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

"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

"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

("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)

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.

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

"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

"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

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.

"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.

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.