 miles per hour, then the treadmill would be moving backward at 100 miles per hour, so the plane, would in essence, be stationary.

Boy did I misunderstand that one.

Premises:

Plane's AIRSPEED = 100 mph

Conveyor's GROUND SPEED (in the opposite direction) is 100 mph

The plane *still* moves through the air at 100 mph.

Air flows over the wing; lift is generated.

A mechanical speedometer attached to the wheels would *INDICATE* a ground speed of 200 mph.

ACTUAL speed over ground (assuming still air) would remain 100 mph.

Move the conveyor to 1,000 mph, and all you'll change is the INDICATED ground speed.

If the plane moved forward BY DRIVING WITH ITS WHEELS, the whole thing would be different. But it doesn't.

(Hence my remark -- way back there -- about a paddle-driven seaplane.)

 

[Paendragon]

Premises:

Plane's AIRSPEED = 100 mph

Conveyor's GROUND SPEED (in the opposite direction) is 100 mph

The plane *still* moves through the air at 100 mph.

Air flows over the wing; lift is generated.

A mechanical speedometer attached to the wheels would *INDICATE* a ground speed of 200 mph.

ACTUAL speed over ground (assuming still air) would remain 100 mph.

Move the conveyor to 1,000 mph, and all you'll change is the INDICATED ground speed.

If the plane moved forward BY DRIVING WITH ITS WHEELS, the whole thing would be different. But it doesn't.

(Hence my remark -- way back there -- about a paddle-driven seaplane.)

I know that. Next time I'll edit my post, instead of quoting it, with the addendum. I just wasn't expecting to see them pulling a tarp dragged by a car.

 

[MechaBlade]

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

The plane won't move without the wheels moving. Unless the wheels are dragging on the ground, which is the only way the plane could take off. But then the ground speed is still important.

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 . . ."

I'm trying to give metaphors so people understand that if a gust of wind blows a stationary object, it doesn't go whizzing down the street. Even with the wheels turning, there is still friction.

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 wheels. Planes don't taxi around the airport with their jet propulsion.

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 ground has EVERYTHING to do with the riddle.

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.

It's not the steel on steel of the wheel bearings. Turning the wheel faster will just turn the treadmill faster. It's the friction of the rubber on the treadmill, which, admittedly is probably less than concrete on asphalt. I always thought the riddle was meant to imply that the wheels won't slip.

I still feel I'm totally missing something obvious

It took me a while, too.

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."

It's not the steel on steel of the wheel bearings. Turning the wheel faster will just turn the treadmill faster. It's the friction of the rubber on the treadmill.

 

[Sean]

The plane won't move without the wheels moving. Unless the wheels are dragging on the ground, which is the only way the plane could take off. But then the ground speed is still important.

How does a seaplane take off?

 

[Legenda]

1. Didn't I just read a thread about this a month or so ago?

2. The plane takes off.

3. Thank god mythbusters is around to prove physics works.

4. What the fuck is up with the "woof!"??? It's even more annoying than "Ishmeal"

 

[MechaBlade]

Premises:

Plane's AIRSPEED = 100 mph

How is the plane's airspeed going to get up to 100 mph? We're not in a wind tunnel.

A mechanical speedometer attached to the wheels would *INDICATE* a ground speed of 200 mph.

Then the conveyor belt moves at 200 mph, giving the plane a 0 absolute ground speed and 0 airspeed.

 

[Sean]

1. Didn't I just read a thread about this a month or so ago?

2. The plane takes off.

3. Thank god mythbusters is around to prove physics works.

4. What the fuck is up with the "woof!"??? It's even more annoying than "Ishmeal"

Nothing is more annoying than Ishmael. Except maybe haemorrhoids.

 

[TurdFergeson]

How does a seaplane take off?

Exactly, but the seaplane would have a bit more difficulty, since water has more friction than wheel bearings.

 

[CTYankee]

I know that. Next time I'll edit my post, instead of quoting it, with the addendum. I just wasn't expecting to see them pulling a tarp dragged by a car.

They first did a scale model experiment -- with a radio-controlled plane and an exercise treadmill.

The truck-pulled-tarp was just the only practical way of scaling it up to a real aircraft.

 

[Legenda]

Exactly, but the seaplane would have a bit more difficulty, since water has more friction than wheel bearings.

You really are the dumbest person on lit.

 

[MechaBlade]

How does a seaplane take off?

Beats me. I thought it paddled like a boat until it got to a pretty fast speed, turned on the propeller for extra acceleration and went.

Does the propeller just drag it across the surface of the water?

 

[TurdFergeson]

You really are the dumbest person on lit.

Because I'm right? You fool, a seaplane would have to use MORE power to takeoff than a plane on a treadmill.

 

[Sean]

Does the propeller just drag it along the water?

Yep.

Now do you get it?

 

[Sean]

Beats me. I thought it paddled like a boat until it got to a pretty fast speed, turned on the propeller for extra acceleration and went.

Does the propeller just drag it across the surface of the water?

Here's a pic of a small plane. Look at the undercarriage, there's nothing driving the wheels.

http://www.flightsim.com/feature/porterer.jpg

 

[Legenda]

If the thrust of a rocket didn't push against the earth, would it take off???

 

[CTYankee]

Planes don't taxi around the airport with their jet propulsion.

That's *precisely* how they move around on the ground.

And it's why they need to be "pushed back" from the gate with a tractor.

Aircraft wheels are not "powered" in any way.

Nor do seaplanes have little propellers on the back of the pontoons, or paddle-wheels, or water jets.

The aircraft achieves airspeed by virtue of the THRUST created by its propeller or turbine. It moves through the air by pushing against the mass of air behind the aircraft -- regardless of whether whatever is beneath it (water, earth) is stationary or moving.

 

[Paendragon]

They first did a scale model experiment -- with a radio-controlled plane and an exercise treadmill.

The truck-pulled-tarp was just the only practical way of scaling it up to a real aircraft.

Ah, okay.

I was trying to say, that I could understand the confusion to someone who isn't really thinking about the problem. They would think "If the pane is moving forward at 200 MPH, and the treadmill moving backward at the same speed, then the plane would be staitonary." I admit, my first reaction to it was to think the plane wouldn't take off, because it wouldn't be moving forward. Then I realized that a plane pulls the air. It's the same principle that allows a plane to take off while being piggybacked on top of another plane.

 

[Wok]

Yep.

Now do you get it?

Bernoulli's principle also helps.

 

[TurdFergeson]

If the thrust of a rocket didn't push against the earth, would it take off???

Probably not but they also push against the atmosphere.

 

[Legenda]

Probably not but they also push against the atmosphere.

See, e.g., post 64.

 

[Paendragon]

You really are the dumbest person on lit.

He actually has a point. Like a boat, water actively moves a sea plane. River plane captain always like to get the water at their backs if they can. At least, that's what I've heard.