The Impossibility of Flying Heavy Aircraft Without Training

Italian?



"Dan" wrote in message
news:CqZMf.55312$Ug4.33718@dukeread12...
| Richard Lamb wrote:
| Bryan Martin wrote:
|
|
| Bryan,
|
| Ex-nay!
|
| Or wander over to alt.politics to feed the loons...
|
| I brought up this whole Bernouli mess just to get
| rid of these guys.
|
| It worked quite well.
|
| Now don't screw it up again!
|
| Richard
|
| Isn't a Bernouli what an Arab wears?
|
| Dan, U.S. Air Force, retired

Jim Macklin wrote:
Italian?



"Dan" wrote in message
news:CqZMf.55312$Ug4.33718@dukeread12...
| Richard Lamb wrote:
| Bryan Martin wrote:
|
|
| Bryan,
|
| Ex-nay!
|
| Or wander over to alt.politics to feed the loons...
|
| I brought up this whole Bernouli mess just to get
| rid of these guys.
|
| It worked quite well.
|
| Now don't screw it up again!
|
| Richard
|
| Isn't a Bernouli what an Arab wears?
|
| Dan, U.S. Air Force, retired



Drat, wasted a pun

Dan, U.S. Air Force, retired

Jose wrote:
Wrong. Momentum change is momentum. The time rate of momentum
change is Force. Neither is pressure.

What I wrote (or intended to write) is that pressure is manifested by
many momentum changes. Each molecule that collides with a wall
transfers momentum to that wall, and the net force caused by all those
momentum changes (over time) manifests itself as pressure, (which is
force divided by area). The essential point is that pressure arises
from momentum transfer on a molecular level.

IOW, the causual basis for macroscopic gas laws is governed
by statistical mechanics. Agreed.


Why does Newton require that air be accelerated downwards?

To counterbalance the wing being accelerated upwards due to lift. The
wing is at an AOA which generates lift.


I think you are refering to Newton's third law, often stated as: "For
every
action there is an equal and opposite reaction."

For an aircraft in level flight, the upwards acceleration due to lift
is
counterbalanced by the downward acceleration due to gravity.
This satisfies Newton's third law.

For a wing in level flight, the vertical component of momentum is
zero. Therefor, conservation of momentum requires that the vertical
componenet of momentum of the air also be zero. The wing imparts
as much upward momentum to the air as it does downward momentum.

The pressure differential through the wing, from bottom to top,
integrated
over the wing area, provides an upward force for a wing in level
flight.

The downwash behind the aircraft, which is counterbalanced by a more
diffuse upwash around it, is real but not relevent to the issue of
lift.

--

FF

cjcampbell wrote:
wrote:
Dylan Smith wrote:
On 2006-02-24, Greg Esres wrote:
There is a *net* downward momentum of air.

I have several aerodynamics books that say differently.


I guess that depends on what you mean by "net" downward movement. Air
does move downward from an airfoil. There is no difference between a
fan blade and wing.

For a fan in open air the momentum of the air moving through the
fan is equal and opposite to the momentum of the air moving around
the fan to replace the air removed from the front of the fan. There is
no net momentum change in the air. For ducted flow that returns the
air to the front fo the fan, the net momentum is also zero. Net flow
and
net momentum through any closed loop is zero--else the 'loop'
is not 'closed'.

Followjng a wing in level flight, the downward momentum of the
air in the downwash is equal and opposite to the upward momentum
of the air to either side that moves up to replace the air that washes
down. There is no net momentum change in the air.

...

In the real world airplanes have flown with pressure sensors
on the wings, confirming lift from the Bernojuli effect in actual
flight.


In the real world there are many photographs of huge canyons carved in
layers of cloud and smoke as airplanes fly over them,

Cool! Got any links to some? How about pictures of airplanes
flying just below the ceiling?

as well as
photographs of ripples and spray in water below them. The downward
deflection of air is caused by the low pressure area above the wing, so
of course the Bernoulli effect is confirmed. The downward flow of air
is predicted by Bernoulli.

This does NOT disprove the notion that there is localized downward
flow from some parts of the aircraft. However, there is no NET flow
of air down or up from airplane wings or helicopter blades. Otherwise,

ambient pressure at ground level would steadily increase as more
and more aircraft pushed the air down...

No it would not, once the aircraft was out of ground effect. The
downward flow dissipates rapidly after the aircraft has passed.

'Dissipation' is flow. If you include that dissipation into your
sum, there is no net flow. Otherwise, as stated above, the
ambient pressure at ground level would steadily increase and,
as you note below, the pressure higher up woudl steadily drop.

Otherwise you could say that all the air is being sucked out of the
space above airplanes and nothing is moving in to replace it, so that
eventually everything above heavily travelled altitudes will become a
vacuum.

Precisely my point. The downwash hypothesis sucks. It _is_
quite intuitive, it makes a lot of sense, but nature is not bound
by intuition or common sense.

Are you saying that a fan will eventually increase the ambient
pressure on one side of the room and leave a vacuum on the other side?

Are you saying that if there is net flow from one side of the room
to the other the pressure of both sides will stay the same?

It would make half of my living room kind of uncomfortable, wouldn't
it? Air moves in from the sides and quickly equalizes the air pressure.

Precisely. There is no net flow.

--

FF

Richard you give away your age. Only an "Old Fart" would know that.

Al


"Richard Lamb" wrote in message
ink.net...
Al wrote:
Remember, Time flies like an arrow...
Fruit Flies Like a Banana...

Grouch Marx!

Richard Lamb wrote:
Al wrote:
Remember, Time flies like an arrow...
Fruit Flies Like a Banana...

Do all fruit flies have bannana ratings ?
:-)

Al wrote:
Richard you give away your age. Only an "Old Fart" would know that.

Al


"Richard Lamb" wrote in message
ink.net...
Al wrote:
Remember, Time flies like an arrow...
Fruit Flies Like a Banana...

Grouch Marx!



Not quite, he misspelled Groucho.

Dan, U.S. Air Force, retired

Sez one old fart to another???

Al wrote:
Richard you give away your age. Only an "Old Fart" would know that.

Al


"Richard Lamb" wrote in message
ink.net...

Al wrote:

Remember, Time flies like an arrow...
Fruit Flies Like a Banana...


Grouch Marx!

george wrote:
Richard Lamb wrote:
Al 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.

Dan, U.S. Air Force, retired

I think you are refering to Newton's third law, often stated as: "For
every action there is an equal and opposite reaction."

Yes.

For an aircraft in level flight, the upwards acceleration due to lift
is counterbalanced by the downward acceleration due to gravity.
This satisfies Newton's third law.

Yes.

For a wing in level flight, the vertical component of momentum is
zero.

No.

That is, on a microscopic scale, no. The wing is constantly
freefalling, then being bounced back up by impact with air molecules.
Averaged over all the molecules, yes, the net is zero (the wing flies)
but on a microscopic scale, the wing is in constant brownian motion.
This implies momentum transfer, and following the momentum on a
microscopic scale is instructive.

The wing imparts
as much upward momentum to the air as it does downward momentum.

This is where I disagree. Upward momentum gets imparted, but not
(directly) by the wing. Rather, it is imparted by the ground, mediated
through other air molecules. Of course this wouldn't happen if the wing
didn't pass through and throw the air down to begin with, but the ground
is what ultimately imparts the upwards momentum.

The pressure differential through the wing, from bottom to top,
integrated
over the wing area, provides an upward force for a wing in level
flight.

That's the shortcut. Where does this pressure differential come from -
that is the question.

The downwash behind the aircraft, which is counterbalanced by a more
diffuse upwash around it, is real but not relevent to the issue of
lift.

I disagree here too. It's important in seeing the entire picture.

The wing is ultimately being supported by the ground, the same way
somebody standing on a stool is ultimately supported by the ground.

Well, ok, a slightly different way, but only in detail.

Jose
--
Money: what you need when you run out of brains.
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