The Impossibility of Flying Heavy Aircraft Without Training

Jose wrote:

fredfighter wrote:

Please show us your arithmetic. Suppose a 1500 lb airplane is
flying horizontally at 120 mph at 5000 feet above MSL. What
are the vertical and horizontal components of the momentum
of that aircraft?
....

If so, then during the time it is in freefall, it acquires a downward
velocity. Small, no doubt, but nonzero.

Sometimes it does, sometimes it does not. I'll allow as the vertical
component of velocity decreases during that time, for a positive up
coordinate system and a plane in (macroscopic) level flight.

Ok. (I was sloppy - it doesn't "acquire a downward velocity", it really
"endures a downward acceleration", which depending on the initial
vertical velocity may or may not end up with the plane going downward.)

Right, but don't forget that the downward acceleration is constant
without regard to the velocity of the aircraft.

So we are saying the same thing here.

Do you agree that in each collision momentum is transferred to the
air molecule that is equal and opposite to the momentum transferred
to the wing?

Yes I do. This is what I call "throwi ng the air down". That downward
momentum will remain with the air (dissipated across many other
molecules as it keeps colliding, but never disappearing) until it is
transferred to the earth, which has been accelerating upwards in the
same fashion.

Do you agree that the net momentum transfered to the Earth by the
air molecules is equal and opposite to the net momentum transferred
to the wing by the air molecules?

Do you agree, therefor that there is no net momentum transfered to
the air?


I agreed quite some time ago that the theoretical basis for
macroscopic gas laws is to be found in statistical mechanics.

Ok.

On a macroscopic level, the vertical component of momentum of the
wing is zero.

Yes.

Therefor on a macroscopic level, the sum of the
momenta transferred to the air molecules, integrated over all of
the air molecules must also be zero by Newton's third law.

Right?

Only in a nonaccelerated frame. We are dealing with an accelerated
frame. Consider a rocketship hovering over the moon. The (macroscopic)
vertical component of its momentum is zero also. However it has to
continually throw down rocket exhaust to stay there.

Instead, let's consider a wing in level flight.

So, without
looking at the rest of the picture, your conclusion about momentum is
flawed.

In the case of the wing, the momentum is transferred a few times... once
when the wing hits the air molecule (throwing the air down), again when
that molecule hits the earth and bounces back (throwing the earth away
from the wing),

At which ponit the Earth throws the air molecule back up so that the
net momemtum transferred to the air molecule is zero (averaged over
the entire atmosphere)

and then again when that air molecule (or its proxy)
hits the wing on the way back up.

Which again transferes an equal and opposite momentum to the
molecule which again is transferrred to the Earth leaving no net
transfer
of momentum to the air.


Think about a person sitting on a stool. No momentum transfer (or so it
would seem). But then think about a person supporting himself by
dribbling a basketball. There is a lot of momentum transfer, but no
=net= change. The reason there is no net change is that the basketball
keeps pushing the earth away too.

And there is no net transfer of momentum to the basketball. This is
clear as the average velocity of the basketball is zero, even though
the average speed is non-zero.

Think of the example we had earlier of a piston supported by air
pressure in a cylinder. The momenta transferred by air molecules
to the piston is equal and opposite to the momenta transfered by the
air molecules to the bottom of the cylinder. There is no net transfer
of momentum to the air.

--

FF

Do you agree that the net momentum transfered to the Earth by the
air molecules is equal and opposite to the net momentum transferred
to the wing by the air molecules?

Yes.

Do you agree, therefor that there is no net momentum transfered to
the air?

Overall, yes. Similarly, there is no net momentum transferred to the
basketball when it is being used to support a (very fast) dribbler. But
that is not to say that there is no momentum transfer. The basketball
certainly moves around. I do agree that the net overall is zero. The
air does not pile up permanently.

At which ponit the Earth throws the air molecule back up so that the
net momemtum transferred to the air molecule is zero (averaged over
the entire atmosphere)

Yes.

[it hits the wing on the way up]
Which again transferes an equal and opposite momentum to the
molecule which again is transferrred to the Earth leaving no net
transfer of momentum to the air.

Yes.

Overall, there is no net (or "permanent") transfer of momentum to the
air. The air is an intermediary, keeping the wing and the earth apart.
There is certainly =energy= transfer to the air (mv^2/2), and there is
a lot of momentum transfer =back=and=forth= with the air, but I will
agree that the net is zero. The air is sort of a catalyst - ending up
unchanged as it transfers momentum to the earth and then transfers it
back from the earth to the wing.

So.. after all that, I think we are in agreement - there is no =net=
(permanent) vertical momentum transfer to the air, but there is locally
momentum transferred to the air, which carries it to the earth and uses
it to neutralize the momentum the earth has acquired being attracted to
the plane, in doing so it acquires momentum in the opposite direction
and transfers it to the wing, ending the cycle and leavint the air ready
to act as momentum messenger again.

It carries momentum messages both ways, they (overall) cancel out, but
do keep the earth and the wing separated.

===

In addition, the wing is throwing air forwards, due to its AOA and its
own forward motion. (this acts as drag, counteracted by the engine).
The air thrown forwards increases the pressure in front of the wing,
that plus the air thrown down makes the air pressure in front of and
below the wing higher, causing the air to rise in front of the wing.
This rising air helps lift the wing; this is the source of induced drag.
Some of the rising air spills around the wingtips, causing vortices.
The vortices are not the cause of lift, they are an inescapable side
effect of lift.

Concur?

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

OK, Jose (just had to say that one) explain delta wings.

http://ernest.isa-geek.org

Oh, that's a tough one. Looking at the CAD drawings, I was at first
inclined towards the helicopter methods (it's ugly; the earth repels it)
but the composite of several deltas belies that simpleminded conclusion.
It resembles a bird in flight, maybe the air can be fooled into
thinking feathers are on their way... but that requires the air to do
the lifting. We know this can't be true. Obviously some out-of-the-box
thinking is in order. Fortunately I'm up to the task; people have been
trying to put me back in my box for ages.

I am drawn to the 200 mph cruise speed; this is pretty fast for a single
engine prop plane. Maybe we are thinking this whole lift thing
backwards. An airplane's natural habitat is the air, and it =wants= to
go into the air. Very often what brings airplanes down are gremlins,
usually traced to the control system, the avionics, or even the pilot
himself. The object of the propeller is to shake the gremlins off the
plane and allow the plane to achieve its natural state. Since gremlins
are pretty fast, the airplane has to also move forward to keep them off
the plane.

This is a homebuilt, which is the natural habitat of gremlins. So, it
has to move =very= fast in order to shake them off and keep them off.

When you consider how hard gremlins are, and how soft feathers are, it's
a natural that feathers repel gremlins, and lift is sometimes
erroniously attributed to feathers. Many researchers have been down
this path, and there is a large body of accepted literature in support
of the feathers theory. At low speeds, the feather theory and the
gremlin theory give pretty much the same answers, but at high enough
speeds the relationship breaks down and the feather theory gives
erronious answers. This is where gremlin theory shines (it should be
noted that lift fairies are just gremlins gone bad).

Gremlin theory holds the potential for explaining a lot of aviation that
is otherwise unexplainable, but experiments are difficult and fraught
with peril. However, I would be happy to conduct the appropriate
research. Send grant money to Jose, care of Usenet.

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

("Jeff" wrote)
Remember, Time flies like an arrow...
Fruit Flies Like a Banana...

Do all fruit flies have bannana ratings ?

Only visual banana rules in most cases. I heard the IBR are a tad
tough.

The scarcity of tiny instrument training hoods or banana simulators makes
it even more difficult.


Apparently the FAA waived the requirement for a safety pilot. They feel
there's a sufficient number of eyes in the cockpit already.


Montblack

Montblack wrote:
("Jeff" wrote)
Remember, Time flies like an arrow...
Fruit Flies Like a Banana...

Do all fruit flies have bannana ratings ?

Only visual banana rules in most cases. I heard the IBR are a tad
tough.

The scarcity of tiny instrument training hoods or banana simulators makes
it even more difficult.


Apparently the FAA waived the requirement for a safety pilot. They feel
there's a sufficient number of eyes in the cockpit already.


Montblack

The 200 eye rule?

Dan, U.S. Air Force, retired

If you feed the gremlins hot chili with lots of beans, the
rocket like exhaust provided lift and propulsion.


"Jose" wrote in message
om...
| OK, Jose (just had to say that one) explain delta wings.
|
| http://ernest.isa-geek.org
|
| Oh, that's a tough one. Looking at the CAD drawings, I
was at first
| inclined towards the helicopter methods (it's ugly; the
earth repels it)
| but the composite of several deltas belies that
simpleminded conclusion.
| It resembles a bird in flight, maybe the air can be
fooled into
| thinking feathers are on their way... but that requires
the air to do
| the lifting. We know this can't be true. Obviously some
out-of-the-box
| thinking is in order. Fortunately I'm up to the task;
people have been
| trying to put me back in my box for ages.
|
| I am drawn to the 200 mph cruise speed; this is pretty
fast for a single
| engine prop plane. Maybe we are thinking this whole lift
thing
| backwards. An airplane's natural habitat is the air, and
it =wants= to
| go into the air. Very often what brings airplanes down
are gremlins,
| usually traced to the control system, the avionics, or
even the pilot
| himself. The object of the propeller is to shake the
gremlins off the
| plane and allow the plane to achieve its natural state.
Since gremlins
| are pretty fast, the airplane has to also move forward to
keep them off
| the plane.
|
| This is a homebuilt, which is the natural habitat of
gremlins. So, it
| has to move =very= fast in order to shake them off and
keep them off.
|
| When you consider how hard gremlins are, and how soft
feathers are, it's
| a natural that feathers repel gremlins, and lift is
sometimes
| erroniously attributed to feathers. Many researchers have
been down
| this path, and there is a large body of accepted
literature in support
| of the feathers theory. At low speeds, the feather theory
and the
| gremlin theory give pretty much the same answers, but at
high enough
| speeds the relationship breaks down and the feather theory
gives
| erronious answers. This is where gremlin theory shines
(it should be
| noted that lift fairies are just gremlins gone bad).
|
| Gremlin theory holds the potential for explaining a lot of
aviation that
| is otherwise unexplainable, but experiments are difficult
and fraught
| with peril. However, I would be happy to conduct the
appropriate
| research. Send grant money to Jose, care of Usenet.
|
| Jose
| --
| Money: what you need when you run out of brains.
| for Email, make the obvious change in the address.

Apparently the FAA waived the requirement for a safety pilot. They feel
there's a sufficient number of eyes in the cockpit already.

I thought that only applied to flying potatos.

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

You seem to think [rising air in front of the wing]
requires the presence of a ground.

No, the rising air is caused by the high pressure in front of the wing,
caused by the wing throwing the air down (and ahead). The ground is not
required for that.

However, the ground =is= required for there to be "no net vertical
motion of air". Were there no ground, the air thrown down would not
bounce back up. The molecules would bounce around the other molecules,
dissipating the motion, but the downward momentum imparted by the wing
to keep it in the air would be equal to the downward momentum the wing
would have acquired had it not been flying. Although dissipated across
the rest of the atmosphere, it would not "disappear".

If air just "smooshed" away wings would not
work to hold us up.

If the wing is motionless, the air =does= just smoosh out of the way,
unlike a runway, which will hold an airplane up. To hold an airplane up
requires a special kind of motion - the kind that has the wing throwing
air down. Landing gear does not (usually!) throw the runway down.

If all this sounds a bit like perpetual motion, it's because
we've left out some details.

Yes.

we're looking at the wing long after it has started
up and everything is in steady state.

Yes. This obscures the "what causes what" question.

Essentially, it causes air
to rise ahead and get pushed down.

I see it as "it throws air down, which causes air in front to rise ahead".

A wing not only keeps the plane away from the earth, it keeps the earth
away from the plane. If you could measure the total forces on the earth
due to everything on top of it (essentially making the earth a giant
bathroom scale), the reading would not change when an airplane takes
off. Even though the plane is not touching the earth, it is throwing
air down at the earth, and that impact registers as weight.

Agreed, but this does not help explain the basics of lift.

It does belie the claim that there is no net downward momentum transfer.
This is only true if the air is allowed to bounce against the earth,
and as you stated earlier, the wing itself doesn't care about the earth.
As far as the wing is concerned, it is throwing air down, dealing with
the side effects (high pressure below and in front) and riding the wave
that it =caused= by throwing the air down in the first place.

If the earth were air-transparant, there would for sure be net downward
momentum of air, equal to the momentum the wing would have acquired had
it been freefalling (which is what flying is preventing).

(from the next post)
The upward momentum comes
from the air molecules. There is no requirement for the
ground. The approaching air molecules below the wing at
higher pressure cause the air molecules ahead to try to
escape. They preferentially escape upwards towards the
approaching low pressure above the wing.

Some upward momentum comes from there. But now that I think further,
the downward momentum imparted by the wing to the air (which then
bounces against the ground) only partly gets transferred back to the
wing. Most of it misses the (relatively) small wing and simply causes a
few more air molecules to escape the earth completely, or at least to
rise higher before gravity reclaims them.

This seems to imply that a wing would not produce lift,
i.e., could not fly, without the ground. That's clearly
incorrect.

Agreed (that a wing could produce lift without the ground). However,
without the ground, there would =not= be no net downward movement of air.

(from the next post)

[The Bernoulli effect] does explain [how the upwash starts]
- by virtue of pressure differentials.

Since pressure is derived from molecular collisions, and the Bernoulli
effect is also ultimately derived from those same collisions, we are
looking at the same thing, but in one case with a shortcut, the other
case on a microscopic level. For those for whom the Bernoulli effect is
a bit mysterious, or at least not obvious, looking at the newtonian
microscopic version is instructive. For those comfortable with
Bernoulli's equations, it provides a quick way to get numeric answers.

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

Two years ago when I was in college I used to read science journals for
fun... One particular, just published within the past two years
(spring '04?) caught me.

It discussed the Bernuolli theory of flight- and (if I recall) quite
conclusively proved that one of the _fundamental_ assumptions of the
Bernuolli theory- that air that travels path over the top of the wing
is flowing appreciably faster than air that flows over the bottom- is
simply incorrect in a compressible fluid....

Obviously, you should take this with a grain of salt because A- this is
my first post on this board and B- I can't remember either the journal
or the exact date... but take it for what its worth

Most aerodynamic equations dealing with low subsonic speeds treat air as an
incompressible fluid because compressibility doesn't have a significant
effect until you approach sonic speeds.

Isn't compressiblity what causes pressure changes (absent temperature
changes)?

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