Mxsmanic , IFR sensations, and some other stuff

In rec.aviation.student Gezellig wrote:
On Thu, 22 May 2008 10:52:15 -0500, Michael Ash wrote:

In rec.aviation.student Gig 601Xl Builder wrote:
Mxsmanic wrote:
Stealth Pilot writes:

aeroplanes fly because of lift generated by pressure differences on
the wing surfaces.

Airplanes fly because the wings divert the air through which they pass
downwards, creating a downwash and exerting a force in doing so that engenders
an opposite force that is lift.

... these pressure differences are caused by the shape
of the aerofoil of the wing ...

The air is diverted because the wing has a positve angle of attack. It can be
perfectly flat and it will still generate lift.

If that were the case a 747 would have to be producing over 250,000
pounds of force straight down. Why then am I not crushed when a 747
flies over me?

At sea level the atmosphere pushes down with about 14.7 pounds of force
for every square inch of exposed surface. On the average man, this works
out to about 43,000 pounds, all the time. Why aren't your crushed by this?

Because I eat beans?

Score yet another point for the musical fruit.

--
Mike Ash
Radio Free Earth
Broadcasting from our climate-controlled studios deep inside the Moon

In rec.aviation.student Tina wrote:
Interesting phrase, "pushes down". Why would you think atmospheric
pressure pushes down?

It was just bad phrasing.

I was thinking about how atmospheric pressure is created by gravity
pulling the air down. But of course as you imply, the pressure itself
pushes in all directions.

--
Mike Ash
Radio Free Earth
Broadcasting from our climate-controlled studios deep inside the Moon

seniours pass dunce 101 you didn't!
Gezellig laid this down on his screen :
Sensory inputs are checkpoints.

I see
I feel
I see
I see more
I resolve to what I see.

Basic piloting, best constrained and confirmed to the sciences of engineering
and physics. This is what I struggle the most, I am neither physicist,
mathmetician or engineering inclined. :-? I flunked Legos. :')

Gezellig brought next idea :
seniours pass dunce 101 you didn't!
Gezellig laid this down on his screen :
Sensory inputs are checkpoints.

I see
I feel
I see
I see more
I resolve to what I see.

Basic piloting, best constrained and confirmed to the sciences of
engineering and physics. This is what I struggle the most, I am neither
physicist, mathmetician or engineering inclined. :-? I flunked Legos. :')

Another Forged Message :-[

On May 23, 9:32*am, "Capt. Geoffrey Thorpe" The Sea Hawk At Wow Way
D0t C0m wrote:


You can use either Newton or Bernoulli to explain lift, but the correct
way to explain it is to explain how both are correct.

That's because Bernoulli's equation is nothing more than Newtons law
(conservation of momentum) applied to a streamline. It's not that hard to
derive Bernoulli's equation from Newtons...

Nope. It's an energy equation, not inertial.

Cheers

On May 23, 12:46*pm, wrote:

* * * So it's a process to cause the air to exert a force in a
direction perpendicular to the airflow. It fools the air, if you like,
which is why we call it an "air foil." A foil is a device to deceive.

Nonsense, the derivation is from a blade or leaf.

Cheers

On Thu, 22 May 2008 20:13:44 +0200, Mxsmanic
wrote:

Stealth Pilot writes:

downwash occurs after the wing has passed.

Downwash is the result of the wing's passing. The wing accelerates air above
it downwards. That downward movement continues after the wing has passed, and
it is called downwash. It is the acceleration that produces the downwash that
is responsible for lift.

no.
what pushes the aeroplane up into the air is the pressure differences
at the surface of the wing.

the whole purpose of the rest of it is to create those pressure
differences *at the surface*.

a wingtip vortex is an example of pressure differences not at the
surface and those just cause drag.

keep at it son. one day it is sure to sink in.
Stealth Pilot

On Thu, 22 May 2008 08:22:49 -0500, Gig 601Xl Builder
wrote:

Mxsmanic wrote:
Stealth Pilot writes:

aeroplanes fly because of lift generated by pressure differences on
the wing surfaces.

Airplanes fly because the wings divert the air through which they pass
downwards, creating a downwash and exerting a force in doing so that engenders
an opposite force that is lift.

... these pressure differences are caused by the shape
of the aerofoil of the wing ...

The air is diverted because the wing has a positve angle of attack. It can be
perfectly flat and it will still generate lift.


If that were the case a 747 would have to be producing over 250,000
pounds of force straight down. Why then am I not crushed when a 747
flies over me?

bloody long wings combined with you being a bit slow on the uptake
(...I'm joking :-) )

it is 250,000lbs or whatever the aircraft weight is but it isnt a
point load and it is a variation in an existing unperceived pressure.

the pressure variations over the wing of a 747 are discussed in an
aero engineering book. because of the wing area involved and the speed
the pressure variations are a lot less than you'd think.
( I wish I could remember which book it was)

Stealth Pilot

wrote in
:

On May 22, 5:36 pm, Some Other Guy wrote:
BDS wrote:
There is an interesting article in Flying magazine by Peter
Garrison that talks about lift theory.

I thought that one of the most interesting points he made was that
the lift force generated by an airfoil is greater at the optimum
angle of attack than would be the force imparted to it if you were
to move it through the air perpendicular to the air flow at the
same speed.

I first experienced this as a kid, sticking my hand out the car
window with the thumb as a leading edge, forming a crude airfoil.

When at the right shape and angle of attack, the lift is amazingly
strong. I always found it remarkable that when my hand was completely
perpendicular to the wind, the force didn't seem as strong.

Definitely a visceral lesson in lifting versus stalling.

I have a copy of that article here. Very, very good. The
coefficient of lift, as he described it, was a ratio related to the
lift generated by a unit area of wing compared to the flat-plate drag
created by the same unit area perpendicular to the airflow. The Wright
brothers did this in their wind tunnel, so they were able to develop
efficient airfoils. A common airfoil (NACA 23012, IIRC) has a max lift
coefficient of 1.8 , which means that it generates 1.8 times the lift
as the drag of the perpendicular surface of the same area.
He made things really clear when he pointed out that this is why
boats and ships no longer use paddlewheels. The wheel will produce
forward thrust equivalent to the power required to force the paddle
back through the water, while the propeller (they call it a "screw")
will produce much more forward thrust for the same torque required by
the paddlewheel.
So it's a process to cause the air to exert a force in a
direction perpendicular to the airflow. It fools the air, if you like,
which is why we call it an "air foil." A foil is a device to deceive.


Actually it's a synonym for blade.

Bernoulli is right, and so is Newton. There's a pressure
difference because of the difference in airspeeds between top and
bottom, and there's a movement of air downward to which there's an
upward reaction. The equal-transit time theory is bogus, since the
airfoil is much more efficient than that theory would imply. See this
page:
http://www.av8n.com/how/htm/airfoils.html
And, again, Mxmanic has declared, for about the 12th time, that
positive AOA is necessary for lift. If this was so, and it isn't, and
he has been shown many times that it isn't, then airfoils like the
Clark Y wouldn't generate lift at AOAs as low as -4 degrees. That's
negative 4 degrees, airfoil chord pointing downward. A graph can be
found a third of the way down this page:
http://lpmpjogja.diknas.go.id/kc/a/air/airplane.htm
That page also deals properly with both Newton and Bernoulli.

Good link but I think he kind of munged up the lift/drag thing as being
seperate entities, when they're inextricably linked. IOW you create lift
and drag is a by product. Not to say, BTW, that the correlation is
rigid!


Bertie

On May 23, 7:27 am, Stealth Pilot
wrote:
It's easy to write the equations, it's classic physics stuff. Start
from basic principles.

You need not involve chaos theory, although some posters seem to try.