So...about that plane on the treadmill...

"Darkwing" theducksmailATyahoo.com wrote in message
...

"John T" wrote in message
...
"Darkwing" theducksmail"AT"yahoo.com wrote in message


First, the question posed in the link by the OP of this thread is an
incorrect variation of the original. The original problem asks: "A plane
is standing on a giant treadmill. The plane moves in one direction, while
the treadmill moves in the opposite direction and at the same speed as
the plane. Can the plane take off?"

As has been explained, placing a car on the question's treadmill would
result in a stationary vehicle relative to the observer standing beside
the treadmill. The reason is the car derives its propulsion through the
wheels sitting on the treadmill and the speed of the car is measured by
how fast the wheels are turning. The faster the wheels turn, the "faster"
the car moves. However, this is only relative to the treadmill belt. To
the observer standing beside the treadmill, the car is motionless. If the
driver placed his hand out the window, he would feel no wind even though
his "speed" as indicated by the speedometer may be 100 miles per hour.

Hmm. That presumes that "at the same speed as the plane" means "as fast as
necessary to cancel the forward motion." If you take your car analogy and
apply it to the plane, then the treadmill must try to run backwards as fast
as necessary to cancel forward motion - which is, Ah, let's just say
difficult.

To be consistent with your conclusions about the plane's motion, then the
car would also move. Using the object's motion as the defining parameter to
determine the treadmill speed, then a stable state can be reached with
either
1) a plane with forward motion X, treadmill with motion -X, wheels
spinning at 2X, thrust applied to achieve speed X
2) a car with forward motion X, treadmill with motion -X, wheels
spinning at 2X, thrust applied to achieve speed 2X

Accelerate either the plane or the car with X from 0 to, say, 65. The plane
will take off. The car will drive off the end of the treadmill.

John T


Thank you for your reply. Here is my .02, it would seem that the plane
never actually moves in respect to the observer no matter how fast the
treadmill moves, the plane will just take off like it is hovering and then
slowly accelerate away?

I guess I'll have to set this up and try it, I do have a few RC planes
laying around and I have a treadmill so I guess I'll know one way or
another, unless Mythbusters beats me to the punch.

-------------------------------------------------------
DW


DW,

None of the people that believe the plane will fly say that it will fly with
no forward motion. The claim is that the plane will accelerate to flying
speed in spite of the treadmill moving in the opposite direction.

"Bob Noel" wrote in message
...
In article ,
Jose wrote:

The wheels don't have to push on anything for an aircraft to take
off...there's no drivetrain feeding power to the wheels!

Right. Phrasing it the way I did may get people to realize this, or at
least to think about it themselves.

If you put an airplane on the roof of a speeding train, would it take
off? What if the train were shaped like a runway? What if it were very
thin?

hmmmm, if you put the airplane on, say, a fast moving ship, could it
take off?

I wonder....

--
Bob Noel
Looking for a sig the
lawyers will hate


I don't think so. I've seen videos of planes launching from an aircraft
carrier (that's a fast moving ship, right) fall right off the end. I guess
it's because the forward motion of the carrier negated the forward thrust of
the plane.

--
-------------------------------
Travis
Lake N3094P
PWK

Here is my .02, it would seem that the plane never
actually moves in respect to the observer no matter how fast the treadmill
moves, the plane will just take off like it is hovering and then slowly
accelerate away?

How about we make life easy for the moment and forget about the
treadmill. The airplane is magnetically suspended over the runway. No
part of the plane is touching the runway at all. It's all done with
electromagnets. (and for the nitpickers, let's ignore linear induction
motor effects).

The (otherwise ordinary) plane is magnetically suspended over the runway
with nothing touching the runway at all. Can the plane take off? How
does it do so?

Jose
--
"There are 3 secrets to the perfect landing. Unfortunately, nobody knows
what they are." - (mike).
for Email, make the obvious change in the address.

"Travis Marlatte" wrote in message
et...
"Bob Noel" wrote in message
...
In article ,
Jose wrote:

The wheels don't have to push on anything for an aircraft to take
off...there's no drivetrain feeding power to the wheels!

Right. Phrasing it the way I did may get people to realize this, or at
least to think about it themselves.

If you put an airplane on the roof of a speeding train, would it take
off? What if the train were shaped like a runway? What if it were very
thin?

hmmmm, if you put the airplane on, say, a fast moving ship, could it
take off?

I wonder....

--
Bob Noel
Looking for a sig the
lawyers will hate


I don't think so. I've seen videos of planes launching from an aircraft
carrier (that's a fast moving ship, right) fall right off the end. I guess
it's because the forward motion of the carrier negated the forward thrust
of the plane.

Ok, maybe you're yanking people's chains but...

Planes that fail to get airborne off a carrier are sometimes the victim of
what is known as a "Cold Cat." If the steam pressure is not set correctly
for the weight of the aircraft being shot it may not acheive sufficient
airspeed to fly. Or, sometimes the holdback may break prematurely meaning
the plane does not get the benefit of the entire stroke of the catapult
shuttle and may fail to acheive flying speed. Or, sometimes the part of the
nosegear that hooks into the shuttle (name?) may break or tear off yielding
a similar result.

The forward motion of the ship aids in reaching the necessary airspeed for
flight by creating a relative wind over the deck:
-Windspeed is 10Kts
-The ship is moving at 30Kts (or more...and the carrier is turned into the
wind for flight ops)
-The jet needs 120Kts to get airborne (or whatever...)

With 10Kts of wind + 30Kts of relative wind from the speed of the carrier
you only need 80Kts via catapult for the jet to fly.

After all, planes used to launch off carriers without catapults...even
medium bombers (B-25) have done it. Doolittle Raid anyone?

Jay Beckman
PP-ASEL
Chandler, AZ

"Travis Marlatte" wrote

I guess it's because the forward motion of the carrier negated the forward
thrust of the plane.

What?????????????????????????

You really didn't mean what you said, or say what you believed, did you?

If that is what you meant to say, you better get your money back from whoever
taught you the ground school portion of your ticket, and then go back and take
high school physics again.
--
Jim in NC

("Jose" wrote)
The (otherwise ordinary) plane is magnetically suspended over the runway
with nothing touching the runway at all. Can the plane take off?


Yes. But, ...Lord only knows what direction he's heading. g


Montblack

("Darkwing" wrote)
Thank you for your reply. Here is my .02, it would seem that the plane
never actually moves in respect to the observer no matter how fast the
treadmill moves, the plane will just take off like it is hovering and then
slowly accelerate away?


Not unless the plane's "wheels" are coupled to the shaft of a gyro's rotor.

Try this one:

You're in a Class B airport terminal.
You're on roller-skates, Rollerblades, a skateboard... whatever.

You find yourself on an (evil) moving sidewalk - facing the wrong way.
The (evil) sidewalk ALWAYS matches your wheels' forward speed.

Someone moves a huge Hollywood 'film set' fan, in a few feet behind you.
They point the fan at your back and turn it on.

You hold open your jacket to make a sail (...like kids at the ice skating
rink have done for ages)

1. Will you get blown down to the far end of the moving sidewalk - your
destination?

2. Will you remain in the same spot - relative to the wall - no matter how
hard the giant fan blows?

3. Forgetting the fan, if you try pulling yourself forward using the
stationary handrails, will you in fact move forward? Or will the (evil)
moving sidewalk thwart your forward motion by speeding up? Or will your
upper body pull itself forward, while your feet remain behind ...(or
stationary, relative to the wall and the handrail)?

4. How is this the same as the airplane and the treadmill question? How is
it different?


Montblack

"Montblack" wrote in message
...
("Jose" wrote)
The (otherwise ordinary) plane is magnetically suspended over the runway with
nothing touching the runway at all. Can the plane take off?


Yes. But, ...Lord only knows what direction he's heading. g

The thrusters will take care of that, until the inertial dampeners take effect.
g
--
Jim in NC

"Ray" wrote in message
...
Looks like airplane treadmill problem, regularly a spark for flame wars on
R.A.P., has made it into the mainstream.

http://pogue.blogs.nytimes.com/

Let the arguing begin!

- Ray

"The conveyer belt is designed to exactly match the speed of the wheels,
moving in the opposite direction"

Speed of the wheels in relation to what?

The runway under the treadmill, or the surface of the treadmill itself?

If the answer to this question is the surface of the treadmill, the answer
to the original question is undefined (as in division by zero is undefined).

If the answer to this question is the runway under the treadmill, then the
aircraft will take off at the normal airspeed, with the wheels rotating at
twice the airspeed. Should take about the same distance over the runway
(under the treadmill)

"Darkwing" theducksmail"AT"yahoo.com wrote in message
...

"Gig 601XL Builder" wrDOTgiaconaATcox.net wrote in message
...

"Darkwing" theducksmail"AT"yahoo.com wrote in message
...

"Brian" wrote in message
ups.com...

The only way the treadmill can stop or slow the airplane is to create
more Drag than Thrust.

The reason the airplane will be able to accelerate is that the
treadmill does not create any significant drag aircraft.

When the treadmill hits 500MPH how much force will it take to hold the
airplane in position?

With perfect frictionless bearings it will take 0 force. If the engine
is generating any thrust the airplane will move forward no matter what
the treadmill does.

Brian.


So lets say I know my little RC plane takes off at exactly 25mph. So I
crank up the treadmill to step up to 25mph so I can keep the RC plane up
on the treadmill, the plane is completely stationary in regards to
anyone standing next to the plane but when the treadmill hits 25mph and
my little RC plane is staying even with the treadmill you are telling me
I can pull back on the elevator stick and the plane will take off? I
don't think so.

------------------------------------
DW


If the plane will take off at 25mph and you are standing on the treadmill
holding the plane, when the treadmill reaches 25 mph the plane will fly
if you let go of the plane.

If the engine on the plane is set to the proper power it will continue to
fly right beside you.


How is that possible if the wings are stationary? Are you saying the thing
will take off due to the pure power setting to keep up at 25mph (or
whatever), nothing to do with the wings?



Screw the treadmill. The wings aren't stationary in regards to the wind. The
AIRSPEED of the aircraft is 25 MPH.

Let's make it a real world example. When aircraft carriers are launching
aircraft they turn into the wind the air speed of the aircraft when it
releases from the catapult is (Wind Speed + Carrier Speed + Catapult speed).

Another real world example is a normal take off of a normal airplane. Let's
say you have a take off speed of 50 MPH. The wind is blowing right down the
runway towards you at a even 10 MPH. You will take off when you have a
ground speed of 40 MPH.

Switch the wind to a 10 MPH tailwind and you will take off when you have a
ground speed of 60 mph.