The Impossibility of Flying Heavy Aircraft Without Training

On Sat, 4 Mar 2006 10:14:36 -0700, "Matt Barrow"
wrote:


"Dallas" wrote in message
ink.net...

"cjcampbell"
Actually, he is not. Not in the US, anyway. There is no one by the name
of Sagadevan currently holding a pilot certificate of any kind in the
US

Here he is:
http://www.warpaintofthegods.com/wp/about.cfm

WOW!! What a fruticake!!

Too bad that, or those, mind altering experiences didn't give him a
grasp of rationality and reality.

Roger Halstead (K8RI & ARRL life member)
(N833R, S# CD-2 Worlds oldest Debonair)
www.rogerhalstead.com

wrote:

A fluid can transmit force without flow in the conventional sense.
That is the basis for hydraulics.

I guess it depends on what you mean by "conventional sense."

Nothing can transmit a force without some deflection. Some molecules in
the fluid have to move in order to generate a force and typically
movement of a fluid, however minute, is flow.


Matt

So in Larry Niven's Ringworld, when people swim through the ring of
atmosphere to the next Integral Tree, do they set it rotating ever so
slightly in the opposite direction?

(Livin' in a fantasy world since nineteen-sixty-mumblemumble....)


Alan Baker wrote:



No. It is balanced by the downflow eventually transferring its momentum
back to the earth.

But it is also experiencing a constant change in momentum in the
vertical direction. That's what a force is: a change in momentum over
time.
No. The airplane is in level flight at constant speed.

I'm with fredfighter here, but it is primarily a semantic argument
having to do with frame of reference. Looking from an accelerated frame
of reference (a standstill in the earth's gravitational field) one gets
one answer. Looking from an unaccelerated frame of reference
(freefall), one gets a different answer.

To reconcile them, it is important to treat =everything= from the same
frame of reference, and make appropriate adjustments.

Jose
--
Money: what you need when you run out of brains.
for Email, make the obvious change in the address.

It does that
because there are fewer air molecules transfering momentum
to it from above, that there are from below. But it does not
do that via a coherent stream of air.

I guess I should have appended this to the previous response...

This is correct. However, a coherent stream of air is not necessary for
this:

The movement of the plane towards the earth is transferred to
movement of the air towards the earth, which it does until it eventually
transfers its momentum back *to* the earth, leaving the system with the
same relative momentum with which it began.

to also be correct. A coherent stream of air is not required, nor is it
what I am proposing.

A fluid can transmit force without flow in the conventional sense.
That is the basis for hydraulics.

We are not really talking about "flow in the conventional sense", we are
talking about microscopic collisions. Flow may be involved (as in the
flow that causes upwash upflight) but it needn't be (as in the case of
the microscopic dribbler).

The downflow observed from the wing initiates above the wing
and flows down behind the wing after the wing has passed.
It is not the air that suppors the wing.

Well, the only air that supports the wing is are the molecules that
impact it from below. They not only support the wing, they also fight
against the molecules impacting from above. They win, because there are
more of them. There are more of them because of downflow and the
collisions it causes.

Well then if the downflow is NOT balanced by upflow why doesn't
the upper atmosphere run out of air?

Because the wing is not of infinite weight. The upper atmosphere in
fact =is= deprived of air while the airplane is in flight... that air is
squeezed down below the wing, increasing the pressure on the surface of
the earth, in an amount exactly equal to the weight of the airplane
(divided by the area of the earth).

If a sufficient (huge!) number of aircraft took to the air, the upper
atmosphere would become measurably thinner. Maybe we should get a grant
to do this experiment using general aviation aircraft - for the good of
Science and the benefit of GA pilots.

Jose
--
Money: what you need when you run out of brains.
for Email, make the obvious change in the address.

So in Larry Niven's Ringworld, when people swim through the ring of atmosphere to the next Integral Tree, do they set it rotating ever so slightly in the opposite direction?

Yep.

Jose
--
Money: what you need when you run out of brains.
for Email, make the obvious change in the address.

Matt Whiting wrote:
wrote:

A fluid can transmit force without flow in the conventional sense.
That is the basis for hydraulics.

I guess it depends on what you mean by "conventional sense."

Nothing can transmit a force without some deflection. Some molecules in
the fluid have to move in order to generate a force and typically
movement of a fluid, however minute, is flow.


One does not generally refer to compression as flow.

A fluid can transmit force without molecules flowing from the
point of origin to the point of application.

--

FF

Jose wrote:
It does that
because there are fewer air molecules transfering momentum
to it from above, that there are from below. But it does not
do that via a coherent stream of air.

I guess I should have appended this to the previous response...

This is correct. However, a coherent stream of air is not necessary for
this:

The movement of the plane towards the earth is transferred to
movement of the air towards the earth, which it does until it eventually
transfers its momentum back *to* the earth, leaving the system with the
same relative momentum with which it began.

to also be correct. A coherent stream of air is not required, nor is it
what I am proposing.

I inferred coherent flow from 'downwash'. Some persons, perhpas not
yourself, pointed to disturbances on the surface by low flying aricraft
as evidence of downwash. That sounds like coherent flow.


A fluid can transmit force without flow in the conventional sense.
That is the basis for hydraulics.

We are not really talking about "flow in the conventional sense", we are
talking about microscopic collisions. Flow may be involved (as in the
flow that causes upwash upflight) but it needn't be (as in the case of
the microscopic dribbler).


When we are discussing the microscopic transmission of momenta
between air molecules whic is the basis for presure, yes. Is that what

you mean by 'downwash' or downflow, as opposed to something that
involves a flow of mass?

The downflow observed from the wing initiates above the wing
and flows down behind the wing after the wing has passed.
It is not the air that suppors the wing.

Well, the only air that supports the wing is are the molecules that
impact it from below. They not only support the wing, they also fight
against the molecules impacting from above. They win, because there are
more of them. There are more of them because of downflow and the
collisions it causes.

Then it doesn't matter which way the air above the wing flows. If
the air flows sideways, you still have lift. It doesn't have to flow
down.


Well then if the downflow is NOT balanced by upflow why doesn't
the upper atmosphere run out of air?

Because the wing is not of infinite weight. The upper atmosphere in
fact =is= deprived of air while the airplane is in flight... that air is
squeezed down below the wing, increasing the pressure on the surface of
the earth, in an amount exactly equal to the weight of the airplane
(divided by the area of the earth).

I think that the downflow dispaces other air which flows up to
replace it--conserving momentum and mass.

--

FF

I inferred coherent flow from 'downwash'.

That coherent flow is not necessary does not mean that coherent flow
does not exist. My point is that the downwash does not have to be
directly from the wing to the earth. It can be very indirect - in a
multiple collision scenario, the existance of new momentum somewhere
imples the existance of opposte new momentum elsewhere, mediated by
collisions which may or may not be "coherent", however you wish to
define it. Momentum is conserved. Always.

When we are discussing the microscopic transmission of momenta
between air molecules whic is the basis for presure, yes. Is that what
you mean by 'downwash' or downflow, as opposed to something that
involves a flow of mass?

There is downwash, involving a "coherent" acceleration of mass
downwards. Due to an increase in microscopic collisions below (and a
scarcity of them above), there is an incoherent transfer of momentum
(called pressure) to the surrounding air (and ultimately to the earth).

This leads to a condition described as "low pressure above, high
pressure beneath", or equivalently described as "less momentum
transferred via collisions above, more momentum transferred via
collisions below", which supports the wing, propping it up again and
again as it tries to succumb to gravity. We call this lift.

There are some neat bulk equations which help quantify this, which come
embodied in a concept which is useful for understanding this in some
contexts. However, an equivalent (newtonian) concept is more useful for
understanding in other contexts, and explains a few things that are not
addressed by the B word.

Then it doesn't matter which way the air above the wing flows. If
the air flows sideways, you still have lift.

No, at least not directly. If there is less momentum transferred from
above than from below, you have lift. This comes from lower pressure
above and higher pressure below. How you get that is ultmately
Newtonian, not magical. Once Newton has his say, Bernoulli can
reformulate it in a useful bulk form.

Consider a flying saucer, composed solely of two disks with no
appreciable space between them. The one below does not spin, the one
above spins rapidly. Should there be lift? Why? Does it matter if the
top disk is rough or smooth?

The upper atmosphere in
fact =is= deprived of air while the airplane is in flight... that air is
squeezed down below the wing, increasing the pressure on the surface of
the earth, in an amount exactly equal to the weight of the airplane
(divided by the area of the earth).

I think that the downflow dispaces other air which flows up to
replace it--conserving momentum and mass.

What happens to the downward momentum of the downflowing air when this
happens? The displaced air, flowing upwards, has acquired upward
momentum - where did that come from? (and so far, conservation of mass
has not been an issue)

Jose
--
Money: what you need when you run out of brains.
for Email, make the obvious change in the address.

In article .com,
wrote:

Alan Baker wrote:
In article .com,
wrote:


...

In level flight at constant speed the aircraft has constant horzontal
and zero vertical momentum.

True. But it is also experiencing a constant change in momentum in the
vertical direction. That's what a force is: a change in momentum over
time.


No. The airplane is in level flight at constant speed. Therefore there
is no change in momentum. The net force on an aircraft in level
flight at constant speed is zero.

When there is a constant change in momentum the vertical
direction the airplane climbs or dives.

Incorrect.

You're going to want to go back to your basic physics texts again. Check
the formal definition of "force".

http://www.rwc.uc.edu/koehler/biophys/2c.html

"Just as force is the time derivative of momentum, ..."


...

Yes, no question about weight being balanced by lift.


But the wings also exert a force on the air (Newton, remember: for every
force there is an equal and opposite, etc., etc.). That force is not
countered by *anything*. Hence, the air is accelerated downward; a
continuous stream of air receives an constant change in momentum.

If the air has a net increase in downward momentum, how is
momentum conserved.

By the increased upward momentum of the earth.

The earth pulls the plane downward, and the plane pulls the earth
upward. The movement of the plane towards the earth is transferred to
movement of the air towards the earth, which it does until it eventually
transfers its momentum back *to* the earth, leaving the system with the
same relative momentum with which it began.


It is the coilumn of air under the wing that supports the weight
of the plane. It does that, on the statistical mechanical level
via a series of minute momentum exchanges. It does that
because there are fewer air molecules transfering momentum
to it from above, that there are from below. But it does not
do that via a coherent stream of air.

A fluid can transmit force without flow in the conventional sense.
That is the basis for hydraulics.

The downflow observed from the wing initiates above the wing
and flows down behind the wing after the wing has passed.
It is not the air that suppors the wing.

...

I don't deny that downflow occurs. The point is that downflow is a
consequence of lift, not the cause of lift, and it is balanced by
upflow, (albeit a more diffuse flow) otherwise the upper atmosphere
would run out of air.

No. It is balanced by the downflow eventually transferring its momentum
back to the earth.

Well then if the downflow is NOT balanced by upflow why doesn't
the upper atmosphere run out of air?

Because the air contacts the earth and *stops* moving downward.

--
Alan Baker
Vancouver, British Columbia
"If you raise the ceiling 4 feet, move the fireplace from that wall
to that wall, you'll still only get the full stereophonic effect
if you sit in the bottom of that cupboard."