Shelby Daytona Coupe and Alfa Romeo TZ1: Different designs, same influence | Column

By Peter Brock
Jan 5, 2023 | Alfa Romeo, Shelby, Cobra, Peter Brock, Aerodynamics, Column, Shelby Cobra Daytona Coupe, TZ1, Alfa Romeo TZ1 | Posted in Columns | From the May 2019 issue | Never miss an article

The inspiration for my design of the 1965 FIA GT World Championship-winning Daytona Cobra Coupe was actually formulated in Germany back in 1937. Aero specialists Baron Reinhard von Koenig-Fachsenfeld and Dr. Wunibald Kamm had determined that air flowing over any form would stay “attached” to the surface, providing the least amount of aerodynamic drag, if that surface didn’t depart from the direction of flow by more than 7degrees.

[The famed Cobra Daytona Coupe that almost didn’t win, as told by Its designer]

Should that occur, as it does on all automotive forms, the air begins to create turbulent eddies that create drag, reducing efficiency. The more extreme the deviation, the greater the drag.

The Germans’ 7-degree ideal was, of course, impractical for general use. It would be impossible to create an automotive form that kept all the surfaces–top, bottom and sides–in a perfect 7-degree taper with no interruptions, like wheel openings or windscreens. The important point was the fact that their discovery had serious potential to improve performance. Resistance to their concept, however, persisted for some 30 years because it wasn’t aesthetically accepted. Eventually, it proved useful in generating higher top speeds and greater fuel efficiency.

Koenig-Fachsenfeld began his career working for famed Hungarian aerodynamicist Paul Jaray at the Zeppelin works during WWI. Jaray determined the ideal shape to improve the performance of the giant German dirigibles.

Later, Koenig-Fachsenfeld began racing motorcycles and studying the effects of airflow over his own body. He used that empirical data to become a German motorcycle champion in 1924. He also realized that it would be impractical to apply what he’d learned working for Jaray to automotive forms, as car bodies would have to be stretched to extreme, unusable lengths. So he began experimenting by keeping the sides and rooflines of his own designs as flat as possible. He then simply chopped their tails to trick the flow of rushing air into staying attached, and voilà, his odd-looking concept easily outperformed the tapered forms of Jaray-style designs so popular on the gorgeous French classics of the late 1930s.

[Everything changed when this radical Mercedes-Benz SSKL won at Avus in 1932]

Since Koenig-Fachsenfeld was working under Dr. Kamm at the time of his discovery, his blunted rear design became known as the K-line tail, Kamm tail or Kammback, as those names were far easier for the media than “Koenig-Fachsenfeld-back tail.”

Dr. Kamm and Koenig-Fachsenfeld created several running prototypes with radical chopped tails to prove the advantages of their discovery. Efficiency was proven, but the appearance was so radically unfamiliar that no company would risk putting such a “strange-looking” design on the market. The best of these was an elegant BMW coupe built especially for the Berlin Rome race in 1939, an event that never took place because of the advent of WWII. In the hostilities that followed, the advantages of the K-line designs were almost completely forgotten.

When racing resumed in 1948, existing prewar designs were resurrected but left virtually unchanged until increasing speeds demanded a review of the lost advantages of superior aerodynamics.

In 1963 a young Italian, Ercole Spada, working for then-unknown carrozzeria Zagato, created a radical chopped-tail coupe for Alfa Romeo called the TZ1. It quickly became dominant in its class, winning numerous European championships. When asked why Spada had used the unfamiliar coda tronca form on his TZ1, he explained that research on the German designs of the ’30s proved they were simply too good to ignore.

By coincidence, at the same time I was trying to convince Carroll Shelby of the K-line concept in my quest to make the Cobras competitive for European racing. Under extreme resistance from his team, the Texan finally relented when his top driver, Englishman Ken Miles, convinced him that he also knew of the Germans’ success with the concept in the late ’30s.

Today, when the Daytona Cobra Coupe and the Alfa TZ1 are compared side by side, they appear almost identical in form.