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

"Richard Riley" wrote in message
...
On Mon, 11 Dec 2006 22:06:30 -0500, "Peter Dohm"
wrote:

A "rolling road" gets rid of the boundry layer, and better simulates
what a race car will see on the track.

There was a lot of talk 30+ years ago about what a nice thing this would
be;
mainly to test the effectiveness of anti-lift devices for sports car
racing.


It's state of the art now. They said in the cars they're building the
ride hight is 1/4" in front, 3/4" in the rear, since they're testing
1/2 scale in the tunnel a boundry layer would make a huge difference.

Apparently the really, REALLY advanced tunnels in europe use a
stainless belt that can turn in relation to the wind, and they're
testing multiple cars at once to model drafting. Just the stainless
rolling road costs $10 million - before you build the rest of the
tunnel. Some even use a big air bearing under the belt so the full
weight of the car can rest on the wheels.

It's just as well that I got away from all that. I'd be really bummed that
I couldn't have one of my own to play with! g

And, just to keep it on topic, the only planes that could take off
from a treadmill are the Osprey and the Harrier.

C'mon Richard! I know that you know better than that. Remember that a
moving floor treadmill moves in lock-step with the air in the tunnel, and
that it does so even if the speeds can be offset and the moving floor angled
to simulate a surface wind condition.

Peter

"Peter Duniho" wrote in message
...
"Richard Riley" wrote in message
...
[...]
And, just to keep it on topic, the only planes that could take off
from a treadmill are the Osprey and the Harrier.

If you're going to try to stay on topic, you ought to at least try to get
the answer right. At this point plenty of sources, from individuals here
in
this thread and the one we had a while back, as well as those cited in the
comments to the blog article referenced, have clearly stated the correct
answer.

Anyone attempting to refute the correct answer, however futile that effort
may be, at least owes it to themselves as well as the rest of us to take
the
time to read and understand the references that explain the correct
answer.

Pete


It appears that the OP had it nailed from the start.

This "puzzler" is a deliberately trivial, and well tested problem, which
allows the problem to be restated slightly to allow the correct answer to be
refuted--at least enough to convince anyone who believes that the airplane's
wheels perform some function other than steering and removing friction [of
the aircraft sliding along the runway] so that the airplane can accellerate
and take off.

It is really depressing that so many in a group of this type [seem to] have
been taken in.

Peter :-(

The problem is that:

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

is a meaningless statement. It =sounds= like an English sentence, the
nouns and verbs are in the right place, and it gives the impression of
conveying a thought, but it has no actual meaning.

Restate that sentence and you have a question that has an answer.

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.

Ok, how about this one. Everyone knows pilots love a tailwind.

You have a giant fan mounted on a truck positioned behind the airplane.
The fan blows air towards the airplane, helping it to accelerate down
the runway (literally blowing it down the runway) while the truck
follows, keeping up with the airplane. Pretty soon the plane will be
thundering down the runway and the pilot pulls back on the yoke.

Does the pilot have to wait until the airplane's speed down the runway
is twice Vr before he can take off?

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.

"T o d d P a t t i s t" wrote in message
...


But anyone who does *not* violate the stated assumption (and
consequently thinks this is *not* about real airplanes and
real treadmills) can argue the plane cannot take off because
its speed relative to the air is zero. To get that
conclusion, however, they've got to assume an engine that is
so weak, it couldn't take off on a real runway, or friction
so much higher than reality as to again prohibit a takeoff.

Well, I choose a treadmill with zero internal friction. [If the treadmill
can be the length of the runway, I can make it frictionless.]

Now, lock up the brakes and advance the throttle(s) to 100%. Thrust is going
to overcome drag and move the airplane forward. Nothing in Aerodynamics 101
says thrust is related to wheel rotation. The treadmill belt is going to
maintain the zero rotation speed of the wheels by slipping forward instead
of rearward. When the aircraft reaches takeoff speed, it flys. Problem
solved.

"N2310D" wrote in message
news:YfBfh.3650$LL4.2817@trnddc04...
Thrust is going to overcome drag and move the airplane forward.

Not in my Cherokee.

Thrust is going to overcome drag and move the airplane forward.

Not in my Cherokee.


Sure it will!

If we can have a treadmill the size of a runway, and [which is] able to
sense the rotation of the airplane's wheels; then we can require it to be
both frictionless and inertia-free.

There are other amusing combinations as well; but the point the central
point remains: So long as the airplane is not attached to (or restrained
by) anything other than the "belt" of the treadmill, it will take off and
fly quite normally--without regard for humorous statements (including mine)
regarding doubled wheel speed.

Since the original problem statement made no assertion that the airplane
would be tied down, it obviously is not, and the the problem is
solved--quite simply because there was no problem.

Peter

Ok, how about this one. Everyone knows pilots love a tailwind.

You have a giant fan mounted on a truck positioned behind the airplane.
The fan blows air towards the airplane, helping it to accelerate down
the runway (literally blowing it down the runway) while the truck
follows, keeping up with the airplane. Pretty soon the plane will be
thundering down the runway and the pilot pulls back on the yoke.

Does the pilot have to wait until the airplane's speed down the runway
is twice Vr before he can take off?

Jose
--
There is not enough beer in the world to fuel such a discussion!!!!

Peter

"T o d d P a t t i s t" wrote in message
...
[...]
To put this mathematically:
wheel speed = treadmill speed + airspeed
If we assume:
wheel speed = treadmill speed
then airspeed =0

Well, IMHO the problem with taking the question literally is that, as Jose
says, the literal reading is meaningless.

Taken literally, "wheel speed" means nothing. Or rather, it requires
further interpretation. Are we talking angular velocity? If so, how can
the treadmill moving in a linear fashion have equal speed? The measurements
aren't even in the same units. Are we talking linear speed? If so, what's
so wrong with assuming the treadmill exactly matches the speed?

I do understand the point that "peter" is trying to make, but I find it no
more compelling than simply interpreting the question in a more reasonable
way. Both interpretations require assumption-making, so as long as one is
making assumptions, it makes more sense to make the same assumptions the
average human being would make.

Pete

"Richard Riley" wrote in message
...
Sure, any airplane could take off from a treadmill in a wind tunnel.
But climb out is a real pain.

No, it's not. Airspeed is airspeed. If the airplane can take off in the
wind tunnel, it can climb (to the physical limits of the wind tunnel, of
course).

I was going back to the original premise of a treadmill in still air.

And you were incorrect.

Pete