The wrong "Bernoulli" explanation in Sci. American for April 2005

[stau...@usfamily.net]

> > All new airliners of Airbus or Boeing make and all top bizjets, have
> > low drag "supercritical wings", with almost flat upper surface and
> > curved lower surface (to host wing beam and fuel)!
> >
> > I have never seen Scientific American explain that wing and why it
> > physically create Lift!
>
> A supercritical wing is, by definition, designed to operate in a
> compressible flow regime. You can throw Bernoulli out the window for such
> wings.
>
> They still generate lift the same way as all other wings; they induce a
> circulation in the airflow. They have a "fat" shape to control adverse
> transonic effects and prevent shock separation on the upper surface from
> occuring too far forward.

Keep in mind that the air is not constrained to follow the surface
contour perfectly. Smoke tunnel test photos are very revealing. The
airflow once you get a fair fraction of the chord away from the surface
begins to look the same on almost any airfoil generating lift.

To use Bernoulli's law, you must use it in small local regions, then
integrate the pressures completely around the foil.

All camber does is shift the lift vs aoa curve right or left, not up
and down. A flat plate generates lift, so do reverse cambered
airfoils. But they do so over different ranges of AOA, and the PEAK
lift coefficient will differ from airfoil to airfoil. At lower AOA,
all airfoils generally have the same change in Cl per change in angle.

[new...@algonet.se]

> > All new airliners of Airbus or Boeing make and all top bizjets, have
> > low drag "supercritical wings", with almost flat upper surface and
> > curved lower surface (to host wing beam and fuel)!
> >
> > I have never seen Scientific American explain that wing and why it
> > physically create Lift!
>
> A supercritical wing is, by definition, designed to operate in a
> compressible flow regime. You can throw Bernoulli out the window for such
> wings.
>
> They still generate lift the same way as all other wings; they induce a
> circulation in the airflow. They have a "fat" shape to control adverse
> transonic effects and prevent shock separation on the upper surface from
> occuring too far forward.
>

Flowwise Circulation is a pure mathematical model, for correcting the
Potential flow field!

It愀 very easy to see that in real flight there is no flowwise
circulation around the wing, only the spanwise circulation in
connection with the downwash!

http://www.team60.mil.se/article.php?id=8120

http://www.grc.nasa.gov/WWW/K-12/airplane/downwash.html

> As a side benefit, you can fit more fuel in there and use deeper chords, but
> it's not strictly necessary...the 747 doesn't have a supercritical wing and
> does just fine.
>

Because the "old" B747-400 does not have the new supercritical wing,
it愀 draglosses is some 15-20 % higher than the new 787.

The Bernoulli equation is not valid without corrections above M 0.3,
which means the a jetaircraft goes over that speed at the runway end
and short beyond!

But Bernoulli is very useful in calculating pipes in slopes and
waterchannels, where the gravity force gives you the driving pressure
(hight potential) or in connections with pipes and pumps, where the
pump creates the pressure need to keep the flow going ala "the
continuity equation"! In a pipe the flow will not disappear!

But any discussion saying the a wing is a split venture and that it
will work due to 2the continuity equation" is false and should be
removed from all books and physics lectures!