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Subject: Aerodynamics in auto design
From: (richard welty)
Date: 20 Sep 89 21:34:09 GMT

In article <>, richard welty writes: 
*In article <504@odin.SGI.COM>, Scott Fisher writes: 
**The chopped-in-the-back design is called the Kamm back, after 
**an engineer named Kamm who determined that unless you were 
**going to provide a long aircraft-like tail section, you might
**as well chop it off...  That is, a clipped rear section or
**a short but rounded rear section, *at automotive speeds*,
**work about equally well.

ok; i've done a modest amount of research on this, and
here's what i've learned ...

An engineer named Paul Jaray is responsible for the basic
automotive shape of a rounded nose and a long, tapered
tail.  This shape is impractical due to the extreme length
required of the tail, and so has never appeared on a
production car.  Drag coefficients as low as 0.20 were
acheived in experiments, though.

Baron Reinhard Koenig-Fachsenfeld invented the chopped
tail; his patent is dated 1936.  in essence, if you try
to have a shorter tapered tail, you get worse airflow
at the rear than if you design the long tail and simply
cut it off sharply.  Professor Wunnibald Kamm adapted
the theory, and began lecturing about it in the University.

Kamm was responsible for a series of tests on Mercedes
and BMW chassis in the 1937-1938 time frame that proved
the concept.  After the war, he continued to espouse the
design, and so his name became attached to the design.
in particular, in 1951 Road & Track magazine published
one of Kamm's articles, ``Can the $1,000 car be efficient?''

*the earliest appearance of a Kamm style tail that i know
*of is on the prototype Alfa Giuletta Sprint Speciale, from
*the mid-50s.

obviously there were earlier cars, as i stated above.

*  all the Sprint Speciales had it, although it
*didn't become common Alfa practice until partway through the
*production run of Giuletta Sprint Zagatos, a couple of
*years later.  

the second production run of Giuletta SZ cars got the
Kamm treatment, they were variously called SZTs (by
Zagato) or Coda Troncas.  Alfa never assigned a special
designation to the kamm-tailed version of the car.

richard welty    518-387-6346, GE R&D, K1-5C39, Niskayuna, New York

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