Can a Plane on a Treadmill Take Off?

....continue my previous post
TAILWIND equal to x MPH:
*Assume a tailwind has suddenly come up! Suddenly means that the plane
didn't have time to react to it and since the tailwind equals Vlof this
means that your entire true airspeed drops away! So airspeed now is 0!
But your groundspeed for the moment remains x MPH as in previous case
and so does the tirespeed/tredmill speed which is 2x.
Briefly:
GS=x TAS=0!
Tirespeed=2x plane would not anymore takeoff!! WINDSHEAR,
WINDSHEAR!! Dangerous condition which can happen in real life!

*Now assume the plane has overcome the tailwind and the airspeed has
recovered and is again equal to x MPH. Good! Now the groundspeed will
be 2x and the tirespeed 3x! Because vector 2 is counteracted by an
opposite and equal in magnitude wind vector, there is now a new vector
4 (see drawing previous post). Oh God, maybe I should have drawn that
sketch a little differently! I'm not going to go through all this
again. Anyway, would you now do me a favor and CLOSE THE DISCUSSION
PLEASE!!

In short, the article from the first post is correct! End discussion,
"point final", over and out!!

PS:If you would like to know, I'm an engineer and an airline pilot!
Jeeeeezus!

"Michael Ware" wrote in message
. ..

"muff528" wrote in message
news:OW2Ff.179$DV2.5@trnddc07...

.....OR relative to each other? If so, there could be just enough thrust
applied to overcome frictional
forces and the airplane doesn't move relative to the world so airspeed
is
0.

That would have to be either a very underpowered airplane, or wheels with
a
lot of friction.

Yes!..that's why I said "COULD be just enough thrust..." More thrust than is
necessary
to overcome friction would result in the airplane moving forward relative to
the air. Then
it's only a question of how much thrust would be necessary to move the plane
forward fast
enough through the air to overcome gravity :-) A little less thrust would
result in the airplane
going backwards but not as fast as the conveyer. In any case the relative
velocities of the
plane to the conveyer would be equal to observers on either object but NOT
to an observer
standing on dirt.


BUT WAIT!!! .... ANY two objects can be said to be moving (or not) at
equal
speeds relative to each other. A point
on the conveyer belt moving east at 4mph and a jet moving west at 600mph
each have a relative velocity of 604

But there's the trick. A treadmill belt isn't really moving at all, it's
turning.

Again, Yes....but that's why I said "a POINT on the conveyer.." not the
conveyer
system itself.

The trick is that the original question as posted asks a question (will the
plane take off) and gives just enough info
to cause assumptions that aren't specified.

Try this for a brain scrambler. Think about a tire on your car, driving
down
the highway. At the point where the tire contacts the ground, it's speed
is
zero. 180° away, at the top, it is moving forward at twice the speed of
the
car.

Yes, but only for a very brief instant in time. And since velocity is
measured as a function of
time, is that point on the tire really moving at all at that one brief
instant when the measurement
is taken? :-)

As posed by the question, I agree that the belt is a distracter. However, it
is not irrelevant as the thrust applied to achieve flying speed must
overcome not only the normal tire rotation friction but twice that. That the
plane will fly presumes that there is enough excess thrust to do just that.

--
-------------------------------
Travis
"Morgans" wrote in message
...

"alexy" wrote

Reread the stated problem:

"a conveyer belt that moves in the
opposite direction at exactly the speed that the airplane is moving
forward."

All it is, is a trick question, aimed at testing your reading and
comprehension ablility. The plane moves off in exactly the same manner as
on a regular runway. The moving belt is a distracter.
--
Jim in NC

The propulsion system is irrelevant as long as it is independant of the
treadmill.

--
-------------------------------
Travis
"alexy" wrote in message
...
"Doug" wrote:

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.

Not at all complicated. The propulsion system is irrelevant. The given
fact is that the airplane's speed (not it's speed relative to the
conveyor) is equal to the conveyor's speed, but in the opposite
direction. When that speed is sufficient for flight, it will fly.
--
Alex -- Replace "nospam" with "mail" to reply by email. Checked
infrequently.

"Kpi$LyLcEhRo" wrote in message
oups.com...

Gary Drescher wrote:
The plane would take off from the treadmill even if there were a tail
wind
equal to Vr (though in that case, the wheels would be turning at *four*
times their usual speed).

in the case of a tailwind equal to Vlof, when the plane leaves
the ground, the wheels would spin at a speed 3 times their usual speed
and not 4.

Suppose the plane lifts of at an airspeed of 30 knots, and suppose a 30 knot
tailwind. At takeoff, the plane then has a 60 knot ground speed. By
stipulation, the treadmill moves backward as fast as the plane moves
forward, hence at 60 knots too. Thus, the wheels are turning at 120
knots--four times the usual speed.

Actually this entire question and solution is about adding
and substracting velocity vectors and a perfect example of Einstein's
relativity theory.

No, this is strictly Galilean relativity (from four centuries ago);
Einstein's relativity has no bearing on this discussion.

--Gary

No. The plane is moving forward at 80mph. The wheels are the only thing
feeling the 160mph effect of the treadmill. This isn't a ground propelled
vehicle.

--
-------------------------------
Travis
"Robert M. Gary" wrote in message
ups.com...
and a speedometer that
measures off of tire rotation would indicate the plane's speed (before
getting airborne) as 160mph, the speed relative to the conveyor.

While an airspeed indicator would indicate zero.

-Robert, CFI

Taken to the extreme, it might be considered ambiguous but that is only
nit-picking the puzzle. The general answer to the riddle is: if the plane
has enough excess thrust to overcome the additional drag of friction of the
wheels turning at twice the liftoff speed, the plane will fly. It will
accelerate slower and require a longer run due to the excess friction, but
it will fly.
--
-------------------------------
Travis
"Doug" wrote in message
oups.com...
Taxi is just nomenclature for the airplane moving along the ground.
"Takeoff run" would be more correct I guess, but in this case things
are so weird, as it is ambiguous whether the plane is going to takeoff
or not.

Peter, I think you lost the relative perspective. Given the original riddle,
the treadmill only moves backward at the same rate the plane moves forward.
If the plane was developing exactly enough thrust to counteract the
headwind, it will not move and neither will the treadmill.

--
-------------------------------
Travis
"Peter Duniho" wrote in message
...
"Damian" wrote in message
...
Paul...dont look now, but that airplane is NOT flying off the ground
until the AIRSPEED is up...the treadmill is only moving the TIRES, that
means diddly squat to an airplane.

Damian, don't look now but Paul is exactly right (except for his rude
nature, of course).

The treadmill is irrelevant to the airplane's motion. If the airplane is
stationary on the treadmill, it's because it has a headwind the same speed
as the treadmill and enough thrust to fly into the headwind at the same
speed as the treadmill. Of course, the wheels will be turning on the
treadmill, but only because the treadmill is rotating them against the
air-based stationary nature of the airplane.

Without a suitable headwind for the airplane to fly into, the treadmill
would just push the airplane backward. Airplanes don't use their wheels
for transmitting power to forward motion (most don't, anyway ).

Pete

How about this, you chain the plane to the ground with a 120kt headwind and
six 600HP engines mounted on a 172 all developing max thrust. Will it fly?

The answer, of course, is yes because no tiedown at any airport I've ever
seen would keep that on the ground. By the way the tires and wings are
irrelevant to the puzzle.
--
-------------------------------
Travis
wrote in message
oups.com...
If you restate the problem as follows the aircraft will obviously NOT
fly.

The aircraft is on a conveyor belt.

The conveyor is programmed to move in such a way as to maintain the
aircraft at an airspeed of zero as measured at the pitot.

propwash?

No - It's a Skymaster and the examiner cut the front engine.

Oh-wait - It's a jet...

a.


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.

My dear Gary, how could I forget that in post number1 there is a line
saying "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..." so in other words, the belt adapts it's speed to the
forward motion of the plane?? Another communication problem I guess.
I'm not surprised though, after 55 freakin' posts this topic is
becoming off limits in my personal opinion! But I do hope that now
everyone agrees that the explanation on that website is correct. It's
just a matter of explaining the question properly with all details and
eliminating possible communication problems, right?

No, this is strictly Galilean relativity (from four centuries ago);
Einstein's relativity has no bearing on this discussion.

I don't agree completely. But your right that Galilean blabla has to do
with this but then saying that it's all about Newton's laws would also
be correct. So does Einstein! May I remind you of one of Einstein's
many mind experiments... The one about a train moving at a certain
speed, an observer inside the train walking to the front of the train
and an observer outside the train, standing still... As I said, it all
depends on what reference you take! To the observer outside the train,
the train may be traveling at 100km/h and the guy inside the train will
be walking at 105km/h! But to the guy inside, the train seems
stationary, while he himself is going at 5km/h and the guy outside to
him appears to be going backwards at 100km/h! It all sounds very
complicated and silly but relativity (and communication problems) is
all this topic is about! Now why don't y'all go and get a nice cup of
coffee and then start another topic.
No hard feelings I hope!