Re: Denker vs Anderson and Eberhardt

[David_Anderson <dfa@FNAL.GOV>]

On Sat, 21 Aug 1999, Jerome Epstein wrote:

> Anderson and Eberhardt seem to me to have given by far the best
> exposition of the core of the matter in all of the immensely long
> history of this thread. The posts have often dissolved into long debates
> about clearly minor side issues.
>
> It has always seemed clear to me that -- idealizing by ignoring small
> corrections -- the lift of the plane is exactly analogous to a small
> speedboat riding on the surface of the water ("planing" as we called it)
> when it achieves enough speed. When one rides in such a boat, as I have
> countless times, one immediately feels the change when the boat stops
> floating by displacement and starts planing. The boat rises out of the
> water and the resistance to forward motion abruptly drops. It is clear
> that this is caused by a 3rd law effect, where water is driven downwards
> and the boat is raised by the reaction force.
> J. Epstein

I regret to say after reading the flattering beginning introduction of
this message that I have to disagree with it.  Only in that the speedboat
is a particularly bad analogy.  It implies that the air is deflected by
the bottom of the wing causing lift, that the wing "surfs" through the
sky.  It is interesting to note that Newton made the same mistake.  In
fact the air is pulled down primarily from the top of a well-designed
wing.  In the case of a flying barn door it is true that almost 50% of the
lift is caused in this way.

David Anderson
Dfa@fnal.gov