For the record, I do not believe the plane takes off if the both opposing speeds are set to match.

MythBusters failed on providing an accurate simulation to the original scenario.
1. The plane is a special plane, probably takes off without very much forward travel.
2. The maximum speed of the plane's travel was not met.
a. The vehicle used (in leu of the treadmill) must be able to match the maximum speed of the plane, not just the minimum as the plane will simply out-run the treadmill and thus take-off.

I'd like this myth to be revisited by Myth Busters.

quote:

Originally posted by tictactoe:
For the record, I do not believe the plane takes off if the both opposing speeds are set to match.

MythBusters failed on providing an accurate simulation to the original scenario.
1. The plane is a special plane, probably takes off without very much forward travel.
2. The maximum speed of the plane's travel was not met.
a. The vehicle used (in leu of the treadmill) must be able to match the maximum speed of the plane, not just the minimum as the plane will simply out-run the treadmill and thus take-off.

I'd like this myth to be revisited by Myth Busters.

1. Special plane: Well, it wasn't VTOL so, it wasn't 'special' enough to effect anything.

2. How do you know the maximum speed of the plane's travel was not met? The usual speed for take off for that kind of ultralight was 25 to 30 mph. How is the truck unable to go faster than 30 mph?

3. AND Retesting this myth is arguably dangerous. They could have had that burlap tarp continue to thrash around like it did before the winds became still (luckily). Should they try it again and this time the tarp becomes entangled with the wheels, -- big, big problem. I can't say I'd agree with a retest.

quote:

Originally posted by powertool64:
Regardless which version you want to hold on to, the myth was not “can you stop a plane from taking off,” yet that is the approach most of you are taking. The myth, regardless of version, was “can a plane take off,” and the answer is YES. Even the “thought experiments” fail to prevent this.

Wrong -- the question of the original myth is "WILL IT TAKE OFF?", and if the conditions of the myth are met the answer is "no". If you want to argue that certain models of airplane are incapable of meeting the conditions of the myth, that is irrelevant. If you want to argue that it is too difficult to build such a treadmill, that is likewise irrelevant. The question is what happens under the conditions of the myth.

You'll need to be a little more specific. What is your version of the original version of the Myth.

The Mythbuster's version is posted on page one of this thread. The Mythbusters conclusively showed that myth is busted, the plane flies.

A second version surfaced after the show, claiming to be the "original" version, requiring that the belt speed equals the wheel speed. This was argued vehemently by certain members of this board until it was pointed out that this version is a tautology - a self proving argument. In order for the wheel speed to equal the belt speed, the plane body must not move. I have called this one an engineer's practical joke that has succeeded beyond the originator's wildest expectations.

The discussion then shifted to what can best be described as a theoretical discussion of what can exert rearwards force on the airplane and how much power is needed. The answer was something like 1.21 Gigajoules. Ok, not really, but if that much energy can turn a DeLorean into a time macine, it can probably keep a plane from taking off. Unfortunately, this discussion has been entirely divorced from reality, so whatever the final answer is changes every time someone says "yes, but what about....".

Do you have something new to add to this?

A couple of corrections on bflynn's last post. It is not a tautology, there is some very sound physics that shows how the treadmill can keep the plane from flying, he just does not like the answer, or cannot understand the physics. Second, that "alternate" version was alive and very healthy on the web before they did their episode. The Mythbusters did this myth a serious disservice by totally ignoring the version that was on at least half of the websites out there. Also it seems to be the earliest version of this myth that existed. It was not an engineers practical joke but an actual question asked that bflynn is too lazy to answer.

@Subductionzone: That was the RUSSIAN version, and the main English version was the one tested by Mythbusters.

Also, (this is not specifically at Subductionzone) the Mythbusters version was a bit ambiguous, since "plane speed" is not well defined. Speed relative to what?

Actually I checked this out on various websites before the Mythbuster's episode and saw a rough 50/50 distribution to both versions. If any one was running in the majority it was the "Russian" version.

Yes, but until the Russian one was re-discovered, well after the episode aired, the original English posting was the EXACT wording the Mythbusters used. They did their best at tracking down the "original" question.

And they tested the "original" question.

The Russian wording turned up afterwards.


It's not irrelevant if the setup described can not be achieved.

Wouldn't you all jump all over me if I asked what would happen if an electron was travelling at 3 times the speed of light in vacuum and hit another electron? Which is the "proper" answer? That it can't happen? Or the calculated collision derived from insisting it must happen because the question says so?

To be honest I don't know which English version was the original one. I have not seen any proof either way which was the first English version, though I do seem to remember people on this website claiming that the Mythbusters' version was the original. I was the one who got tired of seeing the wheel speed version constantly shot down for bad reasons and did some research. If someone else could do some research and show that the Mythbusters' version was the original English version I will shut up.

To your electron question the answer is it could not happen since there is no know way to accelerate an electron to even the speed of light. Even tachyons are theoretical at best, and they are not electrons. So the correct answer is that it could not happen, therefore the question is meaningless. With the treadmill question there is a physics answer on what could stop the plane. The fact that it is not testable to any extent is besides the point. So is the thought experiment of a hole drilled through the Earth. That does not stop you from analyzing what would happen in the world of physics.

quote:

Originally posted by Subductionzone:
The Mythbusters did this myth a serious disservice by totally ignoring the version that was on at least half of the websites out there.

And what would you have them do? Should they have built a conveyor capable of supporting a plane and accelerating to over 10,000 miles per hour? Are you going to do the engineering necessary to pull this off? Are you gonna foot the bill? Frankly, you would have a hard time building a conveyor capable of holding back a model airplane, let alone the smallest of real planes.

How come you keep ignoring the fact that even your myth fails for any plane with a thrust to weight ratio larger than the coefficient of static friction? The myth doesn't specify plane type, so if one plane causes it to fail, then it fails. Once the tires break traction, the conditions of your myth regarding wheel speed can still be met, and the plane still takes off (contrary to the joker a few posts above).

A theorem can be shown valid thousands of times, and never be proven true, but it takes only a single occurrence of showing it false to disprove it or prevent it from being a scientific law.

powertool you are wrong on so many different levels here that I don't know where to start. Let's just take a few of them. What would I have them do? I would have them do some basic research before testing a myth incompletely and calling it busted. The wheel speed version was wide spread on the net and they totally ignored it. As I said earlier if they drilled a horizontal hole one mile through the Earth and called the hole through the center of the Earth myth busted would you be satisfied? If you can't properly test a myth then you don't call it busted, that is pretty obvious.

Second, yes there are a few planes that could possibly take off, but that does not bust the myth. It says can you stop A plane, not all planes from taking off, try again.

Your last point again is not applicable, it is not a theorem. It is a basic physics in how you would stop a plane from taking off. It would help if you knew the difference between a theory and between application of physics.

quote:

Originally posted by Subductionzone:
It says can you stop A plane, not all planes from taking off, try again.

In NO VERSION of the myth does is ask "can you stop is from taking off," and yet that is the approach you keep taking, and I have pointed this out several times. The myth is NOT can you stop it from taking off. It is, will it take off.

quote:

Originally posted by powertool64:

quote:

Originally posted by Subductionzone:
It says can you stop A plane, not all planes from taking off, try again.

In NO VERSION of the myth does is ask "can you stop is from taking off," and yet that is the approach you keep taking, and I have pointed this out several times. The myth is NOT can you stop it from taking off. It is, will it take off.

Can you try this again in English? What do you mean by "can you stop is from taking off"? The original version of the myth quite clearly says that a plane is on a treadmill that can match the speed of the wheels of the plane, can the treadmill stop the plane from taking off? Now that does not say a F18 jet, it says the rather generic "a plane". I am starting to think that my nickname for you is not too far off.

quote:

So the correct answer is that it could not happen, therefore the question is meaningless.

That's my point. Why take that stance about a meaningless question with the "3 times the speed of light in vacuum electron", but not with any plane whose thrust-to-weight ratio exceeds the available coefficient of static friction?

Several keep saying we're not allowed to choose "a plane" if such a choice prevents the question from being valid. I don't see why. Such planes are not excluded by either version. Drop such a plane on the belt and the belt CAN'T match the wheelspeed, whether the question says it does, or not. That's makes the question meaningless, not the choice of plane.

quote:

I have not seen any proof either way which was the first English version, though I do seem to remember people on this website claiming that the Mythbusters' version was the original.

Every search I've ever done (and that several other websites have done) can not find any English posts that predate this forum post from July 19, 2005:

http://www.physforum.com/index.php?showtopic=2417

And the poster, Dirak, apparently has since said:

quote:

Yes, I'm sure I was the first who brought this topic to the English-speaking internet. However, I wasn't the one who invented this question. I'm half-Russian and I read about it on one of Russian forums back in 2005.

He then linked to the August 4, 2003 Russian forum post that K² has translated for us.

Until Dirak pointed back to the Russian forum on February 7, 2008, as far as the English-speaking world could tell, the July 2005 physforum post was the "original". The Mythbusters episode was aired (and thus produced) before February 2008 and thus would not have known about the Russian question.

quote:

Originally posted by Subductionzone:
It is not a tautology, there is some very sound physics that shows how the treadmill can keep the plane from flying,

I believe you have failed to understand what I've said multiple times.

The requirement that the wheel speed equals the belt speed creates a condition where the plane body cannot move. If you want to say that is physics, then you're talking simple vector mathematics. If the plane moves forward, it requires that the wheels move faster than the belt, if the plane moves backwards, it requires that the wheels move slower.

Therefore, it IS a tautology to require that the wheels move at the same speed as the belt. The preconditions of the myth create the situation where the plane cannot fly - nothing at all to do with the belt.

Fine call it a tautology if you want to but the physics point of the question is can the belt keep the plane in place so that you do not violate the tautology and the answer to that question is yes. So it has everything to do with the belt.

It is not because I want to call it a tautology, it is because that is what it is.

I will state again for clarity - it is the preconditions of the myth that prevents the airplane from moving, not the belt.

bflynn, there are limits to what written language can get across, especially if you are over rigorous in your interpretation of a statement. Sometimes you have to know the difference between what was written and what was meant. When you start nit picking at a physics argument over English it is an indication that you are losing. The question was, ultimately, whether the belt could do anything to stop the plane from taking off, the answer is yes.

I cannot believe there are still people saying the plane will not move forward on a treadmill going in the opposite direction. The plane is not driven by its wheels, if it was, it would loose power when it leaves the ground. A Plane or Jet are powered by engines that move air. Now are we saying the treadmill is also moving the air above it? I did not major in physics, but do understand why it still takes off. I think if you wanted to stop the plane from taking off, you have to place it inside a vacuum or have a giant fan in front of it blowing air at take off speed.

borg, the question on the original Russian site was, and I am paraphrasing a bit here, if a conveyor belt could match the speed of the wheels of a plane could it keep the plane from taking off? This is significantly different from the version of the myth that the Mythbusters used. With this wording you can keep the plane back if you accelerate the wheels fast enough. It is fairly basic physics. It takes a very healthy acceleration but it can be done for a very short time period in real life. Then you would have some sort of catastrophic failure. It is more of a thought experiment than anything else. Just as the thought experiment of a hole drilled through the Earth cannot be done, but can still be solved. The myth as tested by the Mythbusters was thoroughly busted, but it was a bit disappointing that they did not even mention this other version of the problem, which is actually older.