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

[Ray]

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

[Peter Duniho]

"Ray" > wrote in message
...
> 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/

And handled with every bit as much intelligence and consideration as we've
seen here. Which is to say, there's no shortage of people convinced that
the airplane won't take off, even though it will.

> Let the arguing begin!

Why? Haven't you had enough by now?

[FLAV8R]

"Ray" > wrote in message ...
> 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

That would depend on what has the greater resistance,
the air in front of the plane or the belt on the treadmill.
If it was harder for the plane to push through the air in
front of it then the plane would merely roll stationary
on the treadmill.
If the resistance of the treadmill rollers was greater
than the air in front of the plane then the plane would
push forward thereby achieving lift through air flow
passage over the wings.

You can equate it to an airboat in a river.
Will the river push the airboat down stream or
will the propulsion of the engine move it forward?

Just my two cents worth....

David
Greer, SC

[Peter Duniho]

"FLAV8R" > wrote in message
...
> That would depend on what has the greater resistance,
> the air in front of the plane or the belt on the treadmill.

No, it would not depend on that at all. Both of those effects are creating
a resistance in the same direction, and thus are additive. Which one is
greater is irrelevant. The only relevant question is whether they combined
exceed the thrust from the engines.

They don't even come close to doing that, and so the engines can easily push
the airplane forward to a high enough speed for flight.

> [...]
> You can equate it to an airboat in a river.
> Will the river push the airboat down stream or
> will the propulsion of the engine move it forward?

It's similar, yes. Except that the drag due to friction from the treadmill
is miniscule, whereas hydrodynamic drag is significant.

Pete

[Peter Dohm]

"Peter Duniho" > wrote in message
...
> "FLAV8R" > wrote in message
> ...
> > That would depend on what has the greater resistance,
> > the air in front of the plane or the belt on the treadmill.
>
> No, it would not depend on that at all. Both of those effects are
creating
> a resistance in the same direction, and thus are additive. Which one is
> greater is irrelevant. The only relevant question is whether they
combined
> exceed the thrust from the engines.
>
> They don't even come close to doing that, and so the engines can easily
push
> the airplane forward to a high enough speed for flight.
>
> > [...]
> > You can equate it to an airboat in a river.
> > Will the river push the airboat down stream or
> > will the propulsion of the engine move it forward?
>
> It's similar, yes. Except that the drag due to friction from the
treadmill
> is miniscule, whereas hydrodynamic drag is significant.
>
> Pete
>
>
As pictured, the runway is much to short, which is just as well since the
uprights of the treadmill would impinge on the wings. <bfg>

Actually, I agree that the drag from the treadmill is trivial. Therefore,
if sufficient distance was provided to accellerate to an appropriate
airspeed, the only problem would be the maximum speed rating of the tires.

Peter

[BucFan]

"Ray" > wrote in message
...
> 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

It is a trick question. The obvious assumption being that the plane will
not move, therefore no airflow over the wings. The plane, however WILL move
down the runway. The propeller or the jets will pull or push on the air and
move the plane. The wheels are not providing the moving force, the reaction
of the thrust mechanism against the air is.

One of two things would happen before the plane took off though, the
bearings in the planes wheels would burn up or the motor driving the
treadmill would burn up. The control system is in an infinite feedback
loop. The plane would move due to the forces described above and the
treadmill would try to speed up, so the wheels would move faster, then the
treadmill would move faster etc etc etc......

[Morgans[_2_]]

"Ray" > wrote in message ...
> 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!

It is truly amazing how many clueless people have commented on the problem. MX
should go hang out there. He would look like a rocket scientist.
--
Jim in NC

[muff528]

"Peter Duniho" > wrote in message
...
> "Ray" > wrote in message
> ...
>> 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/
>
> And handled with every bit as much intelligence and consideration as we've
> seen here. Which is to say, there's no shortage of people convinced that
> the airplane won't take off, even though it will.
>
>> Let the arguing begin!
>
> Why? Haven't you had enough by now?
>

It seems that the "non-believers" think that the treadmill is somehow
holding the airplane back.
The way that the problem is posed on the blog states that the treadmill
matches the wheel speed of
the airplane. ("The conveyer belt is designed to exactly match the speed of
the wheels, moving in the
opposite direction.") If friction is taken into consideration then one of
four conditions can exist.
1. no thrust (or not enough thrust to overcome frictional forces) ...
neither the plane nor the conveyor are moving.
2. minimal thrust... the wheels and conveyor are moving but the conveyor
drags the plane backwards.
3. just enough thrust to match friction forces... the airplane remains
motionless relative to the earth but the wheels
and conveyor are moving a little faster.
4. more than enough thrust.... the airplane accelerates until it can take
off. The conveyor also accelerates to match
the wheel's speed until lift off when the wheels rotate to a stop and
the conveyor, somehow sensing this, also
comes to a standstill.
The treadmill's speed is dependent on the wheel's speed, not the other way
around.

[Darkwing]

"Ray" > wrote in message
...
> 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

This looks like a job for the MythBusters!!!

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

[Darkwing]

"Peter Duniho" > wrote in message
...
> "Ray" > wrote in message
> ...
>> 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/
>
> And handled with every bit as much intelligence and consideration as we've
> seen here. Which is to say, there's no shortage of people convinced that
> the airplane won't take off, even though it will.
>

Nope the plane won't take off.

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

[Peter Dohm]

"Richard Riley" > wrote in message
...
> On Mon, 11 Dec 2006 21:27:16 -0500, "Morgans"
> > wrote:
>
> >
> >"Ray" > wrote in message
...
> >> 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!
> >
> >It is truly amazing how many clueless people have commented on the
problem. MX
> >should go hang out there. He would look like a rocket scientist.
>
> Quite by coincidence, last week I visited a wind tunnel with a
> treadmill in it.
>
> http://www.swiftengineering.com/06Other/Windtunnel/Windtunnel.htm
>
> A "rolling road" gets rid of the boundry layer, and better simulates
> what a race car will see on the track.

There was a lot of talk 30+ years ago about what a nice thing this would be;
mainly to test the effectiveness of anti-lift devices for sports car racing.

Peter

[Bob Martin]

Darkwing wrote:

>>
>
> Nope the plane won't take off.
>

You'd better not just be trolling...

Friction generated by wheels is almost negligible. Even for very large aircraft like a
747, wheel friction is nearly constant, regardless of speed (at least at sane speeds). It
only depends on the amount of force pushing down on the wheel.

So let's look at all of the forces acting on this airplane. In the horizontal direction,
we have:
Thrust from the engine (nearly constant at these speeds)
Aerodynamic drag (goes up as the square of speed)
Wheel friction (again, nearly constant)

For any object to accelerate in a given direction, the total force acting on it in that
direction must not be equal to zero. For a normal airplane, on a normal runway takeoff,
thrust must obviously be greater than the other two forces, since we see airplanes take
off every day. Even at the moment of takeoff, aerodynamic drag may have increased, but
the airplane still has a fair bit of excess thrust, and (assuming you don't pull up too
steeply) will continue to accelerate.

So now, let's put the plane on the treadmill. Once again, the ONLY forces acting on it
are thrust (which stays the same), drag (which still increases as speed squared, and wheel
friction (which, again, IS CONSTANT! no matter how fast the treadmill runs, until we start
talking about silly cases like 5000mph treadmills). Sticking to sane, airplane-like
speeds for the treadmill (80-160mph or so) We see that, once again, thrust is greater than
the other two. Therefore, the plane MUST accelerate.

I'd like to also point out that I have tried this on an actual treadmill with a small
model airplane. It takes right off, no problem. Now I just need to go fin

[peter]

Peter Duniho wrote:
> "Ray" > wrote in message
> ...
> > 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/
>
> And handled with every bit as much intelligence and consideration as we've
> seen here. Which is to say, there's no shortage of people convinced that
> the airplane won't take off, even though it will.
>

The problem is that as it is stated, the scenario is not one that could
ever be created with a real treadmill subject to normal engineering
constraints.

Let's imagine that the plane gets started in a slow roll down the
runway at a steady 10 mph relative to the calm air & earth. Now the
treadmill has to speed up to 10 mph, but that makes the plane's tires
start spinning at 20 mph. Therefore the treadmill has to speed up to
20 mph which makes the tires spin at 30 mph, which makes the treadmill
speed up to 40 mph, etc.
Even though the plane is only moving slowly relative to the earth, the
tires and treadmill speeds are in an infinite loop to ever higher
speeds.

As soon as the plane starts moving at all relative to the earth, the
tires and treadmill will start their endless positive feedback loop to
try and reach an infinite speed. If the treadmill has a fast enough
response mechanism to keep up with the increasing tire speed the system
will reach some kind of physical limit before the plane can get any
appreciable speed relative to the air. The tires might explode, the
wheel bearings may fail, the treadmill propulsion system may run out of
power, but you can't satisfy the conditions as stated and have the
plane get up to takeoff speed.

Of course the above is based on a particular interpretation of "speed
of the wheels" i.e. that it is measured based on the speed of rotation
and therefore measures show fast they are rolling on the treadmill
surface. If instead the "speed of the wheels" is measured by seeing
how fast the wheel hub is moving forward relative to the earth then the
above infinite feedback loop doesn't arise and the plane can take off
fairly normally although the wheels will be spinning twice as fast as
normal at takeoff.

But that second interpretation of wheel speed doesn't strike me as
consistent with normal usage - i.e. when a bicyclist is on a stationary
trainer we would normally measure the speed of his rear wheel based on
rotation rate, not say that it's zero since the hub is just spinning
but not moving forward.

[Andrew Sarangan]

Actually the question makes sense, at least to the non-aviation public,
because the normal use of a treadmill suggests the opposite, ie a
person walking on the treadmill remains stationary, yet he burns energy
as if he were walking on solid ground. The same would be true if it
were a car, except it would burn slightly less fuel because of the lack
of wind resistance (same is true for a person walking too, but the wind
resistance is even more negligible for walking).

A better way to pose the airplane question would be " what would
happen if the airplane is landing on a treadmill that is moving in the
opposite direction and speed?"






Peter Duniho wrote:
> "Ray" > wrote in message
> ...
> > 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/
>
> And handled with every bit as much intelligence and consideration as we've
> seen here. Which is to say, there's no shortage of people convinced that
> the airplane won't take off, even though it will.
>
> > Let the arguing begin!
>
> Why? Haven't you had enough by now?

[Jose[_1_]]

> A better way to pose the airplane question would be " what would
> happen if the airplane is landing on a treadmill that is moving in the
> opposite direction and speed?"

How about dispensing with the treadmill entirely. What would happen if
the airplane were on a frictionless surface? The wheels couldn't push
on anything, so how would the airplane take off?

Jose
--
"There are 3 secrets to the perfect landing. Unfortunately, nobody knows
what they are." - (mike).
for Email, make the obvious change in the address.

[Peter Duniho]

"peter" > wrote in message
oups.com...
> The problem is that as it is stated, the scenario is not one that could
> ever be created with a real treadmill subject to normal engineering
> constraints. [...]

You can interpret the question in that way of course. However, the intent
of the "puzzler" is clear, and the fact that it is poorly stated should not
interfere with making a reasonable, good faith effort to address the
intended question.

It's well and good to nitpick about physically impossible situations, but
rest assured if you started doing so in a true interactive situation in
which the person stating the puzzle had the opportunity to restate it, you
would quickly get past the nitpicking and get to the intended question.

It's a waste of time to do the nitpicking in the first place. It's easy
enough to infer what the interesting question really is. And the
interesting question doesn't have the treadmill blowing up.

Pete

[Peter Duniho]

"Andrew Sarangan" > wrote in message
ps.com...
> Actually the question makes sense, at least to the non-aviation public,
> because the normal use of a treadmill suggests the opposite, ie a
> person walking on the treadmill remains stationary, yet he burns energy
> as if he were walking on solid ground.

Who says the question doesn't make sense?

The problem that the people who don't "get it" have is that a typical
treadmill is used in a situation where propulsion is via the interface with
the ground, whereas airplanes get their propulsion via other means. (And I
don't think this has anything to do with aviation public vs non-aviation
public...plenty of pilots don't understand the physics either, as has been
amply demonstrated here).

> [...]
> A better way to pose the airplane question would be " what would
> happen if the airplane is landing on a treadmill that is moving in the
> opposite direction and speed?"

That's not a better way at all. That asks an entirely different question
and takes advantage of a completely different prejudice the answerer might
have.

Pete

[Peter Duniho]

"Darkwing" <theducksmailATyahoo.com> wrote in message
...
> This looks like a job for the MythBusters!!!

*Yawn*

That would be a boring show. Either they'd have to fill 19 minutes with the
construction of the treadmill itself, or they'd have the airplane taking off
in the first 30 seconds, leaving them with 19 minutes of filler at the end.

You don't need MythBusters. You just need a little knowledge of physics and
some common sense.

Pete

[Darkwing]

"Bob Martin" > wrote in message
...
> Darkwing wrote:
>
>>>
>>
>> Nope the plane won't take off.
>>
>
> You'd better not just be trolling...
>
> Friction generated by wheels is almost negligible. Even for very large
> aircraft like a 747, wheel friction is nearly constant, regardless of
> speed (at least at sane speeds). It only depends on the amount of force
> pushing down on the wheel.
>
> So let's look at all of the forces acting on this airplane. In the
> horizontal direction, we have:
> Thrust from the engine (nearly constant at these speeds)
> Aerodynamic drag (goes up as the square of speed)
> Wheel friction (again, nearly constant)
>
> For any object to accelerate in a given direction, the total force acting
> on it in that direction must not be equal to zero. For a normal airplane,
> on a normal runway takeoff, thrust must obviously be greater than the
> other two forces, since we see airplanes take off every day. Even at the
> moment of takeoff, aerodynamic drag may have increased, but the airplane
> still has a fair bit of excess thrust, and (assuming you don't pull up too
> steeply) will continue to accelerate.
>
> So now, let's put the plane on the treadmill. Once again, the ONLY forces
> acting on it are thrust (which stays the same), drag (which still
> increases as speed squared, and wheel friction (which, again, IS CONSTANT!
> no matter how fast the treadmill runs, until we start talking about silly
> cases like 5000mph treadmills). Sticking to sane, airplane-like speeds
> for the treadmill (80-160mph or so) We see that, once again, thrust is
> greater than the other two. Therefore, the plane MUST accelerate.
>
> I'd like to also point out that I have tried this on an actual treadmill
> with a small model airplane. It takes right off, no problem. Now I just
> need to go fin

I am a regular on RAP, not a troll.

Show me video and I will believe it, if the plane is not moving relative to
the wind then the wing isn't making lift. I have ran on treadmills and I
never felt a "wind" blowing in my face.

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

[peter]

Peter Duniho wrote:
> "peter" > wrote in message
> oups.com...
> > The problem is that as it is stated, the scenario is not one that could
> > ever be created with a real treadmill subject to normal engineering
> > constraints. [...]
>
> You can interpret the question in that way of course. However, the intent
> of the "puzzler" is clear, and the fact that it is poorly stated should not
> interfere with making a reasonable, good faith effort to address the
> intended question.
>
> It's well and good to nitpick about physically impossible situations, but
> rest assured if you started doing so in a true interactive situation in
> which the person stating the puzzle had the opportunity to restate it, you
> would quickly get past the nitpicking and get to the intended question.
>
> It's a waste of time to do the nitpicking in the first place. It's easy
> enough to infer what the interesting question really is.

My view was that it was exactly the infinite feedback mechanism that
made the problem as stated interesting. Otherwise it's trivial and
boring.

[Peter Duniho]

"Darkwing" <theducksmailATyahoo.com> wrote in message
...
> I am a regular on RAP, not a troll.

Then read the extensive thread that we already had on this subject before
you put your two cents in.

> Show me video and I will believe it, if the plane is not moving relative
> to the wind then the wing isn't making lift.

True.

> I have ran on treadmills and I never felt a "wind" blowing in my face.

That's because you're using your feet for propulsion, and the treadmill was
negating your effort. There's no such effect for airplanes, as they don't
use their wheels for propulsion.

Your experience running on treadmills is irrelevant to the question at hand
(except for the intended effect of course, which is to confuse people like
you who haven't thought the whole thing through).

Pete

[Jay Beckman]

"Jose" > wrote in message
...
>> A better way to pose the airplane question would be " what would
>> happen if the airplane is landing on a treadmill that is moving in the
>> opposite direction and speed?"
>
> How about dispensing with the treadmill entirely. What would happen if
> the airplane were on a frictionless surface? The wheels couldn't push on
> anything, so how would the airplane take off?
>
> Jose

???

The wheels don't have to push on anything for an aircraft to take
off...there's no drivetrain feeding power to the wheels!

Jay B

[Jose[_1_]]

> The wheels don't have to push on anything for an aircraft to take
> off...there's no drivetrain feeding power to the wheels!

Right. Phrasing it the way I did may get people to realize this, or at
least to think about it themselves.

If you put an airplane on the roof of a speeding train, would it take
off? What if the train were shaped like a runway? What if it were very
thin?

They are all ultimately the same question.

Jose
--
"There are 3 secrets to the perfect landing. Unfortunately, nobody knows
what they are." - (mike).
for Email, make the obvious change in the address.

[Jay Beckman]

"Jose" > wrote in message
. net...
>> The wheels don't have to push on anything for an aircraft to take
>> off...there's no drivetrain feeding power to the wheels!
>
> Right. Phrasing it the way I did may get people to realize this, or at
> least to think about it themselves.
>
> If you put an airplane on the roof of a speeding train, would it take off?
> What if the train were shaped like a runway? What if it were very thin?
>
> They are all ultimately the same question.
>
> Jose

Is that an European Train or an African Train?

:O)

Jay B

[[email protected]]

Darkwing wrote:
> Show me video and I will believe it, if the plane is not moving relative to
> the wind then the wing isn't making lift. I have ran on treadmills and I


The problem is, that the aeroplane does move forward, it must, there is
nothing to stop it from doing so.

Imagine (or try)...

1. Hold a wheel between your fingers so it can spin.
2. Put wheel on a treadmill which is not moving.
3. Provide thrust (forward motion) to the wheel from your arm.
4. Observe wheel moves forward.
5. Turn on treadmill, and place wheel on the moving treadmill.
6. Apply SAME amount thrust as you did in 3.
7. Observe same forward movement (discounting the very small friction)
is produced, although the wheel spins much faster.

The thrust acts independantly of the treadmill, you need a treadmill at
least as long as a short field takeoff :)

[Chris W]

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

If we take the statement, "The conveyer belt is designed to exactly
match the speed of the wheels, moving in the opposite direction", to
mean that the plane can not move forward, because some how the conveyor
is moving so fast the wheel friction becomes great enough that the
engine thrust can not over come it. Obviously this isn't going to
happen, but if it were, I think we can all agree that the conveyor would
be moving extremely fast, several hundred MPH if not thousands of MPH.
Now consider a 150 foot wide, 10,000 foot long conveyor moving at that
speed. Would that not cause enough air to move with it that there would
be enough air speed for the plane to lift off? Of course once that
happened, the wheels would quickly stop, as would the conveyor and the
air. Then with no forward ground speed, the plane would probably fall
because it could not accelerate as fast as the "head wind" was dying.

How's that for an interesting twist?

--
Chris W
KE5GIX

"Protect your digital freedom and privacy, eliminate DRM,
learn more at http://www.defectivebydesign.org/what_is_drm"

Gift Giving Made Easy
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[Peter Duniho]

"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.

If you're going to try to stay on topic, you ought to at least try to get
the answer right. At this point plenty of sources, from individuals here in
this thread and the one we had a while back, as well as those cited in the
comments to the blog article referenced, have clearly stated the correct
answer.

Anyone attempting to refute the correct answer, however futile that effort
may be, at least owes it to themselves as well as the rest of us to take the
time to read and understand the references that explain the correct answer.

Pete

[Montblack]

("Jose" wrote)
> If you put an airplane on the roof of a speeding train, would it take off?


Yes!

The top of the tunnel would (take) the A.C.M.E High Wing Airplane's wings
and rudder section clean (off).


Montblack ....(Beep! Beep!)

[Bob Noel]

In article >,
Jose > wrote:

> > The wheels don't have to push on anything for an aircraft to take
> > off...there's no drivetrain feeding power to the wheels!
>
> Right. Phrasing it the way I did may get people to realize this, or at
> least to think about it themselves.
>
> If you put an airplane on the roof of a speeding train, would it take
> off? What if the train were shaped like a runway? What if it were very
> thin?

hmmmm, if you put the airplane on, say, a fast moving ship, could it
take off?

I wonder....

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

[muff528]

"Ray" > wrote in message
...
> 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

You're standing on the conveyor wearing a pair of roller skates. The rope
you are holding
is attached to the rear bumper of a truck. The truck is on the ground and
begins to move
away from you. As you begin to move forward the conveyor begins to turn
backwards
to match the wheel's speed. (Here's another point... as long as the wheels
are rolling and
not sliding the conveyor is "matching the wheel's speed". Just depends on
the observer's
reference frame whether the conveyor is moving or even needs to move to meet
the
conditions of the problem.) Eventually the truck will pull you off the end
of the conveyor.
Just substitute a propeller coupled to the atmosphere for the truck's wheels
coupled
to the ground. The conveyor is irrelevant.

[Peter Dohm]

"Richard Riley" > wrote in message
...
> On Mon, 11 Dec 2006 22:06:30 -0500, "Peter Dohm"
> > wrote:
> >>
> >> A "rolling road" gets rid of the boundry layer, and better simulates
> >> what a race car will see on the track.
> >
> >There was a lot of talk 30+ years ago about what a nice thing this would
be;
> >mainly to test the effectiveness of anti-lift devices for sports car
racing.
> >
>
> It's state of the art now. They said in the cars they're building the
> ride hight is 1/4" in front, 3/4" in the rear, since they're testing
> 1/2 scale in the tunnel a boundry layer would make a huge difference.
>
> Apparently the really, REALLY advanced tunnels in europe use a
> stainless belt that can turn in relation to the wind, and they're
> testing multiple cars at once to model drafting. Just the stainless
> rolling road costs $10 million - before you build the rest of the
> tunnel. Some even use a big air bearing under the belt so the full
> weight of the car can rest on the wheels.
>
It's just as well that I got away from all that. I'd be really bummed that
I couldn't have one of my own to play with! <g>

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

C'mon Richard! I know that you know better than that. Remember that a
moving floor treadmill moves in lock-step with the air in the tunnel, and
that it does so even if the speeds can be offset and the moving floor angled
to simulate a surface wind condition.

Peter

[Peter Dohm]

"Peter Duniho" > wrote in message
...
> "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.
>
> If you're going to try to stay on topic, you ought to at least try to get
> the answer right. At this point plenty of sources, from individuals here
in
> this thread and the one we had a while back, as well as those cited in the
> comments to the blog article referenced, have clearly stated the correct
> answer.
>
> Anyone attempting to refute the correct answer, however futile that effort
> may be, at least owes it to themselves as well as the rest of us to take
the
> time to read and understand the references that explain the correct
answer.
>
> Pete
>
>
It appears that the OP had it nailed from the start.

This "puzzler" is a deliberately trivial, and well tested problem, which
allows the problem to be restated slightly to allow the correct answer to be
refuted--at least enough to convince anyone who believes that the airplane's
wheels perform some function other than steering and removing friction [of
the aircraft sliding along the runway] so that the airplane can accellerate
and take off.

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

Peter :-(

[Jose[_1_]]

The problem is that:

"The conveyer belt is designed to exactly match the speed of the wheels,
moving in the opposite direction."

is a meaningless statement. It =sounds= like an English sentence, the
nouns and verbs are in the right place, and it gives the impression of
conveying a thought, but it has no actual meaning.

Restate that sentence and you have a question that has an answer.

Jose
--
"There are 3 secrets to the perfect landing. Unfortunately, nobody knows
what they are." - (mike).
for Email, make the obvious change in the address.

[Jose[_1_]]

Ok, how about this one. Everyone knows pilots love a tailwind.

You have a giant fan mounted on a truck positioned behind the airplane.
The fan blows air towards the airplane, helping it to accelerate down
the runway (literally blowing it down the runway) while the truck
follows, keeping up with the airplane. Pretty soon the plane will be
thundering down the runway and the pilot pulls back on the yoke.

Does the pilot have to wait until the airplane's speed down the runway
is twice Vr before he can take off?

Jose
--
"There are 3 secrets to the perfect landing. Unfortunately, nobody knows
what they are." - (mike).
for Email, make the obvious change in the address.

[N2310D]

"T o d d P a t t i s t" > wrote in message
...

>
> But anyone who does *not* violate the stated assumption (and
> consequently thinks this is *not* about real airplanes and
> real treadmills) can argue the plane cannot take off because
> its speed relative to the air is zero. To get that
> conclusion, however, they've got to assume an engine that is
> so weak, it couldn't take off on a real runway, or friction
> so much higher than reality as to again prohibit a takeoff.

Well, I choose a treadmill with zero internal friction. [If the treadmill
can be the length of the runway, I can make it frictionless.]

Now, lock up the brakes and advance the throttle(s) to 100%. Thrust is going
to overcome drag and move the airplane forward. Nothing in Aerodynamics 101
says thrust is related to wheel rotation. The treadmill belt is going to
maintain the zero rotation speed of the wheels by slipping forward instead
of rearward. When the aircraft reaches takeoff speed, it flys. Problem
solved.

[Steve Foley]

"N2310D" > wrote in message
news:YfBfh.3650$LL4.2817@trnddc04...
> Thrust is going to overcome drag and move the airplane forward.

Not in my Cherokee.

[Peter Dohm]

> > Thrust is going to overcome drag and move the airplane forward.
>
> Not in my Cherokee.
>
>
Sure it will!

If we can have a treadmill the size of a runway, and [which is] able to
sense the rotation of the airplane's wheels; then we can require it to be
both frictionless and inertia-free.

There are other amusing combinations as well; but the point the central
point remains: So long as the airplane is not attached to (or restrained
by) anything other than the "belt" of the treadmill, it will take off and
fly quite normally--without regard for humorous statements (including mine)
regarding doubled wheel speed.

Since the original problem statement made no assertion that the airplane
would be tied down, it obviously is not, and the the problem is
solved--quite simply because there was no problem.

Peter

[Peter Dohm]

> Ok, how about this one. Everyone knows pilots love a tailwind.
>
> You have a giant fan mounted on a truck positioned behind the airplane.
> The fan blows air towards the airplane, helping it to accelerate down
> the runway (literally blowing it down the runway) while the truck
> follows, keeping up with the airplane. Pretty soon the plane will be
> thundering down the runway and the pilot pulls back on the yoke.
>
> Does the pilot have to wait until the airplane's speed down the runway
> is twice Vr before he can take off?
>
> Jose
> --
There is not enough beer in the world to fuel such a discussion!!!!

Peter

[Peter Duniho]

"T o d d P a t t i s t" > wrote in message
...
> [...]
> To put this mathematically:
> wheel speed = treadmill speed + airspeed
> If we assume:
> wheel speed = treadmill speed
> then airspeed =0

Well, IMHO the problem with taking the question literally is that, as Jose
says, the literal reading is meaningless.

Taken literally, "wheel speed" means nothing. Or rather, it requires
further interpretation. Are we talking angular velocity? If so, how can
the treadmill moving in a linear fashion have equal speed? The measurements
aren't even in the same units. Are we talking linear speed? If so, what's
so wrong with assuming the treadmill exactly matches the speed?

I do understand the point that "peter" is trying to make, but I find it no
more compelling than simply interpreting the question in a more reasonable
way. Both interpretations require assumption-making, so as long as one is
making assumptions, it makes more sense to make the same assumptions the
average human being would make.

Pete

[Peter Duniho]

"Richard Riley" > wrote in message
...
> Sure, any airplane could take off from a treadmill in a wind tunnel.
> But climb out is a real pain.

No, it's not. Airspeed is airspeed. If the airplane can take off in the
wind tunnel, it can climb (to the physical limits of the wind tunnel, of
course).

> I was going back to the original premise of a treadmill in still air.

And you were incorrect.

Pete

[Peter Duniho]

"Jose" > wrote in message
. net...
> [...]
> Does the pilot have to wait until the airplane's speed down the runway is
> twice Vr before he can take off?

As long as the fan is blowing the airplane forward, it will be impossible
for the airplane to take off. The only way for the fan to move the airplane
forward would be for the airplane to be moving more slowly than the air,
which means the airplane has a continuous tailwind.

If, on the other hand, you make the assumption that you can remove the fan
at any time, you can arbitrarily decide to remove the fan at the normal Vr
and the airplane can take off normally.

There are a variety of other assumptions one could make, due to the
incredibly ambiguous nature of your question, and the exact outcome depends
on how those assumptions are made. I simply provided the two "most
reasonable" assumptions that came to mind, for the sake of discussion.

Pete

[Gene Seibel]

Jose wrote:
> Ok, how about this one. Everyone knows pilots love a tailwind.
>
> You have a giant fan mounted on a truck positioned behind the airplane.
> The fan blows air towards the airplane, helping it to accelerate down
> the runway (literally blowing it down the runway) while the truck
> follows, keeping up with the airplane. Pretty soon the plane will be
> thundering down the runway and the pilot pulls back on the yoke.
>
> Does the pilot have to wait until the airplane's speed down the runway
> is twice Vr before he can take off?
>

Down wind takeoffs require a higher ground speed.
--
Gene Seibel
Tales of Flight - http://pad39a.com/gene/tales.html
Because I fly, I envy no one.

[Steve Foley]

"Peter Dohm" > wrote in message
...
>> > Thrust is going to overcome drag and move the airplane forward.
>>
>> Not in my Cherokee.
>>
>>
> Sure it will!
>
> If we can have a treadmill the size of a runway, and [which is] able to
> sense the rotation of the airplane's wheels; then we can require it to be
> both frictionless and inertia-free.

Whell Hell, if that's the case, 'my' Cherokee runs on H2O!

[Steve Foley]

"Peter Duniho" > wrote in message
...
> "Richard Riley" > wrote in message
> ...
>> Sure, any airplane could take off from a treadmill in a wind tunnel.
>> But climb out is a real pain.
>
> No, it's not. Airspeed is airspeed. If the airplane can take off in the
> wind tunnel, it can climb

> (to the physical limits of the wind tunnel, of course).

I think that's the 'pain' part.

>
>> I was going back to the original premise of a treadmill in still air.
>
> And you were incorrect.
>
> Pete
>

[Peter Duniho]

"Steve Foley" > wrote in message
news:NYDfh.5004$%T5.3873@trndny05...
>>> Sure, any airplane could take off from a treadmill in a wind tunnel.
>>> But climb out is a real pain.
>>
>> No, it's not. Airspeed is airspeed. If the airplane can take off in the
>> wind tunnel, it can climb
>> (to the physical limits of the wind tunnel, of course).
>
> I think that's the 'pain' part.

Maybe. Though, if so then I'd say that *any* operation of an airplane in a
wind tunnel could be characterized as "a real pain". I don't see how
climbing is any different than, say, getting to some actual destination for
example.

[Darkwing]

"Peter Duniho" > wrote in message
...
> "Darkwing" <theducksmailATyahoo.com> wrote in message
> ...
>> I am a regular on RAP, not a troll.
>
> Then read the extensive thread that we already had on this subject before
> you put your two cents in.
>
>> Show me video and I will believe it, if the plane is not moving relative
>> to the wind then the wing isn't making lift.
>
> True.
>
>> I have ran on treadmills and I never felt a "wind" blowing in my face.
>
> That's because you're using your feet for propulsion, and the treadmill
> was negating your effort. There's no such effect for airplanes, as they
> don't use their wheels for propulsion.
>
> Your experience running on treadmills is irrelevant to the question at
> hand (except for the intended effect of course, which is to confuse people
> like you who haven't thought the whole thing through).
>
> Pete
>

The plane IS hauling ass in relation to the moving treadmill BUT the wings
see zero lift due to the plane not moving relative to any air in the room. I
really think I am right the plane will not take off. The type of propulsion
is irrelevant. I guess we will have to agree to disagree until someone
actually does the experiement and video records it.

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

[Brian[_1_]]

The only way the treadmill can stop or slow the airplane is to create
more Drag than Thrust.

The reason the airplane will be able to accelerate is that the
treadmill does not create any significant drag aircraft.

When the treadmill hits 500MPH how much force will it take to hold the
airplane in position?

With perfect frictionless bearings it will take 0 force. If the engine
is generating any thrust the airplane will move forward no matter what
the treadmill does.

Brian.

[mike regish]

You propel yourself on the treadmill by the friction interface between your
feet and the conveyor, not by jet propulsion.

mike

"Darkwing" <theducksmailATyahoo.com> wrote in message
...
>
> I am a regular on RAP, not a troll.
>
> Show me video and I will believe it, if the plane is not moving relative
> to the wind then the wing isn't making lift. I have ran on treadmills and
> I never felt a "wind" blowing in my face.
>
> ----------------------------------------
> DW
>

[mike regish]

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.

[Darkwing]

"Brian" > wrote in message
ups.com...
>
> The only way the treadmill can stop or slow the airplane is to create
> more Drag than Thrust.
>
> The reason the airplane will be able to accelerate is that the
> treadmill does not create any significant drag aircraft.
>
> When the treadmill hits 500MPH how much force will it take to hold the
> airplane in position?
>
> With perfect frictionless bearings it will take 0 force. If the engine
> is generating any thrust the airplane will move forward no matter what
> the treadmill does.
>
> Brian.
>

So lets say I know my little RC plane takes off at exactly 25mph. So I crank
up the treadmill to step up to 25mph so I can keep the RC plane up on the
treadmill, the plane is completely stationary in regards to anyone standing
next to the plane but when the treadmill hits 25mph and my little RC plane
is staying even with the treadmill you are telling me I can pull back on the
elevator stick and the plane will take off? I don't think so.

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

[Darkwing]

"Peter Duniho" > wrote in message
...
> "Darkwing" <theducksmailATyahoo.com> wrote in message
> ...
>> This looks like a job for the MythBusters!!!
>
> *Yawn*
>
> That would be a boring show. Either they'd have to fill 19 minutes with
> the construction of the treadmill itself, or they'd have the airplane
> taking off in the first 30 seconds, leaving them with 19 minutes of filler
> at the end.
>
> You don't need MythBusters. You just need a little knowledge of physics
> and some common sense.
>
> Pete


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.

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

[Jose[_1_]]

> It's not meaningless in the sense we can't
> understand the equality being stated.

Yes it is. That's exactly the sense in which it is meaningless.

Jose
--
"There are 3 secrets to the perfect landing. Unfortunately, nobody knows
what they are." - (mike).
for Email, make the obvious change in the address.

[Peter Duniho]

"Darkwing" <theducksmail"AT"yahoo.com> wrote in message
...
> So lets say I know my little RC plane takes off at exactly 25mph. So I
> crank up the treadmill to step up to 25mph so I can keep the RC plane up
> on the treadmill, the plane is completely stationary in regards to anyone
> standing next to the plane but when the treadmill hits 25mph and my little
> RC plane is staying even with the treadmill you are telling me I can pull
> back on the elevator stick and the plane will take off? I don't think so.

The scenario you suggest is impossible. The RC plane will accelerate
regardless of how fast the treadmill is running. Your "little RC plane"
will NOT be "staying even with the treadmill". It will take off, just as it
would from a normal runway surface.

And it doesn't take a video of such an attempt to prove it. All it takes is
a person who has a minimal education in physics and (key point here) is
willing to listen until they understand, and someone else willing to explain
it. You clearly fail to meet either the first or second criteria, or
possibly both, since we do have the third criteria met here in the
newsgroup.

You are disrespectful of the various posters here who have made an honest
effort to explain the situation to you and others. This is because you
refuse to bother to read the wealth of information on the topic that already
exists. Until you have done so, it would be a waste of time for anyone to
bother responding to any more of your assertions or questions. I know that
I won't.

Pete

[Peter Duniho]

"T o d d P a t t i s t" > wrote in message
...
> [...]
> 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

[Gig 601XL Builder]

"Darkwing" <theducksmail"AT"yahoo.com> wrote in message
...
>
> "Brian" > wrote in message
> ups.com...
>>
>> The only way the treadmill can stop or slow the airplane is to create
>> more Drag than Thrust.
>>
>> The reason the airplane will be able to accelerate is that the
>> treadmill does not create any significant drag aircraft.
>>
>> When the treadmill hits 500MPH how much force will it take to hold the
>> airplane in position?
>>
>> With perfect frictionless bearings it will take 0 force. If the engine
>> is generating any thrust the airplane will move forward no matter what
>> the treadmill does.
>>
>> Brian.
>>
>
> So lets say I know my little RC plane takes off at exactly 25mph. So I
> crank up the treadmill to step up to 25mph so I can keep the RC plane up
> on the treadmill, the plane is completely stationary in regards to anyone
> standing next to the plane but when the treadmill hits 25mph and my little
> RC plane is staying even with the treadmill you are telling me I can pull
> back on the elevator stick and the plane will take off? I don't think so.
>
> ------------------------------------
> DW
>

If the plane will take off at 25mph and you are standing on the treadmill
holding the plane, when the treadmill reaches 25 mph the plane will fly if
you let go of the plane.

If the engine on the plane is set to the proper power it will continue to
fly right beside you.

[Darkwing]

"Peter Duniho" > wrote in message
...
> "Darkwing" <theducksmail"AT"yahoo.com> wrote in message
> ...
>> So lets say I know my little RC plane takes off at exactly 25mph. So I
>> crank up the treadmill to step up to 25mph so I can keep the RC plane up
>> on the treadmill, the plane is completely stationary in regards to anyone
>> standing next to the plane but when the treadmill hits 25mph and my
>> little RC plane is staying even with the treadmill you are telling me I
>> can pull back on the elevator stick and the plane will take off? I don't
>> think so.
>
> The scenario you suggest is impossible. The RC plane will accelerate
> regardless of how fast the treadmill is running. Your "little RC plane"
> will NOT be "staying even with the treadmill". It will take off, just as
> it would from a normal runway surface.
>
> And it doesn't take a video of such an attempt to prove it. All it takes
> is a person who has a minimal education in physics and (key point here) is
> willing to listen until they understand, and someone else willing to
> explain it. You clearly fail to meet either the first or second criteria,
> or possibly both, since we do have the third criteria met here in the
> newsgroup.
>
> You are disrespectful of the various posters here who have made an honest
> effort to explain the situation to you and others.

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.

>This is because you refuse to bother to read the wealth of information on
>the topic that already exists. Until you have done so, it would be a waste
>of time for anyone to bother responding to any more of your assertions or
>questions. I know that I won't.
>
> Pete


Thank God for that, because you are a prick. Oh yeah, *PLONK*!

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

[Darkwing]

"Gig 601XL Builder" <wrDOTgiaconaATcox.net> wrote in message
...
>
> "Darkwing" <theducksmail"AT"yahoo.com> wrote in message
> ...
>>
>> "Brian" > wrote in message
>> ups.com...
>>>
>>> The only way the treadmill can stop or slow the airplane is to create
>>> more Drag than Thrust.
>>>
>>> The reason the airplane will be able to accelerate is that the
>>> treadmill does not create any significant drag aircraft.
>>>
>>> When the treadmill hits 500MPH how much force will it take to hold the
>>> airplane in position?
>>>
>>> With perfect frictionless bearings it will take 0 force. If the engine
>>> is generating any thrust the airplane will move forward no matter what
>>> the treadmill does.
>>>
>>> Brian.
>>>
>>
>> So lets say I know my little RC plane takes off at exactly 25mph. So I
>> crank up the treadmill to step up to 25mph so I can keep the RC plane up
>> on the treadmill, the plane is completely stationary in regards to anyone
>> standing next to the plane but when the treadmill hits 25mph and my
>> little RC plane is staying even with the treadmill you are telling me I
>> can pull back on the elevator stick and the plane will take off? I don't
>> think so.
>>
>> ------------------------------------
>> DW
>>
>
> If the plane will take off at 25mph and you are standing on the treadmill
> holding the plane, when the treadmill reaches 25 mph the plane will fly if
> you let go of the plane.
>
> If the engine on the plane is set to the proper power it will continue to
> fly right beside you.
>

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?

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

[Jose[_1_]]

> So lets say I know my little RC plane takes off at exactly 25mph. So I crank
> up the treadmill to step up to 25mph so I can keep the RC plane up on the
> treadmill, the plane is completely stationary in regards to anyone standing
> next to the plane but when the treadmill hits 25mph and my little RC plane
> is staying even with the treadmill you are telling me I can pull back on the
> elevator stick and the plane will take off? I don't think so.

Ok, now you've changed the problem. The way you state it here, your RC
plane will not take off, because it has no airspeed. However, in =your=
case, the treadmill speed is the independent condition, and the pilot is
adjusting his throttle to compensate. The pilot is ensuring that
airspeed is zero (assuming no wind). It will require about as much
power as it does to taxi, because all he's doing is overcoming wheel
friction.

There will be excess power available to the pilot, which he could use to
move forward faster than the treadmill is moving backwards, acquiring
airspeed and thus taking off. (but the pilot won't do that due to the
constraints of your problem, which says he won't do that).

In the =original= problem, the =pilot= is the independent variable. He
can do what he wants, and it's the treadmill that is tasked with
"keeping up" (whatever that means). Let's consider the following three
cases:

1: The treadmill is frictionless. In this case, we can ignore it. The
problem is the same as taking off from a maglev rail. The plane's
engines will push against the air, the plane will move forward, whatever
the treadmill does will not affect the forward motion of the airplane,
and the airplane will take off.

2: The treadmill and the plane's wheels are very sticky. The plane's
engines will push against the air, the plane will attempt to move
forward, pulling the treadmill bed with it. IF this is permitted, the
plane will gain airspeed and will take off, perhaps with the treadmill
dangling below its wheels. This may be a problem on landing. If the
treadmill bed is -not- permitted to move, then (by hypothesis) the
plane, being glued thereto, will not move. It's a static test stand,
not an airplane. But in that case all the king's horses couldn't move
the plane either.

5: The test is announced on usenet first. Everybody comes out to see
the test stand, and the resulting bluster of hot air allows the airplane
to easily reach a high enough airspeed even while standing still. The
airplane takes off before the test is even begun.

Jose
--
"There are 3 secrets to the perfect landing. Unfortunately, nobody knows
what they are." - (mike).
for Email, make the obvious change in the address.

[Jim Logajan]

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/

http://www.straightdope.com/columns/060203.html

[Jose[_1_]]

> I really think I am right the plane
> will not take off. The type of propulsion
> is irrelevant.

Here's a similar problem. You, personally, are standing on a long
treadmill. You are holding a rope which is attached to the wall in
front of the treadmill. The treadmill is set up so that when you walk
(forwards), the treadmill bed moves (backwards) at an approprate speed
to keep you on the treadmill. This is equivalent to trying to walk on a
frictionless surface.

If you walk forwards, can you walk off the treadmill? (no)

If you pull on the rope, can you pull yourself off the treadmill? (yes)

If this were a real treadmill, would you have any issues? (yes, as you
pull yourself using the rope, the treadmill will spin backwards faster
and faster until you fall down, but you are still holding on to the
rope. You can still go hand over hand and move forward, while the
treadmill grinds through your clothing and racks up medical bills.

Jose
--
"There are 3 secrets to the perfect landing. Unfortunately, nobody knows
what they are." - (mike).
for Email, make the obvious change in the address.

[N2310D]

"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?

[Rip]

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

[Bob Martin]

> 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.aspx?fileid=35E964D9-38DB-4EFD-BE8D-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.

[Morgans[_2_]]

"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

[Bob Noel]

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

[John T]

"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
____________________

[Peter Duniho]

"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

[Peter Dohm]

"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

[Darkwing]

"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

[Travis Marlatte]

"Peter Duniho" > wrote in message
...
> "T o d d P a t t i s t" > wrote in message
> ...
>> [...]
>> 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

[Travis Marlatte]

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

Hmm. That presumes that "at the same speed as the plane" means "as fast as
necessary to cancel the forward motion." If you take your car analogy and
apply it to the plane, then the treadmill must try to run backwards as fast
as necessary to cancel forward motion - which is, Ah, let's just say
difficult.

To be consistent with your conclusions about the plane's motion, then the
car would also move. Using the object's motion as the defining parameter to
determine the treadmill speed, then a stable state can be reached with
either
1) a plane with forward motion X, treadmill with motion -X, wheels
spinning at 2X, thrust applied to achieve speed X
2) a car with forward motion X, treadmill with motion -X, wheels
spinning at 2X, thrust applied to achieve speed 2X

Accelerate either the plane or the car with X from 0 to, say, 65. The plane
will take off. The car will drive off the end of the treadmill.

>> 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
>

DW,

None of the people that believe the plane will fly say that it will fly with
no forward motion. The claim is that the plane will accelerate to flying
speed in spite of the treadmill moving in the opposite direction.

[Travis Marlatte]

"Bob Noel" > wrote in message
...
> In article >,
> Jose > wrote:
>
>> > The wheels don't have to push on anything for an aircraft to take
>> > off...there's no drivetrain feeding power to the wheels!
>>
>> Right. Phrasing it the way I did may get people to realize this, or at
>> least to think about it themselves.
>>
>> If you put an airplane on the roof of a speeding train, would it take
>> off? What if the train were shaped like a runway? What if it were very
>> thin?
>
> hmmmm, if you put the airplane on, say, a fast moving ship, could it
> take off?
>
> I wonder....
>
> --
> Bob Noel
> Looking for a sig the
> lawyers will hate
>

I don't think so. I've seen videos of planes launching from an aircraft
carrier (that's a fast moving ship, right) fall right off the end. I guess
it's because the forward motion of the carrier negated the forward thrust of
the plane.

--
-------------------------------
Travis
Lake N3094P
PWK

[Jose[_1_]]

> 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?

How about we make life easy for the moment and forget about the
treadmill. The airplane is magnetically suspended over the runway. No
part of the plane is touching the runway at all. It's all done with
electromagnets. (and for the nitpickers, let's ignore linear induction
motor effects).

The (otherwise ordinary) plane is magnetically suspended over the runway
with nothing touching the runway at all. Can the plane take off? How
does it do so?

Jose
--
"There are 3 secrets to the perfect landing. Unfortunately, nobody knows
what they are." - (mike).
for Email, make the obvious change in the address.

[Jay Beckman]

"Travis Marlatte" > wrote in message
et...
> "Bob Noel" > wrote in message
> ...
>> In article >,
>> Jose > wrote:
>>
>>> > The wheels don't have to push on anything for an aircraft to take
>>> > off...there's no drivetrain feeding power to the wheels!
>>>
>>> Right. Phrasing it the way I did may get people to realize this, or at
>>> least to think about it themselves.
>>>
>>> If you put an airplane on the roof of a speeding train, would it take
>>> off? What if the train were shaped like a runway? What if it were very
>>> thin?
>>
>> hmmmm, if you put the airplane on, say, a fast moving ship, could it
>> take off?
>>
>> I wonder....
>>
>> --
>> Bob Noel
>> Looking for a sig the
>> lawyers will hate
>>
>
> I don't think so. I've seen videos of planes launching from an aircraft
> carrier (that's a fast moving ship, right) fall right off the end. I guess
> it's because the forward motion of the carrier negated the forward thrust
> of the plane.

Ok, maybe you're yanking people's chains but...

Planes that fail to get airborne off a carrier are sometimes the victim of
what is known as a "Cold Cat." If the steam pressure is not set correctly
for the weight of the aircraft being shot it may not acheive sufficient
airspeed to fly. Or, sometimes the holdback may break prematurely meaning
the plane does not get the benefit of the entire stroke of the catapult
shuttle and may fail to acheive flying speed. Or, sometimes the part of the
nosegear that hooks into the shuttle (name?) may break or tear off yielding
a similar result.

The forward motion of the ship aids in reaching the necessary airspeed for
flight by creating a relative wind over the deck:
-Windspeed is 10Kts
-The ship is moving at 30Kts (or more...and the carrier is turned into the
wind for flight ops)
-The jet needs 120Kts to get airborne (or whatever...)

With 10Kts of wind + 30Kts of relative wind from the speed of the carrier
you only need 80Kts via catapult for the jet to fly.

After all, planes used to launch off carriers without catapults...even
medium bombers (B-25) have done it. Doolittle Raid anyone?

Jay Beckman
PP-ASEL
Chandler, AZ

[Morgans[_2_]]

"Travis Marlatte" > wrote

> I guess it's because the forward motion of the carrier negated the forward
> thrust of the plane.

What?????????????????????????

You really didn't mean what you said, or say what you believed, did you?

If that is what you meant to say, you better get your money back from whoever
taught you the ground school portion of your ticket, and then go back and take
high school physics again.
--
Jim in NC

[Montblack]

("Jose" wrote)
> The (otherwise ordinary) plane is magnetically suspended over the runway
> with nothing touching the runway at all. Can the plane take off?


Yes. But, ...Lord only knows what direction he's heading. <g>


Montblack

[Montblack]

("Darkwing" wrote)
> 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?


Not unless the plane's "wheels" are coupled to the shaft of a gyro's rotor.

Try this one:

You're in a Class B airport terminal.
You're on roller-skates, Rollerblades, a skateboard... whatever.

You find yourself on an (evil) moving sidewalk - facing the wrong way.
The (evil) sidewalk ALWAYS matches your wheels' forward speed.

Someone moves a huge Hollywood 'film set' fan, in a few feet behind you.
They point the fan at your back and turn it on.

You hold open your jacket to make a sail (...like kids at the ice skating
rink have done for ages)

1. Will you get blown down to the far end of the moving sidewalk - your
destination?

2. Will you remain in the same spot - relative to the wall - no matter how
hard the giant fan blows?

3. Forgetting the fan, if you try pulling yourself forward using the
stationary handrails, will you in fact move forward? Or will the (evil)
moving sidewalk thwart your forward motion by speeding up? Or will your
upper body pull itself forward, while your feet remain behind ...(or
stationary, relative to the wall and the handrail)?

4. How is this the same as the airplane and the treadmill question? How is
it different?


Montblack

[Morgans[_2_]]

"Montblack" > wrote in message
...
> ("Jose" wrote)
>> The (otherwise ordinary) plane is magnetically suspended over the runway with
>> nothing touching the runway at all. Can the plane take off?
>
>
> Yes. But, ...Lord only knows what direction he's heading. <g>

The thrusters will take care of that, until the inertial dampeners take effect.
<g>
--
Jim in NC

[Steve Foley]

"Ray" > wrote in message
...
> 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

"The conveyer belt is designed to exactly match the speed of the wheels,
moving in the opposite direction"

Speed of the wheels in relation to what?

The runway under the treadmill, or the surface of the treadmill itself?

If the answer to this question is the surface of the treadmill, the answer
to the original question is undefined (as in division by zero is undefined).

If the answer to this question is the runway under the treadmill, then the
aircraft will take off at the normal airspeed, with the wheels rotating at
twice the airspeed. Should take about the same distance over the runway
(under the treadmill)

[Gig 601XL Builder]

"Darkwing" <theducksmail"AT"yahoo.com> wrote in message
...
>
> "Gig 601XL Builder" <wrDOTgiaconaATcox.net> wrote in message
> ...
>>
>> "Darkwing" <theducksmail"AT"yahoo.com> wrote in message
>> ...
>>>
>>> "Brian" > wrote in message
>>> ups.com...
>>>>
>>>> The only way the treadmill can stop or slow the airplane is to create
>>>> more Drag than Thrust.
>>>>
>>>> The reason the airplane will be able to accelerate is that the
>>>> treadmill does not create any significant drag aircraft.
>>>>
>>>> When the treadmill hits 500MPH how much force will it take to hold the
>>>> airplane in position?
>>>>
>>>> With perfect frictionless bearings it will take 0 force. If the engine
>>>> is generating any thrust the airplane will move forward no matter what
>>>> the treadmill does.
>>>>
>>>> Brian.
>>>>
>>>
>>> So lets say I know my little RC plane takes off at exactly 25mph. So I
>>> crank up the treadmill to step up to 25mph so I can keep the RC plane up
>>> on the treadmill, the plane is completely stationary in regards to
>>> anyone standing next to the plane but when the treadmill hits 25mph and
>>> my little RC plane is staying even with the treadmill you are telling me
>>> I can pull back on the elevator stick and the plane will take off? I
>>> don't think so.
>>>
>>> ------------------------------------
>>> DW
>>>
>>
>> If the plane will take off at 25mph and you are standing on the treadmill
>> holding the plane, when the treadmill reaches 25 mph the plane will fly
>> if you let go of the plane.
>>
>> If the engine on the plane is set to the proper power it will continue to
>> fly right beside you.
>>
>
> 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?
>


Screw the treadmill. The wings aren't stationary in regards to the wind. The
AIRSPEED of the aircraft is 25 MPH.

Let's make it a real world example. When aircraft carriers are launching
aircraft they turn into the wind the air speed of the aircraft when it
releases from the catapult is (Wind Speed + Carrier Speed + Catapult speed).

Another real world example is a normal take off of a normal airplane. Let's
say you have a take off speed of 50 MPH. The wind is blowing right down the
runway towards you at a even 10 MPH. You will take off when you have a
ground speed of 40 MPH.

Switch the wind to a 10 MPH tailwind and you will take off when you have a
ground speed of 60 mph.

[Gig 601XL Builder]

"Rip" > wrote in message
. net...
> 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?

Of course it will at airspeed X. And it will do so at a power setting that
creates airspeed X.

> 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).
>

Yes it will and it will do so at a power setting that creates airspeed X x2

[Gig 601XL Builder]

"Travis Marlatte" > wrote in message
et...
> "Bob Noel" > wrote in message
> ...
>> In article >,
>> Jose > wrote:
>>
>>> > The wheels don't have to push on anything for an aircraft to take
>>> > off...there's no drivetrain feeding power to the wheels!
>>>
>>> Right. Phrasing it the way I did may get people to realize this, or at
>>> least to think about it themselves.
>>>
>>> If you put an airplane on the roof of a speeding train, would it take
>>> off? What if the train were shaped like a runway? What if it were very
>>> thin?
>>
>> hmmmm, if you put the airplane on, say, a fast moving ship, could it
>> take off?
>>
>> I wonder....
>>
>> --
>> Bob Noel
>> Looking for a sig the
>> lawyers will hate
>>
>
> I don't think so. I've seen videos of planes launching from an aircraft
> carrier (that's a fast moving ship, right) fall right off the end. I guess
> it's because the forward motion of the carrier negated the forward thrust
> of the plane.
>

What you saw was an aircraft that failed to achieve and or retain a critical
airspeed. Either the catapult failed or the engine failed or, well any
number of things. There is a reason carriers turn into the wind to launch
aircraft. There is also a reason that carriers can't launch fixed wing
aircraft while tied to the dock. Well they might be able to but a lot of
things have to be perfect.

[[email protected]]

Rip wrote:
> Yes, the airplane will take off. The thrust of the engine is against the
> AIR. NOT the treadmill.

The thrust of the engine is not against the air. It generates
thrust as a Newtonian reaction to the prop moving air back, not
"pushing on other air." A rocket in space has nothing to push against,
yet it generates the same thrust as it did in the atmosphere.

> 1) Will an airplane on an essentially frictionless surface (say, wet
> ice) take off?

Of course, as forward motion creates airflow over the wings.
There is no forward motion on the treadmill.

> 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).

Yes, it would, but it's waterspeed at takeoff airspeed would
be double the usual takeoff speed. However, this would require
considerable power to overcome the extra drag of the floats on the
water, being a lot more than wheels on pavement.

I have a hard time believing that so many people can't see that it's
airflow over wings, not wheel speed or prop blast, that lifts
airplanes. What do they think wings are for, anyway?

Why don't we discuss something truly valid, like the downwind
turn feared by some (especially a few RC modelers) that they think will
reduce airspeed and cause a stall?

Dan

[Peter Dohm]

"Travis Marlatte" > wrote in message
et...
> "Peter Duniho" > wrote in message
> ...
> > "T o d d P a t t i s t" > wrote in message
> > ...
> >> [...]
> >> 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
>
>
That's what I call an INDUSTRIAL STRENGTH nuance!

Peter

[Leonard Milcin Jr.]

wrote:
> Rip wrote:
>> Yes, the airplane will take off. The thrust of the engine is against the
>> AIR. NOT the treadmill.
>
> The thrust of the engine is not against the air. It generates
> thrust as a Newtonian reaction to the prop moving air back, not
> "pushing on other air."

Oh, I see. Basically, you try to say that moving air back is not pushing
it back?


Leonard

[Jose[_1_]]

> The thrust of the engine is not against the air. It generates
> thrust as a Newtonian reaction to the prop moving air back, not
> "pushing on other air." A rocket in space has nothing to push against,
> yet it generates the same thrust as it did in the atmosphere.

Actually, it's not that way. (but read carefully)

The thrust of a propeller engine is created when the propeller (an
airfoil) creates a high pressure area behind and a low pressure area in
front of the prop, as it pushes air back. The prop is pushing against
the air in order to do this. The air is constantly trying to get out of
the way, but it is not entirely successful, which leads to the pressure
differences. There's nothing funamentally wrong in saying that the
airplane pushes against the air to move forward. The prop (a part of
the airplane) is doing the pushing.

Rockets are different. The tail of fire coming out of the rocket does
push against the air (push the air out of the way to make room for the
fire), but it is =not= part of the rocket. If there were no air to
"push against", the rocket would work just as well, for that reason.
Where the rocket gets its thrust is the tail of fire pushing (the other
way) against the engine bell of the rocket itself. The rocket is
pushing against the fire, in essence. The fire is =not= part of the rocket.

Both cases can be viewed in the newtonian "action/reaction" paradigm,
but something has to push against something else in order to get the
thrust to happen in the first place. In a plane, the propeller pushes
against the air (to make the air go backwards fast and create thrust. In
a rocket, the engine bell pushes against the tail fire (pushing the fire
out, and the rocket forward). I suppose it may be clearer to say that
the expanding gasses of the tail fire push against the engine bell, but
the two are equivalent.

Although the expanding rocket gasses do push the air out of the way,
that doesn't help the rocket in any meaningful way.

Jose
--
"There are 3 secrets to the perfect landing. Unfortunately, nobody knows
what they are." - (mike).
for Email, make the obvious change in the address.

[Peter Dohm]

> wrote in message
ups.com...
>
> Rip wrote:
> > Yes, the airplane will take off. The thrust of the engine is against the
> > AIR. NOT the treadmill.
>
> The thrust of the engine is not against the air. It generates
> thrust as a Newtonian reaction to the prop moving air back, not
> "pushing on other air." A rocket in space has nothing to push against,
> yet it generates the same thrust as it did in the atmosphere.
>
> > 1) Will an airplane on an essentially frictionless surface (say, wet
> > ice) take off?
>
> Of course, as forward motion creates airflow over the wings.
> There is no forward motion on the treadmill.
>
> > 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).
>
> Yes, it would, but it's waterspeed at takeoff airspeed would
> be double the usual takeoff speed. However, this would require
> considerable power to overcome the extra drag of the floats on the
> water, being a lot more than wheels on pavement.
>
> I have a hard time believing that so many people can't see that it's
> airflow over wings, not wheel speed or prop blast, that lifts
> airplanes. What do they think wings are for, anyway?
>
> Why don't we discuss something truly valid, like the downwind
> turn feared by some (especially a few RC modelers) that they think will
> reduce airspeed and cause a stall?
>
> Dan
>
And, after we've resolved that one, we can move on to the turn to the final
turn for a left crosswind landing from a tight left pattern or a right
crosswind landing from a tight right pattern.

Peter

[BDS[_2_]]

You have to remember that the plane's airspeed is completely independent of
its wheel speed. As you know, a plane can have sufficient airspeed to fly
even if the wheels are stopped, and it can have insufficient airspeed even
if the wheels are spinning at 200 mph.

The treadmill spins the wheels - it has absolutely no affect on airspeed.
The plane gathers airspeed by means of the propeller acting on the
surrounding air. No matter how fast the treadmill belt is moving it is not
taking the surrounding air with it.

If you tie a rope to the wall and then sit in a wheelchair on the treadmill,
as long as you hold onto the rope the chair will not move no matter how fast
the treadmill goes. Likewise, by simply pulling on the rope you can move
yourself forward on the treadmill no matter how fast the belt is going. The
reason is because the force moving you forward on the treadmill (pulling on
the rope) is not related at all to how fast the belt is going. The plane is
"pulling on the rope" (air) using its propeller - it doesn't care what its
wheels are doing.

BDS


"Darkwing" <theducksmail"AT"yahoo.com> wrote
> 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?
>
> ---------------------------------
> DW
>
>

[DaveB]

On Wed, 13 Dec 2006 17:29:04 GMT, "BDS" > wrote:

>You have to remember that the plane's airspeed is completely independent of
>its wheel speed. As you know, a plane can have sufficient airspeed to fly
>even if the wheels are stopped, and it can have insufficient airspeed even
>if the wheels are spinning at 200 mph.
>
>The treadmill spins the wheels - it has absolutely no affect on airspeed.
>The plane gathers airspeed by means of the propeller acting on the
>surrounding air. No matter how fast the treadmill belt is moving it is not
>taking the surrounding air with it.
>
>If you tie a rope to the wall and then sit in a wheelchair on the treadmill,
>as long as you hold onto the rope the chair will not move no matter how fast
>the treadmill goes. Likewise, by simply pulling on the rope you can move
>yourself forward on the treadmill no matter how fast the belt is going. The
>reason is because the force moving you forward on the treadmill (pulling on
>the rope) is not related at all to how fast the belt is going. The plane is
>"pulling on the rope" (air) using its propeller - it doesn't care what its
>wheels are doing.
>
>BDS
>
>
OK ! I'm putting my pa-28-140 on a treadmill and will report back to
clear this up once and for all.


>"Darkwing" <theducksmail"AT"yahoo.com> wrote
>> 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?
>>
>> ---------------------------------
>> DW
>>
>>
>
>

Daveb

[DaveB]

On Wed, 13 Dec 2006 19:04:48 GMT, (DaveB) wrote:

>On Wed, 13 Dec 2006 17:29:04 GMT, "BDS" > wrote:
>
>>You have to remember that the plane's airspeed is completely independent of
>>its wheel speed. As you know, a plane can have sufficient airspeed to fly
>>even if the wheels are stopped, and it can have insufficient airspeed even
>>if the wheels are spinning at 200 mph.
>>
>>The treadmill spins the wheels - it has absolutely no affect on airspeed.
>>The plane gathers airspeed by means of the propeller acting on the
>>surrounding air. No matter how fast the treadmill belt is moving it is not
>>taking the surrounding air with it.
>>
>>If you tie a rope to the wall and then sit in a wheelchair on the treadmill,
>>as long as you hold onto the rope the chair will not move no matter how fast
>>the treadmill goes. Likewise, by simply pulling on the rope you can move
>>yourself forward on the treadmill no matter how fast the belt is going. The
>>reason is because the force moving you forward on the treadmill (pulling on
>>the rope) is not related at all to how fast the belt is going. The plane is
>>"pulling on the rope" (air) using its propeller - it doesn't care what its
>>wheels are doing.
>>
>>BDS
>>
>>
>OK ! I'm putting my pa-28-140 on a treadmill and will report back to
>clear this up once and for all.
>
>
>>"Darkwing" <theducksmail"AT"yahoo.com> wrote
>>> 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?
>>>
>>> ---------------------------------
>>> DW
>>>
>>>
>>
>>
>
>Daveb
Forgot to mention I will use two treadmills one for each wheel so I
can control the speed on both.
Daveb

[Christopher Campbell[_1_]]

On Tue, 12 Dec 2006 21:23:56 -0800, Darkwing wrote
(in article >):

>
> "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
>
>

You assumption is that the plane never moves relative to an observer. In
fact, the airplane will accelerate normally and run down the treadmill and
take off normally no matter how fast the treadmill is moving. The only thing
that would stop it is the wheels coming off. The treadmill cannot keep the
airplane from accelerating in this way. An observer standing next to the
treadmill will see the airplane moving down the treadmill and taking off,
just like it would from a normal runway.

Airplane engines cannot feel the wheels. They do not turn the wheels. So the
wheels will automatically spin fast enough to keep up with the accelerating
aircraft. This is easily demonstrated. All you need is a pair of roller
blades, a rope, and a treadmill. You stand on your roller blades on the
treadmill with a rope attached to the front. Measure the force needed to pull
yourself to the front of the treadmill with the treadmill off. Then try it at
different speed settings. It always requires about the same amount of force
to pull yourself forward. The only that changes is that your wheels spin
faster to compensate. The treadmill could be moving many times faster than
the airplane; it does not matter. The airplane will move down the runway and
take off normally.

The other gotcha in this little puzzle is that it attempts to get you to
divide by zero. This is the old Achilles vs. the Tortoise conundrum that so
puzzled ancient Greek mathematicians. The puzzle was this: Achilles and a
Tortoise agree to have a race. Achilles agrees to let the Tortoise have a
head start of getting half way to the finish line. The starting gun sounds
and they are off! (Well, the Tortoise is, anyway.) The Tortoise reaches the
half-way mark and Achilles starts running. But by the time that Achilles
reaches the half-way mark, the Tortoise has moved forward. And by the time
that Achilles reaches the point where the Tortoise has moved to, the Tortoise
has moved forward again, albeit not as far as before. Again Achilles reaches
the third point where the Tortoise was, but the Tortoise has moved forward
again. No matter how fast Achilles runs, he can never catch up with the
Tortoise. It was this sort of logic that led the Greeks to conclude that
everything was imaginary and that motion was impossible. They could not solve
the problem because they did not have the number zero.

The False Pythagorean theorem is similar; it postulates that the shortest
distance between two points is always a right angle, or in other words, the
hypotenuse of a right triangle is equal to the sum of the other two sides. It
is false on the face of it; we can see that this is obviously not true, but
nevertheless you can make a powerful argument that it is. If you have a right
triangle ABC where the hypotenuse is AC, you can measure the sum of AB and
BC. If you turn the hypotenuse into a series of steps, the rise of the steps
will always equal BC and the run of the steps will always equal AB. No matter
how large or small you make the steps, the rise will equal BC and the run
will equal AB. A straight line hypotenuse and be seen to be simply a series
of infinitely small steps; the sum of the rise of the infinite steps must be
BC and the sum of the run of the infinite steps must be AB. Therefore AC must
equal AB plus BC. Bzzzt. The Greeks could not solve that puzzle, either,
until Pythagoras was able to prove that it is the square of the hypotenuse
that equals the sum of the squares of the other two sides. But even then a
lot of people did not believe him.

The airplane-on-a-treadmill is just a restatement of the same problem. It
attempts to convince you that the airplane cannot move relative to an outside
observer if the treadmill always moves at the same speed as the wheels. If
the wheels accelerate, then the treadmill accelerates, so the plane cannot
move, right? Wrong. The airplane does move, and it accelerates relative to an
outside observer at the same rate as it would if the treadmill remained
stationary. The only thing that changes is that the wheels spin faster. None
of the thrust of the engines on an airplane is being used to overcome the
force of the treadmill because the wheels spin freely. It would be different
with an automobile. There the motor has to overcome the force of the
treadmill. But the only thing resisting the airplane is air, which remains
constant no matter how fast the treadmill is moving.

Think of it like this: raise the airplane a few inches off the treadmill, put
the engines to full power, and for grins leave the gear down and add a little
motor to keep the wheels spinning at the same speed as the treadmill. Have
the wheels accelerate at the same speed as they would on a normal takeoff,
and have the treadmill match speed with the wheels. Now the airplane is not
even touching the treadmill. Do you believe that the airplane will still
remain stationary with respect to an outside observer? Yet the treadmill's
relevance to the speed of the speed of the wheels is just the same as it was
before when the airplane actually sat on the treadmill. And the treadmill is
having exactly the same effect on the airplane's forward motion as it did
when the airplane was touching the treadmill, which is to say none.

[mike regish]

Surely you jest. Please tell me you're joking.

mike

"Darkwing" <theducksmailATyahoo.com> wrote in message
...
>
>
> 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]

Christopher Campbell wrote:

> The other gotcha in this little puzzle is that it attempts to get you to
> divide by zero.

Explain to us please where the statement of this problem ever involves
division by zero.
One can readily see where the statement implies a value of zero for air
speed since in the absence of wheel slip:

Treadmill speed = wheel speed (stated explicitly in the problem)
and
Air speed = wheel speed - treadmill speed (assuming calm air)
this directly implies that
Air speed = 0.

But I don't see where division by zero ever comes into play.
The stated problem does imply a runaway positive feedback in the
treadmill speed control. I.e. the moment the plain starts to roll
forward the control system would speed up the treadmill to match the
wheel speed. The motion of the treadmill would then speed up the wheel
rotation to a higher speed thus forcing the treadmill to move still
faster to catch up. The result would be an ever increasing treadmill
and wheel speed until something gives - most likely the tires (if we
ignore the technical difficulty of building the specified treadmill).

>This is the old Achilles vs. the Tortoise conundrum that so
> puzzled ancient Greek mathematicians. The puzzle was this: Achilles and a
> Tortoise agree to have a race. Achilles agrees to let the Tortoise have a
> head start of getting half way to the finish line. The starting gun sounds
> and they are off! (Well, the Tortoise is, anyway.) The Tortoise reaches the
> half-way mark and Achilles starts running. But by the time that Achilles
> reaches the half-way mark, the Tortoise has moved forward. And by the time
> that Achilles reaches the point where the Tortoise has moved to, the Tortoise
> has moved forward again, albeit not as far as before. Again Achilles reaches
> the third point where the Tortoise was, but the Tortoise has moved forward
> again. No matter how fast Achilles runs, he can never catch up with the
> Tortoise. It was this sort of logic that led the Greeks to conclude that
> everything was imaginary and that motion was impossible. They could not solve
> the problem because they did not have the number zero.

Zeno's Paradox. But I doubt if you could find any ancient Greeks who
actually concluded that motion was impossible. Even while puzzling
with Zeno over his problem, they continued to go to the markets to do
their shopping and to their respective work places.

And there's no need to have the concept of the number zero to solve
Zeno's paradox, just the idea of the convergence of some types of
infinite sums. I.e. if each successive run of Achilles is half as long
as the previous one (say he walks twice as fast as the tortoise) then
we have a sum for the total distance 'D' of the form:
D = x + x/2 + x/4 + x/8 +...
multiplying this by 2 gives:
2D = 2x + x + x/2 + x/4 + x/8 + ... = 2x + D
subtract D from both sides and we solve for the total distance Achilles
needs to walk:
D = 2x; i.e. twice the distance of the headstart he gives the tortoise.

> The airplane-on-a-treadmill is just a restatement of the same problem. It
> attempts to convince you that the airplane cannot move relative to an outside
> observer if the treadmill always moves at the same speed as the wheels. If
> the wheels accelerate, then the treadmill accelerates, so the plane cannot
> move, right? Wrong. The airplane does move, and it accelerates relative to an
> outside observer at the same rate as it would if the treadmill remained
> stationary. The only thing that changes is that the wheels spin faster.

Sure, but airplane wheels have some maximum speed. Once the treadmill
gets up to that maximum speed the airplane wheels would fail and the
airplane is now sitting on a treadmill with a bunch of failed tires.
So the question becomes whether a plane can still take off after you
shoot out all the tires when it first begins its takeoff roll.

And yes, postulating a frictionless surface for the treadmill gets
around the problem and allows a normal takeoff. But the very term
treadmill implies a surface with reasonable friction, i.e. the tread.

[Travis Marlatte]

"Morgans" > wrote in message
...
>
> "Travis Marlatte" > wrote
>
>> I guess it's because the forward motion of the carrier negated the
>> forward thrust of the plane.
>
> What?????????????????????????
>
> You really didn't mean what you said, or say what you believed, did you?

That would be a no. I thought it was in keeping with the ridiculous debate
over the treadmill "puzzle."

>
> If that is what you meant to say, you better get your money back from
> whoever taught you the ground school portion of your ticket, and then go
> back and take high school physics again.
> --
> Jim in NC


-------------------------------
Travis
Lake N3094P
PWK

[Travis Marlatte]

"Gig 601XL Builder" <wrDOTgiaconaATcox.net> wrote in message
...
>
> "Travis Marlatte" > wrote in message
> et...
>> "Bob Noel" > wrote in message
>> ...
>>> In article >,
>>> Jose > wrote:
>>>
>>>> > The wheels don't have to push on anything for an aircraft to take
>>>> > off...there's no drivetrain feeding power to the wheels!
>>>>
>>>> Right. Phrasing it the way I did may get people to realize this, or at
>>>> least to think about it themselves.
>>>>
>>>> If you put an airplane on the roof of a speeding train, would it take
>>>> off? What if the train were shaped like a runway? What if it were
>>>> very
>>>> thin?
>>>
>>> hmmmm, if you put the airplane on, say, a fast moving ship, could it
>>> take off?
>>>
>>> I wonder....
>>>
>>> --
>>> Bob Noel
>>> Looking for a sig the
>>> lawyers will hate
>>>
>>
>> I don't think so. I've seen videos of planes launching from an aircraft
>> carrier (that's a fast moving ship, right) fall right off the end. I
>> guess it's because the forward motion of the carrier negated the forward
>> thrust of the plane.
>>
>
> What you saw was an aircraft that failed to achieve and or retain a
> critical airspeed. Either the catapult failed or the engine failed or,
> well any number of things. There is a reason carriers turn into the wind
> to launch aircraft. There is also a reason that carriers can't launch
> fixed wing aircraft while tied to the dock. Well they might be able to but
> a lot of things have to be perfect.
>

Thanks. But it was a joke. I do question the word "can't" in your
explanation. I would believe "can't launch some fixed wing aircraft but not
as a general statement.

--
-------------------------------
Travis
Lake N3094P
PWK

[Travis Marlatte]

"Montblack" > wrote in message
...
> ("Darkwing" wrote)
>> 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?
>
>
> Not unless the plane's "wheels" are coupled to the shaft of a gyro's
> rotor.
>
> Try this one:
>
> You're in a Class B airport terminal.
> You're on roller-skates, Rollerblades, a skateboard... whatever.
>
> You find yourself on an (evil) moving sidewalk - facing the wrong way.
> The (evil) sidewalk ALWAYS matches your wheels' forward speed.
>
> Someone moves a huge Hollywood 'film set' fan, in a few feet behind you.
> They point the fan at your back and turn it on.
>
> You hold open your jacket to make a sail (...like kids at the ice skating
> rink have done for ages)
>
> 1. Will you get blown down to the far end of the moving sidewalk - your
> destination?
>
> 2. Will you remain in the same spot - relative to the wall - no matter how
> hard the giant fan blows?
>
> 3. Forgetting the fan, if you try pulling yourself forward using the
> stationary handrails, will you in fact move forward? Or will the (evil)
> moving sidewalk thwart your forward motion by speeding up? Or will your
> upper body pull itself forward, while your feet remain behind ...(or
> stationary, relative to the wall and the handrail)?
>
> 4. How is this the same as the airplane and the treadmill question? How is
> it different?
>
>
> Montblack
>

It's basically the same question with the same ambiguities. The crux of most
of the hilarious debate is really over what defines the speed of the
treadmill. It seems like a more interesting puzzle if the treadmill (or evil
moving sidewalk) tries to match the forward speed of the object on the
wheels resulting in the wheels simply spinnning at twice the speed of the
forward movement of the object.

The other interpretation, which leads to an impossible solution, is that the
treadmill moves to counteract all forward motion - which results in a
treadmill accelerating to infinite speed (or until the wheels explode which
ever comes first).
--
-------------------------------
Travis
Lake N3094P
PWK

[Travis Marlatte]

"Gig 601XL Builder" <wrDOTgiaconaATcox.net> wrote in message
...
>
> "Rip" > wrote in message
> . net...
>> 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?
>
> Of course it will at airspeed X. And it will do so at a power setting that
> creates airspeed X.
>
>> 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).
>>
>
> Yes it will and it will do so at a power setting that creates airspeed X
> x2
>

Uh. That would not be true. At least not as a general statement. Unless you
somehow believe that the extra friction of water moving at twice the takeoff
speed requires X power to overcome - which seems unlikely.
-------------------------------
Travis
Lake N3094P
PWK

[Travis Marlatte]

> wrote in message
ups.com...
>
> Rip wrote:
>> Yes, the airplane will take off. The thrust of the engine is against the
>> AIR. NOT the treadmill.
>
> The thrust of the engine is not against the air. It generates
> thrust as a Newtonian reaction to the prop moving air back, not
> "pushing on other air." A rocket in space has nothing to push against,
> yet it generates the same thrust as it did in the atmosphere.
>
>> 1) Will an airplane on an essentially frictionless surface (say, wet
>> ice) take off?
>
> Of course, as forward motion creates airflow over the wings.
> There is no forward motion on the treadmill.

Why isn't there forward motion on the treadmill? The pressure differential
around the prop or the thrust from a jet will propel the plane forward to
takeoff speed on glare ice (wheels don't have to spin at all) or the
treadmill (wheels spin at twice the speed).



--
-------------------------------
Travis
Lake N3094P
PWK

[Bob Noel]

In article >,
"mike regish" > wrote:

> Surely you jest.

don't call me... aw heck, it doesn't work closed captioned

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

[Christopher Campbell[_1_]]

On Wed, 13 Dec 2006 14:34:54 -0800, peter wrote
(in article om>):

> Christopher Campbell wrote:
>
>> The other gotcha in this little puzzle is that it attempts to get you to
>> divide by zero.
>
> Explain to us please where the statement of this problem ever involves
> division by zero.
> One can readily see where the statement implies a value of zero for air
> speed since in the absence of wheel slip:
>
> Treadmill speed = wheel speed (stated explicitly in the problem)
> and
> Air speed = wheel speed - treadmill speed (assuming calm air)
> this directly implies that
> Air speed = 0.
>
> But I don't see where division by zero ever comes into play.
> The stated problem does imply a runaway positive feedback in the
> treadmill speed control. I.e. the moment the plain starts to roll
> forward the control system would speed up the treadmill to match the
> wheel speed. The motion of the treadmill would then speed up the wheel
> rotation to a higher speed thus forcing the treadmill to move still
> faster to catch up. The result would be an ever increasing treadmill
> and wheel speed until something gives - most likely the tires (if we
> ignore the technical difficulty of building the specified treadmill).
>
>> This is the old Achilles vs. the Tortoise conundrum that so
>> puzzled ancient Greek mathematicians. The puzzle was this: Achilles and a
>> Tortoise agree to have a race. Achilles agrees to let the Tortoise have a
>> head start of getting half way to the finish line. The starting gun sounds
>> and they are off! (Well, the Tortoise is, anyway.) The Tortoise reaches the
>> half-way mark and Achilles starts running. But by the time that Achilles
>> reaches the half-way mark, the Tortoise has moved forward. And by the time
>> that Achilles reaches the point where the Tortoise has moved to, the
>> Tortoise
>> has moved forward again, albeit not as far as before. Again Achilles reaches
>> the third point where the Tortoise was, but the Tortoise has moved forward
>> again. No matter how fast Achilles runs, he can never catch up with the
>> Tortoise. It was this sort of logic that led the Greeks to conclude that
>> everything was imaginary and that motion was impossible. They could not
>> solve
>> the problem because they did not have the number zero.
>
> Zeno's Paradox. But I doubt if you could find any ancient Greeks who
> actually concluded that motion was impossible. Even while puzzling
> with Zeno over his problem, they continued to go to the markets to do
> their shopping and to their respective work places.
>
> And there's no need to have the concept of the number zero to solve
> Zeno's paradox, just the idea of the convergence of some types of
> infinite sums. I.e. if each successive run of Achilles is half as long
> as the previous one (say he walks twice as fast as the tortoise) then
> we have a sum for the total distance 'D' of the form:
> D = x + x/2 + x/4 + x/8 +...
> multiplying this by 2 gives:
> 2D = 2x + x + x/2 + x/4 + x/8 + ... = 2x + D
> subtract D from both sides and we solve for the total distance Achilles
> needs to walk:
> D = 2x; i.e. twice the distance of the headstart he gives the tortoise.
>
>> The airplane-on-a-treadmill is just a restatement of the same problem. It
>> attempts to convince you that the airplane cannot move relative to an
>> outside
>> observer if the treadmill always moves at the same speed as the wheels. If
>> the wheels accelerate, then the treadmill accelerates, so the plane cannot
>> move, right? Wrong. The airplane does move, and it accelerates relative to
>> an
>> outside observer at the same rate as it would if the treadmill remained
>> stationary. The only thing that changes is that the wheels spin faster.
>
> Sure, but airplane wheels have some maximum speed. Once the treadmill
> gets up to that maximum speed the airplane wheels would fail and the
> airplane is now sitting on a treadmill with a bunch of failed tires.
> So the question becomes whether a plane can still take off after you
> shoot out all the tires when it first begins its takeoff roll.
>
> And yes, postulating a frictionless surface for the treadmill gets
> around the problem and allows a normal takeoff. But the very term
> treadmill implies a surface with reasonable friction, i.e. the tread.
>

Well, if you understand Zeno's paradox, then you understand enough that the
airplane will move forward on the treadmill. If the tires don't blow, it will
take off. I will refer you to the book "Godel, Escher, Bach" for a discussion
of how the problem is created by an attempt to divide by zero.

If your only argument is that airplane tires will not stand the stress, then
you are placing a constraint on the problem that is not originally stated.
You are basically changing the question.

Some airplane tires might stand the stress; others might not. Tires are
highly variable in their design and intended purpose. You cannot flat-out
declare that all tires would fail. In fact, why would not the treadmill break
down before the tires? The motor could overheat and stop the treadmill
entirely, or the treadmill surface could disintegrate, or it might be crushed
by the airplane. The airplane could be so heavy that the treadmill could not
turn at all. We cannot assume that the treadmill is any less immune to stress
than anything else stated in the problem. So, lacking any further limitations
as stated in the problem, tires must be assumed to be capable of withstanding
the stress of the treadmill. Otherwise, why not throw in all other kinds of
variables not stated in the problem, like flap settings, wind, temperature,
density altitude, fuel on board, payload, visibility, clearance, and whether
it would violate FAA rules?

No, go with the problem as stated, and let us not make it a trick question by
assuming facts not presented to the audience.

[Christopher Campbell[_1_]]

On Tue, 12 Dec 2006 14:50:04 -0800, Nomen Nescio wrote
(in article >):

> -----BEGIN PGP SIGNED MESSAGE-----
>
> From: "Brian" >
>
>> With perfect frictionless bearings it will take 0 force. If the engine
>> is generating any thrust the airplane will move forward no matter what
>> the treadmill does.
>
> As long as a magical massless wheel is attached to the magical frictionless
> bearing.

There is no reason to assume that the treadmill will not fail first! So, not
having enough information to determine if the treadmill will stop running
before the wheels do, we cannot categorically say that the airplane will not
take off because the wheels will fail. The motor of the treadmill might
simply burn out first and the treadmill come to a stop.

[Christopher Campbell[_1_]]

On Mon, 11 Dec 2006 21:10:32 -0800, peter wrote
(in article m>):

> Peter Duniho wrote:
>> "peter" > wrote in message
>> oups.com...
>>> The problem is that as it is stated, the scenario is not one that could
>>> ever be created with a real treadmill subject to normal engineering
>>> constraints. [...]
>>
>> You can interpret the question in that way of course. However, the intent
>> of the "puzzler" is clear, and the fact that it is poorly stated should not
>> interfere with making a reasonable, good faith effort to address the
>> intended question.
>>
>> It's well and good to nitpick about physically impossible situations, but
>> rest assured if you started doing so in a true interactive situation in
>> which the person stating the puzzle had the opportunity to restate it, you
>> would quickly get past the nitpicking and get to the intended question.
>>
>> It's a waste of time to do the nitpicking in the first place. It's easy
>> enough to infer what the interesting question really is.
>
> My view was that it was exactly the infinite feedback mechanism that
> made the problem as stated interesting. Otherwise it's trivial and
> boring.
>

Heh, heh. So use a ski plane. Since the speed of the skis is "zero" under the
terms of the problem, the treadmill will remain motionless! Problem solved.

[peter]

Christopher Campbell wrote:
> On Wed, 13 Dec 2006 14:34:54 -0800, peter wrote
> (in article om>):
>
> > Christopher Campbell wrote:
> >
> >> The other gotcha in this little puzzle is that it attempts to get you to
> >> divide by zero.
> >
> > Explain to us please where the statement of this problem ever involves
> > division by zero.
> > One can readily see where the statement implies a value of zero for air
> > speed since in the absence of wheel slip:
> >
> > Treadmill speed = wheel speed (stated explicitly in the problem)
> > and
> > Air speed = wheel speed - treadmill speed (assuming calm air)
> > this directly implies that
> > Air speed = 0.
> >
> > But I don't see where division by zero ever comes into play.
> > The stated problem does imply a runaway positive feedback in the
> > treadmill speed control. I.e. the moment the plane starts to roll
> > forward the control system would speed up the treadmill to match the
> > wheel speed. The motion of the treadmill would then speed up the wheel
> > rotation to a higher speed thus forcing the treadmill to move still
> > faster to catch up. The result would be an ever increasing treadmill
> > and wheel speed until something gives - most likely the tires (if we
> > ignore the technical difficulty of building the specified treadmill).
> >
> >> This is the old Achilles vs. the Tortoise conundrum that so
> >> puzzled ancient Greek mathematicians. The puzzle was this: Achilles and a
> >> Tortoise agree to have a race. Achilles agrees to let the Tortoise have a
> >> head start of getting half way to the finish line. The starting gun sounds
> >> and they are off! (Well, the Tortoise is, anyway.) The Tortoise reaches the
> >> half-way mark and Achilles starts running. But by the time that Achilles
> >> reaches the half-way mark, the Tortoise has moved forward. And by the time
> >> that Achilles reaches the point where the Tortoise has moved to, the
> >> Tortoise
> >> has moved forward again, albeit not as far as before. Again Achilles reaches
> >> the third point where the Tortoise was, but the Tortoise has moved forward
> >> again. No matter how fast Achilles runs, he can never catch up with the
> >> Tortoise. It was this sort of logic that led the Greeks to conclude that
> >> everything was imaginary and that motion was impossible. They could not
> >> solve
> >> the problem because they did not have the number zero.
> >
> > Zeno's Paradox. But I doubt if you could find any ancient Greeks who
> > actually concluded that motion was impossible. Even while puzzling
> > with Zeno over his problem, they continued to go to the markets to do
> > their shopping and to their respective work places.
> >
> > And there's no need to have the concept of the number zero to solve
> > Zeno's paradox, just the idea of the convergence of some types of
> > infinite sums. I.e. if each successive run of Achilles is half as long
> > as the previous one (say he walks twice as fast as the tortoise) then
> > we have a sum for the total distance 'D' of the form:
> > D = x + x/2 + x/4 + x/8 +...
> > multiplying this by 2 gives:
> > 2D = 2x + x + x/2 + x/4 + x/8 + ... = 2x + D
> > subtract D from both sides and we solve for the total distance Achilles
> > needs to walk:
> > D = 2x; i.e. twice the distance of the headstart he gives the tortoise.
> >
> >> The airplane-on-a-treadmill is just a restatement of the same problem. It
> >> attempts to convince you that the airplane cannot move relative to an
> >> outside
> >> observer if the treadmill always moves at the same speed as the wheels. If
> >> the wheels accelerate, then the treadmill accelerates, so the plane cannot
> >> move, right? Wrong. The airplane does move, and it accelerates relative to
> >> an
> >> outside observer at the same rate as it would if the treadmill remained
> >> stationary. The only thing that changes is that the wheels spin faster.
> >
> > Sure, but airplane wheels have some maximum speed. Once the treadmill
> > gets up to that maximum speed the airplane wheels would fail and the
> > airplane is now sitting on a treadmill with a bunch of failed tires.
> > So the question becomes whether a plane can still take off after you
> > shoot out all the tires when it first begins its takeoff roll.
> >
> > And yes, postulating a frictionless surface for the treadmill gets
> > around the problem and allows a normal takeoff. But the very term
> > treadmill implies a surface with reasonable friction, i.e. the tread.
> >
>
> Well, if you understand Zeno's paradox, then you understand enough that the
> airplane will move forward on the treadmill. If the tires don't blow, it will
> take off.

On the contrary, *if* the treadmill is able to perform as explicitly
stated in the problem; i.e. to always keep increasing speed so that it
is moving at the speed of the wheels but in the opposite direction,
then the plane won't be moving forward relative to the ground or still
air. The ability of a real treadmill to do that isn't relevant since
that performance is stipulated in the problem statement.

> I will refer you to the book "Godel, Escher, Bach" for a discussion
> of how the problem is created by an attempt to divide by zero.

You're the one making that claim - how about supporting it rather than
just handwaving about it being somewhere in a book?
>
> If your only argument is that airplane tires will not stand the stress, then
> you are placing a constraint on the problem that is not originally stated.
> You are basically changing the question.

No, the problem doesn't say that there's anything out of the ordinary
about the plane, so characteristics that are common to all actual
planes will also apply to the one in the problem.
>
> Some airplane tires might stand the stress; others might not. Tires are
> highly variable in their design and intended purpose. You cannot flat-out
> declare that all tires would fail.

The statement is true of all airplane tires that at some speed they
will fail.

> In fact, why would not the treadmill break
> down before the tires? The motor could overheat and stop the treadmill
> entirely, or the treadmill surface could disintegrate, or it might be crushed
> by the airplane. The airplane could be so heavy that the treadmill could not
> turn at all. We cannot assume that the treadmill is any less immune to stress
> than anything else stated in the problem.

But the problem explicitly states that the treadmill *will* keep up
with the speed of the airplane wheels. Unlike the airplane, the
treadmill is clearly a hypothetical construct that is only invented for
the purposes of posing the problem. I am not assuming anything about
it other than what is stated in the problem; i.e. that it is a
"tread"mill and therefore can be assumed to have a reasonable friction
surface, and that it is controlled and propelled in such a way as to
always keep up with the speed of the airplane wheels as they spin. If
the treadmill were to break and therefore no longer keep up with the
wheel speed that would be a direct contradiction of the explicit
problem statement.

> So, lacking any further limitations
> as stated in the problem, tires must be assumed to be capable of withstanding
> the stress of the treadmill. Otherwise, why not throw in all other kinds of
> variables not stated in the problem, like flap settings, wind, temperature,
> density altitude, fuel on board, payload, visibility, clearance, and whether
> it would violate FAA rules?

The problem makes no statement about these variables, nor about the
tire strength, for the very reason that these are not hypothetical
constructs like the treadmill, but common to everyday airplane
operations at every airport on a daily basis. The question is whether
a normal plane, operated with normal engines, normal controls, normal
tires, etc. can take off under the very abnormal condition of being on
a hypothetical treadmill with the given characteristics.
>
> No, go with the problem as stated, and let us not make it a trick question by
> assuming facts not presented to the audience.

I *am* going with the problem as stated. In particular where it
explicitly states that the treadmill will move backwards at the speed
of the airplane's wheels. Unless the tires are slipping, which rubber
tires shouldn't do appreciably on a 'treadmill' surface, then

Ground speed = wheel speed - treadmill speed
and since the problem stipulates that treadmill speed = wheel speed we
can easily solve this as:

Ground speed = wheel speed - wheel speed = 0.
If you're claiming that the ground speed (i.e. relative to the earth
and still air) is something other than zero, then it is you who is not
going with the explicit statement of the problem.

As for making it a trick question, I'd note that it is a puzzle
question, not an engineering design question. Puzzle questions are
generally intended to be trick questions in one or more ways - that's
what makes them interesting and provokes contradictory responses.

If it were given to me as an engineering question then I'd immediately
point out that the treadmill being requested can't possibly be built
since it requires instant acceleration of a massive structure and would
request that the project be modified to come up with something
feasible. But as a puzzle question having a gigantic treadmill that
can instantly accelerate to thousands of miles per hour is perfectly
legitimate - just don't ask me to build one.

[Grumman-581]

On Wed, 13 Dec 2006 23:37:37 -0800, peter wrote:
> On the contrary, *if* the treadmill is able to perform as explicitly
> stated in the problem; i.e. to always keep increasing speed so that it
> is moving at the speed of the wheels but in the opposite direction, then
> the plane won't be moving forward relative to the ground or still air.
> The ability of a real treadmill to do that isn't relevant since that
> performance is stipulated in the problem statement.

Lock the brakes and do the takeoff... The treadmill will sense it as an
attempt of the wheels to go backwards and and start moving in the
direction that the plane wants to go anyway...

[peter]

Grumman-581 wrote:
> On Wed, 13 Dec 2006 23:37:37 -0800, peter wrote:
> > On the contrary, *if* the treadmill is able to perform as explicitly
> > stated in the problem; i.e. to always keep increasing speed so that it
> > is moving at the speed of the wheels but in the opposite direction, then
> > the plane won't be moving forward relative to the ground or still air.
> > The ability of a real treadmill to do that isn't relevant since that
> > performance is stipulated in the problem statement.
>
> Lock the brakes and do the takeoff... The treadmill will sense it as an
> attempt of the wheels to go backwards and and start moving in the
> direction that the plane wants to go anyway...

If the brakes are locked then the wheel speed is zero and the treadmill
speed (as specified in the problem) must also immediately go to zero.

[Montblack]

("peter" wrote)
> If it were given to me as an engineering question then I'd immediately
> point out that the treadmill being requested can't possibly be built
> since it requires instant acceleration of a massive structure and would
> request that the project be modified to come up with something
> feasible. But as a puzzle question having a gigantic treadmill that
> can instantly accelerate to thousands of miles per hour is perfectly
> legitimate - just don't ask me to build one.


The treadmill need only be (approx) 6-ft wide x 8-ft long.
(If it needs to be any longer, your answer is wrong)

The object (the plane) isn't THAT heavy.

Our GIGANTIC treadmill only needs to average both accelerations - not have
instant acceleration. (Kind of like your home's thermostat keeping the room
at 68F. It has a 3 or 4 degree temp spread so it isn't "popping" on all the
time. BTDT)

When the plane roles forward two inches, the electric motors speed up
....until the 'curb feeler' sensors detect the axle has returned to point X.

Then, with basic computing, the treadmill readjusts its speed. It might be
only an inch for the "forward" or "back" tolerances ...or it might be a
foot.

It's a small Cessna/Piper/Cri-Cri we're dealing with, here. NOT an F-18 off
a carrier deck!

If you can't slap one of these puppies together in an afternoon... :-)


Montblack-to-the-drawing-board

[peter]

Montblack wrote:
> ("peter" wrote)
> > If it were given to me as an engineering question then I'd immediately
> > point out that the treadmill being requested can't possibly be built
> > since it requires instant acceleration of a massive structure and would
> > request that the project be modified to come up with something
> > feasible. But as a puzzle question having a gigantic treadmill that
> > can instantly accelerate to thousands of miles per hour is perfectly
> > legitimate - just don't ask me to build one.
>
>
> The treadmill need only be (approx) 6-ft wide x 8-ft long.
> (If it needs to be any longer, your answer is wrong)

Unlike other responders here, I'm trying to go by what the problem
actually states, not what they think it should state instead. In
particular, the problem says "Imagine a plane is sitting on a massive
conveyor belt, as wide and as long as a runway." So it needs to be as
wide and long as a real runway to be in agreement with the problem
statement - that's much bigger than 6' x 8' - at least based on the
real runways I've come across. (But I commend you on your short field
landing and take off skills.)
>
> The object (the plane) isn't THAT heavy.
>
> Our GIGANTIC treadmill only needs to average both accelerations - not have
> instant acceleration. (Kind of like your home's thermostat keeping the room
> at 68F. It has a 3 or 4 degree temp spread so it isn't "popping" on all the
> time. BTDT)

Your home heating system is in a negative feedback, well-controlled
situation as opposed to the treadmill which is in a positive feedback,
runaway and out-of-control situation. In the first case the action
taken in response to the stimulus (turning on the furnace when it gets
too cold) acts to reduce the stimulus. But in the second case,
speeding up the treadmill when the wheels speed up, only acts to make
the stimulus worse. So the faster the treadmill goes, the more it
pulls the wheels of the plane around and makes them spin even faster.
I've experienced that kind of positive feedback in miswired electronic
control circuits and it results in rapid escalation out of the physical
bounds of the devices - i.e. as soon as it was turned on there was a
sudden flash, a puff of smoke, and generation of lots of heat.
>
> When the plane rolls forward two inches, the electric motors speed up
> ...until the 'curb feeler' sensors detect the axle has returned to point X.

But that won't happen easily since the plane is being pushed forward by
the thrust of its motor (a substantial force) and the only thing
pushing it back to point X is the slight frictional drag of the
spinning wheels. So until the treadmill reaches a really high speed
where that frictional drag becomes significant (probably when either
the wheel bearings start to overheat or the tire starts to fail) the
plane will keep moving forward and triggering the treadmill to go ever
faster.
>
> Then, with basic computing, the treadmill readjusts its speed. It might be
> only an inch for the "forward" or "back" tolerances ...or it might be a
> foot.

Let's give it your maximum tolerance of a foot. That means that in the
time it takes your Cessna 150/whatever to move forward just one foot
the treadmill needs to speed up to the point where the wheel drag is
enough to equal the thrust from propellor. A 150 may not have a whole
lot of thrust, but it's still large compared to the drag of the wheels
turning at say 100 mph. I'd call an acceleration from 0 to 100mph in
the time it takes the plane to move a foot pretty impressive for a
treadmill the size of a runway - and that wouldn't even be enough since
the thrust is still larger than the 100 mph drag force. So the
treadmill has to go still faster until something in the plane's landing
gear (tires/bearings/etc.) breaks and results in a greater frictional
drag force which can counter the propellor thrust.
>
> It's a small Cessna/Piper/Cri-Cri we're dealing with, here. NOT an F-18 off
> a carrier deck!
>
> If you can't slap one of these puppies together in an afternoon... :-)

I think you're seriously underestimating the difficulty of the design,
but you're welcome to prove me wrong with a working model.

[Bob Noel]

In article . com>,
"peter" > wrote:


> On the contrary, *if* the treadmill is able to perform as explicitly
> stated in the problem; i.e. to always keep increasing speed so that it
> is moving at the speed of the wheels but in the opposite direction,
> then the plane won't be moving forward relative to the ground or still
> air. The ability of a real treadmill to do that isn't relevant since
> that performance is stipulated in the problem statement.

What keeps the wheels in contact with the treadmill when the treadmill
(and wheels) are going supersonic?

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

[Gig 601XL Builder]

"Travis Marlatte" > wrote in message
...
> "Gig 601XL Builder" <wrDOTgiaconaATcox.net> wrote in message
>> What you saw was an aircraft that failed to achieve and or retain a
>> critical airspeed. Either the catapult failed or the engine failed or,
>> well any number of things. There is a reason carriers turn into the wind
>> to launch aircraft. There is also a reason that carriers can't launch
>> fixed wing aircraft while tied to the dock. Well they might be able to
>> but a lot of things have to be perfect.
>>
>
> Thanks. But it was a joke. I do question the word "can't" in your
> explanation. I would believe "can't launch some fixed wing aircraft but
> not as a general statement.
>

That's why I added the sentence that immediately follows the one you have a
problem with.

[Peter Dohm]

"Bob Noel" > wrote in message
...
> In article . com>,
> "peter" > wrote:
>
>
> > On the contrary, *if* the treadmill is able to perform as explicitly
> > stated in the problem; i.e. to always keep increasing speed so that it
> > is moving at the speed of the wheels but in the opposite direction,
> > then the plane won't be moving forward relative to the ground or still
> > air. The ability of a real treadmill to do that isn't relevant since
> > that performance is stipulated in the problem statement.
>
> What keeps the wheels in contact with the treadmill when the treadmill
> (and wheels) are going supersonic?
>
> --
> Bob Noel
> Looking for a sig the
> lawyers will hate
>
In the original problem statement; nothing except gravity causes contact of
the wheels, or any other part of the airplane, to the treadmill at any
speed.

Peter

[Jose[_1_]]

> If the brakes are locked then the wheel speed is zero and the treadmill
> speed (as specified in the problem) must also immediately go to zero.

.... until the propeller starts to pull the airplane (with its locked
wheels) forward.

Jose
--
"There are 3 secrets to the perfect landing. Unfortunately, nobody knows
what they are." - (mike).
for Email, make the obvious change in the address.

[[email protected]]

Travis Marlatte wrote:
>
> Why isn't there forward motion on the treadmill? The pressure differential
> around the prop or the thrust from a jet will propel the plane forward to
> takeoff speed on glare ice (wheels don't have to spin at all) or the
> treadmill (wheels spin at twice the speed).

The Original Question said that the treadmill speed was such as
to counter wheel speed so that the airplane stood still. That's what I
was thinking. Somewhere along this thread the assumption must have
changed and I'm arguing apples against oranges.
No airspeed, no lift. Period. Propeller or jet blast is not going
to lift the airplane. We need forward motion relative to the
atmosphere, or a really strong headwind.

The tires used on light aircraft are Type III and are rated for
120 MPH max. They'd probably explode before 150 MPH, seeing that the
forces increase by the square of the rotational velocity. Or. more
likely, the average lighplane tire being as out-of-round and imbalanced
as it is, the vibration would shake the airplane apart by the time we
got to 120.

Dan

[BDS[_2_]]

> wrote in message
ups.com...
>

> The Original Question said that the treadmill speed was such as
> to counter wheel speed so that the airplane stood still. That's what I
> was thinking.

That's where you fell into the trap. The statement was that the treadmill
moves backwards at the same speed as the airplane is moving forward - it
didn't say that the airplane stood still (but that's the conclusion it
wanted you to reach). But, since the propeller and not the wheels is
driving the plane forward it doesn't matter how fast the belt on the
treadmill runs backwards, the plane will still move forward.

> No airspeed, no lift. Period. Propeller or jet blast is not going
> to lift the airplane. We need forward motion relative to the
> atmosphere, or a really strong headwind.

[Peter Dohm]

> wrote in message
ups.com...
>
> Travis Marlatte wrote:
> >
> > Why isn't there forward motion on the treadmill? The pressure
differential
> > around the prop or the thrust from a jet will propel the plane forward
to
> > takeoff speed on glare ice (wheels don't have to spin at all) or the
> > treadmill (wheels spin at twice the speed).
>
> The Original Question said that the treadmill speed was such as
> to counter wheel speed so that the airplane stood still. That's what I
> was thinking. Somewhere along this thread the assumption must have
> changed and I'm arguing apples against oranges.
> No airspeed, no lift. Period. Propeller or jet blast is not going
> to lift the airplane. We need forward motion relative to the
> atmosphere, or a really strong headwind.
>
> The tires used on light aircraft are Type III and are rated for
> 120 MPH max. They'd probably explode before 150 MPH, seeing that the
> forces increase by the square of the rotational velocity. Or. more
> likely, the average lighplane tire being as out-of-round and imbalanced
> as it is, the vibration would shake the airplane apart by the time we
> got to 120.
>
> Dan
>
I am not sure what sort of perversity is causing me to continue reading this
insane thread, much less respond to it.

Here is a copy of the text, lifted from the New York Times web site as
linked; except that I have edited out the special characters which appeared
as a result of the text conversion:

-----------begin NY Times excerpt---------

December 11, 2006, 4:37 pm
The Airplane-Treadmill Conundrum
OK, this 's driving me crazy. This brain-teaser is ripping around the
Internet, plus I actually overheard it THREE TIMES in airport conversations
on a recent trip to Canada.'s how I found it presented at
http://boards.straightdope.com/sdmb/showthread.php?t=348452 Imagine a plane
is sitting on a massive conveyor belt, as wide and as long as a runway. The
conveyer belt is designed to exactly match the speed of the wheels, moving
in the opposite direction. Can the plane take off? I say no, because the
plane will not move relative the the ground and air, and thus, very little
air will flow over the wings. However, other people are convinced that since
the wheels of a plane are free spinning, and not powered by the engines, and
the engines provide
thrust against the air, that somehow that makes a difference and air will
flow over the wing. The guy behind me at the airport told his buddy that,
in fact, the plane WOULD take off, and his buddy seemed to agree. Do we have
any physicists in the audience?

---------end NY Times excerpt-------

Please note that the embedded link still works.
Please note also that nothing new can be added.

I submit that there are really only two logical presumptions, both of which
have been explored:
1. The aircraft will take off normally.
2. The magic treadmill has no inertia and no limiting speed; and, by some
unexplained means, can sense the rotation of the wheels. Therefore, if the
aircraft is placed very near the departure end of the runway and connected
to an airport tug which is placed on solid ground; then, as the tug begins
to slowly pull the aircraft forward, the magic treadmill will quickly
accelerate until the wheels and tires of the airplane have catastrophically
failed.

I further submit that the second presumption is ridiculous.

Peter

[Bob Noel]

In article <Ueegh.387$Iz.365@bigfe9>, "Peter Dohm" >
wrote:

> > What keeps the wheels in contact with the treadmill when the treadmill
> > (and wheels) are going supersonic?

> In the original problem statement; nothing except gravity causes contact of
> the wheels, or any other part of the airplane, to the treadmill at any
> speed.

so, eventually, the treadmill won't have the ability to apply drag to the
airplane.

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

[Peter Dohm]

"Bob Noel" > wrote in message
...
> In article <Ueegh.387$Iz.365@bigfe9>, "Peter Dohm"
>
> wrote:
>
> > > What keeps the wheels in contact with the treadmill when the treadmill
> > > (and wheels) are going supersonic?
>
> > In the original problem statement; nothing except gravity causes contact
of
> > the wheels, or any other part of the airplane, to the treadmill at any
> > speed.
>
> so, eventually, the treadmill won't have the ability to apply drag to the
> airplane.
>
That has been my position.

However, my position has been based upon the presumption that the word
problem was only intended to test whether a respondent understood that there
is no connection between the wheels and the engine(s) of a typical airplane,
and my position was further based upon the idea that the word problem was
originally intended to be solved by the airplane taking off normally.

I must admit that the most precise parsing of the language in the problem
statement does suggest that the wheels will be quickly spun to failure as
soon as the airplane begins to move. No limit speed was stated in the
problem, so the possibility of infinite speed and instantaneous response
would be linguistically correct--one of the other contributors used the
analogy of "division by zero."

Peter

[Grumman-581[_1_]]

On Thu, 14 Dec 2006 00:32:09 -0800, in <11660851
> If the brakes are locked then the wheel speed is zero and the treadmill
> speed (as specified in the problem) must also immediately go to zero.

Depends upon the definition of "wheel speed" then...

Either the treadmill moves to the rear and the wheel rotation increases
significantly and the plane manages to take off because takeoff is
determined by air speed, not the rotational speed of the tires

OR

the treadmill is set to keep the wheels from rotating in which case you
manage to takeoff with no rotational movement on the wheels...

[Travis Marlatte]

Several of you are debating two different kinds of wheels speeds. I happen
to believe that the original question was of a simple nature and meant that
the treadmill speed matched the forward motion of the plane (or forward
motion of the wheel). Those who want the wheels to explode before the
treadmill reaches an infinite speed assume that the original question meant
that the treadmill speed somehow stops forward motion by matching a wheel
speed I haven't seen you define.
--
-------------------------------
Travis
Lake N3094P
PWK
"Jose" > wrote in message
et...
>> If the brakes are locked then the wheel speed is zero and the treadmill
>> speed (as specified in the problem) must also immediately go to zero.
>
> ... until the propeller starts to pull the airplane (with its locked
> wheels) forward.
>
> Jose
> --
> "There are 3 secrets to the perfect landing. Unfortunately, nobody knows
> what they are." - (mike).
> for Email, make the obvious change in the address.

[Travis Marlatte]

Unbelievable."Montblack" > wrote in
message ...
> ("peter" wrote)
>> If it were given to me as an engineering question then I'd immediately
>> point out that the treadmill being requested can't possibly be built
>> since it requires instant acceleration of a massive structure and would
>> request that the project be modified to come up with something
>> feasible. But as a puzzle question having a gigantic treadmill that
>> can instantly accelerate to thousands of miles per hour is perfectly
>> legitimate - just don't ask me to build one.
>
>
> The treadmill need only be (approx) 6-ft wide x 8-ft long.
> (If it needs to be any longer, your answer is wrong)
>
> The object (the plane) isn't THAT heavy.
>
> Our GIGANTIC treadmill only needs to average both accelerations - not have
> instant acceleration. (Kind of like your home's thermostat keeping the
> room
> at 68F. It has a 3 or 4 degree temp spread so it isn't "popping" on all
> the
> time. BTDT)
>
> When the plane roles forward two inches, the electric motors speed up
> ...until the 'curb feeler' sensors detect the axle has returned to point
> X.
>
> Then, with basic computing, the treadmill readjusts its speed. It might be
> only an inch for the "forward" or "back" tolerances ...or it might be a
> foot.
>
> It's a small Cessna/Piper/Cri-Cri we're dealing with, here. NOT an F-18
> off
> a carrier deck!
>
> If you can't slap one of these puppies together in an afternoon... :-)
>
>
> Montblack-to-the-drawing-board
>
>
>

You'd better make it a little bigger 'cause the plane is going to roll many
hundreds of feet and take off.

-------------------------------
Travis
Lake N3094P
PWK

[Travis Marlatte]

"peter" > wrote in message
oups.com...
> Montblack wrote:
>> ("peter" wrote)
>> > If it were given to me as an engineering question then I'd immediately
>> > point out that the treadmill being requested can't possibly be built
>> > since it requires instant acceleration of a massive structure and would
>> > request that the project be modified to come up with something
>> > feasible. But as a puzzle question having a gigantic treadmill that
>> > can instantly accelerate to thousands of miles per hour is perfectly
>> > legitimate - just don't ask me to build one.
>>
>>
>> The treadmill need only be (approx) 6-ft wide x 8-ft long.
>> (If it needs to be any longer, your answer is wrong)
>
> Unlike other responders here, I'm trying to go by what the problem
> actually states, not what they think it should state instead. In
> particular, the problem says "Imagine a plane is sitting on a massive
> conveyor belt, as wide and as long as a runway." So it needs to be as
> wide and long as a real runway to be in agreement with the problem
> statement - that's much bigger than 6' x 8' - at least based on the
> real runways I've come across. (But I commend you on your short field
> landing and take off skills.)
>>
>> The object (the plane) isn't THAT heavy.
>>
>> Our GIGANTIC treadmill only needs to average both accelerations - not
>> have
>> instant acceleration. (Kind of like your home's thermostat keeping the
>> room
>> at 68F. It has a 3 or 4 degree temp spread so it isn't "popping" on all
>> the
>> time. BTDT)
>
> Your home heating system is in a negative feedback, well-controlled
> situation as opposed to the treadmill which is in a positive feedback,
> runaway and out-of-control situation. In the first case the action
> taken in response to the stimulus (turning on the furnace when it gets
> too cold) acts to reduce the stimulus. But in the second case,
> speeding up the treadmill when the wheels speed up, only acts to make
> the stimulus worse. So the faster the treadmill goes, the more it
> pulls the wheels of the plane around and makes them spin even faster.
> I've experienced that kind of positive feedback in miswired electronic
> control circuits and it results in rapid escalation out of the physical
> bounds of the devices - i.e. as soon as it was turned on there was a
> sudden flash, a puff of smoke, and generation of lots of heat.
>>
>> When the plane rolls forward two inches, the electric motors speed up
>> ...until the 'curb feeler' sensors detect the axle has returned to point
>> X.
>
> But that won't happen easily since the plane is being pushed forward by
> the thrust of its motor (a substantial force) and the only thing
> pushing it back to point X is the slight frictional drag of the
> spinning wheels. So until the treadmill reaches a really high speed
> where that frictional drag becomes significant (probably when either
> the wheel bearings start to overheat or the tire starts to fail) the
> plane will keep moving forward and triggering the treadmill to go ever
> faster.
>>
>> Then, with basic computing, the treadmill readjusts its speed. It might
>> be
>> only an inch for the "forward" or "back" tolerances ...or it might be a
>> foot.
>
> Let's give it your maximum tolerance of a foot. That means that in the
> time it takes your Cessna 150/whatever to move forward just one foot
> the treadmill needs to speed up to the point where the wheel drag is
> enough to equal the thrust from propellor. A 150 may not have a whole
> lot of thrust, but it's still large compared to the drag of the wheels
> turning at say 100 mph. I'd call an acceleration from 0 to 100mph in
> the time it takes the plane to move a foot pretty impressive for a
> treadmill the size of a runway - and that wouldn't even be enough since
> the thrust is still larger than the 100 mph drag force. So the
> treadmill has to go still faster until something in the plane's landing
> gear (tires/bearings/etc.) breaks and results in a greater frictional
> drag force which can counter the propellor thrust.
>>
>> It's a small Cessna/Piper/Cri-Cri we're dealing with, here. NOT an F-18
>> off
>> a carrier deck!
>>
>> If you can't slap one of these puppies together in an afternoon... :-)
>
> I think you're seriously underestimating the difficulty of the design,
> but you're welcome to prove me wrong with a working model.
>


A couple of good arguements but the treadmill doesn't have to go that fast.
What type of matching wheel speed would cause that? The only reason that the
treadmill would need to accelerate to inifinity is if the question had posed
that the treadmill acted to stop forward motion. Then, I agree that the
treadmill would have to accelerate to a point where the friction was enough
to counteract thrust. However, the question posed only that the treadmill
matched the wheel speed. I take that to mean the forward motion of the
wheels which is the same as the forward motion of the plane.
-------------------------------
Travis
Lake N3094P
PWK

[Travis Marlatte]

"Gig 601XL Builder" <wrDOTgiaconaATcox.net> wrote in message
...
>
> "Travis Marlatte" > wrote in message
> ...
>> "Gig 601XL Builder" <wrDOTgiaconaATcox.net> wrote in message
>>> What you saw was an aircraft that failed to achieve and or retain a
>>> critical airspeed. Either the catapult failed or the engine failed or,
>>> well any number of things. There is a reason carriers turn into the wind
>>> to launch aircraft. There is also a reason that carriers can't launch
>>> fixed wing aircraft while tied to the dock. Well they might be able to
>>> but a lot of things have to be perfect.
>>>
>>
>> Thanks. But it was a joke. I do question the word "can't" in your
>> explanation. I would believe "can't launch some fixed wing aircraft but
>> not as a general statement.
>>
>
> That's why I added the sentence that immediately follows the one you have
> a problem with.
>

I guess I get your point but it still seems to be overstated. Are
restricting your definition of "fixed wing aircraft" to those types
typically launched from aircraft carriers? Maybe I'm taking you too
literally but you seem to be saying that there are no fixed wing planes that
can do a normal takeoff with no headwind advantage in the length of an
aircraft carrier. I find that hard to believe. How about a Piper Cub?
-------------------------------
Travis
Lake N3094P
PWK

[Travis Marlatte]

"T o d d P a t t i s t" > wrote in message
...
> "Peter Dohm" > wrote:
>
>>I submit that there are really only two logical presumptions, both of
>>which
>>have been explored:
>>1. The aircraft will take off normally.
>>2. The magic treadmill has no inertia and no limiting speed; and, by
>>some
>>unexplained means, can sense the rotation of the wheels. Therefore, if
>>the
>>aircraft is placed very near the departure end of the runway and connected
>>to an airport tug which is placed on solid ground; then, as the tug begins
>>to slowly pull the aircraft forward, the magic treadmill will quickly
>>accelerate until the wheels and tires of the airplane have
>>catastrophically
>>failed.
>>
>>I further submit that the second presumption is ridiculous.
>
> You are clearly on one side of the debate. I submit that
> you are absolutely correct that there are only "two logical
> presumptions, both of which have been explored" but I'd try
> to list them more neutrally as:
>
> 1. The aircraft will take off normally because the
> physics of the situation are such that there's nothing to
> prevent the wheelspeed from becoming faster than the
> treadmill speed.
>
> 2. The aircraft will not take off because the problem
> constraint prohibits the wheelspeed from exceeding the
> treadmill speed, without providing the physics of how that
> constraint might be imposed.
>
> At this point do we really care which side people are on?
> --
> Do not spin this aircraft. If the aircraft does enter a spin it will
> return to earth without further attention on the part of the aeronaut.
>
> (first handbook issued with the Curtis-Wright flyer)


Yes. We care. Because the people that think (2) are just trying to come with
excuses why they didn't fall into the trap of the puzzle.

Seriously, it is obvious that the posters in this thread fall into several
categories:

1) Those who understand the physics of the question and believe that the
puzzle was not trying to be devious.

2) Those who understand the physics of the question and are just trying to
add fuel to the fire.

and 3) Those who don't understand the physics of the question and are
grasping at straws trying to explain why they believe the plane will not
take off.

I don't care about (2) but I worry about (3).
-------------------------------
Travis
Lake N3094P
PWK

[Montblack]

("Travis Marlatte" wrote)
> Unbelievable."Montblack"
> You'd better make it a little bigger 'cause the plane is going to roll
> many hundreds of feet and take off.


Exactly, but I was helping peter 'engineer' a treadmill to fit HIS
hypothysis.

Thus this line:
The treadmill need only be (approx) 6-ft wide x 8-ft long.
(If it needs to be any longer, your answer is wrong)

I then presented a [basic] treadmill that could do what he claimed would
happen ...(minus) the need to "instantly accelerate to thousands of miles
per hour."


Montblack-to-the-drawing-board
(I'm a convert from the previous treadmill thread, BTW)

[peter]

Travis Marlatte wrote:
> Several of you are debating two different kinds of wheels speeds. I happen
> to believe that the original question was of a simple nature and meant that
> the treadmill speed matched the forward motion of the plane (or forward
> motion of the wheel). Those who want the wheels to explode before the
> treadmill reaches an infinite speed assume that the original question meant
> that the treadmill speed somehow stops forward motion by matching a wheel
> speed I haven't seen you define.

I thought I was pretty explicit about the definition several days ago
in my first post to this thread when I wrote:
"Of course the above is based on a particular interpretation of "speed
of the wheels" i.e. that it is measured based on the speed of rotation
and therefore measures show fast they are rolling on the treadmill
surface. If instead the "speed of the wheels" is measured by seeing
how fast the wheel hub is moving forward relative to the earth then the
above infinite feedback loop doesn't arise and the plane can take off
fairly normally although the wheels will be spinning twice as fast as
normal at takeoff.

But that second interpretation of wheel speed doesn't strike me as
consistent with normal usage - e.g. when a bicyclist is on a stationary
trainer we would normally measure the speed of his rear wheel based on
rotation rate, not say that it's zero since the hub is just spinning
but not moving forward."

It still seems to me that "speed of the wheels" of something on a
treadmill or similar device such as a stationary bicycle or a vehicle
dynamometer is clearly understood in common usage to refer to the
tangential speed of the outer edge of the wheel, not the linear speed
of the wheel axle. If a mechanic is told to drive a car onto a
dynamometer and keep the speed of the drive wheels at 50 mph, there's
no question about what is meant.

[Peter Dohm]

> >Seriously, it is obvious that the posters in this thread fall into
several
> >categories:
> >
> >1) Those who understand the physics of the question and believe that the
> >puzzle was not trying to be devious.
> >
> >2) Those who understand the physics of the question and are just trying
to
> >add fuel to the fire.
> >
> > 3) Those who don't understand the physics of the question and are
> >grasping at straws trying to explain why they believe the plane will not
> >take off.
> >
> >I don't care about (2) but I worry about (3).
>
> I worry about 3 also, but if we didn't, we'd probably not
> post anything. As for 2, I'd again revise your category to
> a more neutral stance and make it:
>
> 2) Those who understand the physics of the question, but
> think the question is ambiguous enough to provide a
> mathematical justification for the conclusion that the plane
> will not take off.
>
> Personally, I'm confident that a real plane would take off,
> but I'm also confident that the mathematics of the problem
> statement prohibit it from taking off. I don't consider
> that to be adding fuel to any fire, just trying to see
> logically how the problem statement can be parsed. Most
> parse it in the real world and ignore what isn't real, some
> parse it by its own terms and acknowledge the
> non-physicality of the situation. Others are just confused
> :-)
>
When I first read the word problem, I jumped to the conclusion that the
treadmill would approximately double the wheel/tire speed of the aircraft.
That would be trivial for most light aircraft, but would probably result in
tire failure for jet transports.

Long after this discussion really got going, I read the problem again, and
found that the "spin to infinity" scenario is a more precise parsing of the
word problem. That parsing is based upon the wording at the beginning of
this thread, and also upon the discussion in the slightly earlier thread
referenced in its embedded link.

However, I still believe that the original intent was simply to get a laugh
at the expense of unwary pax; who, not thinking about how aircraft are
really propelled, would equate the scenario to a person walking the wrong
direction on one of the moving sidewalks in the terminal.

At this point, I am wondering how the problem statement may have evolved
over time; and, if so, what the original phrasing may have been.

Peter

[Travis Marlatte]

"peter" > wrote in message
oups.com...
> Travis Marlatte wrote:
>> Several of you are debating two different kinds of wheels speeds. I
>> happen
>> to believe that the original question was of a simple nature and meant
>> that
>> the treadmill speed matched the forward motion of the plane (or forward
>> motion of the wheel). Those who want the wheels to explode before the
>> treadmill reaches an infinite speed assume that the original question
>> meant
>> that the treadmill speed somehow stops forward motion by matching a wheel
>> speed I haven't seen you define.
>
> I thought I was pretty explicit about the definition several days ago
> in my first post to this thread when I wrote:
> "Of course the above is based on a particular interpretation of "speed
> of the wheels" i.e. that it is measured based on the speed of rotation
> and therefore measures show fast they are rolling on the treadmill
> surface. If instead the "speed of the wheels" is measured by seeing
> how fast the wheel hub is moving forward relative to the earth then the
> above infinite feedback loop doesn't arise and the plane can take off
> fairly normally although the wheels will be spinning twice as fast as
> normal at takeoff.
>
> But that second interpretation of wheel speed doesn't strike me as
> consistent with normal usage - e.g. when a bicyclist is on a stationary
> trainer we would normally measure the speed of his rear wheel based on
> rotation rate, not say that it's zero since the hub is just spinning
> but not moving forward."
>
> It still seems to me that "speed of the wheels" of something on a
> treadmill or similar device such as a stationary bicycle or a vehicle
> dynamometer is clearly understood in common usage to refer to the
> tangential speed of the outer edge of the wheel, not the linear speed
> of the wheel axle. If a mechanic is told to drive a car onto a
> dynamometer and keep the speed of the drive wheels at 50 mph, there's
> no question about what is meant.
>

There may be no question because, when the object is stationary such as the
bike on a trainer or the car on the dynamometer, the tangential speed is
the same as simulated forward motion. In the puzzle, there is no tangential
speed until the plane starts to roll. Then, there is a huge difference in
trying to match the forward motion (which matches the tangential speed until
the treadmill adds its component) to trying to match the tangential speed
(which now becomes a futile race to destroy the wheels before the plane
becomes airborne).

With the later, you have the equations:

Treadmill speed = Tangential Speed
Tangential Speed = Treadmill Speed + Airspeed

This can only be true for all speeds equal to zero which is kind of
pointless.

I still maintain that the original question merely meant to illustrate the
independence of thrust from wheel rotation which can be accomplished by
having the treadmill match the speed of the forward motion of the plane.
-------------------------------
Travis
Lake N3094P
PWK

[Travis Marlatte]

"Peter Dohm" > wrote in message
...
> Long after this discussion really got going, I read the problem again, and
> found that the "spin to infinity" scenario is a more precise parsing of
> the
> word problem. That parsing is based upon the wording at the beginning of
> this thread, and also upon the discussion in the slightly earlier thread
> referenced in its embedded link.

I'm having trouble seeing how the "spin to infinity" scenario is a more
precise parsing. At best, "wheel speed" can be interpreted in two ways: 1)
forward motion or 2) tangential speed.

(2) leads to a mathmatical violation of the question since the treadmill
speed is supposed to match the "wheel speed" but it can't once the plane
starts moving. I just don't believe that was the point.
-------------------------------
Travis
Lake N3094P
PWK

[peter]

Travis Marlatte wrote:

> I'm having trouble seeing how the "spin to infinity" scenario is a more
> precise parsing. At best, "wheel speed" can be interpreted in two ways: 1)
> forward motion or 2) tangential speed.

If the poser of the puzzle question meant the phrase to just mean the
'forward motion of the plane' then it would be straightforward to use
that term rather than specify the "speed of the wheels." Speed of a
wheel that's spinning is commonly used to refer to the tangential speed
of the outer edge, whether it's of a bike on a trainer, a car on a
dynamometer, or a vehicle that partly slipping on a surface such as
someone who says he started sliding on ice and his wheel speed shot up
to 90 mph even though he was only going 25 mph.

> (2) leads to a mathmatical violation of the question since the treadmill
> speed is supposed to match the "wheel speed" but it can't once the plane
> starts moving. I just don't believe that was the point.

No, it doesn't need to lead to any mathematical violation, but it does
require a hypothetical treadmill that can accelerate much faster than
any real one could. Without any physical limits on its acceleration or
maximum speed, it would be possible for the treadmill to prevent the
plane from moving and therefore satisfy the mathematical condition
implied by the problem wording.

I've seen what I believe is an earlier version of this puzzle where the
question did refer to the speed of the plane rather than the speed of
the wheels. Of course the correct response to that one is that a
normal takeoff is possible as long as the wheels/tires are capable of
spinning twice as fast as during a takeoff on a regular runway. So my
view is that the change in phrasing to refer to speed of the wheels was
deliberately made to lead to the scenario where the treadmill speed
shoots up very fast to keep the plane from moving even though that
implies a capability that real treadmills can't achieve.

[muff528]

"Nomen Nescio" > wrote in message
...
> -----BEGIN PGP SIGNED MESSAGE-----
>
>>From: Christopher Campbell >
>
>>> As long as a magical massless wheel is attached to the magical
>>> frictionless
>>> bearing.
>
>>There is no reason to assume that the treadmill will not fail first! So,
>>not
>>having enough information to determine if the treadmill will stop running
>>before the wheels do, we cannot categorically say that the airplane will
>>not
>>take off because the wheels will fail. The motor of the treadmill might
>>simply burn out first and the treadmill come to a stop.
>
> I'm not thinking in terms of failure. I'm thinking in terms of Inertia.
> Even with a frictionless wheel bearing, it takes power to accelerate the
> wheel.
>
> Given: a frictionless wheel bearing, a treadmill, and a wheel of normal
> mass.
> With all being able to hold up to a velocity and acceleration range of 0
> to infinity
> without failure. And tire that will not skid on the treadmill.
>
> it would be possible to accelerate the treadmill at a high enough rate to
> cause
> a plane, under full power, to move BACKWARD.
>


Nope ... if the wheel bearings were truly *frictionless* there would be no
forces at all exerted
on the aircraft by the treadmill and the plane would remain motionless even
if the
engine was not running. Any transmission of energy would stop at the
interface between the
outer bearing race and the bearings themselves. The airplane would be
further isolated from the
treadmill by the interface between the bearings and the inner race. The only
way the treadmill
could move the plane is by dragging enough air backwards to act on the
plane. If the engine were
running at all the plane would move forward. Also, the speed of the
treadmill always matches the airplane's
wheels as long as the wheels are rolling and not skidding. That is just a
matter of the observer's frame
of reference and is in no way relevant to whether the plane will take off.
To a stationary observer the
wheels will not go any faster than twice the normal speed attained at the
point of takeoff for a given a/c.
Question -- As a non-pilot I wonder if a wheel/tire, for an airplane that
will take off at an airspeed of say
100mph, will fail before 200mph?

Tony P.

[Jose[_1_]]

> Also, the speed of the
> treadmill always matches the airplane's
> wheels as long as the wheels are rolling and not skidding.

If the plane begins to move forward on this magical treadmill, what will
make the wheels turn?

Jose
--
"There are 3 secrets to the perfect landing. Unfortunately, nobody knows
what they are." - (mike).
for Email, make the obvious change in the address.

[EridanMan]

Jose...

not to be too much of an anal nitpicker, but actually, props and
rockets DO work in the same manner...

The Rocket takes a small amount of matter and throws it at great speed
in X direction, getting and equal and opposite reaction in the opposite
direction Y... The prop grabs a large amount of air and throws it in X
direction, getting an equal and opposite reaction in Y... The principal
is the EXACT same.

Its the same principal as aircraft flying - while the common perception
is that aircraft fly because of pressure differential, 'really' they're
flying solely because they're imparting a downward force on the air
that is exactly equal the downward force caused by gravity- that is,
they're forcing exactly enough air downward to accelerate themselves
upward at 1 G...

The simple reality is that these are all various ways of stating the
EXACT same thing (and fundamentally, they all cancel out if you go back
down to the equasions)... Saying that an Aircraft flies via pressure
differential vs. flies via forcing air downward... or saying that a
prop or rocket flies via the same too manners (one might suggest that a
rocket flies with the same pressure differential as an aircraft, just
centered in a MUCH smaller area (inside the bell vs. outside, rather
than in front of the prop vs behind)... in the end, its the same net
result- mass gets forced backwards, I get forced forward... life is
good.


On Dec 13, 8:18 am, Jose > wrote:
> > The thrust of the engine is not against the air. It generates
> > thrust as a Newtonian reaction to the prop moving air back, not
> > "pushing on other air." A rocket in space has nothing to push against,
> > yet it generates the same thrust as it did in the atmosphere.Actually, it's not that way. (but read carefully)
>
> The thrust of a propeller engine is created when the propeller (an
> airfoil) creates a high pressure area behind and a low pressure area in
> front of the prop, as it pushes air back. The prop is pushing against
> the air in order to do this. The air is constantly trying to get out of
> the way, but it is not entirely successful, which leads to the pressure
> differences. There's nothing funamentally wrong in saying that the
> airplane pushes against the air to move forward. The prop (a part of
> the airplane) is doing the pushing.
>
> Rockets are different. The tail of fire coming out of the rocket does
> push against the air (push the air out of the way to make room for the
> fire), but it is =not= part of the rocket. If there were no air to
> "push against", the rocket would work just as well, for that reason.
> Where the rocket gets its thrust is the tail of fire pushing (the other
> way) against the engine bell of the rocket itself. The rocket is
> pushing against the fire, in essence. The fire is =not= part of the rocket.
>
> Both cases can be viewed in the newtonian "action/reaction" paradigm,
> but something has to push against something else in order to get the
> thrust to happen in the first place. In a plane, the propeller pushes
> against the air (to make the air go backwards fast and create thrust. In
> a rocket, the engine bell pushes against the tail fire (pushing the fire
> out, and the rocket forward). I suppose it may be clearer to say that
> the expanding gasses of the tail fire push against the engine bell, but
> the two are equivalent.
>
> Although the expanding rocket gasses do push the air out of the way,
> that doesn't help the rocket in any meaningful way.
>
> Jose
> --
> "There are 3 secrets to the perfect landing. Unfortunately, nobody knows
> what they are." - (mike).
> for Email, make the obvious change in the address.

[Travis Marlatte]

"EridanMan" > wrote in message
ps.com...
> Jose...
>
> not to be too much of an anal nitpicker, but actually, props and
> rockets DO work in the same manner...



At best, you could say that they accomplish the same thing. I don't agree
that they accomplish it in the same manner. Propellers, wings, and sails on
sail boats all work in the same manner. Whether you like to think of them as
redirecting mass or creating a pressure differential, they all do it the
same way. And none of them could do it without moving through a redirectable
mass - like air.

Rockets, on the other hand, carry their own redirectable mass with them, so
to speak.
-------------------------------
Travis
Lake N3094P
PWK

[muff528]

> Incorrect.
> You're missing a force in there.
>
> Picture this:
> Lay a tire on it's side on a frozen lake (close enough to frictionless for
> this
> example). Now wrap a rope around it a couple of times (like you would to
> start an old outboard motor on a boat). Now quickly pull on the rope at a
> tangent
> to the tread.
> You'll see two things happen.
> 1) the tire will rotate (Ok, that's pretty obvious)
> but also
> 2) The center of the tire will move in the same direction that you are
> pulling
> on the rope.
>
> The reason that the center will be displaced from it's original location
> is the
> same reason that the plane WILL move.
>
> Your statement would be valid only under one condition.........If the
> wheel, itself,
> had no mass.
>

Hmmmm.. gotta think about that one. Not suggesting that you're incorrect but
just
wondering how the hub could act on the spindle if the bearing were truly
*frictionless*?!
Something has to push on something at some level. At what point are
frictional forces
described/replaced by more fundamental interactions? (maybe I need to
consult the great
oracle, wiki, to get the true definition of friction ;-)) On 2nd thought it
would seem that the
spindle WOULD be *pushed* backwards by photon pressure. (Holy crap! ... I
didn't want
to let THAT dead/alive cat out of the box.!) :-(

Also, by definition, the treadmill/conveyor will NOT MOVE AT ALL unless the
airplane/wheel hub
IS moving in the opposite direction. We're back again to the point of the
riddle which I believe
is to suggest that the airplane would take off regardless of what the wheels
or conveyor are doing.
(This is starting to sound more & more like the chicken and the egg.)

For Jose's question above, I think that by *frictionless* most people are
thinking of the hub &
bearings and not where the rubber meets the conveyor. If the wheel/conveyor
interface were
frictionless then neither the wheels nor the conveyor would turn unless the
problem can be interpreted
as the conveyor matching the hub's linear speed rather than the wheel's
angular speed. Either way
the plane takes off when it reaches sufficient airspeed.

Tony P.

[peter]

muff528 wrote:
> Hmmmm.. gotta think about that one. Not suggesting that you're incorrect but
> just
> wondering how the hub could act on the spindle if the bearing were truly
> *frictionless*?!
> Something has to push on something at some level.

A 'frictionless' surface can still exert a force normal (at right
angles) to the surface. So you can stand on a frictionless skating
rink and the ice will hold you up. It just won't exert a force
tangential to the surface so you may well slip and fall - at which
point you'll feel considerable force exerted on your body by the
frictionless surface, but it will be normal to that surface..

Similarly, the frictionless bearing can still exert a normal force on
the spindle/axle but it won't exert a torque since that would require a
tangential force.

[Jose[_1_]]

> The Rocket takes a small amount of matter and throws it at great speed
> in X direction, getting and equal and opposite reaction in the opposite
> direction Y... The prop grabs a large amount of air and throws it in X
> direction, getting an equal and opposite reaction in Y... The principal
> is the EXACT same.

Yes, inasmuch as it is action-reaction by Newton. The nit I was trying
to pick was that a propeller is viewed (correctly) as part of the
airplane, and the exhaust fire is also viewed (albeit incorrectly) as
part of the rocket.

The rocket pushes against the fire (in the nozzle, which =is= part of
the rocket). The airplane pushes against the air (against the
propeller, which is part of the airplane). These forces make the
vehicles go.

Although the rocket exhaust does in fact push against the air, the
exhaust isn't part of the rocket, and that "pushing" doesn't make the
rocket go.

Jose
--
"There are 3 secrets to the perfect landing. Unfortunately, nobody knows
what they are." - (mike).
for Email, make the obvious change in the address.

[Matt Whiting]

EridanMan wrote:
> Jose...
>
> not to be too much of an anal nitpicker, but actually, props and
> rockets DO work in the same manner...

Not exactly the same. Rockets work in a vacuum, but propellors do not.

Matt