Can a Plane on a Treadmill Take Off?

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

"cjcampbell" wrote in message
oups.com

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.

Why does the conveyor belt speed have anything to do with the airspeed of
the airplane?

--
John T
http://tknowlogy.com/TknoFlyer
Reduce spam. Use Sender Policy Framework: http://spf.pobox.com
____________________

"cjcampbell" wrote in message

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.

Then you may not be ready for this:

http://www.mste.uiuc.edu/reese/monty/monty.htm

moo

Happy Dog wrote:
"cjcampbell" wrote in message

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.

Then you may not be ready for this:

http://www.mste.uiuc.edu/reese/monty/monty.htm


Now I have a headache. And they call me a troll and a Nazi. :-)

Now I have a headache. And they call me a troll and a Nazi. :-)

That's right, you troll posting, rat bast__d, head banging fascist!
Beginning a thread that *should* be able to be unraveled by a cross-eyed 6
year old, is evil, pure evil. I hope your head inflates to twice it's
normal size, before becoming pink mist! bfg

Well, at least the "pure evil" part is true!

This whole thing has been quite amazing. Who would'a thunk?
--
Jim in NC

CJ, please let us know when the light bulb finally goes on.

"cjcampbell" wrote

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.

Jon Woellhaf wrote:
CJ, please let us know when the light bulb finally goes on.


I am not a real fast learner, but I have some reputation, possibly
undeserved, for intelligence. The lightbulb will probably go on in the
middle of the night. Serves me right for even bringing it up. :-)

Jon Woellhaf wrote:
CJ, please let us know when the light bulb finally goes on.

"cjcampbell" wrote

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.

Okay, I see why the plane moves forward normally no matter how fast the
treadmill is going and even why it would not work in an automobile.

As for that Monty Hall thing, I see that it works, but I have not
figured out why it works yet.

There are certainly some strange things in the world.

176. cjcampbell
Feb 6, 9:41 pm show options

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From: "cjcampbell" - Find messages by
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Date: 6 Feb 2006 18:41:35 -0800
Local: Mon, Feb 6 2006 9:41 pm
Subject: Can a Plane on a Treadmill Take Off?
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"cjcampbell" wrote

Okay, I see why the plane moves forward normally no matter how fast the
treadmill is going and even why it would not work in an automobile.

Well, not exactly. This dead horse is fun to beat. Suppose I tell you
the car is going forward at 60 mph. That means the belt is going the
other way at 60, right? The speedometer would be indicating 120.

The OP said the belt is moving backward as fast as the whatever is
moving forward. When you substitute real numbers into the thing it
becomes more clear.

Or not.