Can a Plane on a Treadmill Take Off?

I would but everytime I start to move toward the edge, this damn treadmill
pulls me back in...

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Travis

wrote in message
oups.com...
What an inane thread! I am amazed at how many people are arguing about
such a silly subject. Get a life people!

Dean

cjcampbell wrote:
Saw this question on "The Straight Dope" and I thought it was amusing.

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

The question goes like this:

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

Cecil Adams (world's smartest human being) says that it will take off
normally.

alexy wrote:
Thomas Borchert wrote:

Alexy,

The conveyor is programmed to move in such a way as to maintain the
aircraft at an airspeed of zero as measured at the pitot.

Absolutely, if you CHANGED the problem, and restated it as above, then
it wouldn't fly.


Actually, you couldn't do that - which is another point the question
makes.

True, from a practical standpoint. As far as the thought experiment
goes, you could if the conveyer moved fast enough that the rolling
friction of the tires plus the bearing friction of the wheels exactly
offset the thrust of the plane's propulsion system.

The question, though, says that the wheels are built to take it. They
must have frictionless bearings. g

Accelerating the mass to the same velocity requires the same energy
regardless of what the surface is doing but wheel drag cannot be totally
ignored.

Why did you suggest that the car is providing the energy for the conveyor?
This would imply wheels with normal friction behavior but a frictionless
conveyor with a brake. The conveyor needs to be frictionless for you theory
that no additional energy is needed but a brake to keep it from being flung
backwards preventing forward motion of the car.

Since the same frictionless conveyor would get dragged along under an
accelerating plane, it seems like a strange experimental model.

A conveyor that is motor driven but controlled makes a more consistent
model.

I agree that very little additional thrust is necessary (either from the
wheels of a car or from the propeller of a plane) to counteract the
counter-moving conveyor. But some additional energy will be needed due to
the additional drag provided by the faster spinning wheels (both for the car
and the plane).

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Travis
"alexy" wrote in message
...
"cjcampbell" wrote:


Tony wrote:
If the car had an airspeed indicator it would, I agree, indicate 60. In
the model I suggested the car is moving to the north at 60, the
treadmill to the south at 60, and the speedometer will indicate 120.

If the car's airspeed indicator said 60 then the speedometer will
indicate 120. But the car would then need to expend the same energy to
accelerate to 60 as it would to accelerate to 120 on a stationary road.
Nope. The same energy as it would take to accelerate to 60 on an
ordinary road, assuming that the mechanical system of the conveyor is
taking care of its motion. The work being done is to accelerate the
same mass to the same velocity in either case. If the car is providing
the energy to move the conveyer (reasonable, if its mass and friction
loads are less than those of the car), how much additional energy it
takes will depend on the conveyer.

An aircraft would need no additional power to accelerate to 60 on a
treadmill.
True. The same laws of physics apply to the car as well.
--
Alex -- Replace "nospam" with "mail" to reply by email. Checked
infrequently.

He suggested a wind that is dynamic and tied to the speed of the conveyor
(and therefore also tied to the speed of the plane).

The plane can feel the conveyor - wheels are not frictionless. The friction
is not even insignificant. An amplified example would be trying to take off
in slushy snow. I think you will agree that the plane will feel that drag.

Back to the original puzzle - yes, the plane will accelerate and takeoff but
it will be a longer takeoff roll to overcome the increasing friction of the
wheels turning at twice the normal speed.

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Travis
"cjcampbell" wrote in message
oups.com...

darthpup wrote:
Must consider the wind at time of experiment. If wind is same speed as
conveyor then real problem??

Wind has nothing to do with it. The airplane will accelerate and move
down the treadmill just as it would a stationary runway. It cannot feel
the treadmill at all. The wheels can, but the wheels spin independently
of the thrust generated by an airplane.

It only says that they can take it. It doesn't say why. My plane lifts off
at 60mph. I'm sure the bearings and wheels would handle 120mph but they
aren't frictionless.

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Travis
"cjcampbell" wrote in message
ups.com...

alexy wrote:
Thomas Borchert wrote:

Alexy,

The conveyor is programmed to move in such a way as to maintain the
aircraft at an airspeed of zero as measured at the pitot.

Absolutely, if you CHANGED the problem, and restated it as above, then
it wouldn't fly.


Actually, you couldn't do that - which is another point the question
makes.

True, from a practical standpoint. As far as the thought experiment
goes, you could if the conveyer moved fast enough that the rolling
friction of the tires plus the bearing friction of the wheels exactly
offset the thrust of the plane's propulsion system.

The question, though, says that the wheels are built to take it. They
must have frictionless bearings. g

("Travis Marlatte" wrote)
I would but everytime I start to move toward the edge, this damn treadmill
pulls me back in...


I'm going to have nightmares about those darn monkeys in the original Wizard
of Oz books.


Montblack
Arrgh. Wheels!

"cjcampbell" wrote in message
oups.com...
If the car's airspeed indicator said 60 then the speedometer will
indicate 120. But the car would then need to expend the same energy to
accelerate to 60 as it would to accelerate to 120 on a stationary road.

No, not really. Most of the horsepower of a car is used to counteract
aerodynamic drag, at that speed. Unless the treadmill (conveyor belt,
whatever) somehow gets the air above it to move rearward along with the
belt, the car barely has to use more power than it would accelerating to,
and cruising at, 60 mph on a regular road. It absolutely doesn't require
anywhere near as much power as it would to travel at 120 mph on a regular
road.

Pete

BUT...the AIRplane isn't in the AIR yet!

Ok, there is some friction involved.

Let's say that the airplane will take off in 1010 instead of 1000 feet,
ok?

Piero

Peter,

I find this outcome hilarious.


I agree. Also, I am always amused at how hard people here find it to
just say "Oops, I was wrong, sorry."

--
Thomas Borchert (EDDH)

Greg,

If you have a motoroized conveyor which
always reduces the plane's forward movement to zero,


Nowhere does it say that in the question.

--
Thomas Borchert (EDDH)