Can a Plane on a Treadmill Take Off?

"BDS" wrote:

Maybe he's not so smart after all :)
Maybe not, but smart enough to see this one.

On a calm day you can run and feel a wind on your face because you are
moving across the ground as well as through the air. But, if you run on a
treadmill there will be no wind because you are not moving through the air -
the air is calm so it has no relative motion with respect to the ground.
Neither do you when you run on a treadmill.
True. Irrelevant, but true.

Assume the airplane is on the conveyor and there is a 10 kt headwind, and
assume we need 60 kts for takeoff. The only way to generate the additional
50 kts of airspeed is by moving across the ground at 50 kts.
Right so far.

If the
airplane is standing still
Hold that thought...
because the conveyor is moving backwards at the
same speed that the airplane is moving across the ground at
Skip back up to see what speed you say the airplane is moving across
the ground. Then go back to the original question and figure out what
speed the conveyor must be moving when the airplane is not moving.


If the conveyor keeps the airplane standing still relative to the ground,
then it cannot take off.
Yeah, but the original statement of the problem made no such claim.


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

Maybe he's not so smart after all :)

On a calm day you can run and feel a wind on your face because you are
moving across the ground as well as through the air. But, if you run on a
treadmill there will be no wind because you are not moving through the air -
the air is calm so it has no relative motion with respect to the ground.
Neither do you when you run on a treadmill.


D*mn you're dumb. Oh sorry, was I thinking out loud? A thousand
pardons. :^)

The plane is NOT powered at the wheels! In this case the plane will be
going 60kts forward relative to the surrounding air and 120kts forward
relative to the treadmill. Think about it.

The Monk

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"Dave Doe" wrote in message
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"Dave Doe" wrote in message
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At the point where the tire contacts the ground, it's speed is
zero. 180° away, at the top, it is moving forward at twice the speed
of
the
car.

Negative - yer forgetting centripetal force.

? Negative what? Talking about a point on the surface of the tire, not
the
wheel as a whole. Centripital force has nothing to do with the forward
velocity of that point (how it travels in one axis).

Are you talking about a round tire or not
What other kind of tire is there?
. Sorry bud, can't make the
initial assumption that's been made -
I'm not your bud,. And what assumption are you talking about?
as it's on a tire, and yep, even
that point, at that time - has the centripetal force.

We aren't talking about the forces at work on the wheel or tire, we are
talking about the forward velocity. I can see this concept is lost on you.

There is no forward velocity - there *is* a change in angular momentum
though. Do you not understand that concept?

--
Duncan

Dave Doe wrote:

We aren't talking about the forces at work on the wheel or tire, we are
talking about the forward velocity. I can see this concept is lost on you.

There is no forward velocity - there *is* a change in angular momentum
though. Do you not understand that concept?

I proudly profess to not understand that a point on the top of a tire
does not move at twice the velocity of the axis of the wheel on which
that tire is mounted.
--
Alex -- Replace "nospam" with "mail" to reply by email. Checked infrequently.

On 4 Feb 2006 20:45:34 -0800, "Flyingmonk" wrote:

The plane is NOT powered at the wheels! In this case the plane will be
going 60kts forward relative to the surrounding air and 120kts forward
relative to the treadmill. Think about it.

I reckon that's true, given the question posed in "The Straight Dope,"
(I've been too lazy to read it myself, but I gather from the other
responses that what you say above is what Adams had in mind.) but what
is the point of the original question in that case? Is it just to
trap a sloppy reader into thinking it's all about a crackpot VTOL
methodology?

The more interesting question is whether you could land real short by
using the treadmill.

Don

I undertand that, for any one given point on a wheel, mounted on a vehicle,
traveling horizontally, more or less, there is a forward velocity (not
constant) for exactly one half the time, and a rearward velocity (not
constant) for exactly half the time, in relation the wheels' point of
rotation. The average of this constantly changing velocity just happens to
be the same as the forward speed of the vehicle.

There is no forward velocity - there *is* a change in angular momentum
though. Do you not understand that concept?

--
Duncan

The more interesting question is whether you could land real short by
using the treadmill.

The treadmill is irrelevant; it is the relative wind that matters.
Whether you are standing on solid ground or on a treadmill, if you have
a head wind of 60kts, you will be airborne period.

The Monk

"jesse" wrote

I read some of my posts in response to comments made about me. The
spelling, punctuation, and grammar mistakes are all because of my
blatant laziness, and excitement to get my post out. \\

Jesse, is that you? I didn't recognize you!

You will find that you will be taken more seriously around here, if you
continue you attempts at correctly (minus a few typo's) written posts. The
small mistakes will always creep in, it seems, no matter how hard we all
try. In this case, a small one was there,

Many people helped my as I was .....

but I'm almost sure there is a mistake in me post. It is a rule, I was
told. g
--
Jim in NC

For an uninteresting problem, it sure generated a lot of traffic.

True. Which really surprised me. When I first saw CJ's post, I thought
it was too obvious to draw in this kind of activity.

Indeed. If it was not a well recognized name posting, it would be a post
more worthy of a troll.

Dang you, CJ! Please refrain, next time!

Or if your post was moving backwards at twice the speed of light, did it
ever appear at all, and did it erase all of the activity before it? g
--
Jim in NC

"Flyingmonk" wrote

Depends on the airplane, certain lpanes are built in such a way that
they can actually attain enough lift just from the prop wash alone.

How many buckets of prop wash would it take?