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MythBusters Airplane Takeoff Myth

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MythBusters Airplane Takeoff Myth

Old 02-19-2009, 09:32 AM
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Flyin Beagle
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Default MythBusters Airplane Takeoff Myth

Did anyone see the Mythbusters last night. It may have been a re-run, but it was new to me.

They tested the Myth that an airplane sitting on a conveyor belt moving at the same speed, but in the opposite direction of the thrust of the prop would just sit there. They tested it with a smal parkflyer, and a treadmill at first, then moved up to a fullscale plane.

The part that really surprised me was when they tested it at full scale with a small experimental aircraft, the owner/pilot of that plane believed that he would just sit in place. To test it they connected a large peice of canvas about 12' wide by a couple hundred feet long to the back of a truck and drove in the opposite direction of the airplane. The plane took off normally.

For a lot of people it is apparently very difficult to grasp the idea that the forward motion of an airplane is due to the thrust of the prop, and that the wheels of the airplane are free spinning, and that no matter how fast the surface under the plane is moving the plane will still move forward at the exact same speed as if it was taking off in a normal fashion. It was surprising to me how difficult it is for people to grasp this concept.
Old 02-19-2009, 10:19 AM
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HighPlains
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Default RE: MythBusters Airplane Takeoff Myth

Well, not exactly the same. As the wheels spin up, they are taking energy and storing it up as rotational energy. But not at a high enough rate to keep the airplane grounded.

This was the subject of a incrediblely long and tedious thread that you can find by searching "treadmill". Please leave it where you find it.
Old 02-19-2009, 11:25 AM
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Default RE: MythBusters Airplane Takeoff Myth


ORIGINAL: Flyin Beagle

Did anyone see the Mythbusters last night. It may have been a re-run, but it was new to me.
It was, indeed, a rerun from January of 2008.

You would have thought it would have put the thread HighPlains mentions to rest...but even the clear demonstration of the facts didn't seem to do so.

ORIGINAL: HighPlains
Please leave it where you find it.
Aww, come on...you don't think it'd be fun to stir it up AGAIN??
Old 02-19-2009, 11:38 AM
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Flyin Beagle
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Default RE: MythBusters Airplane Takeoff Myth

Sorry, Didn't mean to throw salt in old wounds. Just found it surprising that even the pilot didn't understand.
Old 02-19-2009, 12:21 PM
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Default RE: MythBusters Airplane Takeoff Myth


ORIGINAL: Flyin Beagle
Just found it surprising that even the pilot didn't understand.
I've got a theory on that very subject if you're really curious to read a long and boring psychobabble post.
Old 02-19-2009, 12:47 PM
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Tall Paul
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Default RE: MythBusters Airplane Takeoff Myth

Speaking of psychobabble, there's 5825 messages (as of this posting) on this silliness at:
http://community.discovery.com/eve/f...6/m/4441931059
Old 02-19-2009, 02:20 PM
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Default RE: MythBusters Airplane Takeoff Myth

The discovery.com forums are interesting because the "no fly" people make it clear that they thought the motion of the treadmill would keep the plane stationary relative to the ground. (Some of them used a plane with its tail tied to a tree as an example.) If that had been the case, it wouldn't have taken off. The real mystery is why so many people think that moving a treadmill under a plane with wheels that are free to turn will keep the plane from moving forward.
Old 02-19-2009, 03:49 PM
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Default RE: MythBusters Airplane Takeoff Myth

The problem is that the problem statement is impossible to achieve. The original problem statement says that the treadmill must match the speed of the plane's wheels. Eventually, the wheels will over heat, melt, or simply achieve a terminal velocity. The plane hasn't moved up until this point in time, since this happens instantaneously. Then, the plane might as well be tied to a tree.
On a simple treadmill, however, the plane will take-off as was shown in Mythbusters.

Regardless, this is just BEGGING to open up a serious can of worms and an even more serious pissing match.
Old 02-19-2009, 03:54 PM
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Default RE: MythBusters Airplane Takeoff Myth


ORIGINAL: Top_Gunn
The real mystery is why so many people think that moving a treadmill under a plane with wheels that are free to turn will keep the plane from moving forward.
Now...I'm not aeronautical engineer (grew up with one, but that's a different story) and, as has been pointed out, the PHYSICS of this whole issue are 'debated" at great length to little result elsewhere.

I DO have rather extensive experience and formal education in the context of how people teach and learn, and the barriers (both within communication and our own little brains) to those activities.

And...to be honest...the mystery to me is why MORE people don't think that way.

(I know...nobody asked, but I've gotten going now...)

There are, imo, two issues in play here.

Cognitive dissonance (specifically our resistance to it) and our frame of reference.

Cognitive dissonance first.

It's really just a big fancy phrase for "close minded". In general, we humans are QUITE discomforted by the idea of contradiction. In the context of philosophy, an example might be a man who supports the death penalty but wants a ban on abortions. (This is NOT an attempt to start either debate, merely an example of a condition) He may feel uncomfortable at what he believes to be a contradiction. "How can I" he may ask himself, "favor killing one human being, but be opposed to killing another?"

In more "empirical" contexts, cognitive dissonance might be expressed as the discomfort of receiving new information that conflicts with something we already believe we know. Call it "My mind's made up, don't confuse me with the facts."

Pretty much anything that presents a contradiction to us, we'll seek to avoid. Interestingly, there are even some studies recently that seem to indicate (and I happen to agree, but that's another thread) that our brains will actually SABOTAGE our efforts to learn something if it conflicts with existing notions.

Perhaps pointedly, one study I saw actually used comparisons between boats and airplanes. Fundamentals of fluid dynamics common to BOTH were presented to people with "naval" backgrounds, 'aviation" backgrounds, and a control group of random backgrounds.

Interesting things happened. In one case, for example, pilots quite readily accepted fundamental concepts about how boats do what they do. When presented with EXACTLY the same concepts regarding airplanes, however, they found the information 'challenging", "difficult to comprehend", and indeed some expressed outright INABILITY to learn the information.

The theory is that the brain seems to protect itself from the contradiction of "If this is right, then I must be wrong about ____" by actually obfuscating information to make it appear "too advanced" to learn.

The other issue is frame of reference...and it's a whole lot simpler.

We be ground critters.

Let's face it...it was only VERY recently that ANYTHING heavier than air flew...particularly in the context of "human history". Indeed, there are STILL survivors of the "before heavier than air flight" days. We haven't even "turned over" a whole generation yet. In general, then, EVERYTHING we've ever done to get from A to B (walk, run, ride a bike, drive a car, whatever) has been done, in one way or another, by "pushing off the ground".

Without the resistance of the ground, there is no thrust.

We're hard wired to it. Push = shove, and we move.

Even when we DID manage to get in the air, a vast majority of us have no physical contact with it. There we sit, in a pressurized (or at least enclosed) cockpit, as the air "rushes by" outside. Indeed, even a great many PILOTS have never been in so much as an open cockpit.

Even those few who've experienced an open cockpit, or perhaps a balloon ride, didn't interact DIRECTLY with the air. They pulled a switch or lever, or moved a stick, or turned a wheel, and a machine did something that had so-and-so effect.

I heard it said, once, that only a skydiver REALLY understands how airplanes fly. While i don't buy that statement as fact, I'd sure as heck buy that they may be the only ones who really "feel" what an airplane does.

=================

So...take these two problems :

EVERYTHING I believe leads me to EXPECT a different result...indeed, I may even have some experience or education that establishes that expectation

And:

The ONLY way my expectation can be wrong is by the actions of an invisible medium I have no "feel" for producing an invisible force through and action I CAN NOT experience.

===========

Makes ya wonder how the Wright brothers EVER got it right, doesn't it?
Old 02-19-2009, 04:16 PM
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Default RE: MythBusters Airplane Takeoff Myth

Intelligence is often difficult to qualify
Some argue that the level formal eduction is a mark of intelligence
It ain't.
In the case of the treadmill and the plane ,
the obvious canard is readily apparant to some - to others it is a mystery to be unraveled .
Old 02-19-2009, 06:00 PM
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Default RE: MythBusters Airplane Takeoff Myth


ORIGINAL: dick Hanson

Intelligence is often difficult to qualify
Some argue that the level formal eduction is a mark of intelligence
It ain't.
In the case of the treadmill and the plane ,
the obvious canard is readily apparant to some - to others it is a mystery to be unraveled .
Indeed! And even knowing the correct answer to this particular question, or whether one finds it difficult to wrap one's mind around, is not a good measure of intelligence.
Old 02-19-2009, 06:03 PM
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Default RE: MythBusters Airplane Takeoff Myth

Let's face it...it was only VERY recently that ANYTHING heavier than air flew...particularly in the context of "human history". Indeed, there are STILL survivors of the "before heavier than air flight" days. We haven't even "turned over" a whole generation yet. In general, then, EVERYTHING we've ever done to get from A to B (walk, run, ride a bike, drive a car, whatever) has been done, in one way or another, by "pushing off the ground".

thats the reason
people relate a plane to something they know, maybe a car
they know if a car were to be going on a tredmill 20mph and the tredmill was going 20 mph in the other direction that the car wouldnt move
they try to relate this information to planes



daRock.... edited to fix the quote parameters so the quote would show up as a quote (using the quote button above the window works perfectly).
Old 02-19-2009, 06:36 PM
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Default RE: MythBusters Airplane Takeoff Myth

balloons "push off the ground"??!!
Old 02-19-2009, 08:56 PM
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Default RE: MythBusters Airplane Takeoff Myth

The argument will forever exist until we are more specific about the speed of the conveyor belt.
The mythbusters said the speed of the belt would be the minimum flying speed for the AC. like 11.2 mph I think?(for the model test)In whick case the plane will fly unless it has really high rolling resistance.
Other ways the question is raised act as if the conveyor will move as fast as needed to keep the AC on the ground. At the point resistance from wheel friction,etc offsets the thrust to an amount less than necessary to propel the plane to takeoff speed, It will stay on the ground or possibly roll backward.
I promise if you out that ultralight on the 12 ft canvas tied to a fuel dragster and you'd get a different result until you ran out of "Carpet" I'm sorry to even drag this thread out , But wanted to point out either answer can be true depending on the specifics of the original question. [:-] Todd
Old 02-19-2009, 08:57 PM
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Default RE: MythBusters Airplane Takeoff Myth

Not possible. I'm sorry but if you watch the mythbusters episode, the plane IS MOVING forward according to the groundspeed... you can see easily that the "treadmills" not matching the planes speed.... why don't think try tying to big ropes to the wing tips and tying them to two trees... try and get that "treadmill" going and throttle up so the plane would actually "stay still" it would never take off. no air going over the wings NO LIFT.. it won't fly... very skewed and wrongly done experiment
Old 02-19-2009, 09:08 PM
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Default RE: MythBusters Airplane Takeoff Myth

I will set up a model with infinite traction, perfect traction. A cogged belt with cogged tires on the plane. The plane will be at the mercy of the belt and it will never achieve enough forward speed or thrust for flight. I will see to it that the plane has sufficient weight to need the equivalent of 15 mph [in still air] to fly.
Typical of many [over weight] sport planes.
There are many who are on "this side" of the argument who visualize this paradox having perfect traction. Traction will rule in the end.
Old 02-19-2009, 09:31 PM
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Default RE: MythBusters Airplane Takeoff Myth

Not possible. I'm sorry but if you watch the mythbusters episode, the plane IS MOVING forward according to the groundspeed... you can see easily that the "treadmills" not matching the planes speed.... why don't think try tying to big ropes to the wing tips and tying them to two trees... try and get that "treadmill" going and throttle up so the plane would actually "stay still" it would never take off. no air going over the wings NO LIFT.. it won't fly... very skewed and wrongly done experiment
Well, of course it's moving forward. Why wouldn't it (burnt out wheel bearings aside)? The treadmill's moving backward doesn't keep the plane from moving forward, except just a bit because of friction in the wheels. It seems that the "no fly" people are assuming that moving the treadmill backward at (say) 50 mph would move the plane backward at that speed, but since the wheels are free to turn, it wouldn't. Nobody thinks the plane can take off without airspeed; the point is that it can achieve the necessary airspeed despite the motion of the treadmill.

Why is this hard?
Old 02-19-2009, 10:37 PM
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Default RE: MythBusters Airplane Takeoff Myth

As noted previously If one does not see the "gag" here the fact that the treadmill has NOTHING to do with the plane taking off and flying, - it is easy to become caught in a quagmire of one's own making.
Old 02-19-2009, 10:40 PM
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Default RE: MythBusters Airplane Takeoff Myth

now if the wheels were the thing that propelled the airplane.......but really people??
Old 02-19-2009, 11:01 PM
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Default RE: MythBusters Airplane Takeoff Myth

Duhhh... it's not the prop or the wheels that make a plane move it's the turbine..... Geez I thought you guys were smarter then that..














Just kidding about the smart thing.... I might be asking some really dumb questions later it the kit building forum...
Old 02-19-2009, 11:37 PM
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Default RE: MythBusters Airplane Takeoff Myth

Hummmm. Airplane treadmill; would that be called a WIND TUNNEL?

I love Mythbusters, but I have found more than once that they either they happen get free equipment to test but that equipment is always the caveat to what they want to do and they dont know it, or they dont know what is really going on to make it work. Aviation is one of their weak spots.
Old 02-20-2009, 06:43 AM
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Default RE: MythBusters Airplane Takeoff Myth

My brain hurts.....
Old 02-20-2009, 09:04 AM
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Default RE: MythBusters Airplane Takeoff Myth

Ooops. Look what I did.

Sorry, HighPlains.
Old 02-20-2009, 09:53 AM
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Default RE: MythBusters Airplane Takeoff Myth

Perfect traction.... a supercharged turbine with afterburner assisted treadmill........... anything you want, and all you'll have is a faster rotation of the wheels that're attached to an airplane that is taking off. Your magic treadmill and it's absolute traction can only turn the wheels faster. And that will have to be even faster when you add their acceleration to takeoff speed. The treadmill can hold back the rubber it contacts, but has no leverage or purchase on anything beyond that. It can only spin the tire faster, not hold it back. In the description of the problem, the trick is that they know most people don't understand what the treadmill can't do, and that hold back anything. So the statement that the treadmill will match the speed of the airplane is basically a lie.

There is no "traction" in the connection between the wheels and the airplane that can directly oppose the forward motion created by the airplane's power plant. Improving the wheel to ground attachment only adds to the speed the wheel will rotate before it leaves with the airplane.

Want a pertinent example from real life? Some jet fighters restrict throttle position for takeoff. Because they will tear the gear off before the tires leave the ground. But the plane does. Leave the ground. And leaves the wheels behind. And the traction in that example is more than enough for the experiment.




Time to quit wrestling with pigs........
Old 02-20-2009, 02:13 PM
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Default RE: MythBusters Airplane Takeoff Myth

I'd never thought about this before because I had never seen the previous discussions or the episode of Mythbusters in question. It took me a while, but I finally had that "a-ha!" moment and I completely understand it now... and of course feel like an idiot for not having seen it sooner. So, anyone want to get back to discussing why a helicopter won't lift off if it's attached to a large plate?

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