Can a Plane on a Treadmill Take Off?

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.

There will be airspeed felt by the plane in the area of the propellor
wash. Out of the prop wash, since the plane is not moving relative to
the surrounding air, there will be no relative wind felt by the
airplane. The airplane MIGHT take off, but it will not be a normal
takeoff, at least not for a normal airplane with 36' wingspan and a 6'
propellor. I really don't think there is enough information to know the
answer for sure. Too many unknowns.

This is one of these "frame of reference" problems.

"Doug" wrote in message
oups.com...
There will be airspeed felt by the plane in the area of the propellor
wash. Out of the prop wash, since the plane is not moving relative to
the surrounding air, there will be no relative wind felt by the
airplane. The airplane MIGHT take off, but it will not be a normal
takeoff, at least not for a normal airplane with 36' wingspan and a 6'
propellor. I really don't think there is enough information to know the
answer for sure. Too many unknowns.

This is one of these "frame of reference" problems.

Re-read it, Doug. The plane is not getting its motion from the wheels, so
it matters not what the wheels or wheel speed is doing.
--
Jim in NC

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.

"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

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.

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.

That's not what the original problem stated. And we have explained at least
ten times why the conveyor belt CANNOT prevent the plane from moving
forward. My attempt, an earlier post:

You are taking the statement 'a conveyer belt that moves in the opposite
direction at exactly the speed that the airplane is moving
forward' to mean that somehow there is a force being applied to the mass of
the aircraft, equal and opposite the thrust generated by the propellor. The
only place the treadmill can exert any force an the airplane is the only
place the treadmill is touching the airplane: the wheels. Any motion of the
treadmill belt will be translated into rotation of the wheels. This will not
prevent the aircraft from moving forward, through the air and taking off.

Greg,

If you have a motoroized conveyor which
always reduces the plane's forward movement to zero,


Nowhere does it say that in the question.

--
Thomas Borchert (EDDH)

First I'm not a pilot.... But the engine is providing thrust, not driving
the wheels like a car. The airplane is gonna move regardless of what speed
the wheels are or are not turning. What the wheels do is only slightly
relevant if at all unless you're holding the brake....and even that wouldn't
matter if you're on a treadmill. Second.....are we talking about a
treadmill or a conveyer belt? The treadmill may or may not move at all
relative to the world if it's the "classic" kind ... (i.e. non-motorized).
Depends on whether the wheels or treadmill has better bearings.

"Morgans" wrote in message
...

"Doug" wrote in message
oups.com...
What is keeping the airplane's speed up with the conveyor belt? The
propeller. Said propeller moves air. Air causes lift. The problem is
more complicated than it seems to be at first read.

Another way to say it; it had better be a long conveyer belt, cause the
prop
is pulling the plane forward, without caring how fast the wheels are
going.
That will make the necessary airspeed to lift off.
--
Jim in NC