The Impossibility of Flying Heavy Aircraft Without Training

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.

wrote

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.

I think I will create a new award. I'm not sure what the prize or trophy
will be yet.

I'm calling it "Rec.Aviation Geek of the Decade", or perhaps of "The
Century."

I am in total awe and amazement, that you and Jose have tied for this award,
based on how long you two have kept this amazingly boring subject alive. I
just CAN'T believe it !!!

Now, continue on, or not.

Please, use your restraint, and common sense. Use the "or not." g
--
Jim in NC
(mostly, using his right to use the "ignore thread" button! g

Morgans wrote:

...

Now, continue on, or not.

Please, use your restraint, and common sense. Use the "or not." g


Well I'm really hoping that Jose tries the card thumbtack soda straw
thing.

--

FF

Well I'm really hoping that Jose tries the card thumbtack soda straw
thing.

Actually, I did try it and it didn't "work" (that is, the card didn't
float, which is what I think you expect to happen). I'm probably doing
it wrong so I'll keep at it. When I get it to work, I'll report what
happened and why (in newtonian terms) I think it did.

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

Jose wrote:
Well I'm really hoping that Jose tries the card thumbtack soda straw
thing.

Actually, I did try it and it didn't "work" (that is, the card didn't
float, which is what I think you expect to happen). I'm probably doing
it wrong so I'll keep at it. When I get it to work, I'll report what
happened and why (in newtonian terms) I think it did.


Well after reading that I went and tried it myself and blew the card
off the end of the straw so I must be doing it wrong too!

I've known of this trick from childhood, (yes, I realize that some
of you are thinking that could mean I first learned of it a few days
ago) so by now I can't remember exactly how or even if I did it
myself. Memory is like that.

Could we reduce the crossposting? I think one newsgroup is more
than sufficient. You chose, and I'll follow.

--

FF

Could we reduce the crossposting? I think one newsgroup is more
than sufficient. You chose, and I'll follow.

It's being posted to piloting, homebuilt, and student. We could easily
lose homebuilt. Should we lose student?

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

Could we reduce the crossposting? I think one newsgroup is more
than sufficient. You chose, and I'll follow.

Absent protest, from just after "now" on, I'll reply and post this
thread only to r.a.piloting.

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

I am in total awe and amazement, that you and Jose have tied for this award,
based on how long you two have kept this amazingly boring subject alive.

Great discoveries are often made in the seventh decimal place.

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