Olin Lathrop wrote:

> Gerhard Fiedler wrote:
>> I agree that it is very likely that there is a downdraft in the air
>> to provide the upward force on the wing ...
>=20
> What, so the remaining unlikely part is magic?

I don't know about you, but science is about probabilities, not about
certainties. It is not possible to reach certainty with science; if you
want certainty, you need to resort to religion. Sometimes it sounds as
if you take stuff "religiously", though... :)

>> And Olin, however hard he tried, wasn't able to stay within one
>> single reference system and do a momentum balance that would result
>> in a downdraft, parting from still air and a wing in horizontal
>> movement.
>=20
> Actually I mentioned it several times.  The earth goes towards the
> plane a little bit to ballance the momentum of the air going down.

No, this is at best inconsistent, and I'm sure it is way below what you
could achieve if you really thought about what I wrote -- however
difficult this may be for you.


I don't know what your problem is, but it seems to have to do with
either textual understanding or maybe simply not reading what others
write because you think it's not worth it. In any case, our
communication is severely limited here, by you not having captured or
having forgotten things I wrote several times before.


A few of the things I mentioned repeatedly before (including in the
email to which you just responded):

1- You need to choose a reference system, define it so that we (and you)
know what you are talking about, /and stay within it/ if you want to
talk about preservation of momentum. "The Earth [I'm assuming you're
talking about the Earth, and not some earth] goes towards the plane"
means "the distance between the Earth and the plane becomes smaller",
which, in the reference system of the Earth means that now not only has
the air a downward momentum, but also the plane.=20

2- From the get-go we have assumed a plane flying at constant speed and
constant height (that is, constant distance from the Earth). Not on a
slight down slope, but at constant height. According to your
explanation, the plane would not be able to keep height, because it
always goes down a little bit. If it keeps height, it needs to go up a
little bit after going down a little bit, to keep the same height (on
average), but even /if/ the going down of the plane would explain the
preservation of the momentum, where's the preservation when the plane
goes up a little bit, to keep its average constant height?


We assumed a plane flying at constant height, in a "macro" vision, as
you called it, and you said how this all works is easily explained by
Newtonian physics, especially the preservation of momentum. I'm just
trying to /really/ apply physics here. For this you need to define a
reference system within which we then can apply the rule of preservation
of momentum. You started with this, so I assume you already have a
reference system in your mind -- don't you? So why don't you define the
reference system, and then stay with it and explain how the momentum is
balanced?

If you really want to understand the problem, re-read the last message
and try to understand it. Most of it is pretty clearly spelled out
there.


To summarize the most important parts in short, simple sentences for the
attention span challenged:

1- We need to define a reference system.

2- We need to stay within the reference system.

3- The speed of the reference system within itself is zero, and so is
its momentum -- at all times.

4- Momentum is preserved only within a reference system.

5- We look at a "macro" view of things, because that's what was
suggested by Olin as enough to explain what happens, with basic
Newtonian physics.

6- Item 5 means that a plane flying at constant height doesn't go micro
up and micro down to achieve a macro constant height; it simply flies at
constant height.=20

(If you really think the micro down and micro up helps you explain
preservation of momentum, by all means use it -- but explain how the
momentum is preserved in both phases, not only in one.)

Gerhard
--=20
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