Re: refutation of the scoop theory

[David_Anderson <dfa@FNAL.GOV>]

> The scoop model makes quantitatively wrong predictions about the effect of
> span and chord on induced drag, as I wrote to Prof. Eberhardt at 06:09 PM
> 1/7/99 -0500.  He wrote back at 01:08 PM 1/8/99 -0800.  He disparaged my
> analysis by pointing out a 15% correction term that I had omitted for
> simplicity.  I reiterated on 08 Jan 1999 19:06:51 -0500 that the scoop
> model was in error by something like 600%, with or without the 15%
> correction terms.

Scott and I do not have a "scoop model" as such.  We just introduced the
idea of a scoop as a visualization tool so that the pilot will understand
why the angle of attack is reduced when the speed is increased. It was
also used as an aid in deriving for the reader the CORRECT functional form
of the power curve and the relationships between induced power and load,
as well as the relationship between load and stall speed.

The problem so often found with aeronautics types is that they tend to
talk over the head of the average reader, and that they far too often
confuse mathematics with physics.  Our physical description was not
intended to be a calculation tool.  It was intended to impart the true
physics of flight to pilots.  I'm often asked how I would design a wing
with this "new" (really old: see Stick and Rudder, 1944, and the quote at
the end of this message) viewpoint.  My answer is always that I'd hire an
aeronautical engineer to do it.  Unfortunately I would by shy of hiring
the same engineer to teach the physics of flight.

We, of course dispute your statement on the error in the "scoop model" by
the same 600%.  What if we were off by a factor of two?  The objective was
to show that the wing diverts a lot of air down.  In the tons and that
lift is not a skin effect on top of a wing.

"Notwithstanding the importance of circulation, the Kutta-Joukowski
condition, and the theorem of [the previous section relating lift to the
airspeed and circulation], an aerofoil obtains lift essentially by
imparting downward momentum to the oncoming airstream."
Elementary Fluid Dynamics, D.J, Acheson

        "Notwithstanding the importance of circulation, the
Kutta-Joukowski condition, and the theorem of [the previous section
relating lift to airspeed and circulation], an aerofoil obtains lift
essentially by imparting downward momentum to the oncoming airstream."
Elementary Fluid Dynamics, D.J. Acheson "Notwithstanding the importance of
circulation, the Kutta-Joukowski condition, and the theorem of [the
previous section relating lift to airspeed and circulation], an aerofoil
obtains lift essentially by imparting downward momentum to the oncoming
airstream."
Elementary Fluid Dynamics, D.J. Acheson


David Anderson
dfa@fnal.gov