On May 24, 10:03*pm, a wrote:
On May 24, 10:35*am, Dudley Henriques
wrote:









On May 23, 9:31*pm, a wrote:

On May 22, 10:02*pm, brian whatcott wrote:

On 5/22/2011 5:15 AM, Dave Doe wrote:

Does anyone have any figures and references for about what ratio lift is
produced by Newton's Laws and Bernoulli's Laws?

I appreciate this is not a static figure - but say a yer average C-172,
or perhaps a 737.

I would hazard a semi-educated guess that lift is *primarily* produced
by angle of attack (or deflection if you like) - Newton's Laws - and by
a much lesser degree by Bernoulli's Law. *I would guess that Bernoulli's
principle might create 20% of the lift a wing generates. *A friend
believes it would be much lesser - about 5%.

Think of it this way:
Newton: force is proportional to the mass and its acceleration.

In this context, the meaning is, to produce the aircraft's weight in
lift i.e. upwards , an airmass has to move *with sufficent acceleration
to provide that up force.

Bernoulii: the mass of air flowing through a channel times its speed
gives the same product even if the channel then narrows to a waist:
the air mass has to flow faster, but its pressure drops..

In this context: air flowing in an airstream over a wing sees it bulging
(or waisting) and so that it needs to speed up, and pressure drops over
the upper wing. Arguments of this type can be used as evidence that 2/3
of the wing lift is produced at the upper surface, and 1/3 at the lower
wing surface.

The larger truth: air pressure drops over the upper surface of a wing,
and increases over the lower surface of a wing, and the resultant
downflow balances the lift on the wing.

Brian W
*theories
anyone here really believe there is no change in air density as if
flows at speeds of a hundred miles an hour past an airfoil? The
equation works well for water flow in pipes and around boat hulls. It
does not do such a good job of predicting pressures along an airfoil.
Stick with Newtonian Physics and the gas laws.

The ideal gas law still applies. Compressing airflow does indeed
complicate Bernoulli as do the density changes involved but Bernoulli
still holds up. Both theories remain correct even with compressible
flow. But you are correct in that the Newton explanation is FAR easier
of the two for people to deal with and understand. The only caveat I
stress to instructors when getting into the lift issue is that they
NEVER explain lift using ONLY one theory without mention of the other,
as student pilots, once exposed to the lift question will invariably
find through a credible source that BOTH Newton and Bernoulli are
correct and that each can explain exactly the same thing to the 100%
point.
Lift can be explained to death. The deeper one goes into the
explanation the more complicated it can get. Denigrating Bernoulli due
to changing density and airflow speeds causing compression factors is
NOT the way to present lift. Bernoulli stands. It's the math that gets
harder when you compress the flow that's all. All this can be avoided
by simply explaining to students that lift results when an airflow is
TURNED, and BOTH Newton and Bernoulli can be shown to cause the
airflow to turn as lift is being produced. Circulation, density,
vortices..........all part of it, but it's the turning of that airflow
that produces lift force and BOTH Bernoulli and Newton are working
equally to produce that force, only doing it differently.
Dudley Henriques

Actually, a quick meander through the literature will not find
Bernoulli mentioned: in 2 D airflow studies it's gas laws and
Newtonian physics, with a heavy emphasis on experimental results.
These days, numerical methods -- what we used to call difference
equations -- seem to yield results that seem to come pretty close to
predicting experimental results. Notice especially in experiments that
chord sections have end plates so that flow really is confined to 2 D.

What is really interesting is that high performance glider wings are
long and slender: that's how they get the most efficient use of
potential energy in the form of altitude and turn it into range. *I
don't know of any 4 seat complex SEL that uses the same principle and
am not sure why. *My Mooney gets 20 mpg or so, sure would enjoy seeing
that change to 30!

It's nice to see a real aviation topic here, isn't it?

I don't know what "literature" you're referring to that doesn't
mention Bernoulli when discussing lift, but I'd avoid that literature
if I were you. It's incomplete! :-))
DH