Can a Plane on a Treadmill Take Off?

In article ,
says...

"Dave Doe" wrote in message
. nz...
In article ,
says...
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 - are you then talking about a
big long flat tire of say infinite length. Sorry bud, can't make the
initial assumption that's been made - as it's on a tire, and yep, even
that point, at that time - has the centripetal force.

--
Duncan

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


When this question was raised on Sci.aeronautics it lasted 14 replies, (as
archived by Google groups, but I think that some other posts were dropped by
the news servers.)

http://groups.google.ca/group/sci.aeronautics/browse_thread/thread/e344b133e57880a0/57a2a6789dd92bf6?lnk=st&q=(treadmill)+group%3Asci. aeronautics&rnum=1&hl=en#57a2a6789dd92bf6

One of the posters raised the issue of what would happen when the aircraft
returned for landing.

we are up to about 110 replies here on r.a.s, r.a.p.

A similar question was posed in the Airliners.net forums, what a great
discussion it was! See he
http://www.airliners.net/discussions...d.main/136068/ over
400 replies!

I am quite surprised that this question has received the amount of
consideration that it has. Must be a slow news month or maybe is an
indication that there are more people thinking about flying than there are
actually doing it.

In article , rmoore16
@tampabay.rr.com says...
BillJ wrote
The earth is a treadmill. Goes about about 900 knots (at equator).
Does that bother your takeoff? Suppore treadmill stopped (rotation
stopped). Takeoffs any different?

You forgot one major difference....in the case of the earth, the
airmass is travelling at the same 900kts, ignoring any localized
wind effect....not so in the treadmill case.

So when a treadmill runs the wind starts blowing ? OK... wot are yer
saying then?

--
Duncan

"Dave Doe" wrote in message
. nz...
In article ,
says...

"Dave Doe" wrote in message
. nz...
In article ,
says...
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.

--
Duncan

"cjcampbell" wrote

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.

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.

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. If the
airplane is standing still because the conveyor is moving backwards at the
same speed that the airplane is moving across the ground at, then the
airspeed will still be 10 kts.

If the conveyor keeps the airplane standing still relative to the ground,
then it cannot take off. If it could, then we'd all have problems during
run up because the brakes do the same thing that the theoretical conveyor
does - prevent motion across the ground.

BDS

"BDS" wrote in message
t...

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.

Yes, but an airplane isn't propelled by its feet.

"BDS" wrote in message
t...

50 kts of airspeed is by moving across the ground at 50 kts. If the
airplane is standing still because the conveyor is moving backwards at the
same speed that the airplane is moving across the ground at, then the
airspeed will still be 10 kts.

But the airplane *isn't* standing still (as others have pointed out).

Since the wheels are able to spin freely, the reverse thrust by the
conveyor belt is *not* transferred past the wheels to the plane's
fuselage, and so the only remaining applied force is the unbalanced
forward force of the thrust of the engine.

The conveyor *doesn't* "drag" the plane backwards to compensate
for the engine's thrust. All it does (as others have pointed out) is
spin the wheels faster.

If the conveyor keeps the airplane standing still relative to the ground,

It doesn't.

(Don't worry... I didn't understand it at first either.)

BDS

Jeff Shirton (PP-ASEL)

"One of the posters raised the issue of what would happen when the
aircraft
returned for landing."

If the belt were moving backwards at the speed of the aircraft when it
touched down, it would be similar to landing with that much tailwind,
basically, your ground speed would double you airspeed at touch down.
Jester

Dave Doe wrote:


Try this for a brain scrambler. Think about a tire on your car, driving down
the highway. 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.

http://www.wordiq.com/definition/Centripetal

Well, I'm impressed that you know of the existence of centripetal
force. But in what possible way do you think it negates the comment
about the speeds (relative to the ground) of points at the top and
bottom of the tire on a moving car?
--
Alex -- Replace "nospam" with "mail" to reply by email. Checked infrequently.

"Peter Duniho" wrote:

"alexy" wrote in message
.. .
Yes, the problem could have been made uninteresting by removing any
ambiguity. But as stated, it is very common (almost universal) to
speak of movement of a terrestrial object with respect to the surface
of the earth. If another frame of reference is intended, it is almost
always specified.

Very amusing.

According to you:

On the one hand, the problem is uninteresting if one removes the ambiguity
in the phrasing.

On the other hand, there is no ambiguity, because if a different frame of
reference were intended, "it is almost always specified".

So, the logical conclusion you arrive it in your post is that the problem is
uninteresting.

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.

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