Can a Plane on a Treadmill Take Off?

"Gary Drescher" wrote:

"Don Tuite" wrote in message
.. .
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?

I think the more interesting point is to notice the implications of not
transmitting force through the wheels. Even people who know that planes and
cars differ in that way may fail (at least at first) to draw the appropriate
conclusion about what happens to the treadmill plane when it applies takeoff
power.

Totally irrelevant. The answer is the same for a glider being towed to
take-off by a ground vehicle (except that you would want to change the
rear end or wheel size of the vehicle to cut the final drive ratio in
half, so that it could attain the doubled wheel speed necessary to
attain the needed forward speed.)

--Gary


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

"cjcampbell" wrote in message
oups.com

"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.)

The conveyor belt is simulating groundspeed. How many of you fly airplanes
by reference to groundspeed?

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John T
http://sage1solutions.com/TknoFlyer
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____________________

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.


Oops, my bad. I meant apparent (to the conveyor) groundspeed.
Jester

To : Michael Ware

Maybe you should stop replying, as all you give is negitive feedback to
other people. !!!!!

I'm not sure what negative feedback you are referring to. I just scanned
back through a few of his posts and they seemed pretty reasonable to me. He
also supports the most popular theory - that the plane will accelerate and
fly in spite of the treadmill spinning the tires twice as fast.

I agree.

--
-------------------------------
Travis
"The Flying Scotsman" wrote in message
oups.com...
To : Michael Ware

Maybe you should stop replying, as all you give is negitive feedback to
other people. !!!!!

Nice article explaining this:

http://www.avweb.com/news/columns/191034-1.html

"Helen Woods" wrote in message
...
Nice article explaining this:

http://www.avweb.com/news/columns/191034-1.html


C'mon Helen! .....How can reading that article in 5 minutes possibly
be as much fun as arguing about the problem in a public forum over the
course of 2 days??? ....Huh?!?

Omigod! ....What's happened to me!?! :~(

"cjcampbell" wrote:

"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.)

Now, there are two references to motion in the problem, and the
correct (IMHO) solution is based on both of those motions being from a
consistent frame of reference, i.e., relative to the ground.

The incorrect (IMHO) solution seems to depend on reading these two
motions as related to inconsistent frames of reference, to wit: "An
airplane on a runway sits on a conveyer belt that moves relative to
the surface of the earth in the opposite direction at exactly the
speed that the airplane is moving relative to the surface of the
conveyer [Not sure how those who read it this way fit the word
"forward" into their interpretation.] This reading leads to the
conclusion that the plane is standing still, but flies in the face of
what really would happen if such a device were built, given how a
plane's propulsion is provided -- i.e., this reading of the problem
assumes facts inconsistent with what conceivably could happen were
such a device built. (BTW, many seem to focus on this practical aspect
of propulsion, but that misses the pure logic of the thought
experiment, it seems to me.)

But think about the opposite inconsistent reading of the statement:
"An airplane on a runway sits on a conveyer belt that moves, relative
to the airplane, in the opposite direction at exactly the speed that
the airplane is moving forward relative to the ground." That
inconsistent frame of reference seems just as justifiable as the
other, and is in fact MUCH easier to imagine actually implementing!

I think we should do something to make sure that all future airports
are built with runways that work like this third interpretation of the
stated problem! g
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Alex -- Replace "nospam" with "mail" to reply by email. Checked infrequently.

cjcampbell wrote:
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.

I confess to having difficulty understanding the difference between a
conveyer belt and a treadmill, although it seems important to some
folks.

Cecil does not seem to be arguing that prop wash or jet thrust are
generating enough lift by providing downwash over the wings. He claims
the airplane will take off normally -- that is, the airplane will move
forward just as in a normal takeoff, developing airspeed as it goes. He
also claims that this will not take any extra thrust.

He likens the situation to someone on rollerblades on a treadmill who
is holding onto a rope fixed to an object at the front of the
treadmill. No matter how fast the treadmill is moving, it takes the
same energy to pull yourself to the front of the treadmill as it would
if the treadmill was stopped. The only difference is that the wheels
would turn twice as fast.

Cecil appears to be saying that the airplane cannot be prevented by the
conveyer belt from moving forward, no matter how fast the conveyer belt
moves, because the thrust is generated independently from the wheels.
The airplane will accelerate and take off, using the same length of
conveyer belt as it would an ordinary runway. The only difference is
that the wheels will be spinning twice as fast at rotation as they
would otherwise, thus the caveat "assuming the wheels hold out."

I am not sure I understand why Cecil thinks this. If I understand him
correctly, the drag of the treadmill against the wheels does not
increase just because the treadmill is moving. Okay, I guess I can
believe that. Still, it seems counterintuitive to me that if a plane is
sitting on a conveyer that is moving backwards at exactly the same
speed (I assume they mean groundspeed here) as the airplane is moving
forward that the airplane will move forward at the same speed as if it
was not on a conveyer at all.

Who's on first? Third base!

The Monk