# Re: BCF& COMMENTS ON IT (really long)

```Dinogeorge@aol.com wrote:

> Airfoils must be asymmetric, because it is the difference between the airflow
> over the top and bottom surfaces that provides the lift; a symmetric wing
> would have the same kind of airflow over top and bottom and thus generate
> near-zero lift.

This is false.  Ask anyone who designs aircraft or any aerobatic pilot.
Competition aerobatic airplanes have perfectly symmetrical wings so that
they can fly equally well rightside up or upside down.  If you don't
believe this, go watch an aerobatic competition and then measure the
wings on the planes.  A high aspect ratio plank and a high aspect ratio
asymmetric wing both have the same lift slope, approximately 0.10966 per
degree of angle of attack, which is 2*pi/radian.  The principal
difference between the two is the angle of attack at which zero lift
occurs, and the slightly lower attack angle at which the plank stalls.
Even a plane with a highly asymmetric wing will fly quite well upside
down if braced to do so.  Typical examples are the clipped-wing cub and
the Citabria (airbatic spelled backwards), both having highly asymmetric
wings.  Anyone who thinks that asymmetry is a precondition for flight
should read a good aerodynamics textbook or take a course in fluid
mechanics at the local university.  I would suggest THEORY OF WING
SECTIONS by Abbot and Doenhoff or AERODYNAMICS, AERONAUTICS, AND FLIGHT
MECHANICS by McCormick as a good starting point.  Actually, I'd also
recommend both these books to anyone who thinks asymmetry is NOT a
precondition to flight.

> Wing asymmetry occurs everywhere in the wing:
snipped
> The BADD model, in which the forelimbs must preacquire their asymmetry for
> some
> reason unrelated to flight, has tremendous difficulty explaining it.

It doesn't need to explain it, because there is no need for a
preacquistion of asymmetry. See above. Asymmetry can come later.
Best wishes,
Jim Cunningham

```