MythBusters tackles "plane on a conveyor belt problem"

[kernatch]

Alright, I don't agree with what they did in Mythbusters!. When they pull that curtain with the truck the other way, the plane is still going and moving, it's gaining forwardness, it has to pick up! but when the belt is going the same speed with the plane, it wont allow it to move so no air on the wings, this isn't possible, mythbusters did this wrong, what do you guys think.

The plane can move forward regardless of the ground below. See my post above.

[Mathachew Veteran]

Something just didn't seem right about it, because it seemed like once the gas was pushed for the plane, it moved forward, never really matching the speed of the conveyor belt. It seems like that they want to achieve the same speed of both directions and then see if the plane takes off. Maybe I'm looking at this wrong?

They should build a large conveyor belt that doesn't require dragging a large belt on the ground. Those guys can do it!

[kernatch]

The question describes the belt moving at the same speed of the plane (but in the opposite direction) just so that, at first, you incorrectly picture the plane being still ('cancelling it out'). But even if the question said the belt moved twice as fast as the plane, which would, at first, make you (incorrectly) picture the plane moving backwards, in reality the plane would still move in exactly the same way as if the ground was still. The speed of the belt really is of no importance (apart from technical details like how fast the plane's wheels can spin before overheating). Essentially the question is asking: does a moving runway affect a plane's take off?

[The_Decryptor Veteran]

Episode just aired, plane took off no problem. What was sad was that the pilot appeared not to understand how his plane functioned and believed his plane would remain stationary.

It's surprising how many people don't know how planes work, but you'd think pilots would understand.

[Kushan]

It's surprising how many people don't know how planes work, but you'd think pilots would understand.

The problem (For most people, at least) wasn't that they didn't know how planes work, but that they didn't know quite what exactly the question was asking in the first place.

I always assumed the conveyor belt was just a way of saying "the plane is being kept stationary, can it still take off?" and if you look at the vast majority of the arguments against the plane taking off, they all talk about air flow and such.

If the plane is moving forward, there will be air flow, if not, there wont (and it wont take off). The myth was testing if the conveyor would stop the plane moving forward, that's clear now, but a lot of us (myself included) thought the myth was testing if the plane could take off from a stationary position.

The end result? Most people weren't really WRONG, it was more a case of whoever came up with the question didn't explain it well enough.

[kernatch]

The end result? Most people weren't really WRONG, it was more a case of whoever came up with the question didn't explain it well enough.

But I think the whole point of the question was to catch out the people who thought it would stay stationary.

It's an excellent question because to answer to 'no' you have to have some understanding of aerodynamics, e.g. that a plane needs air going over its wings to gain lift. This knowledge makes you feel a bit smug and sure of your answer. The twist is that you need even more knowledge, about how planes get their thrust, to answer it properly.

[Kushan]

But I think the whole point of the question was to catch out the people who thought it would stay stationary.

It's an excellent question because to answer to 'no' you have to have some understanding of aerodynamics, e.g. that a plane needs air going over its wings to gain lift. This knowledge makes you feel a bit smug and sure of your answer. The twist is that you need even more knowledge, about how planes get their thrust, to answer it properly.

People on both sides of the argument were incredibly smug about their answer, plus you don't really need THAT much knowledge to know that a plane gathers thrust from it's engines.

I still say the question was poorly worded, it should have asked "will the plane be able to gather enough forward momentum to take off?" rather than just "will the plane fly?".

[+StevoFC MVC]

Something just didn't seem right about it, because it seemed like once the gas was pushed for the plane, it moved forward, never really matching the speed of the conveyor belt. It seems like that they want to achieve the same speed of both directions and then see if the plane takes off. Maybe I'm looking at this wrong?

They should build a large conveyor belt that doesn't require dragging a large belt on the ground. Those guys can do it!

During the show they said what they did...

They first had the plane take off without the belt. They recorded the speed the plane was going when it lifted off the ground.

Then they put the plane on the conveyor belt and moved the truck at the speed previously recorded and started the plane moving. And as everyone saw it took off with no problem still.

I don't understand what doesn't seem right? They explained that a plane is nothing like a car and the ground has absolutely nothing to do with how a plane moves.

[curme]

I think the reason the pilot didn't think it would take-off is because he wasn't a real pilot. He was an ultralight pilot. Ultralight pilots don't have to go through all of those pesky years of flight training and theory, I don't even think you need a license.

I didn't see the episode, I don't live in the states, but I read about it. You would think with so much controversy, they wouldn't half-ass it like it sounds like they did. It sounds like the plane was traveling much faster then the trap. If anyone knows a link to the episode, please post!

[kernatch]

People on both sides of the argument were incredibly smug about their answer, plus you don't really need THAT much knowledge to know that a plane gathers thrust from it's engines.

I still say the question was poorly worded, it should have asked "will the plane be able to gather enough forward momentum to take off?" rather than just "will the plane fly?".

I didn't mean people were smug in a derogatory sense. I was just trying to explain how the question works on a psychological level. To answer no you have to have knowledge, which makes you feel like you know how to answer the question (sompare with someone who knows nothing about how planes work: they might not know how to answer at all, or will give a yes or no answer but for entirely the wrong reasons). I also realise that knowing how a plane gets thrust isn't a terrible amount more knowledge, I just mean that to answer properly you have to go beyond the initial bit of knowledge most rested on.

I also agree the question can be reworded, but like I said, the phrasing of the original is completely intentional in catching some people out. It's called a trick question.

[Fred Derf Veteran]

I always assumed the conveyor belt was just a way of saying "the plane is being kept stationary, can it still take off?" and if you look at the vast majority of the arguments against the plane taking off, they all talk about air flow and such.

...

The end result? Most people weren't really WRONG, it was more a case of whoever came up with the question didn't explain it well enough.

The entire point of this question was to root out the people who thought the plane would remain stationary. This exposes the people who think of a plane as a winged car.

[curme]

I knew something like this would happen:

Not A Believer! says:

It's a lie! It's all a lie!

I cannot accept their findings as they did not follow a method that I approve of, one that will guarantee that I am right that it's dumb to believe that an airplane can take off from a conveyor belt. Their test was stupid and not done correctly, the airplane was MOVING and that is so obviously wrong that I'll stop watching their show , their "treadmill" should have been moving much faster than the plane.

No matter what they say or prove, I cannot be made to believe that an airplane can take off from a conveyor belt. Better luck next time Myth-"busters".

? by Not A Believer! on Jan 31, 2008 at 07:15 AM

kottke.org

:laugh::

[Kushan]

The entire point of this question was to root out the people who thought the plane would remain stationary. This exposes the people who think of a plane as a winged car.

Except that it didn't, not in my case anyway. I'm fully aware that a plane works completely different than a car. As I said, I never took the conveyor into the equation because the question was "can the plane still fly?" and not "can the plane outrun the conveyor?" or something.

[Fred Derf Veteran]

Except that it didn't, not in my case anyway. I'm fully aware that a plane works completely different than a car. As I said, I never took the conveyor into the equation because the question was "can the plane still fly?" and not "can the plane outrun the conveyor?" or something.

If you never took the conveyor into the equation then the answer to "can the plane still fly?" would be an easy yes.

[Kushan]

No, that's what I mean. Like I said, I took the conveyor belt to be a way of saying "the plane is stationary on the ground". So the engines are at full force, but the plane isn't moving forward. That's how I (and many others) interpreted the question and in THAT scenario, the plane definitely would not take off.

Everything Mythbusters did was absolutely correct and I'm not disputing their findings or anything, I'm just saying that there seems to be two real interpretations to the question and depending on which one you took would decide what your answer was.

[Fred Derf Veteran]

No, that's what I mean. Like I said, I took the conveyor belt to be a way of saying "the plane is stationary on the ground". So the engines are at full force, but the plane isn't moving forward. That's how I (and many others) interpreted the question and in THAT scenario, the plane definitely would not take off.

Yes, you got caught in that trap. That is the trap for the people who think of a plane as a winged car.

The people who understood that a plane was not a winged car knew that the plane would go forward.

[Kushan]

Yes, they knew it would go forward, but that never even factored into it for me and many others. Read what I'm saying, I interpreted the conveyor to just be a way of keeping the plane stationary, nothing more. It may as well have said "an anti-gravity field is placed upon the plane to prevent it moving forward" for all I cared.

[Fred Derf Veteran]

...except that I didn't, because I know it's absolutely nothing like a car...

Yet you thought it would remain stationary.

[The_Decryptor Veteran]

The question never stated the plane can't move, it asks if the plane could fly if the tread mill matches it's speed (and it doesn't say what speed, air speed, ground speed, what part of the plane, etc.)

[sundayx Veteran]

Chat more?

[kernatch]

interpreted the conveyor to just be a way of keeping the plane stationary

How could you interpret it that way and NOT be exactly the type of person this question was trying to catch out?

I've never seen someone try to make so many excuses about getting a trick question wrong. Deal with it! It's meant to be light hearted!

[Kushan]

Yet you thought it would remain stationary.

No, I thought the question stated it would be stationary, there's a big difference.

[Lt-DavidW]

It may be easier for some people to visualise the physics if they imagine the plane having frictionless pads in place of wheels and sat upon slippery ice. The plane's contact with the ground has little influence on the thrust driving the plane forward.

Wheels do not anchor planes to conveyor belts...

[Fred Derf Veteran]

No, I thought the question stated it would be stationary, there's a big difference.

I don't really see a difference. If you understand how a plane works then you would know that it would not be possible to stay stationary.

I initially made the same mistake (if you look at my first post in this thread) but I quickly caught on and accepted that I was wrong.

[Kushan]

I don't really see a difference. If you understand how a plane works then you would know that it would not be possible to stay stationary.

I initially made the same mistake (if you look at my first post in this thread) but I quickly caught on and accepted that I was wrong.

What I'm saying is that I thought the question was saying "the plane is stationary, what happens?" and not "will the plane BE stationary?". I thought the focus of the question was on how flight works and not on how ground force affects planes.