Mythbusters airplane/treadmill video

"PeeCeeElf" wrote in message
...

I've just posted to another forum on the subject. I think the
Mythbusters demo was completely flawed and didn't address the question
as it was originally asked. Of course the aircraft was going to fly
given the nature of their experiment.


How was the question originally asked?

PeeCeeElf wrote in
:


I've just posted to another forum on the subject.

Well, if you;re loking for someone to agree with you then that's probably
the best thing to do.

Might I suggest alt.conpsiracy or alt.fluffy.bunnies?


Bertie

PeeCeeElf,

didn't address the question
as it was originally asked


There is no way to ask the question without the aircraft taking off.
The only difference is in the speed of the wheels. In one variant, it
is twice that of a "stationary runway" situation, in the other it is
infinite. In both cases, nothing keeps the aircraft from flying.

Einstein had a hard time convincing people, too.

--
Thomas Borchert (EDDH)

"Steven P. McNicoll" wrote:
How was the question originally asked?

Will be interesting to see "PeeCeeElf" says the "original" question was. I
believe it was this variant though [1]:

"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?"

But some versions use something like this:

[Blah blah] "speed of wheels" [blah blah].

I suspect the debate in those version is over the meaning of "speed of
wheels" which arguably can have two commonly used meanings:

(1) Translational motion of the center axle of the wheel relative to the
ground.

(2) Rotational motion of the outer rim of the wheel relative to the wheel's
axle.

Of course (1) appears synonomous with saying "Can a plane take off if the
conveyor belt moves at whatever speed it takes to keep the wheel's axle
stationary relative to the ground?" or more briefly: "Can a plane take off
if it is held stationary on the ground?"

The problem with at least one variant that includes "speed of wheels" was
covered by Cecil Adams TWO YEARS AGO:

"However, some versions put matters this way: "The conveyer belt is
designed to exactly match the speed of the wheels at any given time, moving
in the opposite direction of rotation." This language leads to a paradox:
If the plane moves forward at 5 MPH, then its wheels will do likewise, and
the treadmill will go 5 MPH backward. But if the treadmill is going 5 MPH
backward, then the wheels are really turning 10 MPH forward. But if the
wheels are going 10 MPH forward . . . Soon the foolish have persuaded
themselves that the treadmill must operate at infinite speed. Nonsense.
The question thus stated asks the impossible -- simply put, that A = A + 5
-- and so cannot be framed in this way. Everything clear now? Maybe not.
But believe this: The plane takes off." [1]

[1] http://www.straightdope.com/columns/060203.html

Jim Logajan Wrote:
"Steven P. McNicoll" wrote:
How was the question originally asked?

Will be interesting to see "PeeCeeElf" says the "original" question
was. I believe it was this variant though

Something like that Jim. The way I see it is that the question causes
more confusion than the inevitable outcome. Any way you look at it, the
aircraft will fly. You could turn that treadmill over at virtually any
speed and a little ultralight would probably blast off.

I did have problems with the way the question was worded (originally)
but I've cleared it up in my feeble mind. I'm Australian, and ya gotta
talk a little s-l-o-w-e-r for us cobbers to understand what ya sayin'.
It must be all that time I've spent flying inverted.. all the blood has
rushed to my head


--
PeeCeeElf
Posted at www.flight.org

Dallas wrote:
In case you missed it, here's the segment on You Tube:

http://youtube.com/watch?v=KSBFQOfas60&feature=related

And yet, the debate continues. :- (

Dear God, let it end already.

It's like that friend of mine who was convinced that if an airplane
does a U-turn against a 40-knot headwind, it will stall and crash.

As if wings are somehow aware of the planet beneath them.
It's the same damn thing.

"PeeCeeElf" wrote in message
...

Jim Logajan Wrote:
"Steven P. McNicoll" wrote:
How was the question originally asked?

Will be interesting to see "PeeCeeElf" says the "original" question
was. I believe it was this variant though

Something like that Jim. The way I see it is that the question causes
more confusion than the inevitable outcome. Any way you look at it, the
aircraft will fly. You could turn that treadmill over at virtually any
speed and a little ultralight would probably blast off.

I did have problems with the way the question was worded (originally)
but I've cleared it up in my feeble mind. I'm Australian, and ya gotta
talk a little s-l-o-w-e-r for us cobbers to understand what ya sayin'.
It must be all that time I've spent flying inverted.. all the blood has
rushed to my head


This whole thing is done and over the Mythbusters busted the myth that it
wouldn't take off, can we PLEASE let it die!

To solve this puzzle, you need to ask how the control system works.

Method #1: A device attached to the vehicle monitors the speed of the
wheels and transmits this to the conveyor belt's control system which
runs the belt in the opposite direction at the same speed.

Method #2: Some sort of position-detecting system observes the vehicle's
position on the belt, and feeds back to a servo system that increases
the belt's backwards speed if the vehicle starts making forward progress,
or decreases it if the vehicle starts sliding backwards.

(Someone want to propose a different control system?)



Both systems are actually equivalent in their effects on automobiles
and airplanes.

An automobile is held in position no matter what the driver attempts
to do.

With airplanes, the situation is different. Because the plane has
free-wheeling wheels, and doesn't depend on pushing against the belt in
order to move forward, it begins to make progress.

At this point, the belt -- which is a perfect conveyor belt -- instantly
speeds up to infinite speed. The airplane's wheels -- which are perfect
wheels -- likewise instantly spin up to infinite speed. Since the wheels
are perfect and have no friction, the airplane is not affected and takes
off anyway.

If you don't assume perfect abstractions, then the answer depends on
what happens first: Either a) the belt reaches its upper speed limit
and the plane takes off, b) the plane's bearing seize and the plane is
flung backwards off the belt, or c) the breeze caused by friction between
the belt and the atmosphere is sufficient for the plane to take off
before a) or b) happens.

--
-Ed Falk,
http://thespamdiaries.blogspot.com/

In article ,
NEWS theducksmail"AT"yahoo.com wrote:

This whole thing is done and over the Mythbusters busted the myth that it
wouldn't take off, can we PLEASE let it die!

Actually, PeeCeeElf was correct; they didn't do the experiment right.
The puzzle assumes some sort of feedback mechanism to keep the belt
moving exactly at the opposite speed as the airplane. The mythbusters
guys didn't do that.

However, Cecil Adams is also right; it's not possible. Doing the test
right assumes that you believe in A = A + 5.
--
-Ed Falk,
http://thespamdiaries.blogspot.com/

(Edward A. Falk) wrote:
To solve this puzzle, you need to ask how the control system works.

No. You need to first write out the "puzzle" precisely as you first found
it.