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

[WaltBJ]

Symmetrical airfoils will not generate lift if the angle of attack is
zero. The F104 has a symmetrical airfoil and cruises at about 3 degrees
positive AOA. Similarly, constant altitude inverted flight is possible
only if the airfoil has a positive angle of attack relative to the
earth. Lots of forward stick, in other words. In knife flight, the
fuselage is yawed so it has a positive angle of attack and is
generating lift and it is usually symmetrical, too. The slab-sided F4
flew fine on its side at 500 KIAS. As for the 'true' explanation of
lift, any time you have to juggle four simultaneous differential
equations, pilot instruction becomes very unwieldy and the students
doze off. This approach, to me, is picking nits.

Walt BJ.

[Tom Sanderson]

> Or just ask yourself this: if airfoils *must* be more curved on
> top, doesn't this prove that symmetrical airfoils cannot work,
> and that upside-down flight is impossible?

That's not true, even by the faulty lifting theory. The essential
requirement (of the bad theory) is that the path length over the wing has to
be longer than the path length under it. No matter the airfoil section or
camber (for real airfoils, anyway), you can screw with the angle of attack
enough to move the stagnation point around so that the flow length over the
top is longer.

Symmetrical airfoils don't generate any lift unless they're at positive
angle of attack (i.e. the stagnation point is below the geometric "front").

Tom.

[rgrego...@yahoo.com]

> A recent issue of Scientific American carries a mind virus! :)
>
> In the "Working Knowledge" column, the author presents an incorrect and
> long-debunked explanation of how wings work:
>
> "because the wing top is curved, air streaming over it must travel
> farther and thus faster than the air passing underneath the flat bottom.
> According to Bernoulli's principle, the slower air below exerts more force
> on the wing than the faster air above, thereby lifting the plane."
> http://www.scientificamerican.com/article.cfm?chanID=sa006&colID=9&articleID=00009993-1F9A-1417-9F9A83414B7F012B
>
>
> The above explanation is wrong, and is known as the "Equal Transit-Time
> Fallacy." This incorrect explanation is widespread among children's
> books, but I'm suprised to see it in a reputable magazine like SciAm.
>
> It's debunked here:
> NASA GRC: Incorrect lifting-force theory #1
> http://www.grc.nasa.gov/WWW/K-12/airplane/wrong1.html
> http://www.grc.nasa.gov/WWW/K-12/airplane/bernnew.html
>
>
> Also see other debunkings:
> Anderson/Eberhardt: a physical description of flight
> http://www.aa.washington.edu/faculty/eberhardt/lift.htm
>
> Denker: How Airplanes Fly
> http://www.av8n.com//how/htm/airfoils.html#sec-inverted-camber
>
> Irrotational inviscid flow: Streamline animations
> http://www.idra.unige.it/~irro/profilo1a_e.html

>
> Or just ask yourself this: if airfoils *must* be more curved on
> top, doesn't this prove that symmetrical airfoils cannot work,
> and that upside-down flight is impossible?

Yes, but the NASA page *does* say the air flow over the top of the an
airfoil that is producing lift *is* faster, and furthermore that this
*does* create lift from the Bernoulli principle!
The only fact that is incorrect is that the streams over the top and
bottom have to meet at the trailing edge. In fact the flow over the top
is faster even than this. The question is *why* does it have to be
faster than the flow over the bottom?
Also, notice in the animation with a symmetrical airfoil there is *no*
lift at zero angle of attack. Then this might suggest in the
symmetrical case it is just Newton's force laws at work.

Bob Clark

[new...@algonet.se]

Very curious that not even a respected magazin like Scientific American
does not understand the physics of flight!

Bernoulli equation seems to very misunderstod by americans, even
respected universities and Professors should know better about the
physics!

To change a veolocity a change in force is needed!

There is no other way around!

I asked for years for an explanation of the airflow thru the Windsock,
seen at every airport.

I seems like Bernoulli equation does not explain the Windsock very
good!

Some person has destroyed Otto Lilenthal Museum exibition in Anklam,
Germany, by putting some Bernoulli rubbish in the halls!

I asked if Otto Lilienthal himself wrote the false explanation, but that
had been done by the museum chief!

jan-olov newborg