So...about that plane on the treadmill...

"Darkwing" theducksmail"AT"yahoo.com wrote in message
...


Man you are a dick. This has NOT been adequately explained or there would
be no question about it. If the plane is not moving on the treadmill but
rather keeping up with the speed that the treadmill is moving (yes planes
DO have throttle controls) the thing is going to takeoff with no air
moving over the wings? NO WAY.

Maybe, in your infinite wisdom, you can explain to me why the
treadmill is moving. Eh?

Ray wrote:
Looks like airplane treadmill problem, regularly a spark for flame wars
on R.A.P., has made it into the mainstream.

http://pogue.blogs.nytimes.com/

Let the arguing begin!

- Ray
Yes, the airplane will take off. The thrust of the engine is against the
AIR. NOT the treadmill. There are two real life situations analogous to
this:
1) Will an airplane on an essentially frictionless surface (say, wet
ice) take off?
2) Will a sea plane take off upriver in a current equal to it's take-off
speed (this one is a cheat, since it involves drag not involved in the
original situation, but should be a good "fire starter" for further
discussion).

Rip

How is that possible if the wings are stationary? Are you saying the thing
will take off due to the pure power setting to keep up at 25mph (or
whatever), nothing to do with the wings?

What we're saying is that the wings aren't stationary. The airplane moves (and
accelerates) forward, just as if it was on a normal runway. The speed of the airplane
relative to the treadmill belt doesn't matter.

Let us pretend we fly a plane over the treadmill at 80mph, and run the treadmill belt at
80mph the other direction. Now, if the airplane touches down, the wheels are going to be
spinning really fast, but the airplane just keeps moving along at 80mph relative
_to_the_ground_. It certainly doesn't slam to a stop because 80-80=0. Relative to the
treadmill belt, it's doing 160.

Now let's do the opposite. Let's run the treadmill in the same direction that the
airplane is going. Now, when our airplane touches down, the wheels don't turn at all--and
yet the airplane is still moving along at 80, relative to the ground. Google for videos
of planes landing on top of moving cars.

And, if you watch this
(http://videos.streetfire.net/player....D-D6BA1A43A06B)
video, you'll see that, if you have a rolling object powered by an independent (ie,
non-surface-friction) power source, it will move at the same speed relative to the earth
regardless of the motion of the surface on which it is placed. Watch how the skateboard
starts to move forward, then the cloth/paper/whatever it is is pulled out from underneath.
The skateboard doesn't even slow down.

"Peter Dohm" wrote

It is really depressing that so many in a group of this type [seem to] have
been taken in.

Think of it this way.

This was a well worn thread a while back. Most all of the "not able to fly"
believers were convinced, over time. The ones that know the answer, right off,
represented the more intelligent of the group.

Now, there have been many people that came in from other cess pools, following
MX. They are non-believers.

Many of the intelligent ilk that understood, right off, have left, disgusted
from MX ability to troll and remain, and the many members allowing him to remain
with a foothold.

There you have it. MX is by large part responsible for so many responses of the
non-thinking crowd. I see no other possible interpretation.
--
Jim in NC

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

Okay Mr. Cynical, I sent an email off to the Mythbusters explaining this
whole thing and a link to the Google Groups thread so we'll see if they pick
it up and show it on the program.

doubt it. It's not a myth.

--
Bob Noel
Looking for a sig the
lawyers will hate

"Darkwing" theducksmail"AT"yahoo.com wrote in message


This has NOT been adequately explained or there
would be no question about it. If the plane is not moving on the
treadmill but rather keeping up with the speed that the treadmill is
moving (yes planes DO have throttle controls) the thing is going to
takeoff with no air moving over the wings? NO WAY.

Assuming you're a pilot, I don't understand why you think no air would be
moving over the wings, but I'll give this one good "college try"...

First, the question posed in the link by the OP of this thread is an
incorrect variation of the original. The original problem asks: "A plane is
standing on a giant treadmill. The plane moves in one direction, while the
treadmill moves in the opposite direction and at the same speed as the
plane. Can the plane take off?"

As has been explained, placing a car on the question's treadmill would
result in a stationary vehicle relative to the observer standing beside the
treadmill. The reason is the car derives its propulsion through the wheels
sitting on the treadmill and the speed of the car is measured by how fast
the wheels are turning. The faster the wheels turn, the "faster" the car
moves. However, this is only relative to the treadmill belt. To the observer
standing beside the treadmill, the car is motionless. If the driver placed
his hand out the window, he would feel no wind even though his "speed" as
indicated by the speedometer may be 100 miles per hour.

This is very similar to your example of running on the treadmill. You did
not feel a relative wind in your face because you were stationary relative
to the observer standing beside the treadmill. The reason you were
stationary is you generate your propulsion by moving your feet against the
ground (or belt, in this case) and the belt is moving in the opposite
direction and same speed of your "travel". Like the car, your speed is
measured by how fast your feet move from front to rear and they match the
speed of the belt to cancel out each other.

Now, replace the car and runner with an airplane. The airplane derives its
propulsion from its engine pushing air from front to back. None of this
energy is sent to the wheels to propel the airplane. The speed of the
airplane is measured by the flow of air past the airplane, not the turning
of its wheels. As the airplane's engine spools up to takeoff power, air is
forced from front to rear and the plane moves forward regardless how fast
its wheels are turning. The observer standing beside the treadmill would
notice the treadmill speed up, the airplane's wheels turn twice as fast as
normal, and the airplane move forward (not stationary).

Speed is relative and the key here is the means of propulsion. The
airplane's speed is measured by how fast the air is moving past it, not by
how fast its wheels are turning or how fast the ground is flashing by. None
of the airplane engine's energy is transmitted to the wheels to generate
speed. All of the airplane's propulsion is derived from moving air
(otherwise it would never stay in the air after takeoff). Since the
treadmill has very little effect on the air (and what little effect it does
have actually helps the airplane generate more lift), the airplane will
indeed takeoff in the same distance it normally would use without the
treadmill. However, the airplane wheels would be turning at twice their
normal speed at the time of takeoff.


Try this experiment:

Take a toy car and attach it to a string. Tie the other end of the string to
a small spring scale. Place the car on the treadmill belt and hold the scale
in front of the car while you turn on the treadmill. Observe nearly zero
(essentially 1G) force being exerted on the string/scale. Speed up the
treadmill (for simplicity, let's say you set it to a constant 10mph) and
you'll observe no significant difference in force exerted on the string (the
only additional force is the friction of the car's axles). Now gently pull
the string/scale forward. As long as you maintain a 1G force on the string,
the car will continue to accelerate.

Now, to the observer standing beside the treadmill, was the car stationary
or moving forward? It's speed was certainly not zero as the car most
definitely moved from rear to front of the belt. What was the speed of the
car relative to the "driver" sitting inside the toy? The wheels would be
turning faster than 10mph. If the "driver" were to put his hand out the
window, how fast would the air be moving? Much slower than his wheels would
say he's moving, but faster than the driver I mentioned at the beginning of
this post.

Replace the toy with the mythical airplane above, replace your arm with the
airplane's engine (and propeller, if appropriate), then replace the string
with the airplane engine mounts. You should now be able to visualize why the
airplane sitting on that giant treadmill would most definitely takeoff.

If not, I wish you good luck and safe flight. You'll need it.

--
John T
http://sage1solutions.com/blogs/TknoFlyer
Reduce spam. Use Sender Policy Framework: http://openspf.org
____________________

"Richard Riley" wrote in message
...
You have a wind tunnel without a ceiling? Cool.

If you cannot be bothered to be clear about what you mean when you write "is
a real pain", I cannot be bothered to restrict my understanding of such an
ambiguous statement to such mundane issues as a ceiling.

An airplane in a wind tunnel can climb just as well as it can accomplish any
other action an airplane might do. Within the confines of the wind tunnel,
the airplane can behave completely normally, relative to anything an
airplane can do. Climbing or otherwise.

You have a treadmill that's a couple of thousand feet long? Cool.

The question specifically posits a treadmill long enough to serve as a
runway. In any case, you made no indication that your objection was based
on the length of the treadmill. Either way, you are missing the point.

Pete

"Richard Riley" wrote in message
...
On Tue, 12 Dec 2006 16:38:30 -0500, "mike regish"
wrote:

Come on. You can't be serious.

mike

"Richard Riley" wrote in message
.. .

And, just to keep it on topic, the only planes that could take off
from a treadmill are the Osprey and the Harrier.

Unless you have a treadmill that's a few hundred to several thousand
feet long, yes.

Yes we do--according the the original problem statement, the treadmill is as
long and wide as the runway ordinarily used by the aircraft. Further,
despite attempts at humor by me and others, no unusual obstacles were added
to the end of the magic moving runway; nor was any anomaly present in the
atmosphere relative to the surrounding terrain and/or the aircraft.
Therefore, the giant magic treadmill was the ONLY anomaly on the magic
airport--and it was trivial since the wheels did not propel the aircraft.

Peter

"John T" wrote in message
...
"Darkwing" theducksmail"AT"yahoo.com wrote in message


This has NOT been adequately explained or there
would be no question about it. If the plane is not moving on the
treadmill but rather keeping up with the speed that the treadmill is
moving (yes planes DO have throttle controls) the thing is going to
takeoff with no air moving over the wings? NO WAY.

Assuming you're a pilot, I don't understand why you think no air would be
moving over the wings, but I'll give this one good "college try"...


Yes I am a pilot.


First, the question posed in the link by the OP of this thread is an
incorrect variation of the original. The original problem asks: "A plane
is standing on a giant treadmill. The plane moves in one direction, while
the treadmill moves in the opposite direction and at the same speed as the
plane. Can the plane take off?"

As has been explained, placing a car on the question's treadmill would
result in a stationary vehicle relative to the observer standing beside
the treadmill. The reason is the car derives its propulsion through the
wheels sitting on the treadmill and the speed of the car is measured by
how fast the wheels are turning. The faster the wheels turn, the "faster"
the car moves. However, this is only relative to the treadmill belt. To
the observer standing beside the treadmill, the car is motionless. If the
driver placed his hand out the window, he would feel no wind even though
his "speed" as indicated by the speedometer may be 100 miles per hour.

This is very similar to your example of running on the treadmill. You did
not feel a relative wind in your face because you were stationary relative
to the observer standing beside the treadmill. The reason you were
stationary is you generate your propulsion by moving your feet against the
ground (or belt, in this case) and the belt is moving in the opposite
direction and same speed of your "travel". Like the car, your speed is
measured by how fast your feet move from front to rear and they match the
speed of the belt to cancel out each other.

Now, replace the car and runner with an airplane. The airplane derives its
propulsion from its engine pushing air from front to back. None of this
energy is sent to the wheels to propel the airplane. The speed of the
airplane is measured by the flow of air past the airplane, not the turning
of its wheels. As the airplane's engine spools up to takeoff power, air is
forced from front to rear and the plane moves forward regardless how fast
its wheels are turning. The observer standing beside the treadmill would
notice the treadmill speed up, the airplane's wheels turn twice as fast as
normal, and the airplane move forward (not stationary).

Speed is relative and the key here is the means of propulsion. The
airplane's speed is measured by how fast the air is moving past it, not by
how fast its wheels are turning or how fast the ground is flashing by.
None of the airplane engine's energy is transmitted to the wheels to
generate speed. All of the airplane's propulsion is derived from moving
air (otherwise it would never stay in the air after takeoff). Since the
treadmill has very little effect on the air (and what little effect it
does have actually helps the airplane generate more lift), the airplane
will indeed takeoff in the same distance it normally would use without the
treadmill. However, the airplane wheels would be turning at twice their
normal speed at the time of takeoff.


Try this experiment:

Take a toy car and attach it to a string. Tie the other end of the string
to a small spring scale. Place the car on the treadmill belt and hold the
scale in front of the car while you turn on the treadmill. Observe nearly
zero (essentially 1G) force being exerted on the string/scale. Speed up
the treadmill (for simplicity, let's say you set it to a constant 10mph)
and you'll observe no significant difference in force exerted on the
string (the only additional force is the friction of the car's axles). Now
gently pull the string/scale forward. As long as you maintain a 1G force
on the string, the car will continue to accelerate.

Now, to the observer standing beside the treadmill, was the car stationary
or moving forward? It's speed was certainly not zero as the car most
definitely moved from rear to front of the belt. What was the speed of the
car relative to the "driver" sitting inside the toy? The wheels would be
turning faster than 10mph. If the "driver" were to put his hand out the
window, how fast would the air be moving? Much slower than his wheels
would say he's moving, but faster than the driver I mentioned at the
beginning of this post.

Replace the toy with the mythical airplane above, replace your arm with
the airplane's engine (and propeller, if appropriate), then replace the
string with the airplane engine mounts. You should now be able to
visualize why the airplane sitting on that giant treadmill would most
definitely takeoff.

If not, I wish you good luck and safe flight. You'll need it.

--
John T


Thank you for your reply. Here is my .02, it would seem that the plane never
actually moves in respect to the observer no matter how fast the treadmill
moves, the plane will just take off like it is hovering and then slowly
accelerate away?

I guess I'll have to set this up and try it, I do have a few RC planes
laying around and I have a treadmill so I guess I'll know one way or
another, unless Mythbusters beats me to the punch.

-------------------------------------------------------
DW

"Peter Duniho" wrote in message
...
"T o d d P a t t i s t" wrote in message
news
[...]
Agreed, further interpretation is required, although I think
the most reasonable interpretation is pretty clear

But that's my point. Just as a "reasonable interpretation" is required,
one can just as easily assert that a MORE reasonable interpretation would
be to assume the question means to discuss a scenario that is at least
theoretically possibly to reproduce with existing technology.

The question is ambiguous no matter how one looks at it. How can anyone
assert that it makes more sense to interpret it in a way that creates a
physically impossible situation than to interpret in a way that can at
least in theory be tested experimentally?

Pete


Yup. The question can be interpreted in a couple of different ways. This is
what has created the multi-faceted debate. We are not just debating whether
the plane will fly given a single scenario. We are arguing about the
scenario itself. Stupid, really. I mean, the arguing is stupid. I'm all for
discussing alternate scenarios to gain enlightenment (which I got the last
round - no new information this time).

I happen to believe that the point of the scenario is to illustrate the
independence (within limits of friction) of the motion of the plane from its
connection to the ground. I think that the alternate scenarios are
interesting and have their own merit. However, there are those that clearly
do not get the independent nuance of airmotive thrust (e.g. Darkwing).
-------------------------------
Travis
Lake N3094P
PWK