Can a Plane on a Treadmill Take Off?

Not true. The original problem statement was this:

"An airplane on a runway sits on a conveyer belt that moves in the
opposite direction at exactly the speed that the airplane is moving
forward. Does the airplane take off?" (Assuming the tires hold out, of
course.)

I restated it, but either version clearly implies that the airplane must be
moving for the conveyor to be moving. Sure if the plane isn't moving, it
won't take off. But if the conveyor is moving, the plane must be moving in
the opposite direction, because that's what the problem says. The problem
never said that the conveyor somehow moves in a way that cancels the plane's
forward motion.

As many have stated, unless the pilot is applying the brakes, so that there
is friction between the wheels and the belt, the movement of the conveyor
has nothing to do with the speed of the plane. All the problem says is that
the conveyor is moving in the opposite direction at the same speed as the
plane.
--
Bob (Chief Pilot, White Knuckle Airways)


"Peter Duniho" wrote in message
...
"Bob Chilcoat" wrote in message
...
On the contrary, the problem clearly states that the conveyor is moving
at the speed that the plane is moving (but in the opposite direction).

The statement "the conveyor is moving at the speed that the plane is
moving" (the one you say the problem states) is a very different statement
from "which always reduces the plane's forward movement to zero" (the
statement Thomas responded to).

How is your post contrary to Thomas'?

Pete

My post is not contrary to Thomas', it reinforces his comment. My statement
is a further rebuttal to the statement thomas was responding to.

--
Bob (Chief Pilot, White Knuckle Airways)


"Peter Duniho" wrote in message
...
"Bob Chilcoat" wrote in message
...
On the contrary, the problem clearly states that the conveyor is moving
at the speed that the plane is moving (but in the opposite direction).

The statement "the conveyor is moving at the speed that the plane is
moving" (the one you say the problem states) is a very different statement
from "which always reduces the plane's forward movement to zero" (the
statement Thomas responded to).

How is your post contrary to Thomas'?

Pete

"Tony" wrote in message
oups.com...
We don't have enough information. What color is the airplane? What
ratings does the pilot have? How many postings will this thread have
before it dies?

Also need more information on the treadmill.

Is this the same type of treadmill that a guy named George walks his dog on,
a cat jumps onto the treadmill and the dog starts chasing it causing the
treadmill to speed up. George falls down on the treadmill but isn't thrown
off...

Hence, if George can't get off the treadmill, how can a plane???

"Jim Macklin" wrote:
"alexy" wrote in message
news | "Jim Macklin"
wrote:
|
|
| b. If the treadmill was powered [and everything was
timed
| in sync] the belt would be accelerating rearward and the
| engine thrust would be pulling forward at the same rate,
| thus the airframe mounted wigs would have near zero
airspeed
| and lift and would not fly.
|
| Just to "set the hook" here, are you saying that it will
be possible
| to have the conveyer move backwards fast enough that the
plane remains
| still, even under full power, and with no brakes on?


sure, in our imaginary world. in the real world nobody will
try this so mechanical limitations are unimportant.

Okay, if that happens (the treadmill moving fast enough backwards to
offset the thrust of the plane's propulsion system), how fast will the
plane be moving forward? ?

Given your answer to that, how fast will the conveyor be moving, given
that the conveyer moves backward at the same speed at which the plane
moves forward?

Given your answer to that, what's to stop the plane from moving
forward?

The problem says the conveyer moves at the same speed as the plane.
How in the world can it, by moving the same speed as the plane,
prevent the plane's motion?

One more thought: I'm getting ready to get an emissions test on my
car. They put the back wheels on rollers, put it in gear, and run the
engine up until the indicated speed is, e.g., 30mph. This seems to be
the situation that you and a few others picture happening here. But in
my case, my car is NOT moving forward, so I would NOT say that the
roller under my wheels was moving at the same speed as my car. It is
turning at the same rate as my car's wheels, which is a whole 'nother
kettle of fish.
--
Alex -- Replace "nospam" with "mail" to reply by email. Checked infrequently.

"Bob Chilcoat" wrote in message
...
My post is not contrary to Thomas', it reinforces his comment. My
statement is a further rebuttal to the statement thomas was responding to.

You made two replies to my own post, which are in contradiction with each
other.

Furthermore, if you intend to reinforce a person's post, I suggest you not
begin the post with the words "on the contrary".

Bob,

On the contrary, the problem clearly states that the conveyor is moving at
the speed that the plane is moving (but in the opposite direction).


Huh? The OP was saying "If you have a conveyoer which always reduces the
airplane's movement to zero", to which I said "the original question doesn't
say that". What does you statement have to do with what I said, let alone it
being "contrary"?

--
Thomas Borchert (EDDH)

Peter,

Furthermore, if you intend to reinforce a person's post, I suggest you not
begin the post with the words "on the contrary".


I didn't get it, either ;-)

--
Thomas Borchert (EDDH)

"Tony" wrote in message
oups.com...
We don't have enough information. What color is the airplane? What
ratings does the pilot have? How many postings will this thread have
before it dies?

Was there a flight plan filed?

Allen

Thomas Borchert wrote:

Peter,

Furthermore, if you intend to reinforce a person's post, I suggest you not
begin the post with the words "on the contrary".


I didn't get it, either ;-)

Easy, boys!

Bob, it took me a couple of readings initially to realize that what
you meant was "I agree with your comment, Thomas, and furthermore, to
the contrary of the post to which you were replying...". As Perter
says, when you start a post with "on the contrary" it sounds like you
are disagreeing with the post to which you were replying. Then it's
left to the reader to puzzle out whether you didn't understand the
post to which you were replying (and thought you were disagreeing when
in fact you were agreeing) or whether it was just a careless wording,
as I assumed.

But, semantics aside, it sounds like the four of us are solidly on the
side of a plane not just sitting stationary, spinning its wheels on a
conveyer!

--
Alex -- Replace "nospam" with "mail" to reply by email. Checked infrequently.

"Peter Duniho" wrote:

"alexy" wrote in message
news
Just to "set the hook" here, are you saying that it will be possible
to have the conveyer move backwards fast enough that the plane remains
still, even under full power, and with no brakes on?

I thought you had already established that it would be possible, and that
the treadmill speed is "somewhat below the speed of light"? You didn't
appear to solve the "materials integrity" aspect of the problem, but that
seems like a minor quibble.

You know, there is a fallacy in my reasoning that I am surprised no
one has called me on. We are used to aerodynamic drag, which increases
as the square of velocity. But if my memory of high school physics is
correct (and if Newton hasn't changed his mind in the last 40
yearsg) the friction between two bodies is a coefficient of friction
times the force normal to the motion (i.e., the weight of the plane).
No component for the relative velocities of the two bodies! So the
drag due to wheels is small, and speeding up the conveyer will not
increase that small drag, at least until you get to the "noise"
elements that make the idealized drag model imperfect.

I guess that by _accelerating_ the conveyer, you could make the plane
use all of its power for a short while providing the angular
acceleration to the wheels, but you very quickly get to relativistic
speeds, without ever reaching a steady state tradeoff for the
engine/prop's thrust.

Much easier to just read the problem as stated, and have the conveyer
only move as fast backwards as the plane moves forward!!

--
Alex -- Replace "nospam" with "mail" to reply by email. Checked infrequently.