Mythbusters "Plane on a conveyor belt"

[Stef]

Recently I've seen this Mythbusters episode, where they pose the question if you put a plane on a conveyor belt "that matches the plane's forward speed in reverse". Well, they put a real plane on a huge conveyor belt and are all excited when it takes off. (see here: http://www.youtube.com/watch?v=0KsdMuhYJPw)

But I don't see a plane in standstill, I see a plane that moves forward. No wonder it takes off.

Has anyone of you seen this episode? Did I misunderstand the question? Do they mean the plane's speed matches the conveyor belt's speed in relation to the conveyor belt, or in relation to the ground? In my humble opinion, the only way this myth could be controversial in any way, would be if they mean the speed in relation to the conveyor belt.

I always liked Mythbusters, although the experiments are a bit of a stretch sometimes and they sometimes are a bit too quick to declare something busted or confirmed. But this episode misses the point entirely, IMO.

[Fabo]

There is hardly any mechanism that could propel the conveyour belt fast enough for bearings in airplanes wheels to fail and stuck somehow.

The problem with this "myth" is, people are used to propelling themselves by interacting with ground. Running - your shoes are in contact with ground, you push yourself away. Cycling, cars - wheels are in contact with ground, you make them rotate...

While airplanes are more like swimming - you interact with the medium of water, propellers interact with medium of air, so do jets. Think about swimming upstream - if you do nothing, the water takes you down with it. When you start swimming, you are moving relative to the water, even if you are in standstil relative to the surface around. Similar story downstream, only the surface is moving faster away (similarly as conveyor belt would start moving backwards).

Now, if the aircraft stands on a conveyor belt, unless brakes are applied, you can consider it not connected to the belt itself. The wheels have very little inherent friction. Its like when you put your stickshift car in neutral before crossroads - it only slows down ever so slowly.

Now the aircraft wants to move, so you start the engine and add throttle. Unlike in car, where engine turns the wheels that apply force to the ground (conveyor belt), airplane engine moves a prop which applies force to the air. Air is not affected by movement of the belt.

[cotejy]

My first taught was "what were they expecting?" Of course It'll fly. Then I remember how difficult it's for "pedestrians" to see the air as a separate medium from ground.

I'm sure I'm not the only one who had a hard time explaining to someone that it's better to take off facing wind instead of having the wind from behind. When I say, with 10kts wind in your face, your airframe is moving throught air at 10kts even if we are stopped on the ground. If your takeoff speed is 60kts, you only have to accelerate 50kts to be airborne.

Even with explanations, some strongly belive that the wind from behind will "push" the airplane, helping it to accelerate faster.

We should be happy to have hard time explaning things like that. While we talk about relative wind, they don't ask questions about gyroscopic precession. Not that I don't remember what gyro precession is... It's just that I don't feel like explaning it. 

[happylanding]

We should be happy to have hard time explaning things like that. While we talk about relative wind, they don't ask questions about gyroscopic precession. Not that I don't remember what gyro precession is... It's just that I don't feel like explaning it. 

 
That's lovely! given the difficult things one has to learn, it is obvious that he deserves the biggest watch and the biggest sun glasses

Gyroscopic precession? Oh well, I just think I do not feel either like explaining it

[Oddball]

Folks simple answer is: IT'S TELLY VISION!!!  they have to dumb down things we in here at least understand since we deal with it on a daily basis.

[Fabo]

We should be happy to have hard time explaning things like that. While we talk about relative wind, they don't ask questions about gyroscopic precession. Not that I don't remember what gyro precession is... It's just that I don't feel like explaning it. 

 

[Mike]

In their defense: You can kind of tell when you hear the Mythbusters talk to eachother that they knew exactly what the result of this experiment will be and that they tried hard to stay "unbiased".....
;-)

But you have to watch the whole episode!

They kinda had to do this one because there was a huge discussion about it online and people on both sides were very adament it would/wouldn't work.
THAT to me is the shocking part actually . . . that there are "two opinions" on something that's basically law of Physics !!! (which we know are, neither changeable nor negotiable)

Oh, and:

If that pilot was REALLY surprised (and not just for TV), he better turn in his pilot certificate !!!! 

[Fabo]

They kinda had to do this one because there was a huge discussion about it online and people on both sides were very adament it would/wouldn't work.
THAT to me is the shocking part actually . . . that there are "two opinions" on something that's basically law of Physics !!! (which we know are, neither changeable nor negotiable)

Its a question of applying right physical principles... but to a wrong situation. Just people returning to something they are used to, even if it is incorrect.