Can a Plane on a Treadmill Take Off?

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.

"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.

"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.

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

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

There's nothing wrong with being interested in a brain-teaser.

Get a life people!

Oddly, your own busy life leaves you time not only to read a thread you're
not even interested in, but also to post here announcing your lack of
interest.

--Gary

Gary wrote:
What an inane thread! I am amazed at how many people are arguing about
such a silly subject.

There's nothing wrong with being interested in a brain-teaser.

Get a life people!

Oddly, your own busy life leaves you time not only to read a thread you're
not even interested in, but also to post here announcing your lack of
interest.

It is just another way for Dean to tell us that his life is much more
fulfilling than ours Gary. lol

The Monk

An idea that popped into my mind...
ywo subject question lines...
1. Can a plane on a treadmill take off?

2. Can a plane take off from a treadmill?

In the first instance, the airplane is attached to the
treadmill and would have to lift the weight and shape of the
treadmill. In the second, the airplane would behave
differntly depending on whether the treadmill was powered or
just a belt on rollers.
a. If just a belt on rollers, the engine thrust would drive
the airplane forward until it was not on the treadmill
anymore, thus it would have air movement over the wings and
would take-off. If the brakes were not locked, either or
both the tires and treadmill would "roll." If the brtakes
were set, the treadmill would roll and the airplane would
likely come to a stop when it departed the treadmill unless
it was alrady at flying speed.
b. If the treadmill was powered [and everything was timed
in sync] the belt would be accelerating rearward and the
engine thrust would be pulling forward at the same rate,
thus the airframe mounted wigs would have near zero airspeed
and lift and would not fly.
b1. If the treadmill was powered and ran forward, it would
act as a catapult and launch the airplane or at least
assist.


Hey, let's build a really big treadmill and try several
different airplane types, such as a Helio, a Maule, a Cessna
Caravan, and a C5 [a really big treadmill] and see what
happens.


--
The people think the Constitution protects their rights;
But government sees it as an obstacle to be overcome.
some support
http://www.usdoj.gov/olc/secondamendment2.htm
See http://www.fija.org/ more about your rights and duties.


"Flyingmonk" wrote in message
oups.com...
| Gary wrote:
| What an inane thread! I am amazed at how many people
are arguing about
| such a silly subject.
|
| There's nothing wrong with being interested in a
brain-teaser.
|
| Get a life people!
|
| Oddly, your own busy life leaves you time not only to
read a thread you're
| not even interested in, but also to post here announcing
your lack of
| interest.
|
| It is just another way for Dean to tell us that his life
is much more
| fulfilling than ours Gary. lol
|
| The Monk
|

"Jim Macklin" wrote:


b. If the treadmill was powered [and everything was timed
in sync] the belt would be accelerating rearward and the
engine thrust would be pulling forward at the same rate,
thus the airframe mounted wigs would have near zero airspeed
and lift and would not fly.

Just to "set the hook" here, are you saying that it will be possible
to have the conveyer move backwards fast enough that the plane remains
still, even under full power, and with no brakes on?
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Alex -- Replace "nospam" with "mail" to reply by email. Checked infrequently.

"alexy" wrote in message
news
Just to "set the hook" here, are you saying that it will be possible
to have the conveyer move backwards fast enough that the plane remains
still, even under full power, and with no brakes on?

I thought you had already established that it would be possible, and that
the treadmill speed is "somewhat below the speed of light"? You didn't
appear to solve the "materials integrity" aspect of the problem, but that
seems like a minor quibble.

Pete

"Peter Duniho" wrote:

"alexy" wrote in message
news
Just to "set the hook" here, are you saying that it will be possible
to have the conveyer move backwards fast enough that the plane remains
still, even under full power, and with no brakes on?

I thought you had already established that it would be possible, and that
the treadmill speed is "somewhat below the speed of light"? You didn't
appear to solve the "materials integrity" aspect of the problem, but that
seems like a minor quibble.


No fair; that's the next question, not to be asked out of order!! ;-)

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

Another pilot slips into the tar pit.

"alexy" wrote in message
news
"Jim Macklin" wrote:


b. If the treadmill was powered [and everything was timed
in sync] the belt would be accelerating rearward and the
engine thrust would be pulling forward at the same rate,
thus the airframe mounted wigs would have near zero airspeed
and lift and would not fly.

Just to "set the hook" here, are you saying that it will be possible
to have the conveyer move backwards fast enough that the plane remains
still, even under full power, and with no brakes on?
--
Alex -- Replace "nospam" with "mail" to reply by email. Checked
infrequently.