Awesome. Kottke : Mythbusters :: Wonkette : SOTU :: Defamer : Oscars etc.

Thankyou, from an easily distracted procrastinator in Australia.
(and I was right)

Awesome graphic, rendered beforehand right?

I think the episode brought the Mythbuster's official forum down a little while ago, or at least caused it to timeout for me. Looking at the posts though, I don't think people are convinced: http://community.discovery.com/eve/forums/a/tpc/f/9401967776/m/4441931059?r=5311922059#5311922059

How does the plane get lift? There is no air friction as there is no forward momentum... If the conveyor can accelerate to the point that the plane can, there wont be any forward momentum...

So im a little lost around the laws of physics... The engines propel the plane forwards, but not up...

i had to explain to my NASA astrophysicist phd wife why I was interrupting her CSI to tivo this. we ended up watching the last 15 min [what a slow, cheesy show, btw]. Because I set up the situation incorrectly--a conveyor belt counters a plane's thrust and keeps it stationary to the earth/air--we assumed no takeoff because there was no air pressure differential--and so no lift--on the wings.

So the plane engine clearly moving fwd [because thrust > drag and friction] read like a busted experiment, not a busted myth.

No Greg, the experiment is right, you are wrong. You confuse speed with force. The treadmill can move with an opposing speed to the plane, but it cannot apply an equal and opposing force, because wheel bearings transmit only a very small rolling friction. The question nowhere states that the treadmill counters the plane's thrust or keeps it stationary. It only that it moves in the opposite direction at the same speed.

I am completely disappointed at Mythbusters handling of this experiment. The science they used and the “explanations” were both completely flawed. The original myth, and ALL of the discussion, centered around one central conceit: The plane would have NO FORWARD MOTION RELATIVE TO THE GROUND because of the conveyor belt matching the speed of the plane. NOT the “speed of the WHEELS of the plane” or any other contrived version.

Of course the plane is going to take off if it has enough forward motion RELATIVE TO THE GROUND to create the Bernoulli effect required to lift the wing because of the airflow over the wing.

I really expected more “science” from MythBusters. They almost explained it properly with the “model car example”. I guess it was the original Myth that was flawed, or my understanding of the Myth. I guess in their mind the myth is that no plane on a conveyor belt can take off if the “speeds are matching in opposite directions”. That is far too simplistic to make a determination, so it is flawed from the get-go.

Those of us who claimed the plane would not take off without forward motion relative to the ground due to the laws of physics are still correct. The planes both had significant forward motion relative to the ground. I just hope everyone involved in the debate understands these distinctions, otherwise this will just dumb down the TV watching public a bit more. It sure was fun though!

I don't know if many here are fans of MythBusters before tonight. I love the show (maybe the concept), but Jason is spot on about how slow the show is. 99 percent of the time I watch it on DVR so I can skip forward. Just as an aside, if others are going to start recording it some of the smaller, side experiments are often the most interesting.

Once you understand that a plane is not a car, I think the fact of its taking off, every time, becomes more clear. The plane doesn't need the ground. The wheels don't cause anything, they just react to the fact of the plane moving forward.

I see three probabilities. The "plane takes off" camp doesn't understand the question. The "plane stays on the ground" camp doesn't understand the question. Or the Grounders don't understand how airplanes work.

What I saw tonight was a plane overtaking the speed of the pickup, making forward motion and taking off. If they went the same speed he wouldn't have passed any of the traffic cones. What am I not getting?

Awesome coverage.

Troy says that the myth requires that the plane have "NO FORWARD MOTION RELATIVE TO THE GROUND"

Except that is not what the question says. That is what you automatically believe, but you are wrong. I will quote the original question for you and you point out to me where it says that the plane has no forward motion relative to the ground:

"A plane is standing on a runway that can move (some sort of band conveyer). The plane moves in one direction, while the conveyer moves in the opposite direction. This conveyer has a control system that tracks the plane speed and tunes the speed of the conveyer to be exactly the same (but in the opposite direction). Can the plane take off?"

Tommy's spot on about why I've never really gotten around to watching the show. It feel like so much plotting and trying things that almost surely won't work before they finally get to a good interesting experiment. That said, your liveblog has made me think harder about watching it.

I've been pretty firmly rooted in the 'it will fly' camp, so I didn't particularly need it demonstrated to believe it, but I just happened to catch Mythbusters this evening while flipping channels, so I immediately popped over to kottke.org and was delighted to find the livecast. I think more things should be reported live via blogs. Good job, Jason.

Did you have a different image prepared for the mind-explodingly-impossible possibility that the plane didn't take off?

If it helps you, I will point out that a plane does not measure it's speed by how fast its wheels are going, but rather by how fast it is moving relative to the Earth. Similarly, a treadmill does not measure it's speed relative to objects on top of it, but on how fast it's surface is moving relative to the Earth.

im impressed with that coverage and that is awesome that it works

im impressed with that coverage and that is awesome that it works

Troy:

If it helps any further, you should realize that no conveyer belt, traveling at any speed, is ever able to stop the forward motion of the plane. The plane ALWAYS moves forward relative to the ground.

Thanks so much for putting the result in a giant graphic at the top of the page. So glad I didn't want to find out by actually WATCHING it myself.

>:|

With the side experiments (Kari, Grant, and Tory) David they usually use one segment to explain the concept, another to do a test on a smaller and/or model scale to test their thinking, then to a full scale production. The problem is they can do two side tests while the main one is made to last for the entire show.

Now it is clear my technical knowledge on this subject is lacking compared to others, so I am not sure I should put forth my two cents .....

But I tend to agree with Rob said:

"What I saw tonight was a plane overtaking the speed of the pickup, making forward motion and taking off. If they went the same speed he wouldn't have passed any of the traffic cones. What am I not getting?"

As I was watching I almost jumped up when I saw this and they also pointed it out and said "WAIT .... that isn't right is it?"

Haha this was a very funny post, Jason!! Specially for the rendered image with the result! You probably had one prepared in case the myth was busted too, right? Please show it to us!! I bet it was something like "oh noez the plane didnt fly!", lolcats-style!

By the way, nice font. Which is it?

I guessed wrong but for the wrong reasons -- my thinking was that it wouldn't take off, because if it had, the discovery would have revolutionized the way commercial airports are built, since there would be far less land required to construct runways. What I hadn't counted on was the fact that the conveyor belt wouldn't affect the distance required for the plane to take off.

As far as the show being slow, that's not the half of it -- those three twits really drive me crazy. I don't care about whatever dumb ass shit they're doing, Adam and Jamie are the reason I ever watch the show.

Like many others, I was originally convinced that the plane could not take off. I've since come around, and I think I might have a useful thought experiment to share.

First, I'd like to point out that any reasonable person agrees that if the plane can't move forward relative to the air, then it will not take off. The real question is whether the conveyor belt's matched motion can make this so. The intuitive (and incorrect answer) is that it can. Just like running on a treadmill, or driving a car on one, if the speed of the treadmill is matched in real time to the forward speed of the person or car then surely there will be no movement relative to an observer on the ground. You're just "spinning your wheels."

So here's my thought experiment. You have a treadmill and an object with wheels—let's say a skateboard. Standing on the ground next to the treadmill, you place the skateboard on the treadmill and hold on to it. Imagine the treadmill is moving at any speed you like. Won't you still be able to move the skateboard relative to the ground? Even if the treadmill is moving really fast, you can hold the skateboard where it is, right? And also, you can slide it along the length of the treadmill with no trouble. That seems like it is also intuitive to me. I'm not sure if it will convince any of the skeptics.

If you agree that you can roll a skateboard around on the treadmill pretty much however you like regardless of treadmill speed as long as you have a good grip, then consider this: A plane's engines work pretty much the same way: they "grab" onto the air and pull it forward. In other words, just like with the skateboard the plane has access to something that isn't moving with the treadmill. With the skateboard there is someone holding it, and with the plane there is the air.

In order to keep the plane from moving forward relative to the ground, you would have to make sure not the runway, but the air surrounding the plane, was moving backwards.

"What I saw tonight was a plane overtaking the speed of the pickup, making forward motion and taking off. If they went the same speed he wouldn't have passed any of the traffic cones. What am I not getting?"

Nobody ever said that the plane was standing still. That was your misconception. The treadmill is moving backwards, the plane is moving forwards at the same speed the treadmill moves backwards. No matter the speed of the treadmill, it can never impart any force to the plane other than a tiny constant rolling friction. The treadmill can go 1000 mph and it still can't stop the plane. It is impossible for a treadmill to hold a plane in one spot because it has no way to apply any force to the plane. I can't believe people still delude themselves that they are right, even when faces with irrefutable proof.

Hey Dan Boland, You better not be Dan Boland from UBC Mechanical Engineering. You bring shame to all of us if you guessed wrong.

Is it possible that the description of the puzzle presents an impossible situation?

So here's an similar experiment:
I put a bike on a treadmill. Instead of riding it, I stand to the side of the treadmill and hold the bike upright with my hands. The treadmill is rigged so that it moves as fast as the bike's wheels move, but in the opposite direction (sound familiar?). Now, from my position off the treadmill, I push the bike forward. Does the bike move forward?

I think the answer is clearly yes. The situation with the plane is the same, the thrust of the plane is based on propulsion that's not related to the wheels. If the bike/plane does move forward, that would mean it's wheels either slide or they revolve faster than the treadmill. So isn't the problem really that the puzzle presents an impossible situation, namely that the treadmill is able to keep up with the wheels?

you have your frames of reference all mixed up Noel. You should be using the common reference frames for conveyor speed and plane speed, that being the Earth. If the bike is not moving relative to the Earth, the conveyor is not moving relative to the Earth. If the bike is moving 25 mph relative to the Earth, the conveyor is moving backwards 25 mph relative to the Earth.

What you are describing is a physical paradox. Basically that the speed of the conveyor belt = speed of conveyor belt + speed of bicycle. What you have is A=A+B, which is impossible when B>0. And that isn't what the question is talking about. Speed of the plane is obviously the speed of the plane relative to the Earth, nobody measures plane speed by how fast the wheels spin. And speed of the conveyor belt is obviously speed relative to the Earth.

Not to be a jerk. But, after all of the explanations about this topic for the time this has been debated, I really feel bad for those who still can't quite understand how the plane, the plane's thrust, and the plane's wheels work together.

Then for the love of God bfos7215, don't go to the mythbusters message boards. There are about 100 people yelling that the experiment was wrong, get this "because the plane moved forward".

http://community.discovery.com/eve/forums/a/tpc/f/9401967776/m/4441931059/p/8

An analogy someone brought up was this:
Person 1: If I let go of a bowling ball, it will drop to the ground
Person 2: No it won't
Person 1: Okay, let's see (drops the bowling ball)
Person 2: No, the experiment was wrong, the bowling ball didn't float in the air
Person 1 commits suicide.

Wow, people still think it won't take off? Embarrassing.

I always read the problem as whatever forward speed the plane gains is matched by the opposite speed of the conveyor belt- meaning if the plane begins to lurch forward on the conveyor belt the experiment is already a failure because if the plane has lurched forward and the conveyor belt is no longer matching the speed of the plane.

Don't misunderstand- the wheels are there to decrease friction on takeoff- but even the tiniest amount of friction (like, say, the amount the White House Press corps gives the President) is enough when you're increasing the speed exponentially, as one would have to do. Don't give me this "you could have it going 1000 mph! It wouldn't matter!" crap- I'm not talking about 1000 mph or a million mph- I'm talking about an exponentially increasing speed to generate enough friction to keep the plane stationary.

If we're talking 25 mph one way and 25 mph in the other of course the plane takes off- that's not even up for debate.

If we're talking 25 mph one way and a speed which increases at the rate that the plane's thrust moves it forward from a fixed point going the other way (again- we're talking exponential speed increases) the plane sits "like a brick" with the wheels spinning faster and faster until a hole is ripped in the space-time continuum and Doc Brown shows up. Time dialation and length contraction ensue.

MythBusters was very specific tonight- they were only testing the easy-to-get-your-head-around version of the problem- the one that can be tested in the real world. They could have at least acknowledged the other reading and not accuse everyone who doesn't think the plane will fly of thinking a plane is a car- that's just silly.

If the plane didn't move forward, it wouldn't fly.

But the plane does move forward -- regardless of whether or not there's a treadmill moving in the opposite direction below it -- because the forward movement of the plane doesn't rely on the free-spinning wheels. It relies on the propeller, which propels the plane forward no matter how fast the free-spinning wheels are spinning.

I hadn't heard this one before ... but this was even controversial? People really thought that something going on with the planes silly little vestigial unpowered wheels would somehow stop the its big beefy engines from pushing it forwards against the air?!

Jesus. I'm at a loss for words.

that was awesome!!!! i knew it would work. i just can't believe how many people (pilots included) thought it wouldn't take off.

This is really funny... of course the plane will take off. The plane could care less what the ground under is doing (or the earth for that matter), it only cares about the air over it's wings. The engine will still provide the thrust to push the plane forward THROUGH THE AIR, and it will take off regardless of what the wheels are doing. (unless the speed is so great to do damage to tires or bearings).

It's fun to put someone not used to planes in the copilot seat, and start steering the control wheel off the taxiway. They don't realize your actually steering the plane mostly with the rudder (foot pedals), by the air blowing past it. Of course tight turns require differential braking or some planes have the rudder linked to steerable wheels (many just caster freely).

Note also that icy runways don't really cause too much problems for most small planes, as they really don't need there brakes to slow down. It actually smooths out the landing, and any accidental sideways movement is not much of a problem, as it can be on a dry runway.

Why is this so obvious?... I'm a recreational pilot =]

that was awesome!!!! i knew it would work. i just can't believe how many people (pilots included) thought it wouldn't take off.

It's not a physics problem - it's a trick question.

I've yet to see a good explanation from any of the people who think the plane will stay on the ground to this central question:

How does the conveyor belt stop the plane from moving?

The original questions does NOT say "the conveyor belt pushes backwards on the plane". That's because the conveyor belt CANNOT push on the plane in any direction but UPWARDS. The conveyor belt cannot put any significant sideways force on the airplane.

Therefore the plane will always move forward, and therefore it will always take off.

The upshot is that if the experiment were performed ideally, then the speed the wheels are turning (as measured by the sort of speedometer that cars use) would be exactly twice the speed of the airplane as the wheels left the treadmill (as measured by a radar gun, say).

In a related matter, an airplane WILL lift off the ground - it will technically "take off" - while standing still on the tarmac, provided there is a fast enough stream of air blowing over the wings.

This can happen in a strong storm, or even when another aircraft generating enough thrust taxis in front of it.

This is why small-plane pilots "tie down" their aircraft, not just chock the wheels. It doesn't matter whatsoever how fast the aircraft is moving relative to the ground. All that matters is how fast the aircraft is moving relative to the air flowing over the wings.

The speed of the plane on the conveyor belt is irrelevant. The plane's forward motion is not caused by the movement of the wheels. In fact the wheels move freely. What pulls the plane forward is the propeller. If the air moves fast enough over the wings, the plane flies. The speed of the plane relative to the ground matters not. The crucial thing is the speed of the plane relative to the air. What creates lift is the air moving over the wings.

everything's a physics problem, literally. And this falls under the category of everything.

Stewart- friction. The friction of the wheels- while incredibly slight, would, at exponentially increasing speeds, be enough to keep the plane stationary.

I'm not thinking of a plane as a car, by the way- I hope that's clear- I'm talking about steadily increasing the speed of the conveyor belt to keep pace with the speed of the plane- the only drag on the plane would be the wheels- but as stated in the original problem we apparently have a conveyor belt capable of keeping up with the plane- therefore it would need to increase speed rapidly and endlessly. That plane wouldn't move.

That being said, if it's just 25 mph in opposite directions it'll of course take off immediately. Duh.

Sigh. So much confusion.

As a pilot, a plane with normal (working) easily spinning wheels WILL be able to accerate THROUGH THE AIR MASS pretty normally once take-off (full) engine power is applied and proceed to take off with no problem.. (as shown on the show). Only effect of the belt is that wheels are spinning much faster than normal.

In the theoretical statement of the problem the belt would have had to accerate backwards MUCH MUCH faster than flight normal speeds to try to get rolling wheel friction to match foward propeller thrust. May take a belt speed of 100's mph -- (and would make even a tiny plane need high speed jet tires). But I suspect that even with the belt going and Indy car speeds it's a lost cause because the engine/propeller can still provide MUCH more forward thrust than any reverse drag from wheel friction. (Even a car going 150 mph straight is expending 95% of it's energy pushing air out of the way rather than wheel/road friction. Even more so for a plane.)

The ONLY simple way I can think of to demonstrate the 'failure to fly' situation is to put OVERSIZE ALMOST FLAT tires on the plane so that rolling resistance is VERY LARGE. At that point the tires rolling on the belt could probably be made to keep matching the forward thrust provided by propeller. So THEN maybe you can force a situation where plane won't accelerate forward on this moving belt.

(And the belt acts differently than low/flat tires on a runway. On a normal runway the plane's slowly gathering forward speed would slowly lift weight off the flat tires and allow an actual takeoff to occur (but with a REALLY BAD landing to follow). But with high enough wheel rolling resistance an increasing belt speed could probably keep up with propeller thrust and prevent any lift and lessening of weight on the wheels -- and plane would stay rolling (poorly) on belt even at full engine/propeller thrust.

That's my two cents on this whole thing.

I can't imagine a pilot willing to risk a real plane in such a setup with such mis-behaving wheels. So I suspect this will stay unproven for a long time. ;-)

I'm amazed.

Not because the plane took off, but because I just read the Mythbusters comments and the number of people who misread the question and who are *still* trying to argue that the plane should have remained stationary is truly extraordinary.

So the basic problem with this problem is that it can't be defined to mean what some people think it seems like it means.

There are really only 2 possible cases, either the "speed of the plane" is measured relative to the ground, or it's measured relative to the conveyor.

I hope everyone sees that if the "speed of the plane" is relative to the surrounding ground that the conveyor can only move if the plane moves relative to the ground. Therefore, the plane has to be moving forward if the conveyor is moving at all. The wheels will spin twice as fast as they would if there was no conveyor, but that's of no import, and is easily accomplished.

The speed being relative to the conveyor is a contradictory definition. If the conveyor starts at 0 speed, then it can only start moving if the plane starts moving relative to the conveyor, but we already decided that the conveyor is stationary relative to the ground, which means that the only way the conveyor could ever start to move *in the infinitesimal boundary case* is if the plane moved *relative to the ground* in the first place. This is a contradiction to the notion that the plane can't move relative to the ground, and, in fact, a contradiction to the notion that the plane can move relative to the conveyor.

If the plane ever *tried* to move forward, the conveyor would have to *instantaneously* come to the speed required to exert an equal and opposite force on the plane through the wheel bearings, which is a physical impossibility. And that's not to mention that the tires would fail *way* before the bearings, causing the plane to crash onto the conveyor, and the conveyor would have to instantaneously stop in order to avoid flinging the plane backwards, another physical impossibility.

The only way this second definition can remain consistent is if the plane never moves relative to the conveyor or the ground. And the only way that could happen, by Newton's Laws, is if you left the brakes on. Which is *technically* consistent, but a trivial statement.

So we're left with 2 possible meanings of the original puzzle, one of which is sane and easily consistent and easily attained, and one that's contradictory, physically impossible, and insane.

Which definition do you think is the "right" one (assuming this problem has any practical application at all)?

Totally disappointing. Of course, the plane would take off for the reasons mentioned. However, I thought I was going to see the myth as I heard it, which was: the conveyor belt was to counter the plane's forward motion so that it could take off with essentially no runway. Given that, of course I would say it wouldn't work since it would require no forward motion of the airplane relative to the air, however, as we know, the conveyor couldn't prevent the forward motion, so for that reason as well, I knew the version of the myth I heard was wrong. Of course, the version the Mythbusters tested was not this version I'd heard. It's quite common for there to be several versions of a myth, and I think this might be the cause of some of the disagreement.

Jason: Please please please make some "HELL YEAH THE PLANE TAKES OFF" t-shirts and sell them. I would stand in line to buy one.

Ray- we're talking about putting planes on conveyor belts and you want to restrict the discussion and keep it realistic?

Really?

I second Lewis on the t-shirt proposition. If you don't make them, I will.

l-o-v-e the graphic and that roaches won't make it...still trying to catch up on the whole shaving cream/car exploding bit...

Jason, I'll tell you why people watch this show - that female assistant is cute and charming. I've never been able to watch the show longer than the time frame during which she is on.

It's just on now on the west coast.....where is she? It's been 10 minutes since she last made an appearance. sigh.

as someone who copped right up front to remembering the assumptions wrong from the original question, I'm kind of amused at how pissed off I get to read replies that start with "No, you're wrong..." and "that's your misconception!"

Makes me glad to not have to attend offsites with know-it-all engineers very often.

And about the Mythbuster twits, the phoniness of their TV enthusiasm is surpassed only by those jokers on Pimp My Ride, who sit around a conference table and try to act [sic] like a checklist is somehow dramatic.

How about a nice, old-school-style science show that's as deadpan as a classroom film? It could still be absurd as hell, content-wise, just throw in John Hodgman and a couple of narrating silhouette heads? Maybe call it Science Mystery Theater 3000 or something?

The question as asked allows for only one outcome - the plane taking off.

Now, if the question was instead the control system maintains the velocity of the conveyor belt at the same level as the tangential velocity of the wheels but in the opposite direction what do people believe the answer to be?

Addendum:
A variation of the myth as I heard it, which I just made up, would be that rather than a conveyor belt, there is a really fast headwind, which keeps the plane stationary relative to the ground, but is fast enough for take off. The problem then is that the plane is "flying", but it's not getting anywhere relative to the ground. Remember the version of the myth I heard (above) was some system to have essentially zero runway. So, to get the plane to have some ground speed to get anywhere, you'd have to slow down this headwind, or turn a right angle to it.

Wow, lots of disappointed people are still making excuses as to why the plane

took off.

"put OVERSIZE ALMOST FLAT tires on the plane", haha thats my favorite!

Why not just strap the plane down to the conveyer belt?

Could a plane equipped with fixed ice skates instead of wheels take off on a vast sheet of ice? What about a plane in a strong head wind, does it have to move relative to the ground to take off? Or a plane in a strong tail-wind, does it have to move relative to the ground to take off?

The first question is basically the same as the one the mythbusters considered. (Someone will argue with me I'm sure).

But the point is that a plane taking off has absolutely nothing to do with it's motion relative to the ground. It's the plane's motion relative to the AIR that matters. The whole point of the airplanes engine is to push air. It never pushes ground. The airplanes wings also push air, in a somewhat different fashion.

Think about a car equipped with wheels (but no propellor or jet). Can it take off? If it can, how long will it remain airborne? Can the car take off on the giant conveyor belt? What about a car with (fixed) ice skates, can it take off on a vast sheet of ice?

Ryan- that would be a really neat no-runway takeoff followed by a really spectacular crash... I'd pay to get in to watch that.

Consider this version of the experiment...

I'm riding a bicycle on a treadmill. The speed of the treadmill matches the speed of my bicycle. In that case, it's pretty clear that I wouldn't move forward. My cycle's tires are propelling me forward against the surface of the treadmill, but the surface of the treadmill is moving backwards at the same speed, negating my progress.

Now, consider this. There's a handrail on either side of the treadmill. I grab hold of those, and allow my bike's wheels to spin freely.

So, the wheels are spinning at the same speed as the treadmill, and I'm at a standstill.

This is a huge point - it takes no effort to hold myself in place. The treadmill exerts no force on me at all - my freespinning wheels allow negate it completely.

Now, I start pulling on the handrail. Clearly, I'm going to start moving forward. Even if the treadmill speeds up, it can't impede my progress at all. My free-spinning wheels will spin faster (in synch with the treadmill), but I can still pull myself forward with the handrails, with minimal effort.

No matter how fast the treadmill moves, my bike's wheels spin to match, and I can still pull myself forward. That's because I'm exerting my force against the handrails, not the treadmill's surface (as was the case in my first example).

The airplane does the same thing - it's not exerting any force against the treadmill. Nor is the treadmill exerting any force against the plane - the plane's freespinning wheels make sure of that.

The plane's propeller, however, IS exerting a force against the air, which is pulling it forward. Eventually, it pulls against the air with sufficient force to propel it towards takeoff speed.

Todd, I'm not making excuses for why the plane flew. I'm on your side.

I first stated in my earlier post that of course a plane, with properly working wheels, would accerate forward through the air and down the belt and take off -- regardless of belt speed.

But I can say from experience that small planes take MUCH more engine power to roll on severely underinflated wheels, taking up to 40-50% of engine power rather than the normal 10-20% used for taxiing. So severely underinflated tires would be one way to drastically increase wheel/ground friction to force a takeoff failure. Is it a fair test of the problem? No. But it seemed a simple way to describe what level of increase in wheel friction would be needed before the wheel forces would affect forward plane accerlation.

I'm with Felipe way up above. What font is that?

I thought it was hilarious that they insisted this episode would "quell" the debate or somehow "settle it once and for all."

Kottke, your non-enthusiasm for the greatest television show ever conceived disappoints me greatly. There isn't enough shows like Mythbusters on television.

And, predictably, disagreement about what actually happens to the plane can be traced back to a misunderstanding of the question. Seems like every time I debate somebody it gets really heated then when we come back to the original premise and actually try to understand exactly what is being discussed it ends in agreement.

And/or I get a drink in the face.

I'm watching the show in the late-night rerun, and about halfway through I thought, "I wonder if Kottke did anything for this?" Beautiful.

(sigh) It's still an invalid test: If the conveyor was matching the FORWARD SPEED of the plane (as stated in the original question), it wouldn't have moved forward; if it hadn't moved forward, there would have been no air flowing over the wings; if there was no air flowing over the wings, it wouldn't have taken off.

So, yes, obviously: If you don't match the forward speed of the plane, and therefore allow it to still move, it's going to still have air over the wings, generating lift. Obvious result.

If this test could be performed to the original specifications (quite likely impossible to achieve), it would be obvious that the plane would NOT take off. But, I'm so sick of hearing about it, I'm happy to have all the "yay, it took off!" idiots amuse themselves that they think they are correct.

@kottke please make tshirts

How did you make the "HELL YEAH THE PLANE TAKES OFF" graphic in less than 60 seconds?

Stephen, there is only one correct way to interpret the question. The people who think the plane should stand still and not fly always end up arguing that the plane speed (measured relative to the treadmill) should equal the treadmill speed (relative to the ground) such that the plane speed relative to the ground is always 0. This is physically impossible, because the treadmill can't apply a force to the plane, as soon as the plane starts moving (relative to the ground) the theoretical treadmill speed should shoot up to infinity. This is because the plane speed relative to the treadmill will equal the plane speed relative to the ground + the treadmill speed. And that has to equal the treadmill speed. So you have treadmill speed equals treadmill speed + plane speed. If you want to get silly with it, as the treadmill speed instantly approaches the speed of light it creates a layer of super hot plasma and generates more heat energy than a thousand atom bombs, vaporizing the plane and sending everything in the area high into the air (so the plane does fly).

The much more sensible and correct way to measure speeds is relative to the Earth, the same way we always measure speeds in everyday usage. So the plane speed (relative to the Earth) is equal to the treadmill speed. As we saw, the plane goes 25 mph forward, and the treadmill goes 25 mph backwards... and the plane takes off. The end. It really isn't complicated or anything.

So you have a choice, the physically impossible paradox of measuring plane speed against the treadmill, or the commonly accepted definition of speed (measured relative to the Earth). Neither way results in the plane standing still.

I third the t-shirt comments-- I'd be up for one of those.

Hey, Logical Pilot. You're wrong. If the conveyor was matching the FORWARD SPEED of the plane, it WOULD have moved forward. The plane would have been pulled through the air by its engines, dragging its tiny little wheels over anything below.

One more vote for the tshirt! :D submit to Threadless!

@Logical Pilot, the conveyor belt does not apply backward force (in any significant measure) to the plane. It doesn't matter how fast it is going. It is no relevant to how a plane takes off. You are wrong. Live with it.

IF the plane wasn't moving forward then it wouldn't take off. IF. Explain how a conveyor belt stops a plane moving forward when the wheels of a plane apply no forward/backward force to a plane (not a measurably significant one anyway).

What is it with people refusing to accept overwhelming evidence and reason?

Another vote for the shirt!

This has been really interesting and I wish I had the time right now to read through all the comments. That said, maybe this has gone over already:

I think the reason that a lot of us feel that the plane won't fly is that we know that it won't take off if it isn't moving in relation to the air around us. That being that there's no practical use to researching this problem. We won't be able to make shorter runways if we use conveyor belts because they'd just be incredibly expensive runways with unnecessary treadmills on them.

So the real question that's being asked (I believe) is: "If we need to get a plane up to a certain speed to take off, can't we just put them on treadmills and take off in no space at all?" The answer of course is no, it's the airspeed over the wing that's important, not the speed of the wheels. That's something we all agree on.

Now what if we tried some sort of wind tunnel/tread mill combination? Could that be used to create a practical, short runway?

I like this myth a lot, and it's obviously a big topic for debate. As the original question asks, if the conveyor matches the plane speed, it will not take off. This is very simplified, first of all, it depends on the plane. The scaled down version used a plane that could take off almost instantaneously, this is a stretch for the myth, because the bernulli effect is the reason the plane cannot take off. Because the force of the model planes engine is so high relative to its mass, it acts as a small rocket. And we all know that a rocket doesn't require air resistance to take off ,( rockets in space... a vacuum)
sooo they used too small of a plane, or the myth cannot cover all types of planes, Adam's jubulent declaration of the plane only requiring "80ft" to take off proves this point. The thrust of the engine is so great, it doesn't require very much air resistance to take off. but your saying, "with the tarp, there was no air resistance?!?!" RONG! the plane is always accelerating, with the reference frame being the plane and tarp, because it moves by the cones. There is no way Jamie's truck accelerates as fast as a plane, and remember, for air resistance to become negligible, (as in no forward motion) the tarp would have to be moving perfectly with the plane. Also this is nothing like a plane on ice, or a friction less surface. Because if it was frictionless a plane would take off even faster, ( bearing are used to reduce friction therefore making forward motion easier) Obviously the plane took off, but it was still moving but it is generally not testing the principle that the wright brothers used to create their wings. I liked this controversial myth, because of it's physics. But they effed it up big time. For the people who understand the physics of flight (like the pilot!!) this seemed pretty straight forward. Oversimplification, and misunderstanding of how a planes wings, and engine thrust work lead to a defeat. This will defiantly be revisited. And for Christ's sake, They have a physicist on the show! (Grant) they shoulda asked him to math it up!

im still confused....

if the wheels and the conveyor belt have nothing to do with the plane taking off, then why do planes have wheels in the first place.

if the speed of the wheels has nothing to do with the plane taking of, then why dont they just put some soft rubber pads on the bottom of the plane?

why do planes have to use such a long runway to take off?

I'm want to identify a good way to explain this to non-believer. If you once believed the plane would not fly but now (correctly) see that it will, what changed your mind? Was there a particularly good comment or thought experiment that flipped your switch?

Lol, this thread is hilarious... but I have a few comments, and I hope people get them. Seriosuly read on though, I actually tried to convey my flawless points in the midst of this.

Ok, i skipped the last... 403538402 posts, because I got sick of seeing the same arguments without my thought being conveyed at all... I cna only assume this hasn't been said.

The "grounders" keep on saying that the plane CANNOT FLY W/O FORWARD MOTION RELATIVE TO THE GROUND.... ok, good for you for yelling that in my face 500 times. But there is one thing you have not considered... in what other situations will a plane take off without forward relative motion?

Ok, Whoa buddy, you've crossed the line here. Thats what you might be thinking, but I don't see where I can be wrong here. If I am not mistaken, the plane takes off, because of the benoulli effect, yadda yadda yadda. More or less, AIR has to move FAST ENOUGH over the wings. Correct? That is pretty much the main requirement here.

Ok, I wish the mythbusters did THIS experiment which would pretty much put this to rest. Put a giant iron stake in the ground. Run a steel cable downwind, attach to front of plane. Stick this setup in wind tunnel, Turn on giant fans.

WOW! The plane flies! and guess what guys(and gals), theres no forward motion relative to the ground. But, because enough wind is moving across the wings, lift is created, and the plane flies.

Ok. Now bear with me. If IN THEORY (actually I don't know if any plane can actually do this) the propeller can provide ENOUGH wind movement(this is what its job is, after all) to PUSH wind OVER the wings, lift is created. Yes? Ok. myth not busted yet.

Now a key component here is the TREADMILL. This myth wants to say that treadmill is the (bear with me) WIND in the WIND TUNNEL, PULLING(or pushing, whatever) the plane backwards. If you chain the front of the plane to a stake ahead, and you pull the tarp(treadmill, whatever) underneath the plane, are not all of the requirements of this myth completed?( note, plane is not running, to prove my point) A- Treadmill moving same "speed" as plane in opposite direction. plane has no relative motion to ground. Plane does not fly. Physics is true, this is obvious.. no air moving over wings. Myth true???????

Alex Ross said it correctly. A big problem with this myth, that everyone kind of takes into consideration, but not really, but is also an argument( its too early to make sense) is that whole argument with the bike that Alex said, how the external force of the propeller(or chain) affects the plane. Everyone keeps on bringing up the retarded argument that "Oh man, you dumbies, the wheels provide no friction cause of the bearings in them, so the planes forward force easily surpasses that reverse friction force, and it moves forward along the tarp and the flies. OK GENIUS! Standing applause for that man.. ok I'm kidding. Did i not state before those people who kept on yelling "W/O FORAWRD MOTION" in our faces? Guess what! The plane has forward motion!!!! SO THAT IS WRONG. You cannot test hte myth when you don't follow it!!!

Essentially, all of this writing was to prove this one point. THE TREADMILL(Tarp, sheet, etc) IS ONE HUNDRED PERCENT POINTLESS. ABSOLUTELY USELESS!!!!!!

I am 99.999% sure that is a right statement unless some professor from MIT proves me wrong, and I humbly accept that. But hear me out.

The treamill is pointless. You know what can replace the treadmill? AN IRON STAKE WITH A CABLE TO THE PLANE in the back!!!!!!! Lets see whats fufilled,shall we?

Plane's ENGINE is running, providing full force of air. CHECK
Plane isn't allowed forward momentum... CHECK

DO THE TEST NOW!!!!

Now, I think that this is testable , however, results will vary with a plane. If you are going with, IS IT POSSIBLE, then yes you will get a plane that can fly, and you will see why in a second. If it is "for every plane", ... well, thats not gonna happen, and i'll say why in a min.

IN THEORY (this is because I have no clue if a plane like this exists), if you stake the plane in the back to the ground, and you have a propeller engine, that is drastically overpowered to the plane, and in even a better situation, two props on the wings.. WHATEVER> the prop in theory, going fast enough(or if it is large enough) will push ENOUGH air over the wings, for them to create lift, and the plane will take off. Yes? I can be flawed, i'm no aeromechanical dynamical thercanical engineer. Guess what ??? MYTH FREAKIN BUSTED!!!! THE plane FLIES.. A- plane is working. B- no forward momentum(replaced treadmill with stake, because as said before they do exactly the same thing)... assuming the original treadmill can provide so much friction on almost frictionless wheels(like 5000mph) that the plane HAS to go full power and provide X much wing like i just said will be enough for lift.

Now, this will not work with pusher props behind the wings, or jets, because they themselves aren't actually pushing air over the wings.

I hope people understand my theory/point/provingness. It doesn't matter is its a treadmill, stake, whatever, for this myth. Because in this myth, all it wants to do is really say " X is preventing the plane from having forward momentum when its under power, can it take off?" I say that you just need a powerful enoguh engine that will blow enough air over the wings.

As a high school student with one year of physics... Yeah, I say it flies under these circumstances. And bring it, I'm prepared to defend this.

Thanks if you've actually read it, and I think you shouldn't type any replies below if you didn't read it and just scrolled to the end to read my conclusion to bash me.

Thanks

Chris @ 2:27am,

On takeoff, planes have wheels to prevent them from dragging their fuselage across the ground. Other than this support, they apply no significant force to body of the plane on takeoff. On landing, they're used for braking.

Rubber pads could work instead of wheels, but they will possibly burn up from being dragged across the ground. Once they burn up, you're back to the plane dragging its fuselage across the ground. I suppose that if you slicked up the runway with a nice coat of lubricant, rubber pads would work just fine. Like a plane on skis taking off from a frozen lake.

On takeoff, planes use runways to obtain the speed necessary to generate lift from their wings. Lighter planes need less runway. Planes with bigger wings need less runway.

Hope this helps.

And planes have such a long runway to take off because they need to build enough speed to have enough air moving over the wings to create enough lift to counteract the weight of the plane so that it rises. You'd be surprised how little plane needs to take off. That ultralight takes off in 80 feet, i believe the shortest take off for a bushplane is TWENTY FOUR FEET. I know. You're used to giant jumbo jets and C-130 planes in the army.. thats because, as I said, Jet engines dont work in pushing air over wings it pushes the plane into the wind (Or acts as the pulling stake in the windtunnell) and Giant giant prop planes... well i'm sure a powerful enough engine would rip itself out of the plane lol as my point was saying before

A plane's wing produces lift because the air above it flows faster than the air below it (due to the wing's shape). Therefore: no air flow, no lift, no takeoff, period.

So what is relevant is the plane's speed relative to the air (i.e. a ground-stationary airplane can take off in a wind tunnel that blows air over the wings). Haven't seen the show, but if the conv. belt is rigged so the plane does not move relative to the air it does not take off. No ifs and buts, thrust, friction, wheels, bearings and tarmac have nothing to do with this, any 'scientist' going that route towards explaining this is really rather laughable.

Think about it: if this would really work would we be building aircraft carriers and runways the way we do?

Oh, stubby got it, and he used better puncutation than I did..... See two above lol

If you start with the assumption that the treadmill will keep the plane from moving forward, then no, the plane won't take off. The plane needs air moving past it's wings to generate lift.

But you're missing the point - the treadmill DOES NOT - CAN NOT - keep the plane from moving forward.

A treadmill can keep a jogger, or a car, from moving forward, because joggers and cars generate forward motion by pushing against the ground. If that ground is moving backwards (in the case of a treadmill), then their forward progress is negated.

But a plane doesn't generate forward motion by pushing against the ground - it generates it by using its propellers to move air. So, the treadmill can spin as fast as it wants - the plane's freespinning wheels will just spin faster - but the plane itself will continue to pull itself through the air. Eventually, it pulls fast enough to take off.

All the treadmill has done is make the freespinning wheels spin twice as fast as they otherwise would have.

Matt, correct, and the point that I was trying to prove was that IF the treadmill somehow got fast enough, and you had crappy bearings in the wheels to provide enough reverse friction, it WOULD hold the plane back. The whole point of this myth is to capture the attention of someone who won't think about it so they can wonder "Oh man, a plane on a treadmill, NEAT-O"... however, again, its easily proven wrong by the fact that a treadmill provides no friction through the wheels!

Thats why I went with the "chain the plan back" style, cause THAT actually tests the theory that the MYTH REALLY WANTS TO TEST>.... the idiot that made up the myth just threw in the treadmill to piss people off.Like me.

Why is this even newsworthy? The answer is so obvious. Planes are not propelled by their wheels.. I never understood why this became such a debate. It obviously doesn't matter how fast or what direction the wheels are spinning as long as the plane is propelling itself forward via the propeller.

Yes, John, but thats not What I-Other people who looked more into it are arguing(NOT INSULTING YOU. i just don't know how to say it) WE're arguing that if you actually look INTO the myth, the principles are that can the plane not move and take off.. hence my novel that i wrote.

chris asks, “if wheels don't affect the planes ability to take off why does a plane need wheels?”

well, chris... the truth is that a plane doesn't need wheels! there are float planes, which land on water and have no wheels. There are planes with ski's too. The thing is that planes have to spend some of their time on the ground. When they're on the ground they need to remain mobile. Actually, a plane with soft rubber pads on the bottom would probably be able to land onto a large sheet of ice. But on concrete, the rubber pads would have a tendency to stick and so landing would become a dangerous proposition.

Runways are very long because it can take a while for an airplane to generate enough airspeed to lift off. Sometimes, a plane might have a problem while it is taking off and might need to have enough room to slow down without running off the end of the runway and into a building or river or what have you. Also, it's important for a plane to have plenty of room to slow down while it's landing.

I'm wondering if any of the “plane stays on the ground” people can explain why a kite will fly? They don't move relative to the ground, at least not very much. But, you need wind to fly a kite right? If the wind isn't blowing, you can make your own by running around. If the wind isn't blowing and you're standing on a conveyor belt that counters your speed exactly, then you won't be able to generate any air flow for the kite. The kite won't fly. But notice, this has nothing do with the ground or the conveyor belt at all. It has to do with the wind! If a breeze kicks up, suddenly your kite will fly. It doesn't matter if you run on the conveyor belt, or stand still. Actually, running and standing still are the same thing from the kite's point of view, because it's anchor to the ground is holding still.

Most of you have your minds so stuck in the physical theory's that you can't see the very basic logic of the situation. The wheels being on the ground have absolutely nothing to do with the air speed and friction that the motor and propellers create. Get it the wheel speed has only an infinitesimal amount of friction but it won't impede the air friction at all. and any of you who claim to have Phd's in physics and think that the plane wouldn't be able to get off the ground are morons, cause it happened, your all just upset that you thought you were so smart when it turns out you were really just stupid.

As a pilot myself, I'm kind of embarrassed for the ultralight pilot who thought the plane wouldn't take off. I guess that's because ultralight pilots never have to go to ground school, where you learn about the four basic forces acting on an aircraft? :)

As for the rest of the debate - what we continue to have here is again a case of not really understanding the question. If the question is "Does the plane take off?", then the answer is always yes, it doesn't matter the surface, since at full power the plane will be moving forward unless physically attached to the treadmill.

But if you think the question being asked involves a precondition that the plane is stationary somehow, even though it's at full thrust, then you are asking a different question. What needs to be done is to prove that it's possible for a plane at full takeoff power to have it's thrust completely and exactly negated by wheel friction drag. If you can prove that this is possible, more power to you.

But as a pilot and aircraft engineer - I can tell you that won't be able to. Let's be practical, not theoretical. There isn't a plane in the world that can generate enough wheel friction to match that thrust, because the axles will catastrophically fail before reaching that. If you did engineer such a plane, it wouldn't be able to take off under it's own power even without the treadmill, which means it's not a plane in the first place. This, maybe, is what the Mythbusters need to prove for everyone.

But lets be practiacl. I know it's tempting to dive into the theoretical world of "what if" here, but this is kind of like chasing down perpetual motion devices. Good on paper, but they don't work in reality situations, for simple reasons.

So the question the Mythbusters answered tonight is this - If a plane applies takeoff thrust on a moving treadmill, will the plane take off? For every plane ever built, and every plane that will ever be built, the answer is yes.

Most of us? Cmon, keep it simple. Let's keep it civil.

Once again, I'll fight against windmills on conveyor belts and try to clear up some misconceptions:

The original myth, and ALL of the discussion, centered around one central conceit: The plane would have NO FORWARD MOTION RELATIVE TO THE GROUND because of the conveyor belt matching the speed of the plane. NOT the “speed of the WHEELS of the plane” or any other contrived version.
Ah, so you're aware that there are bastardised versions of the 'myth' that make crazy/nonsensical/uninteresting assumptions, and that the belt actually has to match the speed of the plane. I'm intrigued, go on.

Of course the plane is going to take off if it has enough forward motion RELATIVE TO THE GROUND to create the Bernoulli effect required to lift the wing because of the airflow over the wing.
Oh well ... it started of so well, but here you reveal that you know jack squat of some critical concepts involved. Firstly, it has been taught in schools for decades that planes fly because of the Bernoulli effect, but that's not true. It's one of those things where every good pupil can recite the 'correct' answer and get points for it, but no one really understands what's going on ... they just assume that the teacher understands it, but they can't yet because it's very complicated, almost like magic. Which seemed plausible back then, because wasn't it also this mysterious effect that caused water circling down a drain go in one direction on the northern hemisphere and in the other direction in the southern hemisphere? Only no one could ever remember which direction was which ... because that's another myth without a basis in reality (and it has also been busted on TV). So all you could do is learn the 'correct' solution by heart, without fully understanding it. There is a component of force here contributed by the Bernoulli effect, but it's way too weak to trump the other parameters; the real-world result is random. In the same vein, pupils were taught that the shape of a wing makes the air on the top side travel faster along the surface than on the bottom side. You can't really see why this would be the case, but you assume the teacher does, so you just believe it. Well, it's wrong. What really happens is that wings deflect air downwards, which results in the equal but opposite force known as lift. Your intuition might not tell you that this is a totally natural, common-place phenomenon unless you've tried standing on a skateboard and throwing a heavy weight away from you, which makes you move in the opposite direction. But it becomes blindingly obvious when you think of helicopter rotors instead of airplane wings. The helicopter throws/pushes air downwards, right? And the craft lifts upwards as a result, right? So there.

Secondly, the conveyor belt does not cause the air above it to move along with it. Well, it does take a tiny sliver of air with it, and above that is a tiny sliver of turbulence, but the wings of the plane are way above that. So, conveyor belt or not, ground speed has no effect on lift, only air speed. I totally agree that it would have been way cool if the Mythbusters would have done another experiment with the belt running in the opposite direction, matching the speed of the plane relative to the earth directly instead of inversely. (I don't think either variation is canonical.) But the truth of the matter is: it doesn't matter anyway!

I guess it was the original Myth that was flawed, or my understanding of the Myth.Yes. There is a lot of confusion. Most wordings of the 'myth' are ambiguous, but most people don't even begin to consider that it could be ambiguous, because they find their interpretation so obvious. And rightly so, in your case. You seem to be quite clever, and you came up with a very good interpretation. (Stupider people have came up with gems such as "the speed of the wheels matches the thrust", which is just nonsensical gibberish.) The flaw was that other people had different interpretations, but too often they assumed everyone was on the same page, and you were just talking past each other, on different, err, planes.

Those of us who claimed the plane would not take off without forward motion relative to the ground due to the laws of physics are still correct. Firstly, this is only correct when by 'ground' you mean the earth and not the conveyor belt (potential source of confusion there!), and secondly, even mentioning this in the discussion at hand is a complete non-sequitur. There never was any component mentioned capable of holding the plane in place. The statement above is correct, but it doesn't matter much.

Is it possible that the description of the puzzle presents an impossible situation?
Some descriptions definitely are impossible, yes. The one that was on Boingboing, for example, didn't make any sense at all.

HTH!

What really scares me is that, in that Mythbusters episode, the 'expert' who'd guessed wrong wasn't some anonymous guy posting to the web and claiming to be a pilot, but for the first time (for me) it definitely was an actual, real-world pilot. In my vividly exaggerating imagination, the sort of people who'll fly a plane without really understanding what keeps it up there are also the sort of people who'll put their poddle in the microwave in order to dry it after a walk in the rain.

after reading all the comments, i think the spirit of the myth has been overlooked. if you hold onto the handrail of a treadmill, and pull yourself "forward", the treadmill is supposed to match the speed of the wheels EXACTLY. no matter how much you pull, the wheels underneath you will compensate....likewise, if you push yourself backward, the treadmill will accelerate to keep the wheels @ a constant speed. THE MYTHBUSTERS basically had a CONSTANT treadmill...(stall speed)...and yes, of course the plane was able to overcome this, and eventually accelerate..AND TAKEOFF!! woo-hoo....if the treadmill was able to keep the wheel speed constant, the plane would not move ANYWHERE...as soon as the treadmill was removed, the plane would accelerate down, and into, the bow of the aircraft carrier that was so bold to experiment with our brave men. LISTEN TO YOUR PILOTS......THEY STUDIED.

Eek! When I wrote my above comment, I'd thought I could use blockquote tags ... sorry! The quoted parts are the paragraphs with the ALL CAPS WORDS and this: "I guess it was the original Myth that was flawed, or my understanding of the Myth."

> "As a pilot myself, I'm kind of embarrassed for the ultralight pilot who thought the plane wouldn't take off. I guess that's because ultralight pilots never have to go to ground school, where you learn about the four basic forces acting on an aircraft? :)"

You mean the gal/guy who takes me to my holiday destination in a Jumbo is not prone to getting this wrong? Boeing Bob, this is a real relief for me, seriously. I want to hug you!

Read the definitive analysis:
http://www.airplaneonatreadmill.com

nex,

uhm. bernoulli's principle describes why wings generate lift. Because of the wings shape, air passing over the wing must move farther, than air moving under the wing. Since it moves farther, it becomes thinned out and moves faster. This generates lower pressure. The higher pressure air then actually pushes up on the wing. This Bernoulli's effect, and it is why airplanes fly.

If wings had to deflect air to the ground they would generate TONS of drag, and we probably wouldn't have the fancy, efficient airplanes we have today. Also, how would planes at high altitudes remain aloft? They are so high up, they can't possibly be pushing on the ground!

Go purchase a foam airplane wing. Play around with it a little bit. Move it through the air flat, you'll feel it pushing up! Now turn it slightly, and move it again. It won't push away from the ground, it will push perpendicular to whatever plane (sorry!) you're moving the wing through.

> "if the treadmill was able to keep the wheel speed constant, the plane would not move ANYWHERE..."
Bullshit! (Whoops, wrong TV show.) Now, you don't mean the speed with which the wheels as a whole move around, right? This would be exactly the speed of the plane, of course. So you have to be referring to the speed with which the wheels turn. At the start of the experiment, the wheels are stationary, at rest, no rotational velocity. Now you want to keep it constant. OK: the wheels will therefore never turn. What does this mean? Simple: the surface of the conveyor belt moves along with the plane, tracking its ground (the 'real' ground here, i.e. earth) speed exactly. The wheels have constant speed now, but the plane accelerates and takes off exactly as on a normal runway.

> "if the treadmill was able to keep the wheel speed constant, the plane would not move ANYWHERE"
As I said, bullshit!

HTH!

(My procrastinating ass is sorry for posting three in a row ...)

are you drunk nex?

The problem is poorly worded but brings up many interesting ideas. I have flown planes similar to the one in mythbusters and I am also majoring in physics, so I hope I can provide some insights.

The main point I can see is that the problem is trying to demonstrate Newtons 1st law; objects at rest stay at rest unless acted on by another force. It is trying to show that mass has inertia, and if you have frictionless wheels under any mass, then moving the ground under said mass in any direction will not cause the mass to move.

Of course, to complicate this point, the mass is a plane. The speedometer in a small prop plane measures its speed relative to the air, not the ground (unless you've got a gps system or something measuring speed). A plane like the one shown is perfectly capable of flying into the wind while actually moving backwards relative to earth. In other words, if you are in a plane you could look down and watch yourself move backwards relative to the earth, as long as the wind is moving faster relative to the earth than the plane is relative to the wind.

So, onto the problem. First we use the physics model: You sit in your plane on the treadmill. They start the conveyor belt, and assuming no friction, nothing happens. You start the engine, and the thrust of the prop moves you forward relative to the ground. But wait, the treadmill speeds up to keep you in place -- except it does nothing as Newtons 1st law dictates. So the problem breaks down here. It both demonstrates that the plane will move forward (newtons 2nd law)regardless of the treadmill (1st law), and negates itself by saying the treadmill will keep it in place, when the treadmill has no say in the matter.

A fundamental problem here is this physics model. If you model the wheels and surface as frictionless, the wheels wouldn't even be spinning, so the entire plane is frictionless relative to the ground. In anycase, if you discard the problems requirement at this point that the treadmill keep the plane from moving forward relative to the earth, then the plane will slide without friction forward and eventually takeoff at some point away from your starting point, as if the treadmill never existed.

Now what would happen in the real world? I believe this would be dependent on many variables such as: type of plane, surface of treadmill, coefficents of friction of tires, of wheel axles, wind speed, etc., which could make for very different outcomes. But this is what I would guess before I saw the show: They start the treadmill the moment you start your plane. The coefficent of static friction means you will move backwards at some rate. You start the engine of the plane and it provides some thrust. The wheels overcome the static friction and lurch you forward a bit because kinetic friction is less than static friction. You would begin to move forward, but again we run into the problem of the treadmill trying to hold you in place. It can't. BUT, if you made the surface/wheel axles so full of friction that it effectively held the plane in place, here is what would happen: The plane would not take off unless met with a wind with a speed almost as great as the planes takeoff speed. A prop does not provide that kind of lift, it provides a force to accelerate a plane to a speed at which the speed of the wind relative to the wing is great enough to provide lift. I saw someone mention a rocket. This is not the same problem. The problem involves a wing and lift, while a rocket does not need lift to takeoff. A rocket could fly on the moon, a prop plane could not.

Here is the lift problem simplified: You get in the plane on the runway instead of the treadmill. You put the breaks on the wheels and then power up full throttle. Disregarding a freakish gust of wind, you will NOT take off. You must be moving forward relative to the wind to generate lift. I hope this clarifies some of this.

Sorry for the novel, I didn't intend to write so much, but that's insomnia for ya.

Ray, above, nailed it.

But for your amusement, and for those still pondering, I submit this, which I wrote prior to seeing it all laid out in the open :

OK, I 'm really going to blow your minds here. Not only will the plane take off, but a car-glider, powered only by it's wheels, will do the same thing.

Let's slide into this backwards, looking first at the moment of takeoff. Consider the takeoff moment for a plane:

Plane going forward at 100 mph.
Conveyer belt going the other way at 100mph.
Plane wheels spinning madly.
Plane takes off.


Now imagine a car with large glider wings. Could it be in the above takeoff scenario: going forward at 100mph (relative to earth), with the conveyor going backwards at 100mph (relative to earth)? Sure, and the speedometer will happily read 200mph (pretty beefy engine!). Lucky us, 100mph happens to be the takeoff speed for the car-glider. Whoosh--off it goes, settling down moments later somewhere nearby.

Back to the beginning of the process. Note that if the car is stationary, then per stated conditions, the belt is stationary. Can't have a stationary car and a moving belt. If the car begins moving forward, the belt begins moving backwards at the same speed. Car moving 1mph, belt 1mph, speedometer 2mph. Carry that relationship forward until takeoff speed is reached.

THE ONLY REAL QUESTION ON THIS MYTHBUSTERS EPISODE IS ..............did the treadmill match the rotation of the wheels on the plane?
correct answer.....NO
we might be able to correctly test this myth in another 500 years, but as for now...if the wheels are turning @ the same velocity as the treadmill, the only way this plane is flying is with a HEAVY HEADWIND

MikeM,

The only problem with your analysis is that the car's speedometer will read relative not to the earth but to the treadmill, as that's what it's wheels are touching. Presumably, the treadmill's speed will be adjust so that no matter what the cars speedometer is reading, the car will not actually be moving relative the earth.

BY THE WAY...IF THE TREADMILL IS READING 1 MPH.....THE WHEELS OF THE PLANE ARE MOVING 1 MPH..........not 2

But Michael, that was not the myth, and it never was. The myth was the speed of the plane. Speed of plane is measured against the Earth, not the treadmill. I will explain... AGAIN:

The Noflys claim that the experiment was performed incorrectly. Their issue is that the speed of the plane should be measured relative to the treadmill, and that the speed of the treadmill should be measured relative to the ground. Thus, the condition that the plane speed equal the treadmill speed implies that the speed of the plane and the speed of the treadmill cancel out and the speed of the plane relative to the ground is 0. So because the speed of the plane relative to the ground was not 0, the experiment was not performed correctly.

This is the incorrect interpretation for many reasons (the correct interpretation is that the speed of the plane is measured relative to Earth, just like everything else): First off, this interpretation uses two separate reference frames, the treadmill and the ground. Nowhere in the question did it implicitly state the reference frames, but if speeds are being compared (and they are) and the reference frame is not stated (and it isn't), it would be a safe bet that both speeds should use the same reference frame. Why would one state that the plane speed equals the treadmill speed if the two weren't measured in relation to the same object?

The second reason that the Nofly interpretation is incorrect, is that the common reference frame that we almost always use for everything is the Earth. If I say that a car is going 50 mph and don't state with relation to what, it is safe to assume that it is going 50 mph relative to the Earth, and not some bird in the sky or the planet Venus. When I am on a moving sidewalk at the airport, I consider myself to be moving faster. This is because I measure my speed relative to the Earth, and the moving sidewalk speeds me up relative to the Earth.

If you measure the speed of the plane relative to the Earth, on takeoff, the plane is going 25mph. The treadmill is also going 25mph in the other direction. The initial conditions are satisfied. The plane flies... it's simple, it's obvious. But apparently it isn't obvious enough.

Now, let's look at it from the Nofly perspective. If the experiment were performed the way they want it. As soon as the plane begins to move (rolling friction is already overcome so the treadmill has no frictional effect), the treadmill must instantly spin up to such a speed that it applies a force which slows down that movement. How might this work? You can't apply a force through an ideal free wheel. For theoretically perfect bearings and no air viscosities it is impossible. The treadmill cannot slow down the airplane, so it accelerates to the speed of light, time comes to a stop and the universe implodes. So in the theoretical world, it is a nonsensical assumption to make.

Now, what about the real world? Well industrial bearings go up to many thousands of rpm. A 2ft diameter plane wheel going 25mph spins at about 350 rpm. So the treadmill would have to go about 10 times faster than that to begin to push the bearing past its working zone and begin to create any frictional forces which can slow down the plane. We'll say at 250 mph the treadmill can start to slow down the plane (just the very light amount of thrust that got the plane to start moving). But wait, in the real world air is a viscous fluid. If this treadmill is very long and very wide, we can assume laminar flow over the surface. And since fluids have a no-stick condition at the surface of the treadmill, the treadmill will pull air along with it. Normally this would be a very thin layer, but it depends on the size of the treadmill. You can use the Navier-Stokes equation to determine the speed at a given height. If the treadmill is large (the size of a runway), the velocity of the air moved by it will indeed by quite high, especially considering that the Cessna's wings are not that high above the treadmill surface. The wind speed will become high enough that it will lift the plane up before the treadmill melts the bearings. The drag from the incoming air is counteracted by additional thrust from the plane's engine. So the plane flies in this case as well.

So no matter which way you cut it, the Noflys are wrong. Their assumption is silly and nonsensical, but it still leads to them being wrong no matter what.

... make that four posts in a row ... I can't resist trying to educate Alex Ross, above.

> "bernoulli's principle describes why wings generate lift."
That's what you learned in school. It's wrong. If you're as old as me, you were also told as a kid that spinach contains lots of iron. Doesn't mean it's true and still state-of-the-art scientific knowledge.

> "Because of the wings shape, air passing over the wing must move farther, than air moving under the wing. Since it moves farther, it becomes thinned out and moves faster."
No! I assume you're confused because that diagram in your textbook that illustrated the flow of air over the wing made you think the 'upper stream' and 'lower stream' must meet up behind the wing at the same time (counting from when they were parted by the wing's front edge). When in fact, nothing forces them to do that. Yes, the air passing over the wing must move farther, but that doesn't necessarily make it move faster. Also, when you say it is 'thinned out', you're considering only the variable of speed. What about the other variable that compresses the air above because it's moving over that bulge in the wing, causing the lines in the diagram to become smooshed (is that a word?) together? The diagram is actually misleading, it exaggerates the shape of the wing to make it easier to see, but in the real world, the wings are pretty much flat. This is why some planes can fly upside-down.

> "The higher pressure air then actually pushes up on the wing."
That's a myth. Many people learned it in school that way, but it's wrong. Go look it up on Wikipedia.

> "If wings had to deflect air to the ground they would generate TONS of drag"
First of all, they don't deflect air to the ground (sorry if I'd said it that way, I'm not a native English speaker, please have mercy), they deflect air towards the ground. The plane is not actually pushing on the ground! Except for very low altitues, which is the ground effect and results in a much reinforced lift. Again, go look it up. Secondly, now I'm confused, for a change. Are you saying that helicopters don't deflect air towards the ground? Or are you saying that the airfoiles on a helicopter's rotor are working on a completely different principle than the airfoils on a fixed-wing craft?

> "Now turn it slightly, and move it again. It won't push away from the ground, it will push perpendicular to whatever plane (sorry!) you're moving the wing through."
The component of the force that generates LIFT (which, by definition, means away from the ground) still points straight up. When banking, of course there is a second component that makes the plane turn and also drift sideways. That other component is irrelevant here, we're talking about what keeps planes up in the sky, not what makes them go in circles. I totally appreciate the word-play, though :-)

if you guys cant explain your position in a paragragh.....quit talking

MICHAEL says: "Ooga booga, too many words, me confused, don't read so good"

Dan said:

"If you measure the speed of the plane relative to the Earth, on takeoff, the plane is going 25mph. The treadmill is also going 25mph in the other direction. The initial conditions are satisfied. The plane flies... it's simple, it's obvious. But apparently it isn't obvious enough."

So then the problem boils to this: Can a given planes engine provide enough thrust to reach double its normal takeoff speed?

Is that it?

not confused, einstien said if u cant explain your position simply, u dont understand the problem........keep talking.

damn typo...

So then the problem boils down to this: Can a given plane's engine provide enough thrust to reach double its normal takeoff speed?

Is that it?

airspeed........how do u accelerate to takeoff velocity, if your wheels are spinning at the same velocity as the ground???????????

nex,

You took the bait, and I am glad. Wikipedia actually has a pretty great article on Bernoulli's effect, and I think that if YOU read YOU'LL educated. Here is the link, so you don't have to go looking. http://en.wikipedia.org/wiki/Bernoulli's_principle. Scroll down to the part entitled “A common misconception about wings.”

The reason that (some) planes can fly upside down, actually has to do with the shape of their specialized wings. They have a more symmetric, tear-drop shape. The pilot changes the wings angle-of-attack to create the bernoulli effect. Wings like this can fly manage to fly upside down, but not very efficiently.

I hope you don't have too much trouble digging the hook out of your cheek. :)

Why keep talking if you are content to ignore what I say and wallow in your own ignorance? Sticking your head in the sand does not make you correct, it makes you an ostrich.

airspeed....how do you reach takeoff velocity, if your wheels are moving at the same speed as the earth?
HURRICANE

MICHAEL... the wheels don't matter. Think of a plane on skis and the treadmill as covered in snow.

I DONT TRUST WIKIPEDIA........quote another source

thats my POINT mateo...the wheels dont matter......the airspeed is ALL that matters.....the "experiment" the mythbusters conducted is flawed because they could not match the velocity (exactly) of the wheels under the plane to the "earth" .......when/if they do, they will discover that the plane cannot take off because the wings will not function with zero airspeed.

Micheal,

Perhaps you'll have the patience to read this website then: http://howthingswork.virginia.edu/airplanes.html

The University of Virginia seems like a reputable source.

Dude. It's a state school.

nex,

A helicopters blades are just wings fixed to a central hub. The wings are spun, generating lift. This lift occurs due to the Bernoulli effect.

originally, i thought the myth was asking if the the plane could takeoff with a c-belt working FOR the plane.....like a catapult .....i think it absolutely insane to think that if you could match the wheel speed of ANY aircraft (exactly, and opposite) that it would do anything other than be a wonderful flowe pot.

Lying. But for what purpose? Anticipating the next post with the dignity of a dog belonging to Pavlov.

thats a great website , alex.....thank you, how does a 747 takeoff from a runway of ice, with a dumptruck parked at its nosegear?

It moves the dumptruck.

Alex Ross, I'm glad you read my lenghty reply, did the research, and came back to inform me! Turns out I've been correct in everything except my stupid, stupid misunderstanding that it isn't Bernoulli's effect at work there, when actually the truth is that Bernoulli's effect is just that nasty thing high-school students (me included) fail to understand fully, which is why it's better to explain the situation differently. And you have been correct in everything except that you believed that airfoils aren't throwing air downwards in order to generate lift. Now we've both learned something and (I hope) are on the same page; this is great! Thanks for your patience with me.

> "A helicopters blades are just wings fixed to a central hub. The wings are spun, generating lift. This lift occurs due to the Bernoulli effect."
Yes. And when you get out of a helicopter while the 'wings' are still spun, you can feel that they're essentially a huge fan that throws air downwards at you.

> "I hope you don't have too much trouble digging the hook out of your cheek. :)"
It hurt a bit, but, as some famous scientist has said, it doesn't matter for how long a researcher strongly believed in a theory and how devastating it may at first be to be proved wrong, the joy of enlightenment outweighs that blow and the true scientist always is happy to embrace the superior teaching. I can't find that quote or its source right now, so this quote by Stephen Jay Gould will have to do:
>> "The story of a theory's failure often strikes readers as sad and unsatisfying. Since science thrives on self-correction, we who practice this most challenging of human arts do not share such a feeling. We may be unhappy if a favored hypothesis loses or chagrined if theories that we proposed prove inadequate. But refutation almost always contains positive lessons that overwhelm disappointment, [...]"

Oh, and please note that Wikipedia still explains that the "equal transit-time theory" is a fallacy. This is the wrong explanation of Bernoulli's effect many of us have been taught in school. In the same section, it also says, "However, it appears some people have incorrectly assumed that the fallacious nature of this equal transit-time theory extends to Bernoulli’s Principle, and that Bernoulli’s Principle is also a fallacy when applied to the lift generated by a wing." So both of us have a crow to swallow ... could you pass the salt?

Obviously my self-esteem has hit an all-time low and I desperately want to justify my position some more; I guess this affords me the level of dignity of a dog belonging to Pavlov :-)

MICHAEL says:
> "are you drunk nex?"
Have you run out of logical arguments and therefore deemed it appropriate to resort to irrelevant ad-hominem attacks, MICHAEL? Are you so resistant to learning something new that you'll keep grapsing for straws when you're already at the bottom of the sea, just so you'll never have to admit to having made a mistake? No? Good! :-)

> "THE ONLY REAL QUESTION ON THIS MYTHBUSTERS EPISODE IS ..............did the treadmill match the rotation of the wheels on the plane?
correct answer.....NO"
So? This proves nothing. It's meaningless and nonsensical to specify that the speed of the conveyor belt's surface relative to the ground has to match the speed of a point on the wheel's outer circumference around the axle. Why? Simple: as the wheels spin more or less freely around their axles, there's absolutely nothing the conveyor belt could do to enforce this constraint, even if it was logically possible to do so. Yes, it is only logically possible as long as the entire plane remains stationary relative to the ground. So? This doesn't mean the belt has the power to hold the plane in place. (A implies B) does not imply (B implies A). An example for those not trained in formal logic: When it rais, the street becomes wet. This does not mean that if the street is wet, it must have been raining. The water could have come from a fire hydrant.

> "if you guys cant explain your position in a paragragh.....quit talking"
Look, we do what we can to explain the situation so even you can understand it, but we can't work magic. If you can't understand a one-paragraph explanation (several have been provided), the 'teacher' may have failed, but that doesn't mean he's wrong.

> "So then the problem boils to this: Can a given plane's engine provide enough thrust to reach double its normal takeoff speed? Is that it?"
No. Take-off speed is air speed, and a plane always takes off at its take-off speed, it doesn't have to accelerate to twice that, even if a hypothetical speedometer connected to the wheels would show the greater number.

> "how do u accelerate to takeoff velocity, if your wheels are spinning at the same velocity as the ground???????????"
Look, 'einstien', the ground isn't 'spinning'. And anyway, you're measuring the velocity of the ground in relation to ... what? If you can't explain your position simply (let alone coherently), you don't understand the problem!

> "how does a 747 takeoff from a runway of ice, with a dumptruck parked at its nosegear?"
The pilot will politely ask someone to get the damn truck out of the fucking way. Now go back under your bridge, troll.

Don't forget the Coanda effect. You couldn't fly without it

Michael... if only you understood the question. I explained it to you, but you refused to even read it. I can try again, but you will still refuse to see what you don't want to see:

The Noflys (Michael) claim that the experiment was performed incorrectly. Their issue is that the speed of the plane should be measured relative to the treadmill, and that the speed of the treadmill should be measured relative to the Earth. Thus, the condition that the plane speed equal the treadmill speed implies that the speed of the plane and the speed of the treadmill cancel out and the speed of the plane relative to the Earth is 0. Because the speed of the plane relative to the Earth was not 0 on the show, the experiment was not performed correctly.

This is the incorrect interpretation for many reasons (the correct interpretation is that the speed of the plane is measured relative to Earth, just like everything else): First off, this interpretation uses two separate reference frames, the treadmill and the ground. Nowhere in the ques