Can a Plane on a Treadmill Take Off?

Once again: assume the airplane is moving at 60 miles an hour to the
north. The tread mill then by definition is turning so that the belt is
going 60 miles an hour to the south. The wheels are turning as though
the airplane was going 120 miles an hour on the runway. If 60 is enough
airspeed for this airplane to lift off, the pilot just needs to apply
back pressure to the yoke. It's a question nicely phrased to make some
of us draw the wrong inferences: that's how come this is the 197th
response, and I think it's correct but then again others who don't
agree think they are correct as well. They have a right to be wrong
:-)!

"Thomas Borchert" wrote in message
...
What irks me most is how violent people attack those of a different
opinion over this rather trivial matter - all the while being wrong...

I find it amusing, *because* of the strong correlation between abusive
language and ignorance.

As you noted, the folks who "get it" have been reasonably polite, while the
people who use the worst language, calling others "idiots" and "morons" etc
are the ones who don't have a clue.

I find this outcome hilarious. I don't mind the name-calling; it's par for
the course on Usenet, and the above-noted correlation holds true nearly all
of the time, not just in this thread. It's an easy way to filter out the
people who really *are* morons.

Pete

Actually, I believe you are incorrect. That passage only implies the
belt will move inversely proportional to the wheels on the plane;
meaning the delta is conantly zero. They never actually state the
plane is moving forward. Thus, with a wheel speed of zero, the delta
is still zero. Therefore, I would suggest the only correct answer,
based on that sole passage is, "no".

Now, if we look at the actual question posted on straight dope, the
answer is, "maybe", for many reasons. Having said that, we can
*easily* tear up the explanation provided on straight dope. Simple
fact is, Cecil makes a huge assumption which causes his whole house of
cards to come tumbling down. Simply stated, there is nothing which
precludes the belt from being motorized. Given a sophisticaed enough
implementation, one can absolutely state, the plane would never leave
the ground; assuming no head wind is involved.

Long of the short, there is simply not enough information to provide an
exact answer, other than maybe. If the belt is not motorized, AND the
plane is moving (positive delta), yes, the plane will fly. If the belt
is motorized, and it is intelligent enough to ensure a belt/wheel delta
of zero, no, the plane will never fly.

Sorry....the plane would not fly as you described. For if your
statement were true, we would not need wings...only a engine and a
prop. We must have air flow over the wings to generate lift. Propwash
does not generate enough lift, especially for planes wihch have a
centrally located engine/prop between the wings.

Only if you make many assumptions. Otherwise, he's wrong. The only
correct answer is "unknown" because of lacking information. The only
way to get off of, "unknown", is to make assumptions, which Cecil
happily did. Therefore, if he's allowed to make assumptions, so are
the rest of us. Which means, the answer is equally, "no".

Either way, he's wrong because he made an assumption or he's wrong
because we are allowed to make assumptions in the other direction,
thusly proving he's wrong.

"Greg Copeland" wrote

Sorry....the plane would not fly as you described. For if your
statement were true, we would not need wings...only a engine and a
prop. We must have air flow over the wings to generate lift. Propwash
does not generate enough lift, especially for planes wihch have a
centrally located engine/prop between the wings.

Nitpicking aside, I suspect that everyone agrees that in order for the plane
to take off it must move forward along the conveyor. Since the prop applies
a force to the plane which acts independent of what the conveyor and the
wheels are doing, the plane can definitely move forward, and therefore it
can take off.

Tie a rope to the plane and to your car which is parked in front of the
conveyor and not on the belt. Start the conveyor and run the belt at any
speed you wish. The plane sits still on the conveyor as the wheels spin
away. Now, if you drive your car forward the plane will move forward along
the conveyor at the speed that you are driving your car forward, regardless
of how fast the conveyor belt is moving. The conveyor cannot keep the plane
from moving forward, it can only spin the plane's wheels. The example says
that the belt moves backwards at the same speed that the plane moves
forward, but that doesn't mean that the plane must be standing still.

Get rid of the rope and the car and use the prop and the engine to pull you
forward along the conveyor (because it pulls you by exerting a force on the
air) and voila, you're flyin' the friendly skies.

BDS

"Greg Copeland" wrote:

Actually, I believe you are incorrect. That passage only implies the
belt will move inversely proportional to the wheels on the plane;
What problem are you reading? The one I saw said "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." I didn't see
anything about wheel speed mentioned or implied. If you inferred it,
I'd suggest that is a product of your inference, not of the author's
implication.

meaning the delta is conantly zero.
What delta?
They never actually state the
plane is moving forward.
That's true. One does have to make the radical assumption that the
question is not about a plane parked on a non moving treadmill.

Thus, with a wheel speed of zero, the delta
is still zero. Therefore, I would suggest the only correct answer,
based on that sole passage is, "no".

Now, if we look at the actual question posted on straight dope, the
answer is, "maybe", for many reasons. Having said that, we can
*easily* tear up the explanation provided on straight dope. Simple
fact is, Cecil makes a huge assumption which causes his whole house of
cards to come tumbling down. Simply stated, there is nothing which
precludes the belt from being motorized.
In fact, I would argue that it would need to be motorized to go
backwards at the same speed at which the plane is moving forward. In
what way does that "cause the whole house of cards to come tumbling
down"?

Given a sophisticaed enough
implementation, one can absolutely state, the plane would never leave
the ground; assuming no head wind is involved.

Long of the short, there is simply not enough information to provide an
exact answer, other than maybe. If the belt is not motorized, AND the
plane is moving (positive delta), yes, the plane will fly. If the belt
is motorized, and it is intelligent enough to ensure a belt/wheel delta
of zero, no, the plane will never fly.
Of course, if it did that, it would assure that the plane did not move
forward, thus meaning that the belt would not move forward, which is
back to your rather uninteresting parked plane analysis. I think it
far more likely that the problem intended what it said, that the
conveyor moves backward at the same rate the plane moves forward,
rather than your different problem statement having to do with wheel
speed.


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

What problem are you reading?

The one provided....but I clearly stated that I was replying to a
speciifc section...see message I replied to. What are you reading?
The section is,
"a conveyer belt that moves in the opposite direction at exactly the speed that the airplane is
moving forward."

I didn't see anything about wheel speed mentioned or implied. If you inferred it,
I'd suggest that is a product of your inference, not of the author's
implication.

Actually, you're reading into the statement...which is exactly my
point. Yet, after pointing this out, you still completely missed it.
Even funnier, you then turn an imply that I completley missed the boat.
If I state, "when I jump out of a window, I will hit the ground", it
does not mean I'm falling as I type this. It clearly means, when one
happens, so will the other. It in no way, shape, or form, implies that
it's happening or has happened. Which clearly opens the door that the
speed is zero, or at least can be. A plane will not fly with zero air
over it's wings, producing zero lift.

In other words, you ASSUMED that speed was not zero and Cecil ASSUMED
the runway was not driven by it's own motor. Lots of assumptions.
What are you reading?

You then go on to talk about left turns you madel. Simply stated, it
is *all* about wheel speed and lift; depending on wihch assumptions you
want to make. If the plane is moving forward, the wheel is turning
faster than the treadmill.; thusly allowing you to generate lift as
forward motion allows for air over the wings. If the wheel is turning
slower than the treadmill, then you are moving backwards. Thusly, a
delta of zero or less means NO LIFT...NO FLIGHT.

This isn't exactly rocket science...

Nitpicking aside, I suspect that everyone agrees that in order for the plane to take off it must move
forward along the conveyor.

Which is exactly my point! If you have a motoroized conveyor which
always reduces the plane's forward movement to zero, no lift is
generated, preventing the plane from flying. In other words, the plane
generates lift by moving air over its wings. It moves air over its
wings by moving forward. If you zero out forward movement, by a
motorized conveyor, resulting in a zero delta, no lift is generated.
it's a question of the plane making forward movement.

Specifically, as it relates to your reply, while prop wash would indeed
produce some lift over the wing, it would not be nearly enough to
obtain take off....which is why we have wings. Thusly, if forward
movement is zero and you're full throttle, you're not airbound....which
is exaclty the same thing as a plane with no wings.

"Greg Copeland" wrote
Nitpicking aside, I suspect that everyone agrees that in order for the
plane to take off it must move
forward along the conveyor.

Which is exactly my point! If you have a motoroized conveyor which
always reduces the plane's forward movement to zero

It doesn't say that the plane has no forward movement - it says that the
conveyor moves backwards at the same speed at which the plane moves
forward - that does not prevent the plane from moving forward.