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

"Rip" wrote in message
. net...
Ray wrote:
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
Yes, the airplane will take off. The thrust of the engine is against the
AIR. NOT the treadmill. There are two real life situations analogous to
this:
1) Will an airplane on an essentially frictionless surface (say, wet ice)
take off?

Of course it will at airspeed X. And it will do so at a power setting that
creates airspeed X.

2) Will a sea plane take off upriver in a current equal to it's take-off
speed (this one is a cheat, since it involves drag not involved in the
original situation, but should be a good "fire starter" for further
discussion).


Yes it will and it will do so at a power setting that creates airspeed X x2

"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.


What you saw was an aircraft that failed to achieve and or retain a critical
airspeed. Either the catapult failed or the engine failed or, well any
number of things. There is a reason carriers turn into the wind to launch
aircraft. There is also a reason that carriers can't launch fixed wing
aircraft while tied to the dock. Well they might be able to but a lot of
things have to be perfect.

Rip wrote:
Yes, the airplane will take off. The thrust of the engine is against the
AIR. NOT the treadmill.

The thrust of the engine is not against the air. It generates
thrust as a Newtonian reaction to the prop moving air back, not
"pushing on other air." A rocket in space has nothing to push against,
yet it generates the same thrust as it did in the atmosphere.

1) Will an airplane on an essentially frictionless surface (say, wet
ice) take off?

Of course, as forward motion creates airflow over the wings.
There is no forward motion on the treadmill.

2) Will a sea plane take off upriver in a current equal to it's take-off
speed (this one is a cheat, since it involves drag not involved in the
original situation, but should be a good "fire starter" for further
discussion).

Yes, it would, but it's waterspeed at takeoff airspeed would
be double the usual takeoff speed. However, this would require
considerable power to overcome the extra drag of the floats on the
water, being a lot more than wheels on pavement.

I have a hard time believing that so many people can't see that it's
airflow over wings, not wheel speed or prop blast, that lifts
airplanes. What do they think wings are for, anyway?

Why don't we discuss something truly valid, like the downwind
turn feared by some (especially a few RC modelers) that they think will
reduce airspeed and cause a stall?

Dan

"Travis Marlatte" wrote in message
et...
"Peter Duniho" wrote in message
...
"T o d d P a t t i s t" wrote in message
news
[...]
Agreed, further interpretation is required, although I think
the most reasonable interpretation is pretty clear

But that's my point. Just as a "reasonable interpretation" is required,
one can just as easily assert that a MORE reasonable interpretation
would
be to assume the question means to discuss a scenario that is at least
theoretically possibly to reproduce with existing technology.

The question is ambiguous no matter how one looks at it. How can anyone
assert that it makes more sense to interpret it in a way that creates a
physically impossible situation than to interpret in a way that can at
least in theory be tested experimentally?

Pete


Yup. The question can be interpreted in a couple of different ways. This
is
what has created the multi-faceted debate. We are not just debating
whether
the plane will fly given a single scenario. We are arguing about the
scenario itself. Stupid, really. I mean, the arguing is stupid. I'm all
for
discussing alternate scenarios to gain enlightenment (which I got the last
round - no new information this time).

I happen to believe that the point of the scenario is to illustrate the
independence (within limits of friction) of the motion of the plane from
its
connection to the ground. I think that the alternate scenarios are
interesting and have their own merit. However, there are those that
clearly
do not get the independent nuance of airmotive thrust (e.g. Darkwing).
-------------------------------
Travis
Lake N3094P
PWK


That's what I call an INDUSTRIAL STRENGTH nuance!

Peter

wrote:
Rip wrote:
Yes, the airplane will take off. The thrust of the engine is against the
AIR. NOT the treadmill.

The thrust of the engine is not against the air. It generates
thrust as a Newtonian reaction to the prop moving air back, not
"pushing on other air."

Oh, I see. Basically, you try to say that moving air back is not pushing
it back?


Leonard

The thrust of the engine is not against the air. It generates
thrust as a Newtonian reaction to the prop moving air back, not
"pushing on other air." A rocket in space has nothing to push against,
yet it generates the same thrust as it did in the atmosphere.

Actually, it's not that way. (but read carefully)

The thrust of a propeller engine is created when the propeller (an
airfoil) creates a high pressure area behind and a low pressure area in
front of the prop, as it pushes air back. The prop is pushing against
the air in order to do this. The air is constantly trying to get out of
the way, but it is not entirely successful, which leads to the pressure
differences. There's nothing funamentally wrong in saying that the
airplane pushes against the air to move forward. The prop (a part of
the airplane) is doing the pushing.

Rockets are different. The tail of fire coming out of the rocket does
push against the air (push the air out of the way to make room for the
fire), but it is =not= part of the rocket. If there were no air to
"push against", the rocket would work just as well, for that reason.
Where the rocket gets its thrust is the tail of fire pushing (the other
way) against the engine bell of the rocket itself. The rocket is
pushing against the fire, in essence. The fire is =not= part of the rocket.

Both cases can be viewed in the newtonian "action/reaction" paradigm,
but something has to push against something else in order to get the
thrust to happen in the first place. In a plane, the propeller pushes
against the air (to make the air go backwards fast and create thrust. In
a rocket, the engine bell pushes against the tail fire (pushing the fire
out, and the rocket forward). I suppose it may be clearer to say that
the expanding gasses of the tail fire push against the engine bell, but
the two are equivalent.

Although the expanding rocket gasses do push the air out of the way,
that doesn't help the rocket in any meaningful way.

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.

wrote in message
ups.com...

Rip wrote:
Yes, the airplane will take off. The thrust of the engine is against the
AIR. NOT the treadmill.

The thrust of the engine is not against the air. It generates
thrust as a Newtonian reaction to the prop moving air back, not
"pushing on other air." A rocket in space has nothing to push against,
yet it generates the same thrust as it did in the atmosphere.

1) Will an airplane on an essentially frictionless surface (say, wet
ice) take off?

Of course, as forward motion creates airflow over the wings.
There is no forward motion on the treadmill.

2) Will a sea plane take off upriver in a current equal to it's take-off
speed (this one is a cheat, since it involves drag not involved in the
original situation, but should be a good "fire starter" for further
discussion).

Yes, it would, but it's waterspeed at takeoff airspeed would
be double the usual takeoff speed. However, this would require
considerable power to overcome the extra drag of the floats on the
water, being a lot more than wheels on pavement.

I have a hard time believing that so many people can't see that it's
airflow over wings, not wheel speed or prop blast, that lifts
airplanes. What do they think wings are for, anyway?

Why don't we discuss something truly valid, like the downwind
turn feared by some (especially a few RC modelers) that they think will
reduce airspeed and cause a stall?

Dan

And, after we've resolved that one, we can move on to the turn to the final
turn for a left crosswind landing from a tight left pattern or a right
crosswind landing from a tight right pattern.

Peter

You have to remember that the plane's airspeed is completely independent of
its wheel speed. As you know, a plane can have sufficient airspeed to fly
even if the wheels are stopped, and it can have insufficient airspeed even
if the wheels are spinning at 200 mph.

The treadmill spins the wheels - it has absolutely no affect on airspeed.
The plane gathers airspeed by means of the propeller acting on the
surrounding air. No matter how fast the treadmill belt is moving it is not
taking the surrounding air with it.

If you tie a rope to the wall and then sit in a wheelchair on the treadmill,
as long as you hold onto the rope the chair will not move no matter how fast
the treadmill goes. Likewise, by simply pulling on the rope you can move
yourself forward on the treadmill no matter how fast the belt is going. The
reason is because the force moving you forward on the treadmill (pulling on
the rope) is not related at all to how fast the belt is going. The plane is
"pulling on the rope" (air) using its propeller - it doesn't care what its
wheels are doing.

BDS


"Darkwing" theducksmail"AT"yahoo.com wrote
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?

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

On Wed, 13 Dec 2006 17:29:04 GMT, "BDS" wrote:

You have to remember that the plane's airspeed is completely independent of
its wheel speed. As you know, a plane can have sufficient airspeed to fly
even if the wheels are stopped, and it can have insufficient airspeed even
if the wheels are spinning at 200 mph.

The treadmill spins the wheels - it has absolutely no affect on airspeed.
The plane gathers airspeed by means of the propeller acting on the
surrounding air. No matter how fast the treadmill belt is moving it is not
taking the surrounding air with it.

If you tie a rope to the wall and then sit in a wheelchair on the treadmill,
as long as you hold onto the rope the chair will not move no matter how fast
the treadmill goes. Likewise, by simply pulling on the rope you can move
yourself forward on the treadmill no matter how fast the belt is going. The
reason is because the force moving you forward on the treadmill (pulling on
the rope) is not related at all to how fast the belt is going. The plane is
"pulling on the rope" (air) using its propeller - it doesn't care what its
wheels are doing.

BDS


OK ! I'm putting my pa-28-140 on a treadmill and will report back to
clear this up once and for all.


"Darkwing" theducksmail"AT"yahoo.com wrote
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?

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





Daveb

On Wed, 13 Dec 2006 19:04:48 GMT, (DaveB) wrote:

On Wed, 13 Dec 2006 17:29:04 GMT, "BDS" wrote:

You have to remember that the plane's airspeed is completely independent of
its wheel speed. As you know, a plane can have sufficient airspeed to fly
even if the wheels are stopped, and it can have insufficient airspeed even
if the wheels are spinning at 200 mph.

The treadmill spins the wheels - it has absolutely no affect on airspeed.
The plane gathers airspeed by means of the propeller acting on the
surrounding air. No matter how fast the treadmill belt is moving it is not
taking the surrounding air with it.

If you tie a rope to the wall and then sit in a wheelchair on the treadmill,
as long as you hold onto the rope the chair will not move no matter how fast
the treadmill goes. Likewise, by simply pulling on the rope you can move
yourself forward on the treadmill no matter how fast the belt is going. The
reason is because the force moving you forward on the treadmill (pulling on
the rope) is not related at all to how fast the belt is going. The plane is
"pulling on the rope" (air) using its propeller - it doesn't care what its
wheels are doing.

BDS


OK ! I'm putting my pa-28-140 on a treadmill and will report back to
clear this up once and for all.


"Darkwing" theducksmail"AT"yahoo.com wrote
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?

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





Daveb
Forgot to mention I will use two treadmills one for each wheel so I
can control the speed on both.
Daveb