Can a Plane on a Treadmill Take Off?

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.

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.

An aircraft would need no additional power to accelerate to 60 on a
treadmill.

I agree that it would not require much more additional power to overcome the
additional friction drag of wheels spinning at twice the normal speed but it
is not zero.


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

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.

An aircraft would need no additional power to accelerate to 60 on a
treadmill.

"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.

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.

"Travis Marlatte" wrote:

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.

True. Another factor that I ignored as being insignificant (and this
applies to the plane or car) is the extra energy it takes to provide
the angular acceleration of the wheel to higher rotational velocities.
E.g, at speed, one car includes 4 flywheels spinning with rim
velocities of 60mph, while the other car has 4 flywheels spinning with
rim velocities of 120mph. This additional energy need will cause
slower acceleration if the same power is available.

Why did you suggest that the car is providing the energy for the conveyor?
We've had one recent poster who apparently thought that the power
source for moving the conveyer was key to the problem. I'm not
suggesting THAT the car was providing the energy, but only examining
what IF it did.

This would imply wheels with normal friction behavior but a frictionless
conveyor with a brake.
Not needed. As long as the conveyer has less friction and mass than
the car, and has a brake to control its speed, the car can power it.
And how much power that absorbs will determine how much the car's
acceleration is lowed down. At the limit, it is CJ's speculation of
the car's acceleration to 120 (on the speedometer) matching a regular
road acceleration to 120.

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

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).
And to accelerate the wheels to a higher angular velocity, assuming
they are not massless.
--
Alex -- Replace "nospam" with "mail" to reply by email. Checked infrequently.

"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

cjcampbell wrote

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.


An aircraft would need no additional power to accelerate to 60 on a
treadmill.

To which I'll note that you're on the right track, but remember kinetic
energy varies as velocity squared: it takes 4 times the energy (at non
relativistic velocities) to get to 120 as it does to 60: actually a lot
more than that because windage losses and the like are not linear,
either.

"Tony" wrote:


cjcampbell wrote

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.


An aircraft would need no additional power to accelerate to 60 on a
treadmill.

To which I'll note that you're on the right track,
Not really. Except for minor factors (having to do with wheel friction
and mass), getting a car to 60 (ground speed) on the treadmill takes
no more energy than getting it to 60 on a regular road.
but remember kinetic
energy varies as velocity squared: it takes 4 times the energy (at non
relativistic velocities) to get to 120 as it does to 60: actually a lot
more than that because windage losses and the like are not linear,
either.

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

("Tony" wrote)
An aircraft would need no additional power to accelerate to 60 on a
treadmill.


Yeah, well I just set that sucker to...."Incline Setting # 12"

If you set your comms to the frequency, posted up there under that TV in
front of you, you'll be able to listen to Oprah.


Montblack