Can a Plane on a Treadmill Take Off?

It's one of those strange Usenet phenomena.

How do start a big argument on Usenet? Ask a simple question.

"Brien K. Meehan" wrote in message
oups.com...
It's one of those strange Usenet phenomena.

How do start a big argument on Usenet? Ask a simple question.


It would be fun to see this worked out on 'Mythbusters'.

Mike

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

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.

Flyingmonk wrote:
It's surprising and refreshing
that this thread, with so many posts, hasn't (yet) degraded into a
flame-fest. )

Amen to that!

The Monk

Shockingly, no one has even called anyone a Nazi yet, nor has anyone
called me a troll for posting this and then departing for the weekend
without checking back to see if there were any replies. :-)

I hope none of you people are pilots!

All right, dammit, you're a Nazi and a troll. And I'm taking off for a
couple of days. Satisfied?

{;-)


Jim


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

Flyingmonk wrote:
It's surprising and refreshing
that this thread, with so many posts, hasn't (yet) degraded into a
flame-fest. )

Amen to that!

The Monk

Shockingly, no one has even called anyone a Nazi yet, nor has anyone
called me a troll for posting this and then departing for the weekend
without checking back to see if there were any replies. :-)

"Jane! Stop this crazy thing!"

"Montblack" wrote in message
...
("Michael Ware" wrote)
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.

That's one of the best so far.


THE AIRPLANE WILL NOT MOVE. (That's my vote)

The rotating wheels + gravity (Thank you Sir Isaac!) ANCHOR the plane to
the
treadmill. Plane/prop move forward, treadmill/wheels fall back. The plane
is
attached to the wheels. Try it in front of you with a ruler and a magic
marker.

That airplane is doing 150 mph down that runway, only the runway is really
a
treadmill which is matching that speed. End result is = to an Olympic
sprinter on the same treadmill - I can stand next to him for his entire 10
second (27 mph) race.

Lordy. BDS answered this pretty well. But, imagine that the plane is held
still by a rope secured in front of the conveyor. That rope is attached to
a strain guage that measures the force, in kg, say, that the moving conveyor
exerts on the plane. This will increase with the speed of the conveyor, but
let's use a reasonable number and we will see that the force is minimal
since it's only whatever is converted to heat in the wheel bearings.
Probably less than a few hundred watts. The amount of power required to
move the plane forward will be more than required on a stationary runway by
only this much. Dig?


Montblack 83.7
(I thought some of double-digit people needed to be heard from. g)

moo

www.mensa.org

"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