Kammback

A Kammback is a car body style that derives from the research of the German aerodynamicist Wunibald Kamm in the 1930s, this research itself deriving from that of another pioneer German aerodynamicist, Baron Reinhard Koenig-Fachsenfeld. "Kammback" is an American coinage. In Europe the design is generally known as a Kamm tail or K-tail.

History

Freiherr Reinhard Koenig-Fachsenfeld "developed a body style whose tail was cut off to form a flat rear surface"Eckermann, Erik, and Albrecht, Peter L. "World History of the Automobile" p. 117. SAE International, August 2001. ISBN 0-768-00800-X.] while working on an aerodynamic design for a bus, and he patented the idea. [ [http://www.ireland.com/newspaper/motors/2007/0808/1186424868676.html Montgomery, Bob. "Designing a spin for the tail end of things", "The Irish Times", August 08 2007] . Retrieved on June 18 2008.]

The innovative tail treatment also minimized turbulence created by Paul Jaray's [ [http://www.coachbuilt.com/des/j/jaray/jaray.htm "Paul Jaray", "Coachbuilt.com"] . Retrieved on June 18 2008.] aerodynamic designs on certain 1935 passenger cars. In 1936, "further research by the FKFS--Forschungsinstitut fur Kraftfahrwesen und Fahrzeugmotoren Stuttgart (Stuttgart Research Institute for Automotive and Automobile Engine Technology), under the direction of Wunibald Kamm, proved that vehicles with the so-called K- or Kamm tail, following Koenig-Faschsenfeld’s lead, offered a good compromise between everyday utility (e.g. vehicle length and interior dimensions) and an attractive drag coefficient."

The earliest use of "Kamm" to describe an automobile body incorporating this design was the prototype 1940 'Kamm' Coupe based on a BMW 328 chassis. [ [http://www.cardesignnews.com/news/2004/041203mcd-history3/ Ihrig, Ron "Part 3: Production, Physics, Politics - Only the Strong Survive" German Design History in Car Design News, December 3, 2004] , retrieved on 2008-05-25.]

Aerodynamics

While the realities of fluid dynamics dictate that a teardrop shape is the ideal aerodynamic form, Kamm found that by cutting off / flattening the streamlined end of the tear at an intermediate point, and bringing that edge down towards the ground, he could gain most of the benefit of the teardrop shape without incurring such a large material, structural, and size problem. The airflow, once given the suggestion of the beginning of a turbulence-eliminating streamlined teardrop tail, tended to flow in an approximation of that manner regardless of the fact that the entire tail wasn't there. This is called the Kamm effect.

There is controversy about the proportions of a true Kamm tail. According to the classic definition the tail should be cut off where it has tapered to approximately 50% of the car’s maximum cross section, which Kamm found represented a good compromise - by that point the turbulence typical of flat-back vehicles had been mostly eliminated at typical speeds. Thus a minivan is not a Kammback, and neither are numerous cars that have truncated tails.

Automakers’ use of the term “Kammback” has diminished as Kamm's principles have become more generally assimilated into modern car design.

Kammback examples

High-performance cars

The Kamm tail was used on many high-performance and competition cars, such as:
* 1940 BMW 328 "Mille Miglia" Kamm coupé [ [http://www.classicrallies.com/blog/index.php?/archives/305-BMW-at-Techno-Classica-highlights-from-90-years-of-history.html BMW Press Release dated 27 March 2007. "BMW AT TECHNO CLASSICA: HIGHLIGHTS FROM 90 YEARS OF HISTORY", “BMW Motorsport”: "Kamm was a key figure in the design of the body for this . . .car, which was built specially for the Mille Miglia 1940."] Retrieved on July 10 2008.] [ [http://bmw-motorsport.com/ms/en/fascination/history/early_days/moments/mille_miglia.html "Official BMW Motorsport Website" "Victory in Italy": "(In the) 1940 Mille Miglia . . .Lurani and . . . Cortes retire(d) . . . their BMW 328 'Mille Miglia' Kamm coupe."] Retrieved on 25 May 2008.]
* 1962–1964 Ferrari 250 GTO
* 1963 Aston Martin DP215
* 1963-1974 Bizzarrini Iso Grifo [ [http://auto.howstuffworks.com/iso-sports-cars.htm "Consumer Guide", Editors of: '. . . tail chopped Kamm-style.' "How Stuff Works", "Iso Grifo" ] Retrieved on 25 May 2008.]
* 1965-1968 Ford GT40 [ [http://www.ultimatecarpage.com/car/3406/Ford-Mk-IV.html ". . .cut-off 'Kamm' tail", "Ultimate Car Page", "Ford Mk IV"] . Retrieved on 25 May 2008.]
* 1965-1970 Aston Martin DB6
* 1968-1973 Ferrari 365 GTB/4 (“Daytona”)
* 1968-1976 Ferrari Dino [ Nye, Doug: ". . . a cut-off Kamm-theory tail . . ." "Dino, The Little Ferrari", p. 110. Motorbooks 2004. ISBN 0760320101.]
* 1970-1975 Citroen SM
* 1970-1977 Alfa Romeo Montreal
* 1972-1982 Maserati Khamsin

Mass-production cars

Kamm (and Kamm-like) tails can be seen on numerous mass-production cars, such as:
* 1970-1986 Citroën GS
* 1970-1993 Alfa Romeo Spider
* 1974-1991 Citroen CX
* 1984-1991 Honda CRX
* 1985-1996 Autobianchi/Lancia Y10
* 1992-1998 Mazda MX-3
* 1991-2005 Audi A2
* 2001-2008 Volvo S60

AMC and GM have publicized certain models with truncated tails as “Kammbacks” even though it is obvious to the eye that they do not meet the classic "50% cross-section" definition, i.e. the AMC AMX-GT and Pontiac Firebird-based "Type K" concept cars, [ [http://auto.howstuffworks.com/chevrolet-camaro-and-pontiac-firebird-concept-cars1.htm "Pontiac Type K Concept Cars" by the Auto Editors of Consumer Guide, undated] , retrieved on 2008-05-25.] a Chevrolet Vega station wagon, [ [http://www.oldcarbrochures.com/main.php?g2_itemId=24775 “Chevy’s New Car is Open for Business” Chevrolet Division of General Motors, 1970. Hosted by the Old Car Manual Project] , retrieved on 2008-05-25.] and a version of the AMC Eagle. [ [http://amceaglenest.com/history1981.html History of the 1981 AMC Eagle] , retrieved on 2008-05-25.]

Hybrid mass-production cars

As the Kamm tail’s low drag helps improve fuel consumption, it features on subcompact hybrid cars designed for maximum economy, for example:

* 1996-2006 Honda Insight
* 2004-2008 Toyota Prius

References

External links

* [http://homepage.mac.com/christopher.z/hobby/80-AMXitems/Information/production/KammbackStory.html Article on the origins of Kammback design]
* [http://www.landcrab.net/mainframes/main_pinafarina1800.htm The Pininfarina 1800] - an explicitly Kamm-influenced design which informed the Citroën CX and Rover SD1