The Impossibility of Flying Heavy Aircraft Without Training

Jose wrote:
The flying wing has some horizontal momentum which is secondary here,
How much?

mv

The air thrown forward (or, if you will, the higher pressure ahead)
tries to reduce that, the engine presumably makes up for it.

Energy is 'pumped' into the air by the plane.

Yes, and what form does that energy take?

Heat.

I maintain that it takes the
form of a net increase in mv^2/2 over all the air molecules.

Yes.

Since m
doesn't change, and 2 only changes in a pentium, that leaves v to
change. This changes mv, thus momentum.

Mass and energy are scalers but velocity is a vector.
You can increase the average velocity of the air molecules
without changing the momentum of the air mass. Indeed,
that is exaclty what happens when you heat air.


We agree that there is (microsocopic) momentum transfer at each
collision. We disagree as to whether the net is zero, and I think that
part of that disagreement has to do with just how much of the system we
are looking at.

More importantly we disagree on what causes lift.

If there is lower pressure on the upper surface of a wing than there
is underneath there will be an upward force on that wing. I think
we agree on this.

You argue that the presssure difference and resulting force
is secondary, lift is actual caused by the reaction of the wing
to the momentum change it induces in the air. But suppose
the wing creates low pressure on the upper surface by throwing
air sideways? You still have a pressure differential and the
resultant force but the only downwash is the air flowing
toward the upper surface of the wing from above to fill in
the rarefied region.

For that matter, consider the common demonstration using a
notecard, thumbtack and a straw. Put the tack through the
middle of a 3x5 index card or something similar. Put a drinking
straw over the thumbtack. Hold the aparatus with the straw
vertical and the notedard down. Blow through the straw and
let go of the notecard. The notecard will be supported by the
Bernouli effect.

The only downwash is through the straw, directed at the notecard,
pushing it down. There is no downwash from the card. The card
does not deflect any air down, it deflects the air sideways.
Yet the card is supported by the pressure differential created
by the Bernouli effect. Horizontal flow accross the upper surface
of the card creates that pressure difference.

Downwash does not cause lift. Downwash is a secondary effect
caused by the same phenomenum that causes lift.

--

FF

to neutralize the momentum the earth has acquired being attracted to
the plane,
No. Being attracted to something does not cause momentum. There
must be relative motion for momentum.

Being attracted to something and having no force resisting the
attraction (which is the case microscopically inbetween collisions)
allows relative motion to occur. That's how things fall down, acquiring
momentum in the process. Of course the earth falls up at the same time,
so depending on whether or not you include the earth, you can argue no
net momentum change.

No, it is not momentum that keeps the aircraft from falling, it is
lift. The lift is produced by a pressure difference through the
wing.

.... which is caused by microscopic collisions, which each transfer
momentum from an air molecule to the wing. This is what pressure is.

"Lift" is a shorthand for this process, the same way raising to a power
is a shorthand for repeated repeated addition.

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

After equilibrium
occurs the fan no longer puts any net momentum into the air
mass. The momenta of the individual air molecules cancel.

Yes, but only because of the wall, which allows the pressure to build up
on the far side of the fan. Were there no wall (such as for an airplane
propeller), this would not be the case.

The collison with the dribbler is inelastic. Energy is conserved,
momentum is not.

Well, only if you treat momentum as a scalar, or deal only with the
momentum of a single particle at a time. If two glueballs collide, (for
simplicity assume they were of equal mass, equal and opposite velocity),
the net (vector) momentum before is zero, but each glueball will have a
finite momentum because it is moving. After the collision, the net
(vector) momentum is zero (the splatball is motionless), and each
glueball component of the splatball is also motionless. The glueballs
have each lost momentum, because they have stopped.

So, while the vector sum of the momenta have not changed, the (scalar)
sum of the absolute values of the momenta have.

Kinetic energy (mv^2/2) is =not= conserved in an inelastic collision,
since v changes, and v^2 is scalar. It is transformed into other forms.
Some of that kinetic energy becomes heat and noise (which is
ultimately molecular kinetic energy), some of it shakes electrons
around, but macroscopic kinetic energy is not conserved for an inelastic
collision.

He uses energy to impart momentum to the basketball

So, he is "throwing basketballs down". They could just as easily be
very very tiny basketballs; the kind with eight electrons or so.

Precisely. He does not need the earth beneath him any more than
an airplane wing needs the Earth beneath it.

No, he doesn't need the earth in order to =stay=up=. But the system
=does= need the earth to satisfy the "no net momentum change in the
basketballs/air" criterion. Absent the earth's surface, there =is= a
net momentum change, whether the basketballs are the size of
basketballs, or the size of air molecules.

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

Perhaps you are not familiar with nerf balls. Nerf balls are foam
rubber. When a cue ball hits a nerf ball (sufficiently large) nerf
ball it stops and the nerf ball just quivers a bit. The center of
mas quits moving. The kinetic energy of the cue ball has been
converted to heat. Energy is conserved, momentum is not.

There is more to that. If this collision occurs in outer space, I
guarantee you that the center of mass will =not= quit moving.

On a pool table, friction with the table is involved, (as is to some
extent rolling moment). The nerf ball starts its quiver in the
direction the cue ball was going. If there is not enough force in the
quiver to break starting friction, then the momentum gets imparted to
the table (and the entire earth, which has no problem absorbing it).

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

If the air has a net increase in downward momentum, how is
momentum conserved.
...by the air's eventual collision with the earth.
How is it conserved at the air/airplane collison?

(sorry, should have added this to the prevous post)

It is conserved because the wing gets pushed (back) up when the air
molecule gets pushed down.

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

"Dallas" wrote in message
nk.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!!

Jose wrote:
Perhaps you are not familiar with nerf balls. Nerf balls are foam
rubber. When a cue ball hits a nerf ball (sufficiently large) nerf
ball it stops and the nerf ball just quivers a bit. The center of
mas quits moving. The kinetic energy of the cue ball has been
converted to heat. Energy is conserved, momentum is not.

There is more to that. If this collision occurs in outer space, I
guarantee you that the center of mass will =not= quit moving.

But it will not move in a manner that conserves momentum.

--

FF

In article om,
wrote:

Jose wrote:
Perhaps you are not familiar with nerf balls. Nerf balls are foam
rubber. When a cue ball hits a nerf ball (sufficiently large) nerf
ball it stops and the nerf ball just quivers a bit. The center of
mas quits moving. The kinetic energy of the cue ball has been
converted to heat. Energy is conserved, momentum is not.

There is more to that. If this collision occurs in outer space, I
guarantee you that the center of mass will =not= quit moving.

But it will not move in a manner that conserves momentum.

You really need to study basic physics...

--
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."

Alan Baker wrote:
In article om,
wrote:

Jose wrote:
Perhaps you are not familiar with nerf balls. Nerf balls are foam
rubber. When a cue ball hits a nerf ball (sufficiently large) nerf
ball it stops and the nerf ball just quivers a bit. The center of
mas quits moving. The kinetic energy of the cue ball has been
converted to heat. Energy is conserved, momentum is not.

There is more to that. If this collision occurs in outer space, I
guarantee you that the center of mass will =not= quit moving.

But it will not move in a manner that conserves momentum.

You really need to study basic physics...


Doh!

You'd never guess it but I did get A's in freshman Physics.

Of course I had that bass akwards. Energy can change from
kinetic to gravitatonal potential to heat etc. An elastic collision
is one in which kinetic energy is conserved. In an inelastic collison
some kinetic energy is converted to another form, typically heat.
Momentum is always conserved, as you noted earlier.

--

FF

I'll tell ya what.
I do admire it.

This is the nicest pair of debaters on the planet!

Polite.
Considerate.
Seeem to take time to read, and understand(!) what somebody wrote.
Patiently explaining their own position.
No yellin.
No screamin.
No ugly name callin.

Archie and Jughead ponder quantum pressure fluctuations.

I do love it so...